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Various cell types play a role in HR, including astrocytes, smooth muscle cells, endothelial cells of blood vessels, and pericytes. These cells control whether the vessels are constricted or dilated, which dictates the amount of oxygen and glucose that is able to reach the neuronal tissue. Brain blood vasculature as a function of blood flow.
Central nervous system fatigue, or central fatigue, is a form of fatigue that is associated with changes in the synaptic concentration of neurotransmitters within the central nervous system (CNS; including the brain and spinal cord) which affects exercise performance and muscle function and cannot be explained by peripheral factors that affect muscle function.
η(δ) = viscosity of blood in the wall plasma release-cell layering; r = radius of the blood vessel; δ = distance in the plasma release-cell layer; 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.
In response to a lowering of the plasma sodium concentration, or to a fall in the arterial blood pressure, the juxtaglomerular cells release renin into the blood. [65] [66] [67] Renin is an enzyme which cleaves a decapeptide (a short protein chain, 10 amino acids long) from a plasma α-2-globulin called angiotensinogen.
Acid–base homeostasis is the homeostatic regulation of the pH of the body's extracellular fluid (ECF). [1] The proper balance between the acids and bases (i.e. the pH) in the ECF is crucial for the normal physiology of the body—and for cellular metabolism . [ 1 ]
A rise in lactate out of proportion to the level of pyruvate, e.g., in mixed venous blood, is termed "excess lactate", and is an indicator of anaerobic glycolysis occurring in muscle cells, as seen during strenuous exercise. Once oxygenation is restored, the acidosis clears quickly.
Potassium resides mainly inside the cells of the body, so its concentration in the blood can range anywhere from 3.5 mEq/L to 5 mEq/L. [14] The kidneys are responsible for excreting the majority of potassium from the body. [14] This means their function is crucial for maintaining a proper balance of potassium in the blood stream.
Lactic acid tends to accumulate in the muscles, which causes pain in the muscle and joint as well as fatigue. [13] It also creates a gradient which induces water to flow out of cells and increases blood pressure. [14] Research suggests that lactic acid may also play a role in lowering levels of potassium in the blood. [15]