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Heart valves and circulation of blood
Both atria and ventricle are relaxed (diastole)
Blood flows into right atrium from superior and inferior vena cava and coronary sinus. Blood flows into the left atrium from the 4 pulmonary verins
2 atrioventricular valves (tricuspid and mitral ) are both open so blood flows unimpeded from atria to ventricle, filling around 80%. 2 semilunar valves (pulmonary and aortic valves) are closed, preventing back flow of blood into right and left ventricles ( pulmonary trunk is on the right and aorta is on the left )
What is the most common cause of heart failure?
In adults - inability of the left ventricle to fill (diastolic performance) and eject blood (systolic performance)
What is a single cardiac cycle?
A complete relaxation and contraction of both atria and ventricles ( diastole and systole )
What is the cardiac cycle defined as?
Coordinated sequence of electrical and mechanical events occurring from the start of one heartbeat to the start of the next
How do pressure changes occur?
By conductive electrochemical changes within the myocardium that result in contraction of cardiac muscle
How does conduction system of the heart travel?
Sinoatrial node - bachmans bundle - Atrioventricular node ( signal passes from SV node here via the anterior internodal, middle internodal, posterior internodal) - AV bundle (bundle of his) - Right and left bundle branches - Purkinje fibres
Phases of the cardiac cycle
Atrial contraction (mitral valve closes)
Ventricular isovolumetric contraction - occurs when both valves are closed (aortic valve opens)
Rapid ventricular ejection
Slow ventricular ejection (aortic valve closes)
Ventricular isovolumetric relaxation occurs when both valves are closed (mitral valve opens)
Ventricular filling
Diastasis
Conduction in the heart - cardiac muscle
Desmosomes - hold muscle cells together tightly
Intercalated discs - link muscle cells together and contain desmosomes and gap junctions
Gap junctions - allow passage of action potentials from one cell to the next, very quickly. This allows the cardiac muscle to function together as a syncytium
Physiology of cardiac muscle
cardiac tissue has distinctive electrical characteristics, intercalated discs allow action potentials to pass adjacent cells, myocardial cells can spontaneously depolarize (automaticity)
Spontaneous depolarization generates a pacemaker potential
Cardiac muscle as a syncytium
Heart is composed of two syncytium's
Atrial: constitutes the walls of the atria
Ventricular: walls of the two ventricles
Atria separated from ventricles by fibrous tissue that surround the two atrio-ventricular valve openings.
What is the importance of fibrous tissue in the heart?
The fibrous tissue that seats the cardiac valve lacks gap junctions and electrically isolates atria from the ventricles (provides a border)
What is the approx blood pressure in the pulmonary and systemic circuit?
Pulmonary - 28/8 mmhg
Systemic - 120/80 mmhg
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