WEEK 12: 12.5 Placenta

Question 1

What does it mean by the human placenta is haemochorial?

Answer 1

the fetal tissue (the chorionic villi) are directly bathed in maternal blood within the intervillous spaces

Question 2

What do the major functions of the placenta include?

Answer 2

• nutrient, gas and waste exchange (between mother & fetus)
• hormone production
• protection from the environment (toxins, pathogens)
• immune protection

Question 3

What kind of nutrient, gas & waste exchange does the placenta do (for the fetus)?

Answer 3

supplying oxygen, removing CO2
supplying nutrients, removing waste
filtering blood

Question 4

How are nutrients exchanged between maternal & fetal blood?

Answer 4

there is a small diffusion distance in the intervillous space, this allows the blood to diffuse easily, and this decreases in distance closer to late pregnancy

Question 5

What are different ways in which nutrients are transported through the placenta, from the mother to the fetus

Answer 5

Diffusion (gas and oxygen)
Transporter-mediated - facilitated or active transport (glocuse, amino acids)
Endocytosis/exocytosis - IgG

Question 6

What are placental hormones secreted during pregnancy

Answer 6

• human chorionic gonadotropin (hcG)
• steroids, progesterone and estrogens
• human somatomammotropin (placental lactogen) and placental growth hormone
• relaxin

Question 7

Describe hCG (function, location, made by)

Answer 7

recognition & maintenance of pregnancy
- made by embryonic trophoblast then by chorion
- levels peak week 9 of pregnancy
- main pregnancy recognition signal & maintains corpus luteum in early pregnancy
- hCG in urine is detected by home pregnancy kits

Question 8

Describe progesterone (function, location, made by)

Answer 8

• increases throughout pregnancy, initially made by corpus luteum then placenta
• relaxes uterine muscle to prevent labour
• induces breast changes in prep for lactation

Question 9

Describe placental lactogen/growth hormone (function, location, made by)

Answer 9

• induce maternal metabolic changes including insulin resistance - maintains maternal glucose concentrations to compensate for placental uptake and maintain fetal glucose supply
• anabolic (growth) actions also support fat deposition in first part of pregnancy - reserves for lactation
• promote breast changes in preparation for lactation

Question 10

Describe relaxin (function, location, made by)

Answer 10

Peaks in early pregnancy - made mostly by corpus luteum; placental production higher in some other species
vascular- systemic and renal vasodilation & decreased myogenic tone
increased cardiac output, increased stroke volume, decreased blood pressure
increased glomerular filtration rate
increases flexibility of pubic symphysis
cervical softening during labor to dilate the uterine cervix

Question 11

Explain the placenta as protector?

Answer 11

• barrier to many bacteria, many viruses can cross the placenta
• drug and hormone metabolism and clearance (eg. deactivating cortisol to cortisone)
  -doesn’t block alcohol

Question 12

How does the placenta contribute to immunity?

Answer 12

it produces hormones that promote immune tolerance.
IgG antibodies are transferred across the placenta in late pregnancy- this is how maternal immunisation can protect the newborn baby against disease