Cardiovascular physiology Flashcards
What is the flow of blood in the body
- From the body to the Vena cava
- Vena cava to the right atrium
- RA to the the RV
- RV to the pulmonary artery
- Pulmonary artery to the lungs
- Lungs to the pulmonary veins
- To the left atrium
- To the left ventricle
- to the aorta
- To the body
Meaning of diastole
Relaxation of the muscle
Meaning of systole
Contraction of the muscle
What is the flow of blood directly proportional to
Change in pressure. So the more blood that flows through a vessel, the higher the pressure.
What is stroke volume
The volume of blood that is pumped by one ventricle
What is cardiac output
Cardiac output is the volume of blood pumped in a minute per ventricle
What is Venus return
The volume of blood returning back to the heart
It should = cardiac output
How do action potentials cause ventricular/ atrial contractions
- AP from adjacent cell causes volume gated CA2+ channels to open
- ca2+ enters
- this causes the sarcoplasmic reticulum to release ca 2+
- the ca2+ binds so troponin causing contraction
- the ca2+ unbinds causing relaxation
- ca2+ is pumped back into the sarcoplasmic reticulum
- ca2+ is exchanged for na+
- na+ concentration is maintained by na+/k+ ATPase
What is the intercalated disk
It’s a disk that holds together numerous cardiomyocytes (singular building block of cardiac muscle) and causes synchronised contractions
In what type of muscle cells are intercalated disks found
Only cardiac muscles
What is the flow of electrical current in the heart
- sinoatrial node
- atrioventricular node
- bundle of his
- purkinje fibres
What is an ECG
Electrocardiography, electrodes are placed on the skin and measure the voltage produced by the heart against time
How is the cardiac output calculated
Stroke volume x heart rate
What determines the heart rate
The rate of depolarisation of autorhythmic cells
What slows down the heart rate
The parasympathetic nervous system
What increases the heart rate
The sympathetic nervous system
What determines the stroke volume
The strength of the contraction of the ventricular myocardium (muscles)
What influenced the strength of ventricular muscle contraction
- Length/ tension relationship, ( if the muscles can reach a a length where it can produce its highest contractile force)
- Contractility, changes in stroke volume without there being a change in the resting ventricular muscle length
What are chronotropic effects
Effects that change the heart rate
What transmitter causes a sympathetic effect on the body
Noradrenaline
What transmitter has a parasympathetic effect on the body
Acetylcholine
What happens when a sympathetic transmitter is released
- Noradrenaline binds to the b1 noradrenaline receptor on the SA node and the myocyte membranes
-this causes the opening of HCN (hydrogen cyanide) channels in the SA node which increases the influx of NA+ - this then causes the ca2+ channels to open and so more ca2+ enters
This results in more depolarisation and so the heart rate increase
What happens when the parasympathetic transmittter is released
- Acetylcholine is released and binds to cholinergic receptors
- this reduces the amount of NA+ entering the cell
- decreasing the amount of ca2+ Chanel’s opening so less ca2+ entering
- this opens more k+ ligand gated Chanel’s so more k+
Thus the heart rate slows down as less myocardial contraction
What is vagal tone
A measure of the parasympathetic input into the heart rate.
The vagus is involved in the parasympathetic autonomic nervous system that reduces heart rate
What is the sequences of the cardiac cycle
1)ventricular diastole
2) atriall systole
3) isovolumic ventricular contraction, when the ventricular pressure rises above atrial pressure and the mitral (2) valve closes
4) ventricular systole, the ventricle contracts
5) isovolumetric ventricular relaxation, when the pressure in the aorta is higher than in the left ventricle so it causes at aortic valve to close
What is preload
The degree of stretch/ the length of the ventricular muscles before contracting at the end of ventricular filling
What is ejection fraction
a fraction of the amount of blood pumped out/ the totoal amount of blood in the heart
What is cardiac workload
How hard the heart must pump to supply blood to the places that need it
What is starlings law of the heart
The force of contraction is directly proportional to the length of ventricle muscle during diastole
What a re the three stages of starlings law
- Almost empty chamber, the amount of blood doesn’t cause enough stretch so the myosin actin overlap isn’t optimal and cannot produce a lot of force
- full ventricle, the vol. of blood causes the ventricular muscles to stretch optimally and so the actin/myosin overlap is optimal, there is also a high troponin c affinity to ca2+ and so maximal force can be produced.
What are the two types of cardiac workload mechanisms
Extrinsic, factors affect the the stroke volume of the heart e.g. sympathetic nervous system causes the SV to increase without a change in the ventricular stretch/ length
Intrinsic, the level of stretch will determine how the SV of the heart and that is set
What is extrinsic mechanism of cardiac workload
The sympathetic input into he cardiac cycle causes the stroke volume to increase without increasing the initial fibre length, an increase in Contractility.
Catecholamines (hormones made in the adrenal cortex) are responsible for this and cause harder but shorter contractions
What controls the mean arterial pressure
The cardiac output and the the resistance of the arteries (caused by the diameter of the arteries)
MAP = CO x TPR
Total peripheral resistance
What are the 4 ways in which the cardiac output can be effected
- parasympathetic neurons, synapses on the SA and AV node cause the heart rate to drop thus causing the CO to drop
- sympatheitc neurons, synapses on the SA node cause the heart rate to increase thus causing the CO to increase
- sympatheitc neurons, synapses on the arteries cause the them to vasoconstric increasing peripheral resistance and so the MAP increases
- sympatheitc neurons, synapses on the arteries cause the them to venoconstric pushing venous blood into the arteries.
