Flashcards in lecture 4: male tracts and testis Deck (25):
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
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
1. basal lamina
3. primary spermatocyte
4. secondary spermatocyte
6. 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
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
• corpus spongiosum
• corpus cavernosa
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