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Flashcards in Cardiovascular - Foetal Circulation Deck (16)
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What structure does the remnant of the urachus form in the adult?

Median umbilical ligament.


Where do the umbilical arteries relay blood to?

They relay deoxygenated blood in the foetus to the placenta via the umbilical cord.


What structures do the remnants of the umbilical arteries form in the adult?

They form the superior vesical arteries in the pelvis and the arteries supplying the ductus deferens in males.


Where does the phrenic nerve originate from?

4th cervical nerve (C4).


What structures does the vagus nerve innervate?

The vagus nerve (CN X) provides motor parasympathetic innervation to all internal organs except for the adrenal glands from the neck down to the second segment of the transverse colon, therefore it innervates the heart, lungs, liver, kidney, stomach, intestines and the glands therein. It also provides parasympathetic motor and some sensory innervation to skeletal muscles including:
- Cricothyroid muscle
- Levator veli palatini muscle
- Salpingopharyngeus muscle
- Palatoglossus muscle
- Palatopharyngeus muscle
- Superior, middle and inferior pharyngeal constrictors - Muscles of the larynx (speech).


From what part of the CNS do the sympathetic fibres that form the sympathetic chain arise?

Sympathetic nerves originate inside the vertebral column, toward the middle of the spinal cord in the intermediolateral cell column (or lateral horn), beginning at the first thoracic segment of the spinal cord and are thought to extend to the second or third lumbar segments. Because its cells begin in the thoracic and lumbar regions of the spinal cord, the SNS is said to have a thoracolumbar outflow.


What is the function of the ductus arteriosus?

To allow oxygenated blood from the placenta that didn’t get shunted from the right atrium to the left atrium through the foramen ovale to bypass the pulmonary circulation. The blood is pumped up from the right ventricle up to the pulmonary artery but is shunted via the ductus arteriosus directly to the aorta so it can reach the systemic circulation.


In what direction does blood flow through the ductus arteriosus prenatally?

Right ventricle to pulmonary artery to aorta, bypassing the lungs.


In what direction does blood flow through the ductus arteriosus immediately post- partum?

At birth it closes and becomes the ligamentum arteriosum. Deoxygenated blood from the systemic circulation enters the right heart, is pumped from the right ventricle to the pulmonary artery to the lungs where it is oxygenated, re-enters the heart via the pulmonary veins into the left atrium, then the left ventricle and finally pumped out to the systemic circulation via the aorta.


What structure does the remnant of the ductus arteriosus form in the adult?

Ligamentum arteriosum.


What is the consequence of the ductus arteriosus remaining patent postnatally?

Patent ductus arteriosus can lead to pulmonary hypertension and possibly congestive heart failure and cardiac arrhythmias.
A patent ductus arteriosus allows a portion of the oxygenated blood from the left heart to flow back to the lungs by flowing from the aorta (which has higher pressure) to the pulmonary artery. If this shunt is substantial, the neonate becomes short of breath: the additional fluid returning to the lungs increases lung pressure to the point that the neonate has greater difficulty inflating the lungs. This uses more calories than normal and often interferes with feeding in infancy. This condition, as a constellation of findings, is called congestive heart failure.


What is the function of the portal vein?

Portal vein carries blood from the gastrointestinal tract and spleen to the liver. This blood contains nutrients absorbed by the intestines from food, as well as waste and toxins. The liver gets 75% of the blood running through it from the portal vein (the rest from the hepatic artery). Blood filtered by the liver leaves the gland via the hepatic vein.


What is the function of the ductus venosus in the foetus?

The ductus venosus acts as a shunt to convey oxygenated blood from the placenta via the umbilical vein directly to the right atrium via the inferior vena cava, bypassing the still developing liver. Together with the foramen ovale and the ductus arteriosus, it ensures that oxygenated blood reaches the foetus’ developing brain and heart.


What structure does the remnant of the ductus venosus form in the adult?

The ductus venosus forms the ligamentum venosum in the adult after it occludes.


What is the function of the foramen ovale in the foetus?

The foramen ovale is a hole between the right and left atria that shunts oxygenated blood entering the right atrium from the placenta to the left atrium, allowing the blood to bypass first the right ventricle and the pulmonary circulation. From the left atrium the blood enters the left ventricle and is pumped to the systemic circulation via the aorta.


What is the consequence of the foramen ovale remaining patent postnatally?

!Patent foramen ovale can result in the mixing of de-oxygenated blood in the right atrium with oxygenated blood from the pulmonary circulation, as blood is able to cross over from the more muscular left side of the heart to the right side.

This can lead to volume overload of the right side of the heart, and ultimately heart failure as the right-side cardiac muscle is unable to handle the increased volume. Also, the increased preload of the right atrium from the left-right shunt will cause the right ventricle to work harder to push more blood into the pulmonary circulation, putting greater pressure on the pulmonary arteries, leading to pulmonary hypertension (higher afterload needed to accommodate the higher pre-load). Right ventricular failure is also possible.

Additionally, once the pressure in the right side of the heart is equal to the left side, the shunt could lead to deoxygenated blood from the right side entering the left side of the heart, mixing oxygenated blood returning from the pulmonary veins with deoxygenated blood from the right side of the heart. This mix of less-oxygenated blood would be pumped into the systemic circulation, potentially leading to cyanosis.

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