Cardiovascular physiology Flashcards
Functions of the CVS
A transport system: gases, nutrients, hormones, water and electrolytes, cells and proteins, heat, waste products
3 components of CVS
a pump (or two in parallel), a series of tubes, specialized fluid
Tow separate circuits of CVS
Pulmonary circulation in series with the systematic circulation. Systematic circulation (organs in parallel)
Blood flow
Systematic circulation to right atrium via systematic veins. Right atrium to right ventricle to lungs via pulmonary artery. Returns to left atrium via pulmonary veins. Left atrium to left ventricle to tissues via systematic arteries.
Cardiac muscle
strong and elastic - withstand stretch when full, and continuous contraction and relaxation. When the heart contracts, the chambers are compressed and reduce in size (volume) ejecting blood
Myocardium
contains interlaced bundles of muscle fibers arranged spirally around circumference. Thickness of myocardium is related to amount of force needed to pump blood - therefore left ventricle thicker than right
Gap junctions
allow ion flow, so action potentials are transferred from cell to cell. Allows synchronized contraction of whole muscle mass. When one cardiac cell undergoes an AP, the impulse spreads to all cells joined by gap junctions. This is referred to as functional syncytium.
Pacemaker cells
Do not have a stable resting membrane potential (RMP). slowly and spontaneously depolarize until threshold is reached. Trigger APs. Cyclically initiate APs which spread throughout the heart.
Steps in cardiac depolarization and contraction
- Atrial contraction - depolarization starts at the SA node
- Transmission between the atria and ventricles is via the AV node causes a delay
- Ventricular contraction occurs due to Bundle of His (AV bundle) and the Purkinje fibers.
- Coordinates spread of excitation to ensure contraction as a unit, ejecting blood into the two circulations simultaneously (pulmonary and aortic)
Electrocardiogram
Using electrodes to measure the flow of electrical activity (APs) passing over the heart and visualize on a graph. ECG measures an electric ‘dipole’.
Cardiac cycle
alternate periods of systole and diastole.
Atrial systole
SA node fires/depolarizes -> impulse spreads through atria = P wave on ECG. Atria contracts - blood is pushed into the ventricle from the atria
Ventricular systole
Impulse slows as it passes through AV node, then reaches ventricle = QRS wave. Ventricular contraction starts immediately after the Q wave. Ventricular pressure increases quickly. As pressure in ventricle increases, AV valves close.
End diastolic volume
Ventricular diastole ends at onset of ventricular contraction. Volume of blood in ventricle at end of diastole is the EDV - contraction commences without changing ventricular volume.
Isovolumetric ventricular contraction
All valves closed -> no change in volume. Ventricular pressure rises rapidly. Muscles contract increasing pressure but no change in volume. Finishes when ventricular pressure exceeds aortic pressure, so aortic/pulmonary valve opens and blood leaves heart.
Ventricular ejection
Increase in pressure opens aortic and pulmonic valves. Aortic pressure rises then declines as ventricular volume decreases.
End systolic volume
Ventricle doesn’t completely empty. Left over blood in ventricle is ESV.
Stroke volume
amount of blood pumped out of each ventricle
SV =
EDV - ESV
Ef (ejection fraction) =
SV/EDV
Isovolumetric ventricular relaxation
Ventricular repolarization after ventricular systole (T wave). Ventricular P drops below arterial P, so aortic and pulmonic valves close. Volume is constant.
Ventricular filling
Ventricular P drops < atrial P so AV valve opens, ventricles start filling.
Ventricular diastole
Isovolumetric ventricular relaxation and ventricular filling
Ventricular systole
Isovolumetric contraction and ventricular ejection
