Physiology Flashcards
What are is the conduction system of the heart made up of?
specialised cardiac muscle fibres
Describe the flow of electrical signals
- The SA node spontaneously discharges an electrical impulse that triggers a wave of depolarisation down the heart
- Signals flow through internodal fibres from SA to AV node. The depolarisation contracts both atria.
- From the AV nodes, signals travel to the bundle of His, which then splits into the right and left bundles and into purkinje fibres
- Depolarisation of the ventricle muscle fibres results in the ventricle to contract.
What is the hierarchy of pacemakers
the pacemaker with the fastest rate of depolarisation sets the rhythm of the heart.
How does the atria function as a priming pump?
The atria contracts before the ventricles so that the ventricles may be fully filled before they contract.
What is the purpose of the fibrous ring?
How to ensure that the atria contract first.
The fibrous ring, together with the delay at the AV node ensures the atria contract first, fill the ventricles with blood, followed by the contraction of the ventricles.
Activation of the sympathetic nervous system results in …
the heart beating faster and harder.
Activation of the parasympathetic nervous system …
reduces the heart rate but does not affect the strength of cardiac contractions
What are the Factors Affecting Heart Rate DIRECTLY Through the SA Node?
What are the Factors Affecting Heart Rate through the Vasomotor Centre and Autonomic Nervous System
Describe the respective neurotransmitters, receptors and ionic changes for the sympathetic and parasympathetic systems
What gradients are involved in establishing resting membrane potential
Concentration gradient and electrical gradient
What is phase 2
This is phase 2 of the action potential, called as “plateau” phase. At this point the calcium influx (movement of positively charged ions into the cell) and the efflux of potassium from the cell balance each another, hence the action potential is “flat” at this point. These are the calcium ions that are responsible for causing the muscle fibre to contract
What is phase 0
voltage-gated sodium channels on the membrane of the ventricular muscle opens. When that happens, sodium, present in much higher concentrations outside the cell than in, rushes into the cell. The cell now becomes positive due to the entry of sodium.
What is phase 3
After a certain period, calcium ion influx stops. When this happens, and potassium continues to leave the cell, the cell continues to become more negative. This is phase 3 of the action potential, and the cell soon returns to its original resting membrane potential of -85 mV, while awaiting the next wave of depolarisation.
what is phase 1
To begin with, the outward rectifying potassium channels open. This is the initial repolarization, or phase 1. When potassium channels open, both the concentration gradient (potassium higher on the inside) together with the electrical gradient (because the cell is depolarised) both combine to push potassium out. So, the cell loses positive charges, and the inside of the cell becomes more negative.
Why are both pressure and flow are further regulated by the vascular system (especially the arterioles)?
so that optimal perfusion pressure and flow occur at the tissues.
What are examples of uncoordinated electrical activity?
ventricular tachycardia, ventricular fibrillation, atrial fibrillation and heart blocks.
How many electrodes are placed on the chest and limbs for an ECG recording?
10
What are the attributes of standard limb leads
What are the attributes of augmented limb leads
What are the attributes of precorial/ chest leads?
Describe the P wave
The P wave is the result of atrial depolarisation.
Describe QRS complex
The QRS complex is ventricular depolarisation. The Q wave results from the vector created when electrical signals depolarise the bundle of His. The R and S waves result from the depolarisation of the ventricles.
Describe the T wave
The T wave is ventricular repolarisation.
Why cant we see atrial repolarisation in ECG?
Atrial repolarisation occurs during the QRS complex. The wave of atrial repolarisation is small and therefore masked by the higher voltage QRS complex, so we do not see it on the ECG.
Describe how electrical signals give rise to P wave
an electrical vector directed towards the positive electrode is designated positive. So, you will see a small magnitude, positive wave. This is the P wave.
Describe how electrical signals give rise to Q wave
Similarly, from the vantage point of lead II, you will see a small vector caused by the depolarisation of the bundle of His. This vector is going away from you, so it is negative. So, the ECG will record a small negative wave called the Q wave.
Describe how electrical signals give rise to R wave
As the wave of depolarisation travels down the septum and depolarises the ventricles, it creates a vector of higher magnitude that is coming towards lead II. This produces a positive R wave on the ECG.
Describe how electrical signals give rise to S wave
The late depolarisation of the ventricles produces a vector that is moving away from lead II and hence a negative S wave.
Describe how electrical signals give rise to T wave
Finally, ventricular repolarisation produces an electrical vector that is directed towards you, hence a positive T wave.
Each lead records the ___________ between 2 electrodes
Potential difference
Normal speed at which ECG run is …
25 mm/s
The RR interval is the time taken for …
1 cardiac cycle
The PR interval is the time taken for the signal to travel from …
SA node into the ventricle (that is, right until the time the signal emerges from the AV node).
What is used as a measure of the AV nodal delay time?
PR interval.
In the case of heart block, the PR interval is prolonged to more than _____.
0.2s
The QT interval is the time taken for …
ventricular depolarisation and repolarisation
What can cause prolongation of QT interval?
a mutation in the potassium channel, certain drugs
What does a tall QRS wave indicate
Tall QRS waves are related to ventricular depolarisation and may represent an increase in myocardial mass called hypertrophy.
What does a tall T wave indicate
Tall T waves may be caused by problems with ventricular repolarisation, hyperkalemia being an example.
What does elevated or depressed ST segment suggest?
An elevated or depressed ST segment may indicate a myocardial infarction or ischaemia, respectively.
How to diagnose angina pectoris using ECG
ST segment depressions can be seen while exercising
The unit of contraction of the heart is _____
sarcomeres
What causes sarcomeres to contract
Ca binding to troponin C
What type of troponin is indicative of cardiac muscle damage
Troponin I
_____ is the key determinant of the strength of cardiac contaction
Calcium
Is ventricular muscle relaxation an active/passive process
active
Describe the role of calcium in the contraction process
What are the 2 mechanisms that regulate the force of cardiac contractions
- Starling’s law
- contractility
What does Starling’s law state
Starling’s Law states that the more the heart is loaded with volume (increase stretch), the greater the strength of contraction (force), up to a limit.
What is contractility
strength of contraction for any given stretch
How is contractility affected?
Sympathetic nervous system
What is the formula of ejection volume?
what is the normal range ejection volume
55%-75%
What does low ejection volume mean
cardiac pump failure
The phase of the cardiac cycle that rapidly builds up of pressure is the …
isovolumetric contraction phase
The phase of the cardiac cycle that rapidly reduces pressure is the …
isovolumetric relaxation phase
Describe the pressure volume loop
What valves gives rise to the first heart sound?
Closure of MV at the start of isovolumetric contraction
What valves gives rise to the second heart sound?
Closure of the AV at the end of the ejection phase
How are the changes in pressure within the right atrium measured?
JVP
What are the 3rd and 4th heart sounds caused by?
They are resulted from vibrations from the flow of blood and may be abnormal
What does RT in the ECG suggest?
Ventricular systole
What is ejection fraction
the fraction of the end-diastolic volume that is pumped out with each stroke or contraction, expressed as a percentage.
How can ejection fractions be determined
non-invasively using cardiac echocardiography (estimated), or invasively by putting catheters into the heart (definitive).
What wave is atrial contraction?
A wave
What wave is atrial filling?
V wave
When is the splitting of the second heart sound heard?
Inspiratory cycle
What are the 2 components of the split in S2?
Aortic and pulmonary valve
Explain the physiological splitting of S2
What type of murmur is a stenosed mitral valve?
Diastolic murmur
Which blood vessel has high pressure but low resistance?
Arteries
What is the dual function of arterioles?
- Control pressure upstream (arterial circulation)
- Control blood flow downstream (capillary circulation)
Which law governs rate of blood flow (vol of blood per unit time)
Ohm’s law
Which law governs resistance of blood flow?
Poiseuille-Hagen formula
State ohm’s law
State Poiseuille-Hagen formula
what is cardiac output?
Volume of blood pumped by left ventricle into the aorta per minute
What is the formula for cardiac output?
SV x HR
What are the factors affecting cardiac output
What can cause decrease in preload?
Hemorrhage
What can affect the heart which in turn affects cardiac output?
Myocardial infarction, Bradycardia
What can affect afterload?
Hypertension
What is the acute phase of heart failure
What is the long-term phase of heart failure
What is the clinical presentation of acute phase of heart failure?
- Increase Heart rate
- Increase strength of cardiac contractions
- Sweating
What is the clinical presentation of long-term phase of heart failure?
- Oliguria (less urine)
- Edema
- Remodelling heart and blood vessels
How can fluid in the kidneys become maladaptive
How is chronically activated levels of Ang II becomes maladaptive
What is used as treatment for renin angiotensin aldosterone system activation
Diuretics and ACE inhibitors
What are 2 types of heart failure
Activation of sympathetic nervous system in heart failure results in …
- Increase heart rate
- Pallor
- Sweating
What are the “Forward” failure effects
- Lowish BP
- Tiredness
What are the “Backpressure” effects
- Breathlessness on Exertion
- Orthopnoea
What is the effect of fluid reabsorption
- Raised JVP
- Peripheral Edema
How does patients with long term chronic heart failure present?
How does Ang II maintain blood pressure?
- Fluid retention
- Vasoconstriction
How does Ang II lead to heart failure
- increases resistance, inflammation, fibrosis, hypertrophy
- reduce NO
What can cause increased JVP?
- Increased venous pressure due to too much fluid in the venous system
- RIght-heart failure (not pumping and filling well)
Therefore there is a back-pressure effect on the RA
What does a prominent “a” wave of JVP suggest?
Increase in pressure to fill right ventricle ( RV hypertrophy, tricuspid stenosis)
What does a prominent “v” wave of JVP suggest?
Tricuspid regurgitation
What condition could result in radial-femoral delay and higher amplitude of arterial pulse in upper limbs compared to lower limbs?
Coarctation of the aorta
The upstroke of pulse in ______ is delayed and less abrupt.
Aortic stenosis
What does the apex beat correspond to?
Ventricular systole (ejection phase)
What can cause absence of apex beat?
Right ventricular hypertrophy
Why is S3 indicative of congestive heart failure in adults?
It is because there is increased blood volume in the vascular system causing increased filling of the ventricle during early diastole
Why is maximal cardiac output reduced in elderly?
What is the arterial pressure formula?
CO x TPR
How to measure blood pressure?
Sphygmomanometer
How is arterial pressure generated?
Contraction of ventricles in ejecting cardiac output
Which factor affects arterial pressure?
resistance in arterioles
How are high pressures generated?
Which baroreceptors detect postural hypotension?
Carotid baroreceptors, Aortic baroreceptors
The signals from the baroreceptors are interpreted by vasomotor centres in the …
Brain stem
How does the sympathetic system regulate blood pressure
How does the parasympathetic system regulate blood pressure
How do kidneys regulate blood pressure?
They regulate fluid status, thus blood volume
How does the kidney regulate fluid status?
Renin-angiotensin aldosterone system
What is present in a Juxtaglomerular apparatus?
JG cells, Macula densa
What do JG cells sense?
Pressure
What does Macula densa sense?
Cardiac output
When is renin released?
When pressure and CO drops
Describe the JGA Action
What are the drugs that target the RAAS?
ACEi, ARBs, Anti-renin drugs
What can predispose to hypertension
Which organs can be damaged by hypertension?
heart, kidneys, brain and the eyes
What indicates circulatory shock?
Systolic BP< 80mmHg, mean Bp < 60 mmHg
Types of circulatory shock are …
Hypovolemic, cardiogenic, obstructive, distributive
What are examples of cardiogenic shock?
Myocardial infarction, Arrhythmias, Severe valve defect
What are examples of obstructive shock?
Significant pulmonary embolus, Tension pneumothorax, Pericardial temponade
