Week 9 - CVS Physiology Part 1 - PDF

Physiology of the Cardiovascular System (Part I) Dr. Rozlin Abd Rahman Learning Objectives: ▪ Describe the composition of blood. ▪ Describe the basic functions of the cardiovascular system. ▪ Explain the cardiac circulation. ▪ Describe the electrical conducting system of the heart ▪...

Physiology of the Cardiovascular System (Part I) Dr. Rozlin Abd Rahman Learning Objectives: ▪ Describe the composition of blood. ▪ Describe the basic functions of the cardiovascular system. ▪ Explain the cardiac circulation. ▪ Describe the electrical conducting system of the heart ▪ Explain the role of calcium in cardiac muscle contraction and relate with the action potential graph. ▪ Explain the ECG ▪ Describe the cardiac cycle, factors influencing the cardiac output, stroke volume and heart rate. Blood – Remarkable fluid  Components of Blood A type of connective tissue ❑ Red blood cells (erythrocytes) ❑ White blood cells (leukocytes ) ❑ Platelets-contains cell fragments ❑ Plasma - fluid part of blood (55% of blood) Blood Plasma Blood plasma is the liquid portion of blood. Consists of: ❑ Mostly water ❑ Nutrients ❑ Mixture of proteins ❑ Amino acids ❑ Albumins ❑ Glucose ❑ Globulins ❑ Nucleotides ❑ Fibrinogen ❑ Lipids ❑ Gases ❑ Electrolytes ❑ Waste products  Functions of blood Transportation Regulation Protection Red Blood Cells ❑ Transport oxygen throughout the body ❑ Are biconcave-shaped cells that are small enough to pass through capillaries ❑ Hemoglobin is a pigment found on RBCs ❑ Oxyhemoglobin carries oxygen and is bright red in color ❑ Deoxyhemoglobin does not carry oxygen and is a darker red color White Blood Cells Granulocytes Neutrophils – (55%) destroying bacteria, viruses, and toxins in the blood stream Eosinophils – (3%) getting rid of parasitic infections such as worm infections Basophils –(1%) control inflammation and allergic reactions Agranulocytes Monocytes – (8%) destroying bacteria, viruses, and toxins in blood Lymphocytes – (33%) immunity for the body Blood Platelets ❑Fragments of cells that are found in the blood stream ❑Thrombocytes are important in the clotting of blood ❑130,000 to 360,000 platelets per cubic millimeter of blood Controlling Bleeding ❑ Hemostasis - the stoppage of bleeding ❑ Three processes of hemostasis ❑ Blood vessel spasm ❑ Platelet plug formation ❑ Blood coagulation Blood – A picture of health  Blood Vessels Blood Vessels ❑ Arteries and Arterioles ❑ strongest of the blood vessels ❑ carry blood away from the heart easily and are under high pressure ❑ have thick walls ❑ Veins and Venules ❑ no pressure in veins - does not move very easily ❑ valves → prevent blood from flowing backwards Blood Vessels - Capillaries ❑Branches of arterioles ❑Connect arterioles to venules ❑Oxygen and nutrients can pass out of a capillary into a body cell ❑Carbon dioxide and other waste products can pass out of a body cell into a capillary  The Lymphatic System ❑ A network of connecting vessels that collect fluids between cells to the blood stream. ❑ Picks up lipids from the digestive organs and transports them to the blood stream ❑ Defend our bodies against disease- causing agents called pathogens The Lymphatic System ❑Lymph Nodes ❑Thymus ❑Spleen Lymph Fluid ❑Tissue fluid that has entered a lymphatic capillary ❑Contain valves that prevent the backflow of lymph Lymph Node Circulation of Blood ❑Circulation is the process ❑This system also of sending blood: circulates waste products ❑To the lungs to pick up to certain organ systems oxygen so these wastes can be ❑To the digestive system removed from the blood. to pick up nutrients ❑For delivery of oxygen and nutrients to all organ systems of the body Systemic and pulmonary circulation - 2 circuits in series ▪ Systemic circuit ▪ Left side of heart ▪ Receives blood from lungs ▪ Ejects blood into aorta ▪ Systemic arteries, arterioles ▪ Gas and nutrient exchange in systemic capillaries ▪ Systemic venules and veins lead back to right atrium ▪ Pulmonary circuit ▪ Right side of heart ▪ Receives blood from systemic circulation ▪ Ejects blood into pulmonary trunk then pulmonary arteries ▪ Gas exchange in pulmonary capillaries ▪ Pulmonary veins takes blood to left atrium  9. Systemic capillaries of head and upper limbs 4. 4. 10. 8. Pulmonary Pulmonary capillaries of capillaries of left lung right lung 3. 5. 6. 5. 1. Key: 7. Oxygen-rich blood Oxygen-poor blood 2. 10. 9. Systemic capillaries of trunk and lower limbs (a) Path of blood flow through heart Pulmonary circuit - from heart to lungs back to heart Systemic circuit - from heart to body back to heart  Coronary circulation – Coronary arteries branch from ascending aorta Anastomoses provide alternate routes or collateral circuits Allows heart muscle to receive sufficient oxygen even if an artery is partially blocked – Coronary capillaries – Coronary veins Collects in coronary sinus Empties into right atrium Heart : A special muscle Cardiac Muscle Characteristics ▪ Shorter and less circular than skeletal muscle fibers ▪ Branching gives “stair-step” appearance ▪ Usually one centrally located nucleus ▪ Ends of fibers connected by intercalated discs ▪ Discs contain desmosomes and gap junctions ▪ Contains many mitochondria (40%) ▪ Same arrangement of actin and myosin Autorhythmic Fibers ▪ Specialized cardiac muscle fibers ▪ Self-excitable ▪ Repeatedly generate action potentials → heart contractions ▪ 2 important functions: ▪ Act as pacemaker ▪ Form conduction system  Cardiac conduction system Frontal plane Left atrium Right atrium 1 SINOATRIAL (SA) NODE 2 ATRIOVENTRICULAR (AV) NODE 3 ATRIOVENTRICULAR (AV) BUNDLE (BUNDLE OF HIS) Left ventricle 4 RIGHT AND LEFT BUNDLE BRANCHES Right ventricle 5 PURKINJE FIBERS (a) Anterior view of frontal section Cardiac conduction system Action Potentials and Contraction Action potential initiated by SA node spreads out to excite “working” fibers called contractile fibers 1. Depolarization 2. Plateau 3. Repolarization Action Potential in a ventricular contractile fiber 2+ 22 Plateau (maintained depolarization) due to Ca inflow 2+ when voltage-gated slow Ca channels open and + 20 K+ outflow when some K+ channels open 0 –20 33 Repolarization due to closure of Ca2+ channels and K+ outflow Membrane –40 11 Rapid depolarization due to when additional voltage-gated potential (mV) Na+ inflow when voltage-gated K+ channels open – 60 fast Na+ channels open – 80 –100 0.3 sec Depolarization Repolarization Refractory period Contraction  Electrocardiogram (ECG) ▪ Composite record of action potentials produced by all the heart muscle fibers ▪ Compare tracings from different leads with one another and with normal records ▪ 3 recognizable waves ▪P, QRS, and T Key: R Atrial contraction Ventricular contraction PR S–T Segment segment Millivolts (mV) T P Q P–R interval S Q–T interval Seconds  ECG ❖ P wave → atrial depolarisation ❖ P-R interval → time for action potential travel from SA node – entering ventricles (AV node) ❖ P-R segment → AV node to bundle of His + Purkinje fibers ❖ QRS complex → rapid depolarisation of the ventricles, contraction ❖ T wave → repolarisation of ventricles. 1 Depolarization of 2 Atrial systole 3 Depolarization of ventricular atrial contractile (contraction) contractile fibers produces fibers produces P QRS complex wave R P P P Q Action potential S in SA node 4 Ventricular systole 5 Repolarization of 6 Ventricular diastole (contraction) ventricular contractile (relaxation) fibers produces T wave T P P P  R–R interval P–R interval (a) Normal electrocardiogram (ECG)  Irregular R–R intervals No detectable P waves (c) Atrial fibrillation  Ventricular tachycardia Ventricular fibrillation (d) Ventricular tachycardia (e) Ventricular fibrillation Cardiac Cycle  Cardiac Cycle ▪ The sequence of events as blood enters the atria, leaves the ventricles and then starts over ▪ In each cycle, atria and ventricles alternately contract and relax ▪ Atrial systole → ventricles are relaxed ▪ Ventricle systole → atria are relaxed The Cardiac Cycle Heart Sounds ▪ Auscultation ▪ Sound of heartbeat comes primarily from blood turbulence caused by closing of heart valves ▪ Only 2 loud enough to be heard ▪ ‘Lub’ – AV valves close ▪ ‘Dup’ – SL valves close  Cardiac Output (CO) ▪ CO = volume of blood ejected from left ventricle into aorta each minute ▪ CO = stroke volume (SV) x heart rate (HR) ▪ In typical resting male ▪ 5.25L/min = 70mL/beat x 75 beats/min ▪ Entire blood volume flows through pulmonary and systemic circuits each minute  Stroke Volume ▪ Amount of blood ejected from the ventricle with each ventricular systole. Regulation of SV Preload Contractility Afterload a) Factors affecting SV: Preload – Degree of stretch on the heart before it contracts – Greater preload increases the force of contraction – Frank-Starling law of the heart – the more the heart fills with blood during diastole, the greater the force of contraction during systole – Proportional to EDV – Determinant for EDV: Duration of ventricular diastole Venous return Preload determinants  b) Factors affecting SV: Contractility ▪ Strength of contraction at any given preload ▪ Positive inotropic agents increase contractility ▪ Often promote Ca2+ inflow during cardiac action potential ▪ Increases stroke volume ▪ Epinephrine, norepinephrine, digitalis ▪ Negative inotropic agents decrease contractility ▪ Anoxia, acidosis, some anesthetics, and increased K+ in interstitial fluid c) Factors affecting SV: Afterload ▪ Pressure that must be overcome before a semilunar valve can open ▪ Increase in afterload causes stroke volume to decrease ▪ Blood remains in ventricle at the end of systole ▪ Hypertension and atherosclerosis increase afterload  Question What effect does increase venous return have on stroke volume?  Regulation of Heart Beat ▪ Cardiac output depends on heart rate and stroke volume ▪ Filling time for ventricles insufficient at higher rates ▪ Autonomic nervous system and epinephrine/ norepinephrine most important Autonomic regulation ▪ Originates in cardiovascular center of medulla oblongata ▪ Increases or decreases frequency of nerve impulses in both sympathetic and parasympathetic branches of ANS o Sympathetic: fight or flight: HR, RR, BP, pupil dilation and bronchodilation o Parasympathetic: rest and digest Nervous System Control of the Heart  Question How would increased sympathetic stimulation of the heart affect stroke volume?  Chemical regulation of heart rate ▪ Hormones ▪ Epinephrine and norepinephrine increase heart rate and contractility ▪ Thyroid hormones also increase heart rate and contractility ▪ Cations ▪ Ionic imbalance can compromise pumping effectiveness ▪ Relative concentration of K+, Ca2+ and Na+ important  Positive inotropic agents such as increased sympathetic stimulation; catecholamines, glucagon, or thyroid Increased end-diastolic volume hormones in the blood; increased Ca2+ in Decreased arterial blood pressure (stretches the heart) extracellular fluid during diastole Increased PRELOAD Increased CONTRACTILITY Decreased AFTERLOAD Within limits, cardiac muscle fibers contract Positive inotropic agents increase force more forcefully with stretching (Frank–Starling of contraction at all physiological levels Semilunar valves open sooner when law of the heart) of stretch blood pressure in aorta and pulmonary artery is lower Increased STROKE VOLUME Increased CARDIAC OUTPUT Increased HEART RATE Catecholamine or thyroid hormones in Infants and senior citizens, females, Increased sympathetic stimulation and the blood; moderate increase in low physical fitness, increased body decreased parasympathetic stimulation extracellular Ca2+ temperature NERVOUS SYSTEM CHEMICALS OTHER FACTORS Cardiovascular center in medulla oblongata receives input from cerebral cortex, limbic system, proprioceptors, baroreceptors, and chemoreceptors Exercise and the Heart  The Significance of the Heart Truly in the body there is a morsel of flesh which, if it be sound, all the body is sound and which, if it be diseased, all of it is diseased. Truly it is the heart. [al-Bukhaari, Muslim]