Cardiovascular System Physiology.pdf

Cardiac Muscles Asst. Prof. Dr. İLKNUR DURSUN Istinye University, Faculty of Medicine, Department of Physiology Structure of Cardiac Tissue Located only in heart Cardiac muscle cells are small One centrally located nucleus Short broad T-tubules Dependent on aerobic metabolism Intercalated discs wher...

Cardiac Muscles Asst. Prof. Dr. İLKNUR DURSUN Istinye University, Faculty of Medicine, Department of Physiology Structure of Cardiac Tissue Located only in heart Cardiac muscle cells are small One centrally located nucleus Short broad T-tubules Dependent on aerobic metabolism Intercalated discs where membranes contact one another Characteristics of Cardiocytes Unlike skeletal muscle, cardiac muscle cells (cardiocytes): – are small – have a single nucleus – have short, wide T tubules Characteristics of Cardiocytes – – – – have no triads have SR with no terminal cisternae are aerobic (high in myoglobin, mitochondria) have intercalated discs Cardiac Muscle Tissue Intercalated Discs Are specialized contact points between cardiocytes Join cell membranes of adjacent cardiocytes (gap junctions, desmosomes) Functions of Intercalated Discs Maintain structure Enhance molecular and electrical connections Conduct action potentials Coordination of Cardiocytes Because intercalated discs link heart cells mechanically, chemically, and electrically, the heart functions like a single, fused mass of cells Cardiac and smooth muscles are: a. Involuntary b. Regulated by autonomic nervous system c. Like skeletal muscle, contraction is due to myosin/actin cross bridges stimulated by calcium Cardiac Muscle Striated Myosin and actin filaments form sarcomeres. Contraction occurs by means of sliding thin filaments. Unlike skeletal muscle fibers, these fibers are short, branched, and connected via gap junctions called intercalated discs (electrical synapses that permit impulses to be conducted cell to cell). Myocardium a. A myocardium is a mass of cardiac muscle cells connected to each other via gap junctions. b. Action potentials that occur at any cell in a myocardium can stimulate all the cells in the myocardium. c. It behaves as a single functional unit. d. The atria of the heart compose one myocardium, and the ventricles of the heart compose another myocardium. Pacemaker Potential a. Cardiac muscle can produce action potentials automatically (without innervation). 1) Begin in a region called the pacemaker b. Heart rate is influenced by autonomic innervation and hormones. Calcium Channels a. Unlike skeletal muscle, the voltage-gated calcium channels are not directly connected to calcium channels in the SR. b. Instead, calcium acts as a second messenger to open SR channels. c. Called calcium-induced calcium release d. Excitation-contraction coupling is slower. Functions Of Cardiac Tissue 1. Automaticity: – contraction without neural stimulation – controlled by pacemaker cells 2. Variable contraction tension: – controlled by nervous system 3. Extended contraction time 4. Prevention of wave summation and tetanic contractions by cell membranes Functions of the Circulatory System 1. Transportation a. Respiratory gases, nutrients, and wastes 2. Regulation a. Hormonal and temperature 3. Protection a. Clotting and immunity Major Components of the Circulatory System 1. Cardiovascular system a. Heart: four-chambered pump b. Blood vessels: arteries, arterioles, capillaries, venules, and veins 2. Lymphatic system a. Lymphatic vessels, lymphoid tissues, lymphatic organs (spleen, thymus, tonsils, lymph nodes) Structure of the Heart 1. Four chambers a. b. c. d. Right atrium: receives deoxygenated blood from the body Left atrium: receives oxygenated blood from the lungs Right ventricle: pumps deoxygenated blood to the lungs Left ventricle: pumps oxygenated blood to the body Pulmonary and Systemic Circulations 1. Pulmonary: between heart and lungs a. Blood pumps to lungs via pulmonary arteries. b. Blood returns to heart via pulmonary veins. 2. Systemic: between heart and body tissues a. Blood pumps to body tissues via aorta. b. Blood returns to heart via superior and inferior venae cavae. Pulmonary and Systemic Circulations Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Superior vena cava Right atrium Left atrium O2 Pulmonary artery CO2 Pulmonary vein Capillaries Lung O2 O2 CO2 CO2 Tricuspid valve Right ventricle Inferior vena cava Aortic semilunar valve O2 Bicuspid valve Left ventricle Aorta CO2 Capillaries Tissue cells Atrioventricular & Semilunar Valves 1. Atrioventricular (AV) valves: located between the atria and the ventricles a. Tricuspid: between right atrium and ventricle b. Bicuspid or mitral: between left atrium and ventricle c. Papillary muscles and chordae tendineae prevent the valves from everting 2. Semilunar valves: located between the ventricles and arteries leaving the heart a. Pulmonary: between right ventricle and pulmonary trunk b. Aortic: between left ventricle and aorta Valves of the Heart Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Pulmonary semilunar valve Aortic semilunar valve Bicuspid valve (into left ventricle) Tricuspid valve (into right ventricle) (a) Aorta Superior vena cava Right atrium Tricuspid valve Papillary muscles Inferior vena cava (b) Pulmonary trunk Pulmonary semilunar valve Left atrium Mitral (bicuspid) valve Chordae tendineae Interventricular septum Heart Sounds 1. Produced by closing valves a. “Lub” = closing of AV valves; occurs at ventricular systole b. “Dub” = closing of semilunar valves; occurs at ventricular diastole Stethoscope Positions for Heart Sounds Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Aortic area Pulmonic area Nipple Tricuspid area Bicuspid (mitral) area Cardiac cycle 1. Cardiac cycle a. Repeating pattern of contraction and relaxation of the heart. b. Systole: contraction of heart muscles c. Diastole: relaxation of heart muscles 2. End-diastolic volume – total volume of blood in the ventricles at the end of diastole 3. End-systolic volume – the amount of blood left in the left ventricle after systole (1/3 of the end-diastolic volume) Cardiac Cycle Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Systole 0.3 sec Atria contract Diastole 0.5 sec Atria are relaxed Pressure Changes During the Cardiac Cycle 1. 2. 3. 4. 5. 6. Ventricles begin contraction, pressure rises, and AV valves close (lub); isovolumetric contraction Pressure builds, semilunar valves open, and blood is ejected into arteries. Pressure in ventricles falls; semilunar valves close (dub); isovolumetric relaxation Dicrotic notch – slight inflection in pressure during isovolumetric relaxation Pressure in ventricles falls below that of atria, and AV valve opens. Ventricles fill. Atria contract, sending last of blood to ventricles Cardiac Cycle and Pressures Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1 Isovolumetric contraction Atria relaxed 0 0.2 Time (seconds) 0.4 0.6 0.8 Systole Ventricles contract 120 2 Artery Pressure (mmHg) 100 Ejection Atria relaxed 80 Pressure changes 60 Ventricles contract 40 3 20 120 Atria relaxed Left ventricle 0 Volume (ml) AV valves closed Systole Diastole 1 5 Ventricles relaxed 4 80 2 Volume changes 2nd Rapid filling Atria relaxed 40 1st 3rd Semilunar valves closed 4 3 Heart sounds Isovolumetric relaxtion Diastole Ventricles relaxed 5 Atria contract Ventricles relaxed Atrial contraction Figure 15.6 SYSTEMIC CIRCULATION PRESSURES Pressure waves created by ventricular contraction travel into the blood vessels. Pressure in the arterial side of the circulation cycles but the pressure waves diminish in amplitude with distance and disappear at the capillaries. Systolic pressure 120 Pressure (mm Hg) 1. Pulse pressure 100 80 60 40 Diastolic pressure Mean arterial pressure 20 Left Arteries Arterioles Capillaries ventricle Venules, veins Right atrium Blood Pressure 1. 2. 3. Pulse pressure = systolic P - diastolic P Valves ensure one-way flow in veins MAP = diastolic P + 1/3(systolic P - diastolic P) SPHYGMOMANOMETRY Arterial blood pressure is measured with a sphygmomanometer (an inflatable cuff plus a pressure gauge) and a stethoscope. The inflation pressure shown is for a person whose blood pressure is 120/80. Cuff pressure > 120 mm Hg When the cuff is inflated so that it stops arterial blood flow, no sound can be heard through a stethoscope placed over the brachial artery distal to the cuff. Cuff pressure between 80 and 120 mm Hg Korotkoff sounds are created by pulsatile blood flow through the compressed artery. Cuff pressure < 80 mm Hg Blood flow is silent when the artery is no longer compressed. Inflatable cuff Pressure gauge Stethoscope Electrical Activity of the Heart and the Electrocardiogram 1. 2. 3. 4. Cardiac muscle cells are interconnected by gap junctions called intercalated discs. Once stimulation is applied, the impulse flows from cell to cell. The area of the heart that contracts from one stimulation event is called a myocardium or functional syncytium. The atria and ventricles are separated electrically by the fibrous skeleton. Electrical Activity of the Heart 1. 2. 3. Automaticity – automatic nature of the heartbeat Sinoatrial node (SA node) - “pacemaker”; located in right atrium AV node and Purkinje fibers are secondary pacemakers of ectopic pacemakers; slower rate than the “sinus rhythm” Pacemaker potential a. b. c. A slow, spontaneous depolarization; also called diastolic depolarization – between heartbeats, triggered by hyperpolarization At −40mV, voltage-gated Ca2+ channels open, triggering action potential and contraction. Repolarization occurs with the opening of voltage-gated K+ channels. Pacemaker potential d. Pacemaker cells in the sinoatrial node depolarize spontaneously, but the rate at which they do so can be modulated: 1) Epinephrine and norepinephrine increase the production of cAMP, which keeps cardiac pacemaker channels open. a) Called HCN channels – hyperpolarization-activated cyclic nucleotide-gated channels b) Speeds heart rate due to Na+ inflow 2) Parasympathetic neurons secrete acetylcholine, which opens K+ channels to slow the heart rate. Myocardial action potentials a. b. c. Cardiac muscle cells have a resting potential of −85mV. They are depolarized to threshold by action potentials from the SA node. Voltage-gated Na+ channels (fast Na+) open, and membrane potential plateaus at -15mV for 200−300 msec. 1) Due to balance between slow influx of Ca2+ and efflux of K+ d. More K+ are opened, and repolarization occurs. e. Long plateau prevents summation and tetanus Action Potential in a Myocardial Cell Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. + 20 Ca2+ In (slow) Millivolts 0 – 20 – 40 Na+ In K+ Out – 60 – 80 – 100 0 50 100 150 200 250 300 350 400 Milliseconds Conducting tissues of the heart a. Action potentials spread via intercalated discs (gap junctions). b. SA node to AV node to stimulate atrial contraction c. AV node at base of right atrium and bundle of His conduct stimulation to ventricles. d. In the interventricular septum, the bundle of His divides into right and left bundle branches. e. Branch bundles become Purkinje fibers, which stimulate ventricular contraction. Conduction System of the Heart Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Interatrial septum Sinoatrial node (SA node) Right and left bundle branches Atrioventricular node (AV node) Atrioventricular bundle (bundle of His) Purkinje fibers Apex of heart Interventricular septum Conduction of Impulses a. Action potentials from the SA node spread rapidly 1) 0.8–1.0 meters/second b. At the AV node, things slow down. 1) 0.03−0.05 m/sec 2) This accounts for half of the time delay between atrial and ventricular contraction. c. The speed picks up in the bundle of His, reaching 5 m/sec in the Purkinje fibers. d. Ventricles contract 0.1–0.2 seconds after atria. 1. Figure 14.9 EC COUPLING IN CARDIAC MUSCLE This figure shows the cellular events leading to contraction and relaxation in a cardiac contractile cell. Ca2+ ECF 3 Na+ 2 K+ ATP ICF 3 Na+ RyR SR Ca2+ L-type Ca2+ channel Action potential enters from adjacent cell. Ca2+ Voltage-gated Ca2+ channels open. Ca2+ enters cell. NCX Ca2+ Ca2+ induces Ca2+ release through ryanodine receptor-channels (RyR). Sarcoplasmic reticulum (SR) Local release causes Ca2+ spark. Ca2+ stores ATP Ca2+ sparks Summed Ca2+ sparks create a Ca2+ signal. T-tubule Ca2+ ions bind to troponin to initiate contraction. Ca2+ signal Ca2+ Ca2+ Actin Relaxation occurs when Ca2+ unbinds from troponin. Ca2+ is pumped back into the sarcoplasmic reticulum for storage. Contraction Relaxation FIGURE QUESTION Using the numbered steps, compare the events shown to EC coupling in skeletal and smooth muscle [see Figs. 12.10 and 12.26]. Myosin Ca2+ is exchanged with Na+ by the NCX antiporter. Na+ gradient is maintained by the NA+-K+-ATPase. Repolarization a. Ca2+ concentration in cytoplasm reduced by active transport back into the SR and extrusion of Ca2+ through the plasma membrane by the Na+-Ca2+ exchanger b. Myocardium relaxes Correlation of myocardial action potential with myocardial contraction – refractory periods Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Action potential +20 Contraction (measured by tension developed) 0 Millivolts –20 Relative refractory period –40 Absolute refractory period –60 –80 A B –100 0 50 100 150 200 Milliseconds 250 300 Electrocardiogram (ECG or EKG) The electrocardiograph records the electrical activity of the heart by picking up the movement of ions in body tissues in response to this activity. a. Does not record action potentials, but results from waves of depolarization b. Does not record contraction or relaxation, but the electrical events leading to contraction and relaxation Electrocardiogram waves and intervals § § § § § P wave - atrial depolarization P-Q interval – atrial systole QRS wave - ventricular depolarization S-T segment - plateau phase, ventricular systole T wave - ventricular repolarization Electrocardiogram Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. R Atria Ventricles contract contract S–T segment ECG T P Q S P–R interval S–T interval QRS complex (a) Action potential of myocardial cell in ventricles (b) Membrane poteential (mV) P–Q segment Poteential (mV) R R +1 T P 0 Q +20 –90 S Relationship between impulse conduction and ECG Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. R Q S (a) (e) QRS complex: Ventricles depolarize and contract (b) (f) T P (g) T wave: Ventricles repolarize and relax (c) P wave: Atria depolarize and contract Depolarization Repolarization (d) ECG, Pressures and Heart Sounds Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 0 0.2 Time (seconds) 0.4 0.6 0.8 Pressure in ventricle (mmHg) 120 100 1. Intraventricular pressure rises as ventricles contract 80 60 2. Intraventricular pressure falls as ventricles contract 40 20 0 Systole ECG Diastole R T P P Q Q S Heart sounds 1. AV valves close S1 S2 2. Semilunar valves close Vessels 1. Types of blood vessels a. Arteries b. Arterioles c. Capillaries d. Venules e. Veins The Structure of Blood Vessels Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Venous Circuit Arterial Circuit Large vein Tunica externa Large artery Tunica externa Tunica media Tunica media Tunica interna Endothelium Endothelium Elastic layer Lumen Inferior vena cava Aorta Medium-sized vein Medium-sized artery Tunica externa Tunica externa Tunica media Tunica media Tunica interna Tunica interna Valve Arteriole Venule Tunica externa Endothelium Endothelium Lumen Valve Precapillary sphincter Fenestrated capillary Endothelial cells Capillary pores Basement membrane Continuous capillary Tunica interna Arteries 1. 2. 3. Elastic arteries: closer to the heart; allow stretch as blood is pumped into them and recoil when ventricles relax Muscular arteries: farther from the heart; have more smooth muscle in proportion to diameter; also have more resistance due to smaller lumina Arterioles: 20−30 µm in diameter; provide the greatest resistance; control blood flow through the capillaries Capillaries 1. 2. 3. 4. Smallest blood vessel: 7−10 µm in diameter Single layer of simple squamous epithelium tissue in wall Where gases and nutrients are exchanged between the blood and tissues Blood flow to capillaries is regulated by: a. Vasoconstriction and vasodilation of arterioles b. Precapillary sphincters Types of Capillaries a. Continuous capillaries: Adjacent cells are close together; found in muscles, adipose tissue, and central nervous system (add to bloodbrain barrier) b. Fenestrated capillaries: have pores in vessel wall; found in kidneys, intestines, and endocrine glands c. Discontinuous: have gaps between cells; found in bone marrow, liver, and spleen; allow the passage of proteins Microcirculation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Blood flow Arteriole Precapillary sphincter Metarteriole (forming arteriovenous shunt) Artery Blood flow Venule Vein Capillaries Net Filtration Pressure (NFP) EDEMA 1. Edema refers to the presence of excess fluid in the body tissues. In most instances, edema occurs mainly in the extracellular fluid compartment, but it can involve intracellular fluid as well. Intracellular Edema 1. Two conditions are especially prone to cause intracellular swelling: 1) depression of the metabolic systems of the tissues, and 2) lack of adequate nutrition to the cells. Extracellular Edema 1. Extracellular fluid edema occurs when there is excess fluid accumulation in the extracellular spaces. 2. There are two general causes of extracellular edema: 1) abnormal leakage of fluid from the plasma to the interstitial spaces across the capillaries, and 2) failure of the lymphatics to return fluid from the interstitium back into the blood. Lymphatic Blockage Causes Edema 1. When lymphatic blockage occurs, edema can become especially severe because plasma proteins that leak into the interstitium have no other way to be removed. 2. The rise in protein concentration raises the colloid osmotic pressure of the interstitial fluid, which draws even more fluid out of the capillaries. 3. Lymphedema- failure of the lymph vessels to return fluid and protein to the blood Summary of Causes of Extracellular Edema I. Increased capillary pressure C. Decreased arteriolar resistance 1. Excessive body heat A. Excessive kidney retention of salt and water 1. Acute or chronic kidney failure 2. Insufficiency of 2. Mineralocorticoid excess sympathetic nervous system B. High venous pressure and venous 3. Vasodilator drugs constriction 1. Heart failure 2. Venous obstruction 3. Failure of venous pumps (a) Paralysis of muscles (b) Immobilization of parts of the body (c) Failure of venous valves Summary of Causes of Extracellular Edema II. Decreased plasma proteins A. Loss of proteins in urine (nephrotic syndrome) B. Loss of protein from denuded skin areas 1. Burns 2. Wounds C. Failure to produce proteins 1. Liver disease (e.g., cirrhosis) 2. Serious protein or caloric malnutrition Summary of Causes of Extracellular Edema III. Increased capillary permeability A. Immune reactions that cause release of histamine and other immune products B. Toxins C. Bacterial infections D. Vitamin deficiency, especially vitamin C E. Prolonged ischemia F. Burns Summary of Causes of Extracellular Edema IV. Blockage of lymph return A. Cancer B. Infections (e.g., filaria nematodes) C. Surgery D. Congenital absence or abnormality of lymphatic vessels Veins 1. 2. 3. 4. 5. 6. 7. Most of the total blood volume is in veins Lower pressure (2 mmHg compared to 100 mmHg average arterial pressure) Thinner walls than arteries, larger lumen; collapse when cut Need help to return blood to the heart: Skeletal muscle pumps: Muscles surrounding the veins help pump blood. Venous valves: Ensure one-directional flow of blood Breathing: Flattening of the diaphragm at inhalation increases abdominal cavity pressure in relation to thoracic pressure and moves blood toward heart. The action of one-way venous valves Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. To heart Valve open Contracted skeletal muscles To heart Valve closed Vein Relaxed skeletal muscles Valve closed Vein Functions of the Lymphatic System 1. 2. 3. Transports excess interstitial fluid (lymph) from tissues to the veins Produces and houses lymphocytes for the immune response Transports absorbed fats from intestines to blood Relation between circulatory & lymphatic systems Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lymph flow Lymphatic capillaries Pulmonary capillary network Lymph node Lymphatic vessels Lymph node Blood flow Systemic capillary network Lymphatic capillaries Vessels of the Lymphatic System 1. Lymphatic capillaries: smallest; found within most organs a. Interstitial fluids, proteins, microorganisms, and fats can enter. 2. Lymph ducts: formed from merging capillaries a. Similar in structure to veins b. Lymph is filtered through lymph nodes 3. Thoracic trunk and right lymphatic trunk a. From merging lymphatic ducts b. Deliver lymph into right and left subclavian veins Relation between blood & lymphatic capillaries Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Interstitial space Lymph capillary Capillary bed Tissue cells Venule Lymph duct Arteriole Organs of the Lymphatic System 1. 2. Tonsils, thymus, spleen Sites for lymphocyte production Organs of the Lymphatic System Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Adenoid Tonsil Left subclavian vein Thymus Cervical lymph nodes Right lymphatic duct Right subclavian vein Axillary lymph nodes Thoracic duct Spleen Bone marrow Lymphatics of mammary gland Cisterna chyli Mesenteric lymph nodes and Peyer’s patches Lymph node Inguinal lymph nodes