Blood Flow Regulation By Dr. Khurram Irshad

Objecctives To describe the mechanisms responsible for the regulation of Blood Flow to different tissues

Why Do We Need to Regulate Blood Flow ?

Mechanisms of Blood Flow Acute Control Rapid changes in diameter of arterioles, metarterioles and precapillary sphincters occurring within seconds to minutes leading to increase or decrease in blood flow.

Slow changes in flow over the period of days, weeks or even months. Long Term Control Slow changes in flow over the period of days, weeks or even months. This is brought about by - Increase or decrease in size of organ - Increase or decrease in No. of blood vessels supplying the organ

Acute Control of Blood Flow Local Metabolic factors Myogenic response Humoral Factors

Local Metabolic Factors responsible for Acute control of blood flow Lack of oxygen according to the tissue needs It will lead to locally accumulation of - Adenosine - carbondioxide - Adenosine phosphate compounds - histamin - K + - H + (Vasodilator Theory)

Lack of Oxygen and Nutrient will directly lead to Vasodilation Glucose Vitamin C Vitamin B Thiamine Niacin Riboflavin

Special Mechanisms for Acute Blood Flow Control in Specific Tissues Kidney’s Tubuloglomerular feed back Brain Heart

Vasodilation and Vasoconstriction in Arteries when there is change in microvasculature - EDRF (endothelium derived relaxing factor) - NO

Examples of Acute Blood Flow Control Reactive Hyperemia Active Hyperemia

Long Term Control of Tissue Blood Flow Change in Tissue vascularity (Oxygen requirement is important factor) Angiogensis (growth of new blood vessels) Collateral circulation

HUMORAL REGULATION Vasoconstrictor agents - Epinephrine and norepinephrine - Angiotensin - Vasopressin - Endothelin

Vasodilator Agents - Bradykinin - Histamin