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Human Biology Concepts and Current Issues Seventh Edition Michael D. Johnson 8 Heart and Blood Vessels © 2014 Pearson Education, Inc. Lecture Presentations by Robert J. Sullivan Marist College Blood Vessels Transport Blood Arteries – Carry blood away from the heart – Transport blood under high pressure – Thick-walled Capillaries – Exchange solutes and water with cells of the body – Microscopic Veins – Return blood to the heart – Thin-walled © 2014 Pearson Education, Inc. Figure 8.1 Direction of blood flow Outer layer: Connective tissue Middle layer: Smooth muscle with elastic fibers Vein Inner layer: Artery Endothelium Connective tissue Smooth muscle Endothelium Venule Arteriole Capillary Tissue cells © 2014 Pearson Education, Inc. Epithelial cells of capillary endothelium Arteries Transport Blood Away From Heart Structure – Thick-walled, three layers – Innermost layer: endothelium of squamous epithelial cells – Middle layer: smooth muscle – Outer layer: connective tissue Function – Arteries carry blood away from heart – Carry blood under pressure © 2014 Pearson Education, Inc. Arteries Transport Blood Away From the Heart Aneurism—defect in arterial wall – – – – – – – Ballooning of the arterial wall Some bulge inward, obstructing flow Others bulge outward Often develop slowly over time Often symptomless, until they rupture Rupture of aortic aneurism—rapidly fatal May be detected by careful screening and surgically repaired © 2014 Pearson Education, Inc. Arterioles and Precapillary Sphincters Regulate Blood Flow Blood flow – Heart Arteries Arterioles Capillaries Arterioles: smallest arteries Precapillary sphincters: control blood flow from arterioles into capillaries – Vasodilation: – Relaxation of vascular smooth muscle – Increases blood flow to capillaries – Vasoconstriction: – Contraction of vascular smooth muscle – Decreases blood flow to capillaries © 2014 Pearson Education, Inc. Figure 8.2 Relaxed precapillary sphincters Arteriole Capillaries Small vein (venule) © 2014 Pearson Education, Inc. Constricted precapillary sphincters Capillaries: Where Blood Exchanges Substances with Tissues Structure – Smallest blood vessels, microscopic – Thin-walled: one cell-layer thick – Porous Capillary beds: extensive networks of capillaries Function: selective exchange of substances with the interstitial fluid © 2014 Pearson Education, Inc. Figure 8.3 Capillary cell Pores through cells Slit between cells A medium-magnification view showing a rich network of capillaries surrounding and interconnecting small arteries and veins. Nucleus RBC A higher magnification showing a single branching capillary. Notice the red blood cells traveling single file in the capillary. © 2014 Pearson Education, Inc. The structure of a capillary. Figure 8.4 Precapillary sphincter Capillary RBCs, most proteins Fluid (water) O2, nutrients, raw materials Venule Arteriole Tissue cell © 2014 Pearson Education, Inc. CO2, wastes Lymphatic System Helps Maintain Blood Volume Function – Maintains blood volume – Returns excess interstitial fluid to circulatory system – Also functions in immune defenses Structure – Blind-ended capillaries – Lymphatic vessels (similar to venous system) – Lymph—derived from interstitial fluid © 2014 Pearson Education, Inc. Veins Return Blood to the Heart Structure – Three layers, thin-walled – Larger lumen than arteries – High distensibility Functions – Carry blood toward the heart – Blood flow – Capillaries Venules Veins Heart – Serve as blood volume reservoir © 2014 Pearson Education, Inc. Veins Return Blood to the Heart Three Mechanisms assisting in blood return 1. Contraction of skeletal muscles 2. One-way valves permit only one-way blood flow 3. Pressure changes associated with breathing push blood toward the heart © 2014 Pearson Education, Inc. Figure 8.5 Valve (open) One-way valves (closed) Calf muscles relaxed © 2014 Pearson Education, Inc. Calf muscles contracted Figure 8.6 © 2014 Pearson Education, Inc. Figure 8.7 Aorta Superior vena cava Right pulmonary artery Left pulmonary artery Pulmonary trunk Left pulmonary veins Pulmonary semilunar valve Right atrium Right atrioventricular (AV) valve Right ventricle Inferior vena cava Left atrium Aortic semilunar valve Left atrioventricular (AV) valve Left ventricle Chordae tendineae Papillary muscles Septum Epicardium Myocardium Endocardium © 2014 Pearson Education, Inc. The Heart Is Mostly Muscle Surrounded by fibrous sac—pericardium – Protects and anchors the heart Layers of the heart – Epicardium: thin layer of epithelial and connective tissue – Myocardium: thick layer of cardiac muscle – Electrical signals flow directly from cell to cell – This is what contracts when the heart beats – Endocardium: thin layer of endothelial tissue – Continuous with lining of blood vessels © 2014 Pearson Education, Inc. The Heart Has Four Chambers and Four Valves Four chambers – Two atria: upper chambers – Two ventricles: lower chambers – Septum, muscular partition separates right and left sides of the heart Four valves—prevent backflow – Two atrioventricular (AV) valves – Tricuspid valve (right side) – Bicuspid (mitral) valve (left side) – Two semilunar valves – Pulmonary valve – Aortic valve © 2014 Pearson Education, Inc. The Pulmonary Circuit Provides for Gas Exchange 1. Deoxygenated blood from the body travels through the vena cava to the right atrium 2. Through the right AV valve into the right ventricle 3. Through the pulmonary semilunar valve into the pulmonary trunk and the lungs 4. Blood is oxygenated and CO2 is given up within pulmonary capillaries 5. Oxygenated blood travels through the pulmonary veins into the left atrium 6. Through the left AV valve into the left ventricle © 2014 Pearson Education, Inc. The Systemic Circuit Serves the Rest of the Body 1. Oxygenated blood travels from the left ventricle through the aortic semilunar valve into the aorta 2. Through branching arteries and arterioles to tissues 3. Through the arterioles to capillaries 4. Within capillaries, nutrients and oxygen are delivered and wastes are picked up 5. From capillaries into venules and veins 6. To the vena cava and into the right atrium © 2014 Pearson Education, Inc. Figure 8.8 Systemic Circuit Head and upper limbs Lung capillaries Pulmonary Circuit Heart Lung capillaries Aorta Torso and Lower limbs © 2014 Pearson Education, Inc. Figure 8.9 Jugular vein Carotid artery Superior vena cava Inferior vena cava Renal vein Common iliac vein Common iliac artery © 2014 Pearson Education, Inc. Subclavian vein Subclavian artery Aorta Renal artery Femoral vein Femoral artery Great saphenous vein The Systematic Circuit Serves the Rest of the Body Coronary arteries – Arteries that supply the heart muscle itself – Supply the myocardium – Small diameter—may become partially or completely blocked by atherosclerosis © 2014 Pearson Education, Inc. Figure 8.10 Aorta Superior vena cava Pulmonary trunk Right coronary artery Cardiac veins Inferior vena cava © 2014 Pearson Education, Inc. Cardiac vein Left coronary artery The Cardiac Cycle: The Heart Contracts and Relaxes Atrial systole – Both atria contract – AV valves open, semilunar valves are closed – Ventricles fill Ventricular systole – Both ventricles contract – AV valves close, semilunar valves open Diastole – Both atria and ventricles relax – Semilunar valves close © 2014 Pearson Education, Inc. Figure 8.11 Right atrium Left atrium Pulmonary semilunar valve Aortic semilunar valve Left AV valve Right AV valve Left ventricle Atrial systole. Both atria Right ventricle 0.1 second Diastole contract, forcing blood into the ventricles. The AV valves are open, and the semilunar valves are closed. Systole 0.4 second Aorta Pulmonary trunk 0.3 second Diastole. The ventricles relax and begin to fill passively with blood through the open AV valves. The semilunar valves are closed, and the atria remain relaxed. © 2014 Pearson Education, Inc. Ventricular systole. Both ventricles contract, causing the AV valves to close and the semilunar valves to open. Blood is ejected into the pulmonary trunk and aorta. The atria relax. Heart Sounds Reflect Closing Heart Valves Lub-dub heart sound – Lub: closing of both AV valves during ventricular systole – Dub: closing of both semilunar valves during ventricular diastole Heart murmurs – Caused when blood flow is disturbed – May be a sign of a defective valve © 2014 Pearson Education, Inc. Cardiac Conduction System Coordinates Contraction Sinoatrial (SA) node—small mass of cardiac cells in upper right atrium – Cardiac pacemaker – Initiates the heartbeat spontaneously – Pace can be modified by nervous system Atrioventricular (AV) node – Located between atria and ventricles – Relays impulse Atrioventricular (AV) bundle and Purkinje fibers – Located in septum and ventricles – Carry impulse to ventricles © 2014 Pearson Education, Inc. Figure 8.13 Sinoatrial (SA) node Atrioventricular (AV) node AV bundle Bundle branches Purkinje fibers © 2014 Pearson Education, Inc. Electrocardiogram (EKG/ECG) Records the Heart’s Electrical Activity Tracks the electrical activity of the heart A healthy heart produces a characteristic pattern Three formations – P wave: impulse across atria – QRS complex: spread of impulse down septum, around ventricles in Purkinje fibers – T wave: end of electrical activity in ventricles EKGs can detect – Arrhythmias – Ventricular fibrillation © 2014 Pearson Education, Inc. Figure 8.14 An ECG being recorded. R T P Q S A normal ECG recording. Ventricular fibrillation. © 2014 Pearson Education, Inc. Blood Exerts Pressure Against Vessel Walls The force that the blood exerts on the wall of the blood vessels – Systolic pressure: highest pressure, as blood is ejected during ventricular systole – Diastolic pressure: lowest pressure, during ventricular diastole Measurement – Sphygmomanometer: device used to measure blood pressure – “Normal” readings – Systolic pressure <120 mmHg – Diastolic pressure <80 mmHg © 2014 Pearson Education, Inc. Blood pressure (mm Hg) Figure 8.15 Systolic pressure 120 80 40 0 © 2014 Pearson Education, Inc. Diastolic pressure Figure 8.16 Blood pressure (mm Hg) 140 Column of mercury indicating pressure in mm Hg Cuff pressure Blood pressure 1 120 100 80 2 60 0 Sphygmomanometer: Squeezable bulb Inflatable rubber cuff Air valve Artery Stethoscope A clinician inflates the cuff with air and then allows the pressure in the cuff to fall gradually while using a stethoscope to listen for the sounds of blood movement through the artery. © 2014 Pearson Education, Inc. 2 4 6 8 10 Time (seconds) A schematic representation of the pulses of arterial blood pressure superimposed over the steadily declining cuff pressure. Systolic pressure is recorded at cuff pressure 1 when sounds are first heard. Diastolic pressure is recorded at cuff pressure 2 when sounds cease. Hypertension: High Blood Pressure Can Be Dangerous Sustained elevation in blood pressure – Systolic pressure 140 mmHg – Diastolic pressure 90 mmHg Risk factor for cardiovascular disease – Higher blood pressure causes greater strain on cardiovascular system – Blood vessels react by becoming hardened and scarred – Strain on heart from having to work harder Silent killer, no symptoms © 2014 Pearson Education, Inc. Table 8.1 © 2014 Pearson Education, Inc. Table 8.2 © 2014 Pearson Education, Inc. Hypotension: When Blood Pressure Is Too Low Low blood pressure If low enough, may cause dizziness or fainting May follow abrupt changes in body position – Standing up suddenly May result from excessive blood loss or fluid loss from burns © 2014 Pearson Education, Inc. How the Cardiovascular System Is Regulated Importance of maintaining a constant arterial blood pressure Constant arterial pressure is achieved by 1. Regulation of heart rate 2. Force of contraction 3. Regulation of diameter of arterioles Local blood flows are adjusted to meet local requirements © 2014 Pearson Education, Inc. Baroreceptors Maintain Arterial Blood Pressure Baroreceptors: pressure receptors in aorta and carotid arteries Steps in mechanism 1. Blood pressure rises, vessels stretched 2. Signals sent to the cardiovascular center in the brain 3. Heart signaled to lower heart rate and force of contraction 4. Arterioles vasodilate, increasing blood flow to tissues 5. Combined effect lowers blood pressure Mechanism reversed if blood pressure is too low © 2014 Pearson Education, Inc. Nerves and Hormones Adjust Cardiac Output Amount of blood pumped into aorta in one minute Cardiac output heart rate stroke volume – Heart rate: beats/minute (bpm) – Resting adult heart rate approx. 75 bpm – Stroke volume: – Resting adult stroke volume 70 ml/beat Resting cardiac output – 75 bpm 70 ml/beat 5.25 liters/min. © 2014 Pearson Education, Inc. Nerves and Hormones Adjust Cardiac Output Medulla oblongata: cardiovascular center of brain – Receives inputs from baroreceptors and other receptors – Output goes through two sets of nerves 1. Sympathetic nerves—constrict blood vessels, raising blood pressure 2. Parasympathetic nerves—dilate blood vessels, lowering blood pressure Hormones: epinephrine and norepinephrin – Secreted by adrenal glands when sympathetic system is activated – Increase cardiac output © 2014 Pearson Education, Inc. Local Requirements Dictate Local Blood Flows Precapillary sphincters allow fine-tuning of blood flow to local tissues as needed Metabolically active tissue—needs more O2, sphincters open, vasodilation If blood pressure drops precipitously, blood pressure control would cause vasoconstriction to many organs and shunt blood to brain and heart where blood supply and pressure must be maintained © 2014 Pearson Education, Inc. Figure 8.17 Blood flow Diffusion of vasodilating substance Cell Arteriole Precapillary sphincter Capillary Vasodilating substance produced during metabolism At rest, very little of the vasodilating substance would be produced, and flow would be minimal. © 2014 Pearson Education, Inc. With increased metabolic activity, the presence of more of the substance in the interstitial space would cause the arteriole and precapillary sphincter to vasodilate, increasing flow. Exercise: Increased Blood Flow and Cardiac Output Blood flow to active skeletal muscles increases Cardiac output (CO) is increased to maintain blood pressure – Non-athletes: up to 20–25 liters/min – Trained athletes: up to 35 liters/min © 2014 Pearson Education, Inc. Cardiovascular Disorders: A Major Health Issue Angina – Sensation of pain and tightness in chest – Caused by narrowing of coronary arteries and diminished blood flow to coronary muscle – May be accompanied by shortness of breath and sensation of choking or suffocating – Usually temporary – Angiography: allows visualization of coronary arteries, enables diagnosis of angina – Treatment: – Medication – Balloon angioplasty – Coronary artery bypass graft © 2014 Pearson Education, Inc. Figure 8.18 © 2014 Pearson Education, Inc. Cardiac Disorders: A Major Health Issue Heart attack (myocardial infarction) – Sudden death of an area of myocardium – Symptoms: – Intense chest pain, tightness or pressure on chest, radiating left arm pain, jaw and back pain, nausea – Requires immediate medical attention – Diagnosis: ECG and presence of certain enzymes in the blood – Treatment and/or prevention – Control of arrhythmias – Clot-dissolving medications – Coronary artery bypass graft (CABG)—vein from leg is grafted to bypass obstructed coronary artery © 2014 Pearson Education, Inc. Figure 8.19 Aorta Vein grafts Plaque blocking blood flow © 2014 Pearson Education, Inc. Cardiac Disorders: A Major Health Issue Heart failure – Heart muscle becomes weaker, less efficient – Congestive heart failure: weakness of heart causes fluid back-up in interstitial spaces – Out of breath, swollen ankles, legs, neck veins – Why does the heart weaken? – Age, prior heart attacks, leaky heart valves, lung disease – Treatment – Improve cardiac performance, efficiency – Prevent accumulation of interstitial fluid © 2014 Pearson Education, Inc. Cardiac Disorders: A Major Health Issue Embolism – Sudden blockage of a blood vessel by material floating in the bloodstream – Often a blood clot broken away from a larger clot elsewhere – May be cholesterol deposits, tissue fragments, cancer cells, clumps of bacterial, bubbles of air – Locations – Pulmonary embolism—chest pain, shortness of breath – Cerebral embolism—may cause a stroke – Cardiac embolism—may cause heart attack © 2014 Pearson Education, Inc. Cardiovascular Disorders: A Major Health Issue Stroke – Damage to part of brain caused by an interruption in blood supply – Two common causes – Embolism blocking a brain blood vessel – Rupture of a cerebral artery – Symptoms: depend on area of brain affected – Immediate medical care is crucial – If embolism, patient receives clot-dissolving drugs – If rupture, surgical repair sometimes possible – Recovery may require extensive rehabilitation © 2014 Pearson Education, Inc. Replacing a Failing Heart Heart transplants – Expensive – Average post-transplant survival: 15 years – Problem: shortage of healthy hearts Temporary solution to shortage of transplant organs: – Artificial heart – Xenotransplant (heart from another animal species) © 2014 Pearson Education, Inc. Figure 8.20 The SynCardia heart. © 2014 Pearson Education, Inc. The AbioCor heart. Reducing Your Risk of Cardiovascular Disease Don’t smoke – Smokers have twice the risk of heart disease Watch cholesterol levels – Risk increases with increasing blood cholesterol Engage in regular moderate exercise Maintain a healthy weight Keep diabetes under control Avoid chronic stress © 2014 Pearson Education, Inc.