Control of CV System and Cardiac Cycle Flashcards
What are the functions of the nervous system?
- Transport of nutrients, oxygen, waste products around the body
- Transfer of heat
- Buffers body pH
- Transport of hormones
- Assists in response to infection
- Assists in formation of urine filtration and circulation
What sounds should we hear when listening to the heart?
- 2 sounds:
- One; sound of AV valves closing
- Two; sound of pulmonary valve and aortic valves closing
What can heart sounds be used for?
Good diagnostic indicator of problems
What should heart sounds not be confused with?
Korotkoff sounds; what you hear when measuring blood pressure using a stethoscope
Clinically, what may a 3rd heart sound may be down to?
Oscillation of blood flow into ventricle
Tensing of chordae tendinae
Various disease states (HF, valve defects etc.)
What is the sequence of the cardiac cycle?
- Artrial systole begins: atrial contraction forces blood into ventricles.
- Ventricular Systole: ventricular contraction pushes AV valves closed, semilunar valves open and blood is pushed out of heart.
- Caridac diastole: semilunar valves close. Blood chambers of the heart relax and fill with blood once more, continuing the cycle.
Are ventricles fully emptied during the cardiac cycle?
No, some EDV remains
What is the stroke volume and can this be increased?
Stroke volume = amount ejected per beat
Can be increased under certain circumstances (Starling’s Law)
What is the standard cardiac output and how can it be calculated?
Cardiac output (CO) = SV x HR Normally around 5L/min (each side)
How is a contraction of the heart started?
The sinoatrial node (SA node) in the top of the right atrium sets the rate at which the heart contracts.
It sends out electrical impulses to do this.
At the start it causes atrial systole.
What is the pathway of the electrical impulse produced by the SA node?
The impulse then passes to the atrioventricular node (AV) in the lower part of the right atrium.
It then progresses past the bundle of HIS and septum.
It is then passed to the purkinje fibres which travel down the central wall of the heart and the impulse splits left and right, up to the ventricles (causing them to contract simultaneously). (Ventricular Systole)
What must conduction of heart beat be?
Rapid and co-ordinated
What are the pacemaker cells of the heart and their roles?
SA node = has the fastest intrinsic rate, so is hearts natural pacemaker.
AV node = slows conductions and can act as a secondary pacemaker if required.
Millions of purkinje fibres = interdiditate with myocytes to spread impulse across ventricles - excitation contraction (EC) coupling.
What are some clinical problems that may arise from problems with conduction of impulses in heart?
- Arrythmias, ectopic beats, tachycardia, bradycardia, fibrillation ; problems with conduction of impulses across heart lead to abberant heartbeat often the result of ischaemic damage to the tissue.
- Bundle branch block (BBB)
- Heart block (1’, 2’, 3’)
What does an ECG do?
Detects phasic change in potential difference between 2 electrodes: -on surface of heart
- on limbs
- recorded on a computer/ paper/ oscilloscope
What is an ECG used for?
Useful in diagnosis of arrythmias, post NI damage, congenital/iotrogenic abnormalities.
What parts make up a typical ECG?
- P wave = atrial depolarization
- QRS complex = ventricular depolarization
- T wave = ventricular repolarization
- P-R interval = delay through AV node
- S-T interval = plateau phase of AP
What causes SA nodal AP?
Once a threshold has been released, Ca2+ channels open (Phase 0) and depolarise.
Eventually repolarisation occurs (Phase 3) as K+ is pushed out.
The threshold is reached as after repolarization overshoots, Ca2+ is coming in to get it back to normal value and there is reduced K+ going out, slowly making us reach the threshold (Phase 4).
What will happen to the AP if K+ permeability increases?
It will take a longer time to reach the threshold = fewer BPM.
So the heart rate would decrease.
This action would be acheived by acetylcholine from vagal nerve, parasympathetic.
What happens to AP and BPM if Ca2+ permeability increases?
Shorter time to threshold = more BPM so HR increases.
This action would be acheived by noradrenaline, sympathetic.
What causes purkinje fibres AP?
-Phase 0 - caused by Na+ in
Initial repolarisation by K+ moving out.
Phase 2 - Ca2+ in
Plateau due to inward Ca2+ and outward K+ movement.
This is plateau phase of ST segment on ECG.
This is so tissue stays refractory longer.
Phase 3 - K+ out
Get down to resting membrane potential
What happens in cardiac muscle to make it contract?
- Calcium entry into cardiac muscle cells triggers contraction
- Comes from exterior of myocyte, sarcoplasmic reticulum
- Calcium induced calcium releases; allows a greater contraction for a small calcium movement, like an amplifier
Clinically, what do some drugs used in heart failure do?
Increase intracellular calcium and/or increase myofilament sensitivity- increases contraction and output from the failing heart.
How is cardiac output modulated?
Either by adjusting heart rate or stroke volume.
By autonomic nervous system.
Changes in CO detected by barroreceptors and fed back to CVS control centre in brain.
What adrenoreceptors are found on the heart?
Predominantly B1 on nodal tissue, conducting system and myocardium.
What are the effects of noradrenaline released by sympathetic nerves on the heart?
- Positive inotropy
- Positive lusotropy
- Positive chronotropy
- Positive dromotropy
What is a clinical use of adrenoreceptors for the heart?
Beta agonists used as short term support in cardiogenic shock, arrest etc.
Where is the vagal nerve in the heart?
Terminates on the nodal tissue:
- Right vagus; SA node
- Left vagus; AV node
What is the effect of Ach on the heart?
Activates M2 receptors which reduces HR (increased K+ permeability).
Clinically, what drugs can be used to increase heart rate?
Vagolytic drugs (atropine) can be used to increase heart rate in bradycardiac patients.
