Foetal Changes at Birth

Question 1

Systemic Vascular Resistance

Answer 1

• Flow in umbilical cord stops
• Cord clamped and cut
• Removal of large low resistance vascular bed from the systemic circulation
• Sudden increase in systemic vascular resistance

Question 2

Pulmonary Vascular Resistance

Answer 2

• Baby breathes and cries
• Lungs expand and fill with air
• Air filled lungs lead to higher oxgygen tension in pulmonary circulation
• Oxygen is a very effective vasodilator in the pulmonary arterioles
• Dramatic drop in pulmonary vascular resistance

Question 3

Ductus Arteriosus Flow

Answer 3

Left side pressure becomes higher than right

Flow changes direction in the duct – now flows from aorta to pulmonary artery

Question 4

Ductus Arteriosus Constriction

Answer 4

• connects pulmonary artery (bifurcation) to descending aorta
• Blood: descending aorta → placenta (to be oxygenated)

Question 5

Ductus Arteriosus closure

Answer 5

• Closure: 7-10 days, ligamentum arteriosum
  
  • faliure - interupted (inc) prostagalndin synthesis, in preterm babies
    (Treatment options include wait and see, NSAIDs and surgery)

Question 6

Ductus Venosus

Answer 6

• Connects the umbilical vein to the inferior vena cava (IVC)
• Blood: bypasses liver, goes to heart

Question 7

Foramen Ovale

Answer 7

• Allows blood to flow from right to left atrium
• Allows the best oxygenated blood to enter left atrium then on to LV, ascending aorta, carotids
• Membrane flap on left atrium side
• Changes after birth: baby’s first breath (crying) → CLOSURE of foramen ovale
  
  • lungs fill w blood

Question 8

Umbilical artery

Answer 8

• Connects illiac artery to placenta