Peripheral Circulation Flashcards
What is blood flow controlled by
The contraction of the smooth muscle of arterioles as arteriolar radius controls resistance
What is arteriolar resistance directly proportional to
1/r^4
What are the intrinsic controls of vascular smooth muscle
Controls located in tissues
- Local temperature
- Transmural pressure
- Local metabolites, antacids and endothelium derived factors
What are the extrinsic controls of vascular smooth muscle
Nerves and hormones from outside the tissue
How can local temperature affect arteriolar radius and vascular smooth muscle
- High temp = vasodilation of cutaneous arterioles and veins
- Skin cooling = vasoconstriction by slowing Na+/K+ ATPase that causes depolarisation
- Skin cooling below 12C = vasodilation by paralysis of smooth muscle
How does the external and internal pressure of transmural pressure affect vascular smooth muscle
External = compresses vessels and impairs blood flow Internal = stretch of the vessel causes the vessel to contract - the myogenic response
How can stretch sensitive membrane areas affect vascular smooth muscle
Stretch in these areas opens a stretch activated ion channel and cells become depolarised and results in a Ca2+ signal and triggers muscle contraction
(local vasodilators from endothelium also help do things)
How can local metabolites affect vascular smooth muscle/arteriolar radius
- Vasodilators released by tissue in proportion to tissue metabolism
- removal rate proportional to blood flow
Name some possible local metabolites that can affect vascular smooth muscle
- K+ ions
- Adenosine
- Hypoxia
- Acidosis
- Increased interstitial osmolarity
What are autacoids
Local hormones and molecules that are released by cells and tissues in response to inflammation
What is the basic mechanism of autacoids in response to inflammation
Increases the permeability of the microcirculation
Give some examples of autacoids
- Histamine
- Bradykinin
- Serotonin (5-HT)
- Arachidonic Acid Derivatives
What are the signs and symptoms of inflammation
Heat Redness Swelling Pain Loss of Function
Give an example of an endothelium derived relaxing factor (EDRF)
Nitric Oxide
Thats all the powerpoint said so if you said something else then fook you
How does Nitric oxide act as an EDRF
- Diffuses to underlying smooth muscle
- Activates soluble granulate cyclase to increased cGMP and cause relaxation
What stimulates EDRF production and when is it stimulated too much
- Basal production stimulated by autacoids and shear stress
- Production stimulated too much in infection
What are endothelins
Endothelins are proteins that affect vasoconstriction of blood vessels and blood pressure
Where are ETa receptors found and what happens when endothelins bind to them
- found in smooth muscle tissue of blood vessels also the nervous system
- binding causes vasoconstriction, retention of sodium and leads to increased blood pressure
Where are ETb receptors found and what happens when endothelins bind to them
- found on endothelial cells that line the interior of blood vessels also the nervous system
- binding causes release of nitric oxide, natriuresis and diuresis that leads to a lower blood pressure
What does poiseuille’s law describe
the factors affecting blood flow
What is flow rate inversely proportional to
The length of the tube and the viscosity of the blood
What is flow rate directly proportional to
Resistance/Pressure difference
Flow = DeltaP/R
In extrinsic regulation of blood flow what happens when the SNS activates the adrenal medulla
Norepinephrine and epinephrine are rebased directly into the blood where they act as the mechanism for the fight or flight response
What does the sympathoadrenal system play a role in maintaining
Glucose levels, sodium levels, blood pressure and other metabolic pathways
How does sympathoadrenal activation affect Cardiac Output and resistance in the periphery and viscera
Increases it all
How does the sympathoadrenal system increase blood flow to the muscles
Their arterioles dilate in response to adrenaline via Beta2 adrenoceptor stimulation. So blood is shunted away from visceral and skin towards the muscles
What effects do AT2 and ADH at high levels have on peripheral circulation
General vasoconstriction of vascular smooth muscle, which increases resistance and BP
Name some paracrine regulators produced by the endothelium that promote relaxation
Nitric Oxide
Bradykinin
Prostacyclin
Which paracrine regulator is involved in setting the resting ‘tone’ of vessels
Nitric Oxide
What extrinsic factor increases NO (endothelial derived relaxing factors) levels
Parasympathetic activity
What paracrine regulator do drugs like nitroglycerin or viagra act through
Nitric Oxide
What is Endothelin 1
(ETa) This is a vasoconstrictor produced by the endothelium
What is the role of intrinsic and extrinsic regulation of blood flow
To maintain a fairly constant blood flow despite BP variation
How do myogenic control mechanisms of blood flow work
Occurs because vascular smooth muscle contracts when stretched and relaxes when not stretched
What effect can arterial pressure have on cerebral vessels
Decreased arterial pressure = dilation of cerebral vessels
What is the role of the metabolic control mechanisms of blood flow
To match the blood flow to the local tissue needs
What is hyperaemia
An excess of blood in the vessels supplying an organ
What factors resulting from high metabolism can cause vasodilation and increased blood flow
Low O2 Low pH High CO2 High Adenosine High K+
