Ch 4 Blood Flow Part 1 Flashcards
What is the starting point of the pulmonary circulation?
The main pulmonary artery
It receives mixed venous blood pumped by the right ventricle.
How does the pulmonary artery branch?
It branches successively like the system of airways.
The pulmonary arteries accompany the airways as far as the terminal bronchioles.
What forms the dense network in the alveolar wall for gas exchange?
Pulmonary capillaries
They form an exceedingly efficient arrangement for gas exchange.
What collects oxygenated blood from the capillary bed?
Small pulmonary veins
These veins run between the lobules and unite to form four large veins draining into the left atrium.
What is the mean pressure in the main pulmonary artery?
About 15 mm Hg
Systolic and diastolic pressures are about 25 and 8 mm Hg, respectively.
How does the pressure in the pulmonary circulation compare to the systemic circulation?
The mean pressure in the aorta is about 100 mm Hg
This is approximately six times more than in the pulmonary artery.
What is the significance of low pressures in the pulmonary circulation?
It allows the lung to accept the whole of the cardiac output at all times.
This reduces the work of the right heart for efficient gas exchange.
What is the pressure drop across the pulmonary circulation?
About 10 mm Hg
Compared to about 98 mm Hg in the systemic circulation.
What is the typical pressure within the pulmonary capillaries?
About halfway between pulmonary arterial and venous pressure
Much of the pressure drop occurs within the capillary bed.
What surrounds the pulmonary capillaries?
Gas
The capillaries are surrounded by a very thin layer of epithelial cells lining the alveoli.
What happens to the pulmonary capillaries when alveolar pressure rises?
They collapse
This occurs when the pressure inside the capillaries is less than the alveolar pressure.
What is the transmural pressure?
The pressure difference between the inside and outside of the capillaries.
What are alveolar vessels?
Vessels exposed to alveolar pressure
They include capillaries and slightly larger vessels in the corners of the alveolar walls.
What are extra-alveolar vessels?
Blood vessels exposed to pressure less than alveolar pressure
Their caliber is affected by lung volume due to the radial traction of surrounding lung parenchyma.
How is vascular resistance calculated?
Vascular resistance = (input pressure - output pressure) / blood flow
This is analogous to electrical resistance.
What is the pulmonary vascular resistance compared to systemic circulation?
Only one-tenth that of the systemic circulation
The pulmonary blood flow is about 6 liters·min−1.
What is the typical value of pulmonary vascular resistance?
About 1.7 mm Hg·liter−1·min
Cardiologists sometimes express this in dyne·s·cm−5, with normal values around 100.
