L7-8 Vascular + Microcirc Flashcards
what does vent constriction results in
- Contraction of veins reduces capacitance.
o Resistance of veins is small so veno-constriction does not change total peripheral resistance much.
what does vast constriction results in
- Constriction of arterioles increases total peripheral resistance.
o Blood volume in arterioles is small so constriction of arterioles does not change capacitance much.
Describe how elastic arteries maintain blood flow during diastole.
- During systole= arteries expand and store pressure (+ energy) in elastic walls
- During diastole= Elastic recoil of arteries propels blood forward
what does flow depend on
depends on pressure + resistance
explain total peripheral resistance
- Total resistance to flow in systemic circuit
role of arteriole in reg of TPR
- Arterioles= most resistance to blood flow (not capillaries as although low flow, parallel high)
- Lots of smooth muscle in arterioles allows control of diameter and resistance
- Control Total Peripheral Resistance
- Active control of diameter- Vaso-constriction
Describe how changes in cardiac output and total peripheral resistance alter mean arterial pressure.
- MAP= CO x TR (Q. x R)
Describe the actions of sympathetic tone on arterioles.
ARTERIOLS o Control total peripheral resistance and the distribution of cardiac output
• Sympathetic stimulation constricts arterioles, increasing blood pressure by restricting blood flow.
What does dec in symp tone of arterioles do
dec symp tone > dec resistance > dec MAP ?
define capacitance
compliance
Describe the role of veins as capacitance vessels.
o Veins are not stiff they contain a large volume of blood and are capacitance vessels
- Blood volume stored in veins= regulated by veno-constriction
o Contraction of veins reduced capacitance
Veins hold less blood
Increases venous return
Increases cardiac output
Sympathetic nerves
Describe how the sympathetic tone alters venous capacitance and venous return.
- Veins are high volume (compliance/capacitance) vessels that can act as a blood store
o Sympathetic stimulation constricts veins reducing the volume of blood they hold, increasing venous return and cardiac output
typical venous press
2-5mmHg
o Low bc veins high capacitance
typical pulmonary art press
25/8mmHg
o Pulmonary blood pressure is much less than systemic.
o Cardiac output of left and right heart are on average the same.
o Since Pa ≈Q×R
Lower total resistance in pulmonary circuit
Shorter tract
components of microcirc
Arterioles, venules, metarterioles, capillaries, arteriovenous shunts
describe starling equilibrium
• Arterial end:
o Higher BP than colloid osmotic pressure= net pressure pushes fluid out, plasma leaves (net movement out)
• Venous end:
o BP drops less than colloid osmotic pressure= pulls fluid back in (net movement into)
define colloidal os pressure
- Plasma proteins remain in the plasma // a protein concentration difference exists between plasma and interstitial fluid.
= move water from the area of higher water concentration in interstitial fluid > area of lower water concentration in plasma
- Plasma proteins remain in the plasma // a protein concentration difference exists between plasma and interstitial fluid.
Describe how changes in arteriolar resistance distribute cardiac output.
- Total perfusion through all systemic vascular beds is equal to cardiac output.
- Arteriolar resistance determines the perfusion through an organ.
- The resistance of the parallel systemic vascular beds determines the distribution of blood flow through organs.
• By controlling tissue perfusion so each tissue receives just enough blood while cardiac output and heart work are minimised
define hyperaemia
increase in blood flow.
define isschema
loss or absence of blood flow
diff b/w active and reactive hyperaemia
active= inc metabolic rate inc blood flow react= flow reastablied after such
what do metabolites do
local control of blood flow= alter smooth muscle tone
actions of O2 CO2 adenosine K and H on vascular resistance
o= constrict
CO2 adenosine K and H = dialte
how is long term reg of blood flow
remodelling and angiogen
