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human development > reproductive endocrinology > Flashcards

reproductive endocrinology Flashcards

1
Q

what are the 2 groups of molecules involved in the menstrual cycle?

A

steroids

glycoproteins

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2
Q

what are steroids?

A

• Lipids with a 27 carbon skeleton

- contains four fused rings with a variety of groups attached

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3
Q

what are properties of steroids

A

small

lipophilic

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4
Q

why do steroids need to be lipophilic?

A

pass through cell membrane via simple diffusion and bind to their receptor which can be nuclear or cytoplasmic

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5
Q

what is the central core molecule to all steroids?

A

cholesterol

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6
Q

why are steroids, oestrogens, progesterone and testosterone different?

A

differences are due to functional groups attached to the four-ring structure.

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7
Q

why do males and females have different amounts of oestrogen and testosterone?

A

different number of receptors for each

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8
Q

what do binding globulins do?

A

binds to testosterone and stops it being metabolised

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9
Q

what affects the levels of binding globulins?

A

levels of oestrogens and thyroids hormones

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10
Q

what are the oestrogen molecules and describe their structures?

A

oestrone - 1x OH molecule on the end
oestradiol - 2x OH molecules
oestriol - 3x OH molecules

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11
Q

where are Leydig cells found?

A

outside the seminiferous tubules

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12
Q

where are Sertoli cells found?

A

found inside the seminiferous tubules

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13
Q

where are thecal cells found?

A

in the ovaries surrounding the oocyte

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14
Q

where is testosterone made in males and females?

A

males: Leydig cells (testes)
females: thecal cells (35%), adrenals (25%), peripheral conversion in adipose tissue (50%)

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15
Q

where is DHT made in males and females?

A

males: conversion from testosterone in Sertoli cells (testes) and target tissues
females: peripheral conversion from testosterone

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16
Q

where is progesterone made in males and females?

A

males: adrenals
females: corpus luteum (ovary), syncytiotrophoblasts (placenta), adrenals as an intermediate

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17
Q

where is oestradiol made in males and females?

A

males: peripheral conversion from testosterone (depending on presence of aromatase) e.g. adipose tissue
females: granulosa cells, peripheral conversion from testosterone, syncytiotrophoblasts

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18
Q

where is Andostenedione made in males and females?

A

males: Leydig cells, adrenals
females: ovary (50%), adrenals (50%)

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19
Q

where is DHEA made in males and females?

A

males: Leydig cells, adrenals
females: ovary (20%), adrenals (80%)

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20
Q

what enzymes does synthesis of steroids depend and where are these found?

A

Synthesis requires oxidative enzymes located in mitochondria and ER

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21
Q

what is the first step in the synthesis of steroids?

A

conversion of cholesterol –> pregnenolone

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22
Q

what does GnRH in hypothalamus stimulate?

A

FSH and luteinising hormone (LH) secretion by anterior pituitary.

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23
Q

what role does LH have in steroid synthesis in males?

A

stimulates testosterone production by Leydig cells

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24
Q

what cells do testosterone and pituitary FSH target?

A

Sertoli cells

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25
Q

what does the enzyme 5a reductase do?

A

converts testosterone to DHT in Sertoli cells

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26
Q

how do Sertoli cells stimulate to spermatogenesis?

A
  • enzyme 5a reductase converts testosterone to DHT
  • Sertoli cells then secrete androgen binding protein (ABDP)
  • Binds to testosterone + carries it to seminiferous tubule where it stimulates spermatogenesis
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27
Q

what does LH do in steroid synthesis in females?

A

• LH stimulates testosterone production by theca cells in the ovarian follicle

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28
Q

how does LH stimulate ovulation?

A

• LH stimulates testosterone production by theca cells in the ovarian follicle.
• Testosterone enters granulosa cells (surround oocyte) where it’s converted by aromatase into oestrogen (mainly 17-beta oestradiol)
• Oestradiol: stimulates formation of LH receptors on granulosa cells.
- Enables follicle to response to LH surge –> ovulation.

29
Q

describe the 2 stage model of oestrogen synthesis?

A
  • Androgen precursors are synthesised in the outer layer (theca cells) of the ovarian follicles –> Driven by LH
  • Diffuse into inner layer (granulosa cells) for conversion to oestrogens –> Driven by FSH
30
Q

what do androgens do?

A
  • Maintain male somatic tissue differentiation
  • Induce male secondary sexual characteristics
  • Support spermatogenesis
  • Influence sexual and aggressive behaviour (male & female)
  • Promote protein anabolism, somatic growth & ossification
  • Regulate gonadotrophin secretion (testosterone)
  • Induce body hair (in females – pubic & axillary)
31
Q

what do oestrogens do?

A
  • Stimulate growth of mammary gland + endometrium (mucous membrane in uterus).
  • Induce female secondary sexually characteristics.
  • Prepare uterus for spermatozoa transport
  • Increase vascular permeability
  • Mildly anabolic
  • Regulate gonadotrophin secretion
32
Q

what does luteal progesterone prepare?

A

prepares endometrium for implantation during the secondary phase of the menstrual cycle

33
Q

what body parts do progestagens affect?

A

cervix, vagina and breast

34
Q

what does placental progesterone do?

A

maintains endometrium (decidua) in pregnancy after 10-12 weeks.

35
Q

what are glycoproteins?

A

contain oligosaccharide chains covalently attached to polypeptide side-chains

36
Q

where are glycoproteins produced?

A

anterior pituitary

placenta

37
Q

where are gonadotrophs produced and by what cell?

A

anterior pituitary

gonadotrophic cells

38
Q

what are the gonadotrophs?

A
  • Luteinising hormone (LH)
  • Follicle stimulating hormone (FSH)
  • Thryotrophs (TSH)
39
Q

what cells produce glycoproteins in the placenta?

A

syncytiotrophoblast cells (epithelial covering of placental villi)

40
Q

what glycoproteins are produced by the placenta?

A

• Human chorionic gonadotrophin (hCG).

41
Q

describe the structure of gonadotrophins?

A

2 glycosylated proteins together form functional glycoprotein - alpha and beta subunits.
Alpha - 92 amino acids
beta - different

42
Q

what glycoproteins is the alpha subunit identical in?

A

FSH, LH and hCG

43
Q

how is the beta subunit different in LH and hCG?

A

o Beta subunit of LH/hCG have the same sequence of aa, stimulate same receptor. However, hCG has an additional 24 amino acids

44
Q

what does FSH do in females?

A

stimulates the growth of immature Graafian follicles in the ovary to maturity

45
Q

what does FSH do in males?

A

enhances production of androgen-binding protein by Sertoli cells of testes and is needed for spermatogenesis

46
Q

what does a surge in LH trigger?

A

ovulation

47
Q

what does LH do?

A
  • Converts residual follicle  corpus luteum.
  • Maintains the luteal phase (latter phase of the menstrual cycle).
  • Stimulates thecal cells in the ovary to produce testosterone for Oestradiol production (female)
  • Acts upon Leydig cells of the testis + is responsible for the production of testosterone (male)
48
Q

what does hCG do?

A

maintains corpus luteum in pregnancy

49
Q

what produces inhibin in males?

A

Sertoli cells

50
Q

what does inhibin do when sperm count is high?

A

inhibin secretion increases and inhibits pituitary release of FSH, hypothalamic release of GnRH.

51
Q

at what sperm count does inhibin secretion decrease?

A

<20

52
Q

what cells produce inhibin in females?

A

Granulosa cells

53
Q

what does inhibin do in females?

A

helps exert negative control on FSH production during menstrual cycle

54
Q

what is activin?

A

a glycoprotein of the transforming growth factor beta family

55
Q

what does activin do?

A

Increases FSH activity, enhances the actions of LH in both males and females

56
Q

when is relaxin produced in females?

A

produced during menstrual cycle (follicular development & oocyte maturation) and pregnancy (relaxation of ligaments and parturition).

57
Q

when is relaxin produced in males?

A

in seminal fluid to enhance sperm motility

58
Q

name peptides, the number of amino acids and the location of peptides?

A
  • Gonadotrophin releasing hormone: 10 aa, HYPOTHALAMUS
  • Growth hormone releasing hormone: 44 aa, HYPOTHALAMUS
  • Oxytocin: 9aa, HYPOTHALAMUS
  • Prolactin: 198 aa, ANTERIOR PITUITARY
59
Q

what is the menstrual cycle

A

Series of cyclic changes in the uterine endometrium

Occurs monthly in response to changes in levels of ovarian hormones

60
Q

what are the stages of the menstrual cycle?

A

menstrual phase
proliferative phase
secretory phase

61
Q

what happens in the menstrual phase?

A
  • Due to withdrawal of steroid support (oestrogen/progesterone) the endometrium collapses.
  • Endometrium is shed with blood from ruptured arteries (spiral arteries contract to reduce bleeding) (blood loss: 50-150ml).
  • Detached endometrial tissue and blood passes through vagina as menstrual flow
62
Q

when is the menstrual phase?

A

day 1-5

63
Q

what happens in the proliferative phase?

A
  • Oestrogen from mature follicle stimulates thickening of the endometrium.
  • Glands/spinal arteries form.
  • Oestrogen also causes the growth of progesterone receptors on endometrial cells
64
Q

when is the proliferative phase?

A

days 6-14

65
Q

what happens in the secretory phase?

A
  • Progesterone from corpus luteum acts on endometrium.
  • Progesterone also stimulates enlargement of glands  secrete mucus and glycogen in preparation for implantation of fertilised oocyte.
  • No fertilisation = corpus luteum degenerates –> corpus albicans. Progesterone levels fall and the endometrium degenerates.
  • Cycles then starts again with the first day of menstrual flow
66
Q

when is the secretory phase?

A

day 15 - 28

67
Q

what is fertilisation?

A

Fertilisation is when the blastocyst implants onto the maternal endometrium

68
Q

what happens if fertilisation does not occur?

A
  • Corpus luteum degenerates and forms the corpus albicans.
  • Progesterone levels fall.
  • Endometrium breaks down.
  • Menstruation occurs.
69
Q

what happens if fertilisation does occur?

A
  • Blastocyst implants into maternal endometrium
  • Developing placenta secretes hCG
  • Corpus luteum does not degenerate due to hCG.
  • Progesterone levels do not fall because progesterone secretion is maintained by the corpus luteum.
  • Progesterone maintains the endometrium.

human development (20 decks)

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