Special mechanism for acute control of blood flow in specific tissues

2021-05-27 02:06 PM

Although the general mechanisms for blood flow control have been discussed that apply to most tissues in the body, there are mechanisms specific to specific regions.

Although the general mechanisms for blood flow control have been discussed that apply to most tissues in the body, there are mechanisms specific to specific regions.

1. In the kidney, blood flow control is assumed by a tubuloglomerular feedback mechanism, where the mixing of fluid in the peripheral tubules is detected by an epithelial structure of the tubule itself, called the tubules. is macula densa. This structure is located where the peripheral ducts are adjacent to the inlet and outlet arterioles in the nephron “juxtaglomerular apparatus”. When too much longitudinal fluid passes from the bloodstream through the glomerulus into the tubular system, the feedback signal from the macula densa can cause constriction of the incoming arterioles, thereby reducing both renal blood flow and the glomerular filtration rate to rotate. almost back to normal. The details of this mechanism are discussed on page 27.

2. In the brain, in addition to controlling blood flow by the concentration of oxygen in the tissues, the concentration of CO2 and H+ plays a major role. An increase in one or both of these ions dilates cerebral blood vessels and allows rapid removal of excess CO2 and H_ from brain tissue. This mechanism is important because brain excitability is highly dependent on precise control of both CO2 and H+ concentrations. 

3. In the skin, blood flow control is closely related to body regulation. Skin and subcutaneous flow regulate heat loss from the body by measuring the flow of the heart from the inside out to the surface of the body, where the heat is released to the environment. Skin flow is controlled primarily by the central nervous system via the sympathetic nervous system. Although blood flow through the skin is only about 3ml/min/100g of tissue in cold weather, there can be large changes in flow as needed. When the body is exposed to the external environment, blood to the skin can increase many times, which can be as high as 7 to 8 l/min for the whole body. As body temperature drops, blood to the skin decreases, dropping just above at very low temperatures. Even with some excessive vasoconstriction, the blood to the skin is usually very large to meet the basic metabolic needs of the skin.