The Placenta

Question 1

What is the placenta?

Answer 1

• a disc-shaped temporary organ
• richly supplied with maternal and foetal blood vessels

Question 2

What does the placenta connect?

Answer 2

• the foetus with its mother’s blood
• at the end of the umbilical cord

Question 3

What does the placenta develop from?

Answer 3

• the chorion and its villi (that penetrate the endometrium)

Question 4

What is the importance of the villi on the chorion that the placenta develops from?

Answer 4

• the villi provide a large surface area of attachment of the placenta to the endometrium

Question 5

What does each placental villus contain and why?

Answer 5

• each villus contains a capillary network
• which provides a large surface area for exchange of substances by diffusion

Question 6

What are the placental villi surrounded by and why?

Answer 6

• the mother’s blood
• so that mother’s blood supply and foetal capillaries are very close to each other

Question 7

Does the foetal and mother’s blood mix? Why or why not?

Answer 7

• no
• because the foetal capillaries have thin walls

Question 8

How do substances move between the maternal and foetal blood?

Answer 8

• by diffusion

Question 9

What would happen if the mother’s blood mixed with the foetal blood?

Answer 9

• it could cause the foetal blood to clot
• resulting in the death of the foetus

Question 10

What is the 1st function of the placenta?

Answer 10

1. Oxygen and dissolved food substances pass from the mother to the foetal blood system for respiration and nutrition

Question 11

What are some examples of dissolved food substances that pass from the mother to the foetal blood system through the placenta?

Answer 11

• glucose
• amino acids
• fatty acids
• ions
• vitamins

Question 12

What is the 2nd function of the placenta?

Answer 12

2. Foetal waste products of metabolism pass into the maternal blood system for excretion

Question 13

What are some examples of foetal waste products of metabolism that pass into the maternal blood system for excretion?

Answer 13

• urea
• carbon dioxide

Question 14

What is the 3rd function of the placenta?

Answer 14

3. Some maternal antibodies pass to the foetus, providing temporary passive immunity to certain diseases

Question 15

What is the result of antibodies being passed to the foetus through the placenta?

Answer 15

• the child enjoys immunity to most infectious diseases for the first 6 months of life

Question 16

What is the 4th function of the placenta?

Answer 16

4. The placenta acts as a barrier (micro filter)
   - preventing many pathogenic organisms and drugs from entering the foetus from the mother

Question 17

What are some examples of pathogens that can pass through the placenta to the foetus?

Answer 17

• German measles (rubella)
• syphilis
• HIV

Question 18

What does the placenta do after 3 months of pregnancy? (5th placental function)

Answer 18

5. The placenta takes over the function of secreting progesterone and oestrogen from the ovaries (corpus luteum)

Question 19

Why are progesterone and oestrogen important in pregnancy?

Answer 19

• these hormones are essential from brining about the necessary changes in the uterus
• and for the maintenance of pregnancy

Question 20

What does progesterone do in pregnancy?

Answer 20

• prevents ovulation and menstruation
• which would result in the loss of the foetus

Question 21

What does the placenta secrete late in pregnancy and why?

Answer 21

• relaxin
• a hormone that relaxes joints and ligaments to assist in the delivery of the baby

Question 22

What kind of harmful substances can pass though the placenta and cause significant damage to the developing embryo and foetus?

Answer 22

• cigarette smoke (carbon monoxide and nicotine)
• alcohol
• illegal drugs
• many medicines