The Cardiac Cycle and Control of Cardiac Output Flashcards
What are the functions of the CVS?
- Transport nutrients, oxygen, waste products around the body
- Transfer of heat
- Buffers body pH
- Transport of hormones e.g. adrenaline
- Assists in response to infection (WBC fight off infection - these travel through the blood)
- Assists in formation of urine - filtration and circulation
Why does the left ventricle have a thicker cell wall than the right ventricle?
- As it is under higher pressure: I order for L ventricle to pass blood through valve needs a lot of energy
- Right ventricle doesn’t need to create as much pressure as left ventricle to eject blood through valve
- Left ventricle also has to pump blood all around the body whereas right ventricle only has to pump blood to the lungs
Where do AV valves separate the blood?
- Separate blood in atria and ventricles
What is the role of chordae tendineae and papillary muscles?
- They orientate the valve flaps - no role in valve opening
- Chordae tendineae play a vital role in holding the atrioventricular valves in place while the heart is pumping blood
Where do semilunar valves control the blood movement from and to?
From ventricles to exit arteries
What is the opening and closing of a valve determined by?
The pressure gradient across the valve
What can septal defects of the heart lead to?
- Reduced efficiency
- Long-term structural changes
What can calcification of valves lead to?
- LV hypertrophy
- Heart failure
What does the first sound of the heart indicate?
Sound of the AV valves closing
What does the second sound of the heart indicate?
Sound of pulmonary and aortic valves closing (semilunar valves)
Why are the sounds of the heart a good diagnostic indicator of problems?
- If hear a third sound can mean there is a 2 way movement of blood
- Third heart sound may be heard due to oscillation of blood flow into the ventricle, tensing of chordae tendineae or various diseased states (HF, valve defects etc)
What are Korotkoff sounds?
- When cuff is inflated above maximum systolic pressure - hear nothing
- When you lower pressure a bit some blood starts to flow and you hear a sound - this is the Korotkoff sounds
What is the process of the cardiac cycle?
- Consists of systole (contraction) and diastole (relaxation) of the atria and the ventricles
What is blood flow controlled by?
- The valves and the sequence of diastole and systole - if this process goes wrong can cause problems with cardiac output
- Blood flows from an area of higher pressure to one of lower pressure
Where in the heart is the blood at its lowest pressure?
When blood gets back to the right atria
Are ventricles completely emptied during systole?
No, some of the end diastolic volume remains
What is the amount of blood ejected per beat of the heart called?
Stroke volume
Stroke volume can be increased under certain circumstances. What are these?
Starlings Law - If you increase end diastolic pressure up to a certain point it will respond to contacting more strongly so SV will go up
What is the cardiac output?
CO = SV x HR
normally about 5L/min - each side
What is the conducting system of the heart?
- Impulses generated within the SA node spread over the atria followed by the ventricles
- Atria and ventricles on the left and right sides of the heart contract at the same time
- Conduction has to be very rapid and coordinated
- Results in a rise and fall of blood pressure in the atria and ventricles
- Heart has to be able to adapt to be able to work when heart rate is increased
What is the natural pacemaker of the heart?
- SA node has the fastest intrinsic rate so determines heart rate
- AV node slows conduction and can act as a secondary pacemaker if required
- Millions of Purkinje fibres interdigitate with myocytes to spread impulses across ventricles - excitation contraction coupling
What are Purkinje fibres?
Special fibres that are located in the AV bundle of the heart. Their function is to send nerve impulses to the cells in the ventricles of the heart and cause them to contract and pump blood either to the lungs or the rest of the body
What is an arrhythmia and what ae examples of them?
- Problems with conduction of impulses across the heart which lead to aberrant heartbeat - often the result of ischaemic damage to the tissue
- Examples: ectopic beats, tachycardia, bradycardia, fibrillation (AF/VF)
What is a bundle branch block?
- A disruption in the normal flow of electrical pulses that drive the heart beat
What does an electrocardiogram detect and what is it useful in the diagnosis of?
- Detects phasic change in potential difference between two electrodes:
- On surface of heart
- On limbs - body is volume conductor
- Recorded on oscilloscope/computer/paper
- Useful in diagnosis of arrhythmias, post-MI damage, congenital/iatrogenic abnormalities
What does the P-wave in an ECG show?
Atrial depolarisation (atrial contraction)
What does the QRS complex in an ECG show?
Ventricular depolarisation (Ventricular contraction)
What does the T wave in an ECG show?
Ventricular repolarisation
What does the P-R interval in an ECG show?
Delay through AV node (measure of time from the onset of atrial contraction to the onset of ventricular contraction)
What does the S-T interval in an ECG show?
Plateau phase of AP
What is sinus bradycardia?
Slow heart rate
What is 2 block ECG result?
Occasionally missing a heartbeat
What is phase 4 in the SA nodal action potential?
- Ca2+ in and reduces K+ out
- Rate of depolarisation increases
- Number of action potentials sent off by SA node per minute is your heart rate
- Activated by vagus and sympathetic nerves
What is phase 0 in SA nodal action potential?
- Influx of calcium
- Once threshold is reached there is a rapid influx of calcium ions which causes depolarisation
What is phase 3 in SA nodal action potential?
- Outward movement of potassium - which lowers it below threshold
- Once below threshold potassium channels close
How does the action of Ach from the vagal nerve affect the SA nodal action potential?
- If K+ permeability increases, longer time to threshold = fewer BPM so HR is decreased (keeps the heart rate artificially low)
How does the action of noradrenaline affect the SA nodal action potential?
- If CA2+ permeability increases, shorter time to threshold = more BPM so HR is increased
What is the process of Purkinje action potential?
- More like what yo would see in a normal nerve
- Phase 0 - sodium moving in (sodium currents are voltage sensitive so as membrane starts to depolarise the channels start to deactivate) then (potassium channels open and efflux out of cell)
- Phase 2 - Calcium channels open and move into cell
- Plateau phase - little change in the membrane potential as potassium moving out and calcium moving in so balancing of outward and inward moving charges (importance = keeps tissue refractory - can be reactivated but gives period of time where it cannot be activated)
Phase 3&4 - Potassium continues to efflux out of cell and brings action down towards base line membrane potential at stage 4
What does calcium entry into cardiac muscle cells trigger?
Contraction
What is sarcoplasmic reticulum?
A system of membrane-bound tubules that surrounds muscle fibrils, releasing calcium ions during contraction and absorbing them during relaxation
- ‘calcium induced calcium release’
- Allows a greater contraction for a small movement - like an amplifies
What do some drugs used in heart failure increase?
- Intracellular calcium and/or increase myofilament sensitivity - increases contraction and output from the failing heart
What are the process of removing calcium are crucial in allowing what?
Allowing the hear to relax
How does our body modulate cardiac output?
- Either by adjusting HR or SV
What is starlings law?
Ernest starling observed in cardiac muscle that the force of contraction increased as the muscle was stretched in response to increased filling of the heart’s chambers. It is essential that heart muscle responds in this way to stretching, otherwise circulation of the blood would fail. This became known as starlings law and is fundamental to understanding the hearts function
What are the 2 main forms of adrenoreceptors?
Alpha and Beta forms with subtypes of each
What is the predominant type of adrenoreceptor sound in nodal tissue, conducting system and myocardium?
Beta-1 adrenoreceptors
What binds to adrenoreceptors?
NorA released by sympathetic nerves but also circulating adrenaline
What are the effects of adrenoreceptors?
- Positive inotropy
- Positive chronotropy
- Positive lusitropy
- Positive dromotropy
What is positive inotropy?
Increasing force of contraction
What is positive chronotropy?
Increasing heart rate
What is positive lusitropy?
Increasing rate of relaxation
What is positive dromotropy?
Increased speed of conduction
What are beta agonists used for?
Short-term support in cardiogenic shock, arrest etc
Isoprenaline (beta-1 and bets-2 agonist) used to be used to treat asthma. Is this a good idea?
No, affects the heart, don’t want to speed up rate of contraction
Where does the vagus nerve terminate in the CVS?
On the nodal tissue
- Right vagus = SA node
- Left vagus = AV node
Which receptors does the release of Ach activate and what does this do?
Activates M2 receptors which reduces HR - increased K+ permeability
How do both branches of the ANS affect CO?
By altering HR and SV
As well as affecting HR and SV, what else does the sympathetic nervous system affect in the CVS?
Blood vessels - so effects on blood pressure can be complex
What are changes in CO detected by?
Baroreceptors and information on blood pressure is fed back to the CVS control centre in the brain
What type of control allows BP to be modulated during sleep and by emotions such as rage etc?
The CNS
