Brianna Laplante

I am really interested in circulation changes that take place from fetuses to newborns.  Increased uptake of oxygen by lungs/first and subsequent breaths induces avasoconstriction of the ductus venosus and the ductus arteriosis.  Aeration of the lungs at birth is assocatied with..1) a dramatic fall in pulmonary vascular resistance due to lung expansion, 2) a marked increase of pulmonary blood flow, which raises the left atrial pressure above that of the IVC and 3) a progressive thinning of the walls of the pulmonary arteries due to stretching as the lungs expand with the first few breaths.

As the baby takes their first breath the pulmonary alveoli open up leading to 1) decreasing pressure in the pulmonary tissues, 2) blood pressure from the right side of the heart rushes to fill the alveolar capillaries, 3) pressure in the right side of the heart decreases, 4) pressure in the left side of the heart increases as more blood is returned from the well-vascularized pulmonary tissue via the pulmonary veins to the left atrium.  Blood pressure is now high in the aorta and systemic circulation is now well established.  

Control of circulation is a reflex function regulated: 1) peripherally by the baroreceptors in the aortic arch and carotid sinus, 2) centrally by baroreceptors in cardiovascular center of medulla and 3) respiratory and circulatory reflexes are usually strong in heatlhy newborns, but their efficiency of controlling cardiovascular function is susceptible to environmental factors. 

The foramen ovale closes at birth due to decreased flow from placenta to IVC to hold foramen open and because of increased pulmonary blood flow and and pulmonary venous return to left side of the heart causing the pressure in the left atrium to be higher than the right atrium.  The right ventricular wall is thicker than the left ventricular wall because the right ventricle has been working harder.  The right ventricular wall becomes thinner as the work load is evened out.  The umbilical arteries also constrict at birth to prevent loss of infantis blood.  The umbilical cord is not tied for 30-60 seconds so that blood flow through the umbilical vein continues, transferring fetal blood from the placenta to the infant.  Pretty amazing how this all happens!! Have a good spring break everyone!!

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