Male repro physiology Flashcards
1
Q
what do testes consist of
A
- seminiferous tubules (sperm production)
- interstitial tissue (vessels, nerves, lymphatics leydig cells - testosterone)
- sperm transport duct system (straight tubules, rete testis, efferent ducts)
2
Q
seminiferous tubules info
A
- convoluted, fluid filled, empty into rete testis
- not penetrated by blood vessels or lymphatics
- basement membrane with myoid cells –> peristaltic contractions to move sperm
- inside: sertoli cells and germ cells (seminiferous epithelium)
3
Q
seminiferous epithelium
A
- sertoli cells and germ cells (various stages of development)
- least differentiated at basement membrane, most differentiated near lumen
- sertoli cells surround and nurture developing germ cells
- germ cells develop as a clone (synchronously)
4
Q
steps in spermatogenesis (formation of spermatozoa)
A
- cellular proliferation by repeated mitotic divisions
- entry into meiosis with chromosome duplication, genetic recombination by crossing over, and then meiotic reduction divisions to give haploid spermatids
- terminal differentiation of spermatids to spermatozoa
5
Q
3 stages associated with differently named intermediate sperm cell types
A
- proliferation: spermatogonia (mitosis)
- meiosis: spermatocytes
- differentiation: spermatide
6
Q
proliferation (mitosis)
A
- germ cells adjacent to basement membrane are type A spermatogonia
- only undergo division when signaled to do so
- once committed to spermatogeneic pathway, course is irreversible
- one remains on basement membrane
- divide by mitosis, remain linked to resulting cells –> communicate to divide synchronously
- several mitotic divisions before becoming type B spermatogonia –> meiosis
- resting spermatogonia on BM signaled to divide by mitosis –> process repeats
- spermatogenic cycle –> timed repeat of cell associations
7
Q
meiosis
A
- each 2N primary spermatocyte undergoes meiosis –> generation of 4 haploid spermatids
- first meiosis is long –> 1N2C secondary spermatocyte
- second meiosis is faster –> haploid spermatid
- even division of cytoplasm
- spermatocytes!
8
Q
differentiation (spermiogenesis)
A
- -long phase of terminal differentiation where haploid round spermatid undergoes changes to form spermatozoa
- nucleus elongates, chromatin condenses
- golgi produces granules that coalesce to form acrosomic vesicle –> acrosome
- pair of centrioles migrate to nucles and bind, form axoneme –> core of tail
- mitochondria migrate to proximal tail –> spiral pattern of midpieve (motility)
- spermatid loses large amounts of cytoplasm –> forms residual body (phagocytosed)
- spermatid tethered to its residual body by cytoplasmic stalks attached to neck region
9
Q
release of spermatids (spermiation)
A
- release of spermatids from its tether
- released cell is a spermatozoa
- remnant of cytoplasm where it was attached is located in mid-piece region –> cytoplasmic droplet
10
Q
functions of apoptosis in spermatogenesis
A
- keeping the number of germ cells to a level the sertoli cells can support (~30 each)
- removal of defective sperm at quality check points (fauly meiosis)
11
Q
where does bulk of sperm loss occur
A
during meiosis –> up to 75% become apoptotic
12
Q
functions of sertoli cells
A
- organize clones of germ cells
- support cells and ensure their timely release as spermatozoa
- secrete controlling factors to regulate germ cell differentiation and maturation, phagocytose degenerating cells
- produce angroen-binding protein into lumen of seminiferous tubule
- form tight junctions in blood-testis barrier
- major source of estrogen in males
13
Q
hypothalamo-pituitary testicular axis
A
- hypothalamic GnRH releases LH/FSH from AP
- LH acts on leydig cells –> increase T synthesis/secretion (also produce estrogen)
- FSH acts on sertoli cells (support, seminiferous tubule growth, androgen-binding protein production, conversion of testosterone to estradiol in sertoli cells)
- in sertoli cells, T converted to DHT –> both can bind to ABP (maintains high levels of hormones in seminiferous tubules)
- T and estradiol feedback on hypothalamus to reduce GnRH secretion
- T inhibition acts on pituitary to reduce FSH secretion
14
Q
hormonal control of spermatogenesis
A
- T levels in testicular interstitial fluid, seminiferous tubule much higher than peripheral blood (25-30x)
- high T levels required for normal spermatogenesis
- T works through actions on sertoli cells by maintaining binding of sertoli cell to developing sperm cell stages (pachytene spermatocyte, early spermatid)
- FSH required for initiation of spermatogenesis at puberty, can maintain spermatogenesis by increasing number of spermatogonia and promoting maturation through meiosis to round spermatig stage (but can’t do spermiogenesis)
- T required to complete the process
- roles for FSH and T actions in preventing cell death
15
Q
blood-testis barrier
A
- fluid in seminiferous tubules, rete testis very different
- more developed spermatozoa express protein antigens that the immune system doesn’t recognize as self
- must maintain fluid differences and immune compartmentalization
- formed by tight junctions between adjacent sertoli cells –> divide seminiferous epithelium into basal and adluminal compartments
- as germ cells divide and enter meiosis, they move away from basement membrane towards lumen of tubule
16
Q
testicular temperature control
A
- maintain below body temperature for normal spermatogenesis
- scrotal skin is free of hair/sparsely covered
- scrotum has abundant sweat glands
- tunica dartos (smooth mm) can raise/lower testes
- cremaster mm raise and lower for sudden variations
- arterial supply and vascular drainage forms counter-current heat exchange –> artery very coiled, veins form pampiniform plexus of interconnected vessels –> cool blood from scrotum cools blood in artery before it enters testicle
17
Q
effects of elevated temp on spermatogenesis
A
- most sensitive are spermatocytes and early round spermatids
- leydig cells more resistant than sertoli
- sperm already in epididymis fairly resistant –> appear in ejaculate for a week or so
- after this will see deleterious effects for a month if minor, longer for severe damage (entire duration of spermatogenesis plus epididymal transit time)
