Week 1 Flashcards
Define contractility
The amount of tension that can be developed at any given stretch of cardiac muscle.
What two factors determine the amount of tension that is generated when a healthy cardiomyocyte contracts?
- Amount of Ca2+ in sarcoplasm
2. Length of cardiomyocyte before contraction
How might you increase the amount of tension a cardiomyocyte can generate for a given length?
Increase intracellular calcium (increase its contractility)
What is an inotrope?
A physiological or pharmacological agent that alters contractility of cardiac muscle (may be positive or negative)
Define preload
The degree of tension on a muscle when it begins to contract
Define afterload
The load against which the muscle exerts its contractile force
Give an example of ‘afterload’
Arterial blood pressure
An ECG measures:
Electrical activity on the surface of the heart cells
Regarding the ECG, what does dipole magnitude depend on (2 things)?
- How many cells are depolarising at that instant
2. Which direction is the wave heading? (vector analysis of dipoles)
What is an ECG ‘lead’?
A particular configuration of electrodes that compares the electrical potential between the two points in relation to the direction of net depolarisation ( of the heart)
What event is responsible for the first heart sound?
The closure of the mitral (mainly) and tricuspid valves (AV valves)
What event is responsible for the second heart sound?
The closure of the aortic (mainly) and pulmonic valves.
What is the electrical axis of the heart?
The orientation of the ECG vector at its maximum amplitude
What two things could change the electrical axis of the heart?
- A change in position of the heart
2. Increase in mass in one of the ventricles e.g hypertrophic cardiomyopathy
Give three examples of an altered sinus rhythm
Sinus tachycardia
Sinus bradycardia
Sinus arrhythmia
Give four possible sources of abnormal heart rate or rhythm
- Vagal or SNS input to SA node (physiological) e.g sinus bradycardia
- A block in impulse conduction either through SA or AV node e.g SA block
- Premature beats e.g ventricular premature contractions
- Fibrillation of heart muscle e.g atrial fibrillation
What is a premature atrial contraction? What might lead to this developing?
Occurs when an ectopic pacemaker develops in the atrial muscle that depolarises spontaneously and sends out impulses in addition to those coming from the SA node. Some of these may make it through the AV node. May develop when an area of muscle has experienced ischaemia resulting in dysregulation of its Ca2+ ATPase pumps, leading to a less stable resting membrane potential
Define end diastolic volume
The volume of blood in the ventricles in the period after atrial systole has finished and before ventricular systole starts
In which phase of the cardiac cycle might you see both the C wave and the QRS complex?
Isovolumetric phase of ventricular systole
When in the cardiac cycle does the C wave occur, and what does it represent?
At the beginning of ventricular systole - once the AV valves have closed, and the continuous rise in pressure in the ventricles causes the AV valves to bulge into the atria, creating the ‘C wave’ of pressure transmitted to the great veins
When in the cardiac cycle does the A wave occur and what does it represent?
Occurs at atrial systole; there are no valves between the atria and great veins, so when they contract there is some blood and pressure pushed back into the great veins.
When in the cardiac cycle does the V wave occur and what does it represent?
Occurs at the end of ventricular systole, during atrial diastole. Build up of blood in the atria generates the pressure wave back into the great veins.
What are the three phases of ventricular diastole?
- Isovolumetric relaxation
* AV valves closed
* SL valves closed - Rapid ventricular filling
* AV valves open
* elastic recoil of ventricles - Reduced refilling
* ventricles truly relax
Does systole or diastole contribute more to MAP? Why?
Diastole - because heart spends more time in diastole
How to calculate SV?
SV = EDV - ESV
Define stroke volume
The volume of blood ejected from the heart with each contraction
Define ejection fraction
The proportion of EDV ejected with each contraction
How to calculate EF?
EF = SV/EDV
What will happen to EF as the heart fails?
It will decrease
In which two species does the R interventricular artery come from the R coronary artery?
The horse and the pig. Cats variable
In which species does the R interventricular artery come from the Left coronary artery?
Ruminants, and the dog. Cats variable
Which species have only the R azygous vein?
Horse and carnivores
Which species have both R and L azygous veins?
Ruminants
- right to the cranial VC
- left to the coronary sinus
Which species has only the L azygous vein?
Pigs
In which species do the brachycephalic trunk and the left subclavian artery arise from the aorta independently?
Carnivores and pigs
Not ruminants or horses
What distinguishes the pig’s brachycephalic trunk from carnivores’?
Pig has extended bicarotid trunk
What sort of sternal attachment does the heart make in the horse? What layer of pericardium is this made of?
Single sternopericardiac ligament
Fibrous pericardium - shallow to parietal pericardium
What sort of sternal attachment does the heart make in ruminants?
Paired sternopericardiac ligaments
What sort of sternal attachment does the heart make in the pig? Do any other species have this arrangement?
Single phrenicopericardiac ligament
Yes cats and dogs
What structures does the vertebral artery supply?
The cervical spine and the brain
What structure does the internal thoracic artery supply?
The thoracic wall
What structure does the superficial cervical artery supply?
The base of the neck and the adjacent scapular region
What causes nodal cell membrane potentials to decay spontaneously and become gradually more positive?
Passive diffusion of Na+ into the cell down its concentration gradient
At about -60mV, what event occurs in nodal cells? How does this compare to cardiomyocytes?
Voltage-gated Ca channels are activated and Ca enters the cell
Cardiomyocyte cell membranes are activated by influx of Na via voltage gated Na channels when they are stimulated. Na channels will open when membrane potential exceeds -90mv
