Regulatory mechanisms in circulation Flashcards
what is the average cardiac output of a human?
4-7 L/min
what is cardiac output affected by? how much?
affected by activity
(can decrease by 10% or increase by up to 500%)
define inotropy
strength of contractions
define chronotrophy
contraction frequency (increased heart rate is called tachycardia; decreased heart rate is called bradycardia)
define dromotropy
velocity of signal conduction by cardiomyocytes
define lusitrophy
myocardial relaxation
define bathmotropy
myocardial excitability
name 4 things thsat increase sympathetic nervous activity
- exercise
- standing up
- stress
- haemorrhage
give 5 effects of sympathetic stimulation
- Ventricular pressure rises more rapidly to a higher systolic pressure
- Ejection fraction is increased
- Diastolic volume falls
- Stroke volume increases
- Duration of systole decreases
what is the Frank-Starling mechanism?
‘The more the ventricle is filled with blood during diastole, the greater the stroke volume’
define preload
defined as the stretch cardiac muscle is exposed to under conditions of diastole
what does preload depend on?
venous blood pressure and rate of venous blood flow
what is preload affected by?
venous tone and volume of circulating blood
what 6 things does venous pressure depend on?
- blood volume
- gravity (or posture)
- peripheral venous tone (regulated by sympathetic innervation of veins in skin, kidney and splanchnic system)
- muscle pump (skeletal muscles)
- respiratory pump (intercostal muscles)
- cardiac output (increase in cardiac output lowers venous pressure)
define afterload
the tension produced by the heart in order to eject blood into vessels
