intergration of cardivascular mechanisms Flashcards
How is systemic vascular resustance regulated?
By vascular smooth muscle
Where is the main site of Systemic vascular resistance?
Arterioles
How is SVR increased by vascular smooth muscle?
Contraction of vascular smooth muscles causes vasoconstriction and increases SVR and MAP
How is SVR decreased by vascular smooth muscle?
Relaxation of vascular smooth muscles causes vasodilatation and decreases SVR and MAP
By which two mechanisms are vascular smooth muscles controlled by?
extrinsic and intrinsic mechanisms
What are the three things resistance is reliant on?
length of blood vessels, blood viscosity and radius of blood vessels
Resistance to blood flow is: indirectly proportional to blood viscosity and length of blood vessel. True/false
False. Resistance to blood flow is: directly proportional to blood viscosity and length of blood vessel
How does radius of blood vessels affect resistance?
The smaller the radius the larger the resistance. Small changes in the radius of the vessels leads to a large change in flow
What is vasomotor tone?
The vessels are partially constricted at rest
What causes vasomotor tone?
continuous release of noradrenaline by sympathetic nervous system at resting conditions causes vasomotor tone which aids in maintaining our regular BP
What effect does decreased vasomotor tone have on vessels?
Causes vasodilation
Why is intrinsic control of vascular smooth muscle important?
At different ties you may need different blood flow to different organs. It is the main way in which local control is maintained
What components are intrinsic control made of?
chemical and physical factors
List the factors that cause vasodilation and metabolic hyperaemia
Decreased local PO2
Increased local PCO2
Increased local [H+] (decreased pH)
Increased extra-cellular [K+]
Increased osmolality of ECF
Adenosine release (from ATP)
Other than metabolites, what else causes contraction of smooth muscle?
local humoral agents
When are local humoral agents realeased?
in response to tissue injury or inflammation.
What are examples of humoral agents that cause vasodilation?
histamine, bradykinin and nitric oxide
What is nitric oxide and why is it important?
a gas produced by vascular endothelium. It is a potent vasodilator with a very short life(coupe seconds). It is important in regulation of blood flow and vascular health
What are examples of humoral agents which cause vasoconstriction?
serotonin, thromboxane A, leukotrienes and endothelin
What can damage to endothelium be caused by?
high Bp, high cholesterol, diabetes and smoking
Why is endothelium important?
It is important in the maintenance of vascular health. It has a lot of functions and is not just a lining. Damage to it can cause many cardiovascular diseases.
What are examples of endothelial produced vasodilators?
anti-thrombotic, anti-inflammatory, anti-oxidants
What are examples of endothelial produced vasoconstrictors?
are pro-thrombotic, pro-inflammatory, pro-oxidants
What are the effects of temperature on vascular smooth muscle?
cold causes vasoconstriction and warmth causes vasodilation
What effect does the myogenic response have on vascular smooth muscle?
If MAP rises resistance vessels automatically constrict to limit flow
If MAP falls resistance vessels automatically dilate to increase flow
What is the effect of sheer stress on vascular smooth muscle?
Dilatation of arterioles causes sheer stress in the arteries upstream to make them dilate. This increases blood flow to metabolically active tissues
What is the normal range for MAP?
70-105
Does the brain usually participate in baroreceptor response?
No. Myogenic response regulates blood flow in important organs like the brain by keeping the blood flow constant despite changes in MAP.
What does increased venomotor tone increase?
venous return. stroke volume and MAP
What does vasomotor tone increase?
Systemic vascular resistance and MAP
What does muscle activity increase?
Venous return to the heart via contraction of muscles.
What are the acute CVS responses to excerise?
- increased sympathetic activity
- increased HR and SV
- reduced flow to kidneys and gut
- increased flow to skeletal and cardiac muscles
- increased systolic but equal/lowered diastolic
What causes post exercise hypotensive response?
pooling of blood into beds with vasoconstricted areas
What are the chronic CVS responses to exercise?
- reduction of sympathetic
- incread parasympathetic tone to heart
- cardiac remodelling
- reduced plasma renin levels
- reduced arterial stiffening
- more vasodilators less vasoconstrictors
