vascular resistance and endothelial cells

1. wall shear stress 2. how does shear stress stimulate nitric oxide production 3. smooth muscle relaxation 4. vasoconstriction and vasodilation 5. role of endothelial cells in arterioles 6. extrinsic control in endothelial cells 7. influence of total peripheral resistance of mean arterial pressure 8. hormones that influence arteriolar radius 9. factors affecting total peripheral resistance

what is shear stress and how is it caused

shear stress is the frictional force parallel to the wall at the surface of the endothelium directly related to blood flow velocity

how does shear stress activate nitric oxide production

1. Blood Flow and Shear Stress: As blood flows through the blood vessels, it exerts shear stress on the endothelial cells that line the vessel walls.

2. Mechanosensors Activation: The endothelial cells have mechanosensors, that can sense the mechanical forces associated with shear stress.

3. Activation of eNOS: Shear stress activates endothelial nitric oxide synthase (eNOS), an enzyme in the endothelial cells. eNOS is responsible for the synthesis of nitric oxide.

4. Nitric Oxide Production: Activated eNOS catalyzes the conversion of L-arginine to nitric oxide (NO) and citrulline. Nitric oxide is then released into the bloodstream.

5. Vasodilation: Nitric oxide has several physiological effects, one of the most important being the relaxation (dilation) of blood vessels. When released in response to shear stress, nitric oxide causes the smooth muscle cells in the blood vessel walls to relax, leading to vasodilation.

6. Improved Blood Flow: Vasodilation resulting from nitric oxide release helps to increase blood flow to tissues and organs, ensuring that they receive sufficient oxygen and nutrients.

how does nitric oxide cause vasodilation

• radius gets bigger

• decreased vasoconstriction

• increaased blood flow

• decreased resistance

how do endothelial cells work with arteriols

release chemical mediators that play a key role in locally regulating the arteriolar caliber

- release locallly acting chemical messengers in response to chemical changes in their environment

amongst best studied local vasoactive mediators is nitric oxide

influence of total peripheral resistance on mean arterial

primary determinants

• cardiac output

• total peripheral resistance

hormones that influence arteriolar radius

adrenal medullary hormones

• adrenaline and noradrenaline

• alpha 1 and beta 2 adrenoreceptors

• vasopressin and angiotensin ll

  • important in controlling fluid balance

  • potent vasoconstrictors

5 intrinsic factors acting on arterial smooth muscle that affect total peripheral resistance

1. heat. cold application

2. response to shear stress - compensates for changes in longitudinal force of blood flow

3. myogenic responses to stress

4. histamine release

5. local metabolic changes in o2

4 extinsic factors acting on regulating the blood pressure of arteriolar radius that affect total peripheral resistance

1. vasopressin

2. angiotensin ll

3. ephrinephrine and norepinephrine

4. sympathetic activity exerts vasoconstriction effect