Lecture 27

Question 1

What are the main roles of progesterone in pregnancy?

Answer 1

1. Suppresses oestrus cycling (does this via the suppression of pituitary LH secretion) 2. Acts on the endometrium of the uterus allowing it to be ready to receive the embryo 3. Suppresses the contractile activity of the myometrium (ensures that it does not accidentally give birth prematurely)

Question 2

Evaluate the statement below: “Progesterone is essential for early embryonic development within all species”

Answer 2

False. The placenta will take over mid gestation

Question 3

What is the name of the hormone that causes the death of the CL?

Answer 3

prostaglandin

Question 4

Describe the recognition of pregnancy within most animals:

Answer 4

The embryo has a chemical response that will prevent the prostaglandin release, stopping prostaglandin from reaching CL via local vascular pathways ensuring that the CL will survive.

Question 5

Describe how recognition of pregnancy occurs within horses:

Answer 5

In the horse the endometrial PGF can only reach the ovary by the peripheral circulation. In the pregnant the direction of the PGF is switched to exocrine into the uterine lumen ensuring it does not go into the peripheral circulation and cause death of the CL.

Question 6

What are the main functions of the placenta?

Answer 6

1. Main function is to allow maternal blood flow supply to occur 2. Placenta also has endocrine function

Question 7

What are the main functions of oestrogen in pregnancy?

Answer 7

1. Proliferative effect- maternal reproductive tissues- including the uterus and on mammary glands 2. Relaxation- pelvic ligaments in preparation for birth

Question 8

A.) Name the hormones in the image below from pregancy in a mare:

B.) What is the function of the spike of the green hormone on the image below

Answer 8

A)Dark blue = progesterone from the ovaries

Light pink = oestrogens from the ovaries

Green = equine chorionic gonatropin

Orange = oestrogens from the placenta

Dark pink = progesterone from the placenta

B.) Equine chorionic gonadotropin associated with the stimulation of ovulation of more follicles, and the development of corpus luteum to release progesterone

Question 9

What are the main hormonal changes that are occuring in the onset of parturition:

Answer 9

1. ) Decreases in progesterone lead to removal of the inhibition on uterine muscular activity. The increase in fetal cortisol secreted from adrenal gland leads to the activation of enzymes in the placenta which will lead to the conversion of progesterone to oestrogen
2. ) Prostaglandin and oxytoxin are the two main hormones that are responsible for parturition
3. ) Low concentrations of oxytoxin lead to rythmic uterine contractions, high concentrations lead to tonic contractions and leads to contraction of the myoepithelial cells of the alveoli

Question 10

Briefly describe the three stages and the hormones that are involved in parturition:

Answer 10

1. This is a stage whereby the animal is restless and uncomfortable and will seek a safe place away from other animals. In this stage prostaglandins are formed this causes the ligaments of the cervix to soften and dilate causing a large amount of discomfort for the mother, oestrogen levels increase.
2. Actual birth of the foetus. The membranes are pushed out and the water breaks resulting in expulsion of the foetus. The positive feeback loops causes more and more oxytocin to be released.
3. Placenta is passed and detaches. The continued release of prostaglandins and oxytocin helps the uterus to contract further assisiting in detachement of the placenta