L20 - Cardiovascular System 3 Flashcards
Why are valves integral to healthy heart function?
ensure unidirectional flow
open / close passively
What causes the opening and closing of valves in the heart?
pressure differences between components of the heart
When do the atrioventricular valves close?
when the ventricles start to contract
When do the semilunar valves close?
when the ventricles relax
When do valves close in general?
when pressure in current compartment becomes greater than pressure in previous compartment
What are the sounds of the heart? What causes these sounds?
sound 1 and sound 2
occur when heart valves close (sudden turbulent flow and vibration)
What is sound 1 caused by?
closure of atrioventricular (AV) valves (contraction)
What is sound 2 caused by?
closure of semilunar valves (relaxation)
What will cause the AV valves to close? (contraction or relaxation of ventricles / greater pressure in ventricles than atria or greater pressure in atria than ventricles)
pressure in ventricles become greater than pressure in atria
ventricles start contracting
What affects the movement of blood?
heart - source of energy gravity skeletal muscle diaphragm movements elastic tissue
What is systolic BP?
max pressure exerted in arteries when blood is ejected into them during systole (heart contracting phase)
What is diastolic BP?
min pressure within arteries when blood draining off into remainder of vessels during diastole (heart relaxing / filling phase)
What is pulse pressure?
a measure of strength of pressure wave
difference between systolic and diastolic BP
What is mean arterial pressure?
average pressure responsible for driving blood forward into tissues throughout cardiac cycle
Why is regulation of MAP important?
essential for efficient function and life
low BP = dizziness, organ failure
high BP = stroke, aneurysm
What determines MAP?
how much blood is pumped out per unit time
how difficult / easy is it for the blood to move through the system
What determines how much blood is pumped out per unit time?
stroke volume x heart rate = cardiac output
What determines how difficult / easy it is for the blood to move through the system?
total peripheral resistance (TPR) = resistance of the peripheral circulation
What is MAP proportional to?
cardiac output x total peripheral resistance
How is stroke volume calculated? How can stroke volume be increased?
end diastolic volume minus end systolic volume
increasing end diastolic volume or decreasing systolic volume via more forceful contractions resulting in less blood leftover in the heart
What is cardiac output?
volume of blood pumped by one ventricle in a given period of time
What is stroke volume?
amount of blood pumped by one ventricle during a contraction
What is stroke volume? What affects stroke volume?
force of ventricular contraction
affected by:
length of muscle fiber (volume of blood in chamber at start of contraction)
contractility of heart (neural influences)
What is the stretch-force relationship in heart? (Frank-Starling Law)
as more blood enters the heart, length of muscle fibres stretches towards optimum length resulting in increased contractile force
What is end-diastolic volume determined by?
venous return which is controlled by the skeletal muscle pump, the respiratory pump and neural control of the venous system
What does neural control of the venous system involve?
sympathetic tone and varying degree of vasoconstriction
How does norepinephrine affect stroke volume?
increases stroke volume as it increases the strength of contraction of muscle fibres
How does the sympathetic nervous system modulate heart rate?
changes ion permeability
depolarises
reaches threshold sooner
β1-receptors (noradrenaline)
How does the parasympathetic nervous system modulate heart rate?
changes ion permeability hyperpolarizes takes longer to reach threshold muscarinic receptors (ACh)
How does the sympathetic nervous system affect conduction of AV node?
enhances conduction
How does the parasympathetic nervous system affect conduction of AV node?
slows conduction
How does the body maintain the same mean arterial pressure if TPR is changing all the time?
modulating cardiac output because MAP = CO x TPR
Why is there a fall in cardiac output when we stand?
pooling of blood in legs -> reduced venous return -> reduced CO -> fall in MAP
Can the body measure cardiac output?
not directly
for a given TPR, MAP is an indication of the adequacy of cardiac output
