Physiology Flashcards

1
Q

describe the hypothalamic-pituitary-gonadal axis (HPG)

A
  • hypothalamus= GnRH
  • anterior pituitary= LH (high frequency pulses) and FSH (low frequency pulses)
  • ovaries= oestrogen and progesterone
  • testes= testosterone
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2
Q

how is GnRH released from the hypothalamus?

A

pulsatile manner

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3
Q

what does GnRH act on in the anterior pituitary?

A

kisspeptin receptors

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4
Q

what does oestrogen concentration above a certain threshold cause?

A

increases GnRH pulses driving release of LH

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5
Q

what does an increase in progesterone cause?

A

reduces the frequency of GnRH pulses causing release of FSH

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6
Q

what does LH surge underpin?

A

ovulation

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7
Q

what is corpus luteum formed from?

A

FSH (lipids) which produces progesterone

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8
Q

what is hCG the same as in terms of hormones from the anterior pituitary?

A

LH

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9
Q

what happens if a developing embryo is not present?

A

levels of progesterone decrease

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10
Q

FSH (follicle stimulating hormone) causes what in males?

A

spermatogenesis

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11
Q

FSH causes what in females?

A

oogenesis (growth of ovarian follicles)

secretion of oestrogen

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12
Q

what happens if oestrogen reaches a certain concentration?

A

it no longer does negative feedback on the pituitary and hypothalamus but instead exerts positive feedback resulting in LH surge leading to ovulation and formation of the corpus luteum (progesterone)

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13
Q

role of progesterone

A

decreases pulsatility decreasing LH secretion

needed for expression of enzymes that break down the follicular wall leading to release of the oocyte

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14
Q

which anterior pituitary hormone acts on the theca cell?

A

LH

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15
Q

which anterior pituitary hormone acts on the granuloma cell?

A

FSH

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16
Q

role of LH (luteinising hormone) in males

A

secrete testosterone

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17
Q

role of LH in women

A

ovulation

progesterone production by corpus luteum

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18
Q

how early does the LH surge precede ovulation?

A

24-36 hours

19
Q

when does progesterone peak?

A

following ovulation produced by the corpus luteum

20
Q

what is the onset of puberty due to?

A

steady acceleration in GnRH pulsatility

21
Q

two phases in the menstrual cycle

A

follicular/proliferative phase

luteal/secretory phase

22
Q

what does an ovarian follicle consist of?

A

an oocyte surrounded by granuloma and theca cells

23
Q

role of theca cells

A

produce androgens (can be overstimulated by hyperinsulinaemia leading to increased free androgens) that are converted to oestrogen by granuloma cells via the enzyme aromatase

24
Q

when does the follicular phase of the menstrual cycle begin?

A

menstruation

25
Q

hone does levels of GnRH increase?

A

when the follicular phase begins (menstruation) causing an increase in FSH and LH

26
Q

LH role

A

causes theca cells to produce androgens

27
Q

FSH role

A

stimulates granuloma cells to convert androgens to oestrogen

28
Q

does oestrogen levels rise in the follicular phase

A

yes

29
Q

what does FSH do during menstruation

A

causes follicles to mature until a dominant follicle emerges which is released from the ovary and the others undergo atresia

30
Q

what happens during ovulation (day 12-14)

A

levels of oestrogen peak triggering a surge in LH which triggers ovulation and the oocyte to be released into the Fallopian tube

31
Q

what happens during the luteal phase (day 15-28)

A

the follicle develops into the corpus luteum in response to LH which produces progesterone and activates secretion from the endometrium (thickens for implantation of the fertilised egg)
increase in basal body temperature and thickness of cervical mucus

32
Q

what do high levels of progesterone do?

A

inhibit FSH/LH

33
Q

describe menstruation

A

if fertilisation does not occur, the corpus luteum degenerates causing levels of progesterone and oestrogen to drop
the arterioles undergo vasospasm which leads to necrosis and bleeding
levels of FSH and LH increase allowing cycle to begin again.

34
Q

what secretes oestrogen

A

ovaries
adrenal cortex
placenta in pregnancy

35
Q

what does oestrogen do to the body?

A

increases thickness of the vaginal wall
regulates LH surge
reduces vaginal pH through increased lactic acid production
decreases viscosity of cervical mucus to facilitate sperm penetration

36
Q

what does high oestrogen inhibit?

A

secretion of FSH and prolactin (negative feedback)

37
Q

what secretes progesterone?

A

corpus luteum

38
Q

role of progesterone

A

maintain early pregnancy until the placenta (HCG) takes over around 5-10 weeks
maintains thickness of endometrium
responsible for infertile thick mucus (infection control)
relaxes myometrium (risk of GI)
increases basal body temperature
inhibits secretion of LH

39
Q

where does spermatogenesis take place?

A

seminiferous tubules

40
Q

what do the seminiferous tubules contain?

A

Sertoli cells and maturing germ cels surrounded by peritubular hyoid cells

41
Q

what do Sertoli cells do?

A

hold and respond to FSH

testosterone is released into the circulation and taken up by Sertoli cells

42
Q

what does testosterone do?

A

maintain blood-testes barrier
spermatogenesis
releases mature spermatozoa from Sertoli cells by influencing peritubular myoid cells

43
Q

what does LH do in males?

A

it stimulates testosterone production from Leydig cells (stimulation of enzymes required for synthesis of cholesterol to testosterone)