Reproductive System
In mammals the sexes are separate organisms. The human embryo will form
both female and male structures which mature or disappear depending upon
whether the individual is genetically male (XY) or female (XX). As the
gonads mature, they secrete hormones that direct the formation of
secondary sex characteristics.
MALE Reproductive Anatomy and Histology
Testes
Paired oval male gonads, the testes, are located in the scrotal sac of
most mammals. Beneath the skin, two connective tissue layers, the tunica
externa and the tunica albuginea surround the glands. The testes are
divided into lobules that house 1 - 3 seminiferous tubules. Surrounding
the outside of the seminiferous tubules are clusters of cells known as
Sertoli, Leydig, or Interstitial cells. These cuboidal cells are
responsible for androgen production under the direction of GnRH from the
Hypothalamus and LH from the AP. Testosterone and its precursor DHEA,
contribute to secondary sex characteristics. Bone growth, muscle
development, body hair patterns, laryngeal changes, and behavioral changes
are seen with secretion of these androgens.
Other cells in the seminiferous tubules are the sustentacular cells. The
sustentacular cells function in spermatogenesis to bind testosterone in
the testes to allow for adequate hormone levels. They also provide the
blood-testes barrier to prevent immune cells from attacking the developing
sperm.
The formation of sperm, called spermatogenesis, occurs in the seminiferous
tubules and is stimulated by the hormone FSH, secreted from the anterior
pituitary. Millions of sperm cells, spermatozoa, are produced in the
testes. This may occur because a population of spermatogonia retain, over
many years, the ability to divide. Spermatogonia (and their immediate
progeny) divide by mitosis. One of the daughter groups, the primary
spermatocytes, then begins the process of meiosis. Meiotic division
creates 4 haploid cells in a two division cycle. A primary spermatocyte
divides (meiosis I and cytokinesis) to produce 2 secondary spermatocytes.
Each of these divides again (meiosis II and cytokinesis) to produce 2
spermatids. These haploid spermatid cells then mature into spermatozoa or
sperm. Final maturation and storage occurs in the epididymis. 300
million sperm are produced daily and once they leave the male reproductive
system, have a life expectancy of about 48 hours in the female
reproductive system.
Mature sperm or spermatozoa have a head, midpiece, and tail. The head
contains the condensed nucleus with a haploid set of chromosomes and a
vesicle, called the acrosome, containing digestive enzymes that aid in
penetrating layers surrounding the ovulated oocyte. The midpiece contains
mitochondria that produce energy in the form of ATP for the tail or
flagellum. Once activated by accessory gland secretions, the flagellum
propels the sperm through the female reproductive tract. *Male
reproductive fertility assessment is based on number and viability of
sperm, normal anatomy, and normal movement.
Activity:
Using the figures provided, examine a slide of a mammalian testis.
Identify as many of the features and cell types as possible.
Duct System
Sperm are stored and mature in the tail of the epididymis. During male
climax, the smooth muscles within the ducts propel the sperm outward.
From the epididymis, the sperm travel through the vas (ductus) deferens
which is part of the spermatic cord. The spermatic cord has a connective
tissue covering that contains vessels, nerves, and ducts that aid and
supply the male reproductive organs. The vas travels over the urinary
bladder and around the ureters to the urethra. As the vas joins with duct
openings from accessory glands, the tube expands to form the ejaculatory
duct. The ejaculatory duct continues as the urethra. In the male the
urethra functions for sperm transport and urine transport, although not at
the same time. The male urethra is 8 inches long and divided into three
regions: the prostatic urethra that travels through the prostate, the
membranous or penile urethra that travels through the body of the penis,
and the spongy urethra that is surrounded by the spongy tissue of the
glans penis. The urethra has a dilated portion, the ampulla, before it
opens at the external urethral meatus.
Accessory Glands
The accessory glands of the male are the seminal vesicles, the prostate,
and the bulbourethral (Cowper's) glands. These glands secrete most of the
liquid portion of the semen with the seminal vesicles producing 60% of the
volume, the prostate producing about 20 % of the volume and the Cowper's
glands producing 10% of the semen volume.
The seminal vesicles are paired structures that sit posterior to the
urinary bladder and they join with the vas deferens to form the
ejaculatory duct. They produce an antibody and nutrient rich fluid
containing sugars such as fructose. The single prostate gland sits at the
base of the urinary bladder and encloses the prostatic urethra. Their
secretions aid in sperm motility. The paired bulbourethral (Cowper's)
glands lie at the bulb or root of the penis. Their alkaline secretions
help neutralize any acidic substances in the urethra, such as urine. All
accessory glands secrete an alkaline rich fluid to help neutralize the
acidic pH of the female reproductive tract.
External Genitalia
The external genitalia of the male are comprised of the scrotum and penis.
The scrotum is a two compartment, connective tissue sac covered by skin
and hair. Each sac of the scrotum contains and supports one of the
testes. The scrotum allows the testes to be external from the abdominal
cavity to allow for proper temperature maintenance, which is 3 degrees
below normal body temperature.
The penis is primarily connective tissue with an extensive blood supply.
The gross regions are the root, shaft (body), and the glans. The root and
body are formed by three erectile tissues: 2 corpora cavernosa and 1
corpora spongiosum. The corpora spongiosum houses the urethra as it
passes through the penis. At the glans penis, only corpora spongiosum is
present. In the male climax, the blood supply in the penis changes.
Arteries dilate, while veins constrict. This allows the connective tissue
sinuses to fill with blood to create an erection to allow the penis to
penetrate the female vagina and deliver semen into the female reproductive
tract. The glans penis is surrounded proximally by an extra fold of skin
called the prepuce or foreskin.
Activity:
1] Using the figures provided, identify the structures (underlined terms)
above.
2] Using the semen anlaysis table, assess the abnormal results.
Semen Analysis
Subject X is a Caucasian male, age 32. Subject and wife have not been
successful in conceiving. He requests an analysis of his semen. His test
results are given in the table below. Reference ranges for the male
population are also provided.
Test Requested Results for Mr X Reference Range
ejaculate volume 5 ml 2-6 ml
viscosity and appearance normal thick, opaque cream
sperm count 22 million 20 million / mL
morphology normal head, midpiece, flagella
for 60%
motility 75 % forward forward, linear for 50%
pH 7.5 7 to 8
dead vs. alive 82 % alive alive > 60%
WBC 0-1 / hpf 1-3 cells/hp field
antisperm antibodies negative negative IgG and IgA
Are the result values for Mr X within normal range for the tests
performed?
Other patients present the following abnormal conditions. Explain the
possible causes for the following abnormal results :
1) Low ejaculate volume
2) Watery, yellow appearance
3) Two heads with one tail, one head with no tail
4) Decreased motility, most circling
5) pH - 6.2
6) 5-8 WBC / high powered field
Section in figure provided:
Detail of wall of seminiferous tubule, showing stages of spermatogenesis.
The large, vertically oriented nucleus at the base on the left belongs to
a Sertoli cell; notice that sperm heads (somewhat out of focus) are
clustered deep down near this nucleus. The horizontally flattened nuclei
along the base of the tubule belong to spermatogonia, the continually
multiplying, diploid germ cells. A few primary spermatocytes, with the
dark, condensed chromosomes undergoing prophase of meiotic division, lie
just above the spermatogonia. Above the spermatocytes are the round,
relatively small, haploid spermatids, which would occupy the rest of the
layers up toward the lumen.
Slide 47
Drawing of stages in the differentiation of sperm directly from
spermatids. This process is called spermiogenesis.
· A = a still-rounded spermatid, with an acrosomal body beginning to
form in the region of the Golgi apparatus. At the opposite pole of the
nucleus lie the centrioles, one of which begins to spin out a long cilium
(or flagellum).
· B = an elongating spermatid, with an acrosomal cap now forming
over the top of the nucleus. The flagellum is longer and the centrioles
are oriented perpendicular to each other. The centriole related to the
flagellum is comparable to the basal body of ordinary cilia.
· C = further development of the acrosomal cap and beginning
pinching off of excess cytoplasm, thanks to the formation of a filamentous
manchette, nuclear ring, and annulus.
· D = further condensing of the nuclear chromosomal material and
separating off of the excess cytoplasm. Notice that the intercellular
bridge connecting this spermatid to its neighbor is still intact.
E = the cytoplasmic mitochondria have now collected along the proximal
portion of the flagellum and are thus conserved (for energy purposes) when
the residual cytoplasm is cast off. The flagellum has meanwhile developed
a complex fibrous sheath which surrounds a central core of microtubules
arranged in the nine plus two arrangement typical of cilia.
FEMALE Reproductive Anatomy and Histology
Ovaries
The ovaries are paired gonads located inferior to the kidneys in the mid
abdominal region, suspended by suspensory, ovarian, and broad ligaments
and covered by a connective tissue capsule, the tunica albuginea. The
ovarian cortex contains ovarian follicles consists of developing immature
eggs (oocytes) and surrounding cuboidal cells, thecal cells. Ovaries
produce gametes by a process called oogeneis. They also produce hormones
that target the uterus and other female tissues.
In a meiotic process similar to that in the male, eggs are produced in the
ovary and released into the oviducts where fertilization may occur. In
mammals, meiosis is not completed until a sperm activates the egg. Due to
unequal cytokinesis, however, only one haploid cell is produced. This
ensures that stored reserves of organelles and nutrients will be retained
in one large (relative to the sperm) cell.
Early maturation of the oocyte occurs in a developing follicle. The
ovarian cycle is named for the events observe in the follicle triggered by
response to gonadotropic hormones.
Follicular Phase ovarian follicles develop from primordial
to Graafian follicle
regulated by FSH from the anterior pituitary
*follicle also functions as endocrine gl -
secretes estogens
Ovulation Graafian follicle ruptures to release secondary oocyte
triggered by LH from AP
Luteal formation of corpus luteum (CL) from remnant
follicle cells
*follical now functions to secrete progestins
and estrogens
regulated by LH
Activity:
Using the figures provided, observe the slides of a mammalian ovary and
identify the features indicated.
Duct System
The fallopian tubes (oviducts) develop separately from the ovaries. At
the lateral end of the tube, there are finger like extensions called
fimbria that function to create vacuum like currents to retrieve the
ovulated secondary oocytes. The fimbria is supported by an enlarged
trumpet shaped base called the infundibulum. The infundibulum continues
as the expanded portion of the tube called the ampulla and it is where
fertilization takes place. As the tube continues, its medial end is
attached to the uterus at the isthmus.
The uterus is a pear shaped structure in the pelvic region of the
abdominal cavity suspended by the broad ligament. The external anatomy
consists of the fundus, body, and neck or cervix. The internal anatomy of
the uterus is composed of three layers. The internal epithelial lining is
the endometrium and is a modified simple columnar epithelium in two
layers, the basilar layer and the functional layer. The muscle wall is
the myometrium and is composed of smooth muscle. The outer layer is a
connective tissue layer called the perimetrium formed by the visceral
peritoneum.
The uterus can change size and shape during pregnancy (see figure). The
lining of the uterus will undergo several cycles known as the uterine
cycle and relates to the hormones produced during the ovarian cycle. The
function of the uterus is to provide protection, support, and nutrition to
the developing fetus and aid in delivery during labor.
Proliferation (pre ovulatory) basilar layer of endometrium replaces
functional layer
triggered by estrogens from the ovary
Secretory (post ovulatory) functional layer secretes nutrients
for fertilized egg
triggered by progestins and estrogens
from the ovary
Menstrual (post luteal) functional layer of endometrium lost
triggered by a dramatic drop in ovarian
hormones
The vagina is a muscular tube that connects the cervix of the uterus at
the fornix. The vagina functions as the female organ of copulation, serve
as pathway for menstrual flow, and the birth canal. The vaginal lining is
stratified squamous and has an acidic pH to prevent overgrowth of
bacteria. A thin fold of tissue called the hymen partially closes the
distal end of the vagina. The vaginal orifice is the opening of the
vagina in the vestibule enclosed by the labia.
External Genitalia
External Genitalia of the female is collectively termed the vulva or
pudendum. The vulva consists of the:
clitoris erectile tissue composed of corpora spongiosum
labia majora analogous to the male scrotum, contains sweat glands
labia minora smaller skin fold that contains sebaceous glands
both labia cover the vagina and urethra to help prevent drying
Accessory Glands
Lesser vestibular glands, Skene's glands - on either side of
the urethral oriface; secrete mucus for vaginal lubrication.
Greater vestibular glands, Bartholin's glands - on either side
of the vaginal orifice; secrete mucus for vaginal lubrication.
Mammary glands modified sweat glands of the skin that is functional in
females; Milk glandular alveoli develop in response to estrogens and
produce milk in response to AntPituitary - Prolactin (PRL) hormone
Milk release is under the control of the Post Pit - Oxytocin (OT)
Ovary slide seen in lab and in figure provided.
Maturing follicle, so called because it contains a definite antrum (or
fluid-filled space) and many layers of granulosa cells. The egg is still a
primary oocyte and sits to one side of the follicle on a mound of cells
called the egg hillock or cumulus oophorus. The cells closest to the
oocyte will be expelled with it at ovulation as the corona radiata.
Surrounding the granulosa cells of the follicle is the theca interna, a
rather cellular and vascular connective tissue layer, which secretes
estrogen. Outside of this is the theca externa a more fibrous connective
tissue layer, not well defined here. Several follicles may start
to develop in any one monthly cycle, but in the human only one will
mature, unless there are to be multiple ovulations and therefore possible
multiple births. All follicles that don't complete their maturation
undergo atresia (i.e., degenerate). The egg dies, the granulosa layer
breaks up, and the whole follicle collapses and undergoes fibrotic change.
Ovarian Hormones and Cycle
The hormones from the thecal cells that line the follicles are:
DHEA is a hormone precursor to other reproductive hormones that control
the ovarian and uterine cycles.
Follicle-Stimulating Hormone (FSH)
FSH is a heterodimer of
· the same alpha chain found in TSH (and LH)
· a beta chain of 115 amino acids, which gives it its unique
properties.
Synthesis and release of FSH is triggered by the arrival from the
hypothalamus of gonadotropin-releasing hormone (GnRH). The effect of FSH
depends on one's sex.
FSH in females
In sexually-mature females, FSH (assisted by LH) acts on the follicle to
stimulate it to release estrogens.
FSH in males
In sexually-mature males, FSH acts on spermatogonia stimulating (with the
aid of testosterone) the production of sperm.
Luteinizing Hormone (LH)
LH is synthesized within the same pituitary cells as FSH and under the
same stimulus (GnRH). It is a heterodimeric glycoprotein consisting of
· the same 89-amino acid alpha subunit found in FSH and TSH
· a beta chain of 115 amino acids that is responsible for its
properties. The effects of LH also depend on sex.
LH in females
In sexually-mature females, LH
· stimulates the follicle to secrete estrogen in the first half of
the menstrual cycle
· a surge of LH triggers the completion of meiosis I of the egg and
its release (ovulation) in the middle of the cycle
· stimulates the now-empty follicle to develop into the corpus
luteum,which secretes progesterone during the latter half of the menstrual
cycle.
Estrogens estradial, estrone
Progestins progesterone
Androgens testosterone
Estrogens also function in creating secondary sex characteristics: Fat
deposition, breast development, hair distribution, skin changes, and bone
development and will travel through lactiferous ducts to the lactiferous
sinus and exit at the nipple.
Prolactin (PRL)
Prolactin is a protein of 198 amino acids. During pregnancy it helps in
the preparation of the breasts for future milk production. After birth,
prolactin promotes the synthesis of milk.