T7: Cardiac muscle and the heart beat Flashcards
How is cardiac output calculated
Stroke volume x Heart rate
what is VO2
Volume of oxygen consumed per minute
define aerobic capacity
the ability to transport and use oxygen
define cardiac output
total volume of blood ejected from the left ventricle (dm3/min)
define stroke volume
volume of blood ejected from the elft ventricle per beat
where is the SAN
upper wall of right atrium
where is the AVN
right atrium
Explain what happens for atrial systole to occur
SAN depolarises, sending an electrical impulse across the top half of the heart
This causes the atria to contract
The action potential arrives at the AVN but the AVN is surrounded by insulating cells which causes a delay before the AVN is depolarised. This allpws all blood from the atria to be discharged
Explain what happens for ventricular systole to occur
AVN depolarises and the action potential travels along the bundles of His towards the apex of the heart
The impulse then travels upthrough the Purkinje fibres- causing ventricular contraction from bottom to top
Why does no contraction occur when the action potential travels down through the bundles of His
They are insulated
Explain what happens for diastole to occur
All parts of the heart relaz and repolarisation occurs
Atrioventricular valves open
Name the parts of an ECG
P wave
PR segment
QRS complex
ST segment
T wave
What does the p wave represent
SAN depolarising (atrial systole)
What does the PR segment represent
blood being discharged from atria
What does the QRS complex represent
AVN depolarising (Ventricular systole)
What does the ST segment represent
Ventricles fully discharging
What does the t wave represrnt
repolarisation of the heart in diastole
What part of the brain is the cardiovascular centre located in
Medulla
Name the two nerves connecting the cardiovascular centre to the SAN
Parasympathetic nerve inhibitor
Symapthetic nerve accelerator
Explain the role of chemoreceptors in determining heart rate
Chemoreceptors detect carbonic acid in the blood which is produced when CO2 dissolves - changes in pH are detected
Name other factors the cardiovascular centre detects in its determination of HR
Pressure receptors
Temperature receptors
Stretch receptors
Explain how hormones are involved in the control of heart rate
Adrenaline is secreted into the blood by the adrenal glands
- it increases SAN electrical activity
- it dilates the arterioles in the muscles
- it constricts the arterioles in the digestive system
Exam questions on ECG and heart conditions
