THE REPRODUCTIVE SYSTEMS
Define reproduction.
Reproduction is the process by which genetic material is passed from generation
to generation, maintaining the continuation of the species.
Identify, then briefly describe, the three groups of reproductive organs according to
function.
gonads -- The testes and ovaries -- function to produce the gametes (sperm and
ova) and to secrete reproductive hormones.
ducts -- Ducts transport, receive, and store gametes. They are particularly
extensive in the male.
accessory glands -- produce materials that support the gametes in the male. In
the female the accessory glands are used to provide lubrication for
intercourse.
A.
MALE REPRODUCTIVE SYSTEM
1.
SCROTUM
Describe the scrotum.
The scrotum is a cutaneous outpouching of the abdomen, consisting of loose skin and superficial fascia. It is divided by a vertical
septum into right and left compartments, each of which contains a
single testis. The scrotum serves as the supporting structure for
the testes.
What is Dartos’ fascia?
The scrotal septum is continuous with the superficial fascia beneath
the skin of the scrotum. This fascia contains smooth muscle called
Dartos’ fascia. This specialized fascia is responsible for tightening
of the scrotal skin, thus playing a role in temperature regulation of
the testes.
What is the function of the scrotum?
The location of the scrotum and the contraction of Dartos’ fascia
and skeletal muscle fibers that wrap the testes regulate the
temperature of the testicular environment. The production and
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survival of sperm require a core temperature of 95° F. Because the
scrotum is outside the body cavity it can provide this environment.
What is the cremaster muscle?
In addition to Dartos’ fascia in the superficial fascia of the scrotal
wall, each testis has a cremaster muscle, a sling-like band of
skeletal muscle derived from the internal abdominal oblique muscle
of that side of the body. The muscle comes to wrap the testis as it
descends the body wall during development to move out of the
abdominal cavity and into the scrotum.
Describe the cremaster reflex.
Contraction of the cremaster muscles (cremaster reflex) elevates
the testes toward the body cavity (and body heat) during exposure
to cold and with sexual arousal.
Exposure to heat causes the cremaster muscle to relax, allowing
the testes to drop away from the body cavity and therefore away
from the core body temperature.
2.
TESTES
Describe the testes as follows:
gross anatomy -- The testes (testicles) are paired oval organs that
reside within the scrotum. Each testis is 2" long x 1" in
diameter.
development -- The testes develop on the posterior wall of the body
and descend through the inguinal canals, passing through
the anterior abdominal wall to enter the scrotum at the end of
the 7th month of fetal life. They are partially covered by the
tunica vaginalis, an extension of the peritoneum formed
during the testicular descent.
tunica albuginea/lobules -- Internal to the tunica vaginalis is the
dense connective tissue capsule of the testis itself, the
tunica albuginea (white coat).
Extensions (septa) of the tunica albuginea into the substance of the testis divide it into 200 - 300 smaller
compartments called lobules.
seminiferous tubules -- Within each lobule are 1 - 3 tightly coiled
tubules called the seminiferous tubules. The tubules are
lined with spermatogenic cells in various stages of develop348
ment (meiosis). The most immature cells type, the
spermatogonium, lies on the outer border of the tubule.
a.
SPERMATOGENESIS AND SPERMIOGENESIS
Describe the process of spermatogenesis and spermiogenesis.
Once sexual maturity is reached (puberty), the spermatogonia may enter one of two cell division pathways. Some
spermatogonia enter mitosis and simply add new spermatogonia to the seminiferous tubules.
Other spermatogonia, in response to appropriate hormonal
signals, move away from the basement membrane of the
tubule toward the lumen, and enter meiosis to begin the
process of spermatogenesis.
Once in meiosis, the cell enlarges to become a primary
spermatocyte. It then enters the first meiotic division, giving
rise to two secondary spermatocytes, each of which now has
half the original number of chromosomes.
Each secondary spermatocyte enters the second meiotic
division, giving rise to two spermatids, each now with the
appropriate number of chromosomes (monads) to fertilize an
egg.
Each spermatid is then partially engulfed within another cell
type of the seminiferous tubule, the sustentacular (Sertoli)
cell, where it enters the process of spermiogenesis. During
this time the spermatid becomes an anatomically mature
sperm.
In this process, the spermatid sheds its cytoplasm, condenses its DNA into a tight “head” and forms a flagellum,
giving rise to the anatomically mature spermatozoon.
During this time, the Sertoli cell nourishes and protects the
spermatid. After spermiogenesis, the Sertoli cell releases
the spermatozoon into the lumen of the seminiferous tubule
for transport out of the testis.
b.
SPERMATOZOA
Describe sperm as follows:
maturation rate and lifespan -- Spermatozoa released from
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Sertoli cells are anatomically, but not functionally,
mature cells, each with 23 chromosomes that are the
male component of fertilization. They mature at the
rate of about 300 million/day in sexually active males
and, once ejaculated into the female reproductive
tract, have a life expectancy of about 48 hours.
head and acrosome -- Each sperm is composed of three
portions: the head contains the DNA and a dense
granule called the acrosome, a package of enzymes
that aid the sperm in penetration into the ovum for
fertilization.
midpiece and tail -- The midpiece contains mitochondria that
provide ATP for locomotion. The tail is a typical
flagellum that propels the sperm along its way in the
female reproductive tract.
c.
HORMONES OF THE BRAIN-TESTICULAR AXIS
Describe the hormones involved in the control of the male
reproductive system. Be sure to include the sources of the
hormones.
Secretions of the anterior pituitary gland, controlled by the
hypothalamus, play a major role in the developmental
changes in the male reproductive system that occur at
puberty and which maintain sexual function in the adult.
In response to gonadotropin-releasing factor (Gn-RF) from
the hypothalamus, the anterior pituitary gland secretes its
two gonadotropins: follicle-stimulating hormone (FSH) and
luteinizing hormone (LH) (aka – interstitial cell stimulating
hormone).
FSH (1) initiates spermatogenesis by stimulating
spermatogonia to enter the meiotic pathway, and (2)
stimulates Sertoli cells to prepare for the newly formed
spermatids and to produce the hormone inhibin.
Interstitial endocrinocytes (Leydig cells) are nests of cells
located between seminiferous tubules. They respond to LH
by secreting testosterone and other male sex steroid
hormones (androgens).
Testosterone and related androgens have the following
functions: (1) stimulate embryonic and fetal development of
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the male primary sexual characteristics (formation of male
sex organs, descent of the testes).
(2) Male secondary sexual characteristics that begin to
appear at puberty (enlargement of genitalia, increased
protein anabolism for musculoskeletal development,
formation of coarse body hair, enlargement of larynx.
Describe blood testosterone levels during the male lifespan. What
is the role of the hormone inhibin in male reproduction?
Prior to puberty, blood testosterone levels are low. This
testosterone is secreted primarily by the testes, as well as
the adrenal cortex.
At and after puberty, blood testosterone levels reach a
genetically determined level and are maintained at this level
until about the age of 50 by negative feedback of
testosterone on LH secretion.
Blood testosterone levels drop about 1/7 per decade after
the age of 50. Even at the age of 80, a gentleman has about
4/7 of the testosterone he had as a teenager.
The hormone inhibin secreted by Sertoli cells in response to
FSH is involved with the negative feedback control of FSH
secretion and the control of the rate of spermatogenesis.
Again, rate of spermatogenesis is genetically determined.
When it proceeds too slowly, inhibin secretion is inhibited, so
that more FSH can be secreted and the rate of sperm
formation can increase.
3.
DUCTS
a.
DUCTS OF THE TESTES
Describe the following:
sperm path out of testis --Sperm and fluid are moved by a
pressure gradient created by new sperm from the
seminiferous tubules into the straight tubules, one per
lobule. Straight lobules open into a network of
tubules at the hilus of the posterior testis called the
rete testis. From here, sperm and fluid are moved
through the efferent ductules into the ductus
epididymis.
b.
EPIDIDYMIS
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Describe the ductus epididymis following:
location -- The highly coiled ductus epididymis is a tubule
that lies within a connective sheath, forming the
epididymis. This comma-shaped organ lies along the
posterior border of each testis.
functions -- Functionally, the ductus epididymis is the site of
sperm maturation. Non-motile and nonfertile new
sperm mature for 10-14 days within the ductus
epididymis, during which time they gain motility and
become capable of fertilization (once in the presence
of seminal fluids). The ductus epididymis also serves
as a storage site for sperm and may hold them as
long as a month. If they are not expelled by
peristalsis into the ductus deferens they are resorbed
by the epithelium of the ductus epididymis.
c.
DUCTUS (VAS) DEFERENS
Describe the ductus deferens as follows:
origin -- At the tail of the epididymis, the ductus epididymis
becomes larger in diameter and straighter. At this
point the duct is known as the ductus (vas) deferens.
path out of scrotum -- The vas deferens passes superiorly
along the posterior border of the epididymis, enters
the spermatic cord, and enters the pelvic cavity.
The spermatic cord is a composite structure of the
male reproductive system that passes superiorly out
of the scrotum and into the pelvic cavity through the
inguinal canal. In addition, to the vas deferens, it also
contains the testicular artery, a plexus of veins that
drain the testis, autonomic nerves, lymphatic vessels,
and the cremaster muscle.
The inguinal canal is an obliquely placed passageway
through the anterior abdominal wall just superior and
parallel to the medial half of the inguinal ligament. It
originates as the deep inguinal ring, a slit-like opening
in the transverse abdominis muscle, passes about 2",
then terminates as the superficial inguinal ring, a
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triangular opening in the external abdominal oblique
muscle just lateral to the pubic symphysis.
path in pelvic cavity -- Once in the pelvic cavity, the vas
deferens loops over the side and down the posterior
surface of the urinary bladder, ending as a dilated
portion called the ampulla, which serves as a second
site for sperm storage.
function -- Functionally, in addition to sperm storage in the
ampulla, the vas deferens conveys sperm by
peristalsis from the ductus epididymis toward the
urethra during ejaculation.
d.
e.
EJACULATORY DUCTS
URETHRA
Describe the following:
ejaculatory ducts -- Lying posterior to the urinary bladder are
the ejaculatory ducts. Each is formed by the union of
the ampulla of the vas deferens with the duct of the
seminal vesicle of that side. The ejaculatory ducts
receive sperm from the vas deferens and eject them
into the prostatic portion of the urethra just before
ejaculation (a process called emission).
male urethra -- The male urethra is the terminal duct of the
reproductive and urinary systems, serving as a
passageway for both sperm and urine. It is divided
into three parts.
The prostatic urethra (1 inch) passes from the urinary
bladder directly through the substance of the prostate
gland, receiving its secretions from many ducts as it
passes through the gland.
The membranous urethra (0.5 inches) passes from
the edge of the prostate gland through the muscular
pelvic (urogenital) diaphragm, which forms the
external urethral sphincter, then passes into the
penis.
The penile urethra (6 inches) passes into the corpus
spongiosum of the penis and opens to the outside at
the external urethral orifice.
4.
ACCESSORY SEX GLANDS
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Describe the accessory sex glands of the male.
While the testes create the cellular portion of the semen, the
accessory sex glands of the male produce most of the liquid portion
of the semen.
Name and then describe the accessory sex glands of the male.
The accessory sex glands of the male are the:
1.
prostate gland
2.
seminal vesicles (2)
3.
bulbourethral glands (2)
Describe the prostate gland and its secretions.
The prostate gland is a single chestnut-sized structure
lying inferior to the urinary bladder surrounding the
origin of the urethra. It secretes a slightly acidic
viscous fluid rich in citric acid, some clotting enzymes,
and fibrolysin/serine protease/PSA .
Describe the seminal vesicles and their secretions.
The seminal vesicles lie posterior to the base of the
urinary bladder, in front of the rectum. They secrete
an alkaline, viscous fluid rich in fructose,
prostaglandins, and fibrinogen/prosemenogelin.
Describe the bulbourethral glands and their secretions.
The bulbourethral glands are about the size of peas
and are located on either side of the membranous
urethra within the pelvic diaphragm. They secrete
alkaline, mucous-rich fluid called, pre-ejaculatory fluid.
List and then describe the function of each of the three major components
of the seminal vesicles fluid (1,2,3) and prostatic fluid (4,5,6).
1.
2.
fructose - used by sperm for ATP production
prostaglandins -- promote sperm motility and stimulate
muscular contractions of the female tract
3.
proseminogelin -- used to coagulate semen after ejaculation
4.
citric acid -- used for sperm motility
5.
clotting enzymes-converts prosemenogelin to semenogelin or fibrinogen to fibrin
6.
serine protease/PSA prostate specific antigen//fibrinolysin -- liquefies clotted
semen after several minutes in the female tract
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What are the two functions of pre-ejaculatory fluid?
1.
2.
5.
neutralize residual acidity within the urethra
lubricate the urethra to facilitate passage of sperm
SEMEN
Describe semen by discussing it components, pH, average volume,
average number of sperm, functions, and fate.
Semen (seminal fluid) is a mixture of sperm and accessory gland
secretions.
Semen has a pH of 7.2 - 7.6.
The average volume of semen is 2.5 - 5 ml/ejaculate.
An average ejaculate contains 50 - 100 million sperm/ml.
(<20 million is considered male infertility)
Semen functions in the transportation and nourishment of sperm
and in neutralizing the acidity of the male urethra and the
female vagina to promote sperm viability.
Once ejaculated into the vagina, semen coagulates, then liquefies
5 - 20 minutes later, liberating the sperm for their journey up
the female reproductive tract.
6.
PENIS
Describe the penis as follows:
functions -- The penis is used to introduce sperm into the vagina
and as an excretory organ for the urinary system.
portions -- The penis consists of three portions: the root, the body
(corpus), and the glans (head).
What is the root of the penis?
The root of the penis is the portion attached to the
body wall. It consists of the bulb of the penis, the
expanded base of erectile tissue known as the corpus
spongiosum, and the crura, connective tissues which
attach the underside of the penis to the pelvic
diaphragm. The bulb and crura are enclosed within
two muscles of the pelvic diaphragm, the
bulbocavernosus and the ischiocavernosus muscles.
What is the body of the penis?
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The body of the penis is composed of cylindrical
masses of erectile tissues, each bound by dense
fibrous connective tissue called the tunica albuginea
and each permeated by blood sinuses.
Name and describe the erectile tissues?
The two dorsolateral masses are called the corpora
cavernosa and the smaller midventral mass is the
corpus spongiosum, which contains the penile urethra
and forms the head of the penis.
Describe the head of the penis.
The distal enlarged end of the penis, the glans penis,
also known as the head of the penis, is formed by the
distal expanded portion of the corpus spongiosum.
Covering the glans penis is the prepuce (foreskin).
erection -- With sexual stimulation, the arteries supplying the penis
vasodilate and large quantities of blood enter the erectile
tissues. As these spaces expand, the penile veins are
compressed so that an erection is formed. The penis returns
to it flaccid state when sexual stimulation ends. The penile
arteries vasoconstrict, allowing the blood to drain from the
erectile tissues.
B.
FEMALE REPRODUCTIVE ORGANS
List the organs of the female reproductive system.
The organs of the reproductive system include the:
2 ovaries
2 uterine (fallopian) tubes (oviducts)
uterus
vagina
external genitalia
In addition, the mammary glands are often grouped into this system
1.
OVARIES
Describe the ovaries as follows:
gross anatomy -- The ovaries, or female gonads, are paired organs
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about the size and shape of an almond. They develop and
descend like the testes, but stop their descent at about the
level of the pelvic brim. Each ovary comes to lie in the upper
pelvic cavity, one on each side of the uterus. They are held
in place by a series of ligaments (folds of the peritoneum)
that anchor them to the uterine tubes and the uterus.
4 main parts -- Each ovary consists of four main parts:
germinal epithelium --The germinal epithelium is a
layer of epithelium that covers the outer surface of the
ovary. It got its name because these cells were once
thought to be the eggs (hence the name germinal.)
tunica albuginea - The tunica albuginea is a capsule of
dense connective tissue lying just deep to the
germinal epithelium. It is homologous to the tunica
albuginea of the testes.
stroma -- The stroma of the ovary is a region of connective
tissue deep to the tunica albuginea that is subdivided
into a cortex and a medulla. The cortex contains the
developing ova, while the medulla houses the ovarian
blood supply.
ovarian follicles -- eggs (ova) in various stages of
development
a.
OÖGENESIS
The formation of haploid ova in the ovary involves several stages of
ovarian follicle development. Describe these stages and structures
of oögenesis and the ovarian cycle.
Ovarian follicles are immature oöcytes surrounded by
support cells called follicular cells. During the course of a
monthly ovarian cycle, some of these immature follicles
develop to the point of ovulation.
Primordial follicles consist of a primary oöcyte, which has
been arrested in meiosis I since about the 6th prenatal month
of the female baby’s life. A single layer of flattened follicular
cells surrounds the oöcyte.
Each, month, some primordial follicles develop into primary
follicles. The primary oöcyte begins to complete its first
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meiotic division and the surrounding follicular cells enter
mitosis and begin to secrete estrogen.
The primary follicle becomes a secondary follicle when the
ovum is a secondary oöcyte arrested in meiosis II and the
follicular cells have formed and antrum (lake) of fluid rich in
estrogen.
The tertiary (Graafian) follicle contains the secondary oöcyte
surrounded by a very large antrum and a wall of follicular
cells that continue to secrete estrogen. This is just before
ovulation.
At ovulation, the secondary oöcyte and some attached
follicular cells are ruptured from the tertiary follicle out of the
ovary and into the peritoneal cavity, leaving behind the
remainder of the follicular cells as the corpus luteum.
The corpus luteum is a temporary endocrine organ (living for
only 12 - 13 days post-ovulation) left behind in the ovary
after ovulation. The luteal cells secrete estrogen and
progesterone.
After 12 - 13 days the corpus luteum dies (if pregnancy has
not occurred). This leaves a bit of scar tissue within the
ovary called the corpus albicans.
How is oögenesis different from spermatogenesis?
Oögenesis is similar to spermatogenesis in the male in that
meiosis is required to produce a secondary oöcyte for
fertilization. It is unlike the male in that oögonia lose the
ability to divide by mitosis during fetal life. During fetal life,
oögonia increase their numbers to about 7 million, and then
lose their mitotic ability. They then either enter meiosis or
die. By puberty, only about 40,000 - 60,000 primary oöcytes
remain in the ovaries, each arrested in meiosis I and waiting
for the appropriate hormonal signal to continue the meiotic
process.
What is the role of the following hormones in oögenesis?
Gn-RF -- Like the male, at puberty female Gn-RF stimulates
the secretion of FSH and LH from the anterior
pituitary gland. These gonadotropins then activate
the ovaries to enter the ovarian cycle. This process
occurs monthly.
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FSH -- Each month FSH stimulates primary oöcytes (up to
50 or so), living within primordial follicles, to resume
meiosis and become secondary oöcytes. FSH also
stimulates the follicular cells to begin mitosis and to
begin secreting estrogen. All but one of the
developing follicles dies after being activated by FSH.
The one that survives becomes a secondary, then a
tertiary follicle, containing a secondary oöcyte that
arrests in meiosis II.
LH -- In response to the rising blood estrogen levels, LH is
secreted. It causes ovulation to occur. The
secondary oöcyte, now liberated, will continue and
finish meiosis only if it is fertilized by a sperm cell.
2.
UTERINE (FALLOPIAN) TUBES
Describe the oviducts as follows:
gross anatomy -- The two oviducts (uterine or Fallopian tubes) are
about 4 inches long, extending laterally from the uterus to
the ovary of that side. Each tube is subdivided into four
sections.
Name and describe each of these subdivisions.
The open, funnel-shaped distal end of an oviduct is
the infundibulum. It ends in a fringe of finger-like
processes called the fimbriae that lie adjacent to the
ovary. The ampulla of the oviduct is the widest
portion, forming the next two-thirds of its length. The
isthmus is the narrowed neck region of the uterine
tube where it attaches to the uterus.
histology -- The oviduct is lined with a ciliated mucosa that aids in
the transport of the ovum down the tube, and secretory cells
that provide nutrition for the passing ovum. In addition, there
is a muscularis layer that, through peristaltic actions, aids
sperm movement up the oviduct and ovum movement down
the oviduct.
function -- At ovulation, the released ovum usually sticks to the
inner surface of the fimbriae and is swept through the
oviduct by ciliary and peristaltic movements. Successful
fertilization, meaning one that results in uterine implantation,
occurs in the ampulla within 24 hours of ovulation.
3.
UTERUS
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Describe the uterus as follows:
gross anatomy -- The uterus is between the urinary bladder
anteriorly and the rectum posteriorly and is held in position
by ligaments formed by folds of the peritoneum. Normally, it
is flexed (bent) between its body and cervix, so that the body
projects anteriorly and superiorly over the urinary bladder
(anteverted).
divisions -- Anatomically the uterus is divided into several parts.
The fundus is the dome-shaped portion above the openings
of the oviducts and the body (corpus) is the major, tapering
central portion. The cervix is the narrow inferior portion
opening into the vagina. It is separated from the body by the
isthmus of the uterus. The interior of the uterus is the
uterine cavity that opens into the cervical canal.
cervical mucous -- The cervical mucosa secretes cervical mucous,
a material that becomes less viscous and more alkaline
during the time of ovulation, thus facilitating fertilization. At
this time, it is very receptive to sperm and provides
nourishment and protection for them. At other times it is
thicker and more acidic.
functions -- The uterus (womb) functions as the:
1.
site of menstruation
2.
implantation and development of the embryo/fetus
during gestation
3.
labor
perimetrium -- The outermost layer of the uterus, the perimetrium,
is the visceral peritoneum that wraps the uterus and holds it
in place. Laterally, it folds over itself to form the broad
ligament.
peritoneal pouches -- Anteriorly, the perimetrium reflects over the
bladder to form the vesicouterine pouch. Posteriorly, it
reflects over the rectum, forming the rectouterine pouch.
The rectouterine pouch is the lowest point in the female
pelvis.
myometrium -- The myometrium, the middle layer, forms the bulk of
the uterine wall. It is formed of three layers of smooth
muscle that are responsible for labor and delivery.
endometrium -- The endometrium, the inner mucosal layer, consists
of two parts:
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1.
2.
The stratum basalis is the deep permanent mitotic
layer.
The stratum functionalis is the superficial portion that
is sloughed off with each menstrual cycle.
blood supply -- Blood is supplied to the uterus by the uterine
arteries, branches from the internal iliac arteries. Ultimately,
there are spiral arterioles that directly supply the stratum
functionalis. This is unlike all other epithelia since no other
has a direct blood supply.
4.
VAGINA
Describe the vagina as follows:
function -- The vagina, passing from the cervix to the exterior of the
body, serves as a passageway for menstrual flow and
childbirth and the copulatory organ of the female, receiving
semen from the male during intercourse.
gross anatomy -- The vagina is a tubular, fibromuscular organ lined
with mucosa. It measures about 4 inches in length in the
unstimulated state. It lies between the urinary bladder and
the rectum. A recess called the fornix surrounds the vagina
at its attachment to the cervix. At the lower end, the introitus
(vaginal orifice), there may be a thin fold of mucous
membrane called the hymen. It forms a border around the
orifice and partially closes it.
mucosa -- The vaginal mucosa is stratified squamous and is thrown
into folds called rugae. The muscularis layer is smooth
muscle that can stretch considerably, lengthening up to a
total of 7 inches or so, to accommodate a penis during
intercourse or to allow passage of a fetus.
role of glycogen -- The vaginal mucosa stores glycogen, a food
source for the normal bacterial flora that live in the vagina.
These bacteria decompose the glycogen and in doing so,
create an acidic vaginal environment. The naturally acidic
vaginal environment retards unwanted microbial growth in
the vagina (yeast, for example). This acidity is also harmful
to sperm, hence the alkalinizing influence of the semen.
5.
VULVA
Describe the following:
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vulva -- The term vulva (also known as the pudendum) is a
collective term that refers to the external genitalia of the
female. It includes the: mons pubis, labia majora (2), labia
minora (2), clitoris, and vestibule.
mons pubis -- The mons pubis is anterior to the vaginal and urethral
openings. It is an elevation of adipose tissue covered by
pubic hair that serves to cushion the pubic symphysis during
intercourse. It is homologous to the mons pubis of the male.
labia majora -- The labia majora are two folds of skin extending
from the mons pubis inferiorly to the anus posteriorly. They
contain adipose tissue, sebaceous and sudoriferous glands,
and are covered by pubic hair. The labia majora are
homologous to the scrotum of the male.
labia minora -- The labia minora are two longitudinal folds of
mucosa just medial to the labia majora. They extend from
the clitoris to just anterior to the anus, where they fuse.
They have no hair or fat, but many sebaceous glands. They
are homologous to the urethral folds of the male.
clitoris -- The clitoris is a small cylindrical mass of erectile tissue
and sensory nerves located at the anterior junction of the
labia minora. A small fold of skin called the prepuce
(foreskin) covers it. The clitoris is homologous to the penis
of the male.
vestibule -- The vestibule is the cleft found between the labia
minora. It contains the urethral orifice anteriorly and the
vaginal orifice posteriorly, and the openings of a number of
small glands. The bulb of the vestibule, similar to the bulb of
the penis, consists of two masses of erectile tissue just deep
to the labia on either side of the vaginal orifice. Like the
male, they become engorged with blood during sexual
arousal.
glands of the vestibule -- Opening into the vestibule are the greater
and lesser vestibular glands. They provide most of the
lubrication for intercourse. There are no vaginal glands for
this purpose. These glands are homologous to the prostate
gland and the seminal vesicles of the male.
6.
PERINEUM
What is the perineum?
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The perineum is the diamond-shaped area between the thighs and
the buttocks of males and females that contain the external
genitalia and the anus.
Describe the boundaries of the urogenital triangle and the anal triangle.
It is subdivided into the urogenital triangle and the anal triangle by
imaginary lines drawn between the symphysis pubis, the two ischial
tuberosities, and the coccyx, with a transverse line between the two
ischial tuberosities.
Why is the perineum important?
The dimensions of the perineum are important considerations
regarding childbirth because it defines the size of the birth canal.
7.
MAMMARY GLANDS
Describe the mammary glands as follows:
location --The mammary glands (breasts) are modified sudoriferous
glands that produce milk. Each gland lies over the pectoralis
major and serratus anterior muscles and is attached to them
by a layer of connective tissue.
lobes and lobules -- Internally, each gland consists of 15 - 20 lobes
separated by adipose tissue. While breast size is
determined by the amount of adipose tissue present, it has
nothing to do with the ability to produce milk. Each lobe is
subdivided into several smaller lobules.
ducts -- Each lobule consists of clusters of milk-producing cells that
are drained by secondary tubules to mammary ducts to
lactiferous sinuses to lactiferous ducts that open at the
nipple.
nipple -- The nipple is the pigmented projection of the mammary
gland through which milk is expressed to the outside. The
nipple is surrounded by the pigmented areola. This area is
rich in tactile receptors.
development -- At birth, the mammary glands are undeveloped. At
puberty, under the influence of estrogen and progesterone,
the duct system matures, fat deposition begins, and the
areolar area becomes pigmented. Development into a milk363
secreting organ is dependent upon the hormones of
pregnancy.
C.
FEMALE REPRODUCTIVE CYCLE
The female reproductive cycle , a cyclical sequence of changes in the ovaries
and uterus, requires about one month and involves both oögenesis and
preparation of the uterus to receive a fertilized ovum. It is divided into two
portions, each of which is hormonally controlled.
Give a brief description of the ovarian and uterine cycle.
The ovarian cycle is a series of events associated with the continued
maturation of an ovum, resulting in a single secondary oöcyte arrested in
meiosis II that is ovulated. FSH and LH control the cycle.
The uterine (menstrual) cycle is a series of changes in the stratum
functionalis of the uterus to prepare for implantation of a fertilized ovum.
The cycle is controlled by estrogen and progesterone.
1.
HORMONAL REGULATION
Describe the role of the following hormones in female reproduction:
Gn-RF -- The uterine and ovarian cycles are ultimately controlled
by Gn-RF from the hypothalamus. Like the male, Gn-RF
secretion begins in puberty and works to stimulate the
secretion of FSH and LH from the anterior pituitary gland.
FSH -- FSH is secreted in response to Gn-RF when blood estrogen
levels are low. It stimulates some primordial follicles
(primary oöcyte and surrounding follicular cells) each cycle
to begin the maturation process towards the tertiary follicle
stage.
LH -- LH, secreted when blood estrogen levels are high, stimulates
final maturation of the remaining tertiary follicle, ovulation,
and formation of the corpus luteum. The corpus luteum will
secrete estrogen, progesterone, inhibin, and relaxin.
estrogen -- Estrogen has 3 main functions:
1.
promotes development of the female secondary sex
characteristics.
2.
helps control fluid and electrolyte balance; and
3.
increases protein anabolism
progesterone -- Progesterone, secreted by the corpus luteum,
works with estrogen to prepare the endometrium for
implantation and the mammary glands for milk production.
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inhibin -- Inhibin, secreted by the corpus luteum, inhibits secretion
of Gn-RF and FSH, and to a lesser extent, secretion of LH.
It is likely to be important in the decreasing secretion of FSH
and LH towards the end of each cycle.
relaxin -- Relaxin, secreted by the corpus luteum during regular
cycles and by the placenta during the last trimester of
pregnancy, relaxes the pubic symphysis and helps to dilate
the cervix.
Answer the following questions concerning estrogen and its controlling
effects on Gn-RF and the gonadotropins.
Which cells secrete estrogen?
Estrogen is secreted by follicular cells prior to ovulation and
by the corpus luteum after ovulation.
What is the effect of high blood levels of estrogen?
High levels of estrogen allow Gn-RF secretion and prime the
anterior pituitary gland to secrete LH, which stimulate
ovulation and formation of the corpus luteum.
What is the effect of low blood levels of estrogen?
Low levels of estrogen allow Gn-RF secretion and prime the
anterior pituitary gland to secrete FSH, which stimulates
follicular development at the beginning of a new cycle.
What is the effect of moderate blood levels of estrogen?
Moderate levels of estrogen inhibit Gn-RF secretion of FSH
and LH.
2.
PHASES OF THE FEMALE REPRODUCTIVE CYCLE
Describe the normal female reproductive cycle in terms of its average
duration and the names of its four major phases.
The female reproductive cycle is on average 28 days long. The
cycle is divided into four major phases: menstrual, preovulatory,
ovulation, and postovulatory. Describe the menstrual phase.
The menstrual phase (menstruation, menses) lasts for roughly the
first five days of the cycle. Day 1 of menstrual bleeding is
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considered to be day 1 of the next cycle. What does menstrual flow
contain?
Menstrual flow consists of 50 - 150 ml of blood, tissue fluid, and
endometrial cells derived from the breakdown of the stratum
functionalis at the end of the last cycle. What initiates the
menstrual phase?
In response to the declining levels of estrogen and progesterone at
the end of the last cycle, the spiral arterioles of the uterus undergo
roughly 6 hour alternating periods of intense vasoconstriction and
vasodilation.
As a result the cells of the stratum functionalis become ischemic,
die, and break off from the underlying stratum basalis. It is this time
that estrogen and progesterone are at their lowest, and FSH
secretion is stimulated.
FSH, in turn, stimulates primordial follicles to develop and in doing
so, to secrete new estrogen so that blood estrogen levels begin to
rise.
a.
b.
c.
d.
MENSTRUAL PHASE (MENSTRUATION)
PREOVULATORY PHASE
OVULATION
POSTOVULATORY PHASE
Describe the preovulatory phase of the female reproductive cycle.
When does ovulation occur?
The preovulatory (proliferative) phase is the period from the
end of menstruation until ovulation, days 6 - 14 of the
average cycle. This phase is the most variable among
women. Describe the hormonal changes of this time.
Increasing blood estrogen (from developing follicles) inhibits
FSH secretion and stimulates the stratum basalis of the
uterus to undergo rapid mitotic divisions, so that the stratum
functionalis is rebuilt.
At the end of the preovulatory phase, blood estrogen level is
at its highest. This stimulates the release of LH that will, in
turn, stimulate ovulation of the new tertiary follicle. Describe
ovulation.
Ovulation, the rupture of the tertiary follicle from the ovary
into the peritoneal cavity occurs on day 14 of the 28 day
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cycle. The secondary oöcyte, with its attached follicular cells
(corona radiata), moves into the oviduct.
Within the ovary, the follicular cells left behind collapse upon
themselves to form the corpus luteum, a temporary
endocrine organ that stimulates estrogen, progesterone,
inhibin, and relaxin for 12 - 13 days (postovulatory phase)
Describe the postovulatory phase of the reproductive cycle.
The postovulatory (secretory) phase is day 15 - 28, the most
constant phase among females. In most cases, regardless
of ovulation day, it lasts only 12 - 14 days. Describe the
hormonal changes in this phase.
In response, to increasing estrogen and progesterone from
the corpus luteum, the stratum functionalis differentiates in
anticipation of a fertilized ovum that will need to implant in
the uterine wall. What are the three major changes that
occur?
One major change is increased endometrial gland activity
resulting in increased glycogen deposition in the stratum
functionalis. This glycogen will be used as an initial food
source for the conceptus after implantation.
A second major change is increased vascularization via the
spiral arterioles. This increases nutrient and oxygen delivery
to the stratum functionalis and aids in water retention, the
third alteration.
These preparatory changes reach their maximum about 7
days after ovulation, corresponding to the arrival of the
fertilized ovum from the oviduct into the uterus. What
happens if fertilization and implantation do not occur?
If fertilization and proper implantation do not occur, the
corpus luteum begins to die at about day 26. Estrogen and
progesterone blood levels begin to decrease and the stratum
functionalis becomes ischemic, leading to menses.
If fertilization and proper implantation do occur, the conceptus produces the hormone human chorionic gonadotropin
(HCG) that maintains the corpus luteum. Estrogen and
progesterone levels continue to support the endometrium.
Describe the hormonal changes occurring at each of the stages shown
below.
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1
Ovulation
5
14
26
28
<-----------><---------------> <----------------><------------>
Menses Proliferative
Secretory Ischemic
<------------------------------> <-------------------------------->
Preovulatory
Postovulatory
(Follicular)
(Luteal)
menses -- estrogen low, progesterone low, FSH level rising
proliferative -- estrogen rising, LH spikes at end, FSH decreasing
secretory -- estrogen rises again, progesterone rising
ischemic -- estrogen falling, progesterone falling
D.
PHYSIOLOGY OF SEXUAL INTERCOURSE
The sexual act, for both males and females, involves four basic stages. The first
two stages are common to both sexes. Name and give a brief description of
these first two stages.
erection -- Psychic and/or tactile stimuli (spinal reflex) cause parasympathetic impulses from the sacral spinal cord to allow vasodilation of
penile or clitoral arteries. Increased blood flow in the erectile
tissues, with subsequent compression of penile or clitoral veins,
results in erection.
lubrication -- Continued parasympathetic outflow from the sacral spinal
cord causes secretion from the bulbourethral glands (male) or the
cervical and greater vestibular glands (female). In the male this
serves to neutralize residual acidity in the urethra prior to the
passage of sperm. In the female this process provides the
lubrication necessary for successful intercourse.
The third stage of the sexual act is orgasm. Name and describe the two
components of the male orgasm.
emission -- When sexual stimulation becomes intense, rhythmic
sympathetic outflow from the spinal cord segments L1 - L2 causes
peristalsis in the male ducts, from the testes through the vas
deferens. This propels sperm and the seminal fluids into the
prostatic urethra.
ejaculation -- Other rhythmic outflow form the spinal cord S1 - S2
(parasympathetic) stimulates contractions of the pelvic diaphragm,
propelling semen through the urethra to the exterior in ejaculation.
In addition, there is a generalized fight-or-flight response (increased
heart rate, blood pressure, and respirations) as well as intense
pleasurable sensations. Immediately thereafter a general
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relaxation of the body occurs and the resolution phase of the sexual
response begins.
Describe the female orgasm.
Female orgasm occurs when tactile stimulation of the genitalia (particularly the clitoris) reaches maximum intensity and orgasmic reflexes are
initiated. Spinal reflexes from L1 - L2 (sympathetic nerves) initiate
contractions of the pelvic diaphragm. There is engorgement of the clitoris
and breasts with blood, increased heart rate, blood pressure, and
respiratory rate, and rhythmic contractions of the uterus. The intensely
pleasurable sensations that accompany this response are followed by a
return to parasympathetic tone and general relaxation of the body.
(resolution phase of the sexual response).
There is no equivalent to male emission and ejaculation, but there is
similar rhythmic contraction of the pelvic diaphragm.
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