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The three principal components: Heart (the pump) Blood vessels (the pipes) Blood (the fluid to be moved) Functions: Supply oxygen/nutrients, remove waste, regulate temperature, distribute hormones, immuno-vigilance
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Autorhythmic Cells: 1% of heart, initiate APs
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Contractile Cells: 99%, mechanical pumping
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Pacemaker Activity:-
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1. Funny channels: (Na⁺ in) and K⁺ channels close.
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2. T-type Ca²⁺ channels open
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3. Threshold: L-type Ca²⁺ channels open
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4. Repolarization: K⁺ channels open
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Note that: : Long refractory period coincides with plateau (Prevents summation/tetanus)
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Type of Cell: Contractile (99% of cardiac cells)
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Resting potential: –90 mV
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1. Depolarization: Fast Na⁺ channels open
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2. Initial Repolarization: Transient K⁺ channels open
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3. Plateau: L-type Ca²⁺ channels open, reduced K⁺ efflux
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4. Repolarization: Regular K⁺ channels open
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Return to Rest: Leaky K⁺ channels restore resting potential
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Pacemaker: gradual depolarization, no true resting potential, Ca²⁺-dependent spike
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Contractile: stable resting potential, Na⁺-dependent spike, plateau from L-type Ca²⁺
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1. SA nodes
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2. AV nodes
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3. Bundle of his
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4. Right/left bundle branches
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5. Purkinje fibers
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Heart Wall Layers:
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Endocardium: Inner layer, lines chambers
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Myocardium: Cardiac muscle layer, responsible for contraction
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Epicardium: Outer layer, also part of pericardium
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Pericardium: Protective sac around the heart
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Valve Composition:
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Connective tissue: Mostly collagen, provides structural support
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Endothelium: Inner lining of heart and blood vessels
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4 Heart Valves: Tricuspid, Pulmonary, Mitral, Aortic Flow Sequence: Right atrium → Right ventricle → Lungs → Left atrium → Left ventricle → Body Oxygenation: Pulmonary arteries = O₂-poor, Pulmonary veins = O₂-rich
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S1 (“lub”) = AV valves close
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S2 (“dub”) = Aortic/pulmonary valves close
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Murmur: Stenotic or insufficient valves → turbulence
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Phases: Mid-to-late diastole → Ventricular systole → Early diastole
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Stenotic = valve doesn’t open completely
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Insufficient = valve doesn’t close completely
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Causes murmurs (turbulent flow)
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Pulse Pressure = Systolic – Diastolic
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Mean Arterial Pressure (MAP) = Diastolic + ⅓(Pulse Pressure)
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Measured by: Sphygmomanometer (Korotkoff sounds)
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Systolic increases
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Diastolic ~same
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MAP increases progressively
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Flow influenced by: Radius (power of 4 effect), Length, Viscosity
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Pressure gradient = Flow × Resistance
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CO = Heart Rate × Stroke Volume
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Stroke Volume = EDV – ESV
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Regulation: 2 Types
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Type 1: Intrinsic: Frank–Starling Law = Increased venous return increases ventricular filling (increased EDV), which results in a larger stroke volume due to the length–tension relationship.
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Extrinsic: Sympathetic stimulation → ↑ , contractility → ↑ SV
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MAP = C.O x TPR
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Contributors: Stroke vol.,Heart rate, Blood Vol., Blood Viscosity, Arteriolar Radius, Sympathetic/Parasympathetic activity
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P wave: Atrial depolarization
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PR segment: AV node delay
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QRS complex: Ventricular depolarization (atrial repolarization hidden)
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T wave: Ventricular repolarization
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TP interval: Ventricles relaxing/filling
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ST segment: Ventricles contracting/emptying
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Rate: Tachycardia
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Rhythm: Extrasystole, ventricular fibrillation
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Conduction: Complete heart block
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Myopathies: Myocardial infarction
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Lipid-soluble substances: pass through endothelial cells
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Small water-soluble substances: pass through pores
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Exchangeable proteins: moved via vesicular transport
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Plasma proteins: generally cannot cross capillary wall
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NFP = Capillary Hydrostatic Pressure − Blood Colloid Osmotic Pressure
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Affects direction of fluid movement (filtration vs. reabsorption)
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Positive NFP = fluid pushed out (filtration)
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Negative NFP = fluid pulled in (reabsorption)
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Stimulus: ↑ or ↓ blood pressure
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Sensors: Carotid sinus and aortic arch
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2 effects can occur:
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↑ BP =↑ afferent firing = ↓ HR, ↓ contractility & vasodilation
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↓ BP = ↓ afferent firing =↑ HR, ↑ contractility & vasoconstriction
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Valves prevent backflow
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Factors that facilitate return:
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Sympathetic stimulation, Skeletal muscle pump, Respiratory activity, Increased blood volume.
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Systole and diastole both decrease, but diastole decreases more
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Systolic & MAP increase; diastolic remains about the same
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Cardiac output shifts to muscles, heart, skin
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