PBL 3 Flashcards
what is the placenta
The placenta is a fetal organ, with the maternal contribution being blood circulating in the intervillous space. It is very active and has the following functions
what are the function of the placenta
Acts as a lung and is responsible for gaseous exchange.
Provides nutrients for the feotus (glucose, amino acids, calcium and electrolytes).
Acts as a kidney by excreting waste products.
Detoxifies drugs and metabolities.
Is metabolically active, producing molecules for example, human chorionic gonadotrophin (HCG) as soon as the first few cell layers (cytotrophoblast and syncytiotrophoblast) are formed and later progesterone and oestrogens.
Is responsible for theproductionof long chained fatty acids essential for brain development.
what is the placenta circulation
In the umbilical cord the twoumbilicalarteries carry deoxygenated blood from the foetus to the placenta and the single umbilical vein carries oxygenated blood back to the foetus
describe what the umbilical vein does
The umbilical vein travels to the foetus within the umbilical cord, and then deposits the oxygenated blood mainly directly into the foetal liver.
what does the ductus venous do
The ductus venosus acts as a shunt, which deposits a portion (aprox. 30%) of the oxygenated blood directly into the IVC.
what is the amniotic fluid produced by
Produced by the amnion (filtered from maternal plasma), foetal kidneys, foetal lungs.
describe what the amniotic fluid looks like
It is clear and slightly yellow, at 34 weeks the maximum volume of fluid is on average 800ml.
describe the role of the amniotic fluid
Amniotic fluid constantly circulates as the baby swallows the fluid and then releases it through urine.
It helps the developing baby; to move in the womb,
it also helps the lungs to develop properly,
it keeps a relatively constant temperature
it also cushions the baby from sudden blows or movements.
describe wha happens to the lungs at birth
At birth, the baby suddenly moves nearweightlessnessto being in gravity and from being in a warmenvironmentto a cold one.
The lungspreviouslyfilled with fluid need to fill with air. There is an initial first gasp generating negative intra-thoracic pressures often as low as -60 to -90cm H20, and air fills the lungs.
With the first 2-3 breaths much of the fetal lung fluid is expelled, and theremainderof the fluid is absorbed into the pulmonary lymphatics and capillaries over the first 6-12 hours.
what is any delay in the first breath called
Any delay in this causes a condition known as transient tachypnoea of the new-born
describe surfactant, what makes it and what it does
Surfactant is a substance composed of phospholipids and proteins. It is secreted by type II pneumocytes and it reduces the surface tension in the alveoli which reduce the likelihood of them collapsing
describe the changes in circulation that happen
Main principle is shunting changing from right-to-left to left-to-right due to decreases pulmonary vascular resistance after the first gasp.
In utero the ductus is kept open under the influence of Prostaglandin E1, but the influence declines as term approaches, and this, together with bradykinins released from the distended alveoli cause the smooth muscle of the ductus to constrict.
After birth there is a fall in pulmonary vascular resistance so that pulmonary blood flow increases. There is a drop in pressure on the right side of the heart so that there is no longer any shunting from right to left atria across the foramen ovale. There is also a decrease in blood flow in the inferior vena cava, and as a result the ductus venosus closes. It remains as the ligamentum teres
what keeps the ductus arterioles open at birth
In utero the ductus is kept open under the influence of Prostaglandin E1
what causes the ductus arterioles to close after birth
- a decrease in prostagladinins and an increase in bradykinin which are released from the distended alveoli cause the smooth muscle of the ductus to constrict
what does the ductus venous turn into
It remains as the ligamentum teres
