Reproductive Cyclicity and the Luteal Phase in Mammals

What is the luteal phase?

The luteal phase lasts from the time of ovulation until luteolysis of the corpus luteum.

What are the stages of the luteal phase?

The stages are metestrus and diestrus.

What is the dominant ovarian hormone during the luteal phase?

Progesterone.

What is luteinization?

Luteinization is the formation of the corpus luteum from the cells of the ovulatory follicle.

What happens to the corpus luteum after ovulation?

It increases in size and loses its hemorrhagic appearance, reaching maximal size and progesterone secretion during diestrus.

What is luteolysis?

Luteolysis is the process where the corpus luteum loses its functional integrity and decreases in size.

What does a regressed corpus luteum become?

It becomes a corpus albicans, which can be observed as white scar-like structures.

What is the role of LH in luteinization?

LH governs the transformation of follicular cells into luteal tissue.

What are the two types of luteal cells?

Large luteal cells (granulosal-lutein cells) and small luteal cells (thecal lutein cells).

How is the functional capability of the corpus luteum measured?

By its ability to secrete progesterone.

What factors influence the vigor of the corpus luteum?

The number of luteal cells and the degree of vascularization.

What is the effect of progesterone on GnRH secretion?

Progesterone exerts a strong negative feedback, reducing GnRH pulse frequency.

What are the target organs for progesterone?

Hypothalamus, uterus, and mammary glands.

What initiates luteolysis?

PGF2α secreted by the uterine endometrium.

What is the significance of the countercurrent exchange mechanism in luteolysis?

It ensures that PGF2α is transported directly to the ovary and corpus luteum without dilution by systemic circulation.

What stimulates the secretion of PGF2α?

Oxytocin synthesized and secreted by large luteal cells.

What are the requirements for luteolysis in subprimate mammals?

Presence of oxytocin receptors, critical levels of oxytocin, and PGF2α synthesis by the endometrium.

What is the effect of exogenous progesterone on estrus and ovulation?

It suppresses estrus and ovulation, acting as an artificial corpus luteum.

What is the Ovsynch protocol?

A synchronization method using GnRH and PGF2α to time artificial insemination.

How does progesterone affect behavioral estrus?

It prevents behavioral estrus and stops the preovulatory LH surge.

What is the physiological action of altrenogest?

It mimics progesterone to induce regular cyclicity and suppress undesired estrous behavior.

What happens to progesterone levels during luteolysis?

There is a dramatic drop in blood concentrations of progesterone.

What is the role of the uterus in luteolysis?

The uterus functions as an endocrine organ, communicating with the corpus luteum.

What is the significance of the corpus luteum in early embryo development?

Insufficient luteal function can lead to reproductive failure due to inadequate progesterone levels.

What is the time frame for luteolysis?

Luteolysis occurs during a one to three day period at the end of the luteal phase.

What is the effect of elevated progesterone on GnRH pulse frequency?

It reduces the pulse frequency of GnRH.

What is the result of luteolysis?

Cessation of progesterone secretion and structural regression to form a corpus albicans.