HD: PBL 3 (Adaptation to Extra-Uterine Life) Flashcards
Where does amniotic fluid come from initially?
Amnion (membrane)
What fluid(s) supplement the amniotic fluid later on in foetal development?
Urine from the foetal kidneys and secretions from the foetal lungs
List the changes that take place in the cardiorespiratory system of the foetus at birth
Lungs inflate, amniotic fluid is replaced, pulmonary vascular resistance drops, umbilical arteries close, umbilical vein and ductus venosus closes and ductus arteriosus closes
What substances are actively transported across the placenta from the maternal to foetal circulation?
Amino acids, fatty acids, calcium, phosphate, iron
What is the main metabolic energy source for the baby in utero?
Glucose
What is the main metabolic energy source for the baby post-delivery?
Fat
How does the foetus obtain nutrition and oxygen supply in utero?
Via the umbilical cord and placenta
Describe the structure of the umbilical cord
Two umbilical arteries and one umbilical vein surrounded by Wharton’s jelly which protects the umbilical vessels from damage
What is the role of umbilical arteries?
Carry waste-laden blood away from the foetus to the placenta
What is the role of umbilical vein?
Carries oxygen and nutrient-rich blood from the placenta to the foetus
What is the role of the placenta?
Responsible for gaseous exchange of CO2 and O2, provides nutrients to the foetus (glucose, amino acids, calcium and electrolytes), acts to excrete waste products from the foetus, detoxifies drugs and metabolites, produces molecules such as hCG, progesterone and oestrogens (metabolically active) and is responsible for production of long-chain fatty acids which are essential for brain development
How can you distinguish between the maternal and foetal side of the placenta?
Flat surface is foetal side, curved surface is the maternal side (embedded into the decidua)
How is amniotic fluid circulated?
Baby swallows the fluid and then releases it through urine
What is the role of the amniotic fluid?
Helps the developing foetus move in the womb, helps lungs to develop properly, maintains relatively constant temperature and cushions the foetus from sudden blows or movements
Describe the changes that occur to the infant’s environment at birth
Baby moves from near weight-lessness to being in gravity and from being in a warm environment to a cold one
What is the ‘first gasp’ at birth?
Where a very negative intra-thoracic pressure is generated and air fills the lungs
Describe the respiratory changes that occur after birth
Very negative intrathoracic pressure generated by the first gasp –> and within the first 2-3 breaths much of the foetal lung fluid is expelled and remainder is absorbed into pulmonary lymphatic and capillaries over the first 6-12 hours and surfactant secretion is initiated
What is surfactant?
Substance of phospholipids and proteins that is secreted by type II pneumocytes and reduces the surface tension of the alveoli to reduce the likelihood of collapse
Describe foetal circulation
Umbilical vein carries nutrient-rich blood to the liver –> some goes to the hepatic veins (supply liver) and some travels in the ductus venosus to the IVC –> travels to the right atrium, there is shunting across the foramen ovale into left atrium (bypass non-functional lungs) –> ductus arteriosus connects pulmonary artery to descending aorta (further shunting) –> pulmonary circulation –> left atrium –> aorta –> eventually to internal iliac artery –> joins umbilical arteries –> blood return to placenta (deoxygenated)
Describe the circulatory changes that occur at birth
PO2 increases from 2-3.5kPa in foetus to 9-13kPa in the first few breaths, and this hyperoxia causes the ductus arteriosus to close
When does the ductus arteriosus functionally close?
Within 12-15 hours of birth
When does the ductus arteriosus anatomically close?
4-7 days after birth
How is the ductus arteriosus kept open in utero?
Under the influence of prostaglandin E1, but this influence declines as term approaches and bradykinins are released from the distended alveoli and cause the smooth muscle of the ductus arteriosus to constrict
When do the umbilical vessels functionally close?
Within 5 minutes of birth (cord is clamped and cut)
