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)
18
Q
spermatozoa structure
A
- contain ~50% water
- 3 main regions: head, mid piece, principal piece
19
Q
sperm head
A
- consists mostly of nucleus and acrosome, some cytoskeletal elements, scant cytoplasm
- head is flattened “spatulate”
- shape and size varies
20
Q
sperm nucleus
A
- haploid DNA
- DNA highly condensed
- protamines replace histones, lots of disulfide bonds
- nuclear envelope has few pores
21
Q
sperm acrosome
A
- derived from golgi
- forms a cap over apical 1/2-2/3 of nucleus
- between nuclear membrane inside, sperm plasma membrane outside
- shape and size are species dependent
- contains complex array of proteins and enzymes (acrosin, hyaluronidase) –> protein receptors
22
Q
sperm equatorial segment
A
- area where caudal part of acrosome thins
- acrosome at this point does not contain enzymes
- plasma membrane of equatorial region fuses with oocyte at fertilization
23
Q
sperm tail
A
- propeller –> provides force of locomotion, egg penetration
- 4 sections: connecting piece, middle piece, principal piece, end piece
- structural components: axoneme, outer dense fibers, mitochondrial sheath, fibrous sheath, plasma membrane
24
Q
sperm axoneme
A
- consists of microtubules, runs down center of entire tail
- 2 central microtubules are surrounded by 9 microtubule doublets –> radial spikes connect central pair to outer doublets
- dynein, nexin (proteins) important for generating force required for axonemal sliding and thus movement
25
sperm outer dense fibers
- 9 dense fibers, one outside and adjacent to each of 9 outer microtubule doublets
- extend through mid piece, for variable length down principal piece
- provide stiffening and elastic recoil (not force generation)
26
sperm mitochondrial sheath
- confined to middle piece, helically arranged around outer dense fibers
- number and arrangement (length of middle piece) varies between species
- use oxidative phosphorylation to provide some (not all) ATP needed for sliding the axonemal microtubules in force generation
27
sperm fibrous sheath
- when mitochondrial wrapping ceases at end of middle piece, it is replaced by fibrous sheath that extends the length of the principal piece
- located outside dense fibers until they disappear
- unique to mammals, some birds
- 2 longitudinal columns connected by transverse ribs
- regulates spatial plane in which the tail beats
- acts as structural site anchoring many enzymes involved in production of ATP by gycolysis
28
sperm end piece
- axoneme tapers and finally terminates
| - consists only of tapering axoneme covered by plasma membrane
29
sperm plasma membrane
- covers entire sperm
- highly specialized and vital for normal sperm physiology and events of fertilization
- divided functionally, structurally, and biochemically into different regions with different tasks
- part over midpiece has proteins important for mitochondrial ATP production, part over head has proteins and lipids important for fertilization
- composition further modified during transit through epididymis and in female repro tract
- damage to plasma membrane responsible for adverse effects of exposing sperm to cold temps
30
overview of sperm transport
- released at spermiation
- carried through seminiferous tubule and into rete testis
- fluid movement aided by peristalsis of tubules in response to oxytocin secretion by leydig cells
- from rete testis, suspension moved through efferent ducts into proximal epididymis
31
what species have epididymis
vertebrates that practice internal fertilization (mammals, reptiles, birds)
32
functions of epididymis
- connects efferent ducts to vas deferens
- transports, protects, sustains, matures, stores spermatozoa (specialized internal environment_
- caput, corpus, cauda
- initial segment: fluid resorption
- middle segment: sperm maturation
- terminal segment: sperm storage
33
fluid resorption
- most fluid leaving testis resorbed in efferent ducts and proximal epididymis
- raises osmotic pressure, sperm become partly dehydrated
34
fluid secretion
- occurs on a regional basis
- resorptive functions and secretion of specific products --> changing environments for sperm --> sequential maturational changes of sperm
35
sperm movement through epididymis
- don't swim --> moved passively through caput and corpus by fluid flow
- induced by continuous peristaltic contractions of the wall
- rate of movement is not influenced by the frequency of ejactulation
- takes 7-14d
36
sperm storage
- cauda epididymis is major site
- ejaculation frequency can alter amount of time spend in the cauda
- cannot increase sperm output by increasing frequency of ejaculation beyond a certain point
- can be stored in fertile state for up to 1 month in cauda
37
hormones influencing epididymis
androgen dependent (DHT)
38
sperm maturation
- sperm are infertile when they leave testis but fertile by the time they are stored in epididymal tail
- gain fertility in process called sperm maturation
- acquire potential for motility
- change in cell surface electrical charge (carb/protein content change)
- alteration of plasma membrane lipids
- movement of cytoplasmic droplet from neck to distal part of midpiece
39
maintaining sperm in metabolic quiescence in storage
- low Na content in bathing fluid (keep pH low)
- high sperm concentration (movement restriction)
- viscous mucoprotein (movement restriction)
- cell permeating acids (keep pH low)
- high pCO2 and sperm dehydration
40
preventing premature sperm activation in storage
- need to be activated before fertilizing egg
- if activated too early, will be incapable of reaching fertilization site or incapable of fertilizing egg
- secretion by epididymis of proteins that coat sperm membranes and stabilize them --> decapacitation factors
- clumping of sperm is protective
41
vas deferens
- extension of epididymis from cauda to pelvic urethra
- thick smooth muscle wall
- may widen near urethra to form ampulla
42
accessory sex glands
- supply bulk of fluid to ejaculate (seminal plasma)
| - ampulla, seminal vesicles, prostate, bulbourethral gland
43
functions of accessory gland fluids (7)
- activation of sperm motility (dilution)
- buffering capacity (alkaline)
- nutrient supply (glucose)
- stimulate uterine contractions (prostaglandin)
- clean urethra
- plug cervix
- decapacitating factors (glycoproteins to stabilize)
