Pressure gradients move blood through the heart and vessels. Pulmonary circulation vs. systemic circulation Circulatory system

head and arms (to pulmonary circuit) aorta (from pulmonary circuit) heart other organs diaphragm liver intestines “Double pump” both ventricles pump an equal volume of blood into systemic and pulmonary circuits Higher resistance through the systemic circuit legs

Pressure - force exerted by pumped blood on a vessel wall Resistance - opposition to blood flow from friction

vena cava Right atrium Tricuspidvalve vena cava Right ventricle

Right atrium Tricuspidvalve Right ventricle Pulmonarysemilunarvalve Left pulmonary artery Right pulmonary artery

Aorta Left atrium Right pulmonary vein Left pulmonary vein Bicuspidvalve Left ventricle

Aorta Left atrium Left pulmonary vein Right pulmonary vein Bicuspidvalve Left ventricle Aorticsemilunarvalve

When pressure is greater behind the valve, it opens. When pressure is greater in front of the valve, it closes Valves ensure one-way flow Leakproof “seams” semilunar valve

Right atrium Tricuspid valve Right ventricle Papillary muscle contracts with ventricle Chordae tendineae Septum Shape of the AV valves is maintained by chordae tendineae

Ventricular Systole Diastole

Blood pressure variation

Cardiac muscle fibers are interconnected by intercalated discs. Heart myocardium

Desmosome Gap junction Intercalated disc Action potential Junctions between cardiac muscle cells

Pacemaker activity Slow depolarizations set off action potentials in a cycle Pacemaker cells only! These cells do not contract

Pacemaker cell Spontaneous action potential Action potential spread to other cells Gap junctions Cardiac muscle Self-excitable muscles - action potential gradually depolarizes, then repolarizes Gap junctions

No gap junctions between atria and ventricles Fibrous insulating tissue prevents AP from directly spreading from atria to ventricles

Sinoatrial (SA) node Purkinje fibers Atrioventricular (AV) node Pacemaker locations: SA node AV node Bundle of His Purkinje fibers Conduction of contraction Bundle of His

AV node rhythm is slower - bradycardia Problems with heart rhythm

Heart block – a type of bradycardia. Ventricles pump slowly and out of rhythm of atria Problems with heart rhythm

Ventricular fibrillation

Atrial fibrillation Problems with heart rhythm

Plateau phase Threshold potential Action potential in cardiac muscle These are contractile cells not pacemaker cells

Action potential Contraction Refractory period Long refractory period ensures no summation of twitches Relaxation of cardiac muscles is required

Currents from heart spread to body tissues and fluid Sum of all electrical activity spread to electrodes and recorded Electrocardiogram P R Q S T P PRSTTP interval

time (seconds) bradycardia tachycardia ventricular fibrillation

Ventricular and atrial diastole Cardiac cycle

Atrial contraction Cardiac cycle

Isovolumetric ventricular contraction “Lub” End diastolic volume is in the ventricles Cardiac cycle

Isovolumetric ventricular contraction Cardiac cycle “Lub” start of ventricular systole

Ventricular ejection Cardiac cycle

Isovolumetric ventricular relaxation “Dub” End systolic volume is in ventricles Cardiac cycle

Systolic or diastolic murmurs Often due to stenosis or regurgitation at a valve (“whistle” vs. “swish”) Heart murmurs Normal heart “lub-dup” Diastolic mitral stenosis “lub-dup-whistle” Diastolic aortic regurgitation “lub-dup-swish” Systolic aortic stenosis “lub-whistle-dup” Systolic tricuspid regurgitation “lub-swish-dup” Diastolic patent ductus arteriosus

Extrinsically: conduction speed contraction strength Sympathetic signals increase stroke volume

Recall: muscle length and force

Optimal length (Cardiac muscle does not normally operate within the descending limb of the length– tension curve.) End-diastolic volume (EDV) (ml) Normal resting length Increase in SV Stroke volume (SV) (ml) B1 A1 Increase in EDV Frank Starling law (intrinsic increase in stroke volume)