Male Reproductive System
The components of the male reproductive system are:
1.Testes: produce sperm and synthesize androgens.
2.Spermatic ducts: facilitate travel of sperm and gland secretions through the reproductive system
and to the exterior. The male reproductive ducts are the epididymis, vas deferens, and ejaculatory
ducts (all paired, right and left).
3.Glands: provide secretions that protect and nourish the sperm. The glands are the right and left
seminal vesicles, the prostate gland, and the right and left bulbourethral glands.
4.Penis: is the external sex organ.
Note: semen is sperm plus secretions from the glands mentioned above.
Function:
The male reproductive system is designed to:

Produce and nourish sperm

Synthesize androgens

Provide movement for sperm and ejaculatory fluid towards and to the exterior
Testis:
The testis (testicle) is covered by the scrotum (skin). Deep to the scrotum are several layers of
tissue that are continuous with those around the spermatic cord. These structures could be called
“extensions” or evaginations of structures in the anterior abdominal wall. From superficial to deep,
the figure shows the skin of the scrotum attached to the superficial (or dartos) fascia of the scrotum
followed by these layers:
•
External spermatic fascia （精索外筋膜） (“extension” of the external oblique fascia)
•
Cremasteric fascia （提睾肌） – connected to Cremaster muscle (“extension” of the
internal oblique fascia)
•
Internal spermatic fascia （精索内筋膜） (“extension” of the transversalis fascia)
Deep to the 3 fasciae just listed are other layers:
The tunica vaginalis covers the anterior and lateral aspects of the testis, and it is peritoneal in
origin. As the testis descended in fetal life it “dragged” the peritoneum (now tunica vaginalis)
from the abdomen.
The tunica vaginalis has 2 portions:
•
The visceral portion or “layer”
•
The parietal portion or “layer”
•
Deep to the tunica vaginalis is the tunica albuginea:
Each testis is covered by a fibrous connective tissue, called tunica albuginea .
From here, fibrous partitions penetrate the testis and divide it into 250 compartments, called
testicular lobules
Within each lobule are 1 to 4 coiled tubes, called seminiferous tubules
The seminiferous tubules are surrounded by loose connective tissue, blood and lymphatic vessels,
autonomic nerves, smooth muscle (for peristalsis), and Leydig cells (more on these cells next
slides).
The tunica albuginea thickens posteriorly to form the mediastinum testis
The development of sperm begins in the seminiferous tubules.
Seminiferous tubule :

A basement membrane surrounds each tubule.

Connective tissue (referred to as the lamina propria by some authors)

Myoid cells are embedded in the lamina propria, next to the basement membrane. These
cells contract the tubules.

Leydig cells or interstitial cells have receptors for LH. This hormone induces Leydig cells to
produce testosterone.

Blood and lymphatic vessels, autonomic nerves.
Structure of Seminiferous tubule:
Seminiferous tubules are lined by a special epithelium called germinal or seminiferous
epithelium ; as it is made primarily of developing germ cells
The wall of the tubules contains 2 types of cells:
•
Non-dividing SUPPORTING cells, called sustentacular or Sertoli cells.
•
PROLIFERATIVE cells of the spermatogenic lineage. These are arranged into 4
to 8 concentric layers. Their sole function is to produce sperm cells.
SUPPORTING Sertoli cells:
Sertoli cells
are columnar cells that surround proliferative cells. One Sertoli cell may
surround many proliferative cells. The base of each Sertoli cell rests on the basement
membrane. The apical portion frequently extends to the lumen of the seminiferous tubule.
Sertoli cells have several important functions:
1. Support, protect, and nourish proliferative cells (specifically, making nutrients available for
them from the interstitial space – where capillaries are abundant)
2. Secrete several substances that play a role in regulation of sperm production
3. Phagocytose debris and residue
4. Protect the proliferative cells from auto-immune attacks – this is perhaps the most important
function
Sertoli cells develop tight junctions between them：
1. Basal compartment
2. Adluminal compartment
As a result, the adluminal compartment is protected from anything in the capillaries, including
cells of the immune system, immunoglobulins, antibodies. This is important because since the
production of sperm cells produces sperm-specific proteins and because sexual maturity takes
place long after development of immunocompetence, the developing cells as well as spermspecific proteins would be considered foreign structures to the immune system and would be
destroyed (an auto-immune response would be provoked).
Spermatogenic Cells:

Spermatogonium: spermatogenic cell closest to the basement membrane (with 46
chromosomes).

primary spermatocyte : Each spermatogonium divides, giving rise to 1 spermatogonium
and 1 primary spermatocyte (with 46 chromosomes).

secondary spermatocytes: The primary spermatocyte divides and gives rise to 2 secondary
spermatocytes.

spermatids: Each secondary spermatocyte divides and produces 2 spermatids. (each with 23
chromosomes).

Spermatozoa: The spermatids undergo a process called SPERMIOGENESIS until each
becomes a sperm cell
The process of spermatogenesis (maturation from spermatogonium to spermatid) lasts about 60
days.
The process of spermiogenesis (maturation of the spermatids until they become sperm cells) lasts
about 20 days.
Sperm cell：
The mature sperm cell has a head and a tail .
The head contains chromatin and it is covered by an acrosomal cap with acrosomal enzymes. If the
sperm cell encounters the ovum, the enzymes are released to break through the ovum wall and
enter it.
The tail of the sperm cell is a specialized cilium that propels the cell. It is referred to as a flagellum.
Movements of this flagellum are the result of the interaction between microtubules, ATP and
dynein, a protein with ATPase activity.
**The secondary spermatocytes enter the second meiotic division within 1 day. Therefore, they
are rarely seen in histological slides because they exist for such a short period of time.
The temperature for the formation of healthy sperm cells：
A temperature of 35 C is critical for sperm formation.
This is achieved by the existence of the following structures:
1. The pampiniform plexus of veins in the scrotum
When the temperature rises, these veins dilate and dissipate heat to cool down the testes.
2. The cremaster muscle in the spermatic cord and partially over the testis
3. The dartos muscle in the scrotum
When the outside temperature decreases, these 2 muscles contract to bring the testes closer to the
body wall, in order to increase their temperature.
The testes at different times in life

The initial components of the fetal testes are testicular cords. These are formed by:
1）Sertoli cells
2）Pre-spermatogonia (called gonocytes) – derived from primordial germinal cells

3）Leydig cells – between the cords
During fetal development (during the 3rd to 4th months), Leydig cells secrete testosterone,
which induces the development of the duct system and accessory glands of the male
reproductive system. Then this process stops.

At puberty, the pituitary gland secretes LH and FSH. LH stimulates Leydig cells to produce
testosterone, which produces the maturation of the male sex organs, including the maturation
of pre-spermatogonia into spermatogonia. FSH regulates the activity of Sertoli cells, which
secrete antigen-binding protein (ABP) and other regulating substances. ABP binds to
testosterone. This complex, in conjunction with mature non-motile sperm cells, is transported
to the epididymis (supposedly, to favor the normal function of the epididymis).
ABP also
concentrates testosterone in the testes to a level necessary for spermiogenesis.

Sertoli cells are predominant in the seminiferous tubule before puberty. At puberty,
spermatogenic cells become predominant. At an older age, Sertoli cells are predominant again,
as the spermatogenic cells decrease markedly in number. Thus, we could say that Sertoli cells
are the permanent component of the seminiferous tubule throughout life.
Spermatic duct system:
•
Intratesticular ducts, which are:
– Straight tubules
– Rete testis
•
•
•
– Efferent ducts
Epididymis
Vas deferens, also called ductus deferens
Ejaculatory duct
The intratesticular ducts are located within or immediately next to the testicle. They are called:
•
Straight tubules
Each seminiferous tubule ends as a straight tubule.
–they are proximally lined by Sertoli cells; and, more distally, they are lined by a simple cuboidal
epithelium.
•
Rete testis
The straight tubules converge forming a network called rete testis.
–it is lined by a simple cuboidal epithelium.
•
Efferent ducts or ductules
These are 10 to 20 short ducts that extend from the rete testis towards the epididymis.
–they are lined by simple cuboidal epithelial cells, some ciliated and some non-ciliated. The
ciliated cells help the sperm cells move towards the epididymis.
Epididymis:

The efferent ducts combine to form 1 single duct, called the epididymis .

The epididymis is about 4 meters in length, yet it is highly coiled into a thin structure of 7
cm.

The epididymis transports sperm and serves as a place where sperm cells mature further,
becoming fully capable of fertilization. Sperm cells can be stored in the epididymis for as
long as a month. The epididymis may secrete proteins that inhibit sperm motility – if it is
necessary to temporarily store sperm cells.

However, the nature of epididymal secretions remains unknown.
Female Reproductive System
The female reproductive system consists of the ovaries, genital tract (fallopian tubes, uterus,
vagina and vulva) and breasts.
Ovaries (paired organs) :
The ovaries have two main functions:
1- They are the site of oogenesis where in sexually mature females, ova (female gametes – singular
is “ovum”) are produced and released cyclically at regular intervals except during pregnancy.
Ovulation is the release of one or more ova
2- The ovaries produce steroid hormones
These functions are regulated by luteinizing hormone (LH) and follicle stimulating hormone (FSH)
which are released by the anterior pituitary gland.
In turn, estrogen and progesterone affect the production of LH and FSH through feedback
mechanisms.
Ovulation is synchronized with the preparation of the uterus to receive the fertilized ovum.
The process of oogenesis:
1.Primordial follicle: A Primordial follicle is a primary oocyte surrounded by a layer of
“follicular cells.”
2. Primary follicle:

The primordial follicle is stimulated by FSH and matures to become a primary follicle .

Oocyte has grown . The layer of Follicular cells has grown. Remember they were few and
flat in the primordial follicle? Here they are large, numerous and clearly cuboidal or low
columnar. The follicular cells are now referred to as granulosa cells.

A new structure is developing: the Zona pellucida .This is seen as a line between the ovum
and the granulosa (follicular) cells. It corresponds to glycoproteins that are secreted by the
ovum. Their function is to bind proteins on the surface of the sperm and induce acrosomal
activation.

Another new structure is developing: the Theca folliculi (follicular theca). It is formed by
stromal cells that differentiate around the follicle.
3. Secondary follicle:

oocyte: continues to grow. It’s still a primary oocyte (arrested in meiosis I).

zona granulosa: now contains numerous layers. An important development at this stage of
secondary follicle is that the cells of the zona granulosa start to secrete estradiol. This occurs
in conjunction with some of the theca folliculi cells.

a small pool of fluid forming: the “follicular antrum.” It is very small here but it’ll grow
significantly.

Zona pellucida is very well defined by now.

The theca folliculi is differentiating into two layers. It’s hard to appreciate at this stage, but be
aware of this for now. The inner layer starts to function as an endocrine structure, secreting
the precursor the granulosa cells use to make the estradiol.

Secondary follicle in late stage:
Cumulus oophorus: mass or group of granulosa cells that attach the ovum and corona radiata
to the rest of the granulosa cells that form the wall of the follicle and surround the antrum.
Corona radiata (forming): rim of granulosa cells that will stay with the oocyte after
ovulation.
4. Graafian follicle: also known as the Tertiary follicle, Vesicular follicle, Mature follicle and
Pre-ovulatory follicle. It can reach a size of 20-30 mm, large enough to be detected by ultrasound.
It takes a primordial follicle 90 days to become a Graafian follicle.
Ovulation: requires an LH surge. About 16 hours later, the now secondary oocyte ovulates.
Remember that hours before ovulation the oocyte completed meiosis I in the Graafian follicle and
entered meiosis II immediately. But meiosis II is arrested and will not be completed until
fertilization.
Atretic Follicles: Most follicles become atretic at different stages of their development. At early
stages, atretic follicles are not visible because they are cleaned up by microphages very quickly.
Follicles that undergo atresia become scar tissue in the ovaries.
Corpus Luteum:

The corpus luteum is a temporary endocrine structure that helps maintain the wall of the
uterus for implantation.

The Corpus luteum is defined as the remains of the Graafian follicle after the ovum is
ovulated. It forms soon after ovulation at around day 14 of the ovarian cycle.

Granulosa lutein cells: They undergo a significant increase in size. They still convert
androstenedione into estradiol but now, under the influence of LH, they also secrete
progesterone.

Theca lutein cells: They continue to produce androstenedione. Under the influence of LH they
also secrete progesterone.

If fertilization occurs, the corpus luteum persists for about 8 weeks; if not, it degenerates, and
becomes a corpus albicans.

If fertilization does not occur, there is no hCG from the trophoblast to sustain the corpus
luteum and thus it degenerates, resulting in a corpus albicans.
Fallopian Tube:
The fallopian tube is divided into 4 regions:

Infundibulum: includes the fimbriae

Ampulla: this is where fertilization usually occurs

Isthmus

Interstitial part or pars interstitialis: part connecting with the uterine wall
Uterus:
Muscular, pear shaped organ. It measures about 7 cm in non-pregnant state. It has 3 portions:
Fundus , Body, Cervix
Endometrium

It provides the environment for the development of the embryo and fetus.

Consists of epithelium and lamina propria.

Before puberty the endometrium is a layer of simple cuboidal epithelium on a thin lamina
propria (also called stroma) bed.

After puberty the endometrium has two distinct layers:
Basal layer or “basalis”
Functional layer or “functionalis

The basal layer is adjacent to the myometrium. The basal layer does not change much during
the uterine cycle. It regenerates the functional layer during portions of the cycle.

The functional layer is more complex. Here are its components:
1- it is covered by a simple columnar epithelium
2- it has a lamina propria (also called stroma)
3- the epithelium invaginates to form uterine glands
Myometrium

Muscular layer that constitutes the bulk of the organ.

It provides protection for the developing fetus.

Its contraction contributes to the expulsion of the fetus during delivery.

It is composed mainly of smooth muscle, with fibrous tissue, blood vessels, autonomic nerves
and lymphatic vessels.
Perimetrium
Outer fibrous layer. Though it is adventitial in some areas, it is mainly serosa and continuous with
the mesometrium of the broad ligament, which you know from anatomy.
Three phases of the uterine cycle:
Menstrual Phase:
•
The functional layer of the endometrium sheds if there is no implantation of the fertilized
ovum
•
The withdrawal of estrogen and progesterone at the end of the ovarian hormonal cycle
causes changes including the helical arteries to constrict. This produces ischemia of the
tissue, which dies and is shed during the menstrual phase.
Proliferative Phase:
•
Influenced by estrogen secreted form the ovaries
•
The endometrial stroma proliferates as it becomes thick and abundantly vascularized
•
The uterine glands become long
Secretory Phase:
•
Influenced by progesterone (and also estrogen to a lesser extent) secreted from the ovaries
•
The arteries engorge with blood
•
The uterine glands produce abundant glycogen-rich secretions
Cervix
The lumen of the cervix is lined by epithelium:

In the endocervical canal (EC), the epithelium is simple columnar.The cells secrete
mucus.

The ectocervix is lined by stratified squamous epithelium

The junction between endocervix and ectocervix (at the point of the external os) is the site
.
of an abrupt transition in epithelia. It is referred to as the squamocolumnar junction.

In the endocervix, the mucus-secreting epithelium invaginates to form furrows and
tunnels that look like tubular glands. They are referred to as endocervical glands.
The secretory activity of the endocervical epithelium changes during the different phases of the
uterine cycle as follows:

During the proliferative phase the secretion of the endocervical glands is thin and
“serous-like.” This is to facilitate the passage of spermatozoa.

During the secretory phase, the mucus is thick, to plug and close the entry of spermatozoa
and pathogens, should pregnancy occur.