Final Exam (Lecture 61) - Placenta and Parturition

Question 1

What is the function of eCG in the mare? What about eCG in other species?

Answer 1

1) In the mare:
- Luteotrophic activity
- Activates LH receptor on small luteal cells (SLCs) in the CL
- LH-R (a GPCR) activation leads to P4 synthesis (P4 is the pro-gestational hormone)
- Promotes the growth of accessory CLs

2) In other species:
- eCG has FSH-like activity
- Used for superovulation in embryo transfer

Question 2

What is placental lactogen and what is its function?

Answer 2

A hormone released by the placenta during pregnancy
- Stimulates the growth and development of the mammary gland
- Stimulates growth and development of the fetus
- For most species (except cattle and goats) it is more involved in lactogenesis

Question 3

What are the hormonal changes at parturition? How is fetal cortisol especially involved?

Answer 3

1) E2 and PGF2-alpha levels coordinately rise and peak at parturition
- Both hormones have direct effects on the myometrium
- PGF2-alpha influences the release of relaxin

Placenta produces relaxin and oxytocin near parturition
  - Oxytocin = stimulates myometrial contractions
  - Relaxin causes a relaxation of connective tissue in vagina and cervix
        - In the bovine, relaxin IS NOT produced by the placenta but by the CL

2) Fetal cortisol rising is the major impetus of the parturition process
- The fetus grows and becomes “cramped”; activating a stress response via the pituitary-adrenal axis
- Fetal anterior pituitary releases ACTH that causes a release of adrenal cortisol
- Fetal cortisol activates cascades that facilitate parturition
- Fetal cortisol activates enzymes that convert placental P4 to E2
- Fetal cortisol activates PGF2-alpha synthesis in the placenta

Question 4

What is the major feedback mechanism of parturition and the postpartum period?

Answer 4

Oxytocin is the primary feedback hormone

Question 5

What are the five general endocrine functions of the placenta?

Answer 5

1) Stimulates ovarian function

2) Maintains pregnancy

3) Influences fetal growth and development

4) Stimulates the mammary gland

5) Assist in parturition

Question 6

What are the classification schemes of the placenta and what are examples of each?

Answer 6

1) Macroscopic (gross) appearance based on the generalized degree of contact between the placenta and the endometrium.
a) Diffuse = Sow and mare
b) Cotyledonary = Ruminants
c) Zonary = Dogs and cats
d) Discoid = Humans (not discussed)

2) Microscopic appearance based on the amount of intimate contact between the placenta and the endometrium (layering).
a) Epitheliochorial = Mare and sow; 6 layers between fetal and maternal blood supplies
b) Syndesmochorial = Ruminants; same as above with addition of binucleate giant cells (fetal side) and
trinucleate feto-maternal hybrid cells
c) Endotheliochorial = Dogs and cats; 5 layers between blood supplies
d) Hemochorial = Primates and rodents; fewest layers between blood supplies

3) Fate of the placenta based on the retention (or lack of) of the placenta after parturition.
a) Deciduous = All of the placenta falls out of the uterus after parturition
b) Non-deciduous = A portion of the placenta stays in the uterus after parturition
- epitheliochorial
- syndesmochorial

Question 7

Which types of molecules can cross the B-P-B?

Answer 7

By Simple Diffusion:
- Water
- Gases (CO2, O2, CO)
- Lipid hormones (estrogen/testost.)

By Facilitated Diffusion:
- Glucose
- Amino acids
- Immunoglobulins

By Active Transport:
- Sodium
- Potassium

• Toxic substances (such as drugs) as well as microbial pathogens can also cross the BPB.