The anatomy and physiology of the circulatory system Flashcards
Heart location
-mediastinum- extends from sternum anteriorly to the vertebral column
-lies medially between lungs
-2/3 mass is to the left of midline
-base (top) of heart tipped up medially and posteriorly
-apex projects inferiorly and laterally
The pericardium
what is it, what it does, what its composed of
-membrane surrounds the heart
-helps retain hearts position within mediastinum
-composed tough outer fibrous layer and lined by delicate serous membrane
-serous membrane divided into parietal layer (outer) and visceral layer (inner)
-between these layers there’s serous fluid
Layers of heart wall
-epicardium- thin, transparent outer layer, also called visceral layer of pericardium
-myocardium- thick middle layer, composed of cardiac muscle
-endocardium- squamous epithelium, known throughout circulatory system as endothelium
Atrial kick
-when atria contract
-responsible for only a 20% increase in amount of blood ejected by the ventricles
Heart valves
-atrioventricular valves- between atria and ventricles
-outflow/ semi lunar valves- from ventricles to outflow vessels
Atrioventricular valves
Right AV valve= tricuspid valve as has 3 leaflets/ cusps
Left AV valve= bicuspid/ mitral valve
Outflow valves
names
-right= pulmonary valve
-left= aortic valve
How heart valves (av) work by preventing backflow
-AV valves tethered to walls of ventricles by heart strings/ chordae tendinae attached to papillary muscles
-papillary muscles pull on AV valves via chordae tendinae, slowing their closure and preventing damage to valve
Outflow valves
-firm cusps that each look like a semi full moon
-each cusp makes up a third of the valve
Why there are no valves between vena cava and right atria and pulmonary vein and left atria
-small amount of blood does flow backwards
-but minimised by the way the atria contracts
-this compresses and nearly collapses the vessels
Arteries
-blood away form heart
-contain oxygenated blood
-thick walls, exposed to high pressures and friction forces
-outer layer= tunica externa
-middle layer= tunica media
-inner layer= tunica interna/ endothelium
Veins
-blood back to heart
-contain deoxygenated blood
-thin walls as exposed to low pressures and minimal friction forces
-same 3 layers as artery- tunica externa, media, interna
-layers just not as thick as an artery
-valves
Arteries and vein that attach to heart
-arch of the aorta
-pulmonary trunk
-coronary arteries
-superior and inferior vena cava
-4 pulmonary veins
-coronary sinus
Arterioles- 3 layers and structures
-thin tunica interna with thin fenestrated elastic lamina
-tunica media consists of one or two layers of smooth muscle cells
-tunica externa consists of connective tissue and sympathetic nerve supply that can vary the rate of flow
Capillaries
-smallest vessels
-one RBC through at a time
-allow exchange of substances between blood and interstitial fluid
-lack tunica media and externa
-single layer endothelial cells
Systemic circuit
-ejects blood into aorta, systemic arteries, and arterioles, powered by left side of heart
Pulmonary circuit
-ejects blood into pulmonary trunk, powered by right side of heart
Coronary circulation
-passive process
-blood flows through coronary arteries only during relaxation phase of ventricular diastole
-LCA- goes to anterior interventricular and circumflex branches
-RCA- to marginal and posterior atrioventricular branches
-coronary veins collect in coronary sinus at the back of heart
-coronary sinus empties into right atrium to be oxygenated by lungs
Cardiac muscle tissue
-shorter fibres than skeletal muscle
-branch
-only have on centrally located nucleus
-communicate with neighbouring cells through gap junctions in intercalated discs
Autorhythmicity
-doesn’t rely on CNS
-just happens automatically
-autorhythmic cells spontaneously depolarise
-when they reach the threshold, an AP is reached causing all cells in that area to depolarise
Myocytes- 2 roles
-form the conduction system
-act as pacemakers
Normal pacemaker of the heart
name, why, location
-sino atrial node (SAN)
-due to fastest rate of depolarisation
-located right atrial wall
How often the SA node fires
-once every 0.8 seconds or 75 AP per min
Cardiac conduction
-AP generated at SAN
-then propagates throughout wall of atria via the bachmann’s bundle to the AVN in the interatrial septum
-at AVN, signal is slowed allow atria chance to mechanically move blood into ventricles
-spreads down bundle of his which separates to the right and left bundle branches to the purkinje fibres
How contractions are coordinated
-band of muscle wind around the heart, working as a unit
-this forms a functional syncytium
-this allows the top and bottom parts to contract in their own way
Role ANS
-regulate changes in BP, blood flow and blood volume
-maintain enough cardiac output to provide for all organs
Refractory period
-longer than the contraction itself, unlike skeletal muscle
-therefore tetanus (maintained contraction) cannot occur in cardiac muscle
ECG
Electrocardiogram
-records electrical changes on surface of the body caused by depolarisation and repolarisation of myocardium
-measures presence or absence of certain waveforms
PQRST waves
P= atrial systole
QRS= ventricular systole
T= diastole/ repolarisation of ventricle
PQ interval- excitation goes from SAN to AVN for the pause to occur
Cardiac cycle
-includes all events associated with one heartbeat
-systole and diastole
-during atrial systole, ventricles are relaxed and vice versa
-lub (S1)= closure of mitral and tricuspid valves
-dub (S2)= closure of aortic and pulmonary valves
Average stroke vol
70 ml
Cardiac output calculation
stroke volume x heart rate
resting adult= 70ml x 75bpm= 5.25 l/min
-on average whole blood volume flows through pulmonary and systemic circuits every minute
3 factors affect stroke volume
-amount of ventricular filling before contraction (preload)
-contractility of ventricle
-resistance in blood vessels the heart is pumping into (afterload)
Cardiac reserve
-difference between cardiac output at rest and the maximum cardiac output the heart can generate
Starlings law of the heart
-the more the heart muscle is preloaded/ stretched, the more forcefully the heart will contract
Functions of blood
-transportation- O2, CO2
-regulation- pH, temp
-protection- clotting, immune system
