HD: PBL 3 (Adaptation to Extra-Uterine Life)

Question 1

Where does amniotic fluid come from initially?

Answer 1

Amnion (membrane)

Question 2

What fluid(s) supplement the amniotic fluid later on in foetal development?

Answer 2

Urine from the foetal kidneys and secretions from the foetal lungs

Question 3

List the changes that take place in the cardiorespiratory system of the foetus at birth

Answer 3

Lungs inflate, amniotic fluid is replaced, pulmonary vascular resistance drops, umbilical arteries close, umbilical vein and ductus venosus closes and ductus arteriosus closes

Question 4

What substances are actively transported across the placenta from the maternal to foetal circulation?

Answer 4

Amino acids, fatty acids, calcium, phosphate, iron

Question 5

What is the main metabolic energy source for the baby in utero?

Answer 5

Glucose

Question 6

What is the main metabolic energy source for the baby post-delivery?

Answer 6

Fat

Question 7

How does the foetus obtain nutrition and oxygen supply in utero?

Answer 7

Via the umbilical cord and placenta

Question 8

Describe the structure of the umbilical cord

Answer 8

Two umbilical arteries and one umbilical vein surrounded by Wharton’s jelly which protects the umbilical vessels from damage

Question 9

What is the role of umbilical arteries?

Answer 9

Carry waste-laden blood away from the foetus to the placenta

Question 10

What is the role of umbilical vein?

Answer 10

Carries oxygen and nutrient-rich blood from the placenta to the foetus

Question 11

What is the role of the placenta?

Answer 11

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

Question 12

How can you distinguish between the maternal and foetal side of the placenta?

Answer 12

Flat surface is foetal side, curved surface is the maternal side (embedded into the decidua)

Question 13

How is amniotic fluid circulated?

Answer 13

Baby swallows the fluid and then releases it through urine

Question 14

What is the role of the amniotic fluid?

Answer 14

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

Question 15

Describe the changes that occur to the infant’s environment at birth

Answer 15

Baby moves from near weight-lessness to being in gravity and from being in a warm environment to a cold one

Question 16

What is the ‘first gasp’ at birth?

Answer 16

Where a very negative intra-thoracic pressure is generated and air fills the lungs

Question 17

Describe the respiratory changes that occur after birth

Answer 17

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

Question 18

What is surfactant?

Answer 18

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

Question 19

Describe foetal circulation

Answer 19

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)

Question 20

Describe the circulatory changes that occur at birth

Answer 20

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

Question 21

When does the ductus arteriosus functionally close?

Answer 21

Within 12-15 hours of birth

Question 22

When does the ductus arteriosus anatomically close?

Answer 22

4-7 days after birth

Question 23

How is the ductus arteriosus kept open in utero?

Answer 23

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

Question 24

When do the umbilical vessels functionally close?

Answer 24

Within 5 minutes of birth (cord is clamped and cut)

Question 25

When do the umbilical vessels anatomically close?

Answer 25

Within 10 days after birth

Question 26

When does the ductus venosus functionally and anatomically close?

Answer 26

Between 1-3 weeks after birth

Question 27

When does the foramen ovale functionally and anatomically close?

Answer 27

Functionally is variable, and anatomically will take 6 months or never, but due to pressure changes very little shunting occurs post-birth

Question 28

What causes the ductus arteriosus to close?

Answer 28

Decline in prostaglandin E1 nearing the end of term and production of bradykinins which are released due to distention of alveoli cause the smooth muscle of the ductus arteriosus to constrict

Question 29

What causes the functional closure of the foramen ovale?

Answer 29

Marked fall in pulmonary vascular resistance shortly after birth –> pulmonary blood flow increases –> drop in pressure on right side of the heart –> no longer an shunting from the right to the left atrium across the foramen ovale

Question 30

What causes the functional closure of the ductus venosus?

Answer 30

Decrease in blood flow to the inferior vena cava due to greater pulmonary blood flow and this causes the ductus venosus to become the ligamentum teres

Question 31

What does the ductus venosus become in an adult?

Answer 31

Ligamentum teres

Question 32

Describe the importance of lipid and carbohydrate stores in a newborn baby

Answer 32

Baby born with plentiful supply of fat and glycogen stores, and in the first few days of life, lipid metabolism to free fatty acids supplies most of the structures of the body (glucose for the brain) whilst breastfeeding isn’t occurring due to the baby mostly sleeping

Question 33

What is the cause of physiological jaundice in newborns?

Answer 33

Common between 2-5 days and this is due to an increased breakdown of RBCs –> more bilirubin in circulation –> immaturity of the enzyme glucuronyl transferase in the liver so the bilirubin cannot be conjugated and excreted into the biliary system –> unconjugated bilirubin levels rise

Question 34

Describe the treatment of physiological jaundice (if necessary)

Answer 34

If there is any doubt that there may be an underlying pathology, phototherapy is used as a precautionary measure which is a bright light at the blue end of the spectrum (400-450nm) and it breaks down the bilirubin into harmless, 2-pyrrol ring (water-soluble) which can then be excreted in the urine

Question 35

What is the neonatal heel prick test?

Answer 35

At approximately day 7 a blood sample is taken from the infant to test for 9 rare but serious health conditions which re: sickle cell disease, cystic fibrosis, congenital hypoththyroidism, PKU, MCADD etc

Question 36

What is being tested for in the heel prick for hypothyroidism?

Answer 36

thyroid stimulating hormone (TSH)

Question 37

What is being tested for in the heel prick for PKU?

Answer 37

Phenylalanine

Question 38

What is being tested for in the heel prick for cystic fibrosis?

Answer 38

Immunoreaective trypsinogen

Question 39

What is being tested for in the heel prick for MCADD?

Answer 39

Octanoylcarnitine

Question 40

What is being tested for in the heel prick for sickle cell disease (and thalassaemia)?

Answer 40

Haemoglobinopathies

Question 41

Besides the heel prick test, what other neonatal tests are conducted?

Answer 41

Hearing tests using oto-acoustic emissions