4 - Male Reproduction II Flashcards
1
Q
Spermatogenesis is subdivided into
A
- Proliferation: spermatoCYTOgenesis
- Differentiation: spermiogenesis
2
Q
Spermatogenesis: basal to aluminal
A
- Proliferation: A1 to A2 to A3 to A4 to I to B
- Meiosis: Primary spermatocytes to secondary spermatocytes
- Differentiation: spermatids
3
Q
Spermatogonial stem cells (SSCs)
A
- Can self-renew and produce differentiated germ cells
- *only adult SCs that can pass on genes to next generation
4
Q
Two proposed models for formation of SSCs from gonocytes
A
- All gonocytes are the same, but randomly some transition to SSCs=can renew and give rise to PROGENITORS
a. Others directly give rise to differentiating spermatogonia - Different types of gonocytes are responsible for forming SSC pool, initial progenitor population and initial differentiating spermatogonial population
a. MORE LIKELY
5
Q
Potential outcomes of SSC division
A
- Symmetrical self-renewal: during neonatal development and regeneration after cytotoxic insult
- Steady state spermatogenesis: Balance of symmetrical self-renewal and symmetrical differentiation:
- Asymmetric division: produce 1 new SSC and 1 transient amplifying progenitor
6
Q
Undifferentiated spermatogonia
A
- Spermatogonia type A single (As)=true SSCs
- 2 new As for self-renewal or Apair
- Aaligned (chains of 4, 8 or 16 cells)
- *similar morphology
7
Q
Apair and Aaligned
A
- Transit amplifying progenitor cells
8
Q
Differentiating spermatogonia
A
- RA causes Aaligned to transition (w/o cell dividson) to A1
- Then 5 synchronized cell divisions, A2, A3, A4, intermediate & B-spermatogonia)
9
Q
B-spermatogonia
A
- Must physical pass thru blood-testis barrier before further germ cell differentiation
10
Q
Primary spermatocytes
A
- Once in adluminl compartment, B-sp divide to produce 2 primary sp that immediately enter 1st phase of meiosis
o Long prophase of 1st meiosis: DNA forms tetrads, followed by cross over - Goes through 5 stages
- *at end: has produced 2 secondary sp (haploid)
11
Q
5 stages that primary spermatocytes go thru:
A
- Preleptotene
- Leptotene
- Zygotene
- Pachytene
- Diplotene
12
Q
Secondary spermatocytes
A
- Relatively short-lived
- Immediately undergo second meiotic division
- *at end has produced 2 haploid ROUND (spherical) spermatids
o No further cell division will occur
13
Q
Spermiogenesis
A
- Testosterone drives round spermatids to undergo extensive morphological differentiation
- *leads to formation of elongating/elongated spermatids
14
Q
Spermiation process
A
- RA causes spermatozoa to be released into LUMEN of seminiferous tubules
15
Q
Changes that occur to turn a round spermatid into a sperm
A
- Formation of acrosome
- Condensation of nuclear materia
- Outgrowth of motile tail
- Loss of excess cytoplasm, organells, water
16
Q
4 phases of differentiation (spermiogenesis)
A
- Golgi phase
- Cap phase
- Acrosomal phase
- Maturation phase
17
Q
Golgi phase (spermiogenesis)
A
- Golgi vesicle s fuse=proacrosomic secretory granules
- Centrioles migrate to opposite sides
- Acrosomal vesicle is formed
- Proximal centriole: attachment point of tail
- Distal centriole: axoneme
18
Q
Cap phase (spermiogenesis)
A
- Golgi migrate to caudal pole
- Distal centriole: axoneme or flagellum
- Acrosomic vesicle flattens and begins to form a cap
19
Q
Cap
A
- Outer acrosomal membrane
- Inner acrosomal membrane
- Enzymes
20
Q
Acrosomal phase (spermiogenesis)
A
- Nucleus elongates
- Acrosome convers most of anterior
- Manchette forms from caudal half and extends down
- Neck and annulus are formed
- All components still within cytoplasm
21
Q
Maturation phase (spermiogenesis)
A
- Mitochondria form a SPIRAL assembly around flagellum=middle piece
- Postnuclear cap formed from manchette microtubules
- Annulus forms JUNCTION between middle piece and principle piece
22
Q
Spermatozoon structure
A
- Vary in length (longest in rodents)
- Under light microscope: head and tail
23
Q
Spermatozoon structure : head
A
o Different species
o Spatula except sickle shaped in rodents
24
Q
Spermatozoon structure : nucleus
A
o Oval
o Flat
o Covered by nuclear membrane
o Anterior 2/3rd covered by acrosome
25
Spermatozoon structure : tail
o Capitulum
o Middle piece
o Principal piece
o Terminal piece
26
Post nuclear cap
* Has fibrous sulphur rich proteins
27
Acrosome
* Membrane covered lysosome containing hydrolytic enzymes
28
Acrosome reaction
* During fertilization acrosome undergoes a specialized EXOCYTOSIS
29
Post acrosomal sheath region
* Contains receptors for recognition of homologous oocyte
30
Capitulum
* Fits into implantation socket of head
31
Middle piece
* Laminated columns (side to side flexibility to neck)
* 9 coarse outer fibers
* Axoneme composed of 9 pairs of microtubules (doublets) around 2 central filaments
* All covered by a helical mitochondrial sheath
32
Principle piece
* Forms majority of tail
* Continues to almost end of flagellum
33
Terminal piece
* Where only microtubules remain
34
Stages of spermatogenesis
* Should be continuous in non-seasonal males
* Before 1 is complete, generally 4 new series are initiated
* All descendants of B-sp develop synchronously
* ‘predictable’ intervals
* Ex. 8 stages in bulls, rams and pigs
35
Stages along tubule
* Different stages can be seen at any given cross-section along a seminiferous tubule
* Each stage follows or precedes adjacent stages
36
Spermatogenic wave
* Complete sequence of stages along a length of tubule
* 10mm long in bull
37
LH and Testosterone
* Each LH pulse drives a pulse of T release by Leydig cells
* Each remain high in serum for 0.5-1hr
38
Hormonal regulation of spermatogenesis
* FSH
* LH
* T and inhibin
39
FSH regulation of spermatogenesis
* Acts on Sertoli cells to promote their function & facilitate spermatogenesis
* Increases PROLIFERATION of spermatogonia
* Within tubules, receptors only found on Sertoli cells (indirect FSH effects on germ cells)
* Little or no direct effect on completion of meiosis and spermatogenesis
40
LH regulation of spermatogenesis
* Acts on Leydig cells to stimulate production of testosterone
41
T and inhibin
* Act thru negative feedback to temporarily inhibit further release of GnRH, FSH and LH
42
Testosterone
* Crucial for transition of spermatocytes to spermatids
* Counter-current system of pampiniform plexus: T in testis is 100-500x higher than in circulation
* Effect on germ cells is INDIRECT and mediate thru somatic cells
43
T withdrawal and lack of androgen receptors car result in
* Lack of post-meiotic germ cells
44
Androgen receptors
* Absent in germ cells
* Abundant in Sertoli, peritubular myoid and Leydig cells
o E2 is converted from T by aromatase in Sertoli cells
45
Lack of ER alpha or aromatase leads to
* Spermatogenesis impairment in mice
