lecture 4: male tracts and testis

Question 1

What are the testes?

Answer 1

• site of spermatogenesis
• consist of seminiferous tubules and interstitial tissue
• encapsulated by a fibrous capsule (tunica albuginea)

Question 2

What is the structure of a testis?

Answer 2

• seminiferous tubule - convoluted, thin, hollow tubes
• rete testis
• efferent ducts
• tunica albuginea
• eipdidymis

Question 3

What are the seminiferous tubules?

Answer 3

• contain germ cells and Sertoli cells
surrounded by a basement membrane and an outer layer of myoid cells
tubule arrangement varies
looped tubules - both ends open into rete testis

Question 4

What are sertoli cells?

Answer 4

• “nurse cells” of the testes
• secrete AMH (during virilisation), androgen binding protein (binds and concentrates testosterone), aromatase (converts testosterone to oestrogens)
• blood-testis barrier: occlusive junctions between sertoli cells, creates a tight barrier that allows for two totally different environments
→ you don’t want sperm getting into main lymphatic/circulatory system → your body would mount an immune response to sperm
→ events that occur within the tubule also need their own environment
• without them you don’t get spermatogenesis occurring
• create a unique microenvironment
the least mature germ cells are closer to the basal lamina and as the germ cells mature they move up to the apical region of the sertoli cell

1. basal lamina
2. spermatogonia
3. primary spermatocyte
4. secondary spermatocyte
5. spermatid
6. mature spermatid

Question 5

What is Scp3?

Answer 5

in adult wallaby testis
→ required for meiosis to occur / aids in the exchange of genetic material
→ cells that stain brown are spermatocytes undergoing meiosis

Question 6

What is the interstitial tissue?

Answer 6

• everything in the testis that isn’t the seminiferous tubule
• leydig cells
• blood vessels
• lymph vessels
→ b&l vessels important bc they circulate a lot of testosterone around the body
• connective tissue
• macrophages

Question 7

What are leydig cells?

Answer 7

• major source of testicular androgens (especially testosterone) under the influence of LH from the pituitary
• testosterone important for spermatogenesis and development of the rest of the male tract
• also convert androgens to oestrogens via aromatase
• if you knock out LH, you don’t get any testosterone production

Question 8

What are the rete testis and efferent ducts?

Answer 8

• fluid resorption – concentrates sperm
• each of seminiferous tubules joins rete testis
• rete testis joins onto efferent ducts
• efferent ducts join the epididymis
• sperm gets from the seminiferous tubules to the rete testis in two different ways
→ STs secrete a lot of fluid, myoid cells contract and peristalsis moves sperm up to rete testis, fluid resorption between these two areas concentrates the sperm

Question 9

Where are the testes located?

Answer 9

• can be scrotal or testicond (internal)
• e.g. elephant has internal, ram and pig have external testes
• no one knows why this happens

Question 10

What is the scrotum?

Answer 10

• numerous sweat glands
• considerable size variation
• position relative to penis varies
• purpose of the scrotum is to keep the testes away from the body, to keep them cool
• a lot of the arrangement of scrotum depends on the animals lifestyle e.g. horse runs fast so smaller relative to body size and kept close

Question 11

What is the spermatic cord?

Answer 11

• suspends testes in the scrotum
• contains vas deferens, pampiniform plexus, cremaster muscle, lymphatic vessels, arteries & nerves
• animals with testicond testes do not have spermatic cord

Question 12

What is the pampiniform plexus?

Answer 12

• intricate arrangement of testicular arterial supply and venous drainage
• absent in animals with abdominal testes
• specialised spermatic blood supply
• countercurrent heat exchange
• role of cremaster
• high temp stops spermatogenesis and increases cancer risk
• main testicular artery that brings blood to the testis, and two rather large testicular veins that take blood away from the testis
• veins are wrapped around the artery
• testicular artery blood before testis is 39.0ºC, 4.8 ng T/ml → 34.4ºC, 5.4 ng T/ml in the testis
• testicular vein in testis = 33.06º, 70 ng T/m → out of the testis 38.6ºC, 70ng T/ml

Question 13

What is the epididymis?

Answer 13

• plural epididymides
• a highly convoluted hollow tube
• three regions:
– caput (fluid resorptive, concentrates sperm)
– corpus (secretory)
– cauda (sperm storage and maturation)
• sperm in the top two regions is immotile and incapable of fertilising anything
• by the time the sperm leaves the cauda of the epididymis it is capable of fertilising an egg (in most species), and it is also motile
• smooth muscle walls - peristalsis promotes sperm movement
• up to 86m long in the stallion

Question 14

What is the vas deferens?

Answer 14

• epididymis is continuous with vas deferens
• posterior region often enlarged (ampulla)
• opens into urethra
• part of the spermatic cord
• smooth muscle – peristalsis
• many muscle layers
• vasectomy – vas deferentia are cut
• quite a small lumen
• component of the spermatic cord

Question 15

What is the urethra?

Answer 15

• extends from bladder to tip of penis
• 3 regions: prostatic, membranous and cavernous
• prostatic urethra – receives sperm from vas deferentia and fluid from seminal vesicles and prostate
• membranous – forms external sphincter of the bladder
• cavernous (penile) – runs the length of the penis

Question 16

What is the penis?

Answer 16

• copulatory organ
• 3 regions: root, shaft, glans
• consists of erectile tissue and urethra
• urethra
• corpus spongiosum
• corpus cavernosa
• corona
• glans
• foreskin

Question 17

What is penile erectile tissue?

Answer 17

• 3 cylinders of erectile tissue:
• a single, ventral cylinder, the corpus spongiosum
– surrounds the urethra
• paired dorsal corpora cavernosa
– both have a large central artery and are enclosed by a dense, fibroelastic tunica albuginea
• all three surrounded by thick fibrous capsule

Question 18

What is the mechanism of penile erection?

Answer 18

• when the brain receives the correct stimulus (whether tactile, physical, or emotional) sends signals via ANS
• ANS stimulates nerves in corpora cavernosa - release NO in artery wall
• NO acts on adjacent cells and gets them to activate an enzyme that converts guanine triphosphate (GTP) to cGMP
• cGMP instructs smooth muscle cells to relax - muscles surround the artery relax → dilate → blood flow increases → 8x volume of blood into penis during erection → as they dilate and fill with blood, the corpora cavernosa expand too → pressure on the rest of the structures in the penis (e.g. flattened vein, stopping a lot of blood flow out of the penis) → erection
• erections in humans based a lot on haemodynamics
• phosphodiesterase catalyses reaction of cGMP back to GTP → arteries contract → less blood flow → less pressure
• phosphodiesterase activity knocked out by viagra

Question 19

What is the baculum?

Answer 19

• penis bone/os penis
• develops in the penis between the paired corpora cavernosa, above the urethra
• may permit longer bouts of intercourse
• humans are the only primates (+ one monkey) that don’t have a penis bone

Question 20

What is the morphology of the penis?

Answer 20

• four pronged echidna penis
• pig penis has an action like a corkscrew - forms an airtight gap to stop sperm leaking out again
• spines on cat penis scrapes inside of female tract which stimulates ovulation

Question 21

What are the prepuce and sheath?

Answer 21

• prepuce - a retractable fold of skin that covers the prescrotal part of the non-erect penis
• sheath - a layer of skin that protects the non-erect penis

Question 22

What are the seminal vesicles?

Answer 22

• form from outpockets of vas deferens ampulla
• absent in some species
• open into vas deferentia or urethra via ejaculatory ducts
• stores seminal fluid between ejaculations
• contributes a significant amount of seminal fluid (in humans, ~60$ of ejaculate volume)
• marsupials and carnivores do not have them
• highly glandular organ
• complex secretions: citric acid, fructose (main energy source for the sperm), mucus, proteins, enzymes, prostaglandins (help dampen female immune response to sperm, also increase sperm motility)
• very alkaline secretion: neutralises acidity of vaginal tract
• responsible for stickiness of semen (may help it be retained in uterus/female reproductive tract)

Question 23

What is the prostate?

Answer 23

• can be lobular, disseminate or a mix of both
• produces significant proportion of the ejaculate
• secretes proteins, bicarbonate, proteolytic enzymes (e.g. PSA), clotting enzymes, citric acid
• a functional prostate is dependent on DHT (dihydro-testosterone)
• most male mammals have prostates
• basically a large exocrine gland
• highly glandular organ

Question 24

What is Cowper’s glands?

Answer 24

• bulbourethral gland
• absent in some animals
• small exocrine glands at base of penis
• at sexual arousal secretes a clear, salty, viscous solution (pre-ejaculate)
• neutralises, lubricates and cleanses the urethra

Question 25

What is species variation in regards to male reproductive organs?

Answer 25

• size and position of organs
• seminal vesicle present?
• SV opens into vas or urethra
• form of prostate
• location of testis
• shape and direction of penis
• scrotum pendulous or compact