lecture 4: male tracts and testis Flashcards
What are the testes?
- site of spermatogenesis
- consist of seminiferous tubules and interstitial tissue
- encapsulated by a fibrous capsule (tunica albuginea)
What is the structure of a testis?
- seminiferous tubule - convoluted, thin, hollow tubes
- rete testis
- efferent ducts
- tunica albuginea
- eipdidymis
What are the seminiferous tubules?
• 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
What are sertoli cells?
• “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
- basal lamina
- spermatogonia
- primary spermatocyte
- secondary spermatocyte
- spermatid
- mature spermatid
What is Scp3?
in adult wallaby testis
→ required for meiosis to occur / aids in the exchange of genetic material
→ cells that stain brown are spermatocytes undergoing meiosis
What is the interstitial tissue?
• 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
What are leydig cells?
- 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
What are the rete testis and efferent ducts?
• 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
Where are the testes located?
- can be scrotal or testicond (internal)
- e.g. elephant has internal, ram and pig have external testes
- no one knows why this happens
What is the scrotum?
- 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
What is the spermatic cord?
- 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
What is the pampiniform plexus?
- 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
What is the epididymis?
• 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
What is the vas deferens?
- 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
What is the urethra?
- 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
What is the penis?
- copulatory organ
- 3 regions: root, shaft, glans
- consists of erectile tissue and urethra
- urethra
- corpus spongiosum
- corpus cavernosa
- corona
- glans
- foreskin
What is penile erectile tissue?
• 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
What is the mechanism of penile erection?
- 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
What is the baculum?
- 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
What is the morphology of the penis?
- 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
What are the prepuce and sheath?
- 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
What are the seminal vesicles?
- 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)
What is the prostate?
- 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
What is Cowper’s glands?
- 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
What is species variation in regards to male reproductive organs?
- 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
