Luteal Phase Flashcards
3 things that the luteal phase consists of?
- Corpus Luteum
- Production of progesterone
- Luteolysis
What does lutenization mean?
Transformation of granulosa and theca cells into luteal cells
Explain the transformation of granulosa cells to luteal cells
Granulosa cells have a high nuclear-to-cytoplasm ratio. During the lutenization, granulosa cells are converted into luteal cells reducing nuclear-to-cytoplasm ratio.
What do newly formed luteal cells produce?
Large amount of progesterone
What triggers the initiation of progesterone production?
Surge of LH
Explain the formation of the CL
- Pre-ovulatory follicle initiates the lutenization of some cells
- Durring ovulation, collagenase and other enzymes are released which break down the basal lamina
- Initiation of progesterone production
- At ovulation small blood vessels rupture and cause a local hemorrhage
- Implosion occurs
- Mix of granulosa and theca cells
- Remnant of the basal lamina will form connective tissue
- Generation of capillaries and veins
- Functional CL is composed of large (granulosa) and Small (theca) cells
- Small cells will duplicate and increase the volume of CL
3 categories of CL
- Long-lived CL
- Short-lived CL
- Ultrashort-lived CL
Explain long lived CL
- Generally monoestrus animal
2. CL can stay from 2 weeks to 6 months disregarding the pregnancy status
Explain short-lived Cl
- Many polyestrus animals
2. Luteal life depends on pregnancy status - if pregnant CL will last longer
Explain ultrashort-lived CL
- Polyestrus Rodent
2. CL is not fully formed
role of StAR enzyme in progesterone production?
Transporter of chol into the mitochondria
Effect of progesterone on the hypothalamus?
Progesterone has a negative effect on the hypothalamus which indirectly reduce the release of LH and FSH
Effects of P4 on the uterus
- Reduction of contractions of the myometrium
2. Induce secretions of the uterine glands (increases thickness of endometrium)
Effect of P4 on mammary gland
Stimulation of the alveolar development in the mammary glands
What is luteolysis?
The regressio of the CL
Irreversible
What is luteolysis characterized by?
Arrest of the progesterone production and a physical involution to the CL
3 Requirements for luteolysis
- PGF2alpha synthesis by endometrium
- Oxytocin secretion
- Reduction of progesterone receptors
What evidence do we have that the uterus plays a role in luteolysis?
- If uterus removed no production of PGF2alpha and CL lifespan increased
- If uterine horn contralateral to CL is removed CL lifespan is relatively normal
- If uterine horn ipsilateral to CL is removed CL lifespan is increased
How does PGF2alpha produced in the uterine horn, reach the ovary where the CL is located?
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
What occurs to PGF2alpha as oxytocin increases?
As oxytocin increases PGFalpha2 increases
What factors stimulate production of PGF2alpha?
High expression of progesterone induces repression of progesterone receptors located in the uterine endometrium. As P4 receptors reduce secretion of PGF2alpha increases
- Oxytocin receptors increase with luteolysis
4 ways in which PGF2alpha works
- Reduce luteal blood flow
- Block the action of lutenization factors
- Inhibit steroidogenesis
- Promote cell destruction
Effect of PGF2alpha during CL growth
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
