Anatomy & physiology of male reproductive tract of domestic animals.

1. Course: Andrology and Male infertility
Lecture-1: Anatomy & physiology of male reproductive
tract of domestic animals
Dr. Farooz Ahmad Lone (Ph.D Gold Medalist)
Assistant Professor
Animal Reproduction

2. • The male reproductive tract constitutes
• Testis and scrotum
• Epididymis and ductus deferens
• Accessory glands
• Penis and prepuce

4. Embryological Development of Male
Primordial germ
cells
Gonocytes Spermatogonia
• Genetic sex is determined at fertilization
• In avian species, females are heterogametic (ZW) contain H-Y
antigen, males are homogametic (ZZ)
• Primary sex cords develop in the medulla
• Secondary sex cords develop in the cortex
• SRY is located on the short arm of the Y chromosome and
codes for a protein called the testis-determining factor (TDF)
which induces the embryonic gonad to become a testis.
• Genes involved
a) SRY and SOX9 for testis development
b) WNT-4 and WNT-7α for ovary development

5. Development of male reproductive system
Embryological structure Mature structure
Yolk sac
Primary sex cords (Medulla)
Secondary sex cords (Cortex)
Mesonephric tubules
Mesonephric ducts
Urogenital sinus
Urethral folds
Genital tubercle
Genital swelling
Primordial germ cells
Testes
Ovaries
Efferent ducts
Epididymis, vas deferens and (SV)
Penile urethra, bulbourethral glands
Prepuce
Glans penis
Scrotum

6. • Immature Sertoli cells produce mullerian inhibiting
substance (MIS), which is responsible for the regression of
the paramesonephric (Mullerian) ducts in the male fetus.
• Leydig cells secrete testosterone which stimulates the
development of the mesonephric (Wolffian) duct and
tubules.
Primary sex organs - Testes
Secondary sex organs - Epididymis, vas deference and penis.
Accessory sex glands - Seminal vesicles, prostate and bulbo-
urethral glands.

7. A. Scrotum
• The scrotum of the domestic animals is located between the
thighs except boar and cat--------scrotum is located caudal to
the thighs.
• Dartos muscle layer: This layer divides the scrotum into two
halves. Controls temperature of testes by thickening and
thinning of scrotal skin (Wrinkle formation during winter)
B. Testes
• The testis is covered by visceral layer tunica vaginalis
(derived from peritoneum), tunica albuginea and tunica
vasculosa from outside inwards.
• Along the caudal border, a mass of tissue projects through the
tunica albugenia into the testis known as mediastinum testis.

8. • Along the caudal border, a mass of tissue projects through the
tunica albugenia into the testis known as mediastinum testis.
• The seminiferous tubule
• Germ cells (spermatogonia)------Spermatozoa
• Sertoli cells------sperm mother cells or nurse cells (secrete
androgen binding protein)
• Leydig cells or interstitial cells…..testosterone
• Seminiferous tubules from both testes of bull……..5m

9. • Testis and scrotum
All domestic farm animals have their testis located
outside the abdomen near the inguinal region
enclosed in a pouch like structure called as
scrotum.
extension of skin and fascia of abdominal wall
modified with the presence of some layers of
fibroblastic and muscular tissue, of which dartos
muscle is the predominant one.
These muscle layers also extend in between the
two testicles forming testicular septum.

10. • In bull, ram, & buck, the scrotum is pendulous and
elongated while as it is rounded and closely applied to
inguinal region in other domestic animals.

11. Split scrotum

12. • The outer layer of peritoneum is closely applied to the testis
forming its serous layer called as tunica vaginalis propria
(vaginal process).
• This outpouching of parietal peritoneum is also accompanied by
the extension of internal abdominal oblique muscle called as
cremaster muscle which raise or lower the testes in response to
temperature.

13. • Each testis is enclosed by a tough capsule principally made of
fibrous tissue called as tunica albuginea and is secured to the wall of
tunica vaginalis propria along the line of epididymal attachment.
• The position and orientation of the longitudinal axis of testis differ
in different species. In bull, ram, & buck, the orientation is vertical
where as in stallion & dog it is horizontal.

14. • Histologically each testis is composed of seminiferous tubules and
interstitial tissue.
• Each seminiferous tubule is a large isolated highly convoluted &
unbranched structure and is lined with seminiferous epithelium.
• The seminiferous epithelium has two main cell lines- somatic Sertoli
cells and sperm producing germ cells.
• The interstitial tissue which is located between the seminiferous
tubules consists of steroid producing cells called as Leydig cells,
blood vessels and lymph vessels.

16. Sertoli cells (Sustenticular or Nurse Cells)
• Sertoli cells are named after Enrico Sertoli, who first described
them in 1865.
• Sertoli cells are the main somatic component of the seminiferous
tubules.
• Sertoli cells have a multi-lobed nucleus, a cytoplasm rich in
endoplasmic reticulum, glycoproteins and cytoplasmic droplets
• Sertoli cells are large pyramidal epithelial cells whose base is in
contact with the basement membrane of the seminiferous tubules
(which they produce with the peritubular cells) and whose apical
part goes up to the level of the height of the seminiferous tubules.

17. • The Sertoli cells establish tight junctions between them at
puberty….. formation of the blood-testis barrier….. which
prevents the free access of the blood components to the germinal
cells located in the ad luminal compartment of the testicle …..toxic
or mutagenic factors and an autoimmune reaction of the body
to its own spermatozoa.
• Under the control of FSH and androgens, Sertoli cells
synthesize large number of proteins
• inhibin and activin play a role in the hypothalamic–
pituitary axis in the release of gonadotropins, but they
also act on the function of Leydig cells within the testis.
 ABP released under the influence of FSH and androgens,
plays a role in the bioavailability of androgens, regulating
spermatogenesis and sperm production.
 Transferrin, a glycoprotein that carries iron to iron-
requiring cells, whose concentration in seminal plasma is
directly linked to spermatic production and fertility.

18. • In the bull, there is no further division of Sertoli cells 6
months after birth, their number reaching a maximum at
28 weeks in Holstein bulls.
• Sperm production is therefore directly correlated with
the number of Sertoli cells fixed before puberty.
DEVELOPMENT OF TESTIS
• Prenatal development: Early in the embryonic development,
primordial germ cells migrate from the yolk sac into the
mesonephros where they form gonadal and genital ridge.
What determine embryonic gonad (genital ridge) to
differentiate into testis?

19. • A gene (SRY) on Y chromosome that encodes testis determining
factor (TDS) which centrally instructs the undifferentiated genital
ridge to develop into testes.
• The differentiated foetal testis produces androgen which causes
development of male reproductive tract.
• Antimullarian hormone (AMH) a glycoprotein secreted by Sertoli
cells of foetal testis cause suppression of the paramesonephric or
mullerian duct which otherwise develops into uterus and vagina.
• As the testis develops in the mesonephros, the embryonic kidney
also starts developing and replaces mesonephros as differentiated
definite kidney………….testis migrates from its original position to
abdomen and then towards its permanent position in the scrotum.

20. Descent of testis
• Migration of testis from the position of mesonephros to the
scrotum via abdomen is called as descent of testis.
• Before this migration the tunica vaginalis, a parietal
extension encloses an inguinal ligament, the
gubernaculum testis which serves as a marking line for
descent.
• In horse, epididymis enters inguinal canal before the testis.
Thus the gubernaculum testis, epididymis and tunica
vaginalis enters the inguinal canal much before and thereby
guide the testicular descent.
• Final entry of testis into scrotum via the inguinal canal
occurs as a result of tension in the gubernaculum testis and
the pressure from the abdominal viscera.

21. Species Time of descent
Bull 3.5 to 4 months of gestation
Ram  80 days of gestation (Noakes,2000)
 Half way through foetal life (Hafez & Hafez, 2000)
Boar  After 85 days of gestation (Noakes)
 Last quarter of foetal life (Hafez)
Stallion  Between 9 month of gestation and a few days after
birth (Noakes)
 Just before or after birth ( Hafez)
Dog just before or after birth
Cat After birth (2-5 days)
Time of testicular descent in different species

22. • Rarely testes fail to descend into the scrotum and are thus
retained within the abdomen. This is known as cryptorchidism
and the individual animal is known as cryptorchid.
• Cryptorchids are sterile because they fail to form spermatozoa
due to high temperature inside the abdomen but show normal
sexual desire due to intact endocrine functions of testis.
• Sometimes in bilateral/unilateral cryptorchid animals, abdominal
viscera may descend into the scrotum resulting into scrotal
hernia, a condition common in pigs.

23. Temperature Regulation of Testes
For an efficient spermatogenesis the mammalian testes must be at a
temperature lower than that of the core body temperature. The low
temperature of the testes is ensured by the anatomical setup of testis
and scrotum.
• Scrotal Skin………temperature receptors, adrenergic sweat
glands…… can elicit panting and sweating. …..tend to lower scrotal
temperature.
• Scrotal skin is devoid of subcutaneous fat hence direct heat loss
may also occur.
• Scrotal skin contain layers of dartos muscle & also spermatic cord
has cremaster muscle.
 Hot temperature………. dartos muscle relaxes thus making
scrotal skin thin & pendulous. Relaxation of cremaster
muscle forces testes away from inguinal canal.

24. • Cold temperature….. cremaster muscle contracts bringing testes
close to inguinal canal & dartos muscle contraction causes
wrinkling & thickening of scrotal skin preventing sweating & heat
loss from scrotal skin.

25. • The most important & efficient
mechanism of testes temperature
regulation is the close apposition of
testicular artery & testicular vein near the
pole of testes.
• Testicular vein that takes blood at
lower temperature away from testes is
a high convoluted structure which is
enmeshed with arterial coils from
inguinal to the cranial or dorsal pole
of the testes.
• This structure has been termed as
pampniform plexus or testicular
cone. This pampniform plexus has a
counter current mechanism in which
arterial blood entering the testes is
cooled by the venous blood.

26. • In ram, the temperature in the testicular artery falls 4°C
during its flow from inguinal ring to the cranial pole of the
testes. However, in case of boar the scrotum is less
pendulous thus the difference in the temperature is 3.2 °C.
Epididymis & Ductus deferens
• The whole epididymis is divided into three anatomical
regions- caput, corpus & cauda epididymis.
• Caput epididymis is a flattened structure applied to dorsal
pole of the testes and continues as a narrow structure
called as corpus or body of epididymis .
• The corpus epididymis terminates at caudal pole of testis
in an expanded form called a cauda epididymis.

27. • Actually 13 – 20 efferent ductules join in the caput to form
duct of epididymis.
• If the duct of epididymis is expanded, it measures about
36m in bull & 56m in boar .The wall of duct of epididymis
has a layer of circular muscle fibres & lined with
pseudostratified columnar epithelium.

28. • Caput & corpus epididymis is concerned with sperm
maturation while as cauda is largely meant for storage. The
average length of epididymis is 16 cm in bull & buffalo.
• The vas deference is a relatively thick walled muscular tube
which acts as both a reservoir for sperm and the means of their
conduction between the epididymis and the penis.
• Its mucous membrane is thrown into longitudinal folds and is
lined with pseudostratified epithelium, vas deferens before
joining urethra becomes expanded called as Ampulla.
• Epididymis serves as a passage way for sperm to travel into
vas deferens. It concentrates the sperm, provides the
environment and fluids necessary for sperm maturation &
finally acts as a storage unit for sperm that are ready for
ejaculation.

29. • In general sperm transport through the epididymis takes
about 9 – 13 days.
• The cauda epididymis is the principle storage organ and
contains about 75% of the total epididymal spermatozoa.
• Wear house of sperm.
• Caput epididymis………absorption
• Caput and corpus epididymis………..Maturation
• Cauda epididymis---storage organ (70% of extra gonadal
reserve)
• Fertile sperm are present in cauda epididymis
• Principal cells form 80% of epididymal cells—secretory
&Absorption.
• Halo cells are considered as lymphocyte of
epididymis….Immune cell.

30. Q. No. 1: Which cell is considered as immune cell in the
epididymis
• Principal cell
• Clear cell
• Halo cell/holocrine
• Giant cell
• Principal cells form 80% of epididymal cells—secretory
&Absorption.
• Halo cells are considered as lymphocyte of
epididymis….Immune cell.

31. Spermatic cord
• Spermatic cord is formed of spermatic arteries, veins,
lymphatics nerves, cremaster muscles and vas
deferens.
• Cremaster muscle……temperature regulation by
lowering and raising of testes
Ductus deferens or Vas deferens
• The terminal portion of the vas deferens is little dilated
and is known as ampulla
• Colliculus seminalis is a small elongate or oval
eminence structure on the urethra into which vas
deferens and duct of seminal vesicle opens.

32. Presence or absence of accessory sex glands in the domestic
animals
Accessory
glands
Species
Bull Ram Stallion Boar Dog Tom
Ampulla Very
small
Very small Large, well
developed
Absent Very
small
Absent
Prostate Large Large Large Small Very
large
Large
Seminal vesicle Very
large
Very large Large Large Absent Absent
Bulbourethral
gland
Small Small Small Very
large
Absent Large
• Prostate: only sex gland present in dog.
• Seminal vesicle: present in all except in dog and cat
• Ampullae contributes ergothioneine (sulphur containing) to equine semen.

33. • Ampullae: The terminal portion of each ductus deferens become
dilated before entering the pelvic urethra called as ampulla.
• It acts as a small reservoir of sperm. …..contributes ergothionine
significantly to the equine ejaculate and in other animals its
importance is less.
Vesicular gland or seminal vesicle:
• Bull & ram: very large, firm & lobulated, lie adjacent to the neck of
bladder & lateral to the ampullae.
• Boar & stallion: Large, glandular sacs
• The duct of vesicular gland and the ductus deferens unite together
forming a common ejaculatory duct which opens into the pelvic
urethra.
• These glands contribute substantially to the volume of ejaculate.
Seminal vesicle in all species secrets citrate and in ruminants (bull,
ram) also release fructose and in boar acts as a main source of
inositol.

34. • Prostate: This gland has two parts- body and disseminated
part. Body surrounds the neck of the bladder and the
second part surrounds the pelvic urethra and extend on the
bulbourethral gland.
• In the dog, it constitutes the male accessory sex gland
forming a discrete organ around the pelvic urethra.
• Its secretions are watery and contain large amount of
chloride ions.
• It contributes significantly to the sperm free fraction in the
dog for maintaining proper pH in the pelvic urethra before
sperm rich fraction comes in order to clear residual urine.
• In the stallion, prostate is wholly external.

35. • Bulbourethral gland/Cowper’s gland: these lie dorsal to
the urethra near the ending of pelvic urethra.
• In the bull, Cowper’s glands are almost hidden by the
bulbospongiosus muscle.
• These secrete watery secretions before coitus to cleanse the
urethra of urine.
• In boar, the bulbourethral glands are large cylindrical
structures secreting a viscid fluid (due to sialomucin)
which combines with the secretions of the seminal vesicles
to make it gelatinous which is important for producing
a plug in the vagina after coitus in sow to prevent its
back flow.

36. Penis and prepuce:
• The length of penis in ruminants & swine is controlled
by retractor penis muscle. It restores the sigmoid
flexure after erection. Sigmoid flexure is caudal or
post scrotal in ruminants but pre scrotal or cranial
in swine.
• Sigmoid flexure is absent in dog and stallion.
• Boar: Penis is corkscrew type with no glans.