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Reproduction > Hypothalamic - Pituitary Gonadal Axis I > Flashcards

Hypothalamic - Pituitary Gonadal Axis I Flashcards

1
Q

What are the 7 things needed to reproduce?

A

→Correct process of sex determination (genotypic sex) and differentiation (phenotypic sex)
→Sexual maturation- Puberty

→Production and storage of sufficient supply of gametes
→Correct number of chromosomes in egg and sperm
→Actual sexual intercourse
→Fertilisation, implantation, embryonic and placental development
→ nurture individual until capable of “independent” life

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2
Q

What is an example of positive feedback?

A

→ Ovulation

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3
Q

Describe how the HPG axis works

A

→+ve drive from the hypothalamus which activates the pituitary
→ +ve drive causing hormonal release from the pituitary

→ Causes release of steroid hormones from the gonads
→ Work in a -ve feedback to regulate their production

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4
Q

What does type of hormones does the hypothalamus produce?

A

→ Peptide hormones

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5
Q

What hormones does the hypothalamus produce?

A

→Gonadotropin releasing hormone

→kisspeptin

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6
Q

What hormones does the pituitary produce?

A

→ Follicle stimulating hormone

→ LH

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7
Q

What hormones do the gonads produce?

A

→ Estradiol
→ Progesterone

→ Testosterone
→ Inhibin
→ Activin

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8
Q

Describe the HPG axis in relation to FSH and LH

A

→ GnRH is released from the hypothalamus
→ This binds to the receptor on the anterior pituitary

→ LH and FSH are secreted
→ FSH and LH are released into the circulation and bind to their receptors on the gonads
→ this co-ordinates the secretion of estrogen, progesterone and androgens

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9
Q

Where is GnRH secreted into?

A

→ Into the primary plexus of the median eminence

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10
Q

Where does GnRH travel after it is secreted?

A

→ Into the hypophyseal portal into the anterior pituitary

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11
Q

What does GnRH act on?

A

→ The gonadotroph cells in the anterior pituitary

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12
Q

What is the function of kisspeptin?

A

→ Master controller of puberty

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13
Q

Where is kisspeptin expressed?

A

→ In the arcuate nucleus

→ AVPV nucleus

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14
Q

What do kisspeptin neurons do?

A

→ They send signals upstream of GnRH to neurons

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15
Q

What receptor do the kisspeptin neurons bind to?

A

→ GPR54 receptor on GnRH neurons

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16
Q

What can kisspeptin 54 cross?

A

→ blood brain barrier

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17
Q

What type of hormone is kisspeptin?

A

→ Peptide hormone that is cleaved from a large pre-pro structure

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18
Q

What is GnRH secreted in response to and where?

A

→ Synthesized and secreted in response to kisspeptin

→ From GnRH neurons

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19
Q

What type of release is GnRH?

A

→ Pusatile

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20
Q

Where does GnRH bind?

A

→ To the GnRH receptor on gonadotroph cells of the anterior pituitary

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21
Q

Where does GnRH travel from and to?

A

→ from the arcuate nucleus to the median eminence to the anterior pituitary

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22
Q

What is GnRH produced from?

A

→ a Prepro protein

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23
Q

What is GnRH spliced into?

A

→ Decapeptide

24
Q

What is GnRh co-secreted with?

A

→ GAP

→ GnRH

25
Q

When is GnRh secreted?

A

→ every 30-120 minutes

26
Q

What does GnRH stimulate?

A

→ A pulse of LH and FSH secretion from the pituitary

27
Q

What types of GnRH pulse favor LH and what types favor FSH?

A

→ slow frequency - FSH

→ rapid frequency - LH

28
Q

What does continuous release of GnRH lead to?

A

→ Cessation of response

29
Q

What hormone gets produced after a surge in LH and estradiol and what happens to the follicle?

A

→ Progesterone

→ Remodelling of the ovarian follicle into the corpus luteum

30
Q

How does native GnRh binding work?

A

→ GnRH binds to its receptor
→ It activates a signaling pathway cascade

→ Stimulates gonadotrophin synthesis and secretion
→ GnRH dissociates from its receptor
→ Receptor is ready to respond to the next GnRH puls

31
Q

How does a GnRH agonist work?

A

→ Binds to the receptor
→ Activates signaling

→ Stimulates gonadotrophin synthesis and secretion at first
→ Doesn’t dissociate
→ GnRH is uncoupled
→ Receptor is unresponsive

32
Q

How does a GnRH antagonist work?

A

→ Binds to the receptor
→ Blocks the receptor

→ No downstream effect and LH and FSH are switched off

33
Q

What are 6 uses of GnRH analogues?

A

→ IVF
→ Prostate cancer

→ Breast , ovarian and endometrial cancer
→ Endometriosis
→ PCOS
→ Fibroids

34
Q

How does GnRH cause FSH and LH to increase?

A

→ Increases the transcription and translation of the subunits that make up LH and FSH

35
Q

What are the gonadotrophin hormones?

A

→ LH
→ FSH

→hCG

36
Q

What type of peptides are the gonadotrophin hormones?

A

→ Heterodimeric peptides
→ Common a subunit

→ Hormone specific B subunit, alpha subunits are the same

37
Q

What is required for biological function of heterodimeric peptides?

A

→ N linked carbohydrate side chains.

38
Q

What happens if N linked carbohydrate chains are deglycosylated?

A

→ They still bind but they are inhibitory

39
Q

Which subunit of the gonadotrophic hormones are made in excess?

A

→A subunits are synthesized in excess

40
Q

What is the function of LH in the testes?

A

→ Stimulation of Leydig cells and androgen synthesis

41
Q

What is the function of LH in the ovary?

A

→ Stimulation of Theca cells and androgen synthesis
→ Ovulation

→ Progesterone production of corpus luteum

42
Q

What is the function of FSH in the testis?

A

→ Regulation of Sertoli cell metabolism

43
Q

What is the function of FSH in the ovary?

A

→ Follicular maturation

→ Granulosa cell - estrogen synthesis

44
Q

Where are the Leydig cells between?

A

→ Seminiferous tubules

45
Q

What do Leydig cells express?

A

→ LH receptor

46
Q

What is lining the seminiferous tubules and what is their function?

A

→ Sertoli cells which express the FSH receptor

→ Co-ordinate spermatogenesis

47
Q

What are the cells that line the ovarian follicle called?

A

→ Theca cells

48
Q

What do Theca cells do?

A

→ Stimulate androgen production

49
Q

What do granulosa cells express?

A

→ FSH receptors

50
Q

How are androgens converted to estrogens?

A

→ Androgens cross the basement membrane and go to the granulosa cells
→ They are converted via the aromatase enzyme.

51
Q

What regulates aromatase?

A

→ FSH receptors

52
Q

What is produced in the corpus luteum?

A

→ Progesterone

53
Q

Describe the HPG axis in females

A

→ Kisspeptin and GnRH are released from the hypothalamus
→ GnRH travels to the gonadotroph cells of the anterior pituitary

→ It causes the synthesis and secretion of LH and FSH
→ LH binds to its receptor on Theca cells
→ Stimulates androgen production
→ FSH binds to its receptor on Granulosa cells
→ This causes the conversion of androgens to estrogens
→ Within the luteal phase you get progesterone produced
→ These feedback negatively except estradiol

54
Q

Describe the HPG axis in males

A

→ From the hypothalamus kisspeptin and GnRH are released
→ GnRH travels to the gonadotroph cells of the anterior pituitary

→ it causes the synthesis and secretion of LH and FSH
→ LH binds to its receptor on Leydig cells to produce testosterone
→ FSH binds to its receptor on Sertoli cells to maintain spermatogenesis
→ They all feedback negatively

55
Q

Which subunit of the gonadotrophin hormones is limiting?

A

β-subunit limiting the hormone concentration as dependent on GnRH activity

Reproduction (12 decks)

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