12.5 Placenta

Question 1

What is apposition?

Answer 1

The process of the blastocyst coming close to the maternal decidua

Question 2

Describe the orientation of the blastocyst during apposition

Answer 2

Inner cell mass faces towards maternal decidua

Question 3

How do gases and urea pass through the placenta to a foetus?

Answer 3

Diffusion from maternal circulation:
- Through pores in placenta
- Through placental cells

Question 4

How is glucose (among other things) transported to a foetus through the placenta?

Answer 4

• Facilitated diffusion (down concentration gradient)

Question 5

How are amino acids transported across the placenta to the foetus? Why does this make sense?

Answer 5

• Exchange transport/active transport
• Makes sense, baby has more amino acids than mother, needs to go against CG

Question 6

How are large molecules such as immunoglobulins carried across the placenta?

Answer 6

Endocytosis followed by exocytosis

Question 7

What important hormones does the placenta make?

Answer 7

• hCG
• Setroids (oestrogen and progesterone)
• Placental lactogen
• Placental growth hormone
• Relaxin

Question 8

How long into pregnancy do hCG levels peak? Why isn’t it needed after this?

Answer 8

• Peak ~Week 9
• After this, placenta does job of luteum, so luteum doesn’t need to be sustained

Question 9

What is the main source of progesterone in early pregnancy?

Answer 9

Corpus luteum

Question 10

What are two effects of progesterone during pregnancy?

Answer 10

• Relaxes uterine muscles to prevent labour
• Induces breast changes to prepare for lactation

Question 11

Importance of placental growth hormone for glucose transport [mech]

Answer 11

• PGH leads to decreased insulin sensitivity
• More glucose in blood
• Easier facilitated diffusion of glucose due to maintained concentration gradient of glucose

Question 12

How do placental lactogen and growth hormone prepare the body for lactation?

Answer 12

• Anabolic
• Fat deposition (reserves for lactation)
• Promote breast changes for lactation

Question 13

What are the effects of relaxin in pregnancy?

Answer 13

• Systemic and renal vasodilation (decreased resting vascular tone)
  
  • Increased cardiac output, increased stroke volume, decreased blood pressure
• Increased GFR
• Increased flexibility of pubic symphysis and ligaments of the pelvis
• Cervical softening during labour

Question 14

When does relaxin peak during human pregnancy? Why?

Answer 14

• Peaks in early pregnancy
• It is made mostly by the corpus luteum, although it is made a little bit in the placenta

Question 15

True or false: the placenta is an effective barrier against many bacteria

Answer 15

True

Question 16

Give some examples of viruses that can cross the placenta

Answer 16

• Rubella
• Zika virus
• Varicella (chickenpox)

Question 17

In what ways does the placenta protect the foetus?

Answer 17

• Clearance through transporters
• Metabolism of hormones and drugs
• Blocks against many bacteria (many viruses can still cross)

Question 18

How does the placenta protect the foetus from cortisol?

Answer 18

• Converts cortisol into cortisone (which is inactive) due to high amounts of enzyme

Question 19

Which enzyme enables the placenta to deactivate cortisol into cortisone?

Answer 19

11 beta dehydrogenase

Question 20

Give one example of a drug that the placenta cannot protect a foetus from

Answer 20

Alcohol

Question 21

What is the role of the placenta in immunity?

Answer 21

• Produces hormones that promote maternal immune cells to tolerate paternal antigens
• IgG antibodies are transferred across the placenta, particularly in late pregnancy

Question 22

Why are pregnant women suggested to get vaccinated against certain diseases?

Answer 22

• IgG antibodies produced in immune response can protect the newborn baby against disease