Corpus luteum

Question 1

Describe the process of luteinisation/formation of the CL

Answer 1

Basement membrane of follicle breaks down
Luteinisation and migration:
- granulosa cells -> large luteal cells
- theca cells -> small luteal cells
Rapid proliferation and hypertrophy
Intense angiogenesis
Steroidogenesis switch and increase (E2 -> P4)

Question 2

Describe the appearance of the different developmental stages of the CL

Answer 2

Early CL/corpus haemorrhagicum - soft and pliable
Developing CL - blood clot in follicular cavity
Mature CL - closed at top (sometimes there is a maintenance of the follicular cavity
Regressing CL - may have corpus aldicans

Question 3

Why are CLs harder to palpate during a rectal exam in mares?

Answer 3

CL is held within body of ovary

Question 4

Name the luteotrophs (hormones that support growth/function of CL)

Answer 4

LH
IGF-1
Growth hormone
PGE2

Question 5

Describe progesterone production in the CL

Answer 5

Large luteal cells produce majority
Small luteal cells are stimulated by LH
Cholesterol transfered into mitochondria (to become progesterone) by StAR (steroid acute regulatory factor)

Question 6

Describe the effect of progesterone on the hypothalamus

Answer 6

-ve feedback:
- reduced GnRH, LH and FSH pulsatility
- limits preovulatory follicle development and oestradiol production
- prevents oestrus behaviour
- prevents LH surge

Question 7

Describe the effect of progesterone on mammary tissue?

Answer 7

promotes alveolar development in mammary gland prior to parturition

Question 8

Describe the effect of progesterone on the uterus

Answer 8

promotes growth of uterine glands and their secretion to support early embryo
Inhibits myometrial contractions

Question 9

What is the result of luteolysis?

Answer 9

release from -ve feedback on GnRH
pre-ovulatory follicular development -> ovulation
return to oestrus

Question 10

Explain the strucural regression of the CL in luteolysis

Answer 10

Reduced blood flow
Increase in macrophages and lymphocytes
Apoptosis and tissue resorption
Forms corpus albicans

Question 11

Explain the functional regression of the CL in luteolysis

Answer 11

down regulation of steroidogenic enzymes
rapid fall in progesterone

Question 12

What is the relationship between the hormones that induce luteolysis?

Answer 12

Oxytocin from the CL communicates with the uterus to produce PGF2a from endometrium
Causes increased oxytocin secretion
positive feedback loop

Question 13

What is the effect of removing the uterus on the CL?

Answer 13

extends CL lifespan as loses production of PGF2a

Question 14

Explain the initiation of luteolysis

Answer 14

luteal cells sewcrete oxytocin which stimulates endometrial PGF2a (+ve feedback loop)
Endometrial oxytocin receptors increase throughout luteal phase until PGF2a is sufficient to cause luteolysis

Question 15

Explain the counter current system in PGF2a transport

Answer 15

PGF2a from uterine endometrium released into uterine branch of ovarian vein
PGF2a picked up by ovarian artery where it is delivered back to the ovary to cause luteolysis
This prevents PGF2a from entering the systemic circulation where it would be rapidly metabolised

Question 16

Explain the CLs sensitivity to exogenous prostaglandins

Answer 16

CL only responds to PGF2a at certain times depending on PGF receptor expression
Important to consider when managing cyclicity
Sows are refractory to PGF2a for longer than cows, ewes and mares