9 - Luteal Phase

Question 1

Stages of the follicular phase? Luteal phase?

Answer 1

F: Proestrus then estrus
L: metestrus then diestrus

Question 2

After ovulation, the follicle becomes the…

Answer 2

corpus hemorrhagicum

Question 3

How are cells arranged in the CH

Answer 3

theca interna and granulosa cells are mixed

Question 4

What happens to the CH?

Answer 4

Its cells become luteal tissue (luteinization)

Question 5

What governs luteinization

Answer 5

Basal levels of LH

Question 6

Two types of cells in corpus luteum

Answer 6

Granulosa cells become large luteal cells (20-40 um)
Theca cells become small luteal cells (<20 um)

Question 7

Which CL cells produce P4

Answer 7

both

Question 8

Until when does the CL continue increasing in size? As it grows, it…

Answer 8

Until ~midway of Luteal Phase

As it grows it produces more and more P4

Question 9

CL capacity (ability to produce and deliver P4) depends on (2):

Answer 9

1. Number of luteal cells (more cells = more P4)
2. Degree of CL vascularization (affects ability of CL to deliver P4 to target tissues)

Question 10

Which CL cells proliferate

Answer 10

Large luteal cells do not, only increase in size as CL grows
Small luteal cells do

Question 11

What is considered to be a major contributor to reproductive failure in domestic animals

Answer 11

Poor CL capacity (ability yo produce and deliver P4)

Question 12

Slides 10-16

Answer 12

Diagrams and such

Question 13

What animal has the highest levels of blood progesterone

Answer 13

The sow
Many corpus hemorrhagicum
No progesterone plateau

Question 14

What does the CL require to produce progesterone? What is the pathway?

Answer 14

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

Question 15

Slides 18, 19***

Answer 15

P4 synthesis by luteal cells
LOOOOK

Question 16

What delivers cholesterol into luteal cells? Why

Answer 16

Low density lipid protein
It is a steroid hormone therefore needs protein transport

Question 17

How does LH act on luteal cells

Answer 17

Binds to specific LH receptors on cell membrane
LH-receptor complex activates G-protein which activates adenylate cyclase

Question 18

Once adenylate cyclase is activated, what does it do

Answer 18

Converts ATP to cAMP
cAMP activates protein kinases which have various roles

Question 19

What are the roles of protein kinases

Answer 19

• accelerate LDL-cholesterol internalization
• activate cholesterol-esterase to modify the cholesterol molecule
• promote entry of cholesterol into the mitochondria

Question 20

What happens to cholesterol inside the mitochondria

Answer 20

Mitochondrial enzymes convert it to pregnenolone

Question 21

What happens once pregnenolone is outside of the mitochondria

Answer 21

It is converted into progesterone by cytoplasmic enzymes
Then leaves the cell and enters circulation

Question 22

Two types of effects progesterone can have

Answer 22

1. Inhibitory
2. Stimulatory

Slide 21

Question 23

What are the inhibitory effects of P4

Answer 23

• 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

Question 24

What are the stimulatory effects of progesterone

Answer 24

• Mammary gland: promotes alveolar development
• Uterus: promotes secretion into lumen

Question 25

What causes CL regression (luteolysis)

Answer 25

Prostaglandin F2a produced by the uterus

Question 26

Luteolysis causes:

Answer 26

• cessation of P4 production
• regression of CL to form a corpus albicans (white body)
• entrance into a new follicular phase (proestrus)

Question 27

Slides 23-26

Answer 27

Ewe uterectomy model

Question 28

What kind of uterectomy yields a CL lifespan similar to a normal cycle?

Answer 28

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)

Question 29

How does PGF2a get from the uterus to the ovary?

Answer 29

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

Question 30

What kind of system gets PGF2a from the uterus to the ovary

Answer 30

Closed system
Transported to the ovary without dilution by general circulatory

Question 31

What stimulates PGF2a production by the uterus

Answer 31

• 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

Question 32

Two theories on the intracellular mechanisms of luteolysis

Answer 32

1. PGF2a causes restriction and eventual degeneration of arteries to the luteal cells: reduced blood flow causes CL to regress
2. PGF2a triggers a cascade of events that inhibit P4 synthesis and result in death of the luteal cells (apoptosis)

Slide 32 = theory 2

Question 33

Luteolysis depends on…

Answer 33

• presence of oxytocin receptors in the uterine endometrium
• oxytocin production by the large luteal cells
• PGF2a synthesis by uterine endometrium