9 - Luteal Phase Flashcards
Stages of the follicular phase? Luteal phase?
F: Proestrus then estrus
L: metestrus then diestrus
After ovulation, the follicle becomes the…
corpus hemorrhagicum
How are cells arranged in the CH
theca interna and granulosa cells are mixed
What happens to the CH?
Its cells become luteal tissue (luteinization)
What governs luteinization
Basal levels of LH
Two types of cells in corpus luteum
Granulosa cells become large luteal cells (20-40 um)
Theca cells become small luteal cells (<20 um)
Which CL cells produce P4
both
Until when does the CL continue increasing in size? As it grows, it…
Until ~midway of Luteal Phase
As it grows it produces more and more P4
CL capacity (ability to produce and deliver P4) depends on (2):
- Number of luteal cells (more cells = more P4)
- Degree of CL vascularization (affects ability of CL to deliver P4 to target tissues)
Which CL cells proliferate
Large luteal cells do not, only increase in size as CL grows
Small luteal cells do
What is considered to be a major contributor to reproductive failure in domestic animals
Poor CL capacity (ability yo produce and deliver P4)
Slides 10-16
Diagrams and such
What animal has the highest levels of blood progesterone
The sow
Many corpus hemorrhagicum
No progesterone plateau
What does the CL require to produce progesterone? What is the pathway?
LH and Cholesterol
Basal LH stimulates P4 production by luteal cells
Cholesterol is the precursor to pregnenolone which is the precursor of progesterone
Slide 17
Slides 18, 19***
P4 synthesis by luteal cells
LOOOOK
What delivers cholesterol into luteal cells? Why
Low density lipid protein
It is a steroid hormone therefore needs protein transport
How does LH act on luteal cells
Binds to specific LH receptors on cell membrane
LH-receptor complex activates G-protein which activates adenylate cyclase
Once adenylate cyclase is activated, what does it do
Converts ATP to cAMP
cAMP activates protein kinases which have various roles
What are the roles of protein kinases
- accelerate LDL-cholesterol internalization
- activate cholesterol-esterase to modify the cholesterol molecule
- promote entry of cholesterol into the mitochondria
What happens to cholesterol inside the mitochondria
Mitochondrial enzymes convert it to pregnenolone
What happens once pregnenolone is outside of the mitochondria
It is converted into progesterone by cytoplasmic enzymes
Then leaves the cell and enters circulation
Two types of effects progesterone can have
- Inhibitory
- Stimulatory
Slide 21
What are the inhibitory effects of P4
- Hypothalamus/pituitary/brain: reduces basal GnRH amplitude and frequency (prevents development of preovulatory follicles, production of E2, LH surge and mating beh)
- uterus: reduces myometrial contractions and tone
What are the stimulatory effects of progesterone
- Mammary gland: promotes alveolar development
- Uterus: promotes secretion into lumen
What causes CL regression (luteolysis)
Prostaglandin F2a produced by the uterus
Luteolysis causes:
- cessation of P4 production
- regression of CL to form a corpus albicans (white body)
- entrance into a new follicular phase (proestrus)
Slides 23-26
Ewe uterectomy model
What kind of uterectomy yields a CL lifespan similar to a normal cycle?
Partial uterectomy on the opposite side of the CL
Total uterectomy = CL lifespan of normal gestation length (148 d)
Partial uterectomy on same side as CL = longer than normal lifespan (35 d)
How does PGF2a get from the uterus to the ovary?
Transported to ipsilateral ovary (same side) via vascular countercurrent exchange mechanism
Blood flowing from the uterus in the uterine vein passes next to blood flowing to the ovary in the ovarian artery
PGF2a produced by the uterus is transferred across the wall of the uterine vein into the blood of the ovarian artery
slide 28
What kind of system gets PGF2a from the uterus to the ovary
Closed system
Transported to the ovary without dilution by general circulatory
What stimulates PGF2a production by the uterus
- large luteal cells produce oxytocin along with P4
- oxytocin receptors on the uterine endometrium trigger PGF2a production
- oxytocin receptors develop on the uterine endometrium as the luteal phase progresses
Slide 29
Two theories on the intracellular mechanisms of luteolysis
- PGF2a causes restriction and eventual degeneration of arteries to the luteal cells: reduced blood flow causes CL to regress
- PGF2a triggers a cascade of events that inhibit P4 synthesis and result in death of the luteal cells (apoptosis)
Slide 32 = theory 2
Luteolysis depends on…
- presence of oxytocin receptors in the uterine endometrium
- oxytocin production by the large luteal cells
- PGF2a synthesis by uterine endometrium
