L24 Systemic Circulation

Question 1

Systemic circulation

Answer 1

Most vascular beds in parallel

Function to maintain sufficient pressure to push blood through all vascular components or mean arterial pressure (MAP)

Question 2

Arterial side v venous side

Answer 2

Arterial:
Lower compliance
Higher pressure
Lower volume

Venous:
Higher compliance
Lower pressure
Higher volume

TPR - total peripheral resistance (resistance heart has to overcome to get blood from arterial to venous side)
It’s variable , we can control TPR and CO

Question 3

Arteriole

Answer 3

Major resistance vessel

Resistance causes a dramatic pressure drop

Convert pulsatile pressure swings of cardiac cycle into non-fluctuating pressure

Radii of arterioles supplying organs can be adjusting to distribute CO and reg BP

Question 4

Pulse pressure

Answer 4

Difference btw systolic pressure and diastolic pressure

Question 5

Compliance

Answer 5

Pressure in blood vessels is determined by the volume of blood in vessel and compliance of vessel

Compliance- ability of vessel to expand/give way to stress

Influenced by: vessel geometry, elastic properties of wall, vascular smooth muscle tone

Decreases with age

Question 6

Arterial pressure

Answer 6

Depends on arterial blood volume and arterial compliance

Rises during ventricular systole as arterial inflow is transiently greater than outflow - volume transiently increases

Pressure falls during diastole as blood leave the arterial side to enter venous system

Transfer of blood to venous circulation during diastole is called peripheral run off

Question 7

Arterial pressure

MAP

Answer 7

Peak pressure = systolic pressure (SP)

Pressure just prior to ventricular ejection= diastolic pressure (DP) - determined by arterial compliance and residual arterial volume immediately prior to next cardiac ejection

Pulse pressure PP= SP-DP

MAP ~ DP + PP/3

Question 8

Capillary flow continues during

Answer 8

Diastole

Elastic recoil of the arterial walls converts the stored energy into capillary flow during diastole (maintains blood flow)

Question 9

Pulse pressure and systolic pressure depend on

Answer 9

Aortic compliance and SV

PP= SP -DP = deltaP =deltaV/C

Question 10

At constant compliance, aortic pulse pressure and systolic pressure

Answer 10

Increase as SV increases

Question 11

At a constant SV, aortic pulse pressure and systolic pressure

Answer 11

Increase as aortic compliance decreases

Question 12

Diastolic pressure mainly influence by

Answer 12

HR (determines time interval for blood transfer from arterial system to venous system (peripheral run off))

And

TPR(determines rate of volume transfer to periphery)

Both affect volume of blood remaining in arterial system at end of diastolic period

Question 13

Reduced TPR

Answer 13

More run off

Decreased DP

Question 14

Elevated TPR

Answer 14

Less run off

Increased DP

Question 15

Increase HR

Answer 15

Less time for run off

Increase DP

Question 16

Decrease HR

Answer 16

More time for run off

Lower DP

Question 17

Increasing SV

Answer 17

Directly increases PP

MAP increases

Question 18

Decreasing HR

Answer 18

Increases run off time

DP and SP decrease

MAP decrease

Question 19

Increase SV while decreasing HR

Answer 19

Increase PP

DP will decrease

SP May increase

Question 20

Venous system

Answer 20

Low resistance

Low pressure

High compliance

75% blood volume may be in venous system at any one time

Question 21

Venous return

Answer 21

Blood flow from the peripheral veins to the right atrium

Equal to cardiac output at steady-state

Pressure gradient for venous return is difference btw peripheral venous pressure (pressure of blood entering peripheral veins from capillaries) and right atrial pressure

Anything that increases pressure of vena cava (central venous pressure), increases venous return

Question 22

Effects of posture on CO

Answer 22

On standing there is a rapid translocation of blood from thorax to lower extremities

Blood pools in peripheral veins and capillary hydrostatic pressure increase

Venous return decreases; CO and MAP falls transiently

Neurally-mediated reflexes are activated to return MAP towards the supine level

Venous return may be augmented by muscle pump mechanism

Question 23

Muscle pump

Answer 23

When standing , skeletal muscles of lower extremities begin rhythmic cycles of contraction and relaxation

Reflex initiated by stimulation of plantar surface of feet

Muscle contractions squeeze veins in muscles and drive blood towards the heart (augments venous return)

Venous valves prevent retrograde blood flow

Veins refill during relaxation of skeletal muscle

Skeletal muscle pump activity is intensified with walking and running