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RED > L01 - The HPG Axis > Flashcards

L01 - The HPG Axis Flashcards

1
Q

Describe the HPG axis in males.

A

1 - The hypothalamus secretes GnRH

2 - GnRH stimulates the anterior pituitary to release FSH and LH

3 - FSH and LH stimulate the testes to produce inhibin and testosterone

4 - Inhibin has a negative feedback effect on the anterior pituitary

5 - Testosterone has a negative feedback effect on the anterior pituitary and hypothalamus

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2
Q

How does the female HPG axis differ from the male HPG axis?

A

1 - Oestrogen and progesterone produced by the ovaries

2 - Both oestrogen and progesterone have a negative feedback effect on both the anterior pituitary and hypothalamus (whereas inhibin only affects the anterior pituitary)

3 - Oestrogen can also have a positive feedback effect on both the anterior pituitary and hypothalamus

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3
Q

Where is the hypothalamus located?

A

Base of the brain between the midbrain and forebrain

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4
Q

What type of molecule is GnRH?

A

Peptide hormone

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5
Q

What is Kallmann syndrome?

A

Failure of GnRH-secreting neurones to migrate during development, causing infertility

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6
Q

At puberty, what triggers gonadal activation?

A

Pulsatile GnRH secretion

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7
Q

How does the pituitary acquire resistance to the effects of GnRH?

A

Continuous GnRH secretion leads to downregulation of GnRH receptors on the surface of anterior pituitary gonadotrophs

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8
Q

Which 6 hormones are secreted by the anterior pituitary?

A

1 - Adrenocorticotropic hormone

2 - Thyroid-stimulating hormone

3 - Growth hormone

4 - Luteinising hormone

5 - Follicle-stimulating hormone

6 - Prolactin

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9
Q

Which 2 hormones are secreted by the posterior pituitary?

A

1 - Antidiuretic hormone

2 - Oxytocin

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10
Q

Which hormones are secreted by gonadotrophs?

Give an example of another other gonadotropin that is not secreted by gonadotrophs.

A

1 - Follicle-stimulating hormone.

2 - Luteinising hormone.

  • Human chorionic gonadotropin (hCG)
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11
Q

Which cells secrete ACTH?

A

Corticotrophs

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12
Q

Which cells secrete GH?

A

Somatotrophs

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13
Q

Which cells secrete prolactin?

A

Lactotrophs

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14
Q

What type of molecules are FSH & LH?

A

Glycoproteins

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15
Q

What type of receptors are targeted by FSH and LH?

A

GPCRs

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16
Q

Which cells secrete hCG?

A

Trophoblast cells

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17
Q

Which cells are the targets of LH?

A

1 - Leydig cells (male)

2 - Theca & granulosa cells (female)

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18
Q

Which cells are the targets of FSH?

A

1 - Sertoli cells (male)

2 - Granulosa cells (female)

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19
Q

Which cells are the target of hCG?

A

Luteal cells of the corpus luteum

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20
Q

What are the receptors for the gonadotropins?

A

1 - Luteinizing hormone-choriogonadotropin receptor (LHCGR): LH and hCG

2 - Follicle-stimulating hormone receptor (FSHR): FSH

21
Q

What are the routes of communication from the hypothalamus to the pituitary?

A

1 - Direct neural connection

2 - Indirect via the vasculature

22
Q

What are the 3 main families of sex steroid hormones?

A

1 - Progestogens (released from gonads and placenta)

2 - Androgens (released from gonads and adrenal glands)

3 - Oestrogens (released from gonads, liver, adrenal glands, adipose tissue and placenta)

23
Q

From which molecule are sex steroid hormones derived?

A

Cholesterol (via acetate)

24
Q

On which domain of which type of receptor do sex steroid hormones act?

A

Steroid response elements (SREs) of nuclear receptors

25
Q

List 3 carrier proteins that bind to sex steroid hormones.

A

1 - Albumin

2 - Sex hormone binding globulin (SHBG)

3 - Androgen binding protein (ABP)

26
Q

List 3 progestogens.

A

1 - Progesterone (P4)

2 - 17⍺-hydroxyprogesterone (17⍺-OHP)

3 - 20⍺-hydroxyprogesterone (20⍺-OHP)

27
Q

List 4 androgens.

A

1 - 5⍺-dihydrotestosterone (DHT)

2 - Testosterone (T)

3 - Androstenedione (A4)

4 - Dehydroepiandrosterone (DHEA)

28
Q

List 3 oestrogens.

In which stages of life are these hormones particularly active?

A

1 - Oestradiol 17β (E2) - puberty to menopause

2 - Oestriol (E3) - pregnancy

3 - Oestrone (E1) - post-menopause

29
Q

List 5 functions of progestogens.

A

1 - Preparation & maintenance of uterus during pregnancy

2 - Growth of mammary glands

3 - Suppression of lactation

4 - Catabolic effects

5 - Regulation of gonadotropins

30
Q

List 5 functions of androgens.

A

1 - Development & maintenance of male reproductive system

2 - Secondary sexual characteristics

3 - Sexual function

4 - Support spermatogenesis

5 - Regulation of gonadotropins

31
Q

List 4 functions of oestrogens.

A

1 - Secondary sexual characteristics

2 - Stimulate growth & activity of mammary glands

3 - Stimulate proliferation of endometrium for progesterone action

4 - Regulate gonadotropins

32
Q

Give an example of a sex steroid hormone that binds to receptors of classes other than their own.

A

Synthetic progestogens in the contraceptive pill can be androgenic and cause side effects such as acne

33
Q

Give an example of a sex steroid hormone receptor antagonist.

A

Mifepristone is an anti-progestogen

34
Q

How do sex steroids interact with gonadotropins?

A

Sex steroids are both regulated by & regulate gonadotropins of the anterior pituitary via feedback loops

35
Q

Which component of the HPG axis is dysfunctional with central hypogonadism?

A

Hypothalamus/pituitary

36
Q

Which component of the HPG axis is dysfunctional with primary hypogonadism?

A

Ovary/testis

37
Q

Which sex is more likely to experience endocrine causes of infertility?

A

Females

38
Q

When do levels of prolactin increase?

A

During pregnancy & breastfeeding

39
Q

What is the function of prolactin?

A

Inhibits gonadal activity through the central suppression of GnRH, which decreases FSH/LH, and induces lactational amenorrhoea

40
Q

How does gametogenesis in males differ from gametogenesis in females?

A
  • Males: gametogenesis is continuous i.e. there is constant sperm production
  • Females: gametogenesis is cyclic i.e. there is one oocyte produced per month
41
Q

What are the 3 phases of the menstrual cycle?

A

1 - Follicular/proliferative

2 - Ovulation

3 - Luteal/secretory

42
Q

What is the average duration of the menstrual cycle?

A

26-32 days (average 28 days)

43
Q

How long is the luteal phase of the menstrual cycle?

A

14 days

44
Q

Which phase of the menstrual cycle is variable in length?

A

Follicular phase

45
Q

By convention, when are FSH and LH measured clinically?

A

Day 2/3

46
Q

Define ovarian reserve.

How can ovarian reserve be measured?

A
  • Ovarian reserve is a term that is used to determine the capacity of the ovary to provide egg cells that are capable of fertilisation
  • It can be measured by measuring FSH & LH on day 2/3
47
Q

Define oligomenorrhoea.

A

<9 cycles in the last 12 months

48
Q

Define amenorrhoea.

A

No bleed in the last 6 months. Either primary (never) or secondary (ceased)

49
Q

What hormonal changes accompany menopause?

A
  • No production of progesterone or oestrogen by the ovaries

- Loss of negative feedback by sex steroids leads to high FSH/LH levels

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