11. circulation of blood Flashcards
what is the function of the cardiovascular system
to maintain an adaptable supply of blood to tissues in order to supply nutrients and signalling molecules and to remove waste products
why does blood supply have to be adaptable
pressure differentials across tissues, eg blood slows for capillary exchange
what is flow of blood determined by
pressure difference/ resistance (impedance/interruption to flow)
what is resistance determined by
length of vessel
radius of vessel
fluid viscosity
resistance is proportional to
1/r^4
if we have two blood vessels of the same length but one vessel has a wider diameter, which will have more resisitance
the vessel with the smaller diameter
has greater impedance as more blood is in contact with the blood vessel walls
the rate of flow of blood through vessels is proportional to
the diameter of the vessel
contraction of the heart muscles generates
CVS pressure gradient
which part of the heart generates the greatest pressure
left ventricle
needs to supply blood to the peripheral and so has to travel the greatest distance
describe a graph of pressure against time in the heart
graph increases to 120mmHg, peaks due to systolic pressure.
then notch due to valves shutting which interrupts the flow of curve
then decreases to 80mmHg, diastolic pressure
what is pulse pressure
the difference between diastolic and systolic pressure
what is the mean arterial pressure plus formula
the average flow of blood through the body
= diastolic pressure + 1/3 pulse pressure
heart tissue is myogenic
can generate electrical impulse by itself
what is the pacemaker of the heart
the sinoatrial node
describe the conduction pathway
SAN generates impulse that travels to the atria then reaches the atrioventricular node which delays the signal to allow the atria to contract
then the signal goes to bundle of his which rapidly sends the signal to ventricular myocardium for the ventricles to contract in unison
describe the cardiac cycle
atrial systole/ contraction
atrial diastole
ventricular systole- shuts the AV valves
pressure in ventricles increases above pressure in the arteries, pushes semi lunar valves open
ventricular diastole - pressure in ventricle drops, semi lunar valves shut
blood flows into atria and ventricles fill passively
order of the ECG wave
P wave
QRS complex
t wave
what is the p wave
when the atria contracts (is depolarised)
qrs complex
spread of electrical signal causing depolarisation and contraction of the ventricles
atria are relaxing but this is masked
t wave
ventricular repolarisation and relaxation
QT interval
time from initiation of ventricular contraction to the end of ventricular relaxation
explain isometric ventricular contraction
marked increase in pressure without increase inn volume
when AV valves shut means blood cant leave the ventricles but the ventricle muscle contracts and places pressure on the blood within the chambers
