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The right-to-left shunt is an abnormal blood circulation that enables deoxygenated blood to pass from the right side to the left side of the heart and skips the lungs. Thus, no oxygenation occurs, and reduced gas exchange results in hypoxemia as fresh oxygen cannot reach the shunted blood. [18]
As the vessels decrease in size, they increase their surface-area-to-volume ratio. This allows surface properties to play a significant role in the function of the vessel. Diffusion occurs through the walls of the vessels due to a concentration gradient, allowing the necessary exchange of ions, molecules, or blood cells.
Most vessels of the microcirculation are lined by flattened cells of the endothelium and many of them are surrounded by contractile cells called pericytes.The endothelium provides a smooth surface for the flow of blood and regulates the movement of water and dissolved materials in the interstitial plasma between the blood and the tissues.
Gas exchange is the physical process by which gases move passively by diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liquid, a gas-permeable membrane, or a biological membrane that forms the boundary between an organism and its extracellular environment.
Blood resistance varies depending on blood viscosity and its plugged flow (or sheath flow since they are complementary across the vessel section) size as well, and on the size of the vessels. Assuming steady, laminar flow in the vessel, the blood vessels behavior is similar to that of a pipe.
Atherosclerosis is characterized by the build-up of plaque inside your blood vessels. It can lead to stenosis, which is a narrowing of your artery walls. Plaque is a fatty substance made up of:
The rete mirabile utilizes countercurrent blood flow within the net (blood flowing in opposite directions) to act as a countercurrent exchanger. It exchanges heat, ions, or gases between vessel walls so that the two bloodstreams within the rete maintain a gradient with respect to temperature, or concentration of gases or solutes.
The process might initially seem counterintuitive, as low oxygen levels might theoretically stimulate increased blood flow to the lungs to increase gas exchange. However, the purpose of HPV is to distribute bloodflow regionally to increase the overall efficiency of gas exchange between air and blood.