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URO > Reproductive hormones & HPG axis > Flashcards

Reproductive hormones & HPG axis Flashcards

1
Q

What is GnRH are where is it synthesised?

A

GnRH: gonadotrophin releasing hormone.

Synthesised in the hypothalamus

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2
Q

Where is prolactin synthesised?

A

Anterior pituitary gland

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3
Q

Where is oxytocin synthesised?

A

Posterior pituitary gland

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4
Q

Where are FSH and LH synthesised?

A

Pituitary gland

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5
Q

Where are the following hormones produced:

oestrogens, progesterone, inhibin, oxytocin, relaxin, some testosterone

A

Ovary

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6
Q

Name some hormones synthesised in the ovary

A
  • Oestrogens
  • Progesterone
  • Inhibin
  • Oxytocin
  • Relaxin
  • (some) testosterone
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7
Q

Where are the following hormones produced:

testosterone, inhibin, oestrogen, some other androgens

A

Testis

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8
Q

Name hormones synthesised in the uterus/placenta

A
  • Prostaglandin F2alpha
  • progesterone
  • oestrogen
  • eCG (equine chorionic gonadotrophin)
    • = hCG = human version
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9
Q

How do gonadotrophins have an effect?

A
  • e.g. FSH, LH, CG
  • These are glycoprotein heterodimers with a shared alpha chain
  • Biological activity is conferred by different beta chains
  • They bind to G-protein linked receptors
  • They then undergo a series of metabolic conversions and are excreted in urine (hence pregnancy testing works)
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10
Q

How do steroids have an effect?

A
  • These are organic compounds produced by a series of enzymatic conversions
  • These enzymes are present in some cells but not others (hence steroid synthesis can be controlled)
  • These steroids at via androgen, progesterone and oestrogen receptors
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11
Q

Describe steroid metabolism

A
  1. Steroid is secreted by gonad
  2. Steroid enters blood, travels to target tissue
  3. Causes a change in target tissue
  4. Steroid in blood passes through liver
  5. Liver renders the steroid water-soluble
  6. Steroid re-enters the blood and enters kidney/bile
  7. Steroid is excreted in urine and/or faeces as glucuronide or sulphate
    1. This is how we track performance-enhancing steroids
    2. Also, we know about repro cycles of exotics species through faeces collection
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12
Q

What is the hypothalamo-hypophyseal-portal system?

A
  • Portal system comprising of hypophyseal artery, primary portal plexus, hypophyseal portal veins and secondary portal plexus
  • This system transports neurohormones e.g. GnRH from the hypothalamus to the anterior pituitary
  • Here the neurohormones bind to receptors on endocrine cells in the anterior pituitary and regulate the secretion of other hormones (E.g. FSH, LH)
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13
Q

Describe the HPT axis

A

HPT axis: hypothalamic-pituitary-testicular axis

  • Male hypothalamus releases frequent intermittent bursts of GnRH that occur day and night
  • Pulse of GnRH –> pulse of LH –> pulse of testosterone
  • The HPT axis forms a simple negative feedback loop
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14
Q

Leydig cells are _________________________ so respond to ________________

A

Leydig cells are LH receptor +ve so respond to testosterone

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15
Q

Sertoli cells are ______________________ so respond to _______ which ________________________

A

Sertoli cells are FSH receptor +ve so respond to inhibin which inhibits FSH

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16
Q

What is the corpus luteum?

A
  • Transient endocrine gland formed from the remnants of the follicle
  • Secretes progesterone to support pregnancy
17
Q

What is a follicle on an ovary?

A
  • A structure inside which the oocyte develops
  • Multiple stages
  • Secretes oestradiol
18
Q

Describe GnRH production in the female vs male

A
  • In females GnRH production in 2 groups of hypothalamic neurones
    • Surge (preovulatory) centre
    • Tonic centre
  • In males, surge centre is inactive
  • Pattern of production: there is basal secretion of small regular pulses. When stimulated by oestrogen, secretion increases and there is a large preovulatory surge before ovulation.
19
Q

Describe the hypothalamic-pituitary-ovarian axis during the follicular phase

A
  • For most of the follicular phase, low level of E2 has negative feedback
  • Approaching ovulation there is a critical switch.
  • Rising E2 switches to positive feedback, leading to LH surge and ovulation
  • Inhibin inhibits FSH production in later stages of follicle growth especially
20
Q

Describe the hypothalamic-pituitary-ovarian axis during the luteal phase

A
  • Luteal progesterone (P4) exerts strong negative feedback on GnRH neurones
  • This acts on mammary and uterine tissue
  • Luteolysis will remove this negative feedback
    • In the absence of fertilisation, the CL undergoes luteolysis
    • This remove progesterone production (its own negative feedback)

URO (8 decks)

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