055 Nervous, Local, Humorol Control of Vascular Resistance Flashcards
Why does radius have such a large impact on resistance?
Resistance is directly proportional to 1/r^4. So a small increase in radius will cause a huge drop in resistance.
Between which vessels is the most significant pressure drop? and why?
Arterioles have a huge drop in blood flow. There is also increase in resistance due to sudden decrease in radius. There is significant blood pressure drop.
What is the relative wall/lumen ratio of resistance vessels and why?
1:1 due to the thick smooth muscle layer that has vascular tone caused by the background sympathetic drive to its a1 receptors.
Explain the mechanism of sympathetic activation causing smooth muscle contraction.
noradrenaline stimulates a1 adrenoreceptors, causing smooth muscle contraction.
In which vascular beds is parasympathetic innervation important?
Erectile tissue and the cerebral system
How is angiotensin II formed from the precursor form? What effect does angiotensin II have?
Angiotensin converting enzyme is found on endothelial cells, converting angiotensin I (found in the blood) to angiotensin II. It is activated by the release of rennin from the juxtagloremular apparatus.
Explain the mechanism of adrenaline on different types of adrenoreceptors and the consequent effects.
a1 receptors - smooth muscle vasoconstriction in all other vascular beds.
b2 receptors - cAMP is increased causing vasodilation of arterioles in skeletal muscle and the heart.
What is the difference between functional and reactive hyperaemia?
Functional hyperaemia occurs when there is an increased metabolic demand for oxygen e.g. exercise, causing an vasodilation to increase blood flow. Reactive hyperaemia occurs after an occlusion to an arterial. The blood flow following the interuption of arterial supply is above the level that occured before the occlusion.
What is the difference between autoregulation and hyperaemia?
auto regulation occurs when there is increased perfusion pressure but constant metabolic demand. Hyperaemia occurs when there is changing metabolic demand and a need for a changing perfusion pressure.
What is endothelin and what can stimulate its release?
This is a vasoconstrictor that released by the endothelium. Humoral factors such as angiotensin, vasopressin, thrombin can induce endothelin.
In which 2 locations are natriuretic peptides produced? What are they?
BNF (Brain natriuretic factor) is produced in the ventricles when stimulated by stretch or sympathetic activity e.g. increased preload. They will cause vasodilation. ANF (Atrial natriuretic factor) is produced in the atrium when stimulated by stretch or sympathetic activity.
Where is vasopressin made and where is it released?
Made in the hypothalamus and released in the pituitary glands
What effect does vasopressin have on the body?
Vasoconstrictor - activates V1 receptors.
What are the 3 endothelium-derived factors that cause smooth muscle relaxation?
EDHF, NO, Prostacyclin
How does exercise cause vasodilation?
When you exercise, the increase in blood flow will raise shear stress. This activates the NOS pathway, producing NO and activating sGC, cCMP etc. Vasodilation then occurs.
