Functional Anatomy Of Heart And Cardiac Cycle Flashcards
Describe the heart
-Muscular pumping organ
-cardiac muscle
-around size of your fist
-Points downwards, outwards & slightly to the left
Describe the course of blood vessels around the heart
Returning blood to the heart:
Superior and Inferior Vena Cava (deoxygenated)
Right & Left Pulmonary Veins (oxygenated)
Away from the heart
Pulmonary trunk then Right & Left Pulmonary Arteries (deoxygenated)
Ascending Aorta (oxygenated)
Where is the heart located
-superior to the surface of the diaphragm
-left of midline
-anterior to vertebral column
-posterior to sternum
describe the layers of the heart wall
-endocardium - endothelial inner layer which is the continuous surface of the heart so blood cells do not stick to it
-myocardium is the cardiac muscle which makes up the bulk of the heart
-outer layer is pericardium
What happens to the thickness of the myocardium
-thickness of myocardium depends on function
-myocardium of left ventricle is thicker to supply systemic circulation
what is the structure of the pericardium?
-inner layer is the epicardium which lines the heart (visceral pericardium)
-outer layer is the pericardium which lines body cavity (parietal pericardium)
-space between the membranes is the pericardial cavity
what is the pericardium?
-double-walled sac that encloses the heart
-protective air-filled space
-anchors heart to mediastinum
-prevents overfilling of the heart
-provides friction-free environment
What is cardiac tamponade?
-clinical syndrome caused by overfilling of the pericardial cavity
-results in decreased ventricular filling bc heart chambers are compressed and reduced cardiac output
-can be caused by cancer, infection and trauma
what is the function of heart valves?
Ensure unidirectional blood flow through the heart
what are the major vessels?
-superior and inferior vena cava
-right and left pulmonary veins
-pulmonary trunk which splits into right and left pulmonary arteries
-ascending aorta
describe the AV valves
-between atria and ventricles
-bicuspid (mitral) valves on left and tricuspid valves on right
-prevents backflow into atria
-chordae tendineae anchor valves to papillary muscles which contract to prevent inversion of valves
describe the semi-lunar valves
-between ventricles and arteries
-intraventricular pressure forces them open
-prevents backflow of blood into ventricles
-Increased pressure in arteries compared to ventricles forces then shut=
Describe the cardiac cycle
phase 1
-blood enters atria passively and enters ventricles
-av valves open
-atrial systole occurs
phase 2
-atria relax
-rising ventricular pressure closes av valves
-ventricular systole occurs
-semilunar valves open
-ventricles relax
-backflow of blood closes semilunar valves
Importance of cardiac cycle
All the events of one heart beat Diastole – relaxation of heart muscle Systole – contraction of heart muscle
Contraction of the myocardium must be co-ordinated to ensure proper pumping
Atrial contraction must be completed before ventricular contraction occurs
Describe the heart sounds
-‘lub-dub’
-this is the sound of the heart valves closing
-‘lub’ (s1) is the av valves
-‘dub’ (s2) is the semilunar valves
-can be used diagnostically to identify heart abnormalities
describe the cardiac muscle
-involuntary, striated, short, fat, branched and interconnected muscle
-rhythmic and contract as a unit - gap junctions allow ions to pass through so heart can beat as one
-intercalated discs anchor cardiac cells together
-stimulated by nerves but is self-exciting
-fatigue resistant bc lots of mitochondria, good blood supply, myoglobin
-Highly specialised cells
What happens to cardiac muscle when inadequate blood supply to an affected area
Incapable of regeneration
Necrosis due to inadequate blood supply to the affected area (ischemia) = infarction
Fibrosis
describe the Sinoatrial (SA) Node
-Cluster of myocytes with pacemaker activity (don’t contract but generate automatic impulses)
-Located at the junction of the crista terminalis in the upper wall of the right atrium and the opening of the superior vena cava (1)
-Under normal circumstances - generates electrical impulses that set the rhythm and rate of the heart
Describe the Atrioventricular (AV) Node
Located near the coronary sinus on the interatrial septum (2)
Connects the electrical systems of the atria and the ventricles
describe the sequence of excitation in the intrinsic conduction system
-SAN is stimulated and is depolarized
-impulse spreads through heart wall and causes atrial contraction
-impulse reaches AVN and there is a small delay to allow atria to contract before ventricular contraction
-impulse is sent down bundle of His
-at apex of heart, impulse travels up Purkinje fibres which causes ventricles to contract
describe the cardiac action potentials with conductive (pacemakers) cells at SA node
-there is no stable resting point at SAN
-spontaneous depolarisation occurs through Na+ channels in autorhythmic cells
-threshold is reached when Ca ion channels open
-Ca ion channels close and K ion channels open which leads to repolarisation
Role of nervous system with action potential at san
Sympathetic nervous system - epinephrine and norepinephrine - accelerate the heart rate
Parasympathetic nervous system - acetylcholine - slow the heart rate
describe action potential in contractile cells
-more stable resting potential
-fast Na+ channel opens bc stimulated by neighbouring cell - causes rapid depolarisation
-slow Ca2+ channels open - causes LONG refractory period – contractions cannot occur
-this keeps heart beat regular
-K+ ion channels open and repolarisation occurs
San vs contractile ap diagram
what do artificial pacemakers do?
send out electrical signals to stimulate contraction
-used for heart blocks or arrhythmia
-can be single chamber or dual chamber
-can be on demand or responsive
Describe Electrocardiogram
Strength and timing of the electrical activity in the heart
-P wave - depolarisation of the atria in response to signalling from the sinoatrial node (atrial contraction)
-QRS complex - depolarisation of the ventricles (ventricular contraction) triggered by signals from the AV node
-T wave - repolarisation of the ventricles (ventricular relaxation) and the completion of a standard heart beat
-Between these periods of electrical activity are intervals allowing for blood flow (PR interval and ST segment)
