Note: You should also use
the multimedia web program for this lesson. Go back to Histology Part 2
Index and choose Male Reproductive System under "Multimedia Lessons,
Reproductive System".
TESTIS
The primary function of the male reproductive system is reproduction, which
includes the production
of spermatozoa, the
transportation
of spermatozoa from the testes out of the male body, the
secretion
by glands, and the placement
of spermatozoa in the female reproductive tract. Spermatozoa are
produced
in the testes then transported
from the testes by a series of ducts which become gradually larger and connect
with the urethra of the penis. Various accessory glands in the male system
secrete
materials which together with the spermatozoa constitutes the semen. A secondary
function of the male reproductive system is the production of the male hormones
which are responsible for the secondary sex characteristics of the male animal.
The male reproductive system is composed of several distinct organs. These
include the testes, epididymis, deferent ducts, accessory glands, and the penis.
The testis (plural, testes) is both an exocrine organ (compound, coiled, tubular
gland) producing cells, i.e., spermatozoa, and an endocrine organ, secreting
hormones, i.e., testosterone. Accessory glands (not all are present in all
species) include the ampullary glands, vesicular glands, prostate gland,
bulbourethral gland and urethral glands.
Seminiferous tubules.
The
stratified epithelium of the seminiferous tubules is composed of different
stages of developing sperm cells. Spermatogonia are stem cells located near the
basement membrane of the tubule which proliferate by mitosis. Some of the
progeny cells differentiate into sperm and move away from the basement membrane
toward the lumen of the tubule. These differentiating cells first undergo
meiosis then undergo a morphological change to become spermatozoa. Some of the
progeny cells undergo mitosis again to produce more progeny cells providing a
continuous source of stem cells for the production of spermatozoa.
Spermatogenesis.
Spermatogenesis: the process by which stem cells develop into mature
spermatozoa. There are three phases: (1) Spermatocytogenesis (Mitosis), (2)
Meiosis, and (3) Spermiogenesis.
| Spermatocytogenesis:(also
called Mitosis): Stem cells (Type A spermatogonia; singular =
spermatogonium) divide mitotically to replace themselves and to produce
cells that begin differentiation (Type B spermatogonia).
Spermatogonia have spherical or oval nuclei, and rest on the basement
membrane. (You are not responsible for distinguishing between Type A and
Type B spermatogonia in lab.)
Spermatogonia |
Micrograph of seminiferous tubules of rat
testis (Lab slide 213)
|
Meiosis:
Cells in prophase of the first meiotic division are primary spermatocytes.
They are characterized by highly condensed chromosomes giving the nucleus a
coarse chromatin pattern and an intermediate position in the seminiferous
epithelium. This is a long stage, so many primary spermatocytes can be
seen. Primary spermatocytes go through the first meiotic division and
become secondary spermatocytes. The cells quickly proceed through
this stage and complete the second meiotic division. Because this stage is
short there are few secondary spermatocytes to be seen in sections. You are
not responsible for identifying secondary spermatocytes in lab. Meiosis is
the process by which the diploid number of chromosomes present in
spermatogonia (the stem cells) is reduced to the haploid number present in
mature spermatozoa.
The
products of the second meiotic division are called spermatids. They
are spherical cells with interphase nuclei, positioned high in the
epithelium. Since spermatids go through a metamorphosis into spermatozoa,
they occur in early through late stages. You are not responsible for
distinguishing the different stages of spermatids, but you are required to
identify a spermatid.
All of these progeny cells remain attached to each other by cytoplasmic
bridges. The bridges remain until sperm are fully differentiated.
|
Micrograph of seminiferous tubules of rat
testis (Lab slide 213). Note that the primary spermatocytes are closer to the lumen
than the spermatogonia which rest on the basement membrane of the seminiferous tubule.
Micrograph of seminiferous tubules of rat
testis (Lab slide 213). Note the presence of early spermatids in one tubule and late
spermatids in the other tubule.
Micrograph of seminiferous tubule of rat
testis (Lab slide 213). High magnification to show the close relationship between
the spermatids and the cytoplasm of the Sertoli cell.
|
GENITAL DUCTS
After
production in the testes, spermatozoa pass through a series of ducts in their
journey out of the male system.
Epididymis:
The
ductus
epididymis is lined with a pseudostratified
stereociliated columnar epithelium. Stereocilia are actually nonmotile, long
microvilli which serve to increase the absorptive and/or secretory surface
of this epithelium. With its associated connective tissue and muscle, the
ductus epididymis coils to form the head, body and tail of the epididymis
which then continues into the ductus deferens. Spermatozoa are stored
within the epididymis while they undergo maturation to become mature sperm.
|
Micrographs of cat epididymis
(Lab slide 89B).
|
ACCESSORY GLANDS
The
products of these glands serve to nourish and activate the spermatozoa, to clear
the urethral tract prior to ejaculation, serve as the vehicle of transport of
the spermatozoa in the female tract, and to plug the female tract after
placement of spermatozoa to help ensure fertilization. Although the glands are
ususally described as being branched tubular or branched tubuloalveolar, they
vary in their organization and in their distribution in different species.
Prostate gland
Grossly the prostate gland can be divided into two parts: the body and the
disseminate part. Low cuboidal to low columnar epithelium provides the
lining for this compound, tubuloalveolar gland which consists primarily of
serous secretory end pieces. The secretion of this gland is more serous in
dogs and more mucous in bulls. It serves to promote the movement of
spermatozoa and to form a vaginal plug. Additionally, in bulls, the
secretion contains high amounts of fructose and citric acid. Concretions
may be present in the secretory end pieces as well as parts of the duct
system.
|
Micrograph of prostate gland of dog
(Lab slide 92).
|
Bulbourethral glands.
The
lining of these paired, compound, tubuloalveloar glands is simple columnar
epithelium. A capsule of dense connective tissue contains some smooth muscle as
well as skeletal muscle of the bulbocavernous and urethral muscles. All
domestic species have these glands except the dog, and their mucous secretion
serves to clear the urethra of urine and to lubricate it and the vagina. The
product may also serve as an energy source for the spermatozoa.
URETHRA
The
male
urethra
consists of two portions; the pelvic urethra and the penile urethra.
Both portions are lined with transitional epithelium, both contain erectile
tissue, and both contain (species variable) branched tubular mucous glands, the
urethral glands. In the pelvic urethra, the three layers of smooth muscle in
the tunica muscularis near the bladder are replaced (or joined in some species)
by the striated urethral muscle. The tunica adventitia is present and typical.
The
tunica muscularis is smooth muscle, and cavernous (corpus cavernosum urethra)
tissue is present in the connective tissue beneath the epithelium. In the penile
urethra, the corpus cavernosum penis is also present.
PENIS
The
penis provides an outlet for both urine and the copulatory ejaculate
(spermatozoa and semen). The histology and gross anatomy of the penis varies
dramatically from species to species and from region to region within the same
species. In general, the body of the penis consists of the urethra, erectile
tissue (corpora cavernosa penis and corpora cavernosum urethra), smooth and
skeletal muscle, touch and pressure receptors (Pacinian corpuscles) and a dense
connective tissue capsule (tunica albuginea).
Erectile tissue and the erectile mechanism.
The
erectile tissue
is composed of dense irregular connective tissue which contains numerous
elastic fibers and sinuses. Under stimulation, the primary blood supply of
the penis is directed through
helicine arteries
which open into the
venous sinuses.
During erection, these vessels and the sinuses become engorged with blood,
and the thin-walled veins beneath the tunica albuginea are effectively
closed, further increasing the rigidity of the organ. Because the
capsule
around the erectile tissue of the corpus cavernosum urethra is not as thick
as that around the corpus cavernosum penis, the urethra is not occluded
during erection. After ejaculation, the helicine arteries contract and
regain their normal tone resulting in a relaxing of the pressure around the
veins which leads to the restoration of normal blood flow to the region.
|
Micrographs of primate penis (Lab slide 91A).
|
Copyright 2002 Charlotte L. Ownby
Histology Part 2 Index
