Male Genital System of Animals (Histology)
Written By Anjani Mishra
Male Genital (reproductive) System
Fig: Genital organs of bull
Fig: Schematic diagram of scrotum and testes
Fig: Longitudinal section of testis
1. Ureter, 2. Prostate gland, 3. Seminal vesicle, 4. Urethral muscle, 5. Bulbourethral gland
General Features of M.G.S.
The male genital system consists of following organs;
1. The
pair gonads, the testes
2. The
male genital ducts
A. Intratesticular
ducts
a)
Tubuli
recti/vasa recti
b)
Rete
testis
c)
Ductuli
efferentes/vasa efferentia
B. Extratesticular
ducts
a)
Ductus
epididymis
b)
Ductus
(vas) deferens
c)
Ejaculatory
duct
3. Accessory
glands
Seminal vesicles, prostate gland, &
bulbo-urethral glands
A
system of duct
Tubuli recti- Rete testis- Ductuli efferentes- ductus epididymis- Ductus deferens-
Ejaculatory duct- urethra
Testes
The testis is suspended within the scrotum
and is immediately surrounded by the testicular capsule, which is composed of
three layers;
i) Tunica
vaginalis, outer layer
ii) Tunica
albuginea, middle layer
iii) Tunica
vasculosa, innermost layer
Fig:Testis, stallion
2. Inrerstitial cells, 7. Seminiferous tubule, 16. Tunica albuginea (smooth muscle),
17. Tunica albuginea (vascular layer), 18. Tunica vaginalis
i) T.
Vaginalis
It is a double layer serous sac. The
visceral layer covers the tunica albuginea, where as the parietal layer is
fused with scrotal fascia.
ii)T.
albuginea
It is the middle and strong thin capsule
of fibro-elastic tissue. It is thickened on the posterior surface of the testis
where it projects into the gland as mediastinum testis. Thin fibrous septa
radiate from the mediastinum testis.
iii) T.
Vasculosa
It is highly vascularized loose connective tissue which
is immediately deep to the tunica albuginea. It forms a vascular capsule at the
testis.
Testicular lobules
Testicular lobules are pyramidal in shape,
separated by inter-lobular connective tissue septa radiating from the mediastinum testis. There are about 250 lobules in a testis. Each lobule contains 1-4 seminiferous tubules. These tubules are embedded in a
meshwork of loose connective tissue containing blood vessels, lymphatics, nerves and
interstitial cells.
Seminiferous
tubules
Each seminiferous tubule is about 150-250um in diameter and
30-70 cm long. The combined length of the tubules of one testis is about 250m.
They are enveloped by a fibrous connective tissue
consists of several layers of fibroblasts.
Each seminiferous tubule is lined with a
complex epithelium (seminiferous, or germinal epithelium). The epithelium
consists of 4-8 cell layers and contain two types of cells; spermatogenic cells
and sertoli cells.
Fig: Testis, Seminiferous tubules, dog
3. Lumen, 4. Myoid cell, nucleus, 5. Primary spematocyte, 8. Sertoli cell (nucleus),
10. Spermatid (early), 11. Spermatid (late), 12. Spermatogonia
Spermatogenic
cells
Spermatogenic cells are stacked in 4-8
layer, occupying the space between the
basal lamina and the lumen of seminiferous tubule.
Various cells at
different steps in the process of spermatogenesis, such as spermatogonia,
primary spermatocytes, secondary spermatocytes, spermatids and spermatozoa are
included in spermatogenic cells.
1.
Spermatogonia
Spermatogonia are small diploid germ cells
located next to the basal lamina of the seminiferous tubules. They are the only
spermatogenic cells that present before puberty.
Two types of spermatogonia are recognized;
Type-A Spermatogonia and Type-B Spermatogonia. Type-A divide by mitosis to
provide a continuous reserve of stem cells, and type-B gives rise to primary spermatocytes.
2.
Primary Spermatocytes
Primary Spermatocytes are large cells with
large spherical nuclei. Each primary spermatocyte undergoes meiosis to give rise to
two secondary spermatocytes with only 23 chromosomes (22+x or 22+y)
3.
Secondary spermatocytes
Smaller in size with small nuclei. These
cells are different to observe, because they remain in interphase for very short
period and enter quickly into the 2nd meiotic division, results in
spermatids that also contain 23 chromosomes.
4.
Spermatid
Small, rounded or elongated cells with
small nuclei. With the spermatid formation spermatocytogenesis ends. There
after, the spermatids undergo a complex process of differentiation
(spermiogenesis), which results in the transformation of the spermatids into
spermatozoa.
5.
Spermatozoa
The spermatozoa are long cells, about 65um in length. It
consists of a head and tail.
A. Head
Shape- Oval
outline
Length- 4
to 5um
Width- 2.5
to 3.5 um
- It is occupied by the condensed nucleus, containing 23 chromosomes.
- The acrosome is a membrane covering the anterior 2/3 of the nucleus. It consists of various enzymes, like hyaluronidase, esterage, zona lysine, acrosin etc.
- The golgi vesicles coalesce to form head cap.
B. Tail
Length- 60um
Thick- 0.5um
The tail is covered by plasma membrane over
its entire length. It is sub-divided into four parts;
a. Neck
Length- 5um
- It connects the head to the remainder of the tail.
- It includes the proximal centriole and a basal body and occasionally mitochondria.
- The posterior centriole form axis filaments of the body and tail.
b b. Middle
piece
Lenght- 5um
- It is located between the neck and the annulus (junction between middle & principal piece)
- It contains axoneme (axial thread of chromosome) nine pair of outer dense fibers (microfilament) and spirally arrange sheath of mitochondria.
c. Principal
piece
Length- 45um
- Longest segment of the tail, extending from annulus to the end piece.
- It contains axoneme with its surrounding dense fibers, encircled by fibrous sheath.
d. End
piece
Length- 5um
- It consists of the axoneme and the surrounding plasma membrane.
Sertoli
cells
- Sertoli cells are tall pyramidal cells.
- The bases of the sertoli cells adhere to the basal lamina and their apical ends frequently extended into the lumen of the seminiferous tubule.
Tubulie
recti
- Short, straight tubules that connect seminiferous tubule with rete testis.
- These are lined by sertoli cells in their initial segment, near the seminiferous tubules, and by a simple cuboidal epithelium in their main segment.
- The epithelium is supported by a dense C.T. sheath.
Rete
testis
- Highly irregular network of channels lined by simple cuboidal epithelium within the mediastinum testis.
- Tubuli recti empty into the rete testis.
Ductus
efferentes
- A collection of 12 or more tubules leading from the rete testis to ductus epididymis.
- They are lined by an epithelium composed of alternating groups of pseudostratified and ciliated columnar cells.
- They have a thin circular layer of smooth muscle beneath the basal lamina.
Fig: Testis, ductuli
efferentes
1. Columnar epithelium, 7. Pseudostratified epithelium, 10. Spermatozoa
Ductus
epididymis
- It is single coiled tube, consists of head, body & tail. It is lined with pseudo-stratified columnar epithelium.
- These cells are supported by basal lamina, surrounded by smooth muscle cells.
Fig: Epididymis (head) stallion
5. Loose connective tissue, 6. Lymphocyte, migrating, 7. Pseudo-stratified epithelium,
9. Smooth muscle
Ductus
deferens
It is thick wall muscular tube with a
narrow-irregular lumen. Two portions are recognized in ductus deferens and these are non-glandular and glandular portion.
A. Non-glandular portion
It consists of following layers;
1. Mucosa
i) Lamina epithelia- lined
with simple column or pseudo-stratified columnar epithelium.
ii) Lamina propria- consists of connective tissue rich in elastic fiber.
Consists of 3 distinct layer, namely;
i) Inner
longitudinal,
ii) Middle circular, and
iii) Outer longitudinal
3. Adventitia/Serosa
A loose collagenous adventitia or subserosa covers the muscular
coat and contain numerous nerves and vessels and also branched longitudinal muscle fibers. In part of its course a serous layer is present composed of peritoneum.
Fig: Ductus(vas) deferens, stallion(non-glandular portion)
2. Lamina propria, 4. Muscularis, 5. Pseudo-stratified epithelium
Fig: Ductus(vas) deferens,x.s., boar(non-glandular portion)
6. Lamina propria, 7. Muscularis, 8. Pseudo-stratified epithelium, 10. Serosa
B. Glandular portion
Ampulla
Ampulla is a glandular portion of ductus deferens shows the same structure as the accessory sex gland; i,e.,it contains branched tubular glands which exhibit saclike dilatations or enlargement of the ductus deference in its terminal portion.
1. Mucosa
i) Lamina epithelia- The epithelium of the gland and duct consist of simple columnar epithelium. The cells vary in height with their functional state.
ii) Lamina propria- The propria consists of branch tubular glands. The ampulla of the cat lacks gland. They are smallest in the boar. They are best developed and show the most branching in the solipeds. In case of dog the glands extend into the initial portion of the urethra.
2. Sub- mucosa- Large fat cells are found in the sub mucosa in the bull.
3. Muscularis externa- The muscularis is arranged in inner circular and outer longitudinal layers or, in ruminants, in interlacing bundles.
Fig: Cross section of ductus deferens(glandular portion) of goat
a. Lumen of the duct, b. Lamina propria, c. Submucosa, d. Interglandular muscular tissue, e. Section through a gland containing secretion, spermatozoa and crystal, f. Musculature
Penis
The penis may be divided into body and glans
The body of penis
The body of penis consists of an envelope, a system of trabeculae, and the true erectile tissue. The fibrous envelope, tunica composed of dense collagenous tissue and elastic fibers. It gives off similarly constructed trabeculae, which are inter-connected to make up a coarse trabecular frame work.
Between the trabeculae lies the spongy erectile tissue proper. This consists of a fine frame work of lamellae and cords, continuous with the trabeculae and albuginea and of variously shaped communicating spaces - Cavernae.
They are bounded by inter cavernosus lamellae and trabeculae, which carry vessels and nerves and are composed of fibro-elastic tissue (in ruminant and boar) and smooth muscle fiber (specially in the stallion and carnivores). Scattered adipose tissue is present in the corpus cavernosum of all domestic mammals.
Fig: Body of penis,x.s., boar
2. Cavernosus space, 5. Corpus cavernosum penis, 7. Retractor penis muscle, 9. Trabeculae,
10. Tunica albuginea
The substance of the penis consists of ;
1. Corpus cavernosum penis
2. Corpus cavernosum urethrae
1. Corpus cavernosum penis- present urethral groove ventrally, which lodges the urethra and corpus cavernosum urethrae. The corpus cavernosum urethrae surrounds the urethra.
2. Corpus cavernosum urethrae- is surrounded dorsally by tunica albuginea, laterally by bulbo-spongiosus muscle and ventrally by retractor penis muscle.
Both erectile bodies has the same structure, but the trabeculae are finer and the cavernosus spaces are fewer, larger and more dilatable.
Glans penis
The end of the penis is covered by a special kind of tissue. It is richly vascularized and in some species contains a true erectile bodies, which forms a terminal enlargement of the penis, the glans. It is prominent only in man, stallion and dog. The glans is covered by a penile prepuce.
The erectile tissue of the glands is separated from the corpus cavernosum penis. In animals other than the boar it communicates with the corpus cavernosum urethrae. In carnivores this continuity is extensive. The structure of the venous erectile tissue of the glans resembles that of corpus cavernosum urethrae.
Fig: Glans penis, l.s., tomcat
5. Dermis, 7. Epidermal spine
The bulbus glandis of the dog is a thick corpus cavernosum, which is rich in elastic tissue and contains muscle fibers. In carnivores, the glans covers the os-penis which is ossified terminal portion of the corpus cavernosum penis.
In the stallion, ram and goat the urethra project beyond the end of the penis forming the urethral process, which is ensheathed in a thin layer of cavernosus tissue. In the stallion it is rich in lymphatic tissue.
If you have any questions you can ask me on :
mishravetanatomy@gmail.com Facebook Veterinary group link - https://www.facebook.com/groups/1287264324797711/
Twitter - @MishraVet
Facebook - Anjani Mishra
Website: mishravetanatomy.blogspot.com
Post a Comment