Corpus Luteum

Question 1

Where does the corpus luteum orginate from?

Answer 1

ovulatory follicle

Question 2

describe luteinization

Answer 2

after ovulation, the theca interna and granulosa cells of the follicle undergo a transformation

Question 3

How does the theca interna change during luteinization

Answer 3

small luteal cells
-mitosis after ovulation (hyperplasia): 5 fold increase

Question 4

How does the granulosa cells change during luteinization

Answer 4

large luteal cells
-hypertrophy cells( increase in cell size): 3 fold increase

Question 5

What does the luteal phase consist of

Answer 5

-luteinization(formation of the CL)
-synthesis and secretion of large quantities of progesterone
-luteolysis

Question 6

Luteal tissue consists of what type of cells

Answer 6

-large cells originate from the granulosal cells
-small cells originate from the cells of the theca interna

Question 7

What are the three main steps of the formation of the CL

Answer 7

1. preovulatory follicle: granulosal and theca cells start to intermingle
   2.”bloody body”: small blood vessels rupture causing a local hemprrhage
2. CL: mixture of small and large luteal cells

Question 8

What does the vigor of the C.L depend on?

Answer 8

-the number of luteal cells
-degree of which the CL becomes vascularized

Question 9

Progesterone is an inhibitor because it..

Answer 9

-reduces GnRH pulse frequency
-prevents behavioral estrus
-stops the preovulatory LH surge
-reduces myometrial tone (not in the mare)

Question 10

what does a vascular countercurrent transport system ensure?

Answer 10

that PGF2a will reach the ovary ins sufficient quantities to cause luteolysis in the ewe, cow and sow

Question 11

describe the counter current exchange system

Answer 11

involves two closely associated blood vessels in which blood from one vessel, flows in opposite direction to that of the adjacent vessel

Question 12

What are the requirements for luteolysis

Answer 12

-presence of oxytocin receptors on endometrial cells
-presence of critical level of oxytocin
-PGF2a synthesis by the endometrium

Question 13

what does luteolysis result in

Answer 13

-cessation of progesterone secretion
-structural regression to form a corpus albicans
-removal of negative feedback by progesterone by GnRH secretion resulting in a new follicular phase

Question 14

What does the CL vigor depend on?

Answer 14

appears to depend upon numbers of cells and vascularization

Question 15

What are the cells found in the CL ?

Answer 15

non-steroidogenic cells (fibroblasts, capillary cells, eosinophilis) increase in number

Question 16

how long foes the luteal phase last till

Answer 16

from the time of ovulation until regression (luteolysis) of the corpus luteum

Question 17

What is the importance of progesterone?

Answer 17

-progesterine synthesis requires cholesterol and LH
-progesterone is necessary for the maintenance of pregnancy

Question 18

What are the actions of progesterone

Answer 18

-affects basal LH secretion
-prevents estrus
-stops the preovulatroy surge of LH
-reduces myometrial tone

Question 19

what is luteolysis and what is responsible for it?

Answer 19

-luteal regression, cessation of function of the CL
-occurs at the end of the luteal phase
-Hormone responsible for luteolysis in domestic farm specis PGF2a from the uterus

Question 20

What is the relationship of oxytocin and PGF2a

Answer 20

oxytocin is coming from the posterior pituitary
-affecting the uterus, releasing PGF2a (from the uterus) to the ovary
-oxtocin also affects the CL

Question 21

how do you initiate luteolysis

Answer 21

up to luteolysis, progesterone suppresses oxytocin receptors in the uterus

Question 22

What are the events leading up to luteolysis?

Answer 22

1. progesterone loses its ability to suppress formation of uterine oxytocin receptors
   2.Estrogen binds to the endometrial receptors to upregulate oxytocin receptor
2. oxytocin binds to receptors to stimulate PGF2a release
3. Amongst other actions, PGF2a increases oxytocin release from CL

Question 23

describe counter current exchange

Answer 23

exchange of PGF2a, uterine PGF2a is transported directly from the uterine vein into the ovarian artery

Question 24

What types of hysterectomy will make the C.L lifespan longer, why

Answer 24

ipsilateral and total hysterectomy, CL on the left/Uterine horn removed from the left or whole structure, no counter current exchange happening

Question 25

Which hysterectomy will have no affect on CL lifespan? why

Answer 25

contralateral hysterectomy, CL is on the left/uterine horns gone on the right, counter current heat exchange is still occurring

Question 26

What regulates the lifespan of the C.L

Answer 26

the uterus

Question 27

Where is PGF2a metabolized in the body

Answer 27

the LUNGS

Question 28

Which species does not need the counter current heat exchange system

Answer 28

the mare, very sensitive

Question 29

Describe counter current exchange

Answer 29

PGF2a is synthesized by the uterine endometrium and is released into the uterine vein
-PGF2a is picked up by the ovarian artery though counter current heat exchange and is delivered back to the ovary where is causes lysis of the CL
-the artery is wrapped around the vein
-vein to artery to ovary (away from the uterus towards the ovary)’
-PGF2a is metobilized very quickly in the body (needs pulsatile secretion)

Question 30

if you give artificial PGF2a,

Answer 30

luteolysis does not even occur

Question 31

Positive feedback example?

Answer 31

The stimulation form the PGF2a on the CL of the ovary is producing more oxytocin release which affects the uterus

Question 32

PGF2a is responsible for..

Answer 32

destruction of the C.L