Kim Hastings – November 2010

 To describe the key elements of the cardiovascular system  To relate structure to function of key components  To describe blood flow around the body  To describe the heart’s conduction system  To explain the cardiac cycle  To briefly describe blood vessels  To briefly describe/explain cardiovascular adaptations to exercise

 Components:  Heart  Blood vessels  Blood  Functions to:  Transport substances Oxygen and nutrients to cells Wastes from cells to liver and kidneys Hormones, immune cells, and clotting proteins to specific target cells

heart  arteries  arterioles  capillaries  venules  veins  Arteries—relatively large, branching vessels that conduct blood away from the heart  Arterioles—small branching vessels with high resistance  Capillaries—site of exchange between blood and tissue  Venules—small converging vessels  Veins—relatively large converging vessels that conduct blood to the heart  Closed system

 Erythrocytes—red blood cells Transports oxygen and carbon dioxide  Leukocytes—white blood cells Defend body against pathogens  Platelets—cell fragments Important in blood clotting  Plasma—fluid and solutes

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 Pulmonary circuit Supplied by right heart Blood vessels from heart to lungs and lungs to heart  Systemic circuit Supplied by left heart Blood vessels from heart to systemic tissues and tissues to heart

 Exchange between blood and tissue takes place in capillaries  Pulmonary capillaries Blood entering lungs = deoxygenated blood Oxygen diffuses from tissue to blood Blood leaving lungs = oxygenated blood

 Systemic capillaries Blood entering tissues = oxygenated blood Oxygen diffuses from blood to tissue Blood leaving tissues = deoxygenated blood

 Cardiovascular system = closed system  Flow through systemic and pulmonary circuits is in series  Left ventricle  aorta  systemic circuit  vena cavae  right atrium  right ventricle  pulmonary artery  pulmonary circuit  pulmonary veins  left atrium  left ventricle

 Parallel with other organs in systemic circuit  Blood in chambers does not supply nutrients to cardiac cells  Heart has own set of capillaries  Heart capillaries are supplied by coronary arteries (left and right) that arise from aorta

 Parallel with other organs in systemic circuit  Blood in chambers does not supply nutrients to cardiac cells  Heart has own set of capillaries  Heart capillaries are supplied by coronary arteries (left and right) that arise from aorta

 Pressure within chambers of heart varies with heartbeat cycle  Pressure difference drives blood flow High pressure to low pressure  Normal direction of flow Atria to ventricles Ventricles to arteries  Valves prevent backward flow of blood  All valves open passively based on pressure gradient

 Atrioventricular valves = AV valves Right AV valve = tricuspid valve Left AV valve = bicuspid valve (mitral valve) Papillary muscles and chordae tendinae Keep AV valves from everting  Semilunar valves Aortic valve Pulmonary valve

 The conduction system of the heart  Spread of excitation through the heart muscle  The ionic basis of electrical activity in the heart  Electrical activity in cardiac contractile cells  Recording the electrical activity of the heart with an electrocardiogram

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Plasma membrane Intercalated disk Sarcomere Desmosome Plasma membrane Gap junction channels Electrical current (b)

 Atria contract, then followed by ventricles  Coordination due to presence of gap junctions and conduction pathways  Intercalated disks Junctions between adjacent myocardial cells Desmosomes to resist mechanical stress Gap junctions for electrical coupling

Copyright © 2011 Pearson Education, Inc. Plasma membrane Intercalated disk Sarcomere Desmosome Plasma membrane Gap junction channels Electrical current (b)

Copyright © 2011 Pearson Education, Inc.

External measure of electrical activity of the heart  Body = conductor Currents in body can spread to surface (ECG, EMG, EEG)  Distance and amplitude of spread depends on size of potentials and synchronicity of potentials from other cells  Heart electrical activity—synchronized

 P wave: atrial depolarisation  QRS complex: ventricular depolarisation and atrial repolarisation  T wave: ventricular repolarisation  PQ segment: AV nodal delay  QT segment: ventricular systole  QT interval: ventricular diastole

 Phases of the cardiac cycle  Atrial and ventricular pressure  Aortic pressure  Ventricular volume  Heart sounds

Two main periods of cardiac cycle  Systole Ventricle contraction  Diastole Ventricle relaxation

 Valves open passively due to pressure gradients AV valves open when Pressure atria > pressure ventricles Semilunar valves open when Pressure ventricles > pressure arteries

 Ventricular filling Pressure atria > pressure ventricles AV valves open Passive phase—no atria or ventricular contraction Active phase—atria contract  Isovolumetric ventricular contraction Ventricle contracts—increases pressure AV and semilunar valves closed No blood entering or exiting ventricle

 Ventricular ejection Pressure ventricles > pressure arteries Semilunar valves open  Isovolumetric ventricular relaxation Ventricle relaxes—decreases pressure AV and semilunar valves closed No blood entering or exiting ventricle

 Isovolumetric ventricular contraction AV and aortic valves closed Ventricular pressure increases until it exceeds atrial pressure  Ventricular ejection Aortic valve opens Blood moves from ventricle to aorta

 Isovolumetric ventricular relaxation Ventricle muscle relaxes so that pressure is less than aorta Aortic valve closes Pressure in ventricle continues dropping until it is less than atrial pressure  Ventricular filling AV valve opens Blood moves from atria to ventricle Passive until atrium contracts

 Aorta (and large arteries)—elastic Pressure reservoir  Store energy during systole as walls expand  Release energy during diastole as walls recoil inward  Maintains blood flow through entire cardiac cycle

 EDV = end-diastolic volume, volume of blood in ventricle at the end of diastole  ESV = end-systolic volume, volume of blood in ventricle at the end of systole  SV = stroke volume, volume of blood ejected from ventricle each cycle.  SV = EDV –ESV

Volume of blood ejected by the ventricle each beat Stroke volume = end-diastolic volume – end-systolic volume = 130 mL – 60 mL = 70 mL

 Due to turbulent flow when valves close  First heart sound Soft lubb AV valves close simultaneously  Second heart sound Louder dubb Semilunar valves close simultaneously

 ECG = measure of electrical events  Electrical events cause mechanical events, so precede mechanical events P wave precedes atrial contraction QRS complex precedes ventricular contraction T wave precedes ventricular relaxation

Volume of blood pumped by each ventricle per minute  Cardiac output = CO = SV  HR  Average CO = 5 litres/min at rest  Average blood volume = 5.5 litres

 Regulate heart rate and stroke volume  Extrinsic and intrinsic regulation Extrinsic—neural and hormonal Intrinsic—autoregulation

 SA node intrinsic firing rate = 100/min No extrinsic control on heart, HR = 100  SA node under control of ANS and hormones Rest: parasympathetic dominates, HR = 75 Excitement: sympathetic takes over, HR increases

Primary factors affecting stroke volume  Ventricular contractility  End-diastolic volume  After-load

 Ventricles never completely empty of blood More forceful contraction will expel more blood  Extrinsic controls of SV Sympathetic drive to ventricular muscle fibres Hormonal control  Intrinsic controls of SV Changes in EDV

 Sympathetic innervation of contractile cells Increases cardiac contractility  Parasympathetic innervation of contractile cells Not significant  Hormones Thyroid hormones, insulin, and glucagon increase force of contraction

 Increased EDV stretches muscle fibres  fibres closer to optimum length  Optimum length = greater strength of contraction  Result = increased SV

Increase venous return Increase strength of contraction Increase stroke volume

 End-diastolic pressure = preload Filling time Atrial pressure Central venous pressure  After-load = pressure in aorta during ejection

FACTORS AFFECTING STROKE VOLUME

FACTORS AFFECTING CARDIAC OUTPUT

 Structure of heart  4 chambers  4 sets of valves  Key blood vessels  Blood flow and vessels  Systemic and pulmonary circuit  Arteries, arterioles, capillaries, venules, veins  Electrical conduction system and activity  ECG waves

 Cardiac cycle  4 phases  Systole and diastole  Pressure differences and consequences  Ventricular volume (SV, ESV and EDV)  Cardiac output (CO)  Regulation of CO  Affecting factors