Exam 4 (Lecture 56) - Luteal Phase

Question 1

Name the two sub-phases of the luteal phase and the concentration trends of the major hormones (P4, E2, LH and FSH) during these two sub-phases.

Answer 1

1) Metestrus
- P4 starts to rise after ovulation

2) Diestrus
- P4 peaks during diestrus

*The other hormones are at insignificant during these two subphases.

Question 2

Describe the transitions of the follicular cells to the luteal cells; that is, which follicular cells become which luteal cells?

Answer 2

Granulosa cells = become the large luteal cells (LLCs)

Theca cells = become the small luteal cells (SLCs)

Question 3

What are the two general facets of luteolysis? (slide 6)

Answer 3

1) The finite lifespan of the LLCs and SLCs

2) A hormone that kills the LLCs and SLCs

Question 4

What are the CA and CH?

Answer 4

CA = corpus albicans
- The very small CL (CL has started to degenerate so that the cycle can restart at the follicular phase)

CH = corpus hemorrhagicum
- The early stage of the CL; named due to the blood vessels that rupture during the progression of the CL

Question 5

Which cells are the major source of progesterone during the luteal phase, and why are they the major source?

Answer 5

Large luteal cells; LH (that normally stimulates theca cells/SLCs to synthesize P4) levels are very low during the luteal phase.

Question 6

Discuss the relationship between oxytocin and PGF2-alpha in regards to the active facet of luteolysis.

Answer 6

The dying CL releases oxytocin (peptide hormone).

As apoptosis increases in the CL, oxytocin release also increases.
- P4 increases the number of oxytocin receptors in the endometrium (uterus)
- Oxytocin then stimulates the synthesis of PGF2-alpha in the uterus
- PGF2-alpha goes to the CL using the vascular counter-current exchange
- PGF2-alpha directly activates apoptosis by activating its cognate GPCR
- The PGF2-alpha activity speeds up the degeneration of the CL and return to the follicular phase

Question 7

Discuss the five feedback mechanisms of the luteal phase.

Answer 7

1) P4 prevents GnRH release at the hypothalamus

2) P4 prevents GnRH activity at the anterior pituitary

3) P4 stimulates oxytocin-R synthesis in the endometrium

4) Oxytocin stimulates PGF2-alpha synthesis in the endometrium

5) PGF2-alpha stimulates oxytocin release from the CL