Flashcards in Physio 9 Deck (16)
unique shunts of fetal circulation
1. oxygenated blood from placenta goes through ductus venosus to bypass liver in mother
2. 40% of fetal IVC flow goes through foramen ovale to left atrium, and the rest goes to the right atrium
3. 3/4 or more of blood from right ventricle is pumped through ductus arteriosus into the descending aorta, bypassing the lung
4. blood in descending aorta passes through hypogastric arteries into two umbilical arteries and into placenta
cardiopulmonary adjustments at/after birth
loss of placental circulation requires newborn to breathe on its own. dramatic increase in pulmonary blood flow, and closure of ductus venosus, foramen ovale, and ductus arteriosus
what triggers first breath?
hypoxia, hypercapnea, tactile stimuli, and cold skin. first inspiratory effort requires a transpulmonary pressure of 60 cm H2O to increase the lung volume by 40 mL. breathing becomes easier once alveoli are open and surfactant is there. deficiency of surfactant causes respiratory distress syndrome
effect of birth on pulmonary vascular resistance, blood flow, and mean arterial pressure
in fetus, pulm vasc resistance is high, pulm blood flow is low, and mean pulm arterial pressure is high. at birth, these all reverse. the primary event is the fall in resistance, which occurs from pulm blood vessels no longer being crushed, breathing causing increased PO2 and vasodilation, and local prostaglandins causing vasodilation. pressure falls after birth due to fall of resistance being greater than rise in flow of blood
4 essential functions of adult organs that the placenta performs
acts as lungs (gas exchange), GI tract (nutrition), liver (nutrition and waste removal), kidneys (fluid and electrolyte balance, waste removal)
insufficiency causes type II intrauterine growth restriction (IUGR). any insult that interferes with gas exchange may lead to fetal asphyxia
when does fetal heart start to beat
1 month after fertilization
where does gas exchange occur between mother and fetus?
intervillous space contains a pool of maternal blood for gas exchange. space is between the endometrium on the maternal side and the villi on the fetal side
what does closure of the placental circulation cause
increases the pressure in the aorta and left ventricle. causes peripheral resistance to double
what causes closure of foramen ovale?
caused by reversal of right/left atrial pressure. increased pulm circulation causes increased venous return to the left atrium, and a decrease in right atrial pressure. this closes the valve of the foramen ovale. permanent seal forms in a few months or years, and becomes the fossa ovalis
what does the closure of the ductus venosus force in the liver?
forces portal blood to perfuse the liver. within 3 hours after birth, constriction of the vascular smooth muscle within the ductus venosus completely occlude this shunt, and it becomes the ligamentum venosum. causes possibly by increased PO2 and reduced prostaglandins. failure to close os a portosystemic shunt
what mediates closure of the ductus arteriosus?
changes in PO2 and prostaglandins. within a few hours, ductus arteriosus closes because of constriction of the wall. thrombosis obliterate the lumen in a month and it becomes the ligamentum arteriosum. increased PO2 and decreased prostaglandin cause constriction. bradykinin from lung is involved. failure to close is patent ductus arteriosus, leading to pulmonary hypertension and congestive heart failure/arrhythmias
patent ductus arteriosus
1 in 2000 newborns end up with this. larger openings lead to diffuculty in feeding, beathing, high HR and sweating, low weight. endocarditis risk is life threatening as germs in blood tend to stick to valves. can do surgery to fix
coarctation of the aorta
smooth muscle of ductus arteriosus that invaded the descending aorta constricts the area following birth. associated with high blood pressure in regions perfused by the aorta above constriction
ventricular septal defects
most common of birth defects. hole in wall between ventricles. small can be fixed on its own and usually doesnt cause major problems. large holes can be problems due to blood flow from left to right ventricle. this can cause congestive heart failure
atrial septal defects
1 in 1500 births. if hole is large enough, could lead to volume overload of right heart. untreated can lead to pulmonary hypertension, right heart enlargement, and heart failure