5. estrous cycle

What is the estrous cycle and its main function?

Repeating reproductive cycle that prepares females for pregnancy.

When does the estrous cycle begin and when does it end?

Begins at puberty and continues until pregnancy or reproductive senescence.

What is estrus?

The period when the female is sexually receptive (heat).

What defines the length of an estrous cycle?

The interval between two successive periods of estrus.

What are the four phases of the estrous cycle?

Proestrus, estrus, metestrus, and diestrus.

Which phases make up the follicular phase?

Proestrus and estrus.

Which phases make up the luteal phase?

Metestrus and diestrus.

What happens during proestrus?

Previous CL regresses, new follicles grow, and estrogen increases.

What happens to the corpus luteum during proestrus?

The previous corpus luteum regresses through luteolysis.

Why does progesterone decrease during proestrus?

Because the previous CL regresses and stops producing progesterone.

What is the dominant ovarian event during proestrus?

Growth and maturation of ovarian follicles.

How does the female behave during proestrus?

Attracts males but usually rejects mating.

What happens during estrus?

Female becomes sexually receptive and shows heat behavior.

What is standing heat in cattle?

The female stands still and accepts mounting by another animal.

What happens to cervical mucus during estrus?

It becomes clearer and more abundant to support sperm transport.

What are the hormonal characteristics of estrus?

Estrogen is high, progesterone is low, and an LH surge occurs.

What hormone surge triggers ovulation?

Luteinizing hormone (LH) surge.

Does estrus mean ovulation has already occurred?

No. Estrus is sexual receptivity; ovulation occurs at a species-specific time.

What happens during metestrus?

Ovulation occurs, corpus hemorrhagicum forms, and the CL begins developing.

What happens to the follicle during ovulation?

It ruptures and releases the oocyte.

What is the corpus hemorrhagicum?

A temporary blood-filled structure formed after follicular rupture.

What is luteinization?

Transformation of follicular cells into progesterone-producing luteal cells.

What happens to estrogen and progesterone during metestrus?

Estrogen decreases while progesterone begins increasing.

What happens during diestrus?

The CL becomes fully functional and produces high progesterone.

What is the main hormone during diestrus?

Progesterone, which maintains uterine conditions for pregnancy.

What happens to the endometrium during diestrus?

Endometrial glands become secretory to support early pregnancy.

Why is the female generally not receptive during diestrus?

High progesterone suppresses estrous behavior.

What is luteolysis?

Regression or destruction of the corpus luteum.

What hormone causes luteolysis in cattle?

Prostaglandin F₂α (PGF₂α), released by the uterus.

What happens when pregnancy does not occur?

PGF₂α causes CL regression, progesterone decreases, and a new estrous cycle begins.