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ASCI 341 > CH 9 The Luteal Phase of the Estrous Cycle > Flashcards

CH 9 The Luteal Phase of the Estrous Cycle Flashcards

1
Q

When does the luteal phase occur? What phases does it consist of?

A

Lasts from the time of ovulation until luteolysis (regression of CL)

Consists of metestrus and diestrus

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2
Q

What key things have to happen in order to have the luteal phase occur?

A
  • Corpa lutea formation
  • Production of progesterone
  • Luteolysis
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3
Q

What happens to a follicle at ovulation?

A

Follicle ruptures as well as the blood vessels within the follicular wall –> forms corpus hemorrhagium (bloody body)

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4
Q

How is the follicle observed from day 1-3 of the estrous cycle?

A

Appear as small, pimple-like structures on surface of ovary

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5
Q

What happens to CL at day 3-5 of the estrous cycle?

A

CL begins to increase in size as loose hemorrhagic appearance. Gains size until middle of estrous cycle.

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6
Q

What is happening to Cl as diestrus?

A

CL has reached mature suze and maximal levels of progesterone

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7
Q

What happens to CL at the end of the luteal phase?

A

At the end of the luteal phase, luteolysis occurs and CL loses functionality and decreases in size

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8
Q

What happens as CL degrades?

A

Forms corpus Albicans - scar-like tissues

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9
Q

What happens to the follicle after ovulation?

A

After ovulation, theca internal and granulosa cells undergo dramatic transformation (lutenization)

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10
Q

What is luteinization?

A

Process whereby cells of the ovulatory follicle are transformed into luteal tissue

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11
Q

What two cells do luteal tissue consist of?

A

large cells and small cells

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12
Q

Where do large cells originate from?

A

granulosa cells

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13
Q

What do large cells contain?

A

Many dense secretory granules near plasma membrane (in ruminants)

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14
Q

What do secretory granules in large cells contain?

A

Oxytocin - CL of estrous cycle
Relaxin - CL od pregnancy

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15
Q

Where do small cells originate from?

A

theca interna cells

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16
Q

What are characteristics of small cells?

A

irregular shape, numerous lipid droplets, no secretory granules

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17
Q

What is growth of CL mass a net effect of?

A
  • Large luteal cells undergo hypertrophy (increase in size)
  • Small luteal cells undergo hyperplasia (increase in #)
  • Non-steroidogenic cells also increase in numbers (fibroblasts, capillary cells, eosinophils)
18
Q

What does the vigor of CL depend on?

A
  • number of luteal cells
  • degree of which CL has become vascularized –> may be due to amount of angiogenic factors produced by follicular fluid
19
Q

What are progesterone target tissues?

A
  • surge and tonic centers of the hypothalamus
  • anterior pituitary
  • alveoli mammary gland
  • Endometrium of the uterus –> produces maximal secretions which are essential to the developing embryo
  • Myometrium of the uterus - reduces contractility and promotes “quiescence” of the tract to support embryo implantation
20
Q

Why is progesterone an inhibitor?

A
  • reduces basal GnRG amplitude and frequency
  • prevents behavioral estrus
  • stops the preovulatory LH surge
  • reduces myometrial tone
21
Q

What does progesterone synthesis require?

A

Requires basal (tonic) LH and cholesterol

22
Q

What is luteolysis?

A

The disintegration of decomposition (lysis) of the CL. CL undergoes irreversible degeneration characterized by a dramatic drop in blood levels of progesterone

23
Q

What are the requirements for luteolysis /and what are the two main hormones that control luteolysis?

A
  • Presence of oxytocin receptors on endomediral glands
  • Oxytocin from the CL
  • PGF2a from uterine endometrium
24
Q

What does PGF2a do in the luteal phase?

A

Causes luteolysis –> vascular counter-current exchage

25
Q

What did sheep surgery experiments tell us?

A
  • uterus is required for successful luteolysis
  • uterus must be near the ovary
26
Q

What is luteal oxytocin made be?

A

synthesized and secreted by large luteal cells

27
Q

What is the difference between luteal secretory granule oxytocin and posterior pituitary oxytocin?

A

Analogous (same)

28
Q

What is significant about PGFa metabolites?

A

Metabolites are easier to measure

29
Q

How does PGF2a secretion occur during late luteal phase?

A

Secretion occurs in pulses

Pulses increase in frequency and amplitude as the end of the luteal phase approaches. A critical number of pulses in a given time period are required for luteolysis to occur.

30
Q

What is required for PGF2a to be released?

A

Elevated levels of progesterone

31
Q

What happens to first half life of PGF2a during the first half of the estrous cycle?

A

Progesterone prevents PGF2a secretion by blocking formation of oxytocin receptors in the uterus

32
Q

What happens to progesterone after 10-12 days after the first half of the estrous cycle?

A

Progesterone loses its ability to black the formation of oxytocin receptors. So, oxytocin receptors can bind to oxytocin in the uterine endometrium which stimulates release of PGF2a

33
Q

What does luteolysis result in?

A
  • cessation of progesterone production
  • structural regression to from a CA
  • follicular development and entrance into a new follicular phase
34
Q

What are the possibilities of intracellular mechanisms that cause luteolysis?

A
  • reduced blood flow to CL
  • capillary degeneration resulting in decreased blood flow to CL
  • PGF2a binds to receptors on large luteal cells resulting in death of these cells and therefrom steroidgenesis
35
Q

What may structural regression of CL be due to?

A

Immune system

Macrophages and lymphocytes present at luteolysis

36
Q

What do macrophages and lymphocytes produce?

A

Cytokines

37
Q

What are cytokines?

A

Non-antibody proteins that produce a variety of immune cells that act as intracellular mediators of the immune response

38
Q

What do cytokines trigger?

A

May trigger process called apoptosis

39
Q

What is apoptosis?

A

Programmed cell death

40
Q

Cell death occurs by what 2 processes?

A
  • necrosis
  • apoptosis
41
Q

What does the final destruction of CL consist of?

A

Performed by macrophages which phagocytize damaged luteal cells. Over time luteal cells completely disappear, leaving only connective tissue behind (CA)

ASCI 341 (13 decks)

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