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VET 410: Reproduction > Male Physiology & Fertility > Flashcards

Male Physiology & Fertility Flashcards

1
Q

HPT axis

A

GnRH –> LH & FSH –>
- LH –> leydig –> testosterone
- FSH –> sertoli –> AMH + inhibin B

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2
Q

feedback loops in HPT axis

A

short: inhibin B inhibits FSH
long: testosterone inhibits GnRH

no feedback: AMH does NOT participate in feedback

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3
Q

what type of feedback loops are used in the male HPT axis

A

negative feedback loops

testosterone binds ARs on KNDy neurons –> decrease GnRH

testosterone converts to estradiol which binds to ERs –> decrease GnRH

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4
Q

what to Sertoli cells secrete

A

estrogen
AMH
inhibin B
ABP (androgen binding protein)

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5
Q

where are Sertoli cells located

A

near the basement membrane (basal compartment) of seminiferous tubules

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6
Q

androgen binding protein (ABP)

A

concentrates testosterone in the seminiferous tubules for spermatogenesis

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7
Q

what do Leydig cells secrete

A

testosterone and estrone sulphate

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8
Q

where are Leydig cells located

A

in the interstitium between seminiferous tubules

separated from developing sperm due to connection to blood vessels

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9
Q

primordial germ cells (PGCs)

A

progenitors for spermatogenesis

do NOT secrete hormones

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10
Q

what stimulates and initiates spermatogenesis

A

local testosterone production by leydig cells

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11
Q

how do LH and FSH support the local androgenic environment

A

LH stimulates leydig cells to produce testosterone

FSH stimulates Sertoli cells to produce ABP to concentrate androgens in tubules

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12
Q

type A spermatogonia

A

diploid cells that divide via mitosis along the basement membrane of the seminiferous tubules

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13
Q

how long are mitotic cycles of type A spermatogonia

A

12 days long
(a new type A cell will divide every 12 days)

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14
Q

type B spermatogonia

A

diploid primary spermatocyte (the daughter cell of type A mitosis that separates from the basement membrane and begins traveling toward adluminal compartment)

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15
Q

how does the type B spermatogonia divide

A

undergoes meiosis to produce a haploid secondary spermatocyte which crosses the Sertoli cell tight junctions to enter the luminal compartment

continues dividing via meiosis until spermatozoa is produced

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16
Q

how often does the tubular release of spermatozoa occur

A

every 50-60 days

(4-5 mitotic cycles will have occurred on the basement membrane by the time the first sperm is released)

17
Q

what does the daily sperm production depend on

A

the number of Sertoli cells

(which is determined by proliferation during fetal/neonatal development)

18
Q

what regulates spermatogenesis

A

pulsatile secretion of GnRH

(will stimulate LH –> testosterone)

19
Q

what happens if GnRH secretion is continuous instead of pulsatile

A

continuous GnRH inhibits LH and testosterone secretion

ultimately decreases spermatogenesis

20
Q

how does bilateral castration affect levels of testosterone, GnRH, LH, and FSH

A
  1. removal of testes –> initial decrease in testosterone
  2. low testosterone stimulates GnRH secretion –> increases LH/FSH
  3. lack of testes prevents an increase in testosterone, which results in no spermatogenesis

low testosterone
high GnRH, LH, FSH

21
Q

how would injecting testosterone into a bilaterally castrated male affect GnRH, LH, and FSH concentrations

A

decreases GnRH, LH, and FSH

22
Q

how would injecting inhibins into a bilaterally castrated male affect GnRH, LH, and FSH

A

only affects short feedback loop

decreases FSH
unaffected GnRH, LH (still high)

23
Q

how does unilateral castration affect levels of testosterone, GnRH, LH, and FSH

A
  1. removal of a single testis –> initial decrease in testosterone
  2. low T stimulates GnRH, LH, and FSH
  3. remaining testis responds to high LH/FSH to increase testosterone production (hypertrophy)
  4. increased testosterone production increases spermatogenesis

causes compensatory hypertrophy of the contralateral testis

24
Q

what does the degree of compensation depend on

A

the number of Sertoli cells (the amount of increase in sertoli cell number)

25
Q

are young/old animals able to compensate better in seasonal vs nonseasonal species

A

seasonal: older
nonseasonal: younger

26
Q

how do functional sertoli and leydig cell tumors affect GnRH, LH, FSH

A

functional tumors secrete estrogen (sertoli) and testosterone & estrogen (leydig) –> decreases GnRH, LH, FSH –> inhibits local testosterone production from contralateral testis

results in atrophy of the contralateral testis

27
Q

cryptorchidism

A

failure of one or both testes to descend

highly heritable, can be estrogen induced or inter-sex associated

28
Q

how do you test for cryptorchidism

A

AMH levels (expect elevated AMH in cryptorchids)

can also test testosterone and inhibin (expect elevated)

29
Q

normal testicular descent

A
  1. testicles migrate across the abdomen to the inguinal ring (independent of androgens)
  2. gubernaculum regresses and draws testicles through the inguinal ring to the scrotum (dependent on androgens)
  3. inguinal ring closes

**testes able to move through inguinal ring until completely closed

30
Q

5-5-5 rule

A

age-based rule used in dogs

day 5: testes pass through inguinal ring
week 5: testes descend into scrotum
month 5: inguinal ring closes

31
Q

how does livestock testes descent differ

A

testes are located in the inguinal canal or scrotum at birth

ring closes in the first few weeks of life

32
Q

cryptorchid testicular descent

A
  1. testicles migrate across the abdomen to the inguinal ring (usually occurs b/c androgen independent)
  2. estrogen presence causes gubernaculum to swell and prevents regression; prevents testis from migrating through inguinal ring
33
Q

where are most cryptorchid testes located

A

near the inguinal ring

VET 410: Reproduction (24 decks)

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