Circulation of Blood Handout - PDF

1. Circulation of blood MD3001 Dr Alun Hughes 1 Cardiovascular physiology 1) 2) 3) 4) 5) 6) 7) 8) 9) Circulation of blood Physiological properties of the heart Cardiac contractility and the cardiac cycle Control of cardiac output Vasculature Microcirculation Control of blood pressure Control of...

1. Circulation of blood MD3001 Dr Alun Hughes 1 Cardiovascular physiology 1) 2) 3) 4) 5) 6) 7) 8) 9) Circulation of blood Physiological properties of the heart Cardiac contractility and the cardiac cycle Control of cardiac output Vasculature Microcirculation Control of blood pressure Control of blood volume Exercise and blood flow through special regions 2 Lecture overview Structure and function Regulation and integration The heart as a pump Features of cardiac muscle 3 Functions of the cardiovascular system Bulk flow of materials – – – – Gases Nutrients Hormones Waste Temperature regulation Homeostasis Host defense Reproduction Regulation and integration of the CVS Heart Autonomic nerves CNS Blood vessels Hormones, etc. Blood (volume) CNS integrates overall activity of CVS with the activity and functions of the respiratory and renal systems. Cardiovascular system Heart muscle – Wall of left ventricle more muscular than right Microcirculation – Arterioles, precapillary sphincters, capillaries, venules Parallel arrangement – Allows independent regulation of blood flow Guyton p158 12th ed, p170 13th ed Normal path of blood flow Pulmonary circulation and systemic circulation linked – At rest, ~5L/min Blood vessels vary – – – – – – In number In diameter In wall thickness In smooth muscle In elastic tissue In fibrous tissue All lined by endothelial cells Blood vessels Berne and Levy p290 Features of the microcirculation Arterioles – Smallest diameter muscular walled arteries Precapillary sphincters – Rings of smooth muscle which control entry of blood from arteriole into each capillary Capillaries – Smallest diameter blood vessel: simple tube, one cell thick, of flattened endothelial cells – Allows for diffusion of nutrients, waste etc in/out tissues Venules – Smallest diameter vessels which drain blood back to the larger true veins Blood flow around the body Ultimate function of the cardiovascular system is to ensure adequate blood flow through the capillaries of various organs – Almost all cells are within a few cell diameters of a capillary – ~10 billion capillaries, ~5L volume Parallel arrangement of vessels – Allows independent regulation of blood flow to different organs – Adapts to the metabolic demands of the tissues The heart as a pump Guyton p101 12th ed, p109 13th ed 11 Valves of the heart Valves open passively Atrioventricular (cuspid) valves – Tricuspid valve between right atrium and right ventricle – Bicuspid (mitral) valve between left atrium and left ventricle – Fairly ‘flimsy’ – Attached to chordae tendineae Guyton p167 12th ed, p116 13th ed. 12 Valves of the heart Valves open passively Semiluminar valves – Aortic valve between left ventricle and aorta – Pulmonary valve between right ventricle and pulmonary trunk – Both tricuspid – More ‘heavy duty’ – Smaller openings, higher pressure  more stress and physical abrasion Guyton p167 12th ed, p116 13th ed. 13 Echocardiography Cardiac muscle Cardiac muscle cells branch, and are connected together by desmosomes at the junction between cells (intercalated disks). Cardiac muscle cell Intercalated disk Nucleus These intercalated disks also contain gap junctions that directly connect the cytoplasm and permit the easy transfer of ions between cells. Guyton p102 12th ed, p110 13th ed 16 Cardiac muscle Features of cardiac muscle Striated – Similar to skeletal muscle – Thick and thin filaments of myosin and actin – Smaller fibers with individual nucleus Connected via intercalated discs – “Branching” of individual cells connected into a network Electrical connection through gap junctions – Allow passage of ions permitting action potentials to spread – Functional syncitium Desmosomes – Strong, cell-to-cell adhesion molecules – Junctional complexes Conduction in cardiac muscle Functional syncitium – Cells of atrial myocardium are all electrically connected – Depolarise and contract synchronously – Ventricles are similar but are a separate functional unit Conduction network – ~ 1% of cardiac fibers don’t contract, but form the excitatory and conductive muscle fibers “Pacemaker” activity – Sinoatrial node (SAN) is the intrinsic pacemaker – Other areas have pacemaker ability Autonomic innervation – Sympathetic nerves increase the rate of SAN depolarisation – Parasympathetic nerves decrease the rate of SAN depolarisation Main points Two pumps, two circuits Parallel arrangement aids distribution Capillaries are ultimately “where it’s at” Cardiac muscle is not skeletal muscle Galen is sometimes wrong 20 Learning outcomes To recognise the basic anatomy and the function of the major components of the CVS, including the heart (including valves), arteries, veins and microcirculation. To identify which body systems the CVS integrates with, and how secondary nervous and hormonal elements control the function of the CVS. To describe the normal distribution and flow of blood through the pulmonary and systemic circulations. To compare the features of myocardial muscle with skeletal muscle.