Central control of reproduction + HPG axis

what does the hypothalamus secrete

• GnRH

what is GnRH

• gonadotrophin releasing hormone

what does the anterior pituitary release in response to GnRH?

• FSH + LH = gonadotrophins

• prolactin

what does the posterior pituitary release (in response to GnRH)

• oxytocin

What do the female gonads release - hormones?

• oestrogens

• progesterones

• inhibin

• oxytocin

• relaxin

• some testosterone

what do the male gonads produce - hormones

• testosterone

• inhibin

• oestrogen

what does the uterus/placenta produce - hormones?

• F2a prostoglandin

• progesterone

• oestrogen

• eCG

• hCG

what is the structure of gonadotrophins?

• alpha subunit

• with variable beta unit

what are the 3 goandotrophin beta subunits?

• FSH

• LH

• CG

what are gonadotrophins?

• glycoprotein hetero-dimers

what receptors do gonadotrophins use?

• G-protein linked receptor

which gonadotrophins share a common receptor?

• LH

• CG

what are gonadotrophins excreted in?

• urine

what is CG, a gonadotrophin released from, therefore what is it used ot detect?

• chorionic girdle in the placenta

  • pregnancy

what do all steriods originate from?

• cholesterol

are steroids water/lipid soluble?

• lipid soluble

as steroids are lipid soluble what does this mean about their signalling method in terms of sex hormones?

• act via nuclear androgen/progesterone and oestrogen receptor

briefly outline the 7 steps of steroid metabolism

1. secreted by gonad

2. enters blood and goes to target tissue

3. causes change in target tissue

4. passes through liver in blood

5. liver renders steroid H2O soluble

6. enters kidney/bile

7. excreted in urine ± faeces

what are the two substrates steroids are secreted as?

• glucoronide

• sulfate

oestradiol:

1. what does it affect behaviourally

2. stimulates what?

3. what does it prepare the reproductive tract for?

4. how does it change the uterus?

5. what other organs does it affect?

1. promotes mating and fertilisation

2. LH surge

3. copulation + sperm transport

4. prepares it to favour early embryonic development

5. mammary tissue

progesterone:

1. what does the name indicate?

2. prevents what and how?

3. what does it prepare the uterus for?

4. what does it stimulate during pregnancy

5. how does it aid milk synthesis?

1. pro gestation

2. ovulation, suppressing GnRH

3. early embryonic development

4. growth + development of the uterus

5. mammary tissue growth + development

Prostaglandins:

1. what are the synthesised from

2. where do we see the highest levels

3. how many types

4. what receptor do they use

5. what are the 2 most important ones reproductively

6. how long do they last?

1. arachidonic acid

2. seminal fluid

3. 6

4. G protein coupled receptors

5. PGF2 alpha, PGE2

6. rapidly degraded

what are PGF2 alpha + PGE2 used for?

• important in ovulation

• parturition

• luteolysis

what makes up the hypothalamo-hypophyseal portal system?

• primary portal plexus

• hypophyseal portal veins

• secondary portal plexus

outline the process of the hypothalamo-hypophyseal portal system

1. portal system transports neurohormones from hypothalamus to anterior pituitary

2. neurohormones bind to receptors on endocrine cells in anterior pituitary

3. secretion of hormones is regulated

how does the hypothalamo-hypophyseal portal system affect oxytocin?

• oxytocin produced in cell bodies of the hypothalamic neurones are transported to posterior pituitary for storage until released + transported

describe how the male hypothalamus released GnRH

• frequent, intermittent bursts day + night

Describe this graph

• pulse of GnRH → pulse of LH → pulse of testosterone

what do leydig cells produce and respond to?

• testosterone

• LH

what do sertoli cells release and respond to?

• inhibin

• FSH

what do the sertoli cells release that causes the negative feedback?

• inhibin

what are the two major structures that form in the ovary?

• follicles

  • corpus luteum

what develops inside the follice in an ovary?

• oocyte

what hormone is screted from a follicle

• oestradiol secretion

what is the corpus luteum

• a transient endocrine gland

what hormone does the corpus luteum produce?

• progesterone

what are the two centres GnRH are secreted from in females?

• surge centre

• tonic centre

what centre of GnRH secretion does a male have?

• tonic

what does a release of GnRH from the surge centre cause in women?

• surge in LH → ovulation

how does oestradiol affect GnRH in the follicular phase?

• low level E2 has a -ve feedback role

how does the affect of oestradiol change nearing ovulation?

• rising E2 becomes a stimulus (not an inhibitor) leading to LH surge + ovulation

what exerts negative feedback in the luteal phase?

• progesterone - P4

what happens in the absence of fertilisation to the CL and with hormoens?

• CL undergoes structural + functional regression → luteolysis

• P4 decreases

what hormone does pregnancy require?

• progesterone

what key progesterone is involved in luteolysis?

• PGF2 alpha