Which body cavity is the heart located?
Mediastinum - posterior to sterum, anterior to spinal column, medical to lungs, anterior to diaphragm
What is the heart’s orientation?
Posterior base, anterior apex, tilted to the left, RV anterior
Dextrocardia is what?
A condition when the orientation of the heart is reversed, in a mirror image
What is the average weigh to a heart
250-300g (person dependent)
What are the 3 layers of the heat?
Endocardium, myocardium, epicardium
What is the myocardium?
Made up of cardiomyocytes which contain the contractile proteins for muscular contraction
What is the endocardium?
Innermost layer of the heart, made up of smooth endothelial cells
What is the epicardium
Also known as the visceral pericardium. Made up of squamous epithelial cells that overlie connective tissue.
How are cardiac muscle fibres orientated?
orientated spirally in 4 groups: two groups wind around both ventricles, 3rd group around both ventricles and 4th innermost group winds around only the LV.
What is the layer surrounding the heart called?
Pericardium which is a double-walled sac
What is the function of the pericardium?
Lubrication, shock absorber, protection (mechanical/infection), holds heart in place
What are the two layers of the pericardium called?
- outer fibrous pericardium, 2. inner serous pericardium
What is the fibrous pericardium composed of?
Tough, white, fibrous connective tissue
Where does the fibrous pericardium attach?
Diaphraghm, great vessels, sterum
What are the two layers of the serous pericardium?
- outer parietal layer (lines the inside of the fibrous pericardium), 2. inner visceral layer
What is the space between the visceral and parietal layer called?
Pericardial cavity - filled with 10-20ml of pericardial fluid
What is pericardial effusion?
Excess pericardial fluid in the pericardial space. This can reduce the ability of the heart to pump (cardia tamponade) and reduce the voltage picked up by skin electrodes during ECG
Name the great vessels of the heart
Superior vena cava, inferior vena cave, aorta, pulmonary artery, pulmonary veins (of which there are 4)
Where does the aortic arch lie?
behind the heart
Name the 4 compartments of the heart
left atria, left ventricle, right atria, right ventricle
What can the atria be considered as?
Blood volume reservoirs
Explain the flow of blood through the heart
- right atria receives deoxygenated blood from vena cava
- right ventricle receive deoxygenated blood from right atria
- deoxygenated blood leaves the heart via pulmonary artery
- oxygenated blood enters the left atria via the 4 pulmonary viens
- oxygenated blood enters the left ventricle from the left atria
- oxygenated blood leaves the heart vai the aorta
What separates the two atria and two ventricles?
Interatrial septum and interventricular septum
Other than the vena cave, from where else does deoxygenated blood drain into the right atria?
Coronary sinus - deoxygenated blood from the myocardium
Why is the LV wall thicker?
The left side of the heart operates under higher pressures and so it requires to do more stroke work.
What is the function of valves?
To prevent the backflow of blood (regurgitation) and thus, maximise the efficiency of blood circulation
Name the valves of the heart
- Tricuspid valve separates the right atria and ventricle
- Pulmonic valve separates the right ventricle and pulmonary artery
- Mitral valve separates the left atria and ventricle
- Aortic valve separates the left ventricle and aorta
When do the semi-lunar valves prevent regurgitation?
When do the atrio-ventricular valves prevent regurgitation?
How many cusps does the mitral valve have?
Which anatomical structures prevent the inversion of the atrio-ventricular valves?
Chordae tendinae connect the valve cusps to papillary muscles in the heart wallwhich contract during systole
What happens if the chordae tendinae are damaged?
Backwards flow of blood into the atria - heart murmur
Explain the change in pressure that allows movement of blood through the circulatory system
- during systole: the pressure in the LV and RV exceeds that within the LA and RA and aorta and pulmonary vein - this forces the tricuspid/mitral valve to close and pulmonic valve/aorta to open. The pressure in the pulmonary artery/aorta will then exceed that of the RV/LV as blood moves in and force the pulmonic/aortic valve to close.
- During diastsole the pressure in the RA/LA exceeds that of the RV/LV, forcing the bicuspid/mitral valve to open.
What is the two circulatory systems in the body?
- pulmonary circulation
2. systemic circulation
How many coronary arteries are there?
Epicardial coronary arteries run where?
Surface of the heart
Subendocaridal coronary arteries run where?
Deep within myocardium
Where supplies the coronary arteries?
Coronary ostium at the base of the aorta
Are the coronary arteries filled with blood during systole or diastole?
Diastole - during systole the aortic valve is open and the coronary artery is partially covered
When is coronary blood supply reduced?
Tachycardia - diastole duration is reduced
Name the 4 coronary arteries and where they supply blood
Right coronary artery (right atrium, bundle of his, right ventricle, AV node, SA node in 50% popn and inferior and posterior sections of LV.
Left main artery:
Left anterior descending (anterior and inferior sections of LV, RBB, interventricular septum, left anterior fasciculus)
Left circumflex (LBB, lateral walls of LV, left atrium, left posterior fasciculus, SA node in 50% popn)
Explain how redundancy is inherent in the myocardium blood supply
When more than one coronary artery supply the same region they connect via anastomes. therefore a blockage can be ‘overcome’ in collateral circulation.
What is collateral circulation?
alternative blood flow routes
How much blood moves from the atria to the ventricles down pressure gradient?
What’s responsible for 30% of ventricular filling
Atrial kick (atrial contraction)
How do tachycardias influence CO?
Filling time is reduced and less blood is ejected
What is preload?
The degree of stretch of the ventricular walls right before contraction (depends on venous return). It is determined by the amount of blood in the ventricles
What is afterload?
The residual pressure within cardiovascular system that the ventricles must work against
What is the Frank-Starling Mechanism
The greater volume of blood entering the ventricles during diastole, the greater volume leaves during systole. The ability of the heart to change it’s force of contraction in response to changes in venous return
What is the consequence of increased afterload
Reduced SV, unless physiological changes allow adaptation - i.e. hypertrophy
What is contractility?
The ability of the myocardium to contract following depolarisation. It is dependent on the stretch of the contractile proteins - actin and myosin and the number of cross-bridges formed.
How is the rhythm of the heart controlled?
By the sympathetic and parasympathetic nervous system
What does the SNS do?
By releasing catecholamines (adrenalin and norardrenalin) it causes an increase in HR, automaticity, AV conduction and contractilty
What dose the PSNS do?
By releasing acetylcholine it causes a reduction in HR, conduction and automaticity.
When cant the PSNS be stimulated?
When the baroreceptors are stimulated
What is automaticity
The ability of pacemaker cells to spontaneously depolarise and generate an electrical impulse
What is excitability?
How well a cell responds to an electrical stimulus and is influenced by ion shifts across the cell
What is conductivity?
How well a cell can transmit an electrical impulse to another cell
What is contractility?
How well a cell can contract after receiving an impulse
At rest, is cardiomyocyte membrane potential negative or positive
What is the ion movements during depolarisation-repolarisation cycle?
(1) sodium ions enter (2) potassium ions leave (3) calcium ions enter (platue) (4) calcium ions stop entering(5) potassium ions leave
When is the absolute refractory period
Before potassium channels open and repolaristion takes place
What are the 5 phases?
Phase 0: sodium moves in (dep) Phase 1: K moves out Phase 2: calcium moves in (plateau) Phase 3: K moves out (rep) Phase 4: resting membrane potential - cell is ready for next stimulus
Electrical conduction through the heart
SA node - intermodal pathways/Bachmann’s Bundle - AV node - bundle of his - RBB/LBB - left anterior fasciculus/left posterior fasciculus - purkinji fibres
PSNS stimulation does what during diastole?
Reducing the rate of depolarisation of pacemaker cells
What is the pacemaker tissue surrounding AV node?
What is the intrinsic rate of junction tissue?
Where does the entire purkinji fibre system originate?
What’s the intrinsic discharge rate of purkinji fibres?
What can increase the automaticity of cells?
Stimulants (adrenalin) - coffee, stress management and moderate exercise
Max HR = 220 - age has a s.d. of what?
Exercise increases the work that can be done at a given HR? T/F