The Luteal Phase of the Estrous Cycle Flashcards
What are the two parts of the estrus cycle that make up the luteal phase?
- Metestrus.
- Diestrus.
What does the pre-ovulatory follicle produce?
- P4 (locally).
- Collagenase (theca interna).
What occurs when the corpus hemmorhagicum forms?
- A blood vessel in the follicle wall has ruptured.
- The follicular walls collapse.
- Cells intermix.
- The old basement membrane becomes connective tissue of the CL.
What are the functional capabilities of the CL?
- The number of luteal cells.
a. Large cells hypertrophy.
b. Small cells undergo hyperplasia. - 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).
What occurs if CL function is insufficient?
Failure to maintain pregnancy.
What occurs when the functional corpus luteum forms?
- Size increase.
- Composed of cells from the theca interna and granulosa.
- Increased P4 production.
- A small cavity may be present where the follicular antrum was.
What organelle is found in both the LLC and SLC?
Mitochondria (cholesterol to pregnenolone).
Where are secretory granules found?
The LLC.
What two hormones do the secretory granules produce, and when?
- OT: During a cycle.
- RLX/RLN: End of pregnancy.
What tissues does P4 inhibit?
- Hypothalamus(hormone release, repro. behavior).
- Anterior pituitary gland.
- Myometrium (decreases muscular contractions).
*HAM
What tissues does P4 stimulate?
- Endometrium(endometrial gland growth and secretions).
- Alveoli in the mammary gland.
What organ is required for luteolysis in most animals?
The Uterus.
When the entire uterus is removed, how is the CL affected?
Its lifespan is longer.
When a contralateral hysterectomy is done, how is the CL affected?
The lifespan of the CL is normal.
When an ipsilateral hysterectomy is done,
how is the CL affected?
The lifespan of the CL is longer.
What are the steps of PGF2a control of luteolysis?
- OT from the CL stimulates the production of uterine PGF2a after day 15*.
- PGF2a synthesis by the uterine endometrium is released into the uterine vein.
- 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.
How much PGF2a is degraded in circulation?
90% is degraded after one pass through the lungs.
What structure is analogous to the PPP?
The ovarian pedicle.
What is different about the uterine and ovarian blood supply in horses?
- PGF2alpha goes into the systemic circulation and comes back because equines do not metabolize PGF2alpha as well as other animals.
- CL’s are more sensitive to PGF2alpha.
Why is prostaglandin rarely used in swine?
It is only effective for 3 days.
What is the relationship between OT and PGF2a?
A positive feedback loop until all of the CL disappears.
*CL–> OT –> Endometrium –> PGF2a –> CL–> OT –> …
What occurs during luteolysis?
- Decreased blood flow.
- Decreased P4 synthesis.
- Increased apoptosis.
- Lymphocytes and macrophages phagocytize the dying CL.
What occurs in primates during luteolysis?
- It does NOT require the uterus.
- 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.
What occurs in dogs and cats during luteolysis?
- No uterine role in CL degradation during a cycle.
- Causes a pseudopregnancy. Can be symptomatic or asymptomatic.
