Blodflyt

Blodflyt, or blood flow, is the movement of blood through the body’s circulatory system, driven by the heart’s pumping action. It supplies tissues with oxygen and nutrients, and removes carbon dioxide and other waste products. Blood flow is controlled both globally, through cardiac output, and locally, to meet tissue perfusion needs.

The rate of flow in a vessel depends on the pressure difference between its ends and the resistance of the vessels. Resistance is strongly influenced by the radius of the vessels, following the principle that small changes in radius produce large changes in flow. Blood viscosity and vessel length also affect flow. Regulation occurs at several levels: the heart and systemic circulation, governed by autonomic input and hormones, and local tissue mechanisms that adjust vasomotor tone in response to oxygen, carbon dioxide, pH, and metabolic signals. Endothelial cells release factors such as nitric oxide to promote vasodilation and endothelin to promote vasoconstriction, contributing to local autoregulation.

Regional regulation ensures tissues receive adequate perfusion despite changes in overall blood pressure. Under resting conditions, cardiac output is about 5 liters per minute, and cerebral blood flow is roughly 50–60 milliliters per 100 grams of brain tissue per minute (about 750 milliliters per minute overall for the brain). Autoregulation maintains stable tissue perfusion across a mean arterial pressure range roughly from 60 to 150 mmHg for many organs.

Clinical relevance: abnormalities in blood flow can lead to ischemia, organ dysfunction, or edema. Conditions such as shock, heart failure, atherosclerosis, stroke, and perioperative perfusion deficits reflect impaired or redistributed blood flow. Assessment and management focus on ensuring adequate cardiac output, vascular tone, and tissue perfusion.