The Luteal Phase of the Estrous Cycle

Question 1

What are the two parts of the estrus cycle that make up the luteal phase?

Answer 1

1. Metestrus.
2. Diestrus.

Question 2

What does the pre-ovulatory follicle produce?

Answer 2

1. P4 (locally).
2. Collagenase (theca interna).

Question 3

What occurs when the corpus hemmorhagicum forms?

Answer 3

1. A blood vessel in the follicle wall has ruptured.
2. The follicular walls collapse.
3. Cells intermix.
4. The old basement membrane becomes connective tissue of the CL.

Question 4

What are the functional capabilities of the CL?

Answer 4

1. The number of luteal cells.
   a. Large cells hypertrophy.
   b. Small cells undergo hyperplasia.
2. Vascularization of the CL.
   a. Initiated by angiogenic factors.
   b. Vascularity effects CL steroid hormone synthesis and delivery of the hormones(P4, OT, or RLX/RLN).

Question 5

What occurs if CL function is insufficient?

Answer 5

Failure to maintain pregnancy.

Question 6

What occurs when the functional corpus luteum forms?

Answer 6

1. Size increase.
2. Composed of cells from the theca interna and granulosa.
3. Increased P4 production.
4. A small cavity may be present where the follicular antrum was.

Question 7

What organelle is found in both the LLC and SLC?

Answer 7

Mitochondria (cholesterol to pregnenolone).

Question 8

Where are secretory granules found?

Answer 8

The LLC.

Question 9

What two hormones do the secretory granules produce, and when?

Answer 9

1. OT: During a cycle.
2. RLX/RLN: End of pregnancy.

Question 10

What tissues does P4 inhibit?

Answer 10

1. Hypothalamus(hormone release, repro. behavior).
2. Anterior pituitary gland.
3. Myometrium (decreases muscular contractions).
   *HAM

Question 11

What tissues does P4 stimulate?

Answer 11

1. Endometrium(endometrial gland growth and secretions).
2. Alveoli in the mammary gland.

Question 12

What organ is required for luteolysis in most animals?

Answer 12

The Uterus.

Question 13

When the entire uterus is removed, how is the CL affected?

Answer 13

Its lifespan is longer.

Question 14

When a contralateral hysterectomy is done, how is the CL affected?

Answer 14

The lifespan of the CL is normal.

Question 15

When an ipsilateral hysterectomy is done,
how is the CL affected?

Answer 15

The lifespan of the CL is longer.

Question 16

What are the steps of PGF2a control of luteolysis?

Answer 16

1. OT from the CL stimulates the production of uterine PGF2a after day 15*.
2. PGF2a synthesis by the uterine endometrium is released into the uterine vein.
3. PGF2a is picked up by the ovarian artery through counter-current exchange and delivered it back to the ovary, where it causes luteolysis
   *Cows only.

Question 17

How much PGF2a is degraded in circulation?

Answer 17

90% is degraded after one pass through the lungs.

Question 18

What structure is analogous to the PPP?

Answer 18

The ovarian pedicle.

Question 19

What is different about the uterine and ovarian blood supply in horses?

Answer 19

1. PGF2alpha goes into the systemic circulation and comes back because equines do not metabolize PGF2alpha as well as other animals.
2. CL’s are more sensitive to PGF2alpha.

Question 20

Why is prostaglandin rarely used in swine?

Answer 20

It is only effective for 3 days.

Question 21

What is the relationship between OT and PGF2a?

Answer 21

A positive feedback loop until all of the CL disappears.
*CL–> OT –> Endometrium –> PGF2a –> CL–> OT –> …

Question 22

What occurs during luteolysis?

Answer 22

1. Decreased blood flow.
2. Decreased P4 synthesis.
3. Increased apoptosis.
4. Lymphocytes and macrophages phagocytize the dying CL.

Question 23

What occurs in primates during luteolysis?

Answer 23

1. It does NOT require the uterus.
2. CL lifespan is 12-14 days or until pregnancy occurs.
   *CL self-destructs in the absence of pregnancy.
   **Possible intra-ovarian OT receptors and PGF2a production. Occurs in the CL.

Question 24

What occurs in dogs and cats during luteolysis?

Answer 24

1. No uterine role in CL degradation during a cycle.
2. Causes a pseudopregnancy. Can be symptomatic or asymptomatic.