Integration of Cardiovascular Mechanisms Flashcards
What are vascular smooth muscles controlled by?
Extrinsic and intrinsic mechanisms
What is resistance to blood flow directly proportional to?
- blood viscosity
- length of blood vessel
What is resistance to blood flow inversely proportional to?
Radius of blood vessel to the power 4
What is resistance to blood flow mainly controlled by?
vascular smooth muscles through changes in the radius of arterioles
When does adrenaline cause vasoconstriction?
When acting on alpha receptors ( predominant in skin, gut, kidney arterioles)
When does adrenaline cause vasodilation?
When acting on Beeta 2 receptors (predominate in cardiac and skeletal muscles arterioles)
What does adrenaline helps with?
Strategic redistribution of blood i.e during exercise
What are important in intermediate control of blood pressure?
angiotensin II and antidiuretic- causes vasoconstriction
What does extrinsic control act on?
Vascular smooth muscles - involves nerves and hormones
What does intrinsic control do?
Match the blood flow of different tissues to their metabolic needs
what control has the ability to over-ride the other?
Intrinsic that over-ride extrinsic
What factors causes relaxation of arteriolar smooth muscles resulting in 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)
What do local metabolic changes within an organ cause?
Contraction of arteriolar smooth muscles
What are local humeral agents and what do they influence?
Local chemicals released within an organ and influence the contraction of arterial and arteriolar smooth muscles
What are local humeral agents released in response to?
tissue injury or inflammation
What humeral agents cause vasodilation?
histamine
bradykinin
Nitric oxide
What causes the activation of Nitric oxide synthase?
shear stress on vascular endothelium as a result of increased blood flow
What does the diffusion of NO into smooth muscle cells activate the formation of?
cGMP- serves as second messenger for signalling smooth muscle relaxation
What humeral agents cause vasoconstriction?
Serotonin
Thromboxane A2
Leukotrienes
endothelin
What is endothelin?
potent vasoconstrictor released from endothelial cells. Its production is stimulated by various agents which cause vasoconstriction
How is endothelial damage/disfuntion caused?
high blood pressure, high cholesterol, diabetes and smoking
What are endothelial produced vasodilators?
anti-thrombotic
anti-inflammatory
anti-oxidants
What are endothelial produced vasoconstrictors?
pro-thrombotic
pro-inflammitory
pro-oxidants
What are the effects of cold and warmth on vascular smooth muscles?
cold- vasoconstriction
warmth- vasodilatation
What happens in a myogenic response?
- If MAP rises resistance vessels automatically constrict to limit flow
- If MAP falls resistance vessels automatically dilate to increase flow
What does dilatation of arterioles cause?
sheer stress in the arteries upstream to make them dilate and this increases blood flow to metabolically to active tissues
What 4 factors increase venous return?
increasing:
- venomotor tone
- skeletal muscle pump
- blood volume
- respiratory pump
What impact does an increased venous return have?
increase in atrial pressure –> increased EDV –>stroke volume
What are venous smooth muscles supplied with and what does stimulation cause?
sympathetic nerve fibres and stimulation causes venous contriction
What does increased venomotor tone cause?
Increased venous return , SV and MAP
what allows blood to move forward towards the heart?
One-way venous valves
During exercise, what increases and what does this cause?
Sympathetic nerve activity increases which increase HR and SV and so CO
How is flow reduced to kidneys and gut during exercise?
sympathetic vasomotor nerves cause vasoconstriction
How is flow increased to skeletal and cardiac muscle during exercise?
Metabolic hyperaemia overcomes vasomotor drive and causes vasodilatation
What does metabolic hyperaemia decrease?
TPR and DBP
