Topic: Regulation of cardiovascular functions
Question: Describe briefly about the effect of humoral control of circulation.
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The humoral control of circulation refers to the regulation of blood flow and pressure by chemicals in the body fluids (humors).
Here are the humoral factors that control circulation along with their source and release in response to:
Vasodilators:
• Atrial natriuretic peptide (ANP): Released from cardiac atria in response to increased blood stretch or atrial pressure. Causes vasodilation and sodium excretion to reduce volume overload.
• Natriuretic peptides (BNP, CNP): BNP released from cardiac ventricles in response to volume expansion or pressure overload. Like ANP, produces vasodilation and natriuresis. CNP also vasodilates but has little role in sodium regulation.
• Nitric oxide: Synthesized by endothelial cells in response to shear stress or acetylcholine. Induces vasodilation of arterioles to regulate blood flow.
• Prostacyclin: Produced by endothelial cells in response to factors like bradykinin. Causes vasodilation and inhibits platelet activation. Prevents thrombus formation.
• Endothelium-derived hyperpolarizing factor (EDHF): Vasodilators released from endothelial cells in response to shear stress and other signals. Their identity is unclear but contribute to blood flow regulation.
• Potassium: Vasodilation in response to elevated serum potassium levels. High extracellular potassium hyperpolarizes smooth muscle cells, reducing vasoconstriction.
Vasoconstrictors:
• Catecholamines (epinephrine, norepinephrine): Secreted from adrenal medulla and sympathetic nerves in response to stress or low blood pressure. Cause vasoconstriction, increasing cardiac output and blood pressure.
• Angiotensin II: Produced in the blood by the renin-angiotensin system in response to low blood pressure, blood loss or sodium depletion. Stimulates vasoconstriction, especially of arterioles, and also aldosterone release to raise blood pressure.
• Vasopressin (ADH): Released from posterior pituitary in response to increased plasma osmolality or low blood pressure. Induces vasoconstriction and acts on kidneys to increase water reabsorption, raising blood volume and pressure.
• Endothelin: Peptides produced by endothelial cells in response to hypoxia or cell injury. Most potent vasoconstrictors and also stimulate aldosterone release to support blood pressure.
• Thromboxane: Synthesized from arachidonic acid by platelets and endothelium in response to vessel injury or inflammation. Causes platelet aggregation and vasoconstriction to promote clot formation and maintain blood flow.
In summary, the humoral control of circulation involves the action of various hormones, peptides and neurotransmitters in the body that regulate blood flow, blood volume and blood pressure. They help maintain homeostasis and make appropriate circulatory adjustments during various stresses and physiological conditions. Failure or dysfunction in these humoral mechanisms can contribute to disorders of blood pressure and circulation
