Physiology

Question 1

describe the hypothalamic-pituitary-gonadal axis (HPG)

Answer 1

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

Question 2

how is GnRH released from the hypothalamus?

Answer 2

pulsatile manner

Question 3

what does GnRH act on in the anterior pituitary?

Answer 3

kisspeptin receptors

Question 4

what does oestrogen concentration above a certain threshold cause?

Answer 4

increases GnRH pulses driving release of LH

Question 5

what does an increase in progesterone cause?

Answer 5

reduces the frequency of GnRH pulses causing release of FSH

Question 6

what does LH surge underpin?

Answer 6

ovulation

Question 7

what is corpus luteum formed from?

Answer 7

FSH (lipids) which produces progesterone

Question 8

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

Answer 8

LH

Question 9

what happens if a developing embryo is not present?

Answer 9

levels of progesterone decrease

Question 10

FSH (follicle stimulating hormone) causes what in males?

Answer 10

spermatogenesis

Question 11

FSH causes what in females?

Answer 11

oogenesis (growth of ovarian follicles)

secretion of oestrogen

Question 12

what happens if oestrogen reaches a certain concentration?

Answer 12

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)

Question 13

role of progesterone

Answer 13

decreases pulsatility decreasing LH secretion

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

Question 14

which anterior pituitary hormone acts on the theca cell?

Answer 14

LH

Question 15

which anterior pituitary hormone acts on the granuloma cell?

Answer 15

FSH

Question 16

role of LH (luteinising hormone) in males

Answer 16

secrete testosterone

Question 17

role of LH in women

Answer 17

ovulation

progesterone production by corpus luteum

Question 18

how early does the LH surge precede ovulation?

Answer 18

24-36 hours

Question 19

when does progesterone peak?

Answer 19

following ovulation produced by the corpus luteum

Question 20

what is the onset of puberty due to?

Answer 20

steady acceleration in GnRH pulsatility

Question 21

two phases in the menstrual cycle

Answer 21

follicular/proliferative phase

luteal/secretory phase

Question 22

what does an ovarian follicle consist of?

Answer 22

an oocyte surrounded by granuloma and theca cells

Question 23

role of theca cells

Answer 23

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

Question 24

when does the follicular phase of the menstrual cycle begin?

Answer 24

menstruation

Question 25

hone does levels of GnRH increase?

Answer 25

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

Question 26

LH role

Answer 26

causes theca cells to produce androgens

Question 27

FSH role

Answer 27

stimulates granuloma cells to convert androgens to oestrogen

Question 28

does oestrogen levels rise in the follicular phase

Answer 28

yes

Question 29

what does FSH do during menstruation

Answer 29

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

Question 30

what happens during ovulation (day 12-14)

Answer 30

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

Question 31

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

Answer 31

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

Question 32

what do high levels of progesterone do?

Answer 32

inhibit FSH/LH

Question 33

describe menstruation

Answer 33

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.

Question 34

what secretes oestrogen

Answer 34

ovaries adrenal cortex placenta in pregnancy

Question 35

what does oestrogen do to the body?

Answer 35

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

Question 36

what does high oestrogen inhibit?

Answer 36

secretion of FSH and prolactin (negative feedback)

Question 37

what secretes progesterone?

Answer 37

corpus luteum

Question 38

role of progesterone

Answer 38

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

Question 39

where does spermatogenesis take place?

Answer 39

seminiferous tubules

Question 40

what do the seminiferous tubules contain?

Answer 40

Sertoli cells and maturing germ cels surrounded by peritubular hyoid cells

Question 41

what do Sertoli cells do?

Answer 41

hold and respond to FSH | testosterone is released into the circulation and taken up by Sertoli cells

Question 42

what does testosterone do?

Answer 42

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

Question 43

what does LH do in males?

Answer 43

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