Physiology 6- Integration of Mechanisms Flashcards
What is the function of capillaries?
Exchange of gas, nutrients and water between blood and tissues
What are the major capacitance vessels with most of the blood at rest contained there?
Veins
What is TPR regulated by?
Vascular smooth muscle
Resistance to blood flow is directly proportional to what?
Blood viscosity and length of the blood vessel
Resistance to blood flow is inversely proportional to what?
Radius of the blood vessel to the power 4
Resistance is mainly controlled by vascular smooth muscle changing what?
The radius of the vessel
In terms of extrinsic control, what is vascular smooth muscle controlled by?
Nerves and hormones
In terms of nerve supply, vascular smooth muscle is supplied by ? through the neurotransmitter ? acting on ? adrenoceptors
Sympathetic fibres
Noradrenaline
Alpha receptors
What is vasomotor tone?
Vascular smooth muscle being partially constricted at rest
What causes vasomotor tone?
Discharge of sympathetic fibres continuously releasing noradrenaline
What is there none of in arterial smooth muscle?
Parasympathetic innervation
The main hormonal influence on TPR is what?
Adrenaline from adrenal cortex
What results from adrenaline acting on alpha receptors?
Vasoconstriction
What results from adrenaline acting on beta2 receptors?
Vasodilation
Where are alpha receptors more common and hence vasoconstriction by adrenaline?
Skin, gut, kidney arterioles
Where are beta2 receptors more common and hence vasodilation by adrenaline?
Cardiac and skeletal muscle arterioles
What can override extrinsic control mechanisms of TPR?
Intrinsic control mechanisms
What is metabolic hyperaemia?
Increased blood flow to tissues
What metabolic factors can cause vasodilation and increased blood flow to tissues?
Low PO2 or high PCO2 Increased H+ (decreased pH) Increased extracellular K+ Increased osmolarity of ECF Adenosine release from ATP
What are examples of local humoral agents (chemicals) which cause vasodilation?
Bradykinin, NO, histamine
What are examples of local humoral agents (chemicals) which cause vasoconstriction?
Serotonin, thromboxane A2, leukotrienes
Nitric oxide is produced by ? from the amino acid ? through the enzyme ?
- Vascular endothelium of arteries and arterioles
- L-arginine
- Nitric oxide synthase (NOS)
How would you describe NO in terms of its effect on blood flow?
Potent vasodilator
What does sheer stress on the endothelium (as a result of increased blood flow) cause release of?
Ca++ and NOS
NO diffuses from the endothelium into the adjacent smooth muscle cells to activate what?
cGMP which signals vasodilation
What is endothelin?
A potent vasoconstrictor which is released from endothelial cells
What 5 factors influence venous return?
Increase venomotor tone, respiratory pump, skeletal muscle pump, blood volume and atrial pressure
Venous smooth muscle are provided with what nerve fibres?
Sympathetic
What is venomotor tone?
Stimulation of the sympathetic nerve fibres in venous smooth muscle gives contraction
