Cardiac cycle

  • Created by: Hindleyc
  • Created on: 03-06-18 16:40
What is the cardiac cycle?
Rythmic sequence of events resulting in each beat of heart- at rest average 72 bpm and one cardiac cycle=0.83 s
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What is diastole?
Relaxation of atria and ventricles, atria fill with blood from veins and semilunar valves close (dub), blood starts to move into ventricles
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What is atrial systole?
Atria contract increasing pressure and pushing blood into ventricles passing through atrioventricular valves and ventricles remain relaxed
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What is ventricular systole?
Ventricles contract and atria relax- higher pressure in ventricles than atria so atrioventricular valve closes-(lub). semi lunar valves open and blood flows into arteries
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Diastole-atrial systole-ventricular systole
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where is the heart beat initiated?
from within the heart muscle
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What is myogenic?
heart muscle- self exciting, can contract on its own without needing nerve impulses
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What does it maintain?
continuous inherent rhythm through electrical excitation
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What does this lead to?
contraction of heart muscle- myogenic stimulation
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What coordinate this sequence of events?
Modified cardiac muscle cells- conduct excitation through walls of heart
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What is the SAN- Sino atrial node
Small group of specialised cells in wall of right atrium near opening of superior vena cava
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what is it referred to as? why?
The pace maker as initiates the heart beat
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what does electrical excitation pass across and what does this cause?
Both atria causing them to contract
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What is the AVN- atrioventricular node
Small group of specialised cells between the 2 atria
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what does it do? what does this allow?
When electrical activity reaches the AVN it delays the passage of excitation down the septum . Enables atria to empty and ventricles to fill before the ventricles contract then passes electrical excitation down the septum
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What is the bundle of his?
Specialised non-contractile cardiac muscles fibres (purkinje fibres) that lead down the inter ventricular septum to apex- electrical excitation passes down this and radiate upwards from apex around the ventricle walls- excitation passes up thru these
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What does this allow?
Ventricle to contract from apex upwards allowing efficient squeeze
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How does blood always flow?
from a high pressure to a lower pressure unless prevented by valves
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Where does the graph start
start at atrial systole- point where atrial pressure rises above 0kPa
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When does ventricular systole occur?
When pressure in ventricles exceeds pressure in atria- a.v valve closes
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When does the blood flow into arteries?
when pressure in ventricles exceeds pressure in arteries- semilunar valve opens
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When does diastole occur?
When pressure in ventricles drops below pressure in arteries- semi lunar valve closes
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How is pressure in arteries maintained relatively high?
Due to elastic recoil of artery walls
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When do the atrioventricular valves open?
When pressure in ventricles drops below pressure in atria- rises back to 0kpa as they fill with blood
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Whats an ECG?
Electrodes placed on skin and changes in voltage displayed on oscilloscope
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Records heart sounds caused by valves closing
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What is cardiac output?
Volume of blood pumped by one ventricle of the heart in one minute- heart rate x stroke volume measured in dm3/min
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What are the 3 layers surrounding a central blood carrying canal (the lumen)?
Outerlayer-collagen tough, smooth muscle possibly. Middlelayer- mainly smooth muscle and layers of elastic tissue. Inner lining- endothelium(flattened epithelial cells) present in all blood cells and sits on basement membrane
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What are arteries?
Carry blood away from heart at high pressure with thick muscle to maintain high blood pressure- elastic to even out pressure and endothelium v smooth to reduce resistance
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What are arterioles?
less than 0.3mm thick- small arteries with less elastic tissue and middle layer mostly smooth muscle- contract to reduce blood flow by narrowing lumen and dilates to increase blood flow by enlarging lumen
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What are veins?
Carry blood back to heart- small veins=venules. little elastic and muscle wider lumen and relatively low pressure. contraction of skeletal muscle squeezes veins enabling movement of blood.
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What else do they contain contain
valves- delicate projections of endothelium mainly in limbs and ensure blood flow towards heart against gravity
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Other cards in this set

Card 2


What is diastole?


Relaxation of atria and ventricles, atria fill with blood from veins and semilunar valves close (dub), blood starts to move into ventricles

Card 3


What is atrial systole?


Preview of the front of card 3

Card 4


What is ventricular systole?


Preview of the front of card 4

Card 5




Preview of the front of card 5
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