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ANIMAL PRODUCTION - Reproduction > 4 - Male Reproduction II > Flashcards

4 - Male Reproduction II Flashcards

1
Q

Spermatogenesis is subdivided into

A
  1. Proliferation: spermatoCYTOgenesis
  2. Differentiation: spermiogenesis
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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
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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
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4
Q

Two proposed models for formation of SSCs from gonocytes

A
  1. 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
  2. Different types of gonocytes are responsible for forming SSC pool, initial progenitor population and initial differentiating spermatogonial population
    a. MORE LIKELY
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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
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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
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7
Q

Apair and Aaligned

A
  • Transit amplifying progenitor cells
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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)
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9
Q

B-spermatogonia

A
  • Must physical pass thru blood-testis barrier before further germ cell differentiation
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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)
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11
Q

5 stages that primary spermatocytes go thru:

A
  • Preleptotene
  • Leptotene
  • Zygotene
  • Pachytene
  • Diplotene
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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
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13
Q

Spermiogenesis

A
  • Testosterone drives round spermatids to undergo extensive morphological differentiation
  • *leads to formation of elongating/elongated spermatids
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14
Q

Spermiation process

A
  • RA causes spermatozoa to be released into LUMEN of seminiferous tubules
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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
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16
Q

4 phases of differentiation (spermiogenesis)

A
  1. Golgi phase
  2. Cap phase
  3. Acrosomal phase
  4. Maturation phase
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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
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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
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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
Q

Spermatozoon structure : tail

A

o Capitulum
o Middle piece
o Principal piece
o Terminal piece

26
Q

Post nuclear cap

A
  • Has fibrous sulphur rich proteins
27
Q

Acrosome

A
  • Membrane covered lysosome containing hydrolytic enzymes
28
Q

Acrosome reaction

A
  • During fertilization acrosome undergoes a specialized EXOCYTOSIS
29
Q

Post acrosomal sheath region

A
  • Contains receptors for recognition of homologous oocyte
30
Q

Capitulum

A
  • Fits into implantation socket of head
31
Q

Middle piece

A
  • 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
Q

Principle piece

A
  • Forms majority of tail
  • Continues to almost end of flagellum
33
Q

Terminal piece

A
  • Where only microtubules remain
34
Q

Stages of spermatogenesis

A
  • 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
Q

Stages along tubule

A
  • Different stages can be seen at any given cross-section along a seminiferous tubule
  • Each stage follows or precedes adjacent stages
36
Q

Spermatogenic wave

A
  • Complete sequence of stages along a length of tubule
  • 10mm long in bull
37
Q

LH and Testosterone

A
  • Each LH pulse drives a pulse of T release by Leydig cells
  • Each remain high in serum for 0.5-1hr
38
Q

Hormonal regulation of spermatogenesis

A
  • FSH
  • LH
  • T and inhibin
39
Q

FSH regulation of spermatogenesis

A
  • 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
Q

LH regulation of spermatogenesis

A
  • Acts on Leydig cells to stimulate production of testosterone
41
Q

T and inhibin

A
  • Act thru negative feedback to temporarily inhibit further release of GnRH, FSH and LH
42
Q

Testosterone

A
  • 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
Q

T withdrawal and lack of androgen receptors car result in

A
  • Lack of post-meiotic germ cells
44
Q

Androgen receptors

A
  • Absent in germ cells
  • Abundant in Sertoli, peritubular myoid and Leydig cells
    o E2 is converted from T by aromatase in Sertoli cells
45
Q

Lack of ER alpha or aromatase leads to

A
  • Spermatogenesis impairment in mice

ANIMAL PRODUCTION - Reproduction (17 decks)

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