Integration of cardiovascular mechanisms Flashcards
What does MAP equal?
CO x TPR
What are the three things that regulate stoke volume?
Pre-load
Myocardial contractility
Afterload
How is total peripheral resistance regulated?
Control of vascular smooth muscle through intrinsic and extrinsic mechanisms
What is the main site of TPR?
Arterioles
What is TPR?
The total periphery resistance in the blood pressure across the body
What is resistance to blood flow proportional to?
Directly proportional to blood viscosity and the length of blood vessels
Inversely proportional to the radius of the blood vessels
What is the equation for resistance to blood flow?
R (fish sign) (n.L)/ r4
Explain the nervous extrinsic control of vascular smooth muscle
Baroreceptor reflex
Sympathetic nerve fibres - noradrenaline and a receptors
What term described the vascular smooth muscles being partially constricted at rest?
Vasomotor tone
What is the result of increased vasomotor tone?
Vasoconstriction
What is the hormone involved in extrinsic control of vascular smooth muscle?
Adrenaline from the adrenal medulla
Largely organ specific effect
What receptor does adrenaline act on to cause vasoconstriction and where are these receptors predominant?
a receptors
Skin, gut and kidney arterioles
What receptor does adrenalin act on to cause vasodilation and where are these receptors predominant?
B receptors
Cardiac and skeletal muscle arterioles
Name two hormones, other than adrenalin, that affect vascular smooth muscle
Angiotensin II (vasocontriction) Antidiuretic hormone (vasoconstriction)
Give 5 metabolic changed within an organ that cause vasodilation
Decreased local PO2 Increased PCO2 Increased local [H+] Increased extra-cellular [K+] Increased osmolality of ECF Adenosin release
Give 4 humoral agents that cause relaxation of arteriolar smooth muscles causing vasodilation
Histamine
Prostaglandins
Bradykinin
Nitric oxide
Where is NO produced?
Vascular endothelium
What enzyme is involved in the formation of NO?
Nitric Oxide Synthase (NOS)
When NO diffuses into smooth muscle cells what does it activate?
The formation of cGMP
Give four humoral agents that cause vasoconstriction
Serotonin
Thromboxane A2
Leukotrienes
Endothelin
What is the affect of cold on the vascular smooth muscles?
Causes vasoconstriction
What is the myogenic response to stretch?
If MAP rises resistance vessels automatically constrict to limit flow
If MAP falls resistance vessels automatically dilate to increase flow
Name two organs where myogenic response to stress is important
Kidney and brain
Explain the effect of sheer stretch on vascular smooth muscles
Dilation of arterioles causes sheer stress in the arteries upstream to make them dilate. This increases blood flow to metabolically active tissues.
Give 4 factors that increase venous return
Increased venomotor tone
Increased blood volume
Increased skeletal muscle pump
Increased respiratory pump
What does venomotor mea?
Controlling dilation or constriction of the veins
What is the affect of increased venomotor tone?
Increased venous return, SV and MAP
What is the affect of increased vasomotor tone?
Increased TPR and MAP
What is the affect of muscle activity on venous return to the heart?
Increases venous return to the heart
