Lecture 3: Male reproductive tract-common species

Urethra (penile urethra)

*Penile urethra* - The portion of the urethra that is located on the *ventral aspect of the organ* - Surrounded by *corpus spongiosum* (a sleeve of cavernous tissue) - Ruminants & horses have *urethral process* extending from the penis

Special preputial feature

*Pigs* - There is a *preputial diverticulum* > A small out-pocketing of the cranial roof of the preputial cavity > A foul smelling material (*smegma*) tends to accumulate in this diverticulum *Horses* - has *2 preputial folds*: > *external preputial fold* comprises external & internal laminae (like other species) > *internal preputial fold* comprises *its own inner & outer laminae* which meet at the preputial ring

Histology of the Male Reproductive Tract: Sertoli Cells vs Leydig Cells

*Sertoli Cells* - They are supportive cells which provide *vital hormones* - Act as *immunological barrier* b/w lumen & rest of body > have *phagocytic capability* > Form the *blood testis barrier* (BTB) - They are *elongated in shaped & have tight junctions* *Leydig Cells* - These are in b/w the *seminiferous tubules* in testis & produce *androgens* - Produce *testosterone* under the impact of *LH*

Urethra (pelvic urethra)

- *Connects the urinary bladder to the urinary meatus for peeing* - The male urethra comprises 2 main sections: *pelvic & penile* *Pelvic urethra* - It is further divided into a *short prostatic portion* & a *longer membranous portion* > pelvic urethra runs from the neck of the bladder to the ischiatic arch, where it enters the penis - Has *urethral crest* on the proximal dorsal mucosal surface = a ridge extending from the bladder neck caudally & *ending at the seminal colliculus* > where the *ductus deferens & the ducts of the accessory glands* open into the *urethral lumen* - Pelvic urethra is enveloped by a *urethralis muscle*

Testicular function & temperature (How are testes kept cool)

- *Production of spermatozoa* is very dependent on temperature - Done via multiple structures include: 1) Counter-current heat exchange by *pampiniform plexus* 2) The *scrotal skin is thin w/ abundant sweat glands* -> easy to lose temperature 3) The *cremaster muscles* can alter the position of the testis relative to the body > Testes being out of the body enables us to thermoregulate - *Cryptorchidism* = *undescended testicle* -> can't make viable sperm as too hot inside body

Penis

- A copulatory organ of the male which is capable of extension & protrusion -> deposit spermatozoa within the female reproductive tract to facilitate the fertilization of the oocyte - Comprises the *root* proximally, the *body* in the middle, & *glans* at the distal extremity - Consists of *2 bodies of cavernous/ erectile tissue*: the *corpus cavernosum penis* & the *corpus spongiosum penis*

Blood supply to the penis

- Arteries of the penis are *branches of the internal pudendal arteries* - Artery of the penis of either side gives rise to 3 branches: 1) The *artery of the bulb* -> *supplies the corpus spongiosum* 2) The *deep artery of the penis* -> *supplies the corpus cavernosum* 3) The *dorsal artery of the penis* -> courses on the dorsal aspect of the penis to *supply the glans*

Spermatic Cord

- Comprised of the *ductus deferens*, *testicular vessels & nerves, & the supporting mesenteries* > the testicular a. winds thru an extensive venous plexus (*the pampiniform plexus*) for *counter-current heat exchange*

Penis - Corpus cavernosum penis

- Corpus cavernosum penis begins as paired columns of erectile tissue (*the crura*) which are firmly attached to the ischiatic arch & form part of the *root of the penis* - The cruras from either side converge towards the midline distally to come together to form bulk of the *body of the penis* - The *ventral surface* of the corpus cavernosum within the body of the penis is longitudinally grooved -> referred to as the *urethral groove* > *accommodates the corpus spongiosum & urethra* - Variation in structure of the corpus cavernosum penis in animals leads to 2 types: 1) The *fibroelastic or fibrous type* > contains *little erectile tissue* - the bulk of the structure being *fibrous & elastic connective tissue* > has a *"S" shaped bend* > present in *ruminants & pigs* 2) The *musculocavernous or muscular type* > contains *abundant erectile tissue* > present in the *horse & carnivores* > In some carnivores the *extremity of the corpus cavernosum is ossified* -> forms the *os penis* (penis bone)

Penis - Corpus spongiosum penis

- Corpus spongiosum penis is a *sleeve of erectile tissue* w/ a connective tissue capsule (*tunica albuginea*) surrounding erectile tissue (red part) - Begins as the *bulb of the penis at the ischiatic arch* where the urethra enters the penis > *sit b/w the 2 crura* & forms the root of the penis - Form a *uniform sleeve of erectile tissue surrounding the urethra* during its passage within the body of the penis - At the distal extremity of the penis it expands again to form the *glans penis* > *cats* have *keratinized barbs on the glans penis* > *pig & ox* have *spiralling twist on the glans penis*

Scrotum

- Derived from the skin & abdominal wall tissues - Pair of flash like cavities > The cavities of either side are separated by a median partition => the *scrotal septum* The wall of the scrotum has 5 layers: 1) *Skin & tunica dartos* > thin & has many sweat glands > tunica dartos acts to regulate the temp of the testicles by *expanding or contracting to wrinkle the scrotal skin* 2) External spermatic fascia > a layer of fibrous connective tissue for attachment 3) *Cremasteric fascia* > for attachment for the *cremaster m.* of each side -> pulls testes up & down 4) Internal spermatic fascia > a layer of connective tissue which supports the innermost layer (parietal vaginal tunic) 5) *Parietal vaginal tunic* > innermost layer, a *serosal membrane lining of each scrotal cavity*

Ductus Deferens

- Each ductus deferens is a thin muscular tube, emerges from epididymis -> join the testicular vessels in the spermatic cord to *pass thru the inguinal canal* into the abdominal cavity -> enter the genital fold -> pass thru the prostate gland & *open into the urethra* at the *seminal colliculus* - *Ampulla of ductus deferens* is an enlargement of the ductus deferens at the bladder > in ruminant, horse & dog (ampulla = animals that pull) - Ductus deferens is supported by a mesentery = the *mesoductus deferens* > anchors ductus deferens into abdominal wall & attached to the mesorchium

Epididymis

- Each epididymis is a firm elongated organ with expanded ends - Has a head (proximally), body (narrow) & tail (distally) - Attached via: 1) The *proper ligament* of the testis > Attach *tail of the epididymis to the caudal pole of testis* 2) The *ligament of the tail of the epidydmis* > Attach *tail of the epididymis to the wall of the scrotum* 3) The *mesorchium & mesepididymis* > mesepididymis attaches the body of epididymis to the testis - Has *efferent ductules* & *epididymal duct*

Testis Features (Part I)

- Most are outside the body *except birds & whales* - Have *cranial (proximal) & caudal (distal) poles*, the border adjacent to the epididymis is the *attached border*, that opposite is the *free border* > also have *medial & lateral surfaces* - *Mesorchium* of the testis = the *stalk* - Outer surface of each testis is covered by a serosa called *visceral vaginal tunic* > except where the epididymis is attached - Under the visceral vaginal tunic is *tunica albuginea* (the capsule of the testis) > contains a vascular layer which carries major branches of the testicular vessels - Have *connective tissue septa or trabeculae* that divide the center into *lobules* - Have a major trabeculae down the middle called *mediastinum* -> contains network of canals called the *rete testis*

Accessory Glands

- The accessory sex glands are grouped around the pelvic urethra 1) *Ampullae* - fusiform swelling of each ductus deferens just before the ducts enter the prostate gland & urethra > contribute to the *fluid part* of semen 2) *Vesicular glands* - located within the genital fold lateral to the ductus deferens of either side > *not present in carnivores* > also contribute to the *fluid part* of semen 3) *Prostate gland* - located external to the urethral muscle > secrete a *colorless, slightly acid fluid w/ proteolytic enzymes* 4) *Bulbourethral glands* - located on the dorsolateral aspect of the distal pelvic urethra > not present in dog & small in cats > secrete *sialoprotein* (a mucinous gelatinous material in boar & stallion semen)

Prepuce (foreskin)

- The prepuce is a cylindrical invagination of skin forming a sheath around the free part of the penis - Comprises of two layers/ laminae: 1) *External lamina* - forms the external surface & comprises *typical haired skin* > can be reflected at the preputial orifice to become the internal lamina 2) *Internal lamina* - *moist & hairless skin which lines the preputial cavity*

Testis Features (Part II)

- The testicular parenchyma comprises of *seminiferous tubules* & *interstitial endocrine cells*: > *seminiferous tubule* is where creation of male gametes (spermatozoa) occur > attach to the canals of the rete testis > *Leydig Cells* are in between the seminiferous tubules -> *produce androgens* - Have *epididymis* (has head, body & tail) > storage space for the sperm & gives sperm time to mature - Have *ductus deferens* (输精管) > Spermatic cord is formed by ductus deferens & surrounding tissue

Phases of Spermatogenesis

1) *Spermatocytogenesis* = *spermatogonia* (BIG cells on outside) give rise to *spermatocytes* 2) *Meiosis* = *spermatocytes* undergo meiosis & become *spermatids* 3) *Spermiogenesis* = *spermatids* transform into *spermatozoa* ∴ spermatogonia -> spermatocytes -> spermatids -> spermatozoa

Muscles of the penis

1) The *Ischiocavernosus mm.* > a pair of relatively powerful *skeletal muscles* *surrounds the 2 crura of the penis* > *arise from the ischiatic arch w/ the crura* & extend to the *beginning of the body* of the penis > function to *pump blood into the corpus cavernosum & position the penis during mating* 2) The *bulbospongiosus m.* > envelopes the corpus spongiosus at the bulb of the penis > *skeletal muscles* > function to *pulses during ejaculation to assist in expulsion of semen* 3) The *retractor penis mm.* > *smooth muscles* > Run in the midline on the ventral/ventro-lateral aspect of the body of the penis > *retracts the penis back into the prepuce*