The placenta
• Function
o Nutrition and O2 to foetus
o Removal of waster products and CO2
▪ After a few months, kidneys are functioning and producing urine
▪ Different foetal cells are performing metabolic functions which create by-products to
be gotten rid of
o Hormone production
o Foetal protection
• Feto-placental unit of endocrine function
o hCG
▪ Maintains corpus luteum in ovaries for 4 months
▪ Similar function and structure to LH
▪ If very early in pregnancy, hCG too low in urine to be detected, need blood test to
confirm pregnancy
▪ Abnormal hCG concentrations are associated with adverse pregnancy outcomes
including foetal growth restriction
▪ Can be a useful marker, but does have a wide normal range
▪ Female foetuses have more hCG than males, 3 weeks after fertilisation
o -endorphin, ACTH-like
o Progesterone
▪ Maintains pregnancy
▪ Low progesterone at full term triggers labour
o Oestrogen
▪ Growth of uterus and mammary glands
▪ Aids in labour
o Placental lactogen (somatomammotropin) – increase maternal blood glucose (antagonises
insulin)
o Relaxin
• Structure
o Placental villi with foetal blood are surrounded by maternal blood in sinuses
o Foetus has 2 umbilical arteries and 1 umbilical vein
o Villi surface area is only a few m2 but this is enough for diffusion – can cause issue if
pathology occurs (e.g., restrictive blood flow – preeclampsia, eclampsia)
o New research suggests cutting of umbilical cord should be delayed by a few minutes – why?
• Major placental function is diffusion
o Initially placenta is thick before it fully develops so is less permeable – surface area is also
less as villi not fully developed so diffusion lower
o Eventually, placenta membrane gets thinner and surface area increase so diffusing capacity
increases
• Trophoblastic nutrition
o Up to 12 weeks, embryo is fed by trophoblasts digesting glycogen- and blood-rich
endometrial layer
o Progesterone swells endometrial stromal cells – which are glycogen protein, lipid and
mineral rich
o Blastocyst implants in endometrium and stromal cells swell even more to form decidual
cells
o Trophoblasts digests decidual cells
• O2 diffusion
o Maternal sinus blood (which is at a low lower than pO 2 than maternal arterial blood) passes
to foetal blood by simple diffusion
• Function
o Nutrition and O2 to foetus
o Removal of waster products and CO2
▪ After a few months, kidneys are functioning and producing urine
▪ Different foetal cells are performing metabolic functions which create by-products to
be gotten rid of
o Hormone production
o Foetal protection
• Feto-placental unit of endocrine function
o hCG
▪ Maintains corpus luteum in ovaries for 4 months
▪ Similar function and structure to LH
▪ If very early in pregnancy, hCG too low in urine to be detected, need blood test to
confirm pregnancy
▪ Abnormal hCG concentrations are associated with adverse pregnancy outcomes
including foetal growth restriction
▪ Can be a useful marker, but does have a wide normal range
▪ Female foetuses have more hCG than males, 3 weeks after fertilisation
o -endorphin, ACTH-like
o Progesterone
▪ Maintains pregnancy
▪ Low progesterone at full term triggers labour
o Oestrogen
▪ Growth of uterus and mammary glands
▪ Aids in labour
o Placental lactogen (somatomammotropin) – increase maternal blood glucose (antagonises
insulin)
o Relaxin
• Structure
o Placental villi with foetal blood are surrounded by maternal blood in sinuses
o Foetus has 2 umbilical arteries and 1 umbilical vein
o Villi surface area is only a few m2 but this is enough for diffusion – can cause issue if
pathology occurs (e.g., restrictive blood flow – preeclampsia, eclampsia)
o New research suggests cutting of umbilical cord should be delayed by a few minutes – why?
• Major placental function is diffusion
o Initially placenta is thick before it fully develops so is less permeable – surface area is also
less as villi not fully developed so diffusion lower
o Eventually, placenta membrane gets thinner and surface area increase so diffusing capacity
increases
• Trophoblastic nutrition
o Up to 12 weeks, embryo is fed by trophoblasts digesting glycogen- and blood-rich
endometrial layer
o Progesterone swells endometrial stromal cells – which are glycogen protein, lipid and
mineral rich
o Blastocyst implants in endometrium and stromal cells swell even more to form decidual
cells
o Trophoblasts digests decidual cells
• O2 diffusion
o Maternal sinus blood (which is at a low lower than pO 2 than maternal arterial blood) passes
to foetal blood by simple diffusion
