Luteal Phase

Question 1

3 things that the luteal phase consists of?

Answer 1

1. Corpus Luteum
2. Production of progesterone
3. Luteolysis

Question 2

What does lutenization mean?

Answer 2

Transformation of granulosa and theca cells into luteal cells

Question 3

Explain the transformation of granulosa cells to luteal cells

Answer 3

Granulosa cells have a high nuclear-to-cytoplasm ratio. During the lutenization, granulosa cells are converted into luteal cells reducing nuclear-to-cytoplasm ratio.

Question 4

What do newly formed luteal cells produce?

Answer 4

Large amount of progesterone

Question 5

What triggers the initiation of progesterone production?

Answer 5

Surge of LH

Question 6

Explain the formation of the CL

Answer 6

1. Pre-ovulatory follicle initiates the lutenization of some cells
2. Durring ovulation, collagenase and other enzymes are released which break down the basal lamina
3. Initiation of progesterone production
4. At ovulation small blood vessels rupture and cause a local hemorrhage
5. Implosion occurs
6. Mix of granulosa and theca cells
7. Remnant of the basal lamina will form connective tissue
8. Generation of capillaries and veins
9. Functional CL is composed of large (granulosa) and Small (theca) cells
10. Small cells will duplicate and increase the volume of CL

Question 7

3 categories of CL

Answer 7

1. Long-lived CL
2. Short-lived CL
3. Ultrashort-lived CL

Question 8

Explain long lived CL

Answer 8

1. Generally monoestrus animal

2. CL can stay from 2 weeks to 6 months disregarding the pregnancy status

Question 9

Explain short-lived Cl

Answer 9

1. Many polyestrus animals

2. Luteal life depends on pregnancy status - if pregnant CL will last longer

Question 10

Explain ultrashort-lived CL

Answer 10

1. Polyestrus Rodent

2. CL is not fully formed

Question 11

role of StAR enzyme in progesterone production?

Answer 11

Transporter of chol into the mitochondria

Question 12

Effect of progesterone on the hypothalamus?

Answer 12

Progesterone has a negative effect on the hypothalamus which indirectly reduce the release of LH and FSH

Question 13

Effects of P4 on the uterus

Answer 13

1. Reduction of contractions of the myometrium

2. Induce secretions of the uterine glands (increases thickness of endometrium)

Question 14

Effect of P4 on mammary gland

Answer 14

Stimulation of the alveolar development in the mammary glands

Question 15

What is luteolysis?

Answer 15

The regressio of the CL

Irreversible

Question 16

What is luteolysis characterized by?

Answer 16

Arrest of the progesterone production and a physical involution to the CL

Question 17

3 Requirements for luteolysis

Answer 17

1. PGF2alpha synthesis by endometrium
2. Oxytocin secretion
3. Reduction of progesterone receptors

Question 18

What evidence do we have that the uterus plays a role in luteolysis?

Answer 18

1. If uterus removed no production of PGF2alpha and CL lifespan increased
2. If uterine horn contralateral to CL is removed CL lifespan is relatively normal
3. If uterine horn ipsilateral to CL is removed CL lifespan is increased

Question 19

How does PGF2alpha produced in the uterine horn, reach the ovary where the CL is located?

Answer 19

Counter Current Diffusion System

As PGF2alpha is carried via the uterine vein it passes in close proximity to the Ovarian artery. Diffusion occurs and PGF2alpha is carried to the ovary

Question 20

What occurs to PGF2alpha as oxytocin increases?

Answer 20

As oxytocin increases PGFalpha2 increases

Question 21

What factors stimulate production of PGF2alpha?

Answer 21

High expression of progesterone induces repression of progesterone receptors located in the uterine endometrium. As P4 receptors reduce secretion of PGF2alpha increases

2. Oxytocin receptors increase with luteolysis

Question 22

4 ways in which PGF2alpha works

Answer 22

1. Reduce luteal blood flow
2. Block the action of lutenization factors
3. Inhibit steroidogenesis
4. Promote cell destruction

Question 23

Effect of PGF2alpha during CL growth

Answer 23

In the first 6 days of CL life PGF2alpha has no effect on the CL

After 7 days when P4 production is optimal, PGF2alpha injection will initiate luteolysis and Estrus will occur in 3 days - this method is used to sync dairy herds