the circulatory system and cardiac cycle Flashcards
(22 cards)
what is a mammal’s circulatory system an example of?
mass flow- there is bulk movement of substances down a pressure gradient.
why is mass flow needed in a mammal?
diffusion alone would be too slow to supply the cells with enough oxygen to maintain the chemical reactions of the cell
what kind of system is the mammalian circulatory system?
a closed, double circulatory system
how is the circulatory system closed?
the transport medium (the blood) is contained within a network of blood vessels
this means high pressure and rapid rate of flow can be maintained
what is the circulation to the lungs called?
pulmonary circulation
here deoxygenated blood is delivered to the lungs where gas exchange takes place to make the blood oxygenated
what is the second circulation to the rest of the body called?
systematic circulation
here oxygenated blood is delivered to the body cells and deoxygenated blood is moved away
why is a separate circulation to the lungs required?
because a lower pressure is required in the lungs to prevent accumulation of fluid in the alveoli and to allow gas exchange to occur in narrow capillaries
if there was just one circulation then the pressure drop required in the lungs would mean that there was not great enough pressure to then move oxygenated blood around body
what is the order of the cardiac cycle?
diastole
atrial systole
ventricular systole
what does systole and diastole mean?
systole- contraction
diastole- relaxation
describe what happens in diastole?
heart muscle is relaxed
blood returning to the heart via the veins flows into the atria
the atria-ventricular valves are open so blood flows into the ventricles too
which node generates electrical impulses during atrial systole and where do these spread to?
syno-atrial node (SAN) generates electrical impulses which spread through the walls of the atria
the impulses cannot reach the ventricles due to a fibrous layer of tissue between the atria and ventricles, stopping both atria and ventricles contracting at the same time
what do the electrical impulses released during atrial systole cause?
muscles of atria walls to contract
this decreases the volume and so increases pressure
blood is forced from atria into ventricles through open atria-ventricular valves, filling ventricles completely
which node releases nerve impulses in ventricular systole and where do these travel?
atria-ventricular node (AVN) releases electrical impulses that are conducted to the bottom of the ventricles by the Bundle of His
they are then spread through the ventricular walls along the purkinje fibres
what do the electrical impulses released during ventricular systole cause?
muscle of ventricle walls to contract from the bottom upwards
volume of ventricles decreases, so pressure increases
atria-ventricular valve closes to prevent backflow to atria and semi-lunar valves open to allow blood to enter the arteries
what happens after ventricular systole?
ventricles relax,
semi lunar valve closes to prevent backflow of blood from arteries to atria, and atria-ventricular valves open again
heart is now fully relaxed (in diastole) and the cycle begins again
when do atria-ventricular valves open and close?
open when pressure in atria is higher than in ventricles
closed when pressure in atria is lower than in ventricles
when do semi-lunar valves open and close?
open when the pressure in the ventricles is higher than in arteries
closed when the pressure in ventricles is lower than in arteries
what is the cause of the LUB- DUB sounds of the heart beat?
LUB is atria ventricular valve closing
DUB is semi-lunar valve closing
what is cardiac output?
the volume of blood pumped by one ventricle of the heart in one minute
what is the equation for cardiac output?
heart rate x stroke volume (volume of blood pumped out at each beat)
what is an ECG and what does it do?
electrocardiogram
measures electrical activity of the heart
on a cardiac cycle graph, how do we know when valves are opening/closing?
cross over points
