the heart Flashcards
what protects the heart
-heart is located in the thoracic cavity and protected by the ribcage and mostly cardiac muscle
-surrounded by protective fluid-filled sacs called pericardium
what are the 4 chambers in the heart
-right atrium - receives deoxygenated systemic venous return
-right ventricle- pushes blood to pulmonary circulation for oxygenation
-left atrium- receives oxygenated blood from pulmonary circulation
-left ventricle- pumps oxygenated blood under high pressure to head and body
what do valves prevent
-back flow of blood
-control unidirectional blood flow in cardiac cycle
-atrioventricular valves (mitral and tricuspid) are connected to the cardiac wall via chordae tendinae and papillary muscles
-semilunar valves (aortic and pulmonary) where small fibrous nodules come together
what are the two different types of cardiac cells
-conducting cells
-contractile cells
what are the cardiac cells like in the heart wall
-epicardium (outer, contains lots of collagen to help with integrity of the heart), myocardium (muscle to protect heart), endocardium (inner lining) in which all are electrically activated
what do the conducting cells do
-rapidly spread action potentials (SAN, atrial internal tracts, AVN, bundle of His, purkinje system)
what do the contractile cells do
-action potentials lead to contraction due to generation of force/ pressure (majority of atrial and ventricular tissues)
how is the cardiac cells and electrophysiology connected
-extracellular Ca2+ is the link between the electrical signals and contraction of the myocytes
-myocytes lead to excitation- contraction coupling
-myocardium is the extensively branched muscle fibre cells which are connected by the intercalated discs
what’s the structure of myocardial cells
-intercalated discs are part of the sarcolemma which is a specialised plasma membrane
-gap junctions are channels which allows depolarising current flows from cell to cell due to electrical coupling
-lots of desmosomes which anchor fibres together
how are the T-tubules involved in excitation- contraction
-sarcolemma forms deep invaginations (T-tubules)
-T-tubules lead to depolarisation relayed to cell core releasing calcium (near Z line)
-sarcoplasmic reticulum is where Ca2+ is released (near all sarcomeres simultaneously)
-binding actin-myosin leads to large instantaneous force
what is the depolarisation sequence in the cardiac cycle
-cardiac cycle is a rhythmic sequence of events within the heart to pump blood through the body, consists of two main stages called distole and systole
-electrical signal originates in sinoatrial node (SAN) which is the primary pacemaker, cells spontaneously depolarise
-action potential intrinsic rate is 60-100/min at rest
-action potential propagation: cell-cell via gap junctions which are electrically coupled from right to left atria leads to contraction, or through conducting pathways (4 conducting bundles)
-0.1second at AVN
-fibrous atrioventricular ring prevents spread to ventricle which optimises atrial emptying
-no propagation due to AV ring
-AVN which is the secondary pacemaker is linked to the His-purkinje fibre system (which is tertiary system)
-action potential carried to ventricular muscle via left and right branches of its specialised conducting cells
-action potential propagation cell to cell then synchronised ventricular contraction leading to optimal ejection of blood
what occurs in atrial systole
-atrial depolarisation (after stimulation of SAN)
-contraction leads to increased pressure
-ventricles relaxed and mitral and tricuspid valves open and the ventricles further fill with blood
what happens in isovolumetric ventricular contraction
-purkinje fibre electrical activation leads to the contraction of ventricles which leads to an increase in pressure
-volume stays the same despite increase in pressure
-mitral and tricuspid valves close so ventricular pressure is higher than atrial pressure
what happens in rapid ventricular ejection
-ventricular pressure rises and exceeds aortic pressure
-semilunar valves open and this leads to rapid blood ejection
-stroke volume ejected (most)
-ventricular volume decreases a lot and arterial pressure increases
-atrial filling begins and pressure increases slowly
what happens in reduced ventricular ejection
-ventricles repolarisation leading to a decrease in pressure (ventricles no longer contracting)
-semilunar valves open so blood is still being ejected (at a decreased rate) so volume decreases
-arterial volume decreases blood volume by elastic recoil
-atrial pressure increases as blood returns to the heart
