Transcript The Reproductive System

The Reproductive System
The reproductive system consists of:
1- The primary sex organs, or gonads (go′nadz;
“seeds”), are the testes in males and the ovaries in
females. The gonads produce sex cells, or gametes
and secrete a variety of steroid hormones commonly
called sex hormones.
2- The accessory reproductive organs :ducts, glands,
and external genitalia .
-Although male and female reproductive organs are
quite different, their common purpose is to produce
offspring.
• The male’s reproductive role is to manufacture male
gametes called sperm and deliver them to the female
reproductive tract, where fertilization can occur.
• The complementary role of the female is to produce
female gametes, called ova or eggs.
• A sperm and egg may fuse to form a fertilized egg, the
first cell of the new individual, from which all body
cells will arise. Once fertilization has occurred, the
uterus provides the protective environment in which
the embryo develops until birth.
• Sex hormones–androgens in males and estrogens and
progesterone in females–play vital roles both in the
development and function of the reproductive organs
and in sexual behavior and drives.
Anatomy of the Male Reproductive
System
• The sperm-producing testes or male gonads, lie
within the scrotum.
• From the testes, the sperm are delivered to the
body exterior through a system of ducts including
(in order) the epididymis, the ductus deferens,
the ejaculatory duct, and finally the urethra,
which opens to the outside at the tip of the
penis.
• The accessory sex glands, which empty their
secretions into the ducts during ejaculation, are
the seminal vesicles, prostate, and bulbourethral
glands.
• The Scrotum
The scrotum is a sac of skin ,covered with sparse
hairs, and contains paired oval testes. A midline
septum divides the scrotum, providing a
compartment for each testis. Because viable sperm
cannot be produced in abundance at core body
temperature (37°C), the superficial location of the
scrotum, which provides a temperature about 3°C
lower, is an essential adaptation.
• Furthermore, the scrotum responds to
temperature changes:
• When it is cold, the testes are pulled
closer to the warmth of the body wall,
and the scrotum becomes shorter and
heavily wrinkled, increasing its thickness
to reduce heat loss.
• When it is warm, the scrotal skin is flaccid
and loose to increase the surface area for
cooling (sweating) and the testes hang
lower, away from the body trunk.
The Testes
Each testis is approximately 4 cm (1.5 inches) long
and 2.5 cm (1 inch) in width and is surrounded by
the tunica albuginea ,the fibrous capsule of the
testis. Septa extending from the tunica albuginea
divide the testis into 250 to 300 wedge-shaped
lobules ,each containing one to four tightly coiled
seminiferous tubules, the actual “sperm factories.”
Surrounding each seminiferous tubule are smooth
muscle cells .By contracting rhythmically, these
muscles squeeze sperm and testicular fluids
through the tubules and out of the testes.
• The seminiferous tubules of testis converge into
the rete testis (re′te), a tubular network on the
posterior side of the testis. From the rete testis,
sperm leave the testis and enter the epididymis
(ep″ĭ-did′ĭ-mis), which hugs the external testis
surface.
Lying in the soft connective tissue surrounding
the seminiferous tubules are the interstitial cells,
also called Leydig cells .These cells produce
androgens (most importantly testosterone).
• Thus, the sperm-producing and hormoneproducing functions of the testis are carried out by
completely different cell populations.
•
• testicular arteries, which branch from the abdominal
aorta superior to the pelvis supply the testes.
• The right testicular vein drains into the inferior vena
cava ,the left drains into the left renal vein superiorly.
• The testes are served by both divisions of the
autonomic nervous system.
• Associated sensory nerves transmit impulses that
result in agonizing pain and nausea when the testes
are hit forcefully.
• The nerve fibers are enclosed, along with the blood
vessels and lymphatics, in a connective tissue sheath
called the spermatic cord which passes through the
inguinal canal .
The Male Duct System
In order (proximal to distal), the accessory ducts
are the epididymis, the ductus deferens, the
ejaculatory duct, and the urethra.
1-The Epididymis
The cup-shaped epididymis is about 3.8 cm long
.Its head, which contains the efferent ductules,
caps the superior aspect of the testis. Its body
and tail are on the posterolateral area of the
testis. Most of the epididymis consists of the
highly coiled duct of the epididymis with an
uncoiled length of about 6 m.
• The immature, nearly nonmotile sperm that leave the
testis are moved slowly along the duct of the
epididymis through fluid that contains a number of
antimicrobial proteins. As they move along its
tortuous course (a trip that takes about 20 days), the
sperm gain the ability to swim. Sperm are ejaculated
from the epididymis, not the testes as many believe,
and when a male is sexually stimulated and ejaculates,
the smooth muscle in the epididymis walls contracts,
expelling sperm into the next segment of the duct
system, the ductus deferens. Sperm can be stored in
the epididymis for several months, but if held longer,
they are eventually phagocytized by epithelial cells of
the epididymis.
The Ductus Deferens and Ejaculatory Duct
The ductus deferens or vas deferens, is about 45 cm
(18 inches) long. It runs upward as part of the
spermatic cord from the epididymis through the
inguinal canal into the pelvic .It then descends along
the posterior bladder wall, then it joins with the duct
of the seminal vesicle (a gland) to form the short
ejaculatory duct. Each ejaculatory duct enters the
prostate; there it empties into the urethra.
Its muscular layer is extremely thick and the duct
feels like a hard wire when squeezed between the
fingertips. At the moment of ejaculation, the thick
layers of smooth muscle in its walls create strong
peristaltic waves that rapidly squeeze the sperm
forward along the tract and into the urethra.
• Part of the ductus deferens lies in the scrotal sac. Some men opt to
take full responsibility for birth control by having a vasectomy. In this
relatively minor operation, the physician makes a small incision into
the scrotum and then cuts through and ligates (ties off) the ductus
deferens. Sperm are still produced, but they can no longer reach the
body exterior. Eventually, they deteriorate and are phagocytized.
Vasectomy is simple and provides highly effective birth control (close
to 100%).
The Urethra
The urethra is the terminal portion of the male duct system. It
conveys both urine and semen (at different times), so it serves both
the urinary and reproductive systems. Its three regions are
(1) the prostatic urethra, the portion surrounded by the prostate;
(2) the membranous (or intermediate part of the) urethra in the
urogenital diaphragm; and
(3) the spongy (penile) urethra, which runs through the penis and opens
to the outside at the external urethral orifice(about 15 cm long) .
• Accessory Glands
The accessory glands produce the bulk of semen (sperm plus
accessory gland secretions).
The Seminal Vesicles
The seminal vesicles (sem′ĭ-nul) or seminal glands, lie on the
posterior bladder surface. Each of these fairly large, hollow
glands is about the shape and length (5–7 cm) of a little
finger.
• Its fibrous capsule encloses a thick layer of smooth muscle
which contracts during ejaculation to empty the gland. Its
secretion is a yellowish viscous alkaline fluid containing
fructose sugar, ascorbic acid, a coagulating enzyme
(vesiculase), and prostaglandins, as well as other substances
that enhance sperm motility or fertilizing power.
• The duct of each seminal vesicle joins that of the ductus
deferens on the same side to form the ejaculatory duct.
Sperm and seminal fluid mix in the ejaculatory duct and
enter the prostatic urethra together during ejaculation.
Seminal gland secretion accounts for some 60% of the
volume of semen.
• The Prostate
The prostate (pros′tāt) is a single doughnut-shaped
.It encircles the urethra just inferior to the bladder.
The prostatic gland secretion enters the prostatic
urethra via several ducts when prostatic smooth
muscle contracts during ejaculation. It plays a role
in activating sperm and accounts for up to one-third
of the semen volume. It is a milky, slightly acid fluid
that contains citrate (a nutrient source), several
enzymes (fibrinolysin, hyaluronidase, acid
phosphatase), and prostate-specific antigen (PSA).
HOMEOSTATIC IMBALANCE
Hypertrophy of the prostate gland, called benign
prostatic hyperplasia (BPH), which affects nearly
every elderly male, distorts the urethra. Although
its precise cause is unknown, it may be associated
with changes in hormone levels as a result of aging.
Traditional treatment has been surgical, but some
newer options are gaining popularity, such as using
microwaves or drugs to shrink the prostate; and
inserting and inflating a small balloon to compress
the prostate tissue away from the prostatic urethra.
• The Bulbourethral Glands
The bulbourethral glands (bul″bo-u-re′thral) are peasized glands inferior to the prostate gland .They
produce a thick, clear mucus, some of which drains
into the spongy urethra when a man becomes
sexually excited and neutralizes traces of acidic urine
in the urethra.
• Semen (se′men) is a milky white, somewhat sticky
mixture of sperm and accessory gland secretions.
The liquid provides a transport medium and
nutrients and contains chemicals that protect and
activate the sperm and facilitate their movement.
Mature sperm cells are streamlined cellular
“missiles” containing little cytoplasm or stored
nutrients. Catabolism of the fructose in seminal
vesicle secretion provides nearly all the fuel needed
for sperm ATP synthesis.
-Prostaglandins in semen decrease the viscosity
of mucus guarding the entry (cervix) of the
uterus and stimulate reverse peristalsis in the
uterus, facilitating sperm movement through
the female reproductive tract. The presence of
the hormone relaxin and certain enzymes in
semen enhance sperm motility.
-The relative alkalinity of semen as a whole (pH
7.2–7.6) helps neutralize the acid environment
of the male’s urethra and the female’s vagina,
thereby protecting the delicate sperm and
enhancing their motility. Sperm are very
sluggish under acidic conditions (below pH 6).
- Semen also contains substances that suppress the
immune response in the female’s reproductive tract
and an antibiotic chemical called seminalplasmin,
which destroys certain bacteria.
- Clotting factors found in semen coagulate it just
after it is ejaculated. Soon, its contained fibrinolysin
liquefies the sticky mass, enabling the sperm to
swim out and begin their journey through the
female duct system.
The amount of semen propelled out of the male
duct system during ejaculation is 2–5 ml, but there
are between 20 and 150 million sperm per milliliter.
Spermatogenesis
Spermatogenesis (sperm formation) is the sequence of
events in the seminiferous tubules of the testes that
produces male gametes–sperm or spermatozoa.
-The process begins around the age of 14 years in
males, and continues throughout life. Every day, a
healthy adult male makes about 400 million sperm.
The normal chromosome number in most body cells
is referred to as the diploid chromosomal number
(dip′loid) of the organism, symbolized as 2n. In humans,
this number is 46, and such diploid cells contain 23
pairs of similar chromosomes called homologous
chromosomes. One member of each pair is from the
male parent (the paternal chromosome); the other is
from the female parent (the maternal chromosome).
• The number of chromosomes present in human gametes is
23, referred to as the haploid chromosomal number
(hap′loid), or n; gametes contain only one member of each
homologous pair. When sperm and egg fuse, they form a
fertilized egg that reestablishes the typical diploid
chromosomal number of human cells.
Gamete formation in both sexes involves meiosis, a unique
kind of nuclear division that, for the most part, occurs only in
the gonads.
• In mitosis (the process by which most body cells divide)
replicated chromosomes are equally distributed between the
two daughter cells. Consequently, each daughter cell receives
a set of chromosomes identical to that of the mother cell.
• In meiosis, on the other hand, consists of two consecutive
nuclear divisions, and its product is four daughter cells
instead of two, each with half as many chromosomes as
typical body cells. Thus, meiosis reduces the chromosomal
number by half (from 2n to n) in gametes.
Mitosis of Spermatogonia: Forming Spermatocytes
The outermost tubule cells are stem cells called
spermatogonia .
-The spermatogonia divide more or less continuously by
mitosis and, until puberty, all their daughter cells
become spermatogonia.
- Spermatogenesis begins during puberty, and from
then on, each mitotic division of a spermatogonium
results in two distinctive daughter cells–types A and B.
The type A daughter cell remains at the basement
membrane to maintain the germ cell line.
-The type B cell gets pushed toward the lumen, where it
becomes a primary spermatocyte destined to produce
four sperms.
Meiosis: Spermatocytes to Spermatids
Each primary spermatocyte generated during the first phase
undergoes meiosis I, forming two smaller haploid cells called
secondary spermatocytes. The secondary spermatocytes
continue on rapidly into meiosis II, and their daughter cells,
called spermatids (sper′mah-tidz), are small round cells with
large spherical nuclei seen closer to the lumen of the tubule.
Spermiogenesis: Spermatids to Sperm
Each spermatid has the correct chromosomal number for
fertilization (n), but is nonmotile. It still must undergo a
process called spermiogenesis, during which it elongates,
sheds its excess cytoplasmic baggage, and forms a tail. The
resulting sperm, or spermatozoon has a head, a midpiece,
and a tail.
-The head of a sperm consists almost entirely of its flattened
nucleus, which contains the compacted DNA. Adhering to the
top of the nucleus is a helmetlike acrosome (ak′ro-sōm; “tip
piece”).
-The lysosome-like acrosome is produced by the
Golgi apparatus and contains hydrolytic enzymes
that enable the sperm to penetrate and enter an
egg.
- The sperm midpiece contains mitochondria
spiraled tightly around the contractile filaments
of the tail.
-The long tail is a typical flagellum produced by
the centriole near the nucleus. The mitochondria
provide the metabolic energy (ATP) needed for
the whiplike movements of the tail that will
propel the sperm along its way in the female
reproductive tract.
Hormonal Regulation of Male Reproductive Function
The Brain-Testicular Axis
Hormonal regulation of spermatogenesis and
testicular androgen production involves interactions
between the hypothalamus, anterior pituitary
gland, and testes, a relationship sometimes called
the brain-testicular axis. The hypothalamus
releases gonadotropin-releasing hormone (GnRH),
which controls the release of the two anterior
pituitary gonadotropins: follicle-stimulating
hormone (FSH) and luteinizing hormone (LH). (Both
FSH and LH were named for their effects on the
female gonad).
- Binding of GnRH to pituitary cells (gonadotrophs)
prompts them to secrete FSH and LH into the blood.
- FSH stimulates spermatogenesis indirectly by
stimulating the spermatogenic cells to bind and
concentrate testosterone, which in turn stimulates
spermatogenesis. Thus, FSH makes the cells
receptive to testosterone’s stimulatory effects.
- LH binds to the interstitial cells, prodding them to
secrete testosterone (and a small amount of
estrogen). Locally, testosterone serves as the final
trigger for spermatogenesis. Testosterone entering
the bloodstream exerts a number of effects at other
body sites.
Male secondary sex characteristics–that is, features
induced in the nonreproductive organs by the male
sex hormones (mainly testosterone)–make their
appearance at puberty.
• These include the appearance of pubic, axillary, and
facial hair, enhanced hair growth on the chest or
other body areas in some men, and a deepening of
the voice as the larynx enlarges. The skin thickens
and becomes oilier (which predisposes young men to
acne), bones grow and increase in density, and
skeletal muscles increase in size and mass.
-Testosterone also boosts basal metabolic rate and It is
the basis of the sex drive (libido) in males and to
some extent in females.
-The testes are not the only source of androgens; the
adrenal glands of both sexes also release androgens.
Female Reproductive System
The reproductive role of the female is far more
complex than that of a male. Not only must she
produce gametes, but her body must prepare to
nurture a developing embryo for a period of
approximately nine months. Ovaries, the female
gonads, are the primary reproductive organs of a
female, and like the male testes, ovaries serve a
dual purpose: They produce the female gametes
(ova) and sex hormones, the estrogens and
progesterone (pro-ges′tĕ-rōn).
The female’s accessory ducts, from the ovary to the
body exterior, are the uterine tubes, the uterus,
and the vagina.
The Ovaries
The paired ovaries flank the uterus on each side
.Shaped like an almond and about twice as large,
each ovary is held in place within the peritoneal
cavity by several ligaments. The ovarian ligament
anchors the ovary medially to the uterus; the
suspensory ligament anchors it laterally to the
pelvic . In between , they are enclosed and held in
place by a fold of peritoneum, the broad ligament.
The ovaries are served by the ovarian arteries,
branches of the abdominal aorta and by the ovarian
branch of the uterine arteries.
• Embedded in the highly vascular connective tissue
of the ovary cortex are many tiny saclike structures
called ovarian follicles. Each follicle consists of an
immature egg, called an oocyte surrounded by one
or more layers of very different cells called follicle
cells. Follicles at different stages of maturation are
distinguished by their structure.
• A primordial follicle, one layer of squamouslike
follicle cells surrounds the oocyte.
• A primary follicle has two or more layers of
cuboidal or columnar-type cells enclosing the
oocyte; it becomes a secondary follicle when fluidfilled spaces appear and then coalesce to form a
central fluid-filled cavity called an antrum.
• At the mature vesicular follicle, or Graafian follicle
(graf′e-an), stage, the follicle bulges from the
surface of the ovary.
• Each month in adult women, one of the ripening
follicles ejects its oocyte from the ovary, an event
called ovulation .
• After ovulation, the ruptured follicle is transformed
into a very different looking glandular structure
called the corpus luteum (lu′te-um; plural: corpora
lutea), which eventually degenerates. As a rule,
most of these structures can be seen within the
same ovary.
• In older women, the surfaces of the ovaries are
scarred and pitted, revealing that many oocytes
have been released.
The Female Duct System
1-The Uterine Tubes
• The uterine tubes (u′ter-in), also called fallopian
tubes or oviducts, form the initial part of the female
duct system .They receive the ovulated oocyte and
are the site where fertilization generally occurs.
• Each uterine tube is about 10 cm (4 inches) long and
extends medially from the region of an ovary to
empty into the superolateral region of the uterus .
• The distal end of each uterine tube expands as
funnel-shaped infundibulum bearing ciliated,
fingerlike projections called fimbriae that partially
surround the ovary.
• Unlike the male duct system, which is continuous
with the tubules of the testes, the uterine tubes
have little or no actual contact with the ovaries. An
ovulated oocyte is cast into the peritoneal cavity,
and many oocytes are lost there.
• The uterine tube performs complex movements to
capture oocytes–it bends to drape over the ovary
while the fimbriae stiffen and sweep the ovarian
surface. The beating cilia on the fimbriae then
create currents in the peritoneal fluid that tend to
carry an oocyte into the uterine tube, where it
begins its journey toward the uterus.
HOMEOSTATIC IMBALANCE
• The fact that the uterine tubes are not
continuous with the ovaries places women at
risk for ectopic pregnancy in which a zygote,
fertilized in the peritoneal cavity or distal
portion of the uterine tube, begins developing
there. Because the tube lacks adequate mass
and vascularization to support the full term of
pregnancy, such pregnancies naturally abort,
often with substantial bleeding.
HOMEOSTATIC IMBALANCE
• Another potential problem is infection spreading
into the peritoneal cavity from other parts of the
reproductive tract causing an extremely severe
inflammation called pelvic inflammatory disease
(PID). Unless treated promptly with broad-spectrum
antibiotics, PID can cause scarring of the narrow
uterine tubes and of the ovaries, causing sterility.
Indeed, scarring and closure of the uterine tubes,
which have an internal diameter as small as the
width of a human hair in some regions, is one of the
major causes of female infertility.
2-The Uterus
The uterus is located in the pelvis, anterior to the
rectum and posterosuperior to the bladder .It is a
hollow, thick-walled, muscular organ that functions
to receive, retain, and nourish a fertilized ovum.
- In a premenopausal woman who has never been
pregnant, the uterus is about the size and shape of
an inverted pear, but it is usually somewhat larger in
women who have borne children.
- Normally, the uterus flexes anteriorly where it joins
the vagina, causing the uterus as a whole to be
inclined forward, or anteverted. However, the organ
is frequently turned backward, or retroverted, in
older women.
-The major portion of the uterus is referred to as
the body .
-The rounded region superior to the entrance of the
uterine tubes is the fundus, and the slightly
narrowed region between the body and the cervix
is the isthmus.
-The cervix of the uterus is its narrow neck, or
outlet, which projects into the vagina inferiorly. The
cavity of the cervix, called the cervical canal,
communicates with the vagina via the external os
(os = mouth) and with the cavity of the uterine
body via the internal os.
The mucosa of the cervical canal contains cervical glands
that secrete a mucus that fills the cervical canal and
covers the external os, presumably to block the spread
of bacteria from the vagina into the uterus. Cervical
mucus also blocks the entry of sperm, except at
midcycle, when it becomes less viscous and allows
sperm to pass through.
HOMEOSTATIC IMBALANCE
• Cancer of the cervix strikes about 450,000 women
worldwide each year, killing about half.
• It is most common among women between the ages of
30 and 50.
• Risk factors include frequent cervical inflammations,
sexually transmitted diseases including genital warts,
and multiple pregnancies.
• A Pap smear is the most effective way to detect this
slow-growing cancer.
• Supports of the Uterus The uterus is supported
laterally by the broad ligament and anchord
anteriorly and posteriorly by the round and
uterosacral ligaments respectively. These ligaments
allow the uterus a good deal of mobility, and its
position changes as the rectum and bladder fill and
empty.
HOMEOSTATIC IMBALANCE Despite the many
anchoring ligaments, the principal support of the
uterus is provided by the muscles of the pelvic floor,
namely the muscles of the urogenital and pelvic
diaphragms .These muscles are sometimes torn
during childbirth. Subsequently, the unsupported
uterus may sink inferiorly, until the tip of the cervix
protrudes through the external vaginal opening. This
condition is called prolapse of the uterus.
The Uterine Wall
Is composed of three layers :
• The perimetrium, the incomplete outermost
serous layer, is the peritoneum.
• The myometrium (mi″o-me′tre-um; “muscle of the
uterus”) is the bulky middle layer, composed of
interlacing bundles of smooth muscle, that
contracts rhythmically during childbirth to expel
the baby from the mother’s body.
• The endometrium is the mucosal lining of the
uterine cavity. If fertilization occurs, the young
embryo burrows into the endometrium (implants)
and resides there for the rest of its development.
• The endometrium has two chief strata (layers):
-The functional layer, undergoes cyclic changes in
response to blood levels of ovarian hormones and
is shed during menstruation (approximately every
28 days).
-The thinner, deeper stratum basalis (ba-să′lis), or
basal layer, forms a new functional layer after
menstruation ends . It is unresponsive to ovarian
hormones.
-The endometrium has numerous uterine glands
that change in length as endometrial thickness
changes.
The Vagina
The vagina is a thin-walled tube, 8–10 cm long. It lies
between the bladder and the rectum and extends
from the cervix to the body exterior .The urethra is
embedded in its anterior wall.
• called the birth canal, the vagina provides a
passageway for delivery of an infant and for menstrual
flow.
• The mucosa is a stratified squamous epithelium
adapted to stand up to friction. The vaginal mucosa
has no glands; it is lubricated by the cervical mucous
glands.
• The pH of a woman’s vagina is normally quite acidic.
This acidity helps keep the vagina healthy and free of
infection, but it is also hostile to sperm.
• In virgins (those who have never participated in
sexual intercourse), the mucosa near the distal
vaginal orifice forms an incomplete partition called
the hymen (hi′men) .
• The hymen is very vascular and tends to bleed
when it is ruptured during the first coitus (sexual
intercourse). However, its durability varies. In some
females, it is ruptured during a sports activity,
tampon insertion, or pelvic examination.
• ccasionally, it is so tough that it must be breached
surgically if intercourse is to occur.
• The upper end of the vaginal canal loosely
surrounds the cervix of the uterus, producing a
vaginal recess called the vaginal fornix. The
posterior part of this recess, the posterior fornix,
is much deeper than the lateral and anterior
fornices .
• Generally, the lumen of the vagina is quite small
and, except where it is held open by the cervix, its
posterior and anterior walls are in contact with
one another. The vagina stretches considerably
during copulation and childbirth, but its lateral
distension is limited by the ischial spines .
The External Genitalia
The female reproductive structures that lie external to
the vagina are called the external genitalia .The
external genitalia, also called the vulva .
• The mons pubis is a fatty, rounded area overlying the
pubic symphysis. After puberty, this area is covered
with pubic hair.
• Running posteriorly from the mons pubis are two
elongated, hair-covered fatty skin folds, the labia
majora . The labia majora enclose the labia minora
,two thin, hair-free skin folds. The labia minora
enclose a recess called the vestibule (“entrance hall”),
which contains the external openings of the urethra
and the vagina.
• anterior to the vestibule is the clitoris ,a small,
protruding structure composed largely of erectile
tissue, which is homologous to the penis of the male.
• Flanking the vaginal opening are the pea-size
greater vestibular glands (Bartholin`s glands),
homologous to the bulbourethral glands of males.
These glands release mucus into the vestibule and
help to keep it moist and lubricated, facilitating
intercourse.
• The female perineum is a diamond-shaped region
located between the pubic arch anteriorly, the
coccyx posteriorly, and the ischial tuberosities
laterally.
The Mammary Glands
They are present in both sexes, but they normally
function only in females .
• They are modified sweat glands that are really
part of the skin, or integumentary system. Each
mammary gland is contained within a rounded
skin-covered breast within the hypodermis
(superficial fascia), anterior to the pectoral muscles
of the thorax. Slightly below the center of each
breast is a ring of pigmented skin, the areola (ahre′o-lah), which surrounds a central protruding
nipple.
• Internally, each mammary gland consists of 15 to 25
lobes that open at the nipple. Within the lobes are
smaller units called lobules, which contain glandular
alveoli that produce milk when a woman is
lactating. These compound alveolar glands pass the
milk into the lactiferous ducts which open to the
outside at the nipple. Just deep to the areola, each
duct has a dilated region called a lactiferous sinus
where milk accumulates during nursing.
• In nonpregnant women, the glandular structure of
the breast is largely undeveloped and the duct
system is rudimentary; hence breast size is largely
due to the amount of fat deposits.
Breast Cancer
Invasive breast cancer is the most common malignancy and
the second most common cause of cancer death of U.S.
women. Thirteen percent of women in the general population
(132 out of 1000 individuals) will develop this condition.
Breast cancer usually arises from the epithelial cells of the
smallest ducts, not from the alveoli. A small cluster of cancer
cells grows into a lump in the breast from which cells
eventually metastasize.
Known risk factors for developing breast cancer include:
(1) early onset menses and late menopause;
(2) no pregnancies or first pregnancy later in life and no or short
periods of breast feeding.
(3) family history of breast cancer (especially in a sister or
mother), and
(4) postmenopausal estrogen-progesterone replacement.
MAMMOGRAPHY
Mammography is an x-ray technique that is used to
evaluate breast tissue for abnormalities. By far the
most frequent usage is to detect breast cancer,
which is one of the most common malignancies in
women.
If detected early, breast cancer may be cured through
a combination of surgery, radiation, and
chemotherapy.
Women should practice breast self-examination
monthly , but mammography can detect lumps that
are too small to be felt manually.
Women in their 30s may have a mammogram done to
serve as a comparison for mammograms later in
life.
Physiology of the Female Reproductive System
Oogenesis
• Gamete production in males begins at puberty and
continues throughout life, but the situation is quite
different in females.
• It has been assumed that a female’s total supply of
eggs is already determined by the time she is born,
and the time span during which she releases them
extends only from puberty to menopause (about the
age of 50).
• Meiosis, the specialized nuclear division that occurs in
the testes to produce sperm, also occurs in the
ovaries. In this case, female sex cells are produced,
and the process is called oogenesis .The process of
oogenesis takes years to complete.
• First, in the fetal period the oogonia, the diploid
stem cells of the ovaries, multiply rapidly by mitosis.
Gradually, primordial follicles begin to appear as the
oogonia are transformed into primary oocytes and
become surrounded by a single layer of flattened
follicle cells.
• By birth, a female has been presumed to have her
lifetime supply of primary oocytes; of the original 7
million oocytes approximately 2 million of them
escape programmed death and are already in place
in the immature ovary. The wait is a long one–10 to
14 years at the very least.
• At puberty, perhaps 250,000 oocytes remain and
beginning at this time a small number of primary
oocytes are activated each month in response to
the LH surge midcycle. However, only one is
“selected” each time to continue meiosis I,
ultimately producing two haploid cells (each with
23 replicated chromosomes) that are quite
dissimilar in size.
• The smaller cell is called the first polar body. The
larger cell, which contains nearly all the cytoplasm
of the primary oocyte, is the secondary oocyte.
• The first polar body may continue its development and
undergo meiosis II, producing two even smaller polar
bodies.
• The secondary oocyte (not a functional ovum) is
ovulated. If an ovulated secondary oocyte is not
penetrated by a sperm, it simply deteriorates. But, if
sperm penetration does occur, it quickly completes
meiosis II, yielding one large ovum and a tiny second
polar body .
• The union of the egg and sperm nuclei, constitutes
fertilization.
• The potential end products of oogenesis are three tiny
polar bodies, nearly devoid of cytoplasm, and one
large ovum. All of these cells are haploid, but only the
ovum is a functional gamete.
• This is quite different from spermatogenesis, where
the product is four viable gametes–spermatozoa.
• The unequal cytoplasmic divisions that occur during
oogenesis ensure that a fertilized egg has ample
nutrients for its six- to seven-day journey to the
uterus. Without nutrient-containing cytoplasm the
polar bodies degenerate and die.
• Since the reproductive life of a female is at most
about 40 years (from the age of 11 to approximately
51) and typically only one ovulation occurs each
month, fewer than 500 oocytes out of her
estimated pubertal potential of 250,000 are
released during a woman’s lifetime.
The Ovarian Cycle
The monthly series of events associated with the maturation
of an egg is called the ovarian cycle. The ovarian cycle is best
described in terms of two consecutive phases.
1-follicular phase is the period of follicle growth, typically
indicated as lasting from the first to the fourteenth day of
the cycle.
2-The luteal phase is the period of corpus luteum activity, days
14–28. The so-called typical ovarian cycle repeats at intervals
of 28 days, with ovulation occurring midcycle.
However, only 10–15% of women naturally have 28-day cycles;
cycles as long as 40 days or as short as 21 days are fairly
common. In such cases, the length of the follicular phase and
timing of ovulation vary, : It is 14 days between the time of
ovulation and the end of the cycle.
The Follicular Phase
Maturation of a primordial follicle to the mature state occupies
the first half of the cycle and involves several events .
• Primordial Follicle Becomes a Primary Follicle When a
primordial follicle is activated ,the squamouslike cells
surrounding the primary oocyte grow, becoming cuboidal
cells, and the oocyte enlarges. The follicle is now called a
primary follicle
• A Primary Follicle Becomes a Secondary Follicle Next,
follicular cells proliferate,forming a stratified epithelium
around the oocyte .
• In the next stage , a layer of connective tissue condenses
around the follicle, forming the theca folliculi. As the follicle
grows, the surrounding cells cooperate to produce estrogens .
• At the same time, the oocyte secretes a glycoprotein-rich
substance that forms a thick transparent membrane, called
the zona pellucida that encapsulates it .
• Clear liquid accumulates between the cells and
eventually coalesces to form a fluid-filled cavity called
the antrum (“cave”). The presence of an antrum
distinguishes the new secondary follicle from the
primary follicle.
• A Secondary Follicle Becomes a Vesicular Follicle The
antrum continues to expand with fluid until it isolates
the oocyte, along with its surrounding capsule of cells
called a corona radiata. When a follicle is full size
(about 2.5 cm, or 1 inch, in diameter), it becomes a
vesicular follicle and bulges from the external ovarian
surface like an “angry boil.” This usually occurs by day
14.
As one of the final events of follicle maturation, the
primary oocyte completes meiosis I to form the
secondary oocyte and first polar body. Once this has
occurred , the stage is set for ovulation.
• Ovulation
Ovulation occurs when the ballooning ovary wall
ruptures and expels the secondary oocyte (still
surrounded by its corona radiata) into the peritoneal
cavity . Some women experience a twinge of pain in the
lower abdomen when ovulation occurs. This episode,
called mittelschmerz (German for “middle pain”), is
caused by the intense stretching of the ovarian wall
during ovulation.
In the ovaries of adult females, there are always several
follicles at different stages of maturation. As a rule, one
follicle outstrips the others to become the dominant
follicle and is at the peak stage of maturation when the
hormonal (LH) stimulus is given for ovulation. The
others degenerate (undergo programmed cell death, or
apoptosis) and are reabsorbed.
• In 1–2% of all ovulations, more than one oocyte is
ovulated. This phenomenon, which increases with age,
can result in multiple births. Since, in such cases,
different oocytes are fertilized by different sperm, the
siblings are fraternal, or nonidentical, twins.
• Identical twins result from the fertilization of a single
oocyte by a single sperm, followed by separation of
the fertilized egg’s daughter cells in early
development.
• Additionally, it now appears that in some women,
oocytes may be released at times unrelated to the
woman’s hormone levels, which may help to explain
why a rhythm method of contraception sometimes
fails and why some fraternal twins have different
conception dates.
The Luteal Phase
After ovulation, the ruptured follicle collapses, and the
antrum fills with clotted blood. The remaining cells
increase in size and they form a new, quite different
endocrine gland, the corpus luteum (“yellow body”),
that begins to secrete progesterone and some
estrogen.
• If pregnancy does not occur, the corpus luteum starts
degenerating in about ten days and its hormonal
output ends. In this case, all that ultimately remains is a
scar called the corpus albicans (al′bĭ-kans; “white
body”).
• On the other hand, if the oocyte is fertilized and
pregnancy ensues, the corpus luteum persists until the
placenta is ready to take over its hormone-producing
duties in about three months.
Hormonal Regulation of the Ovarian Cycle
Ovarian events are much more complicated than those
occurring in the testes.
Gonadotropin-releasing hormone (GnRH), the pituitary
gonadotropins, and, in this case, ovarian estrogen and
progesterone interact to produce the cyclic events occurring in
the ovaries.
• Establishing the Ovarian Cycle
As puberty nears, the hypothalamus begins to release GnRH in a
rhythmic manner. GnRH, in turn, stimulates the anterior
pituitary to release FSH and LH, which prompt the ovaries to
secrete hormones (primarily estrogens).
Gonadotropin levels continue to increase for about four years
and, during this time, pubertal girls are still not ovulating and
thus are incapable of getting pregnant. The young woman’s first
menstrual period is referred to as menarche.
• Usually, it is not until the third year postmenarche that the
cycles become regular and all are ovulatory.
• As LH blood levels fall, the stimulus for luteal activity
ends, and the corpus luteum degenerates. As goes the
corpus luteum, so go the levels of ovarian hormones,
and blood estrogen and progesterone levels drop
sharply. The marked decline in ovarian hormones at
the end of the cycle (days 26–28) ends their blockade
of FSH and LH secretion, and the cycle starts anew.
Although the ovarian events are described as if we
are following one follicle through the 28-day cycle, this
is not really the case. What is happening is that the
increase of FSH at the beginning of each cycle
activates several follicles to mature. Then, with the
midcycle LH surge, one (or more) Graafian follicles
undergo ovulation.
Uterine (Menstrual) Cycle
Although the uterus is where the young embryo
implants and develops, it is receptive to
implantation for only a short period each month.
Not surprisingly, this brief interval is exactly the
time when a developing embryo would normally
begin implanting, six to seven days after ovulation.
The uterine, or menstrual cycle is a series of cyclic
changes that the uterine endometrium goes
through each month as it responds to ovarian
hormones in the blood. These endometrial changes
are coordinated with the phases of the ovarian
cycle, which are dictated by gonadotropins released
by the anterior pituitary.
The events of the uterine cycle, are as follows:
1. Days 1–5, Menstrual phase: In this phase,
menstruation ,the uterus sheds all but the deepest
part of its endometrium. (At the beginning of this
stage, ovarian hormones are at their lowest normal
levels and gonadotropins are beginning to rise).
The thick, hormone-dependent functional layer of
the endometrium detaches from the uterine wall, a
process that is accompanied by bleeding for 3–5
days with about 150 ml of blood. The detached
tissue and blood pass out through the vagina as the
menstrual flow. By day 5, the growing ovarian
follicles are starting to produce more estrogen .
2. Days 6–14, Proliferative (preovulatory) phase
Under the influence of rising blood levels of estrogens,
the basal layer of the endometrium generates a new
functional layer. As this new layer thickens, its glands
enlarge and its spiral arteries increase in number .
Consequently, the endometrium once again becomes
velvety, thick, and well vascularized.
Normally, cervical mucus is thick and sticky, but rising
estrogen levels cause it to thin and become crystalline,
forming channels that facilitate the passage of sperm
into the uterus.
Ovulation, which takes less than five minutes, occurs in
the ovary at the end of the proliferative stage (day 14)
in response to the sudden release of LH from the
anterior pituitary. LH also converts the ruptured follicle
to a corpus luteum.
3. Days 15–28, Secretory (postovulatory) phase:
• This 14-day phase is the most constant timewise.
Rising levels of progesterone convert the functional
layer to a secretory mucosa. The uterine glands
enlarge, coil, and begin secreting nutritious glycogen
into the uterine cavity. These nutrients sustain the
embryo until it has implanted in the blood-rich
endometrial lining.
• Increasing progesterone levels also cause the cervical
mucus to become viscous again, forming the cervical
plug, which blocks sperm entry and plays an important
role in keeping the uterus “private” in the event an
embryo has begun to implant.
• Rising progesterone (and estrogen) levels inhibit LH
release by the anterior pituitary.
• If fertilization has not occurred, the corpus luteum
begins to degenerate toward the end of the
secretory phase as LH blood levels decline.
Progesterone levels fall, depriving the endometrium
of hormonal support, and the spiral arteries kink
and go into spasms so endometrial cells die, setting
the stage for menstruation to begin on day 28.
• The spiral arteries then suddenly relax and open
wide. As blood gushes into the weakened capillary
beds, they fragment, causing the functional layer to
slough off.
• The menstrual cycle starts over again on this first
day of menstrual flow.
Developmental Aspects of the Reproductive System
• Genetic sex is determined (at the time of
fertilization), by the sex chromosomes: an X from
the mother, an X or a Y from the father. If the
fertilized egg contains XX, it is a female and
develops ovaries; if it contains XY, it is a male and
develops testes.
• The development of male accessory structures and
external genitalia depends on the presence of
testosterone produced by the embryonic testes. In
its absence, female structures develop.
• The testes form in the abdominal cavity and
descend into the scrotum.
• Puberty is the interval when reproductive organs
mature and become functional. It begins in males
with penile and scrotal growth and in females with
breast development.
• During menopause, ovarian function declines, and
ovulation and menstruation cease. Hot flashes and
mood changes may occur. Postmenopausal events
include atrophy of the reproductive organs, bone
mass loss, and increasing risk for cardiovascular
disease.
Pregnancy and Human Development
• The term pregnancy refers to events that occur from
the time of fertilization (conception) until the infant is
born.
• The pregnant woman’s developing offspring is called
the conceptus .
• The time during which development occurs is referred
to as the gestation period and extends by convention
from the last menstrual period (a date the woman is
likely to remember) until birth, approximately 280
days. Thus, at the moment of fertilization, the mother
is officially (but illogically) two weeks pregnant!
• From fertilization through week 8, the embryonic
period, the conceptus is called an embryo, and from
week 9 through birth, the fetal period, the conceptus is
called a fetus .
• At birth, it is an infant.
Accomplishing Fertilization
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Before fertilization can occur, sperm must reach the ovulated
secondary oocyte.
The oocyte is viable for 12 to 24 hours after it is cast out of
the ovary; the chance of pregnancy drops to almost zero the
next day.
Most sperm retain their fertilizing power for 24 to 48 hours
after ejaculation.
Consequently, for successful fertilization to occur, coitus must
occur no more than two days before ovulation and no later
than 24 hours after, at which point the oocyte is
approximately one-third of the way down the length of the
uterine tube.
Fertilization occurs when a sperm fuses with an egg (actually
a secondary oocyte) to form a fertilized egg, or zygote ,the
first cell of the new individual.
• Sperm freshly deposited in the vagina are incapable of
penetrating an oocyte. They must first be capacitated over
the next 6 to 8 hours; that is, their mobility is enhanced and
their membranes must become fragile so that the hydrolytic
enzymes in their acrosomes can be released. Thus, even
though the sperm may reach the oocyte within a few
minutes, they must “wait around” for capacitation to occur.
Hundreds of sperms must release their acrosomal enzymes to
break down the egg’s corona radiata and zona pellucida.
When one sperm binds to receptors on the egg, it triggers the
slow block to polyspermy.
• Polyspermy (entry of several sperm into an egg) occurs in
some animals, but in humans only one sperm is allowed to
penetrate the oocyte, ensuring monospermy
• Following sperm penetration, the secondary oocyte
completes meiosis II.
• Then the ovum and sperm pronuclei fuse (fertilization),
forming a zygote.
Results of fertilization
1- Determination of the sex of the embryo
2-Restoration of chromosomal number (2n)
characteristic of the human embryo which is 46.
3-Starting of cleavage.
Events of Embryonic Development: Zygote to Blastocyst
• Cleavage, a rapid series of mitotic divisions without
intervening growth, begins with the zygote and ends with a
blastocyst. The blastocyst consists of the trophoblast and an
inner cell mass. Cleavage produces a large number of cells.
• Implantation The trophoblast adheres to, digests, and
implants in the endometrium. Implantation is completed when
the blastocyst is entirely surrounded by endometrial tissue,
about 12 days after ovulation.
• hCG released by the blastocyst maintains hormone production
by the corpus luteum, preventing menses. hCG levels decline
after four months.
• Placentation The placenta acts as the respiratory, nutritive,
and excretory organ of the fetus and produces the hormones
of pregnancy. It is formed from embryonic and maternal
tissues. Typically, the placenta is functional as an endocrine
organ by the third month.
Gastrulation: formation of Germ Layers
ultimately the inner cell mass is transformed into a
three-layered embryo (gastrula) containing
ectoderm, mesoderm, and endoderm.
• Ectoderm forms the nervous system and the
epidermis of the skin and its derivatives.
• Endoderm forms the mucosa of the digestive and
respiratory systems, and the epithelial cells of all
associated glands (thyroid, parathyroids, thymus,
liver, pancreas). It becomes a continuous tube
when the embryonic body fuses ventrally.
• Mesoderm forms all other organ systems and
tissues.
Events of Fetal Development
- All organ systems are laid down during the embryonic period;
growth and tissue/organ specialization are the major events
of the fetal period.
- During the fetal period, fetal length increases from about 22
mm to 360 mm, and weight increases from less than an
ounce to 7 pounds or more.
Effects of Pregnancy on the Mother
•
Anatomical Changes
1.Maternal reproductive organs and breasts become increasingly
vascularized during pregnancy, and the breasts enlarge.
2. The uterus eventually occupies nearly the entire
abdominopelvic cavity. Abdominal organs are pushed superiorly
and encroach on the thoracic cavity, causing the ribs to flare.
3. The increased abdominal mass changes the woman’s center of
gravity; lordosis and backache are common. A waddling gait
occurs as pelvic ligaments and joints are loosened by placental
relaxin.
4. A typical weight gain during pregnancy in a woman of normal
weight is 28 pounds.
• Metabolic Changes Human placental lactogen has
anabolic effects and promotes glucose sparing in the
mother. Human chorionic thyrotropin results in
maternal hypermetabolism.
• Physiological Changes
1. Many women suffer morning sickness, heartburn,
and constipation during pregnancy.
2. The kidneys produce more urine, and pressure on
the bladder may cause frequency, urgency, and stress
incontinence.
3. Tidal volume and respiratory rate increase, but
residual volume decreases. Dyspnea is common.
4. Total body water and blood volume increase
dramatically. Heart rate and blood pressure rise,
resulting in enhancement of cardiac output in the
mother.
Parturition (Birth) is the culmination of pregnancy—
giving birth to the baby. It usually occurs within 15
days of the calculated due date (280 days from the last
menstrual period).
The series of events that expel the infant from the
uterus are collectively called labor.
Initiation of Labor When estrogen levels are
sufficiently high, they induce oxytocin receptors on
the myometrial cells and inhibit progesterone’s
quieting effect on uterine muscle. Weak, irregular
contractions begin.
Fetal cells produce oxytocin, which stimulates
prostaglandin production by the placenta. Both
hormones stimulate contraction of uterine muscle.
Increasing stress activates the hypothalamus, causing
oxytocin release from the posterior pituitary; this sets
up a positive feedback loop resulting in true labor.
Stages of Labor
• The dilation stage is from the onset of
rhythmic, strong contractions until the cervix
is fully dilated. The head of the fetus rotates
as it descends through the pelvic outlet.
• The expulsion stage extends from full cervical
dilation until birth of the infant.
• The placental stage is the delivery of the
afterbirth (the placenta and attached fetal
membranes).
Adjustments of the Infant to Extrauterine Life
1. After the umbilical cord is clamped, carbon dioxide
accumulates in the infant’s blood, causing respiratory centers
in the brain to trigger the first inspiration.
2. Once the lungs are inflated, breathing is eased by the
presence of surfactant, which decreases the surface tension
of the alveolar fluid.
3. During transition, the first 8 hours after birth, the infant is
physiologically unstable and adjusting. After stabilizing, the
infant wakes approximately every 3–4 hours in response to
hunger.
Occlusion of Special Fetal Blood Vessels and Vascular Shunts
4. Inflation of the lungs causes pressure changes in the
circulation; as a result, the umbilical arteries and vein, ductus
venosus, and ductus arteriosus collapse, and the foramen
ovale closes. The occluded blood vessels are converted to
fibrous cords; the site of the foramen ovale becomes the
fossa ovalis.
Lactation
1. The breasts are prepared for lactation during pregnancy
by high blood levels of estrogen, progesterone, and placental
lactogen.
2. Colostrum, a premilk fluid, is a fat-poor fluid that contains
more protein, vitamin A, and minerals than true milk. It is
produced toward the end of pregnancy and for the first two
to three days after birth.
3. True milk is produced around day 3 in response to
suckling, which stimulates the hypothalamus to prompt
anterior pituitary release of prolactin and posterior pituitary
release of oxytocin. Prolactin stimulates milk production.
Serotonin inhibits prolactin release when the mammary
glands are full of milk, and oxytocin triggers milk let-down.
Continued breast-feeding is required for continued milk
production.
4. At first, ovulation and menses are absent or irregular
during nursing, but in most women the ovarian cycle is
eventually reestablished while still nursing.
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Related Clinical Terms
Abortion Premature removal of the embryo or fetus
from the uterus; may be spontaneous or induced.
Ectopic pregnancy A pregnancy in which the embryo
implants in any site other than the uterus; most often
the site is a uterine tube (tubal pregnancy).
Hydatid (hydatidiform) mole Developmental
abnormality of the placenta; the conceptus
degenerates and the chorionic villi convert into a mass
of vesicles. Signs include vaginal bleeding, which
contains some of the grapelike vesicles.
Ultrasonography Noninvasive technique that uses
sound waves to visualize the position and size of the
fetus and placenta .
• Physiological jaundice Jaundice sometimes occurring
in normal newborns within three to four days after
birth. Fetal erythrocytes are short-lived, and they
break down rapidly after birth; the infant’s liver may
be unable to process the bilirubin (breakdown
product of hemoglobin pigment) fast enough to
prevent its accumulation in blood and subsequent
deposit in body tissues.
• Placenta abruptio Premature separation of the
placenta from the uterine wall; if this occurs before
labor, it can result in fetal death due to anoxia.
• Placenta previa Placental formation adjacent to or
across the internal os of the uterus. Represents a
problem because as the uterus and cervix stretch,
tearing of the placenta may occur. Additionally, the
placenta precedes the infant during labor.