Cardiovascular System Part I PDF

Alice YIP Topics  Overview of Cardio-vascular ( Circulatory ) System  Function of Heart  Function of Circulatory System  Function of Blood and Blood Vessels Overview  Cardio-vascular System is named as Circulatory System  Cardio means heart  Vascular refers to blood vessels  This blood cir...

Alice YIP Topics  Overview of Cardio-vascular ( Circulatory ) System  Function of Heart  Function of Circulatory System  Function of Blood and Blood Vessels Overview  Cardio-vascular System is named as Circulatory System  Cardio means heart  Vascular refers to blood vessels  This blood circulation system is crucial to move blood throughout the body and keeps the organs, muscles and tissues healthy and working to keep you alive Overview Main functions of the Circulatory System  Transport nutrients, hormones, electrolytes, oxygen and carbon dioxide  Maintain constant body temperature and fluid balance within the body  Removes metabolic waste to excretory organs for disposal  Protects the body against disease and infection  Clotting stops bleeding after injury Overview  The Cardio-vascular System composed of a heart which pumps blood through a closed system of blood vessels  The Heart is composed mostly of cardiac muscle, or myocardium. With each heart beat, the heart sends blood through the system to the body  A group of blood vessels work with the heart and lungs to continuously circulate blood through the body and thus taking the role in helping the body meet the demands of activity, exercise and stress and maintain the body temperature as well Overview  One Heart  Two closed Circulations of blood  Systemic circulations  Pulmonary circulations  Three types of Blood Vessels  Arteries  Veins  Capillaries  Four chambers and valves in the heart  Right Atrium and Right Ventricle with the tricuspid valve  Left Atrium and Left Ventricle with the mitral valve  Aortic valve and pulmonary valve Heart Heart  Hollow, cone shaped muscular pump  Varies with body size, usually 14 cm long and 9 cm wide in adult  Bordered laterally by the lungs, posteriorly by the vertebral column and anteriorly by the sternum  Heart wall composed of epicardium, myocardium and endocardium within which there has its own blood supply (mainly coronary arteries )  The flow of the blood throughout the body is produced by pressures created by the pumping action of the heart. Heart ( side and top view) Anatomy of the Heart ( side view) Heart  Blood supply to the heart by Cardiac veins which drain into a single large vein of Coronary sinus and empties the deoxygenated blood into the right atrium  Blood flow through heart from right to left ventricles  Blood being pumped through the heart chambers does not exchange nutrients and metabolic end products with the myocardial cells Cardiac Cycle  Heart actions :  Atria contract (atrial systole) whilst ventricles relax ( ventricle diastole)  Ventricle contract ( ventricle systole )whilst atria relax (atrial diastole)  Divisions of the cardiac cycle:  Systole is the period of ventricular contraction and blood ejection  Diastole is the alternating period of ventricular relaxation and blood filling  Heart rate of 72 beats/min, each cardiac cycle lasts approximately 0.8 sec, with 0.3 sec in systole and 0.5 sec in diastole. Cardiac Cycle Arrows indicate the flow of pressure. Valves kept to closed to prevent backward flow of blood during isovolumetric ventricular contraction and relaxation. Cardiac Cycle  Duration of cardiac cycle if the reciprocal of the heart rate  Heart Rate Cardiac Cycle  Heart beating at a very fast rate does not remain relaxed long enough to allow complete filling of cardiac chambers before the next contraction  The surge of blood entering the arterial system can be felt as a pulse in an artery that runs close to the body https://en.wikipedia.org/wiki/Cardiac_cycle https://en.wikipedia.org/wiki/Cardiac_cycle#/media/File:07_Hegasy_Cardiac_Cycle_Wiki_EN_CCBYSA.png Heart Sound  Two heart sounds resulting from cardiac contraction are normally heard through a stethoscope placed on the chest wall.  These sounds, which result from vibrations caused by the closing valves, are normal.  But other sounds, known as heart murmurs, can be a sign of heart disease.  Murmurs can be produced by heart defects that cause blood flow to be turbulent. Heart Sound  Laminar flow : by blood flowing through valves and vessels in smooth concentric layers  Turbulent flow ( result in Murmur ) : by blood flowing rapidly in the usual direction through an abnormally narrowed valve (stenosis); by blood flowing backward through a damaged, leaky valve (insufficiency); or by blood flowing between the two atria or two ventricles through a small hole in the wall separating them (called a septal defect). Blood Circulation  Blood flow is always from a region of higher pressure to one of lower pressure.  The pressure exerted by any fluid is called a hydrostatic pressure  Resistance is the measure of the friction that impedes flow between two points.  Flow rate is directly proportional to the pressure difference between two points and inversely proportional to the resistance Flow Rate Flow Rate = Pressure Difference / Resistance Flow rate is directly proportional to the pressure difference between two points and inversely proportional to the resistance. Calculation of Resistance: 90 mmHg ÷ 10 mL/min = 9 mmHg/mL/min  Resistance Resistance is determined by 1) Viscosity ( Dehydration; Anemia) 2) Length of the Vessel ( Constant) 3) Radius of the Vessel (Varied ) Resistance is directly proportional to both the fluid viscosity and the vessel’s length, and inversely proportional to the fourth power of the vessel’s radius. Cardiac Output  Cardiac output is the volume of blood each ventricle pumps as a function of time, usually expressed in liters per minute  The cardiac output can be calculated by multiplying the heart rate (HR)—the number of beats per minute—and the stroke volume (SV)—the blood volume ejected by each ventricle with each beat: CO = HR × SV  Heart rate and stroke volume do not always change in the same direction.  For example, stroke volume decreases following blood loss, whereas heart rate increases. These changes produce opposing effects on cardiac output. Heart  The heart receives a rich supply of 1) sympathetic and 2) parasympathetic nerve fibers  The sympathetic postganglionic fibers innervate the entire heart and release norepinephrine, whereas the parasympathetic fibers terminate mainly on special cells found in the atria and release primarily acetylcholine. Heart Autonomic innervation of heart. Neurons shown represent postganglionic neurons in the pathways. M = muscarinic-type acetylcholine receptor; β = beta- adrenergic receptor. Control of Heart Rate  Heart rate is controlled by the autonomic ( involuntary ) nervous systems : Sympathetic and Parasympathetic nervous systems  Sympathetic one releases the hormones ( catecholamines- epinephrine and norepinephrine ) to accelerate the heart rate  Parasympathetic one releases the neurotransmitter acetylcholine to decrease the heart rate Stroke Volume  Volume of blood pumped out of the left ventricle of the heart during each systolic cardiac contraction  Normal SV is the difference between end-diastolic and end-systolic volumes and is the volume ejected with each heart beat  Normal range is about 50-100 ml Control of Stroke Volume Changes in the force during ejection of the stroke volume can be produced by (1) changes in the end-diastolic volume (the volume of blood in the ventricles just before contraction(preload); (2) changes in the magnitude of sympathetic nervous system input to the ventricles; and (3) changes in the arterial pressures against which the ventricles pump (afterload ). Cardiac Conducting System  Rest  Sinoatrial node (SA node )  SA node generate the impulse ( ~75 times / mins – heart rate )  Atrioventricular node ( AV node )  The impulse pause at the AV node and allow atria to complete pumping blood  Atrioventricular bundle ( Bundle of His )  Connect the atria to the ventricle  Right and left bundle branches  Conduct the impulses through the interventricular septum  Subendocardial conducting network ( Purkinje fibers )  Depolarize the contractile cells of both ventricles ( ventricular contraction begins ) Heart  The electrocardiogram is a tool for checking the heart’s rhythm and electrical activity.(ECG )  Sensors attached to the skin are used to detect the electrical signals produced by the heart each time it beats  Atrial fibrillation, cardiovascular disease, heart valve disease, thickening of heart walls and pericardial effusion can be revealed by abnormal ECG  But ECG is of limited diagnostic value as the defect cannot be detected if something is wrong with the heart’s mechanical activity Placement of electrodes in electro cardiography Each of the 12 leads uses a different combination of reference (negative pole) and recording (positive pole) electrodes, thus providing different angles for ‘viewing’ the electrical activity of the heart Placement of electrodes in electro cardiography  ECG comprises recordings made from 6 pericardial electrodes ( V1-V6) with 6 different pairings from 3 limb electrodes ( Left arm, Right arm amd Left leg )  Right leg electrode is used as reference  There are Ambulatory ECG monitoring and Exercise ECG Normal ECG  P wave indicates the first electrical signal originated from the atrial depolarization  The PR interval represents the short physiological delay as the AV node slows the electrical depolarization before it proceeds to the ventricles  Depolarization of the ventricles results in QRS complex  Q wave is the first initial downward or negative deflection  R wave is the next upward deflection  S wave is then the next deflection downwards provided it crosses the isoelectric line to become briefly negative before returning to the isoelectric baseline  T wave show the electrical signal reflecting ventricular repolarization  Sequence of cardiac excitation The yellow color denotes areas that are depolarized. The electrocardiogram monitors the spread of the signals. Absolute Refractory Period of Heart  Occur during and following an action potential when an excitable membrane cannot be re- excited  Incapable of undergoing summation of contractions  Function as a pump ventricles can only filled up while they are relaxed Relationship between membrane potential changes and contraction in a ventricular muscle cell​ Properties of cardiac ion channels Heart Rhythm. 2010 Jan;7(1):117-26.  Selectivity: they are only permeable to a single type of ion based on their physical configuration.  Voltage-sensitive gating: a specific TMP range is required for a particular channel to be in open configuration; at all TMPs outside this range, the channel will be closed and impermeable to ions. Therefore, specific channels open and close as the TMP changes during cell depolarization and repolarization, allowing the passage of different ions at different times.  Time-dependence: some ion channels (importantly, fast Na+ channels) are configured to close a fraction of a second after opening; they cannot be opened again until the TMP is back to resting levels, thereby preventing further excessive influx. Action potential in cardiomyocytes ( 0-4 phases) Phase 4: The resting phase  −90 mV due to a constant outward leak of K+ through inward rectifier channels.  Na+ and Ca2+ channels are closed at resting TMP. Phase 0: Depolarization  An action potential triggered in a pacemaker cell causes the TMP to rise above −90 mV.  Na+ leaks into the cell, further raising the TMP to −70mV, and then rapidly depolarizes the TMP to 0 mV and slightly above 0 mV for a transient period of time called the overshoot  Ca2+ channels open when the TMP is greater than −40 mV and cause a small but steady influx of Ca2+ down its concentration gradient. Action potential in cardiomyocytes ( 0- 4 phases) Phase 1: Early repolarization  TMP is now slightly positive.  Some K+ channels open with an outward flow of K+ and returns the TMP to approximately 0 mV. Phase 2: The plateau phase  Ca2+ channels are still open and there is a small, constant inward current of Ca2+. This becomes significant in the excitation-contraction coupling process.  K+ leaks out down its concentration gradient through delayed rectifier K+ channels.  These two countercurrents are electrically balanced, and the TMP is maintained at a plateau just below 0 mV throughout phase 2. Action potential in cardiomyocytes ( 0- 4 phases) Phase 3: Repolarization  Ca2+ channels are gradually inactivated.  Persistent outflow of K+, now exceeding Ca2+ inflow, brings TMP back towards resting potential of −90 mV to prepare the cell for a new cycle of depolarization.  Normal transmembrane ionic concentration gradients are restored by returning Na+ and Ca2+ ions to the extracellular environment, and K+ ions to the cell interior. The pumps involved include the sarcolemmal Na+-Ca2+ exchanger, Ca2+-ATPase and Na+-K+-ATPase. Refractory period in the cardiac cycle Blood Circulation Blood Circulation Two closed circuits of blood flow 1) ​Systemic Circulation – send O2 rich blood and nutrients to all body cells and remove wastes 2) Pulmonary Circulation – send O2 poor blood to lung and pick up O2 and unload CO2 Exception : blood in the pulmonary veins is oxygenated whereas blood in the pulmonary arteries is deoxygenated The systemic and pulmonary circulations Blood Circulation Pulmonary Circuits Systemic Circuits Deoxygenated blood come from the body Oxygenated blood send out from the in the systemic circulation to the right pulmonary circulation to the left atrium atrium and then the right ventricle via and then the left ventricle via the tricuspid valve and go to the lung in the bicuspid ( mitral ) valve and go to the pulmonary circulation the body in the systemic circulation Blood Circulation Three types of blood vessels  Arteries carry O2 rich blood away from the heart  Veins carry O2 poor blood from the tissue back to the heart  Capillaries are tiny blood vessels that connect veins and arteries Arteries  Thick, elastic for carrying blood away from heart to withstand the high blood pressure and control the diameter of vessels.  Varies in size and the largest one is the aorta which move further from the heart and branch off to smaller one and the smallest arteries are called arterioles  Arterioles then link up to the smallest blood vessels called capillaries Venules and Veins  Microscopic vessels that continue from capillaries and merge to form veins and carry blood to the heart via large veins of vena cava  Parallel to the network of arteries arterioles  Have thinner wall, less smooth muscle and less elastic connective tissue but larger lumens in diameter as compared with those of arteries and arterioles to reduce resistance but increase amount of blood flow  Have flaplike valves and function as blood reservoir Capillaries  Smallest diameter blood vessels  Connect smallest arterioles and smallest venules  Form semipermeable layer through which substances in the blood are exchanged for substances in the tissue fluid surrounding body cells  Supply in high density to those tissue of high metabolism in which abundant O2 and nutrients are required Effect of blood pressure, cross-sectional area and flow velocity on blood vessels Relationship between total cross-sectional area and flow velocity The extremely slow forward movement of blood through the capillaries maximizes the time for the exchange of substances across the capillary wall. Blood Pressure  The force that blood exerts against inner walls of the blood vessels ( commonly refer to the pressure in arteries )  Rises and falls in a pattern corresponding to the phases of cardiac cycle  Maximum pressure found during ventricular contraction, i.e. systolic pressure  Lowest pressure found when ventricles relax and arterial pressure drops before next ventricular contraction i.e. diastole pressure Blood Pressure  The contraction of the ventricles ejects blood into the arteries during systole.  A volume of blood equal to only about one-third of the stroke volume leaves the arteries during systole.  The rest of the stroke volume remains in the arteries during systole, distending them and increasing the arterial pressure.  When ventricular contraction ends, the stretched arterial walls recoil passively like a deflating balloon, and blood continues to be driven into the arterioles during diastole.  As blood leaves the arteries, the arterial volume and pressure slowly decrease.  The next ventricular contraction occurs while the artery walls are still stretched by the remaining blood. Blood Pressure  Movement of blood into and out of the arteries during the cardiac cycle.  The lengths of the arrows denote relative quantities flowing into and out of the arteries and remaining in the arteries. Blood Pressure  The equation relating pressure, flow, and resistance applies not only to flow through blood vessels but also to the flows into and out of the various chambers of the heart.  Measured by using sphygmomanometer, normal 120/80 mmHg  Influenced by cardiac output, blood volume, peripheral resistance and blood viscosity  Blood Pressure = Cardiac output x Peripheral Resistance Using Sphygmomanometer  Sounds are first heard when cuff pressure falls just below systolic pressure  Cease when cuff pressure falls below diastolic pressure.  The heart sounds are also known as Korotkoff’s sounds. Control of vasoconstriction and vasodilation in arterioles  Most arterioles are richly innervated by sympathetic postganglionic neurons which release norepinephrine to cause vasoconstriction.  Decreased rate of sympathetic activity can cause vasodilation  Skin : keep warm in vasoconstriction or help cool down in vasodilation  Kidney : allow more filtration during vasodilation  Brain : increase blood flow during vasodilation  Damage to arteriole walls makes them less able to dilate or constrict affecting both blood pressure and blood flow e.g. hypertension, smoking, high cholesterol, thrombosis, inflammation etc. Blood flow in capillaries  Capillary structure varies from organ to organ  A thin-walled tube of endothelial cells one layer thick resting on a basement membrane, without any surrounding smooth muscle or elastic tissue  Blood flow depends very much on the state of the other vessels that constitute the microcirculation Diagram of a capillary cross section Blood Flow in Capillaries  Velocity of blood flow is fast in the aorta, slows progressively in the arteries and arterioles, and then slows markedly in capillaries  Maximizes the time available for substances to exchange between the blood and interstitial fluid from the Lymphatic System  Three basic mechanisms allow substances to move between the interstitial fluid and the plasma: diffusion, vesicle transport, and bulk flow.  Velocity of blood progressively increases in the venules and veins because the cross-sectional area decreases. Blood Flow in Capillaries Cross-sectional area and velocity in the Diagram of microcirculation systemic circulation. Blood Blood Erythrocytes ( Red blood cells) The hematocrit is defined as the percentage of blood volume that is erythrocytes. Leucocytes (White blood cells) Involved in immune defenses Platelets Plasma It is composed of water ( >90%) dissolved with some plasma proteins ( albumin, globulin, fibrinogen), nutrients, metabolic waste products, hormones, and a variety of mineral electrolytes including Na+, K+, Cl−, and others. Measurement of the hematocrit by centrifugation Blood Production in Bone Marrow Multipotent uncommitted hematopoietic stem cell is differentiated into bone marrow lymphocyte precursor which then gives rise to lymphocytes and committed stem cells which are progenitor cells of different varieties which give rise to red blood cells, white blood cells and platelets along one path. Production of blood cells by the bone marrow Red blood cells  Concave shape of high surface area to volume ratio to facilitate gas exchange ( 7 μm )  Erythropoiesis ( Production of red cells ) controlled by a hormone called erythropoietin  Produced in red bone marrow with sufficient supply of Iron, Vitamin B12 and Folate  Contain a protein of haemoglobin to which O2 and CO2 reversibly combined  Young erythrocytes named as reticulocytes with few ribosomes  Life span is about 120 days Haemoglobin Consists of two parts: 1) Heme – contains Iron and transport O2 from the lung to the tissues and takes CO2 from the tissues to the lung 2) Globin – a protein of complex macromolecule that help to keep the haemoglobin liquefied Haemoglobin level drops in Anaemia which can be caused by blood loss, haemolysis, lack of red cell production, nutritional deficiencies or kidney disease Red Blood Cells White Blood Cells Function of various white blood cells Neutrophils Greatly produced and released from bone marrow during the course of an infection. Lymphocytes Comprised of T- and B-lymphocytes for protection against specific pathogens, including viruses, bacteria, toxins, and cancer cells. Monocytes Large phagocytes capable of engulfing viruses and bacteria. Eosinophils Act by releasing toxic chemicals that kill parasites Basophils Secrete an anticlotting factor called heparin at the site of an infection and also secrete histamine which attracts infection-fighting cells and proteins to the site White Blood Cells White Blood Cells Platelets  Colorless  Non-nucleated cell fragments that contain numerous granules  Much smaller than erythrocytes ( 2 to 4 μm)  Produced from megakaryocytes  Thrombocytosis ( Production of platelets) controlled by a hormone of thrombopoietin  Used for clot formation to stop bleeding Textbook  Widmaier, E.P., Raff, H., Strang, K.T. (2019) Vander’s Human Physiology: The mechanisms of body function, 15th Edition McGrawHill Education. Thank You O Lord, how great is the number of your works! in wisdom you have made them all; the earth is full of the things you have made. ( Psalms 104:24 )