Placental Physiology and Early Embryology ✅ Flashcards
What are the major functions of the placenta?
- Transport
- Immunity
- Metabolism
What happens on day 1 of embryological development?
Fertilisation
What happens on day 2 of embryological development?
Cleavage
What is formed from cleavage in embryological formation?
The blastomere
What happens on day 3 of embyrological development?
Compaction
What is formed between cells during the compaction stage of embryological development?
A tight cell junction
What happens on day 4 of embryological formation?
Differentiation
What is formed from differentiation in embryological development?
An inner cell mass and a outer cell mass
What happens on day 5 of embryological development?
Cavitation
What happens to the embryo in cavitation?
The outer cell mass forms a trophoblast, and the blastocyst cavity develops
What happens on day 6 of embryological development?
Zona hatching
What happens on day 7 of embryological development?
Implantation
What happens on day 9 of embryological development?
Cell mass differentiation
What cell masses are formed from differentiation on day 9 of embryological development?
- Epiblast
- Hypoblast
(and have still trophoblast from before)
What happens on day 12 of embryological development?
Bilaminar disc formation
What happens on day 12 of embryological development?
Mesoderm formation
Where does mesoderm form?
Between the ectoderm and the endoderm
What happens on day 18 of embryological development?
Mesoderm spreading
What happens on day 23 of embryological development?
Amniotic sac enlargement
At what stage of early embryological development does the placenta start to develop?
As soon as the blastocyst implants in the uterine endometrium, forming the trophoblast
How is the blood supply established in development of the placenta?
A network of umbilical vessels develop and branch through the chorionic plate to form villi
At what stage of gestation is the blood supply complete on the maternal side of the placenta?
11-12 weeks
What happens once the blood supply is complete on the maternal side of the placenta?
The uterine spiral arteries dilate and straighten and bathe the intervillous space with blood
What are the transport functions of the placenta?
- Nutrients from mother to foetus
- Waste products from foetus to mother
- Gaseous exchange
What methods of transport are utilised by the placenta?
- Simple diffusion for small molecules
- Active transport for larger molecules
What gases is the placenta responsible for exchange of?
O2 and CO2
What is the pO2 in the mother?
10-14KPa
What is the pO2 in the foetus?
2-4KPa
What happens once oxygen has diffused from the mother to the foetus?
It binds to fetal haemoglobin
What facilitates the off-loading of oxygen from maternal Hb?
- Higher affinity of foetal Hb
- Change in maternal blood pH
How does the affinity of foetal haemoglobin for oxygen compare to that of the mothers?
It has a higher affinity for a given pO2
What is the immune function of the placenta?
- Prevention of rejection of the foetus
- Provides newborn with innate immunity to infectious diseases
Why does rejection of the foetus not occur?
Because the trophoblastic cells appear non-antigenic, and so the maternal immune system does not react to it
What may happen if some foetal cells do cross into the maternal circulation?
They can trigger an immune reaction
Give an example of where disease can be caused by the immune reaction generated when foetal cells cross over into maternal circulation
Rhesus haemolytic disease
Which maternal immunoglobulins are able to cross the placental barrier?
IgG
Why is maternal IgG able to cross the placental barrier?
It is small
Can IgM immunoglobulins cross the placental barrier?
No
What are the metabolic functions of the placenta?
- Production of hormones
- Detoxification of drugs and metabolites
What hormones are produced by the placenta?
- Human chorionic gonadotrophin (HCG)
- Human chorionic thyrotrophin (HCT)
What is the result of the metabolic activity of the placenta meaning it has high energy demands?
It consumes over 50% of the total oxygen and glucose transported across it
Is the placenta solely responsible for foetal homeostasis?
No
What else is responsible for foetal homeostasis?
- Foetal liver
- Foetal endocrine glands
- Foetal kidneys
What is the role of the foetal liver in homeostasis?
It produces albumin, red cells, and clotting factors
What is the role of the foetal endocrine glands in homeostasis?
They produce thyroid hormone, insulin, and corticosteroids
From what gestation do the foetal endocrine glands start to produce hormones?
12 weeks
What is the role of the foetal kidneys in homeostasis?
They excrete large volumes of dilute urine
At what gestation to the foetal kidneys begin to excrete dilute urine?
10-11 weeks
What is the importance of the foetal urine?
It contributes to amniotic fluid volume
