Hi, this is Tom, and in this episode I'm going to be going through neonatal physiology,

and you can find notes at zero to finals.com slash neonatal physiology, and in the neonatology section

of the zero to finals pediatrics book. And you can find flashcards and questions

at members.0 tofinals.com. So let's jump straight in. Let's start by talking about the cardio

respiratory changes at birth. During birth, the thorax is squeezed as the body passes through the vagina, helping to clear fluid from the lungs.

The trauma of birth, temperature change, sound and physical touch stimulate the baby to promote the first breath.

A strong first breath is required to expand the alveoli for the first time. Adrenaline and cortisol are released in response to the stress

of labour and this helps stimulate the respiratory effort.

In the fetus, the pheromone ovalee connects the right atrium with the left atrium,

allowing blood to flow from the right atrium to the left atrium, bypassing the right

ventricle and the lungs.

As the alveoli expand, the pulmonary vascular resistance decreases, causing a fall in the right

atrial pressure.

The left atrial pressure is now higher than the right atrial pressure, which squashes the atrial

septum and causes functional closure of the pheromone ovalee.

This means blood now flows to the right ventricle and the lungs.

The pheromone ovale later closes structurally and becomes the fossa ovallis.

In the fetus, the ductus arteriosus connects the pulmonary artery with the aorta, allowing blood to bypass

the lungs. Prostergladins are blood to bypass the lungs.

Prostaglandins are required to keep the ductus arteriosis open.

Increased blood oxygenation after birth causes a drop in circulating prostaglandins.

The ductus arteriosis closes and becomes the ligamentum arteriosum.

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