Parturition

Question 1

What induces parturition?

Answer 1

the foetus

Question 2

How does the foetus induce parturition?

Answer 2

1. foetus releases CRF from hypothalamus, stimulates anterior pituitary to produce ACTH
2. ACTH causes adrenal hyperplasia & massive increase in cortisol production
3. cortisol is important for final organ growth & differentiation
4. cortisol enters placenta & induces enzymes that are relevant for oestradiol & PGF-2a production
5. causes upregulation of oestradiol & down regulation of progesterone
6. change in steroid ratio causes massive placental production of PGF-2a
7. uterine contractions move the foetus into birth position, towards internal os and into birth canal
8. cortisol induces aromatase enzyme and 17a-hydroxylase to boost oestradiol production from progesterone

Question 3

what are the actions of oestradiol during parturition?

Answer 3

• dilate cervix
• uterine contractions

Question 4

what are the actions of PGF-2a during parturition?

Answer 4

• luteolysis in ovary
• dilation of cervix
• uterine contractions
• oxytocin release from posterior pituitary
• secretion of relaxin from placenta (from CL in ruminants)

Question 5

What are the actions of relaxin during parturition?

Answer 5

relaxes ligaments & muscles around birth canal to allow expulsion of foetus

Question 6

what are the 3 stages of labour?

Answer 6

1. stage 1 - ends at rupture of allantois
2. stage 2 - ends with expulsion of foetus
3. stage 3 - ends with expulsion of foetal membranes

Question 7

describe the 2 reflexes that are involved in stage 2 of labour

Answer 7

1. Ferguson reflex - vaginal and cervical stretching leads to oxytocin release causing SM contractions
2. N. pudenus reflex - vaginal stretching causes strong uterine contractions