foetal circulation and adaption at birth

Question 1

what are the functions of placenta?

Answer 1

• fetal homeostasis
• gas exchange
• acid base balance
• nutrient transport to fetus
• waste product transport from fetus
• hormone production
• transport of igG
• PGE2

Question 2

what happens in the foetus?

Answer 2

• lungs are filled and unexpanded
• only 7% of RV output goes to lungs
• liver has a small role
• gut is not in use

Question 3

what are the 3 shunts?

Answer 3

• ductus venosus
• foramen ovale
• ductus arteriosus

Question 4

what is the anatomy of the ductus venosus?

Answer 4

• connects the umbilical vein to the inferior vena cava

- carries majority of placental blood into IVC, bypassing portal circulation

Question 5

what is the anatomy of the foramen ovale?

Answer 5

• opening in atrial septum connecting RA to LA

Question 6

what is the anatomy of the ductus arteriosus?

Answer 6

• connects pulmonary bifurcation to the descending aorta

Question 7

what is persistent pulmonary hypertension of the new-born (PPHN)?

Answer 7

• when lung vascular resistance fails to fall
• shunts remain = right to left flow at PFO, eight to left flow to PDA
• results in blue baby
• large difference between pre and post ductal O2 saturation
• ventillation, oxygenation, high systemic blood pressure inhaled nitric oxide, ECLS

Question 8

what adaptions do new borns have?

Answer 8

• decreased pulmonary vascular resistance

- increased systemic pulmonary vascular resistance

Question 9

how does the foramen ovale close?

Answer 9

• as PVR falls and SVR rises, the LA pressure exceeds the RA pressure
• the flap is pushed closed

Question 10

how does duct constriction occur?

Answer 10

• decreased flow due to decrease pulmonary vascular resistance
• increased pO2 - O2 sensitive muscular layer
• decreased circulating PGE2 due to increased lung metabolism
• shunt becomes bidirectional then left to right
• physiological closure within first few hours / days
• anatomic closure within 7-10 days

Question 11

what is duct dependent circulation?

Answer 11

• caused by some congenital heart diseases
• IV prostaglandin E2 can be used to keep the duct open until an alternative shunt established or definitive surgery carried out