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Chapter 10
The digestive system consists of a long tube extending from
the mouth to the anus and the accessory structures attached to that tube. The
tube has several names, including the GI tract, the gastrointestinal
tract, and the alimentary canal. The regions of the GI
tract include the mouth, oral cavity, pharynx,
esophagus, stomach, small intestine,
and large intestine (Fig.
10.1). These regions are specialized for certain aspects of digestion. The
accessory structures that assist the functions of the GI tract include the salivary
glands, liver, gallbladder, and pancreas.
Main Functions for Homeostasis
The digestive system has six main functions. One function is
to supply nutrients needed in several ways by body systems. For example,
nutrients are needed for building and maintaining structures such as bones,
producing substances such as glandular secretions and neurotransmitters, and
supplying energy to power the operations of all body systems. To maintain
homeostasis, the nutrient supply must be steady so that the body cells have
adequate amounts of each required material at all times while not being exposed
to excessive amounts of any nutrient.
Converting Foods to a Usable Form Five processes are
involved in supplying nutrients at proper and fairly steady levels. One is
converting foods to a usable form. This is necessary because although foods
provide most of the nutrients later supplied by the digestive system, they are
usually not in a form that can be used by the body. For example, it is
impossible to swallow a whole apple, have chunks of meat float through the
blood vessels, or have a piece of candy enter a brain cell. To pass through the
circulatory system and into cells, foods must be converted into small molecules
that are dissolved. The main aspects of this conversion process include
mechanically breaking large pieces of food into small pieces by chewing; adding
saliva to moisten food and dissolve small molecules; and chemically breaking
large nutrient molecules into smaller ones by using enzymes in digestive
juices.
Absorption Once nutrients are in a usable form, the
digestive system moves them from the GI tract into the circulatory system. This
step is called absorption. The blood and lymph distribute the
absorbed nutrients to other body regions.
Manufacturing Certain Materials Some nutrients
cannot be obtained from foods in adequate amounts. The digestive system
compensates for some of these deficiencies by manufacturing certain nutrients.
For example, only a portion of the substance called vitamin K, which helps form
blood-clotting materials, is obtained from foods. The rest is produced by
bacteria in the large intestine. Also, certain types of foods have inadequate
amounts of the amino acids needed to repair muscle cells and build red blood
cells. The liver can manufacture some of these amino acids so that they are
supplied at proper and fairly steady rates even when they are not eaten regularly.
Storing and Converting Excess Nutrients Though certain
foods have inadequate amounts of some nutrients, they often have a great
abundance of others. Furthermore, people usually eat only occasionally during
the day and eat only a few types of food. Therefore, the GI tract periodically
absorbs large quantities of certain nutrients. To prevent body cells from
receiving excessive amounts of these nutrients and becoming deficient in
others, the liver performs the fourth and fifth steps in supplying nutrients:
storing excess nutrients until they are needed and converting excess nutrients
into other nutrients that are in low supply in the foods eaten.
A second main function of the digestive system is
eliminating toxins and wastes. Though most materials absorbed by the GI tract
are beneficial, some are harmful to body cells (e.g., alcohol, detergents,
industrial solvents, inappropriate medications, bacterial wastes). Body cells
are protected from exposure to many of these substances because the liver
eliminates them. The liver also eliminates toxic substances produced by body
cells, such as ammonia and bilirubin. It converts harmful materials such as
alcohol and ammonia into useful or harmless substances and secretes others (e.g.,
bilirubin) into the GI tract in a liquid called bile. Many
substances in bile pass through the GI tract and are eliminated during a bowel
movement.
Various parts of the digestive system have other functions,
including helping with voice and speech (mouth region), storing blood (liver),
regulating certain components in the blood (liver), and producing hormones (GI
tract and pancreas).
Recall that large nutrient molecules must be broken into
smaller ones before they become usable. These large molecules include large carbohydrates,
all proteins, large lipids, and all nucleic
acids (Chap. 2). Chemical breakdown is necessary because these
molecules cannot usually pass through cell membranes
such as those lining the GI tract. Therefore, unless these molecules are broken
down into smaller ones inside the GI tract, they cannot be absorbed into the
blood. Even if they could enter the blood, they could still not pass through
the cell membranes of body cells.
The digestive system accomplishes chemical breakdown of
large molecules by using water molecules to split them into their constituent
parts. Large carbohydrates such as starch are split into simple sugars,
proteins are split into amino acids, lipids such as fat are split into fatty
acids and glycerol, and nucleic acids are split into nucleotides.
The digestive system assists this splitting through special
molecules called digestive enzymes, which are secreted as part of
the digestive juices. Digestive enzymes seem to work by properly positioning
water molecules at the chemical bonds linking constituents and by applying
pressure or tension to the water and nutrient molecules. As a result, the water
molecules split, and the fragments are used to separate the constituent parts
of the nutrient molecules. This process is called hydrolysis.
Each enzyme molecule can act over and over again, splitting
molecule after molecule without being destroyed. However, each type of enzyme
can help split only one type of nutrient molecule. Therefore, many different
enzymes are needed to split the many different types of nutrient molecules that
are ingested.
Only large nutrient molecules need to be hydrolyzed. Small
nutrients such as water, vitamins, minerals, simple sugars, and small lipid
molecules (e.g., cholesterol) can be absorbed simply by being dissolved in
digestive system fluids.
Age Changes Versus Other Changes
Like the respiratory system, many parts of the digestive
system are in more or less direct contact with substances and conditions from
the external environment. Examples include a wide variety of foods prepared and
eaten in diverse forms, physical trauma, dangerous chemicals, extreme
temperatures, high internal pressures, and unusual and noxious substances in
unregulated concentrations. Therefore, it is difficult to distinguish age
changes from changes produced by regularly ingested materials. However, certain
changes are observed in the digestive systems of essentially all people in the
United States. These changes will be presented as age changes. Alterations in
the digestive system that occur in only some people and alterations believed to
be caused by dietary factors or factors besides aging will be identified where
possible. Many of these alterations are discussed in the sections on abnormal
changes.
The oral cavity extends from the lips and
mouth to the back of the tongue, where the pharynx begins (Fig.
10.1). A moist membrane called the oral mucosa lines the inside
of the oral cavity and covers the tongue. The oral cavity also contains the teeth.
The salivary glands are connected to the oral cavity and secrete saliva
into the cavity through tubes called salivary ducts. Many muscles
for moving the mouth, the cheeks, the tongue, the lower jaw, and the region
leading into the pharynx are also present around the oral cavity. (Suggestion:
Chap 10 - 209-2-5)
The oral mucosa is similar in structure to the
epidermis on the surface of the face except that it is thinner and does not
have a surface layer of keratin. Like the epidermis, it serves as a barrier
against microbes, chemicals, water, and physical trauma. However, because the
oral mucosa is thin and lacks keratin, it is easily damaged and penetrated. For
example, medications such as nitroglycerine pass through it quickly and easily.
The lining of the oral cavity also provides information
about materials that enter the mouth, including their size, shape, texture,
temperature, and chemical composition. Special neurons that detect various
chemicals are located in the taste buds on the tongue. Impulses from these
neurons provide the taste sensations of salt, sweet, sour, and bitter.
A third function of the oral mucosa is the production of a
watery secretion that moistens the oral mucosa and foods. Moistening food
dissolves some of its molecules, which can then stimulate the taste neurons on
the tongue. This process also prepares food for absorption. The secretion from
the oral mucosa also lubricates food, making it easier to swallow.
Age Changes The lining of the
oral cavity undergoes age changes that are similar to those that occur in the
epidermis. For example, it heals more slowly. However, the oral mucosa can
normally perform its functions rather well throughout life. (Age changes in
taste perception are discussed in Chap. 6.)
There are 32 teeth in the oral cavity.
Sixteen of them form the upper row, which is attached to the upper jaw, and the
others form the lower row attached to the lower jaw.
The exposed surface of each tooth is covered with a cap (crown)
that is made of very hard enamel (Fig.
10.2). Internal to the enamel is a firm layer called the dentin.
The dentin surrounds the soft innermost material—the pulp—which
contains nerves and blood vessels serving the tooth. Some pulp nerve cells
extend into the dentin.
The lower part (root) of the tooth is embedded
in the jawbone and is composed of only dentin and pulp. It is surrounded by a
layer of cementum and an outermost periodontal membrane,
which attach the tooth to the jaw. Soft tissue called the gum
surrounds each tooth where it projects from the jawbone.
The role of teeth in supplying nutrients is to cut, tear,
and grind food into small pieces. Small pieces of food mix more easily with
fluids, fit more easily into the GI tract, and are better exposed to digestive
enzymes. Teeth also help in pronouncing words and affect the appearance of the
face.
Age Changes Though aging may have little effect on tooth
enamel, the enamel may become stained from foods. It also becomes thinner with
age because of normal wear from chewing hard materials. Faster thinning of the
enamel results from frequently eating very acidic foods; habitually grinding
the teeth, which often accompanies emotional tension; and excessively brushing
the teeth, particularly with a stiff toothbrush. If enough enamel is lost, the
underlying dentin may become exposed, and since the dentin contains nerve
cells, the tooth may become sensitive to touch or extremes in temperature.
As age increases, the dentin is slower to repair itself when
injured and often enlarges inwardly as the amount of pulp decreases. The loss
of nerve cells in the pulp reduces the sensitivity of the teeth; this increases
the risk of developing more serious tooth decay since it reduces a person's
ability to detect tooth problems. However, reduced pulp sensitivity also
lessens the discomfort from dental procedures.
Though the cementum becomes thicker with aging, there is an
overall weakening of the attachment of the teeth to the jaw, and age changes in
bone cause the jaws to weaken. At the same time the gums recede, exposing more
dentin, and so bacteria are better able to invade the base of the teeth and the
spaces between the teeth and the jaw. The combination of these changes
increases the incidence of disease around the base of the tooth (periodontal
disease).
Periodontal disease is a risk factor for atherosclerosis. The
mechanism by which periodontal disease contributes to atherosclerosis is not
known.
The main salivary glands occur as three pairs of
glands: the parotid, submandibular, and sublingual glands. Saliva produced by
these pairs of glands passes through salivary ducts to reach the oral cavity.
Some additional saliva is produced by small groups of cells and by individual
cells in the oral mucosa. The production of saliva by the salivary glands is
controlled by the autonomic part of the nervous system. Production is slow
under resting conditions but can become rapid and profuse when food is present
in the oral cavity.
Saliva is a watery solution that contains a mixture of
minerals and proteins. The water in saliva functions like the secretion from
the oral mucosa and helps to remove food from the teeth. Therefore, it also
reduces bacterial growth and delays the onset of cavities. The minerals and
proteins in saliva help preserve the mineral content of the enamel by
neutralizing acids and replacing lost minerals. Some proteins inhibit the
growth of certain types of bacteria and fungi. Finally, one salivary protein
(salivary amylase) serves as an enzyme that helps break starch molecules into maltose.
Maltose consists of two glucose molecules linked together.
Age Changes Though aging results in structural changes
in the salivary glands, age changes do not significantly affect the chemical
content of saliva produced by the main salivary glands. Also, aging causes no
important changes in the amount of saliva produced either at rest or after
stimulation by food.
The muscles of the mouth and oral cavity are skeletal
muscles under voluntary control. A few of these muscles open and close the
mouth; others move the cheeks, tongue, and lower jaw. The movements of these
muscles assist in eating, drinking, and speaking. Still other muscles in the
tongue, the region near the back of the oral cavity, and the pharynx are
important in swallowing.
Swallowing involves the coordinated action of many muscles.
First, food other than liquids is formed into a mass. The food mass and liquids
are then pushed to the back of the oral cavity and into the pharynx by the
tongue. When the mass of material in the pharynx has become large, a reflex
causes muscles above the mass to contract. Recall from Chap. 5 that the
swallowing reflex ensures that the pharynx is continually cleared of food (Fig.
5.6). At the same time, the reflex causes muscles below the mass to relax
so that the opening through the pharynx and into the esophagus enlarges. The
remaining reflexive muscle contractions in the region of the pharynx cause the
larynx to elevate, covering the opening into the larynx with a flaplike
structure called the epiglottis. All these muscle contractions
can be set into motion by voluntary contraction of muscles in the oral region
and upper pharynx even if there is little or no material in the pharynx.
As the muscle contractions above the food move farther
backward and downward, the food is pushed into the esophagus. At about this
time the continued downward movement of the contraction wave above the food and
the continued relaxation of muscles below it cause the
food to be pushed all the way down the esophagus and into the stomach. The wave
of contraction down the esophagus is called peristalsis (Fig.
5.6).
Age Changes Muscles in the oral region undergo the same
types of age changes as do all skeletal muscles. These changes, together with
age changes in the nervous system, cause a slight weakening and reduced
coordination in their functioning. There is a tendency to chew food less and
swallow larger pieces. Under normal conditions these changes have no important
effects on eating or speaking. However, when a person is in a stressful
situation, they increase the risk of choking because large pieces of food do
not pass through the pharynx as easily. Choking also may occur because food has
entered the larynx, which may not be completely closed. If food and other
materials being swallowed enter the respiratory system through the larynx,
blockage of airways, pneumonia, and other respiratory problems may develop.
The principal bones of the oral region are the upper and
lower jawbones, which support many oral structures. These bones are especially
important in supporting the teeth. The lower jawbone is attached to the skull
at the temporomandibular joint (TMJ). Proper operation
of the TMJ is important for chewing, swallowing, and speaking.
Age Changes Though the jawbones and the TMJ undergo age
changes similar to those in other bones and joints, these changes are so small
that the functioning of these components is not affected.
Oral Mucosa Many older people have difficulties with the
oral mucosa. The reasons for these problems include atherosclerosis in arteries
serving the oral region, dentures, medications, and many age-related diseases.
The results include weakening, injuries and sores, and slower healing. Some
medications and diseases affect the oral mucosa because they cause drying by
lowering saliva production. Others alter the sense of taste. These undesirable
abnormal changes can have adverse effects on nutrition and personality traits
(e.g., increasing irritability).
Teeth The combined effects of all age changes in
teeth and the passage of time increase the risk and incidence of spots of tooth
decay called cavities (caries). While many new
cavities develop, many are formed where previous cavities were filled by a
dentist. With advancing age, new cavities occur more in the roots of the teeth
than in the crowns.
Periodontal disease and cavities are a major source of
diverse problems for the elderly. First, the pain from these conditions can
reduce chewing. Less chewing leads to attempts to swallow larger pieces of
food, and this in turn raises the chances of choking and developing
indigestion. Difficulty with chewing also reduces the variety of foods eaten
and promotes the selection of foods with little fiber. Malnutrition and
constipation are common consequences of such choices. Oral discomfort can also
affect speaking, emotions, and personality traits.
Second, tooth disease spreads infection from the teeth to
other parts of the body. Third, tooth disease alters taste and can produce
unpleasant taste sensations. Fourth, obtaining professional help to treat tooth
disease is costly. Finally, an altered appearance from diseased teeth can
affect a person's social interactions and self-image and cause considerable
embarrassment. All these problems are made worse by the loss of teeth. The use
of dentures can only partially compensate for functional changes resulting from
tooth loss. Also, dentures are a main cause of injury, irritation, discomfort,
and infections in the oral mucosa.
The higher rates of periodontal disease and cavities with
age are the main causes of the high incidence of tooth loss among the elderly.
On the average, people over age 65 have lost approximately 11 percent of their
teeth. About 65 percent of those over age 65 have lost all their teeth in
either the upper or the lower jaw, and about 40 percent have lost all their
teeth. This number has declined from 50 percent over the last three decades
because of better dental care and, possibly, the introduction of fluoride into
drinking water. However, with more elderly people retaining more teeth longer,
there has been an increase in the incidence of periodontal disease and
cavities.
There are several ways to reduce or prevent dental diseases
among elderly people and the younger people who will become the elderly of the
future. Examples include drinking fluoridated water, especially during youth;
getting regular professional dental care; and following a program of good
dental hygiene. Good dental hygiene includes avoiding sweets, avoiding sugary
beverages such as soft drinks, rinsing the mouth with water after eating, and
brushing and flossing the teeth frequently. Since dental diseases at older ages
usually result from an accumulation of effects during one's lifetime, it is
important to start good dental practices during childhood and continue them throughout
life.
Salivary Glands Though aging has no important effects on the
functioning of the salivary glands, a number of conditions that occur more
frequently at older ages reduce saliva production. Such conditions include
reductions in fluid intake, infections of the salivary ducts, diseases such as
diabetes mellitus, certain medications, and radiation therapy.
Inadequate saliva production and the resulting oral dryness
can lead to (1) discomfort, (2) difficulty speaking, (3) bad tastes in the
mouth, (4) lowered taste perception, (5) increased risk of cavities,
periodontal disease, and oral infections, and (6) difficulty swallowing dry and
solid foods. The dietary modifications that may result, such as selecting only
soft moist foods, can lead to malnutrition and constipation.
Muscles The functioning of the oral muscles can be
adversely affected to a substantial degree by abnormal changes in or diseases
of the nervous system. For example, muscles around the mouth may become so weak
that the mouth has a drooping appearance and drooling occurs. When nerve cells
controlling other muscles are affected, speaking may be altered and swallowing
may occur abnormally.
Swallowing abnormalities are not common among fairly healthy
elderly people. However, up to 50 percent of elderly people in institutions may
have trouble swallowing. Serious consequences of swallowing problems that
result from improper muscle functioning include choking, pneumonia, and death.
Such consequences occur more often when liquids are being swallowed because
liquids can slip into the pharynx and larynx before reflexive muscle
contractions close the opening into the larynx. Since difficulty swallowing is
an abnormal condition that can lead to serious consequences, affected
individuals should seek qualified medical diagnosis and treatment.
Bones and Joints Serious alterations in the jawbones and TMJ
are also caused by abnormal conditions that increase in frequency with age.
First, loss of teeth usually results in shrinkage of the jawbones. As these
bones shrink, dentures fit less well and the appearance of the face changes.
Second, the functioning of the TMJ can be substantially reduced by arthritis.
In some individuals adverse psychological changes also
lead to pain and malfunctioning of the TMJ.
The esophagus is a tube that transports
materials from the pharynx to the stomach (Fig.
10.1). During swallowing, peristaltic muscular contractions in the
esophagus push materials into the stomach (Fig.
5.6). Coordinated contractions of the muscles are reflexively controlled by
a network of nerve cells (Auerbach's plexus) in the wall of the
esophagus. Since this network extends from the esophagus to the end of the
large intestine, it can coordinate many functions throughout the GI tract.
Aging causes esophageal peristalsis to become slightly slower
and weaker. This change seems to be caused by aging of neurons in Auerbach's
plexus. The result is an increase in the frequency with which materials do not
pass into the stomach as fast as usual or pass from the stomach up into the
esophagus and cause discomfort, which may be experienced as heartburn.
Esophageal Rings and Webs Though the esophagus normally functions well
throughout life, many older people develop abnormalities such as the formation
of esophageal rings and webs. These growths project inward from
the wall of the esophagus and partially block the passage through the
esophagus, causing difficulty swallowing.
Strictures A second abnormality is the formation of strictures,
which are rings of scar tissue that develop from repeated injury to the
esophagus. One cause of such injury is repeated passage of stomach contents
into the esophagus. A stricture blocks the esophagus because the collagen in
the scar tissue gradually shrinks, resulting in a narrowing of the passage
through the esophagus and difficulty swallowing.
Sliding Hiatal Hernia A third structural
abnormality of the esophagus is sliding hiatal hernia. In this
condition, the connection between the esophagus and the stomach slips above the
diaphragm rather than remaining in its normal position below the diaphragm. The
incidence of sliding hiatal hernia increases with age, and up to 70 percent of
those over age 70 develop this disease. Most cases result from alterations in
esophageal muscles and decreased elasticity of the diaphragm.
Other Abnormalities A fourth cause of abnormal esophageal
functioning is diabetes mellitus. Diabetes substantially slows peristalsis in
the esophagus and all other parts of the GI tract. Other abnormalities that
disturb esophageal functioning include nervous system diseases (e.g., strokes),
alcoholism, medications, and cancer.
Effects and Complications Abnormalities in the esophagus can result in
a variety of esophageal malfunctions. For example, peristalsis may not begin
during swallowing, or it may be very slow or uncoordinated or occur with
spasms. Each of these situations or partial blockage of the esophagus will inhibit
the movement of materials down the esophagus and into the stomach. Two results
are mild to severe discomfort and difficulty eating. Food selection may be
limited, and completing a meal may take an inordinate amount of time. In
addition, medications that fail to travel through the esophagus quickly can
injure the esophagus. Finally, esophageal malfunction can allow stomach
contents to flow upward and into the esophagus, a process called gastric
refluxing. Since the stomach contains strong acids, this can cause
pain, ulcers, and bleeding in the esophagus as well as esophageal strictures.
Sometimes stomach contents may enter the respiratory passages through the
larynx, causing hoarseness, inflammation of the respiratory system, or death.
For some photos of digestive system diseases, go to Preserved Specimen Photos and
to Microscope Slides.
For Internet images of normal digestive system structures or diseases, search
the Images section of http://www.google.com/ for the name of a
particular structure or disease. For diseases, I highly recommend searching WebPath:
The Internet Pathology Laboratory , the excellent complete version
of which can be purchased on a CD.
Prevention and Treatment The frequency and severity of the adverse
effects of esophageal malfunctioning can be reduced in several ways. The head
and trunk can be kept slightly elevated so that the force of gravity assists in
swallowing and helps prevent gastric refluxing. Avoiding large meals or obesity
results in the same benefits because pressure in the abdomen is kept low. Other
methods to reduce gastric refluxing include; avoiding foods and medications
known to increase stomach acid and gastric refluxing; using medications that
promote esophageal clearance, coat the esophagus, or reduce gastric refluxing;
using antacids to reduce stomach acidity; and undergoing surgical correction of
structural abnormalities.
The stomach is like a large sac (Fig.
10.1) whose walls can stretch to store large amounts of food. Food is
normally prevented from moving back into the esophagus by proper functioning of
the esophagus and proper pressures in the thoracic cavity. Contraction of a
ring of muscle (the pyloric sphincter) at the lower end of
the stomach temporarily prevents food from moving into the small intestine.
The inner lining of the stomach is a thick layer containing
many secreting cells. Some of these cells secrete hydrochloric acid
(HCl), and others secrete pepsin. When HCl and pepsin combine,
they cause the rapid breakdown of large protein molecules, which are usually
split into short chains of amino acids. HCl also kills bacteria and other
microorganisms that have been swallowed. A third secretion from the stomach
lining consists of intrinsic factor. Upon reaching the small intestine,
intrinsic factor promotes the absorption of vitamin B12. This
vitamin is important in the production of red blood cells. Finally, the stomach
secretes a hormone that helps control hunger.
The lining of the stomach absorbs water and small molecules
that have become dissolved (e.g., simple sugars, salts, alcohol, certain
medications). These materials enter the blood.
The middle layer of the stomach wall contains sheets of smooth
muscle. Rhythmic contractions of this muscle churn the food and stomach
secretions. The churning thoroughly mixes all materials and aids absorption by
bringing dissolved materials into contact with the stomach lining.
Once the stomach contents have been adequately liquefied,
the muscular contractions of the stomach become strong peristaltic waves. At
the same time the pyloric sphincter relaxes somewhat so that a portion of the
stomach contents is pushed into the small intestine. The pyloric sphincter then
closes, and stomach churning and absorption continue until the small intestine
is ready to receive more material. The functioning of the smooth muscle and the
pyloric sphincter is controlled by the autonomic nervous system and Auerbach's
plexus.
Aging causes small changes in the structure and functioning
of the stomach, including a slight thinning of the stomach lining, a small
decrease in HCl production, a possible decline in pepsin and intrinsic factor secretion,
and a minimal slowing of stomach emptying. These changes are usually so slight
that they do not prevent the stomach from performing its routine functions.
However, they can alter the absorption of some medications and the functioning
of the small intestine.
Though the normal stomach functions well regardless of age,
several abnormal and disease conditions become more frequent and severe with
age.
Atrophic Gastritis Atrophic gastritis results in
an excessive thinning of the stomach lining. The causes of many cases of this
abnormality are unknown, but many other cases result from the immune system
attacking the stomach.
Atrophic gastritis results in inadequate production of HCl
and intrinsic factor. The consequences include poor protein digestion,
alterations in the number and types of bacteria in the GI tract, and poor
absorption of vitamin B12. Finally, atrophic gastritis is a risk factor for
stomach cancer.
Poor protein digestion can lead to indigestion and
malnutrition. The alterations in bacteria can also adversely affect nutrition.
The reduction in vitamin B12 absorption leads to a significant reduction in red
blood cell (RBC) production. The number of RBCs in the blood eventually becomes
too low, and the person becomes anemic. Anemia caused by
inadequate production of intrinsic factor is called pernicious anemia.
The effects of pernicious anemia include sleepiness and persistent fatigue.
These symptoms are not part of aging.
Atrophic gastritis can be treated with medications to
relieve gastric discomfort and vitamin B12 supplements to prevent anemia.
Acute Gastritis A second age-related stomach disorder is
short-term stomach inflammation (acute gastritis). Reasons for
the increased incidence of acute gastritis include reductions in the resistance
of the stomach to environmental insults; increases in stomach infections due to
lowered stomach acid production; and increases in the use of medications such
as analgesics to relieve pain. Many analgesics (e.g., aspirin, steroids,
nonsteroidal anti-inflammatory drugs) irritate the stomach.
The main problem arising from acute gastritis is the
discomfort it causes. When attacks are frequent or severe, affected individuals
may eat less, lose weight, and develop malnutrition.
Most cases of acute gastritis can be prevented by avoiding
specific foods and medications. Taking antacids can relieve the symptoms in
some situations.
Peptic Ulcer In a peptic ulcer, stomach acid
and enzymes cause cells lining the GI tract to die and peel away, leaving a pit
in the wall of the tract (Fig.
10.3).
The occurrence of peptic ulcers in the esophagus has been
mentioned in connection with gastric refluxing. These ulcers also occur in the
stomach (gastric peptic ulcers) and the beginning of the small
intestine (duodenal peptic ulcers). Although duodenal peptic
ulcers are more common than gastric ones among younger adults, gastric peptic
ulcers become higher in frequency among the elderly.
Gastric peptic ulcers often result from weakening of the
stomach lining. Common causes include bacteria (H.pylori) or having unusually high levels of
anti-inflammatory steroids in the blood. The elderly are
more likely to have such elevated steroid levels since many medications used to
relieve pain and inflammation contain them. Even nonsteroid pain relievers such
as aspirin can increase the risk of gastric peptic ulcers.
A gastric peptic ulcer causes considerable pain. Usually the pain becomes worse shortly after eating because
more stomach acid is produced then. Although the pain is generally of lower
intensity at advanced age, other complications are usually more serious. If
scar tissue forms, it can shrink and narrow the stomach, leading to partial
obstruction. Peptic ulcers that bleed slowly lead to anemia, while those that
bleed profusely can cause sudden death. When an ulcer becomes very deep, the
stomach may perforate, allowing its contents to leak into the abdominal cavity.
The consequences may include severe pain, bleeding, digestion of neighboring
organs, a severe drop in blood pressure, and death.
The incidence and severity of gastric peptic ulcers can be
reduced by avoiding risk factors such as ulcer-promoting medications.
Treatments include antibiotics or avoiding foods and medications that promote
stomach irritation and ulcer formation. Conversely, medications such as
antacids can promote healing or retard worsening of the ulcer. Some ulcers
require surgery.
The small intestine is a tube approximately 6 meters (20
feet) long and 2.5 cm (1 inch) in diameter that extends from the pyloric
sphincter to the beginning of the large intestine (Fig.
10.1). It fits into the expansive region below the stomach by being coiled
and bent.
Like the stomach, the small intestine has a fairly thick
inner lining that secretes digestive juices. Materials in the intestinal
secretions include water and a variety of digestive enzymes. The water
dissolves small molecules and, with the enzymes, breaks down large nutrient
molecules. The breakdown of nutrients is aided by secretions from the liver and
pancreas.
The small intestine is also the section of the GI tract
where most nutrients are absorbed. As in the stomach, churning aids absorption
by bringing materials into contact with the inner absorptive surface.
Absorption by the small intestine is especially efficient because its lining
has a series of inward foldings and many microscopic
fingerlike projections (villi).
The inward foldings and villi
permit rapid absorption by increasing the surface area that is in contact with
dissolved nutrients. Absorption by the villi is aided by the presence of many
capillaries and lymph vessels, which allow nutrients to enter the circulatory
system quickly. Most absorbed nutrients enter the blood vessels, though fat
enters the lymph vessels.
The absorption of three nutrients by the small intestine
requires special assistance. First, iron can be absorbed
effectively only if the stomach has treated it with adequate amounts of HCl.
Iron functions in the production of red blood cells. Second, vitamin B12
can be absorbed in adequate amounts only if the stomach provides the small
intestine with enough intrinsic factor. Vitamin B12 is also important for RBC
production. Finally, calcium absorption requires the presence of
activated vitamin D, which also allows the small intestine to increase the
efficiency of calcium absorption when calcium in the diet or the body falls
below desirable levels. Having adequate calcium is necessary for several
functions, including maintenance of strong bones, muscle contraction, and
nervous system activities.
As digestion and absorption continue, the contents of the
small intestine are moved forward periodically by peristalsis. The basic
actions and control mechanisms for peristalsis are similar to those in the
stomach. By the time the contents have reached the end of the small intestine,
almost all useful nutrients have been fully digested and absorbed. The
remaining indigestible substances, wastes in bile from the liver, bacteria, and
much water are pushed into the large intestine.
Aging seems to have little effect on the structure and
functions of the small intestine. The age changes that have been observed, such
as alterations in villi, apparently do not have important effects on intestinal
functioning.
Lactase Secretion One exception is a gradual decrease in the
secretion of lactase, which splits lactose into two
simple sugar molecules. Lactose is found in milk and many foods made from milk.
The decline in lactase varies from person to person with
respect to time of onset and severity. Because of genetic factors, several
groups (e.g., blacks, Asiatics, people of
Mediterranean descent) have a significant decrease in lactase secretion during
childhood or adolescence while most white people retain adequate lactase
secretion well into adulthood. However, lactase secretion eventually becomes
quite low in many older individuals. When it becomes too low, much of the
lactose consumed in milk and milk products is not broken down. Certain types of
bacteria in the intestine then use the undigested lactose for their own
nutrition, resulting in much intestinal gas production. The gas can cause
considerable discomfort or temporary disability. Such individuals are said to
have lactose intolerance.
Many people with lactose intolerance avoid its consequences
by abstaining from milk and foods containing milk. However, since dairy
products are a major source of calcium, this can lead to calcium deficiency,
which is a main risk factor for osteoporosis.
There are ways to avoid the adverse effects of lactose
intolerance while still consuming milk and milk products. One way is to consume
milk or milk products that have had lactose converted to other substances by
bacterial action or lactase additives. Examples include certain types of yogurt
and hard cheeses. Another way is to take lactase supplements. People who cannot
use these methods should consume nondairy foods containing high levels of
calcium, such as green leafy vegetables, canned fish, and calcium-supplemented
orange juice.
Absorption A second exception is a decline in the
ability of the small intestine to absorb vitamins A, D, K and zinc. These
decreases become important only for individuals whose diets contain low levels
of these nutrients. The consequences of these deficiencies include skin and
vision problems; weak bones; slow blood clotting; and decreased healing, immune
function, and taste sensation, respectively.
Although the small intestine retains most of its absorptive
power, its ability to absorb certain nutrients is adversely affected by other
changes that often accompany aging. These changes include reduced production of
HCl and intrinsic factor by the stomach and declining levels of active vitamin
D.
Low HCl production reduces the absorption of iron and
calcium and alters the numbers and types of bacteria that grow in the small
intestine. As the bacteria change, the ability of the small intestine to absorb
many nutrients declines. Individuals with marginal diets or severe HCl
deficiencies are likely to develop iron or calcium deficiencies as well as
other types of malnutrition. Individuals with very low intrinsic factor
production, such as those with atrophic gastritis, and people with minimal
vitamin B12 intake, are likely to have vitamin B12 deficiency and the resulting
anemia.
Recall that vitamin D is produced in a series of steps and
is finally activated by the kidneys. The amount of active vitamin D in the body
usually decreases with age because of several factors. These factors include
less absorption of dietary vitamin D by the small intestine; less exposure of
the skin to sunlight; less vitamin D production by skin cells; less activation
of vitamin D by the kidneys; and inadequate intake of vitamin D in the diet.
The dwindling levels of active vitamin D and a gradual
decline in the ability of the small intestine to respond to vitamin D cause
calcium absorption by the small intestine to decline. Older people with very
low levels of vitamin D and those with a poor dietary intake of calcium are at
high risk of developing calcium deficiency and osteoporosis.
Peptic Ulcer As was mentioned earlier, one abnormality in
the small intestine is a duodenal peptic ulcer (Fig.
10.3). Factors contributing to duodenal peptic ulcers include bacteria (H.pylori), emotional
stress, excess caffeine consumption, and excess stomach acid production. The
incidence of this condition does not change with age.
Unlike gastric peptic ulcers, the pain associated with
duodenal peptic ulcers usually subsides after eating and intensifies when the
stomach is empty. This pattern probably results because movement of acidic
stomach contents into the small intestine is slowed when the stomach contains
food. Other than the pain, the effects and complications of duodenal peptic
ulcers are similar to those of gastric peptic ulcers.
Duodenal peptic ulcers can be prevented by avoiding the
contributing factors. Treatment strategies are similar to those for gastric
peptic ulcers, though the specific medications used and other details of the
treatment may differ.
Secondary Abnormalities The functioning of the small intestine also
is adversely affected by many abnormal changes and conditions that are more
common among the elderly. Examples include poor diet; infections; poor
circulation; diseases of the skin, stomach, liver, gallbladder, pancreas, or
small intestine; hormone imbalances; medications; and surgery. When any of
these factors lead to detrimental changes in the small intestine, serious
malnutrition can result.
The large intestine, which is about 1.5 meters (5 feet)
long, extends from the end of the small intestine to the end of the GI tract (Fig.
10.1 and Fig.
10.4). Most of the large intestine is referred to as the colon.
The last section of the colon has an S shape and is called the sigmoid
colon. The sigmoid colon leads into the final segment of the large
intestine, the rectum (Fig.
10.4b). The rectum, which is several centimeters long, leads into a very
short passage called the anal canal. This canal ends at the anus,
which is the opening from the large intestine to the outside of the body. The
appendix is a fingerlike projection jutting out from the colon just below the
junction of the small intestine and the colon.
A smooth layer of cells lines the inner surface of the large
intestine. Many of these cells secrete a lubricating mucus that aids the
passage of materials. The materials in the large intestine are called feces.
Many other lining cells absorb water, minerals, and vitamin K from the feces.
Much of the vitamin K is produced by bacteria that normally reside in the
feces. The absorption of most of the water and minerals from the feces is
essential for maintaining adequate supplies of these substances for body cells.
Vitamin K is needed to form blood-clotting materials. Absorbed substances pass
into the blood.
Within the wall of the colon, some smooth muscle lies in
three narrow ribbonlike bands (teniae coli). These
bands run parallel along the length of the colon and are nearly evenly spaced
around its circumference. The remainder of the smooth muscle lies in rings
spaced little more than 2.5 cm (1 inch) from each other. This leaves regularly
arranged patches of the colon wall with little muscular support. Since these
patches (haustra) are weaker areas, they bulge outward.
As in the stomach and small intestine, smooth muscle in the
colon churns materials and moves them along by peristalsis. The activity of
this smooth muscle is encouraged by exercise and other physical activity. The
muscle has diminished activity when a person is sedentary.
The churning action assists in the absorption of useful
substances by mixing the feces and bringing them into contact with the lining
of the large intestine. The absorption of water causes the feces to change in
consistency from a liquid to a soft semisolid. As more indigestible material
continues to enter the large intestine from the small intestine, the total
amount of feces gradually increases.
The accumulation of feces causes the pressure inside the
large intestine to increase, and the intestine is stretched outward. These
changes cause neurons in the intestinal wall to activate large-scale
peristalsis (mass peristalsis) throughout the length of the large
intestine. Eating a meal or having stimulatory chemicals in the large intestine
can also reflexively activate mass peristalsis, which pushes feces into the
rectum.
Initially, the feces are prevented from passing out of the
rectum through the anus by two rings of muscle in the anal canal. The inner
ring (internal sphincter) is made of smooth muscle and is
controlled by reflexes (Fig.
10.4b). The outer ring (external sphincter) is made of
skeletal muscle and is under voluntary control. These muscular rings cause
retention of feces because they are usually in a state of contraction, which
closes the passage through the anal canal and the anus. The internal sphincter
provides about 85 percent of the force needed to retain feces, and the external
sphincter provides the remaining 15 percent.
As the quantity of feces in the rectum increases, the rectum
is stretched outward. When it stretches nearly as far as it can, further influx
of feces causes pressure in the rectum to increase dramatically. Sensory
neurons in the rectum are stimulated, and the person begins to perceive the need
to pass the feces. The stretching and rise in pressure also cause rectal
neurons to produce reflexive relaxation of the internal sphincter muscle, and
there is an increase in the perception that elimination of feces is needed.
Then only the external sphincter prevents the exit of feces through the anus.
It is easier for the external sphincter to retain feces with a more solid
consistency than to retain less solid or more watery feces.
At this point the individual can prevent the release of
feces by voluntarily continuing contraction of the external sphincter.
Alternatively, the person can cause the external sphincter to relax. Then the
pressure in the rectum will begin to push feces out of the body through the
anal canal and the anus. This action is often accompanied by reflexive
peristalsis in the large intestine and voluntary contraction of the abdominal
muscles. Since these additional contractions increase pressure in the large
intestine, they assist in pushing feces through the anus.
As the rectum empties, the stretching and pressure in the
rectum subside. Then reflexive contraction of muscles in and around the anal
canal eliminates the feces still in the canal. Finally, the internal sphincter
contracts again, and elimination of feces stops. Elimination of feces is often
called a bowel movement or defecation.
Voluntary contraction of the external sphincter can delay
defecation for an extended period. If a sizable mass of feces is retained in
the rectum, the rectal muscles relax, allowing the rectum to stretch outward
and the pressure to drop. As a result, the urge to defecate subsides until more
feces enter the rectum and the pressure rises again. However, control of the
external sphincter is retained only as long as the pressure in the rectum
remains low or moderate. Very great pressure in the rectum causes
uncontrollable reflexive relaxation of the external sphincter, and defecation
occurs.
The appendix is a small and unimportant part
of the large intestine (Figs. 10.1 and 10.4a). Though its size and shape
vary considerably from person to person, typically the appendix looks like a slender
finger approximately 5 to 7 cm (2 to 3 inches) in length. The narrow passage
within the appendix has one opening, which leads into the colon, and the wall
of the appendix contains many lymph nodes.
In humans the appendix has no role in digestion. Normally,
no materials from the intestine enter the appendix. Like all other lymph nodes,
its lymph nodes help prevent the spread of infection and serve as part of the
immune system.
With aging, the lining of the large intestine becomes somewhat
thinner and less mucus is secreted. These changes may be due partially to
arteriosclerosis in small arteries that serve the large intestine. There is
also a slight shrinkage of smooth muscle in the large intestine. Usually the extent of these changes is not great enough to
alter the functioning of the large intestine significantly.
Movements An age change in the colon that may produce
important consequences in some older individuals is a decrease in the
responsiveness of the smooth muscle to neuron messages. This tends to delay the
onset of peristalsis, and more time is needed for feces to pass through the
large intestine.
When feces spend more time in the large intestine, more
water is absorbed, and the feces become firmer and more difficult to move.
Bowel movements occur less frequently, and defecation becomes more difficult.
If periods between bowel movements become abnormally long or defecation
requires excessive straining, the abnormal condition called constipation
has developed.
Defecation Aging and other age-related factors cause
three significant changes in the rectum. The other factors include surgery in
the rectal area, forced bowel movements, and childbearing and reduced estrogen
levels. One resulting change in the rectum is an increase in the amount of
fibrous tissue in the walls, which reduces the amount of rectal stretching as
feces enter. A second change is a decline in the strength of contraction of the
internal sphincter. The third change is a decrease in the motor neurons controlling
the external sphincter.
Each of these changes reduces the ability of the sphincter
muscles to delay defecation until it is appropriate. Though inappropriate fecal
elimination can happen to anyone, having such occurrences on a regular or
frequent basis is abnormal. When inappropriate elimination of feces happens at
least once a month, the condition is called fecal incontinence.
Appendix Age changes in the appendix (e.g., narrowing,
increasing fibers, decreasing lymphatic tissue) have no known effect on the
body.
Constipation Though age has little effect on the
structure and functioning of the large intestine, many aging people develop one
or more abnormalities. One of the most common conditions is constipation.
Generally, constipation occurs when bowel movements occur less than three times
a week. However, since there is great variation in the frequency of bowel
movements among individuals, better indicators are having an unusual decrease
in the frequency of bowel movements and needing to strain excessively during
defecation.
Although the incidence of constipation rises with age, it is
difficult to estimate its actual frequency because of preconceived notions
about how frequently bowel movements should occur and the use of laxatives.
(A laxative is a substance that is ingested to promote bowel movements.)
However, regardless of the confusion over the precise incidence, constipation
is a problem for many elderly people. A variety of factors can contribute to
the onset of constipation, including inadequate fluid intake, inactivity,
delayed defecation, inadequate or excess fiber intake, and laxatives.
One of the most abundant types of dietary fiber is
cellulose, which is contained in fruits and vegetables. Bran also contains much
cellulose. Cellulose is especially important because it binds much water and
thus makes feces large in volume but soft in consistency. Large soft feces
stimulate peristalsis and are easy to move and eliminate by defecation.
Laxatives come in a variety of forms and work in different
ways. Among the different types are fiber supplements, oils, magnesium salts,
and intestinal stimulants.
Constipation can lead to significant discomfort and many
complications. The discomfort may include indigestion, a bloated feeling, pain
and embarrassment from intestinal gas, and difficulty defecating. One
complication is an increased risk of future constipation. This occurs because
the sensitivity of rectal sensory neurons declines when the rectum is stretched
for long periods. With reduced rectal sensitivity, the urge to defecate and the
reflexes involved in defecation are suppressed and defecation is delayed.
Additional complications include diarrhea, fecal incontinence, diverticulosis,
hemorrhoids, and cancer, which are discussed below. Still other complications
include obstruction of the large intestine, formation and absorption of toxins,
infections, difficulty urinating, irregular heart functioning, and heart
attack.
Since constipation is not an age change and since its causes
are largely known and controllable, much can be done to prevent its occurrence.
Preventive measures are based on minimizing factors that contribute to
constipation. Special consideration is required to ensure that toilet
facilities and assistance are readily available to those who are disabled.
Treatments for people with constipation are derived from these
preventive measures. They include gradually increasing fluid intake, physical
activity, and dietary fiber. Regular bowel movements can be promoted by
scheduling regular visits to the toilet. Laxatives should be used only when
other treatments fail since regular laxative use promotes constipation and can
cause other serious side effects, such as dehydration, vitamin deficiencies,
and mineral imbalances.
Some cases of constipation can be relieved by using
suppositories containing substances that stimulate mass peristalsis. These
suppositories are inserted into the rectum through the anus. Other cases of
constipation can be relieved by enemas. If feces are especially hard and
difficult to pass, it may be necessary for a physician to remove them through the
anus.
Diarrhea A second abnormality of the large intestine
that is important in elderly populations is diarrhea. Diarrhea is
characterized by the presence of more than three relatively liquid and
voluminous bowel movements a day. Causes of diarrhea are listed in Table 10.1.
One of the most serious consequences of diarrhea is an
abnormally high loss of water and minerals. When body fluid levels drop,
maintaining adequate blood pressure and blood flow to vital organs such as the
heart, brain, and kidneys becomes difficult. These organs begin to malfunction
and fail. Disturbances in mineral homeostasis can also adversely affect the
heart and brain and disrupt muscle functioning.
Three factors make these outcomes from diarrhea especially
likely among the elderly. First, many elderly people already have reduced blood
flow to the heart, brain, and kidneys because of atherosclerosis. Second, aging
reduces the ability of the kidneys to maintain adequate fluid levels. Third,
the decrease in thirst sensation caused by aging reduces the urge to replace
fluids by drinking. Individuals who take medications that increase fluid output
by the kidneys (i.e., diuretics) or that lower blood pressure have an even
greater risk of developing circulatory failure.
Another important consequence of diarrhea is temporary loss
of the ability to retain feces when defecation is inappropriate. An individual
of any age who has diarrhea may have difficulty retaining feces because of
their liquid consistency and large volume and because of the strong urge to
release them. Older individuals have even greater difficulty because of age
changes that weaken and reduce control of the anal sphincters. Any other
condition that reduces conscious control of muscles or delays access to toilet
facilities further increases the risk of unwanted defecation when a person has
diarrhea. Examples of such conditions that are more prevalent among older
individuals include CNS disorders (e.g., Alzheimer's disease) and physical
disabilities (e.g., fractures, arthritis). Repeated incidents of diarrhea can
cause fecal incontinence (see below).
Many cases of diarrhea can be prevented by avoiding factors
that cause diarrhea. A main aspect of treatment is replacing lost fluids and
minerals. However, care must be taken to avoid introducing excess fluids, which
can overwork the heart and cause fluid accumulation in the lungs. When diarrhea
is caused by certain types of bacteria, treatment may include antibiotic
therapy. Good nutrition and anti-inflammatory medications can speed recovery
from diarrhea. Medications that slow motility of the large intestine should be
avoided since they increase the risk of retaining feces and absorbing toxins.
Fecal Incontinence A third abnormal condition of the large
intestine is fecal incontinence, which can be defined as having
inappropriate elimination of feces at least once a month.
Recall that fecal incontinence can be a complication of
constipation. This occurs because mass peristalsis finally becomes strong
enough to force feces into the rectum. Age changes in the rectum and anus that
reduce the ability to retain feces voluntarily contribute to fecal incontinence
from constipation and to the age-related increase in fecal incontinence from
other causes. Among the factors that cause fecal incontinence are constipation;
diarrhea; physical injury to the colon, rectum, or anus; nervous system
abnormalities; diabetes mellitus; disability; and psychological disturbances.
Since many of the causes of fecal incontinence develop
slowly and progressively and since each aging person may encounter more of
these causes as time passes, fecal incontinence usually develops gradually and
becomes worse over time.
The consequences of fecal incontinence are diverse and
devastating. If feces are present on clothes or bed linens, they may also be in
contact with the skin for prolonged periods, irritating the skin and causing
infections. Even if these problems are avoided, people with fecal incontinence
often suffer severe social disruption, social isolation, and psychological
upheaval. The magnitude of the disturbances is sufficient to make fecal
incontinence (together with urinary incontinence) the second leading cause of
institutionalization among the elderly. Only disorders of the nervous system
such as strokes and dementia rank higher as a cause of institutionalization.
Since fecal incontinence is an abnormal condition and since
its causes are well known, much can be done to prevent, reduce, or stop its
occurrence. The main strategy in each case is to identify the specific causes
and reduce or eliminate them. Suggestions for preventing or stopping
constipation and diarrhea were presented above. Individuals with structural
irregularities of the colon, rectum, or anus may be helped by corrective
surgery. Many individuals whose fecal incontinence results from disorders
affecting the nervous system can be helped by biofeedback training combined
with exercising the external sphincter muscle to increase its strength.
Biofeedback training and muscle strengthening can also be helpful for
individuals who are incontinent for reasons other than nervous system
disorders. Such training increases the individual's awareness of the need to
defecate and the individual’s control of the external sphincter. Strengthening
the external sphincter enables the individual to retain feces until defecation
is desired. A combination of training and muscle strengthening is required for
significant and long-lasting progress in reducing or stopping fecal
incontinence.
Another key factor in preventing or reducing fecal
incontinence is making toilet facilities easily accessible or available at
appropriate times by scheduling visits to the toilet at specific times or intervals.
Attempting to defecate shortly after eating is often effective because filling
the stomach leads to reflexive mass peristalsis and a high probability of
having a successful defecation shortly afterward. Using dietary modifications
to regulate intestinal functioning can also increase control of defecation.
Examples include regulating water intake and reducing the intake of foods such
as beans, cabbage, and cauliflower, which cause intestinal gas production.
Control of defecation can be further increased by using medications to regulate
intestinal functioning or by modifying the use of medications for other
disorders.
Many aspects of preventing or reducing the incidence and
effects of fecal incontinence depend on the actions of those who care for affected
individuals. While ample care is important, the extra attention and social
interaction that usually accompany the extra care may perpetuate or increase
the problem by unintentionally providing positive reinforcement for incidents
of incontinence.
Diverticulosis and Diverticulitis Diverticulosis
is characterized by the presence of deep outpocketings
(diverticula) in the wall of the large intestine (Fig.
10.5). Usually, each diverticulum has a narrow opening leading to an
expanded outer region. Most diverticula occur in the sigmoid colon.
Diverticulosis is present in about 30 percent of people over
age 60, its incidence increases to about 50 percent of those over age 70, and
it may occur in 60 percent of those over age 80. The number of diverticula
increases with age.
Though 80 to 85 percent of people with diverticulosis have
no ill effects from this disorder, diverticula in the remaining 15 to 20
percent become inflamed. When this occurs, the condition is called diverticulitis.
The longer a person has diverticulosis, the greater is the chance of developing
diverticulitis.
Diverticulosis develops when excessive pressure from strong
mass peristalsis, such as from constipation or intestinal spasms, cause the
intestinal wall to bulge outward at weak spots such as haustra and blood
vessels. Most cases are believed to result from inadequate amounts of fiber in
the diet over a period of years.
Diverticulosis leads to diverticulitis when fecal material
becomes trapped within the diverticula and produces noxious material.
Irritation of diverticula by entrapped indigestible particles such as seed hulls
may also cause diverticulitis.
Most people who develop diverticulitis experience
significant abdominal pain, constipation, or diarrhea. Diverticulitis causes
intestinal bleeding in approximately 25 percent of cases. Though the bleeding
is usually slow and is not life-threatening, it may lead to anemia. Individuals
with anemia usually become fatigued quickly and may be lethargic because
inadequate amounts of oxygen are delivered to body cells.
Other serious complications of diverticulitis include infection
and perforation of the large intestine. If the large intestine perforates,
feces can pass into the surrounding body cavity. This condition can cause
excruciating pain and lead to death from extremely low blood pressure or
widespread infection.
Prevention of diverticulosis and diverticulitis is
relatively easy if adequate dietary fiber is consumed daily and constipation is
avoided. Those who have developed either abnormality can be helped by
increasing their intake of dietary fiber, avoiding constipation, and avoiding
foods containing seeds or other materials that increase intestinal
inflammation. Antibiotics may be prescribed for those who have developed
infections. Individuals with advanced cases of diverticulosis may require
surgical removal of portions of the large intestine.
Hemorrhoids A fifth abnormality of the large intestine
is the presence of hemorrhoids (Fig.
10.5). These varicose veins in the rectum and anal canal were discussed in
Chap. 4. Their occurrence increases and they become more of a problem as age
advances because the factors that promote them increase with age.
Hemorrhoids result from conditions that cause repeated high
pressure in the rectal and anal areas such as straining during bowel movements
that accompany constipation, straining while lifting heavy objects, chronic
coughing from bronchitis, and cirrhosis of the liver. Hemorrhoids can cause
considerable pain and discomfort and, if they bleed regularly, can lead to
anemia. Injured and inflamed hemorrhoids may become infected.
Preventing hemorrhoids involves avoiding circumstances that
cause high pressures near the rectum and anus. Individuals with hemorrhoids can
relieve discomfort by applying appropriate salves to the affected area. More
advanced cases and hemorrhoids that contain clotted blood can be treated
surgically.
Cancer Cancer
is a disease characterized by uncontrolled reproduction and spreading of cells.
Cancer of the large intestine is called colorectal cancer (Fig.
10.5).
The incidence of colorectal cancer increases dramatically
after approximately age 40, nearly doubling with each 5-year increase beyond that
age. It occurs equally among men and women. Of all forms of cancer in the
United States, only lung cancer occurs with a higher frequency.
Colorectal cancer is a common cause of death. It ranks as
the third leading cause of death from cancer, accounting for about 15 percent
of all deaths from cancer in adults. Only lung cancer and breast cancer cause
more deaths. Since colorectal cancer increases in incidence with age, it ranks
as a major cause of death among the elderly. It is the second leading cause of
cancer deaths for men over age 75 and the leading cause of cancer deaths for
women over age 75.
Though the causes of colorectal cancer are not known,
several factors are known to increase the risk of developing it. They include
diets low in fiber; diets high in meats, animal fat, or sugar; having relatives
with colorectal cancer; having the identifiable gene that promotes familial
colorectal cancer; having cancer of the breast or female reproductive organs;
having noncancerous intestinal growths such as polyps; and conditions that
cause chronic intestinal inflammation, such as ulcerative colitis.
Colorectal cancer can cause obstruction of the large
intestine and destroy the intestinal wall. Obstruction can cause toxic
materials from intestinal bacteria to accumulate and be absorbed into the body.
Obstruction of the large intestine or destruction of the intestinal wall can
lead to intestinal perforation and widespread infection. Colorectal cancer can
also cause substantial bleeding. Finally, it often spreads to other parts of
the body, such as the liver and lungs, and can destroy any organ it enters. The
functioning of organs damaged by cancer is reduced, and their ability to help
maintain homeostasis diminishes. Illness and death result.
One main way to combat colorectal cancer is to reduce the
major dietary risk factors. Such changes seem to minimize the formation and
accumulation of carcinogens in the large intestine. Other important preventive
measures for colorectal cancer and its consequences include early detection and
prompt treatment. Warning signs, such as having blood in the feces and having
noticeable changes in bowel functioning, should be followed up by a
professional examination. People over age 40 should have routine diagnostic
testing for this cancer. People with a family history of colorectal cancer can
be screened for the presence of the gene, for familial colorectal cancer and
can receive more frequent and thorough diagnostic testing if they have the
gene. Finally, removal of polyps may be advisable.
Once colorectal cancer has developed, the only effective
treatment is surgical removal of the affected areas. Chemotherapy or radiation
therapy is sometimes used before surgical treatment of cancer in the rectum or
anus.
Appendicitis
Inflammation of the appendix (appendicitis)
may be caused by entrapment of feces within the blind passageway in the
appendix or infection of the lymph nodes in the appendix wall, both of which
cause the appendix to become infected (Fig.
10.5). The infection can be spread through the body by the circulatory
system. A life-threatening crisis develops if the appendix ruptures and feces
and infected material, such as pus, spread into the body cavity surrounding it.
Older people face the same dangers of infection found in younger people.
The incidence of appendicitis decreases with age. However,
cases in older individuals may be more severe, and the incidence of rupturing
increases because age-related reductions in sensitivity to symptoms and milder
signs of disease cause a delay in seeking diagnosis. In addition, an
age-related reduction in blood flow allows deterioration of the appendix to
occur faster and rupturing to occur sooner. Appendicitis is treated by surgical
removal of the appendix. Antibiotics may be administered to combat infection.
The liver is the largest gland in the body (Fig.
10.1). It is made up of microscopic units called lobules,
which resemble each other in structure and functioning (Fig.
10.6). The liver cells making up each lobule are arranged in a radiating
pattern, allowing blood from the periphery of the lobule to flow through large
capillaries among the cells as it moves to the center of the lobule. These
capillaries are called liver sinusoids.
Blood enters the outer region of the lobule from arteries
and veins at several points around the periphery of the lobule. The blood in
the arteries comes from the heart and delivers oxygen and substances such as
hormones from other organs to the liver cells. The blood in the veins comes
from capillaries in the stomach, small intestine, large intestine, and
pancreas. Blood from the spleen also passes through veins leading into the
lobules. Since all these veins deliver blood to the liver rather than returning
it to the heart, they are called the hepatic portal system (Fig.
10.7).
Once blood from the arteries and the hepatic portal system
has passed through the liver sinusoids, it is collected by a central vein at
the center of the lobule. Blood from all the central veins moves into hepatic
veins, which send it into a main vein going to the heart (the inferior
vena cava). This arrangement of vessels permits the liver cells to adjust the
contents of blood from digestive organs and the spleen before sending it to
other parts of the body. The most abundant type of liver cells (hepatocytes)
regulate the chemical makeup of blood. Other cells (Kupffer's
cells) remove unwanted particles such as bacteria and damaged red blood
cells from the blood (Fig.
10.6).
In addition to blood vessels, each lobule contains other
small passageways called bile canaliculi (Fig.
10.6). Bile, which is produced by hepatocytes, moves through the canaliculi
to the periphery of the lobule, where it is collected into bile ducts.
These ducts converge into one large duct, the hepatic duct, which
carries the bile out of the liver (Fig.
10.8). Bile in the hepatic duct may flow through the cystic duct
for storage in the gallbladder or through the common bile
duct into the small intestine.
Each lobule contributes to every liver function. Many of
these functions were mentioned earlier in this chapter. For example, the liver
helps convert foods to a usable form by secreting bile and sending it to the
small intestine. Bile is a complex mixture of materials,
including water, cholesterol, bile salts, and bile pigments. The salts and
pigments are mostly waste materials removed from the blood. For example, when
red blood cells are destroyed, parts of their hemoglobin molecules are
converted into bilirubin, which is secreted into the bile. Bile
also contains the breakdown products of cholesterol.
Bile helps convert foods to a usable form by breaking up
droplets of fat from foods. This emulsification process allows digestive
enzymes to hydrolyze the fat more easily. Bile also assists with absorption by
allowing some fat to be absorbed by the small intestine without being
hydrolyzed.
Since blood from the stomach and intestines flows through
the liver before it is sent to other parts of the body, the liver can remove
excess amounts of nutrients. The liver uses these extra nutrients to
manufacture substances that are at inadequate concentrations in the blood. For
example, hepatocytes remove excess sugar that is absorbed after one eats a
sweet dessert. Some of the sugar may be converted into other nutrients (e.g.,
fat) that may be in low supply in the food, and some may be stored in the liver
as glycogen. Later, when blood sugar levels drop, the liver converts the
glycogen back into sugar and returns the sugar to the blood. Thus, body cells
receive fat and sugar at a steady rate.
Passing blood from the stomach and intestines through the
liver also allows the hepatocytes to remove harmful or toxic materials that
have been ingested and absorbed, such as alcohol from alcoholic beverages. The
liver also removes unwanted materials produced by body cells, such as ammonia
and bilirubin. Ammonia produced by intestinal bacteria and absorbed by the
intestine is also removed from the blood. The liver converts the toxic ammonia
to a much less dangerous material called urea. Finally, the liver
removes many medications from the blood.
The liver has several other functions. One is helping to
maintain proper and fairly stable blood pressure. Because it has so many large
blood vessels, the liver can hold a large volume of blood. When blood pressure
begins to drop, constriction of liver vessels sends more blood to the heart and
arteries, restoring blood pressure to normal levels. Alternatively, relaxation
and dilation of liver vessels remove some blood from circulation and lower
blood pressure when it becomes too high.
Finally, the liver regulates many substances in the blood
that are not considered nutrients. For example, it manufactures several
substances (e.g., fibrinogen, prothrombin) that are involved in forming blood
clots. It also makes many of the blood proteins that regulate the distribution
of water in the body. Without adequate amounts of these proteins, much water
leaves the blood and accumulates around body cells. This condition (edema)
can cause uncomfortable swelling; when it occurs in the lungs, respiration is
seriously impaired. Finally, the liver plays a major role in removing excess
hormones from the blood. Important examples include aldosterone, which
increases salt and water reabsorption by the kidneys, and sex steroids.
Aging causes little change in the overall structure of the
liver, though there seems to be a slight decrease in size, the total amount of
blood flow through the liver may decline, and liver cells become somewhat
altered.
These slight structural age changes seem to have little or
no effect on the functional capacity of the liver. This maintenance of function
probably stems from two features. First, the liver has a very large functional
reserve capacity. As much as 80 percent can be removed, and the remaining
portion can maintain normal body operations when conditions are favorable.
Second, the liver easily regenerates new cells when older ones are damaged or
destroyed. This regenerative ability is unchanged by aging. Studies of age
changes in the liver suggest that both the storage of vitamin C and glycogen
and the removal of a few medications (e.g., acetanilide, diazepam) declines.
Elimination of particulate material by Kupffer's cells may decline with aging.
It is important to note that smoking significantly reduces toxin, waste, and
drug elimination by the liver.
Cirrhosis A common and serious abnormal condition that
often accompanies old age is the disease called cirrhosis. In
this disease, the liver is converted into a lumpy scar-filled organ with
greatly reduced functioning (Fig.
10.6). Though many cases of cirrhosis occur among younger adults, this
disease ranks among the top 10 causes of death among those over age 55.
Cirrhosis results from long-term repeated or continuous
liver damage. Such damage among the elderly is most commonly caused when
gallstones block large bile ducts. The resulting accumulation of bile in the
liver puts pressure on liver cells and, together with chemicals in the trapped
bile, damages them. Other causes include chronic alcohol consumption, hepatitis
infections, and ingestion or inhalation of toxic substances such as volatile
organic solvents in glue, cleaners, and paint thinners. Malnutrition, which is
often associated with alcohol abuse, amplifies the effects of alcohol on the
liver.
The development of cirrhosis occurs in basically the same
way regardless of the cause. When liver cells are injured, the liver becomes
inflamed and enlarged. Injured hepatocytes are not able to convert nutrients
properly, resulting in accumulations of fat within the cells. Fibrous scar
tissue then forms around the lobules. The presence of scar tissue inhibits the
flow of blood and bile through the liver. With time, the flow of blood and bile
is further restricted because the scar tissue shrinks, distorting and
compressing blood vessels and bile passages. The
liver attempts to compensate by forming new lobules. The growth of new lobules,
along with compression by the scar tissue, gives the enlarged liver a lumpy
appearance.
Since hepatocytes are injured, they are less able to perform
their functions. Bilirubin from hemoglobin breakdown is left in a fat-soluble
form called unconjugated bilirubin rather than being converted to
the water-soluble conjugated form for excretion in bile. Inadequate amounts of
bile are produced for emulsification and absorption. Since bile ducts are
blocked, much of the bile cannot pass out of the liver to the hepatic duct.
Therefore, digestion and absorption of fat and fat-soluble vitamins are
reduced. Blood nutrient levels become unbalanced because of this and because
the hepatocytes are less able to manufacture, convert, and store nutrients. All
body cells become malnourished, as indicated by the onset of fatigue.
Blocked bile passages, together
with the declining conversion of unconjugated bilirubin, result in
accumulations of bilirubin. This gives the affected person a yellow or brown
color, a condition called jaundice. Excessively high
concentrations can eventually cause brain damage because unconjugated bilirubin
accumulates in fatty myelin in the brain. In more advanced stages of cirrhosis,
ammonia poses an even greater threat to the brain. Ammonia increases partly
because of the dwindling conversion of ammonia to urea by hepatocytes. A second
reason is that blocked blood flow causes blood from the intestines to flow
through alternative routes, particularly veins in the esophagus. Thus, ammonia
produced by intestinal bacteria is sent directly to the heart and from there to
other organs, including the brain. Affected individuals show mental confusion,
reduced muscle control, and even coma. This situation can eventually prove
fatal.
The blockage of liver vessels causes other problems. Since
blood cannot pass freely through the liver, it backs up into intestinal veins,
causing them to swell and become varicose veins. When this happens in the
rectum, hemorrhoids develop. When it happens in the esophagus, serious and even
fatal bleeding can occur. As a further complication, extra fluids leak out of
the stomach and intestinal capillaries into the surrounding abdominal cavity.
This accumulation of fluids (ascites) causes abdominal swelling
and imbalances in fluids in body cells in other regions.
Ascites worsens because reduced production of blood protein
by injured hepatocytes allows more of the fluid to remain outside the
capillaries. The reduction in blood proteins also causes edema and swelling in
many parts of the body. The ascites and edema are amplified because injured
hepatocytes do not remove enough steroid hormones from the blood (e.g.,
aldosterone, sex steroids), causing water retention by the kidneys. Edema
causes a puffy appearance and discomfort, and in the lungs
it significantly reduces respiratory functioning.
Many other problems result from cirrhosis. The more serious
ones include bleeding because of reduced production of clotting materials,
anemia because of poor hemoglobin breakdown and blood backing up into the
spleen, weak bones because of reduced vitamin D activation, and reduced sexual
functioning from abnormal hormone levels.
Many cases of cirrhosis are preventable. Individuals with
blocked large bile ducts can usually have the blockages removed. This is
especially true among the elderly, in whom the blocked ducts usually result
from gallstones. Cirrhosis from chronic alcohol consumption (the other common
cause of cirrhosis) can be prevented by avoiding or reducing the consumption of
alcoholic beverages. Excessive alcohol consumption is a serious problem because
many elderly people suffer from loneliness, depression, boredom, and anxiety.
Staying active and receiving social and emotional support can help reduce the
incidence of alcohol abuse, and good nutrition reduces the effects of alcohol
on the liver. Hepatitis, another cause of cirrhosis, can be prevented by using
good hygiene; avoiding contact with affected individuals, especially their
feces, blood, and body fluids; and being immunized. Avoiding exposure to toxic
materials can prevent other cases of cirrhosis.
Treatment of those with cirrhosis involves avoiding further
liver injury by avoiding causative factors. If the cirrhosis is not very
advanced, some liver regeneration and improvement in liver function can occur
spontaneously. Advanced cirrhosis is essentially irreversible. Treatment at all
stages includes minimizing the effects of complications from this disease.
Cancer Most cases of cancer in the
liver develop when cancer cells move through the hepatic portal system to the
liver from other parts of the digestive system or the spleen. Movement of
cancer from one location to another is called metastasis, and a
cancer that metastasizes is called metastatic cancer. Metastatic cancer
of the liver is often widespread and is of diverse types. It may reduce many
liver functions and can cause several of the problems associated with
cirrhosis.
Treatments for metastatic liver cancer, including surgery,
radiation therapy, and chemotherapy, do little more than slow the progress of
this fatal disease. Essentially all cases are fatal within 5 years.
The gallbladder is a sac just under the lower edge of the
liver (Fig.
10.1). Recall that the gallbladder receives bile from the liver through the
cystic duct and that bile in the gallbladder may pass to the small intestine
through the common bile duct (Fig.
10.8).
The gallbladder stores bile until it is needed for
digestion. Recall that bile assists in the digestion and absorption of fat. The
gallbladder absorbs water from bile while the bile is being stored.
Emptying of the gallbladder and passage of bile into the
small intestine is stimulated by a hormone [cholecystokinin (CCK)]
from the small intestine and impulses in parasympathetic nerves. Operation of
the CCK control mechanism is especially important when fat enters the small
intestine.
Aging causes no significant changes in gallbladder
structure. There is a decrease in the sensitivity of the gallbladder to
stimulation by CCK. However, with age, the small intestine compensates by
producing more CCK. Therefore, contraction of the gallbladder in response to
the entrance of fat into the small intestine remains unchanged.
Two age changes associated with the gallbladder involve the
bile ducts: The bile ducts widen over most of their length, and the end of the
common bile duct near the small intestine becomes narrower. Normally, these
changes are not important, but the former one may increase the likelihood that
small gallstones formed in the gallbladder will pass down the bile ducts. The
latter change inhibits the escape of such stones into the small intestine. As
described below, gallstones trapped in the bile ducts can cause cirrhosis and
pancreatitis.
Gallstones
are solid masses formed from materials in bile (Fig.
10.8). They are usually formed in the gallbladder. Gallstones contain
various combinations of materials, including cholesterol, bile pigments and
salts, calcium, and protein. Many individuals may develop one or a few
gallstones. The stones range in size, with some becoming larger than 2 cm in
diameter. Some individuals may have 200 or more small stones.
The incidence of gallstones increases with age, and they are
fairly common among the elderly. Approximately 25 percent of people over age 50
have gallstones. Gallstones are one of the more common reasons for surgery
among older people.
An important cause of gallstone formation is having
excessively concentrated bile in the gallbladder, because this situation leads
to solidification of materials dissolved in the bile. These circumstances occur
more frequently among the elderly because the concentration of bile produced by
the liver increases with aging, particularly in obese individuals. In addition,
many older persons produce unusually low amounts of cholecystokinin. With less
CCK, emptying of the gallbladder is delayed and may be less complete. Since
more bile stays in the gallbladder for longer periods, it becomes even more
concentrated and bile solidification occurs. Gallstone formation can also be
initiated by infections in the gallbladder.
Individuals with gallstones often feel vague discomfort in
the abdominal region and the digestive system. Many cases involve severe pain,
nausea, and vomiting, especially after one has eaten foods containing fat. The
painful attacks are probably caused by contraction of the gallbladder on the
gallstones or by movement of a stone into the cystic duct. The gallbladder or
bile duct may become injured, inflamed, and infected. In very severe cases it
may perforate, spilling bile into the abdominal cavity; this can spread
infection and cause a sudden drop in blood pressure.
If a gallstone moves into the bile duct and blocks it, the
individual may become jaundiced because bile cannot escape, and bilirubin
accumulates in the body. Digestion and absorption of fat are greatly reduced,
and malnutrition, including vitamin deficiencies, may develop. If the gallstone
lodges below the intersection of the common bile duct and pancreatic duct,
pancreatic secretions may be blocked. This can lead to inflammation of the
pancreas (pancreatitis), which is discussed below. Prolonged
blockage of the bile ducts can cause cirrhosis.
There is no effective way to prevent gallstones, though
avoiding obesity reduces the risk of developing them. Gallstones can be removed
by several methods, including dissolving them with solutions infused through
the bile ducts or with medications, fragmenting them with ultrasound, and
extracting them surgically. Surgical removal often includes removal of the
gallbladder to prevent a recurrence. A person whose gallbladder has been
removed can survive and digest food because the liver can store adequate
amounts of bile.
The pancreas is a large gland in the space below the stomach
and above the first section of the small intestine (Fig.
10.1, Fig.
10.9. Most of the pancreas consists of clusters of cells (exocrine
cells) that secrete pancreatic juice into ducts within the pancreas.
The ducts merge to form larger ducts, which finally converge and form one large
pancreatic duct. This duct joins the common bile duct just before it enters the
small intestine (Fig.
10.8, Fig.
10.9). Therefore, bile and pancreatic juice enter the small intestine
through the same opening.
Pancreatic juice contains several enzymes that hasten the
chemical breakdown of large nutrient molecules. It also contains sodium
bicarbonate, which neutralizes stomach acid and prevents it from injuring the
small intestine. This process also helps provide a proper acid/base balance for
the action of enzymes in the pancreatic juice and in small intestine
secretions. The secretion of pancreatic juice is adjusted by the autonomic
nervous system and by hormones from the small intestine.
Small clusters of cells (endocrine cells) that
secrete hormones into the blood are widely scattered among the exocrine cells (Fig.
10.9). These clusters are called islets of Langerhans. The
endocrine cells are of two types: One type (alpha cells) secretes glucagon,
and the other type (beta cells) secretes insulin. These hormones
help maintain proper and fairly stable levels of glucose in the blood and
affect the production and breakdown of proteins and lipids by body cells.
The slight age changes that occur in most components of the
pancreas and its ducts do not have a significant effect on the amount of
pancreatic juice produced. There may be a slight decrease in the production of
certain enzymes (e.g., those for lipid digestion), sodium bicarbonate, and
insulin. None of these changes are great enough to alter the ability of
pancreatic secretions to digest nutrients, neutralize stomach acids, and
regulate blood glucose levels. A main reason for the maintenance of pancreatic
digestive function throughout life is the large reserve capacity of the
pancreas. As little as 10 percent of the young adult pancreas is needed to
produce enough pancreatic juice for normal digestion. Though the effectiveness
of the pancreas is virtually unchanged by aging, hormone production is often
significantly altered by other factors as people get older (e.g., obesity, lack
of exercise) (Chap. 14).
Pancreatitis One of the more common abnormalities of the
pancreas among the elderly is pancreatitis, or inflammation of
the pancreas. Cases that develop quickly are called acute pancreatitis,
and cases that develop over a prolonged period are referred to as chronic
pancreatitis. Repeated or prolonged cases of acute pancreatitis lead to
chronic pancreatitis.
Acute pancreatitis is usually caused by traumatic injury to
the abdominal region (such as when the abdomen strikes the steering wheel in an
automobile accident), consumption of alcoholic beverages (especially binge
drinking), or blockage of the pancreatic duct by a gallstone. Chronic
pancreatitis is usually caused by chronic alcohol consumption or blockage of
the pancreatic duct by a gallstone.
In addition to causing extreme pain, acute pancreatitis may
quickly become life-threatening. Vomiting can severely deplete the body of
fluids and minerals, leading to circulatory, nervous, and muscle malfunctions.
Bleeding or leaking of pancreatic enzymes into the blood or abdominal cavity
can cause blood pressure to drop dramatically, resulting in circulatory failure.
Pancreatic enzymes in the abdominal cavity can begin to digest nearby organs,
causing destruction and perforation of those organs. Long-lasting muscle spasms
may occur as blood calcium levels drop. Blood sugar levels may also drop as
injured endocrine cells release insulin. Since the endocrine cells may be
permanently damaged, individuals who survive these immediate dangers may be
left with diabetes mellitus. Any case of acute pancreatitis can develop into
chronic pancreatitis.
Three main problems develop in patients with chronic
pancreatitis: recurrent pain; poor protein and fat digestion caused by
inadequate production of digestive enzymes; and inadequate regulation of blood
sugar and diabetes mellitus resulting from reduced production of hormones.
Since excessive or chronic consumption of alcoholic
beverages is a main cause of pancreatitis, many cases can be prevented by
avoiding such drinking behaviors. Many other cases can be prevented by removing
gallstones before they block the pancreatic duct.
Treatments for acute pancreatitis primarily involve
preventing or reducing its effects and complications. Surgical procedures may
be required to repair or remove injured organs or remove gallstones. Abstinence
from alcoholic beverages is often necessary.
Pain from chronic pancreatitis is relieved with analgesics,
and enzyme insufficiency is rectified by ingesting enzyme supplements with
meals. Mild cases of diabetes mellitus can be managed by regulating diet and
exercise; more severe cases may require the administration of insulin. As with
acute pancreatitis, surgery may be necessary, and abstinence from alcoholic
beverages is often required.
Cancer Like all cancers, pancreatic cancer involves
uncontrolled reproduction of cells. Almost all cases involve cancer of the
exocrine cells. Cancer of the pancreas is the fifth leading cause of death from
cancer, and it accounts for 3 percent of all cancers and 5 percent of all
deaths from cancer. Within the digestive system, only cancer of the large
intestine occurs more frequently. The incidence of pancreatic cancer rises with
age, and the incidence is highest among men over age 75. Several risk factors
for pancreatic cancer have been identified; smoking cigarettes, eating a diet
high in animal fat, eating many foods containing high amounts of nitrates and
nitrites as preservatives (e.g., bacon, cold cuts), consuming much coffee, and
having diabetes mellitus.
Cancer of the pancreas is especially dangerous because it is
usually detected only after it has become quite advanced. Indications include
being jaundiced, losing weight, having abdominal or back pain, and having
symptoms of diabetes mellitus such as unusually high thirst, hunger, and
excessive urine production. This cancer causes pancreatic failure, which
includes poor digestion of proteins and fat, and diabetes mellitus. Pancreatic
cancer often spreads through the hepatic portal system to the liver, where it
causes liver failure.
The chances of developing pancreatic cancer may be lowered
by avoiding smoking and other dietary risk factors. Avoiding risk factors for
diabetes mellitus, such as being obese and being sedentary, may also help.
Though surgery, chemotherapy, and radiation therapy have
been employed as treatments for pancreatic cancer, no effective treatment for
this disease is known. Pancreatic cancer is usually fatal within 1 year of the
diagnosis.
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Copyright 2020: Augustine G. DiGiovanna, Ph.D.,
Salisbury University, Maryland
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