4.1 Hormonal control of reproduction Flashcards
What is the HPG axis
hypothalamus -> anterior pituitary -> gonads
Compare the anterior and posterior pituitary, give 3 hormones released from each
Anterior pituitary: GH, FSH, LH
- Arises from Rathke’s Pouch
- Not nervous tissue
- Endocrine gland
- Mostly ‘trophic’ hormones
Posterior pituitary: Oxytocin, ADH
- Nervous tissue
- Neurosecretory gland
What is Oxytocin important in?
Hormone release from the PP that is important in reproduction:
- Social interaction
- Orgasm
- Labour
- Lactation
List 3 types of glycoprotein hormones and what cell type secretes them
LH, FSH secreted by gonadotrophs
TSH secreted by thyrotrophs
List 3 types of polypeptide hormones and what cell type secretes them
GH secreted by somatotrophs
ACTH secreted by corticotrophs
Prolactin secreted by lactotrophs
Anterior pituitary secretions are controlled by the hypothalamus via releasing hormones, how do these travel?
Travel in hypophyseal portal circulation
What is a key releasing hormone of reproduction?
How often is this released?
Gonadotrophin releasing hormone (GnRH)
Release is pulsatile (about once an hour)
What do pulsatile secretions of GnRH do?
stimulates gonadatrophs in anterior pituitary to secrete FSH & LH
FSH and LH act on the gonads, what 2 things does this do?
1) Control gamete production
2) Stimulate secretion of gonadal steroids
What do the gonadal steroids act on?
List what these are in both males and females
Released from the gonads and act on the reproductive tract
Males: testosterone
Females: oestradiol and progesterone
How do we control the release of GnRH from neurones? (3)
1) Influenced by other neurones ➞ KISS 1 neurone
2) Environmental effects eg. body weight (Influence KISS1 or GnRH directly)
3) Feedback from gonadal hormones/sex steroids
What is the effect of testosterone on GnRH?
What is the effect of testosterone on FSH and LH
Reduces in both
What are the effects of moderate titres of oestrogen on GnRH and therefore FSH and LH? What type of feedback is this?
What are the effects of moderate titres of oestrogen on GnRH and therefore FSH and LH? What type of feedback is this?
Moderate titres of oestrogen reduce GnRH, FSH and LH secretion
• Negative feedback
High titres of oestrogen promote GnRH, FSH and LH secretion
• Positive feedback
• LH ‘surge’
What is the effect of progesterone on oestrogen in females? (explain the effects at moderate and high oestrogen levels)
Progesterone increases inhibitory effects of moderate oestrogen
Progesterone prevents positive feedback of high oestrogen ➞ No LH surge
How do oestrogen and progesterone affect GnRH amount and frequency
Oestrogen reduces GnRH per pulse (amount)
Progesterone influences frequency of pulses
What do amount and proportion of LH and FSH depend on?
Additional signalling molecules acting on gonadotrophs eg. Gonadal steroids, inhibin, activins
(LH and FSH are controlled independently)
Explain the role of Inhibin and state what cells produce this in both males and females
The amount of FSH and LH secreted in response to GnRH is reduced by inhibin (Inhibin works MORE on FSH than LH)
Secreted by granulosa cells (f) and Sertoli cells (m)
Explain the role of Activins
What produces these?
Activins have many local actions but also feedback to the pituitary to activate FSH secretion
Activins are secreted by the gonads and other tissues
Explain the role of FSH, what cells do these bind to in males?
FSH binds to Sertoli cells to stimulates spermatogenesis
Explain the role of LH, what cells do these bind to in males?
What are the 3 things does this result in (in terms of spermatogenesis)
LH binds to Leydig cells to secrete testosterone (promotes spermatogenesis) resulting in:
1) Spermatogonial mitotic steps
2) Sertoli cell interactions with gametes
3) Sperm release
What 2 hormones can enhance testosterone production?
Enhanced by prolactin and inhibin (but these cannot replace LH)
What is the role of Testosterone on the HPG axis?
How does this ensure we have the correct levels of testosterone?
Testosterone is secreted by Leydig cells in response to LH binding and acts on the reproductive tract
Testosterone negatively feeds back to the Hypothalamus to decrease GnRH secretion
Hence if testosterone levels get high, GnRH and therefore LH levels fall bringing testosterone levels back to normal range
How can we measure rate of spermatogenesis in males?
How does this ensure we achieve the correct rate of spermatogenesis?
Inhibin secretion is a marker of the rate of spermatogenesis in males
If spermatogenesis speeds up MORE inhibin is secreted which reduces FSH secretion bringing rates back to normal
What are the actions of Testosterone on the male reproductive tract?
1) Stimulates gamete production
2) Maintains epididymis and vas deferens
3) Maintains prostate, seminal vesicles, bulbo-urethral glands
4) Production of semen
5) Development and maintenance of external genitalia and secondary sexual characteristics
6) Sexual dimorphism throughout the body and behaviour