Preggers Physiology

Question 1

Outline the fluctuating levels of hormones seen in the menstrual cycle:

• Day 1 - Day 14
• Day 14 - Day 28
• In the case of fertilisation

Answer 1

Day 1 - Day 14

• Oestrogen levels increase and peak at 14 days.
• Progesterone levels remain low throughout the first 14 days.

Day 14 - 28

• Oestrogen levels decrease through the next 2 weeks.
• Progesterone levels peak and then through again by the end of the cycle (if pregnancy has not occurred.)

Fertilisation

• Progesterone levels won’t decrease as normal, instead increasing further than what would be seen in a normal (non-preg.) situation

Question 2

What does progesterone fo to the endometrium?

Answer 2

• Causes thickening of the endometrium, causing cell changes (stromal cells) and turning it into “decidua”
  
  • Initially in preparation for a fertilised egg.
  • Then in the case of fertilisation it thickens further to support the growing embryo.
• Along with thickening there is increased vascularlity.

Question 3

What do the stromal cells of the endometrium do?

Answer 3

The stromal cells enlarge between the vessels and glands and become procoagulant, thereby stopping bleeding.

Question 4

What is another name for a fertilised egg?

What are found on the surface of the egg?

What do these produce?

Answer 4

• Egg fertilised by ‘chorion’
• Outer edge of chorion - Trophoblast cells on outside of fertilised egg.
• These trophoblast cells produce B-HCG

Question 5

What is B-HCG?

What is the target for this hormone?

What is its function?

What is this hormone used for clincially?

Answer 5

• Beta Human Chorionic Gonadotrophin
• Target - Corpus luteum in the Ovary
• Function - stimulate corpus luetum to produce progestrogen throughout pregnancy, which stops the decidua from shedding.
• Clinical - basis of pregnancy tests

Question 6

What happens when the fertilised egg reaches the decidua?

Answer 6

• Fertilised egg burrows into the decidua.
• Trophoblast cells stream off to invade the mother’s blood vessels eventually linking these vessels with that of the foetus
• Projections of chorion (chorionic villi), covered in trophoblast cells, start to move into the decidua.
• The decidual cells are procoagulant and stop bleeding when the trophoblast cells invade mother’s blood.
• Eventually the chorionic villi, covered in trophoblast cells, are bathed in the mother’s blood, forming the forerunner of the placenta.