Cardiovascular changes at birth Flashcards
Three types of mammals
Monotremes, marsupials and placentals.
What is required after birth?
Specific and fully organised neurological reflex pathways.
What changes are required to meet this pathway?
Hormonal function, epidermal function, loss of placenta and cardiovascular changes.
Effect of placenta loss
Heat generation needs to be maintained, intestinal, liver, lung and kindey function starts.
Liver function
Increases after birth and becomes vital for life.
Intestinal function
Movement, digestion and absorption begins.
Renal function
Excretion and increased reabsorption becomes vital.
Why are cardiovascular changes needed?
Loss of placenta, intestinal function, liver function and lung function all increase.
Umbilical cord blood supply
2 arteries and one vein.
What blood enters placenta?
Deoxygenated blood from the mother, maternal venule and arteriole spiral in to deposit into sinuses surrounding villi increasing the pressure.
What is the foetal portion of placenta called?
The chorion.
Placenta structure at birth
12cm in radius, 0.5kg when drained of blood, 2cm thick and 10m^2 exchange surface.
Role of placenta
Transfers respiratory gases, nutrients (not triglycerides), metabolic waste and IgG, acts as a heat sink, as a circulatory reservoir, immune modulator and produces hormones.
How are triglycerides given to foetus?
They are absorbed and broken down by lipase to fatty acids.
Where does NH3 from foetus go?
To maternal kodiney.
Immune modulatory function of placenta
Actively suppresses host vs graft reaction.
Hormones produced by placenta
hCG (maintains CL ), progesterones, CRH/oestrogens, placental lactogen (increases maternal serum glucose) and prostaglandins (auto/paracrine).
Foetal blood distribution
20% lungs (50% in adults), 30% to head and upper limbs and 50% to rest of body.
Three issues with placenta
Before birth need to retain umbilical vessel patent, at birth need to transfer blood from placenta to foetus and need to close placental circulation very rapidly.
How much neonate blood is in the placenta?
33%.
When does the placental blood transfuse to neonate?
30% in the first 15 seconds and the rest in the next 2-3 minutes.
What causes placental blood transfusion to neonate?
Positional differences and contractions of uterus to express placenta immediately after birth, creating a pressure gradient between neonate and placenta.
Blood flow in umbilical cord between weeks 34-39
560ml/min.
Blood pressure in foetal artery
70/45.
Placental blood volume at birth
33%.
Umbilical cord structure
55-60 cm tricanulated tube and an allantoic duct, fairly twisted.
Umbilical arteries
Takes deoxygenated blood away from foetus.
They have no internal elastic membrane with little elastin, no adventitia so have Wharton’s jelly instead.
Umbilical vein
Delivers oxygenated blood from the placenta to the fetus, have an elastic layer but with no valves.
Wharton’s jelly
Gel-like porous ECM with the fibrous scaffold made of collagen and elastin with pores containing proteoglycans and hyaluronic acid that bind water to form a viscous fluid.
Purpose of Wharton’s Jelly
Prevents compression of the umbilical cord and maintains the firmness of it.
Fashion of umbilical arteries
Coil around the vein helically.
Blood flow of placenta and foetus
Pulsatile from the foetus to placenta via arteries and a small palse retained in the passive transfer of blood back.
What does umbilical coiling do?
Appears to confer turgor, producing a strong and flexible cord.
What is low umbilical cord twisting indicative of?
Adverse perinatal outcome.