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The pulmonary arteries carry deoxygenated blood to the lungs, where carbon dioxide is released and oxygen is picked up during respiration. [3] Arteries are further divided into very fine capillaries which are extremely thin-walled. [4] The pulmonary veins return oxygenated blood to the left atrium of the heart. [3]
A capillary is a small blood vessel, from 5 to 10 micrometres in diameter, and is part of the microcirculation system. Capillaries are microvessels and the smallest blood vessels in the body. They are composed of only the tunica intima (the innermost layer of an artery or vein), consisting of a thin wall of simple squamous endothelial cells. [2]
An increase in Pi causes extraalveolar blood vessels to reduce in caliber, in turn causing blood flow to decrease (extraalveolar blood vessels are those blood vessels outside alveoli). Intraalveolar blood vessels (pulmonary capillaries) are thin walled vessels adjacent to alveoli which are subject to the pressure changes described by zones 1-3.
A pulmonary artery is an artery in the pulmonary circulation that carries deoxygenated blood from the right side of the heart to the lungs.The largest pulmonary artery is the main pulmonary artery or pulmonary trunk from the heart, and the smallest ones are the arterioles, which lead to the capillaries that surround the pulmonary alveoli.
The alveolar and pulmonary capillary gases equilibrate across the thin blood–air barrier. [34] [68] [69] This thin membrane (about 0.5 –2 μm thick) is folded into about 300 million alveoli, providing an extremely large surface area (estimates varying between 70 and 145 m 2) for gas exchange to occur. [68] [70]
Diagram of pulmonary shunt in alveoli and pulmonary capillary. Secondly, the pulmonary shunt is caused by zero or low V/Q ratio due to insufficient ventilation and excess perfusion. Improper ventilation lowers blood oxygenation and oxygen supply to body tissues. Although 100% oxygen is inspired, a pulmonary shunt prevents oxygen from being ...
Blood–testis barrier – Physical barrier between the blood vessels and the seminiferous tubules of animal testes; Blood–thymus barrier – Barrier formed by the continuous blood capillaries in the thymic cortex; Pulmonary vein – Veins that transfer oxygenated blood from the lungs to the heart
The rest of the difference is due to the continual uptake of oxygen by the pulmonary capillaries, and the continual diffusion of CO 2 out of the capillaries into the alveoli. The alveolar pO 2 is not routinely measured but is calculated from blood gas measurements by the alveolar gas equation.