Male Reproductive System I Flashcards
Overview of the sperm journey?
- testis (high speed manufacturing)
- epididymis head & body (finishing steps)
- epididymis body (warehouse and shipping)
- accessory sex glands (final alterations & packaging)
- penis (delivery system)
Function of the testis?
High speed manufacturing
- 1-25x10^9 spermatozoa/day (35,000-200,000 per second)
- “plant” must be air conditioned
Function of the epididymis head & body?
finishing shops
- fluid absorption
- 8-25x10^9 spermatozoa (mb changes, nuclear & flagellar stabilization, motility, cytoplasmic droplet translocation)
Function of the epididymis tail?
warehouse & shipping
- storage (10-50x10^9 spermatozoa)
- spermatozoa for 5-10 ejaculations
- smooth muscle contractions upon sexual stimulation
Function of the accessory sex glands?
final alterations & packaging (remove inhibitory signals on sperm & feed them)
- metabolic substrates
- surface coatings
- transport for spermatozoa
Function of the penis?
delivery system (with accessory sex glands)
- erection
- protrusion
- emission
- ejaculation
Testis tissue has to be how much cooler than body temperature for normal sperm production?
4-6 degrees C
Cooling is a function of:
- cremaster muscle, scrotal skin, tunica dartos, vascular counter current
- move the testis closer & further from the body as needed
- bottom of the scrotum is a lot cooler
what is the pampiniform plexus?
venous network wrapped around the testicular artery
What is the pampiniform plexus effective in?
- heat exchange
- pulse pressure reduction
- transfer of testosterone
What is the pulse pressure in the spermatic cord?
- there is a difference in pulse pressure in the testicular artery above & below the pampiniform plexus
- the mechanism & functional significance for this reduction is not clear
- potentially b/c testicular artery becomes more elastic?
- testicular artery @ bottom has same mean pressure as @ top but waay smaller fluctuations in pressure (hypothesized to prevent damage)
How temperature sensitive is the scrotum?
resp rate is 10x higher w/ 10 degree increase in temperature applied to scrotum
Where are the rete testis located in Sw & bulls?
- centrally
Where are the rete testis located in Eq & humans?
- more superficial
What are Leydig (interstitial endocrine) cells?
- produce testicular androgens (& lots of estrogen in Se & Eq)
- occupy approximately: 1% in Rams, 5% in bulls, & 20-30% in Sw of the volume of the testis
- display typical steroid producing cell features (a lot of lipids)
- large polymorphous acidophilic cells w/ round nucleus
What are the 3 distinct populations of Leydig cells during testicular development?
- Fetal Leydig cells (from sex determination to shortly after birth)
- Infantile/Early Postnatal Leydig cells (only in some spp - primates, sw, bull; very short lived)
- Adult Leydig Cells (from puberty through adult life; remain & produce testosterone for that animal)
These populations come & go and then are replaced by the next one
What are seminiferous cords & tubules?
- convoluted double-ended loops (total ~2 m in mice, ~ 5 km in bulls)
- consist of lamina propria, Sertoli cells, & spermatogenic cells
- lamina propria is made up of a basal lamina (collagen & other ECM) surrounded by peritubular cells
- cords are immature, lack a lumen, ~70-90 micrometers in diameter, & are made up of Sertoli & gonocytes
- tubules are more developed, have a lumen, ~150-300 micrometers, & are made up of Sertoli & multiple generations of germ cells
What are peritubular myoid cells?
- 1-5 layers of contractile cells that surround the basal lamina
- contain abundant actin filaments & cytoskeleton proteins
- resemble myofibroblasts (ex: in bull) or smooth muscle fibers (ex: in boar)
- their contractile action assists in the propulsion of sperm & testicular fluid along the lumen of seminiferous tubules toward rete testis
What are Sertoli (sustentacular) cells?
- have oval nucleus w/ a prominent nucleolus near base
- adult cells differ from fetal/early postnatal & lose mitotic capability
- large elongated cells w/ irregular outlines touching basal mb, & laterally & apically fill space among germ cells
- evenly spaced in tubule (~20 cells per cross section)
- provide nutrients & signals to dividing germ cells
- move germ cells along to lumen
- secrete testicular fluid into lumen for sperm transport
- phagocytize faulty germ cells & their excess cytoplasm
- produce chemical mediators to regulate spermatogenesis
What 2 types of specialized junctional complexes do Sertoli cells form?
- SERTOLI-SERTOLI TIGHT JUNCTION btwn adjacent cells (S1 & S2) forms BLOOD-TESTIS BARRIER & divides tubules into BASAL & ADLUMINAL COMPARTMENTS
- it opens like a zipper to allow germ cells to pass from basal to adluminal compartment before meiosis to protect them from the immune system
- SERTOLI-SPERMATID JUNCTIONAL specialization w/ spermatid nucleus (S2 & N)
- both characterized by bundles of microfilaments
What is a gonocyte?
part of male germline stem cells (germ cells that come after primordial germ cells (PGCs) & before spermatogonial stem cells (SSCs)
What is the origin of gonocytes?
- 1st appear @ ~13.5 dpc in rodents & 7 wk of gestation in human embryos (their development is hormone independent)
- they appear when testis cords are formed & PGCs have lost alkaline phosphatase (AP) activity & adopted male germ cell fate
How are gonocytes classified?
- mitotic fetal gonocytes = multiplying (M)-prospermatogonia
- quiescent gonocytes = primary transitional (T1)-prospermatogonia
- mitotic postnatal gonocytes = secondary transitional (T2)-prospermatogonia
What are mitotic fetal gonocytes?
multiplying (M)-prospermatogonia
- immediately after PGCs & before mitotic arrest
- proliferate from 13.5 to 18 dpc in rodents or @ 18 wk of gestation in human embryos
- then become quiescent
What are quiescent gonocytes?
primary transitional (T1)-prospermatogonia
- distinctively large round cells. w/ 1 or 2 nucleoli in a prominent nucleus
- in transition to A-spermatogonia but in the center of cords
- start after mitotic arrest & until 1-2 days (rodents) or wk/mo after birth (depending on spp)
What are mitotic postnatal gonocytes?
secondary transitional (T2)-prospermatogonia
- in transition to A-spermatogonia, residing @ basement mb
- T1-prospermatogonia develop pseudopods, migrate to the basement mb, resume mitosis, & differentiate into T2-prospermatogonia
- failing to develop pseudopods lead to apoptosis & potentially even testicular cancer in young men
- start @ 1-4 days postnatally in rodents or ~8 wk after birth in infant boys
How does gonocyte mal-development lead to testicular cancer?
- Testicular germ tumours (TGTs) are derived from in situ germ cell neoplasia (GCNIS) previously called in situ carcinoma (CIS)
- TGTs are thought to be caused by a combination of negative environmental & genetic factors (multifactorial & polygenic)
- key pathogenic element is inadequate masculinization & deterioration of fetal somatic testicular (Leydig & Sertoli cells) fxns
Normal development pathway:
PGC -> migration -> in fetal testis: Gonocyte w/ normal Sertoli & Leydig cell fxn -> birth -> in prepubertal testis: spermatogonia -> puberty -> (in adult testis: spermatocytes -> spermatids)
Impaired development pathway:
PGC -> migration -> (in fetal testis: gonocyte w/ impaired Sertoli or Leydig cell fxn due to environmental insults or gene mutations -> arrest) -> birth -> (in prepubertal testis: delayed gonocyte “pre-GCNIS” -> “adaptation”: genomic aberrations) -> puberty -> (in adult testis: GCNIS w/ invasive capacity -> (proliferation -> SEMINOMA) OR (re-programming -> EC (epididymal cyst) somatic differentiation -> NONSEMINOMAS)
