Heart as a pump Flashcards
Design of the mammalian cardiovascular system
Four chambered heart, blood flows in one direction, arterial blood flows away from the heart, venous blood flows towards the heart, pumps lie in series, equal flow through the two circuits
Right and left pumps contract simultaneously - at the same time. Atria contract before ventricles
Process of relaxation and contraction in the heart
In relaxation the inlet valves are open but the exit valves are closed (for forward flow), when contraction occurs the atria will contract first and blood will flow from atria to the ventricle (maximum amount of blood in ventricle), as the stimulus passes through the heart the ventricles will contract as the atria relax, causing AV valves to shut and open exit valves allowing us to deliver a pulse of blood around the body, then relaxation occurs
How does blood move through the heart?
AV valves control flow between atria and ventricles. Aortic and pulmonary valves control flow form ventricles out to circulatory vessels (exit valves), will open and close when pressure difference is right. Valves open and close to direct blood
Process of cardiac contraction
Ca is the trigger in cardiac muscle for contraction (T-tubules) and more Ca is released from sarcoplasmic reticulum causing contraction (muscle activated) facilitating binding of actin and myosin, myosin reduces overlap and sarcomere size. Every fibre is activated every time - unusual and involuntary in comparison to skeletal muscle which uses recruitment and is under voluntary control
How can we increase the force of cardiac contraction?
To increase force of cardiac contraction we release more calcium resulting in more cross bridges forming and force of contraction increases; instead of recruiting more fibres, we use all but can control how much strength each contraction varies by. Vary force by varying calcium
How does cardiac relaxation occur?
To relax we need to decrease cytosolic Ca levels which requires energy. Cross bridges release when this energy (ATP) binds to myosin and reduction in force means heart can relax. All cardiac myocytes relax each beat
What does diastole and systole mean?
Diastole occurs when there is relaxation and falling pressure (diastole = dying down)
Systole occurs when there is contraction and rising pressure (systole = squeeze and squirt)
Doesn’t happen at a set time, all different
Main stages of cardiac cycle
Cycle starts just before a beat begins, the atria contract first (atrial systole) and then following on from arterial systole the ventricles contract and then relax
No overlap between atrial and ventricular contraction
How does the Lubb sound occur in a heart beat (first phases of cardiac cycle)?
Atrial systole - atria contract push blood in ventricles and ventricles begin to contract. Once ventricle pressure higher than atria the AV valve closes (the first heart sound you hear when listening to heart beat). In isovolumetric ventricular contraction the volume hasn’t changed, the ventricles are contracting, AV valves closed and exit valves closed
How does the dupp sound occur in a heart beat (last phases of cardiac cycle)?
When the pressure in ventricle is enough the exit valves open and ventricular ejection occurs (blood ejects into aorta), pulse felt is ventricular ejection. In isovolumetric ventricular relaxation pressure drops in ventricle and the valve will close hence the second noise is heard and the atriums begin to become filled passively again
What is are the features of a blood pressure trace?
Pulsatile change in pressure in major arteries linked to ejection of blood. Periods of systole (rising pressure) and diastole (falling pressure). Diastole phase is longer than systole phase (60% diastole compared to 40% systole). Systemic pressure is much higher than pulmonary as it needs to be sent to further away places with more force to reach
What are the four main features on a blood pressure trace graph?
High number : systolic
Low number : diastolic
Difference : pulse pressure
Mean : average of FULL cycle weighed down by diastole as we spend most of our time in this phase hence lots of time in low pressure
What does hypertension and hypotension mean?
Hypertension = high blood pressure
Hypotension= low blood pressure
