Site map Main Index Chapter supplements Copyright
Learning Objectives Outline Lecture Notes Changes/Suggestions
Glossary
Figures
Chapter 13
The male and female reproductive systems each consist of a
pair of primary reproductive organs or gonads (testes
in men, ovaries in women) and a variety of accessory structures,
including ducts, glands, blood vessels, external reproductive structures (genitalia),
and, in women, breasts (Fig.
13.1).
The gonads have two main functions. The first is the
production of sex cells. The purpose of each male and female sex cell (sperm
cell in men, ovum in women) is to unite with the other
type and initiate the life of a human being. The second main function is the
production of gonadal sex hormones. The main purposes of these sex hormones
include stimulating the development, maintenance, and certain functions of the
gonads and accessory reproductive structures. These hormones also influence
structures and functions in other body systems (e.g., integumentary,
circulatory, muscle, skeletal). Some of these activities contribute to
homeostasis (Chap. 14).
The accessory reproductive structures may be considered to
have four main functions, three of which are involved with reproduction.
Reproductive Functions By helping to create new individuals, the
three reproductive functions contribute to the survival of the human species.
One reproductive function is helping to unite a sperm cell with an ovum inside
the female reproductive system. Male reproductive structures seem to contribute
most to this function when they assist in placing sperm cells into the female
reproductive system during sexual intercourse. The second and third
reproductive functions of the accessory reproductive structures are supporting
the development of and giving birth to new individuals. These functions are
performed by the female structures. The breasts help support development after
birth when they provide nourishment to children.
Sexual Activity The fourth main function of the accessory
reproductive structures is performing sexual activity, which can enhance an
individual's psychological well-being and social interactions. For example,
sexual activity involving proper functioning of the accessory structures can
provide intense physical pleasure, enhanced self-esteem, mood elevation, stress
reduction, and a sense of being loved. Furthermore, it can be a means of
establishing and maintaining an emotional and social bond. Finally, it can be a
physical means to express affection, tenderness, and other positive feelings.
However, sexual activity can be accidentally or intentionally misused.
Incorrect, improper, or inappropriate sexual activity leads to many undesirable
biological, psychological, social, and economic consequences.
In conclusion, a main role of the male and female
reproductive systems is to act together to promote the survival of the human
species. This is unlike other body systems, which generally maintain
homeostasis only for the individual. The reproductive systems contribute to
homeostasis indirectly, however, through certain effects of the sex hormones
they produce and through the positive psychological and social effects of
sexual activity.
The male reproductive system contains several paired tubular
structures, including the testes, the epididymides
(sing., epididymis), and the ductus deferentia (sing., ductus
deferens) (Fig.
13.2,
Fig. 13.3). There are also two pairs of glands: the seminal vesicles
and bulbourethral glands. The other important structures in this
system occur singly and include the scrotum, the prostate
gland, the urethra, and the penis. Finally,
the scrotum and the area near the base of the penis are covered with pubic
hair.
The two testes rest within the scrotum,
a sack of skin and fibrous material suspended near the front of the body
between the thighs (Fig.
13.4,
Fig. 13.5). Each oval-shaped testis is divided into 250 to 300 sections by
fibrous sheets, and each section contains up to four long, highly coiled tubes
called seminiferous tubules. Each tubule may be up to 100 feet
long, and the total length of all tubules in one testis is approximately up to
1/8 mile. Spaces among these tubules contain blood vessels and special cells
called interstitial cells (Leydig's cells).
Vessels and Interstitial Cells Blood flow through
the testes delivers needed materials and removes wastes and sex hormones
produced by the testes. The interstitial cells produce and secrete two male sex
hormones: testosterone and dihydrotestosterone (DHT).
These hormones are essential for proper sperm production, development and
maintenance of male reproductive structures, development and maintenance of
other male characteristics (e.g., deep voice, beard), and interest in sexual
activity (libido). They also influence several other activities (Chap. 14).
Seminiferous Tubules and Sperm Production The wall of each
seminiferous tubule is many cells thick (Fig.
13.5). Many cells in the outer region of the tubule wall reproduce rapidly,
and most of the newly produced cells move toward the central channel (lumen).
As each cell moves toward the lumen, it undergoes a special type of cell
division called meiosis, which results in the formation of four
cells called spermatids. In men, meiosis is also called spermatogenesis.
Each spermatid then matures into a long sperm cell through the process of
spermiogenesis. Later, when fully mature, each sperm cell can initiate the life
of a new human being by entering an ovum during the process of fertilization.
Since sperm production occurs continuously throughout the nearly one-eighth of
a mile of seminiferous tubules in each testis, a man produces several hundred
million sperm cells a day.
The seminiferous tubule wall also contains large sustentacular
cells (Sertoli's cells) (Fig.
13.5), which promote sperm production in three ways. First, they produce
and retain androgen-binding protein (ABP), which
binds testosterone and concentrates it in the tubules, stimulating sperm
production. Second, these cells protect sperm-producing cells from attack by
the immune system. Third, they nourish spermatids as they mature into sperm
cells. The sustentacular cells also produce a sex hormone (inhibin)
that helps regulate testosterone levels.
Epididymis A series of conducting tubes connect the
seminiferous tubules in each testis to an epididymis, a coiled
tube behind the testis. Sperm cells and the small amount of fluid produced by
the seminiferous tubules move through the conducting tubes into the epididymis.
While being stored in the epididymis for 10 days or more, sperm cells become
fully mature and capable of swimming. The epididymis also secretes a small
amount of fluid that seems to contain nutrients for the sperm cells.
During sexual arousal and activity, contractions of the
epididymis push the sperm cells and fluid into the tubular ductus
deferens. Mature sperm cells that are not released from the epididymis
within about a month are broken down chemically.
Ductus Deferens and Ejaculatory Duct Each ductus deferens
(also called vas deferens) passes up from the scrotum and into
the body cavity (Fig.
13.2,
Fig. 13.3). There, the ductus deferens loops over the urinary bladder from front
to back and widens just before entering the rear of the prostate gland.
Upon entering the prostate gland, the ductus deferens becomes the ejaculatory
duct, which leads into the center of the prostate gland and joins the
urethra. Rhythmic peristaltic contractions that occur during sexual activity
propel the sperm from the ductus deferens into the urethra.
Urethra The urethra passes through the
prostate gland, exits from the body cavity, and extends through the penis to
its external opening. Rhythmic peristaltic contractions of the urethra, which
occur during the peak of male sexual response (i.e., during ejaculation),
propel the sperm cells and accompanying fluids through the urethra and out of
the body.
The successful delivery of functional sperm cells into the
female reproductive system depends not only on the functioning of the
reproductive ducts but also on secretions from reproductive glands (seminal
vesicles, prostate, bulbourethral glands) (Fig.
13.2,
Fig. 13.3). The mixture of sperm cells and secretions released from a man's body
during sexual activity usually contains 300 million to 500 million sperm cells
and totals approximately 3 ml. to 5 ml. Almost all of this mixture—semen—consists
of secretions from reproductive glands.
Seminal Vesicles Approximately two-thirds of the semen comes
from the seminal vesicles, which lie behind the urinary bladder
just above the prostate gland. The wall of each seminal vesicle consists of
three layers: an inner epithelial layer of secreting cells, a middle layer of
smooth muscle, and an outer layer of fibrous connective tissue. Within the
gland the wall is highly folded, producing many interconnected spaces that
resemble a sponge.
The thick secretion from the inner layer of the seminal
vesicle is stored in the internal spaces of the gland. This secretion contains
a variety of substances, including water, fructose, and alkaline materials.
During sexual activity contraction of the smooth muscle layer forces the
secreted materials out of the spaces, through the duct in the seminal vesicle,
and into the ductus deferens where it leads into the ejaculatory duct. The
secretion then mixes with the sperm and fluids passing from the ductus deferens
into the ejaculatory duct.
The water in this secretion dilutes the sperm cells so that
they have more room to move. The fructose provides energy that allows the sperm
cells to swim actively while trying to reach the ovum. The alkaline materials
protect the sperm cells by neutralizing acid materials in the urethra and the
female reproductive system.
Prostate Gland The prostate gland surrounds
the upper end of the urethra. It is slightly flattened and is little more than
2.5 cm (1 inch) in diameter. It actually consists of numerous small glands that
contain secreting cells and are surrounded by smooth muscle. In addition,
fibrous material is found throughout the prostate gland and a distinct layer of
fibrous material surrounds the entire gland.
During sexual activity, contraction by the smooth muscle
forces the secretion from each small gland through its duct and into either the
ejaculatory ducts or the urethra. The secretion then mixes with the sperm cells
and other fluids. It contains water and alkaline materials, which serve the
same functions as the corresponding substances in the secretions from seminal
vesicles. Secretion from the prostate gland constitutes approximately 15
percent of the semen.
Bulbourethral Glands The bulbourethral glands (Cowper's
glands) are located on opposite sides of the urethra just below the
prostate gland. Each round bulbourethral gland is less than a quarter inch in
diameter.
At the beginning of sexual arousal these glands secrete no
more than a few drops of a clear slippery alkaline liquid into the urethra. The
alkaline material helps neutralize acid materials in the urethra before
contractions in the ejaculatory ducts push sperm cells into the urethra. This
protects sperm cells from any acid urine in the urethra. In addition, some of
the secretion often leaks out of the external urethral opening onto the end of
the penis. This material (precoital fluid) lubricates the end of the penis and
aids in inserting it into the vagina at the beginning of sexual intercourse.
The penis contains the urethra, three
elongated masses of spongy erectile tissue, and several arteries
and veins, all of which run parallel to the urethra ((Fig.
13.2,
Fig. 13.3) and Fig.
13.4). One portion of the erectile tissue (corpus spongiosum) surrounds the
portion of the urethra that passes through the penis. The other two erectile
tissue masses (corpus cavernosa) are above the urethra and its erectile tissue.
The spaces within the erectile tissue can be filled with blood from the penile
arteries. Sheets of fibrous tissue surround all these penile components, and
the surface of the penis is covered with skin.
Under resting conditions, the erectile tissues are narrow
and soft because they contain little blood and the penis is flaccid
(limp and flexible). In this state the penis is only a few inches long, though
its length varies both from time to time and between individuals.
Erection During sexual arousal dilation of penile
arteries causes blood to enter and fill the erectile tissue spaces faster than
the veins carry it away (Fig.
13.6). As a result, the erectile tissues expand and become firmer, causing
the penis to widen and lengthen. As the erectile tissue expands, it compresses
the veins and slows the exit of blood. This further increases the extent of
erectile tissue engorgement. The restricting nature of the surrounding fibrous
sheets causes the pressure in the filling erectile tissue to increase, and the
penis straightens and stiffens. Collectively, these changes constitute the
process of erection. Once erection is complete, the penis can be
inserted into a vagina and semen can be deposited into the female reproductive
system.
An erect penis is often more than 1 inch in diameter and
measures 6 inches to 7 inches in length. The final dimensions of the erect
penis vary somewhat between individuals and bear only a small correspondence to
its dimensions in the flaccid condition.
Erection is a reflexive action controlled primarily by
autonomic nerves. It can be caused by erotic physical stimulation (stimulation
of the penis or scrotum) or by erotic mental processes (sexual fantasies).
Other types of physical stimulation, such as having a full urinary bladder or
mild irritation of the urethra, and certain other mental processes, such as
those which occur during sleep, can also result in erection. Conversely,
erection can be prevented or reversed by other physical stimuli (e.g., pain)
and mental processes (e.g., fear).
The results of erection are reversed when blood flow into
the erectile tissue is slowed by penile artery constriction. Then blood leaves
the erectile tissue faster than it enters, and the penis returns to its flaccid
state.
The skin of the scrotum is covered with fairly sparse pubic
hair. A thicker mat of pubic hair covers the skin near the base of the penis.
AGE CHANGES IN THE MALE SYSTEM
On the average, the testes decrease in size and weight with
age. The degree of shrinkage is highly variable among individuals and is not
present in all men. Therefore, it may be caused by factors other than aging,
such as poor nutrition and diseases in other parts of the body. Within the
testes, the interstitial cells decrease in number but show no significant
changes in structure. Changes in their production of gonadal sex hormones and
the effects of those changes are described in Chap. 14.
Changes in the seminiferous tubules include thinning of the
wall and narrowing of the lumen. At first, the changes occur in small and
widely scattered patches. These modified patches increase gradually in size and
number. In some places the lumen becomes so narrow that it completely blocks
the tubule. Most of the age-related changes in the seminiferous tubules seem to
be due to factors other than aging. Factors include declining blood flow caused
by blood vessel changes; injury to the tubules by the immune system; and
alterations in sex hormone production. Age-related compensatory increases in
stimulatory hormones from the pituitary gland [luteinizing hormone (LH) and
follicle-stimulating hormone (FSH)] may help minimize tubule alterations caused
by other changes.
Because of these changes, there is an average decline in the
rate of sperm production and a higher percentage of irregular nonfunctional
sperm cells are produced. However, the decrease in sperm production is highly
variable among men, and some men show no decline. Furthermore, sperm production
never ceases in a healthy man because only some tubules stop production
completely. In other tubules production slows only in the modified patches.
Therefore, the reserve capacity for sperm production assures that the number of
normal sperm cells produced by a healthy man always remains adequate for
fertilization.
The effects of aging on the structure and sperm-carrying
abilities of the ducts have not been well studied. There is no evidence that
aging results in significant changes in their contributions to reproduction.
Seminal Vesicles Age changes in the seminal vesicles have no
known effect on their contributions to reproduction.
Prostate Age changes
in the lining and muscle layer of the prostate gland, which become thinner, are
apparent by about age 40. At first the changes occur in widespread patches, but
by age 60 essentially all of the prostate has changed. The thickening basement
membrane and declining blood flow may reduce nutrient supply and waste removal
and therefore may account for some of the shrinkage in the lining and muscle
layer. None of the changes in the prostate seem to adversely affect its
contributions to reproduction. However, increased binding of testosterone may
promote the development of an abnormal condition called benign prostatic
hypertrophy. In contrast to the prostate, most body structures show an age-related
decline in the binding of testosterone.
Bulbourethral Glands The decrease in fluid production by the
bulbourethral glands is not sufficient to reduce their contributions to
reproduction significantly.
Age changes in the penis appear between ages 30 and 40. The
accumulation of fibrous material occurs first in the erectile tissue
surrounding the urethra. Some years later fibrous buildup in the other two
masses of erectile tissue begins. By age 55 to 60 all areas of erectile tissue show
gradually increasing fibrosis.
Age changes in the penis seem to contribute to the gradual
decline in the speed with which erection occurs. However, in healthy men under
ordinary circumstances the penis retains the ability to become erect and enter
a vagina and therefore to assist in placing sperm cells into the female
reproductive system.
Although the testes function continuously, many activities
in other parts of the male system are largely restricted to periods of sexual
activity. During these active periods, the chronological sequence in which
these parts operate is different from their anatomic sequence. In keeping with
Masters and Johnson's thorough description of human sexual response, which
forms the basis for the following discussion of sexual activity, this
chronological sequence can be divided into five phases. These phases are listed
in Table 13.1 along with bodily changes that occur in almost all instances
(universal changes) and changes that occur less frequently (common or
occasional changes).
Different men are affected by diverse intensities and
combinations of factors. Therefore, there is great heterogeneity in age-related
changes in sexual activity. Additional heterogeneity occurs because for each
man, each incident of sexual activity may vary as a result of conditions such
as physical environment, partner's involvement, mood, and length of time since
the last sexual experience.
The excitement phase involves the development
and persistence of several changes. Sometimes this phase may last for only a
few seconds, while at other times it may be extended for many minutes.
The first action during this phase is erection of the penis.
This is accompanied by reflexive contraction of the muscular sphincters below
the urinary bladder so that urine cannot leave the bladder and injure sperm
cells. These developments may be completed within several seconds and may be
sustained for many minutes. The onset of erection is accompanied by or shortly
followed by secretion from the bulbourethral glands. These three changes are
often accompanied by other bodily changes, some of which occur more commonly
than others.
As sexual arousal increases during the excitement phase,
peristaltic contractions of the epididymis and ductus deferens move sperm cells
and fluids into the ejaculatory ducts; as the penis reaches peak erection, the plateau
phase begins. This phase is often accompanied by increases in the
bodily changes seen during the excitement phase. Other changes may also occur.
Up to this point distractions or a reduction in sexual stimulation may cause
reduced or complete loss of erection and reversal of all the other concomitant
sexual response changes. Renewed sexual stimulation can restore the conditions
of the plateau phase.
At the end of this phase muscle contractions in the seminal
vesicles and prostate gland force their secretions into the ejaculatory ducts
and urethra. Simultaneously, the external urinary sphincter relaxes, allowing
the semen to flow into the urethra. The internal urinary sphincter contracts
forcefully, preventing semen from entering the bladder and preventing urine
from leaving the bladder and entering the urethra.
The expansion of the urethra by semen often gives the
impression that loss of voluntary control of sexual activity is imminent, and
within a few seconds it triggers the orgasmic phase. During this
phase completely reflexive rhythmic peristaltic contractions of the urethra,
the other ducts, and muscles at the base of the penis force the semen out of
the urethra (ejaculation). The first few contractions are the
strongest and occur at intervals of slightly less than 1 second. After the
first few contractions, the rhythm slows and the force of contraction
diminishes. These activities are often accompanied by extreme levels of
pleasurable sensations, which are usually centered in the penis, and by increases
in the other changes that occur during the excitement and plateau phases. They
may be followed by widespread perspiration. The orgasmic phase may last for a
number of seconds.
As the orgasmic phase subsides, the penis begins to become
flaccid. From seconds to minutes may be required to achieve a completely
flaccid state. All the other bodily changes that occur during orgasm also
quickly diminish and gradually disappear. This return to resting conditions
constitutes the resolution phase.
Refractory Period
The resolution phase is followed by the refractory
period, during which erection of the penis and the accompanying changes
cannot occur. This period may last a few minutes to many hours, after which
erection and the other activities in the cycle of male sexual activity may
occur again.
AGE CHANGES IN MALE SEXUAL ACTIVITY
Significant age-related alterations occur in the functioning
of the male reproductive system during sexual activity. Some of these changes
seem to be due to age changes within the reproductive structures. For example,
alterations in erection seem to be due in part to an increase in fibrous
material in the penis. However, many age-related changes seem to be due to age
changes in other systems, abnormal and disease conditions, or other age-related
factors. Let us consider five examples.
First, since much of the functioning during sexual activity
depends on conscious sensations and reflexive actions, some age-related changes
probably derive from age-related changes in the nervous system.
Second, since several events in male sexual activity (e.g.,
erection, scrotal tensing, testes enlargement) depend on substantial increases
in blood flow to reproductive structures, some age-related changes seem to be
due largely to age changes in arteries, atherosclerosis, and other age-related
conditions that reduce the ability of the circulatory system to quickly
increase blood flow to structures.
Third, advancing age is accompanied by increased use of
medications, many of which adversely affect sexual functioning. Some
medications for high blood pressure reduce erectile ability and the intensity
of erection, many medications that regulate nervous system functioning (e.g.,
sedatives, tranquilizers, antidepressants) suppress erection and ejaculation,
and certain hormones (e.g., ACTH) and drugs decrease blood levels of
testosterone. In this case, deterioration of sexual activity occurs because the
maintenance and function of reproductive structures require sustaining
adequately high levels of testosterone.
Fourth, declining sexual performance by the reproductive
system seems to be directly correlated with declining frequency of use, which
occurs in many aging men.
Fifth, since sexual activity is highly influenced by
psychological factors, some changes in sexual activity may result from
age-related psychological changes such as a deteriorating self-image. These
changes may result from age-related social or economic changes such as
institutionalization, retirement, and loss of income.
These and other factors that seem to affect male sexual
activity are discussed in the section on impotence, below.
Alterations in erection of the penis are perhaps the most
noticeable age-related changes in the excitement phase. Major reasons for these
changes include diminishing penile sensitivity to touch, increasing amounts of
fibrous material in the penis, alterations (e.g., stiffening, narrowing) of
arteries leading to and through the penis, and increased leakage of blood
through veins that drain the penis.
Since the plateau phase consists largely of a heightening of
the excitement phase, age-related changes in these phases are similar. Though
most age-related changes in the plateau phase may be of little consequence,
three of them seem to be significant. One is a more frequent inability to
reestablish erection if it is lost because of decreased stimulation or
distraction. The effect is entry into a refractory period without having
achieved ejaculation. Such occurrences may be considered unsatisfactory
attempts at sexual activity.
A second change, which is often considered desirable, is an
increasing ability to delay ejaculation and prolong the plateau phase. By so
doing, a man can extend his sexually aroused state and the duration of sexual
intercourse and therefore may provide more stimulation for his female partner.
As a result, the woman is more likely to achieve sexual satisfaction by
attaining orgasm before the man ejaculates and loses his erection.
Third, the strength of contractions in the seminal vesicles
and prostate and the amount of fluid forced into the ejaculatory ducts and
urethra often become inadequate to initiate the sensation of imminent
ejaculation. Therefore, ejaculation may begin with no warning sensations. By
contrast, occasionally the perception of imminent ejaculation develops and
lasts several seconds but is not followed by ejaculation. Both situations may
diminish physical pleasure during the transition from the plateau phase to the
orgasmic phase.
As the number and strength of ejaculatory contractions
diminish, the duration of ejaculation becomes shorter. These changes may result
from altered reflex functioning and the decline in the quantity of semen
released. They are accompanied by a diminishing intensity of the pleasant
sensations associated with ejaculation.
Most aspects of the resolution phase occur faster.
The refractory period may last only a few minutes in young
men. With advancing age, it may last from many minutes to several days.
In summary, as age increases, the activities and alterations
in the male reproductive system that occur during sexual activity generally
take longer to develop, reach lower peak levels, and return to resting
conditions more rapidly. More time must pass before the next cycle of sexual
activity can occur. However, the male reproductive system largely retains the
ability to provide satisfactory sexual experiences.
The reproductive system in women contains certain paired
structures, including the ovaries, the tubular oviducts,
external genital structures (labia minora and labia majora),
and breasts (Fig.
13.1,
Fig. 13.7,
Fig. 13.8,
Fig.
13.12). Important female structures that occur singly include the uterus,
vagina, and clitoris (Fig.
13.11).
This section is abbreviated because reproductive functioning
in women ends at menopause. Menopause usually occurs some time
between ages 45 and 55 and is evidenced by the absence of menstrual periods for
at least 1 year.
The ovaries are held in place within the lower
region of the abdominal cavity by several ligaments (Fig.
13.9). Each ovary is shaped like a slightly flattened oval and is
approximately the size of a large almond (2.5 to 5.0 cm long, 1.0 to 2.5 cm
wide, 0.5 to 1.0 cm thick). The bulk of the ovary consists of the stroma,
which contains fibrous material with many blood vessels (Fig.
13.10). Embedded within the stroma and near its surface are many small clusters of cells called follicles.
Each follicle contains an immature ovum. The entire ovary is surrounded by a
thin layer of cells (germinal epithelium)..
Ovarian Cycles Unlike the testes, which produce hormones
and sperm cells at a fairly steady rate, ovarian functioning consists of a
sequence of events during which hormones and ova are produced periodically.
Since this sequence is repeated over and over, it is called the ovarian
cycle
An ovarian cycle begins when two hormones (LH and FSH) from
the pituitary gland stimulate the cells in a few follicles to make more
follicle cells and secrete the hormones estrogen and progesterone.
The blood levels of these hormones rise as the follicles grow and increase
their hormone production. These hormones also cause the immature ovum in each
stimulated follicle to begin to mature. For unknown reasons, one of the
follicles develops faster than do the others, and after several days the other
stimulated follicles begin to degenerate and become masses of scar tissue.
Approximately 14 days after the cycle has begun, elevated
blood estrogen levels cause the pituitary gland to increase production of LH
and FSH. The surge in these hormones causes the fully mature follicle to
rupture and release its ovum in a process called ovulation. The
freed ovum is then transported down the oviducts, where it degenerates unless
it is fertilized within 3 days.
After ovulation, LH and FSH cause the ruptured follicle,
which remains in the ovary, to grow into a mass called a corpus luteum.
The corpus luteum produces estrogen and great quantities of progesterone for
about 10 days after ovulation. Then, as high levels of progesterone cause blood
levels of the pituitary hormones to decline, the corpus luteum degenerates. As
it does so, the production and blood levels of estrogen and progesterone fall
sharply. The degenerated corpus luteum remains in the ovary as a pale mass of
scar tissue. Once estrogen and progesterone levels have become very low, the
pituitary gland initiates the beginning of the next ovarian cycle. Though a
typical ovarian cycle spans 28 days, each cycle may vary by several days.
The estrogen and progesterone produced by the ovaries are
required for the complete development and maintenance of female reproductive
system structures and other female characteristics (e.g., body contour). The
ovary also produces a very small amount of testosterone, which seems to
stimulate interest in sexual activity (libido), just as it does in men. These
three hormones also influence several other activities (Chap. 14).
Approximately 200,000 immature follicles are present in each
ovary when ovarian cycles begin and sexual maturation occurs during
adolescence. Once begun, ovarian cycles are repeated until menopause. Since
usually only one follicle matures fully and releases its ovum during each
ovarian cycle, not more than approximately 500 follicles release ova before
ovarian cycles cease. Most of the other follicles degenerate into atretic
follicles.
An ovum that has been ovulated enters the funnel-shaped
opening of the nearby oviduct (uterine tube, fallopian
tube) (Fig.
13.9). Each oviduct is approximately 10 cm (4 inches) long and extends
from the region near its corresponding ovary to its point of entry into the
upper part of the uterus. The wall of each oviduct consists of an inner lining
of cells, a middle layer containing smooth muscle, and an outer layer
containing fibrous material that helps hold the oviduct in place.
The cells covering the open end of the oviduct and lining
its interior have motile projections called cilia. The cilia beat
in an organized pattern that sweeps fluids from the body cavity into the
funnel-shaped opening of the oviduct. The current produced carries each
ovulated ovum into the oviduct. Movement of the cilia and peristaltic
contractions of the smooth muscle keep the ovum moving toward the uterus, a
journey that takes almost 9 days. The cells in the lining of the oviduct also
secrete fluid that seems to nourish the ovum.
The oviducts also serve as an upward passageway for sperm
cells deposited into the female system during sexual intercourse. This function
is important because an ovum is viable for not more than 3 days after
ovulation. Therefore, for fertilization to occur, the sperm must reach the ovum
while it is in the upper third of the oviduct. The mechanism by which sperm
cells move quickly up the oviduct while an ovum is carried downward toward the
uterus is not clearly understood.
Ova that are not fertilized degenerate. However, once an
ovum is fertilized, the embryo begins to develop immediately. It divides into
many cells and begins to form a hollow sphere of cells before reaching the
uterus. Secretions from the oviduct help support the development of the new
individual by providing it with nutrients.
The uterus is suspended near the bottom of the
abdominal cavity and has a broad upper region into which the oviducts enter. It
is held in place by several ligaments and receives support from the muscular
floor of the pelvic cavity, the urinary bladder, and the end of the large
intestine. The uterus tapers to a narrow lower portion, the cervix, which
protrudes into the vagina (Fig.
13.7,
Fig. 13.8). An average uterus in a young adult woman is 7.5 cm (3 inches) long
and 5.0 cm (2 inches) wide at its broadest point.
Like the oviducts, the uterine wall is composed of three
layers, but the two inner layers are much thicker. The innermost layer (endometrium)
becomes especially thick when its growth is stimulated by estrogen and
progesterone. The middle layer of smooth muscle (myometrium) is
the thickest layer. The outermost layer contains much fibrous material that
attaches to ligaments that hold the uterus in place. The uterine wall surrounds
a narrow space called the uterine cavity, which connects the
passageways in the oviducts with the central channel in the vagina.
Since the uterine cavity extends from the vagina to the
oviducts, it serves as a passageway for sperm cells in the vagina to reach the
ovum. Several days after fertilization, the embryo reaches and enters the
uterus. The embryo remains adrift in the uterine cavity for a few days, after
which it embeds itself into the endometrium.
The endometrium contributes to the formation of the placenta
and thus nourishes the developing child until birth. The placenta also produces
estrogen and progesterone, which further stimulate breast development and help
maintain pregnancy. As the developing child and the placenta grow, the
myometrium stretches to accommodate them. When prenatal development is
complete, contractions of the myometrium (labor contractions) push the infant
through the vagina and out of the mother's body.
Menstrual (Uterine) Cycles Because of hormonal changes during an ovarian cycle, the uterus also undergoes cyclic changes. These changes constitute a menstrual cycle or uterine cycle.
A menstrual cycle begins within 3 days to 4 days after blood levels of estrogen and progesterone start to fall, near the end of the previous ovarian cycle. Since the endometrium is no longer strongly stimulated by these hormones, the arteries serving it constrict, resulting in inadequate blood flow to this thickened layer. Then, except for a thin layer of endometrial cells close to the myometrium, the endometrium dies and is shed along with some blood from the damaged vessels. This material passes through the central passageways in the cervix and the vagina and leaves the woman's body as the menstrual flow. The period of 3 days to 5 days required for endometrial shedding is often called the menstrual period, and the woman is said to be menstruating or "having a period."
By the time menstruation is completed, the
next ovarian cycle has begun and blood levels of estrogen and progesterone
rise. These rising hormone levels stimulate the remaining endometrial cells to
proliferate, and the endometrium thickens considerably for the next 20 days.
This prepares the endometrium to receive and nourish an embryo if fertilization
and the embedding of an embryo occur. If embedding does not occur, estrogen and
progesterone levels fall and the menstrual cycle ends approximately 3 days
thereafter, when the next menstrual period begins. Thus, the end of one
menstrual cycle is marked by the beginning of the next. Since these cycles are
controlled by and parallel ovarian cycles, both cycles take approximately 28
days.
If an embryo is embedded in the endometrium, the developing
placenta produces hormones that stimulate the corpus luteum to continue hormone
production so that menstruation does not occur. Therefore, the developing child
is retained and pregnancy continues. Hormones from the placenta and corpus
luteum also inhibit the production of LH and FSH by the pituitary gland and
prevent additional ovarian cycles until birth has occurred.
The vagina is a tube approximately 7.5 to 10.0 cm (3 to 4
inches) long that extends downward behind the urinary bladder and urethra. It
leads from the cervix to the outside of the body (Fig.
13.7,
Fig. 13.8).
The wall of the vagina is thin and is composed of an inner
lining of cells covering a layer containing smooth muscle, blood vessels, and
much fibrous elastic material. Under resting conditions, the wall of the vagina
is wrinkled and collapsed inward so that the inner surfaces touch and close its
central channel. However, the wrinkles (rugae) and the elasticity of the wall
allow the vagina to be stretched considerably in both length and width. This
allows the entrance of a penis during sexual intercourse and the exit of an
infant during birth.
The vagina makes five contributions to the reproductive
functioning of the female system. It permits the menstrual flow to leave the
woman's body; serves as part of the passageway for sperm cells to reach an
ovum; helps sperm cells reach an ovum by accommodating the entrance of a penis
and permitting the cells to be deposited close to the opening to the uterus;
provides a warm moist environment for sperm cell survival; and provides a birth
canal through which an infant can leave the mother's body during birth.
Since the vagina undergoes physical trauma during sexual
intercourse and provides a relatively wide entry into a woman's body, its
lining has three adaptations to resist abrasion and the entry of microbes.
First, the lining cells form many layers which resemble the epidermis except
that no keratin is present. The surface cells of the lining steadily peel away
and are replaced by underlying cells. Second, lubricating fluids, which seem to
seep through the lining from underlying blood vessels, help reduce friction
during sexual intercourse. Third, lining cells contain glycogen, which is
released from these cells after they peel away. Healthful bacteria in the
vagina use the glycogen as a nutrient to produce acidic waste products that
prevent the growth of harmful microbes. Sperm cells survive the acids because
alkaline materials in the vaginal lubricating fluid and in semen neutralize the
acids.
External
Structures (Genitalia)
Externally, the vaginal opening is flanked by a pair of thin
fleshy folds called the labia minora (Figs. 13.7,
Fig. 13.8,
Fig. 13.11). These
folds also flank the urethral opening, which lies in front of the vaginal
orifice. The labia minora meet a short distance in front of the urethral
opening.
Under resting conditions, the free edges of the labia minora
tend to meet at the midline and cover the vaginal orifice, inhibiting the
entrance of microbes and foreign materials. The labia are very sensitive to
touch because they have many sensory nerve endings. Their surface also contains
many sebaceous glands. Between the rear of the labia minora and the vaginal
orifice lie a pair of Bartholin's glands. During sexual arousal,
these glands secrete a small amount of lubricating fluid.
To the side of the labia minora lie the labia majora, two
thick fleshy folds that contain fat and have hair (pubic hair) on their exposed
surfaces. These labia meet in front of the junction of the labia minora and
blend with the mons pubis, a fatty hair-covered pad overlying the
front of the pelvis at the center. As in the labia minora, the free edges of
the labia majora meet under resting conditions and help block the entrance to
the vagina.
The junction of the labia minora marks the location of the clitoris.
Most of the clitoris is embedded between the front limits of the labia minora
and the junction of the labia majora. However, the tip of the clitoris (glans)
protrudes slightly just behind the junction of the labia minora. The clitoris
is approximately 2.5 cm long and less than 1.3 cm wide.
The clitoris consists primarily of two masses of erectile
tissue. Though much smaller, these masses correspond to the two masses of
erectile tissue along the top of the penis (corpus cavernosa). Also like the
penis, the clitoris is very sensitive to touch and its erectile tissue becomes
engorged with blood during sexual arousal.
Except for preventing the entrance of foreign materials and
providing a small amount of lubricant, the external genitalia contribute little
to the reproductive role of the female system. However, they make major
contributions to the pleasurable sensations derived from sexual activity.
The breasts are attached to the layer of
fibrous material that overlies the large chest muscles (pectoralis major) (Fig.
13.13). Except when a woman is pregnant, each breast consists mostly of fat
tissue. The breast is divided by sheets of fibrous material into approximately
20 segments, each of which contains some glandular material (mammary glands).
The glands remain small unless the woman becomes pregnant. During pregnancy,
the very high blood levels of estrogen and progesterone stimulate them to
enlarge. When a woman is not pregnant, the fat tissue makes the breast firm and
the sheets of fibrous material support the breast, causing the breast to
protrude from the chest wall.
The circular pigmented patch of skin on the front of each
breast is called an areola. The nipple is the
protrusion at the center of the areola. Both structures contain many sensory
nerve endings which make them especially sensitive to touch. When the areola or
nipple is stimulated by touch or other factors (e.g., cold) or when a woman
becomes sexually aroused, smooth muscle cells contract and cause the nipple to
become firmer and protrude farther, a process called erection of the nipple.
The reproductive role of the breasts is to help support the
development of a child by providing nourishment after birth. This is
accomplished when a hormone (prolactin) produced by the mother's pituitary
gland after giving birth causes the enlarged mammary glands to produce milk.
Another pituitary hormone (oxytocin) causes the breasts to eject the milk
through ducts leading out of the nipples.
AGE CHANGES IN THE FEMALE SYSTEM
Aging of the female reproductive system can be divided into
two phases, which are separated from each other by menopause. Menopause
is the time when age changes in the ovaries cause menstrual cycles to cease for
at least 1 year. The average age at which menopause occurs is 51, though it can
occur any time between ages 45 and 55. Women who have not experienced menopause
are called premenopausal, and those who have passed through it
are called postmenopausal.
Women lose reproductive ability quickly during menopause.
Female animals do not have menopause. Animals lose their ability to reproduce
very gradually as they age, though there may be a few animals that have
menopause (e.g., whales). Scientists speculate about why menopause occurs in
humans and in essentially no other animals. One explanation rests on the great
amount and length of care human infants require after they are born. Evolution
by natural selection promotes menopause because it allows women to nurture
children more effectively. Bearing more children at advanced ages would prevent
women from devoting enough time and energy to nurture the children they already
had. Women passed menopause could also help raise children from other women.
Menopause is important for two reasons. First, pregnancy,
and therefore reproduction, is no longer possible because ovulation has
stopped. Second, bodily structures and functions that are influenced by
estrogen and progesterone undergo significant changes after menopause because
blood levels of these hormones drop and stay low when follicles no longer
mature. Some of these hormone-related age changes were described in Chaps. 4
and 9 (e.g., changes in blood lipoproteins, skeletal changes). These and other
postmenopausal changes are also described in Chap. 14. This chapter will discuss
premenopausal, menopausal, and postmenopausal age changes in the reproductive
system.
Before menopause, as more follicles ovulate or become
atretic, the number of follicles capable of ovulation decreases, and by age 50
almost no viable follicles remain. While the number of viable follicles is
decreasing, the follicles that develop during each ovarian cycle develop less
completely, fewer of them ovulate and form a corpus luteum, and therefore less
estrogen and progesterone are produced. Eventually no follicles mature fully,
ovulation ceases, ovarian cycles disappear, and reproduction becomes
impossible. Since the occurrence of menstrual cycles depends on the hormones
produced by ovarian cycles, menstrual cycles also cease and menopause occurs.
After menopause, the ovaries produce very small quantities
of estrogen and progesterone, and this production gradually diminishes. These
hormonal changes are responsible for many other changes, including most age
changes in other parts of the reproductive system.
In spite of age changes, the oviducts do not entirely lose
the ability to carry ova and sperm cells. Of course, this point is moot once
ovulation ceases.
The most noticeable change in the uterus before menopause is
a decrease in the degree of endometrial thickening during menstrual cycles.
Since this decline is due to reduced ovarian hormone production, this change is
observed most frequently during menstrual cycles that accompany ovarian cycles
with no ovulation.
The menstrual flow resulting from cycles that have reduced
endometrial thickening may be so slight that it is not viewed as constituting a
true menstrual period. Menstrual cycles may seem to become very long because
two or more cycles may occur before enough menstrual flow is produced to
definitively mark the end of a cycle.
As the proportion of ovarian cycles involving no ovulation
increases, the time between menstrual periods also increases. When no periods
happen for 1 year, menopause has occurred. Note that occasional periods may
occur after menopause. However, pregnancy becomes impossible when ovulation
ends or when the endometrium fails to thicken enough to form a placenta capable
of supporting the development of an embryo.
Both before and after menopause, the uterus often tips
backward and settles lower in the abdominal cavity as its supporting ligaments
weaken and surrounding structures shift. If the lowering of the uterus is
excessive, it may descend into or through the vagina. This abnormal condition
is called uterine prolapse. Uterine prolapse may also develop as
a complication from childbirth or from surgery in the pelvic area.
After menopause, the entire uterus shrinks. It may decrease
in size by 50 percent within 15 years after menopause and may eventually shrink
to less than 2.0 cm in width.
Age changes have no significant effect on the reproductive
functions of the vagina. However, they significantly reduce its role as a
barrier against abrasion and microbes because as the vagina becomes smaller,
thinner, and less elastic, it is more easily damaged by even mild physical
trauma, such as friction during sexual intercourse. The increased risk of injury
and the decline in lubrication are also more likely to result in pain from
sexual intercourse. As the risk of vaginal injury rises, so does the risk of
developing sores and vaginal infections. The risk of vaginal infections rises
also because as age increases, the lining cells contain and release less
glycogen. As glycogen declines, less acidic material is produced by healthful
microbes and injurious microbes can flourish.
Finally, since the urethra lies immediately in front of the
vagina, thinning of the vaginal wall increases the frequency of urethral and
bladder irritation and inflammation (cystitis) from agitation of the vagina
during intercourse. Painful urination and temporary urinary incontinence may
result.
The rate of age changes in the vagina can be slowed by
continued frequent sexual intercourse and by administered estrogen. Therefore,
the undesirable consequences of these changes can be minimized. Topical
application of estrogen-containing creams directly to the vagina is especially
effective. In addition, because the postmenopausal vagina is relatively thin,
much of the estrogen enters the blood and can have beneficial effects in other
areas.
External
Structures (Genitalia)
Though the changes in the vagina are the main reasons for the
increased risk of developing vaginal infections, age-related shrinkage of the
labia majora may also play a contributing role. This shrinkage causes the labia
to remain separated more of the time, allowing microbes to enter the vagina
more easily. Other age changes in the external genitalia are discussed in
connection with age changes in female sexual activity, below.
Age changes in the breasts result primarily from the decline
in ovarian hormones after menopause. Shrinkage of glandular material, increases
in fat, and weakening of fibrous materials in the breasts reduce their firmness
and support, causing them to sag and droop rather than protrude from the chest (Fig.
13.13). Breasts that have stretched fibers from years with little support from
undergarments may show more sagging. These changes have significant cosmetic
effects. Other age changes in the breasts are discussed in connection with
female sexual activity.
The sequence of changes during female sexual activity can be
divided into phases that resemble the phases seen in men. However, female
sexual activity involves only the first four of these phases because women can
pass from the resolution phase into another excitement phase without an
intervening refractory period. Many women can even cycle between the plateau
and orgasmic phases several times before entering a resolution phase. In
addition and in contrast to the male system, the female system can perform its
reproductive role without undergoing the changes involved in female sexual
activity. If ovulation and endometrial development have occurred, all that is
required for reproduction to begin is the placement of sperm cells into the
female reproductive system.
Several changes occur during female sexual activity in young
adult women (Table 13.2). These physical changes are accompanied by pleasurable
sensations that vary in nature and degree from person to person and from one
sexual experience to another. The intensity of these pleasurable sensations
usually increases from the beginning of the sexual experience through much of
the orgasmic phase and then subsides during the resolution phase.
This section is based largely on the work of Masters and
Johnson. The previous comments on heterogeneity in sexual activity in men apply
to sexual activity in women. Therefore, the age-related changes in female
sexual activity described below represent typical alterations.
Erection of the nipples and lubrication of the vaginal
lining are the first signs of sexual arousal and mark the beginning of the
excitement phase. The lubricating fluid in the vagina eases entry of the penis
and neutralizes some of the vaginal acids to prevent damage to sperm cells.
Substantial nipple erection and vaginal lubrication may be achieved within seconds
after sexual stimulation begins. Both conditions persist and may increase
throughout the excitement and plateau phases.
Nipple erection and vaginal lubrication are quickly followed
by changes in the clitoris and labia minora. Swelling of the labia minora,
which results from an increased input of blood, causes the labia minora to
double or triple in thickness and push outward. In so doing, they separate the
labia majora and protrude from between them. Simultaneously, changes in the
labia majora cause further separation, making the vaginal opening more
accessible. Swelling of the breasts results from an increase in blood flow.
As the excitement phase progresses, the inner portion of the
vagina opens. This change and others in the vagina, uterus, and glands seem to
further prepare the vagina for the entry of the penis. Other changes occur
toward the end of this phase.
Movement of the clitoris marks the transition from the
excitement phase to the plateau phase. If flushing of the skin occurs, it may
spread over more of the body. The changes in the vagina and labia minora result
from increases in blood flow into these structures. Once these changes have
occurred, the orgasmic phase is imminent.
The orgasmic phase begins with rhythmic contractions of the
outer portion of the vagina. As happens during ejaculation in men, the first
few contractions are the strongest and occur at intervals of slightly less than
1 second. After the first few contractions, the rhythm slows and the force of
contraction diminishes. Vaginal contractions, which may number a dozen or more,
are often accompanied by extreme levels of pleasant sensations.
As the vaginal contractions of the orgasmic phase subside,
the resolution phase begins. The changes that occurred during the previous
three phases are reversed, starting with the ones that began last. Thinning of
the outer region of the vagina and fading of the color of the labia minora
occur within a few seconds. Many seconds to several minutes may be required to
completely reverse other changes and fully reestablish resting conditions.
However, if sexual stimulation continues or is repeated any time after the
orgasmic phase, restoration of resting conditions may cease. The changes of the
excitement and plateau phases may then be repeated, and another orgasmic phase
may occur.
AGE CHANGES IN FEMALE SEXUAL ACTIVITY
Age-related changes in sexual activity in women result from
diverse combinations of many of the same factors that produce these changes in
men (e.g., age changes, less frequent sexual activity, nonbiological factors).
However even more frequently than in aging males, sexual activity in aging
females is subject to the effects of reproductive system diseases (e.g., cervical
cancer) and hormone therapies (e.g., estrogen replacement therapy).
The only aspect of the excitement phase that remains
essentially unaffected by aging is erection of the nipples. Because less
vaginal lubrication is present, insertion and movement of the penis is more
difficult and sexual intercourse may become painful. The decline in lubricant
production seems to result primarily from a declining frequency of sexual
activity. Older women who frequently participate in sexual activity maintain
high levels of vaginal fluid production.
Difficulties from low lubricant production can be overcome
by applying a lubricant either near the vaginal opening or to the penis before
sexual intercourse. Lubricated condoms and slippery contraceptive materials can
also be helpful.
During the plateau phase upward and inward movement of the
clitoris changes little with age. Though there is less thickening of its outer
region, the vagina narrows with age, and the final size of the passage though
this region of the vagina remains the same.
As with the decline in vaginal fluid production, there is
less of a decrease in the number of vaginal contractions in women who
frequently engage in sexual activity. Painful uterine contractions may result
from shrinkage of the uterus; they may be relieved by hormone therapy.
The pattern of changes during the resolution phase remains
the same, though virtually all changes occur more rapidly and resting
conditions are achieved more quickly.
In summary, as age increases, the activities and alterations
that occur in the female reproductive system during sexual activity generally
take longer to develop, reach lower peak levels, and return to resting
conditions more rapidly. In spite of this, the female reproductive system
largely retains its ability to provide satisfactory sexual experiences.
FREQUENCY AND ENJOYMENT OF SEXUAL ACTIVITY
A brief examination of age-related alterations in the
frequency and enjoyment (subjective quality) of sexual activity follows. Except
where specific differences are noted, this discussion describes both men and
women.
On the average, the frequency of sexual activity decreases
with age. This decrease accompanies average declines in desire for, interest
in, and enjoyment of sexual activity. However, the degree of change in these
three parameters is highly variable among individuals, and some people
experience increases rather than decreases in one or more parameters.
Among the most important biological factors that reduce the
frequency and enjoyment of sexual activity is declining health of one of the partners,
especially the man. Furthermore, the influence of declining health is often
amplified by treatments that affect sexual functioning (e.g., medications,
radiation therapy, surgery on reproductive or other organs). Other biological
factors that tend to reduce the frequency and enjoyment of sexual activity
include age changes in the reproductive, nervous, and circulatory systems;
faster onset of fatigue; overeating; and excessive consumption of alcohol.
Menopause leads to an average reduction in sexual activity.
However, it results in increased sexual activity for some women because they no
longer fear pregnancy or because sexual activity helps prevent or reverse
negative self-images resulting from menopause.
Male sexual activity is not affected by ordinary changes in
testosterone levels until after approximately age 80. However, abnormally
severe decreases in testosterone reduce the desire for sexual activity and
adversely affect the functioning of the reproductive system.
The frequency and enjoyment of sexual activity are usually
reduced by age-related social changes (e.g., loss of spouse, change in
household) and psychological factors. Relevant psychological factors include
fear of aggravating a heart condition, boredom from lack of variation in sexual
expression, diminished self-image, perceptions of altered physical appearance,
depression, stereotyping, and fear of failure. Conversely, especially for men,
novelty in sexual activity (e.g., new spouse, modified types of sexual
expression) may result in temporary increases in the frequency of sexual
activity.
The consequences of economic changes may also diminish the
frequency and enjoyment of sexual activity. For example, a reduced income may
cause altered living arrangements (e.g., living with relatives) and an
accompanying loss of privacy. Finally, institutionalization can create or
amplify adverse effects in all these categories (biological, social,
psychological, economic).
The physical, social, psychological, and emotional benefits
of sexual activity continue to be important for many older people. Therefore,
actions that prevent or ameliorate factors that adversely affect sexual
activity can help maintain a high quality of life. Such actions include
maintaining good health; accepting age changes (e.g., cosmetic changes, slowed
responsiveness); and using compensatory strategies (e.g., lubricants, modified
sexual techniques). When the frequency or enjoyment of sexual activity becomes unsatisfactory,
medical and psychological evaluation and therapy can help identify and resolve
problems.
ABNORMAL AND DISEASE CONDITIONS
Several abnormal and disease conditions affect the reproductive systems and become especially common or serious with advancing age.
In men, one of these conditions is benign prostatic
hypertrophy (BPH), which is a noncancerous enlargement of
the prostate gland.
Recall that the prostate gland surrounds the urethra
immediately below the urinary bladder (Fig.
13.2). Though the prostate of most 40-year-old men has begun to shrink, in
some men of this age it enlarges because of increases in fibrous material and
muscle cells.
By age 40 few prostate glands have grown enough to cause
problems. However, the percentage of men with substantially enlarged prostates
increases with age so that approximately 90 percent of all men who reach age 80
have a prostate large enough to cause significant problems.
Causes The causes of this abnormal growth are
unknown, though age-related changes in sex hormones and increased binding of
testosterone by the prostate are suspected to be contributing factors.
Consequences Benign prostatic hypertrophy is a serious
disorder primarily because the enlarged gland compresses the urethra. The
resulting partial or complete blockage of urine flow is especially harmful to
the urinary system because it promotes difficult and painful urination;
enlargement and weakening of the bladder; bladder spasms; urinary incontinence;
urinary tract infections; urinary stone formation; kidney malfunction; kidney
damage; and impotence (see below). All these effects can reduce the quality of
life, and most of them diminish the ability of the urinary system to maintain
homeostasis.
Prevention and Treatment Nothing can be done to prevent the initial
abnormal enlargement of the prostate gland in men with BPH. However, BPH
develops gradually and can be detected in the early stages. Once it has been
discovered, treatments to prevent the adverse effects can be initiated.
The simplest method for early detection of BPH is to include
evaluation of the prostate in an annual physical examination. Other conditions
suggesting the development of BPH include (1) slow urine flow, (2) difficulty
starting, continuing, or stopping urine flow, (3) discomfort or pain during
urination, (4) frequent need to urinate, and (5) urinary incontinence.
Some cases of BPH can be treated by regulating dietary fluid
intake and with medications. Many cases are treated surgically. One of the
simpler surgical procedures, transurethral resection of the prostate (TURP),
involves using surgical instruments to remove the inner region of the prostate
piecemeal through the urethra. More advanced cases require more involved
surgical procedures. Though these procedures rarely affect sexual functioning
directly, their negative psychological consequences may adversely affect sexual
activity.
The essential feature of impotence is an inability to engage in sexual intercourse because the penis is not sufficiently erect (not stiff enough) to be inserted into the vagina. In some cases (primary impotence) adequate erection is not achieved in spite of significant amounts of sexual stimulation; in other cases (secondary impotence) an adequate erection is achieved but subsides before insertion of the penis. See videos in Fig. 13.6.
Occasional incidents of impotence occur in many men at every
age and are not considered abnormal. Impotence is considered abnormal only when
it occurs in a high percentage of attempts at sexual intercourse. Opinions vary
widely regarding what rate of impotence constitutes an abnormal frequency.
Identifying abnormal impotence in older men is complicated because the
refractory period may last for several days.
Abnormal impotence seems to be present in far less than 10
percent of men under age 40. Its incidence increases slowly between ages 40 and
50, though it seems to remain below 10 percent. The incidence rises slightly
more rapidly after age 50, reaching perhaps 15 percent by age 60. Thereafter
the incidence rises more rapidly, and impotence may be present in more than 50
percent of men over age 80.
Causes The age-related increase in abnormal
impotence occurs because of the age-related increase in both the incidence and
severity of many factors that contribute to this condition. Since proper
functioning of the nervous and circulatory systems is essential for erection,
factors that adversely affect these systems contribute substantially to
impotence. The highest ranking among these factors are medications, especially
neuroactive drugs and drugs that reduce blood pressure; diabetes mellitus; and
atherosclerosis. Other common contributing factors are nervous system diseases
(e.g., strokes, dementia), surgery of reproductive or adjacent structures
(e.g., prostate, rectum), and alcoholism. Less common contributing factors
include hormone imbalances (e.g., inadequate testosterone production),
malnutrition (e.g., inadequate zinc), and other diseases (e.g., emphysema,
kidney disease). Many older men have more than one contributing factor. Aging
of arteries in the penis may augment the effects of these contributing factors.
Probably more than 50 percent of all cases of abnormal
impotence result primarily from one or more of these physical factors, though
psychological factors may also contribute. Psychological conditions are the
primary cause of all other cases of abnormal impotence, though some degree of
physical impairment may also be present. Relevant psychological conditions
include anxiety, depression, fear of aggravating a physical problem such as
heart disease, boredom, lack of confidence (e.g., fear of repeated impotence),
and poor self-image.
Note that virtually none of these factors are age changes.
Therefore, contrary to a common stereotype of older men, becoming impotent is
not an inevitable part of becoming old but an abnormal condition. Recall that
unless abnormal or disease conditions develop, the male reproductive system
retains the ability to perform its reproductive functions and its operations in
sexual activity throughout life.
Consequences The onset of abnormal impotence is of
concern to many aging adults because it can cause extensive adverse
psychological and social effects, including the breakdown of a relationship.
Therefore, preventing, ameliorating, or eliminating abnormal impotence can
provide a much higher quality of life.
Prevention and Treatment
Obviously, preventing impotence means avoiding
or minimizing factors that contribute to its development. Chaps. 4, 6, 7, and
14 describe methods for avoiding or minimizing many relevant physical factors
(e.g., diabetes mellitus, atherosclerosis, strokes). Good physical health,
positive social interactions, and economic security also help prevent or
minimize some contributing psychological factors.
When abnormal impotence occurs, identifying the specific
contributing factors is the first step in establishing treatment strategies.
Once the principal factors have been identified, appropriate treatments can be
applied. This may involve reducing or removing the cause, which may include
modifying medications, repairing blood vessels surgically, administering
hormones, or instituting counseling or psychotherapy.
When reducing or removing the cause is impossible or
unsuccessful, other techniques can be used. One involves injecting a
vasodilating drug (e.g., papaverine) into vessels in or near the penis when
erection is desired. External pumps that draw blood into the penis can be used
to achieve erection. Various prostheses, pumps, and other devices that provide
temporary or permanent erection can be surgically implanted into the penis or
surrounding areas. Both the number and extent of treatments attest to the
seriousness with which this disorder is regarded.
The drug sildenafil is a recent addition to
treatments for impotence. Sildenafil is produced by Pfizer Labs and is sold
under the brand name Viagra. The drug helps produce and sustain
vasodilation of vessels in the penis by assisting the actions of nitric oxide
(*NO).
During sexual stimulation and arousal, neurons stimulate the
production of *NO in the penis and elsewhere in the body. The *NO causes smooth
muscle cells in penile arteries to produce a special form of nucleotide - cyclic
GMP (cGMP). The cGMP causes the smooth muscle cells to
relax, allowing blood pressure to expand the arteries and produce erection.
Eventually the cGMP is broken down by an enzyme (i.e., cGMP phosphodiesterase),
the smooth muscle contracts, and the penis returns to the flaccid condition.
Sildenafil helps develop and sustain erection by inhibiting
the enzyme the breaks down cGMP. By inhibiting the enzyme, more cGMP can
accumulate and it can last longer, so erection occurs easier and lasts longer.
When sildenafil is taken orally as the drug Viagra, it is absorbed within
minutes. The sildenafil is slowly removed from the blood by the liver, so it
becomes ineffective within a few hours.
The body contains at least six forms of the enzyme that
breaks down cGMP. Different cells have different proportions of these enzyme
forms. Sildenafil has a much greater effect on enzyme form 5, the form that
predominates in penile vessels. Therefore, sildenafil has little effect in
other parts of the body. However, since sildenafil has some effect on other
forms of the enzyme, it may cause extra vasodilation in other vessels. For
example, sildenafil affects vessels in the retina, leading to side effects in
vision such as altered perception of blue and green colors. If sildenafil
affects many body vessels, it can cause widespread vasodilation and low blood
pressure. Blood pressure can become abnormally low if the effects from
sildenafil are amplified by other medications. Examples include medications
that promote *NO formation and medications for vasodilation that contain
nitrates (e.g., nitroglycerine).
Like all cancers, prostate cancer consists of
cells whose relentless reproduction and spreading are not stopped by the body's
normal regulatory mechanisms.
Prostate cancer occurs rarely before age 50; its incidence
rises steadily afterward. In men, the incidence of prostate cancer is second
only to that of lung cancer. Prostate cancer ranks second to melanoma as a
cause of death in men from cancer. For men over age 55, it is the third leading
cause of death from cancer, exceeded only by lung cancer and colorectal cancer.
The fact that cancer ranks second only to heart disease in causing deaths among
older men highlights the importance of these statistics.
Causes Since the causes of prostate cancer are not
known, the specific reasons for the age-related increase are also unclear. The
development of prostate cancer is not related to having BPH. Since prostate
cancer is 50 percent more common in black males than in white males, a genetic
factor may be involved.
Consequences At first the cancerous cells remain within
the prostate gland. As the mass of cells enlarges, the prostate compresses the
urethra. Since this obstructs urine flow, the consequences are similar to those
of BPH.
The cancer eventually spreads out of the prostate and
usually invades the pelvic region first. Because cancer cells can be carried by
blood and lymph, they also spread to other regions. Common sites include the
vertebrae and other bones, the lungs, and the liver. Several organs may be
invaded simultaneously.
The cancer destroys the normal structure and functioning of
every part of the body it enters. The ability to sustain homeostasis
deteriorates, illness develops, and death ensues. Three examples will be
presented. First, prostate cancer weakens bones, causing pain and leading to
fractures and their complications. Second, prostate cancer in the lungs may
block airways, thicken membranes, fill air spaces, and cause hemorrhaging,
significantly reducing respiratory functioning. Third, prostate cancer can
severely impair many of the numerous functions of the liver and may cause
problems similar to those caused by cirrhosis of the liver.
Prevention and Treatment Since the causes of prostate cancer are not
known, virtually nothing can be done to prevent its onset. However, as with
BPH, early detection can lead to early treatment, which may prevent, delay, or
minimize the effects. Unfortunately, prostate cancer produces few signs and
symptoms until it is well developed. Since some cases can be detected by
feeling the prostate during a rectal exam, such an examination should be part
of an annual physical exam, especially for men over age 40. A newer and more
convenient method involves evaluating blood samples for the presence of prostate-specific
antigen (PSA). The PSA test is more accurate than other
diagnostic procedures and is used to test many men. Ultrasound imaging
(sonograms) is used to test for prostate cancer, and small pieces of the
prostate can be removed and tested for the presence of cancer cells.
Sometimes the best treatment is to retest periodically to
see how the disease is progressing. Prostate cancers that grow very slowly may
require no further treatment. Sometimes prostate cancer is treated with
radiation therapy, surgery, or medications that suppress testosterone
production.
In aging women changes in the vagina increase the risk of
developing vaginal infections. Perhaps the most common type of vaginal
infection which results from the age-related decrease in vaginal acidity is
yeast infection. This type of infection often causes intense itching and is usually
accompanied by excessive vaginal discharge.
Wearing underwear made of cotton and avoiding clothing that
fits tightly in the genital area reduce the risk of developing vaginal
infections. Yeast infections can be treated effectively with antibiotic creams
or suppositories.
In aging women as in aging men, reproductive system cancers
are common and serious disorders. The most common cancer of the female
reproductive system is breast cancer.
In women, the incidence of breast cancer is exceeded only by
that of lung cancer. Breast cancer occurs in 10 percent of all women at some
time. The rate of new cases increases with age throughout life, with the most
rapid increase occurring between ages 45 and 65. For women over age 55, breast
cancer is second only to heart disease as a cause of death.
Risk Factors A woman's chances of developing breast cancer
are increased by many risk factors besides age. One of the strongest factors is
having a mother or sister with breast cancer, especially if it occurred during
early adulthood or in both breasts. Other risk factors include using oral
contraceptives containing estrogen, undergoing estrogen replacement therapy,
drinking alcoholic beverages, being exposed to high doses of radiation, having
no children, and, possibly, consuming a high-fat diet.
Consequences Though the dozen or more types of breast
cancer have various effects on the breasts, the most dangerous ones are those
which tend to spread easily to other parts of the body. Spreading usually
occurs through lymph and blood vessels. The structures more frequently invaded
include certain bones (skull, vertebrae, ribs, pelvis), the lungs, the liver,
and the kidneys. The loss of homeostasis resulting from fractures or inadequate
functioning of other vital organs leads to illness and death.
Prevention and Treatment In spite of the serious threat posed by
breast cancer, most of the complications, illnesses, and deaths it causes can
be prevented by early detection and treatment. Knowing and routinely checking
for signs of breast cancer can be helpful. These signs include (1) a thickening
or lump in the breast, (2) changes on the breast skin, areola, or nipples
(e.g., wrinkling, puckering, sores), (3) enlarged lymph nodes near the armpits,
and (4) irregularly shaped or asymmetrical breasts. These signs can be detected
by monthly breast self-examination and by having a breast examination as part
of a routine physical examination. However, the most effective way to detect
breast cancer in the early stages is to receive mammograms (x-rays of the
breast). An annual mammogram is especially recommended for women over age 45
because the risk of developing breast cancer increases markedly after that age.
Another important aspect of prevention is minimizing risks
from estrogen intake by limiting the amount of estrogen used for oral
contraception or estrogen replacement therapy, administering estrogen on a
cyclic basis rather than continuous one, and including progesterone along with
the estrogen.
When breast cancer is suspected, the preliminary diagnosis
can be confirmed or negated by examining a sample of the tissue (biopsy). If
cancer is present, the specific type and its extent are determined. Depending
on the results of these investigations, treatment plans designed to cure the
cancer or reduce the effects by slowing its progress are developed. Such
treatment plans may involve surgery, radiation therapy, chemotherapy, and
hormone therapy.
Endometrial cancer
is cancer of the uterine lining. It has the highest incidence among cancers of
the female reproductive structures, occurring in slightly more than 2 percent
of all women. New cases develop most frequently between ages 50 and 64. Risk
factors include eating excess calories in the diet, having a lowered glucose
tolerance, having no children, having relatives with endometrial cancer, and
receiving estrogen therapy.
The risk of developing endometrial cancer can be reduced by
avoiding overeating and adjusting estrogen therapies in ways similar to those
recommended for preventing breast cancer. Once initiated, endometrial cancer
reveals its presence by causing bleeding from the vagina between menstrual
periods or after menopause. This type of cancer is not as dangerous as others
because it is usually detected early. The most common indicator is abnormal
bleeding from the reproductive system. Because endometrial cancer is usually
detected early, it is easily and effectively treated by surgery and hormone
therapy.
Ovarian cancer
ranks fifth in occurrence among cancers in women and in older women, it ranks
second among cancers of the female reproductive structures. Ovarian cancer
causes more deaths than any other female reproductive system cancer and is the
fifth leading cause of death for women.
Risk factors include never being pregnant, inhaling
cigarette smoke, and estrogen replacement therapy. Avoiding or minimizing these
factors can help reduce the incidence of this cancer. However, little can be
done to prevent it from spreading and destroying other organs because it is
difficult to detect before it is well established in many areas. Surgery,
radiation, and chemotherapy usually can only slow its destructive progress
somewhat.
Cervical cancer
ranks third in older women among
cancers of the female reproductive structures. Recall that the cervix is the
lower part of the uterus and protrudes into the upper part of the vagina ((Figs. 13.7,
Fig. 13.8,
Fig. 13.9). Cervical cancer occurs in 2 to 3 percent of all women before age 80.
Most new cases develop between ages 40 and 60.
Risk Factors The most important risk factor for cervical
cancer is having sexual intercourse soon after sexual maturation. Other risk
factors include having many male sex partners; having male sex partners who
have had sexual intercourse with other women with cervical cancer; inhaling
cigarette smoke; using oral contraceptives; and having sexually transmitted
diseases such as human papillomavirus. This virus sometimes causes genital
warts and often occurs together with genital herpes and chlamydia. Hence, the
incidence of cervical cancer is higher in women with these diseases.
Consequences Once present, cervical cancer usually
spreads by infiltrating nearby organs. Later, it is carried to more distant
organs by the lymphatics. Like other reproductive system cancers, it causes illness
and death by destroying the structure and functioning of any organ it invades.
Prevention and Treatment A primary strategy in the prevention of
cervical cancer is avoiding or minimizing behaviors that increase its risk
factors. Once cervical cancer begins, it provides few indications of its
presence, though it may cause slight bleeding or a watery discharge from the
vagina between menstrual periods or after menopause. However, cervical cancer
can be easily detected in the early stages by a Pap smear, which involves
examining a sample of cells scraped off the cervix. It is recommended that
younger women and women with abnormal cervical cells have a Pap smear as part
of an annual physical examination. Older women who repeatedly have normal Pap
smears may require smears at 2- to 3-year intervals rather than annually. As
with most cancers, early detection and treatment can prevent the development of
complications, illness, and death.
If a Pap smear reveals the presence of cervical cancer, one
or a combination of treatments (e.g., surgery, radiation therapy, chemotherapy)
may be used to cure it or slow its progress.
One type of growth in the female reproductive system that
becomes less of a problem as age increases after menopause is uterine
fibroids, or leiomyomas. A uterine fibroid consists of a spherical mass
of smooth muscle within the muscular wall of the uterus.
Uterine
fibroids may begin to develop during or after puberty and may continue to grow
until menopause. They occur in various sizes and sometimes become larger than a
grapefruit. They usually develop in the upper part of the uterus, though they
may occur anywhere in its wall. Uterine fibroids occur in 20 percent to 25
percent of women beyond age 35, and affected women often have more than one.
Since uterine fibroids do not invade neighboring regions or metastasize, they
are not cancerous.
Most
women with uterine fibroids suffer no adverse effects. However, some fibroids
cause excessive bleeding during menstrual periods, and unusually large ones may
cause problems such as constipation, frequent urination, and kidney disease by
putting pressure on adjacent structures. Finally, fibroids occasionally become
painful. Treatment may consist of removing the fibroids and the affected part
of the uterus or removing the entire uterus (hysterectomy).
Women
with uterine fibroids who do not experience significant problems before
menopause rarely develop fibroid-related problems afterward because fibroids
shrink when blood levels of estrogen and progesterone decline. However,
postmenopausal women on estrogen replacement therapy may develop
fibroid-related problems because this therapy can cause fibroids to enlarge.
Both
male and female reproductive systems are affected by sexually transmitted
diseases (STDs). Commonly encountered examples include
bacterial types (e.g., gonorrhea, syphilis, chlamydia) and viral types (e.g.,
herpes type II, human papillomavirus, AIDS). The incidence of STDs is much
lower among older people than among younger adults, perhaps because older
people have sexual encounters with fewer partners. However, increasing age
seems to have little impact on the causes, effects, methods of prevention, and
treatments for STDs. Therefore, these diseases are not discussed in this book.
©
©
Copyright 2020: Augustine G. DiGiovanna, Ph.D.,
Salisbury University, Maryland
The materials on this site are licensed under CC BY-NC-SA
4.0
Attribution-NonCommercial-ShareAlike
This license requires that reusers
give credit to the creator. It allows reusers
to distribute, remix, adapt, and build upon the material in any medium
or format, for noncommercial purposes only. If others modify or adapt
the material, they must license the modified material under identical
terms.
Previous print editions of the text Human Aging: Biological Perspectives
are © Copyright 2000, 1994 by The McGraw-Hill Companies, Inc. and 2020
by Augustine DiGiovanna.
View License Deed |
View Legal Code