L7-8 Vascular + Microcirc

Question 1

what does vent constriction results in

Answer 1

• Contraction of veins reduces capacitance.

o Resistance of veins is small so veno-constriction does not change total peripheral resistance much.

Question 2

what does vast constriction results in

Answer 2

• Constriction of arterioles increases total peripheral resistance.
  o Blood volume in arterioles is small so constriction of arterioles does not change capacitance much.

Question 3

Describe how elastic arteries maintain blood flow during diastole.

Answer 3

• During systole= arteries expand and store pressure (+ energy) in elastic walls
• During diastole= Elastic recoil of arteries propels blood forward

Question 4

what does flow depend on

Answer 4

depends on pressure + resistance

Question 5

explain total peripheral resistance

Answer 5

• Total resistance to flow in systemic circuit

Question 6

role of arteriole in reg of TPR

Answer 6

• 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

Question 7

Describe how changes in cardiac output and total peripheral resistance alter mean arterial pressure.

Answer 7

• MAP= CO x TR (Q. x R)

Question 8

Describe the actions of sympathetic tone on arterioles.

Answer 8

ARTERIOLS o Control total peripheral resistance and the distribution of cardiac output
• Sympathetic stimulation constricts arterioles, increasing blood pressure by restricting blood flow.

Question 9

What does dec in symp tone of arterioles do

Answer 9

dec symp tone > dec resistance > dec MAP ?

Question 10

define capacitance

Answer 10

compliance

Question 11

Describe the role of veins as capacitance vessels.

Answer 11

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

Question 12

Describe how the sympathetic tone alters venous capacitance and venous return.

Answer 12

• 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

Question 13

typical venous press

Answer 13

2-5mmHg

o Low bc veins high capacitance

Question 14

typical pulmonary art press

Answer 14

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

Question 15

components of microcirc

Answer 15

Arterioles, venules, metarterioles, capillaries, arteriovenous shunts

Question 16

describe starling equilibrium

Answer 16

• 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)

Question 17

define colloidal os pressure

Answer 17

• • 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

Question 18

Describe how changes in arteriolar resistance distribute cardiac output.

Answer 18

• 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

Question 19

define hyperaemia

Answer 19

increase in blood flow.

Question 20

define isschema

Answer 20

loss or absence of blood flow

Question 21

diff b/w active and reactive hyperaemia

Answer 21

active= inc metabolic rate inc blood flow 
react= flow reastablied after such

Question 22

what do metabolites do

Answer 22

local control of blood flow= alter smooth muscle tone

Question 23

actions of O2 CO2 adenosine K and H on vascular resistance

Answer 23

o= constrict

CO2 adenosine K and H = dialte

Question 24

how is long term reg of blood flow

Answer 24

remodelling and angiogen

Question 25

what is remodelling

Answer 25

• Remodelling of existing vessels occurs with an increase in vessel diameter if perfusion drops or metabolic rate increases.

Question 26

what is angiogen

Answer 26

• New blood vessels may also be produced