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Lecture Outline Impacts, Issues: And Then My Heart Stood Still A. Augustus Waller made the first recordings of a beating heart—using his dog Jimmie. 1. The pacemaker in the heart wall causes the heart muscle to contract. 2. Sudden cardiac arrest is the cessation of the beat. B. Normal heartbeat must be restored as quickly as possible. 1. CPR is usually the quickest and requires no special equipment. 2. Defibillators are becoming more available, even in public places. 33.1 The Nature of Blood Circulation A. The circulatory system moves substances to and from cells. 1. A circulatory system is an internal transport system with three components. a. Blood is a fluid tissue composed of water, solutes, and formed elements. b. Blood vessels are tubes of various diameters through which the blood is transported. c. The heart is a muscular pump that generates pressure to keep the blood flowing. 2. Interstitial fluid “bathes” the cells of the body. a. The volume, composition, and temperature of this fluid must be carefully maintained. b. Exchanges between interstitial fluid and blood keep the internal environment tolerable. 3. Arthropods and most mollusks have an open system: a. Blood is pumped from a heart into large tissue spaces where organs are “bathed.” b. Blood is returned to the heart at a leisurely rate. 4. Vertebrates have a closed system. a. All the vessels and the heart are connected so that blood remains enclosed. b. Blood volume is constant and is equal to the heart’s output at any time. c. Flow rate slows as blood moves through the fine capillaries of the capillary beds B. Evolution of Vertebrate Circulation 1. In fishes, blood flows in a single circuit, passing through a heart of two chambers. 2. In amphibians the heart is partially partitioned into right and left halves, permitting a partial separation into two circuits. 3. Birds and mammals have two separate circuits of blood flow. a. The right half of the heart receives deoxygenated blood and pumps it to the lungs of the pulmonary circuit. b. The left half receives blood from the lungs and pumps the oxygen-rich blood to all of the tissues and organs in the systemic circuit. C. Links with the Lymphatic System 1. The lymphatic system picks up excess fluids, solutes, and disease agents from the interstitial fluid. 2. This lymph is cleansed by exposure to the infection-fighting cells before being returned to the general circulation. 33.2 Characteristics of Blood A. Functions of Blood 1. It carries oxygen and nutrients to cells, and it carries secretions and wastes away from them. 2. It helps stabilize internal pH. 3. It contains phagocytic cells that fight infection. 4. It equalizes body temperatures in birds and mammals. B. Blood Composition and Volume 1. Humans have a blood volume of about 4–5 quarts, with a fluid portion and cells that arise from stem cells in bone marrow. 2. Plasma (50–60 percent of blood volume) a. This fluid portion of the blood is mostly water. b. Some plasma proteins transport lipids and vitamins; others function in immune responses and blood clotting. c. Plasma also contains ions, glucose, lipids, amino acids, vitamins, hormones, and dissolved gases. 3. Red Blood Cells (Erythrocytes) a. In mammals, red blood cells are biconcave disks that transport oxygen. b. Red blood cells contain hemoglobin—an iron-containing protein that binds with oxygen. c. They form from stem cells in bone marrow, lose their nuclei, and live about 120 days. d. The number of cells per microliter (about 5 million) is called the cell count. 4. White Blood Cells (Leukocytes) a. Leukocytes remove dead or worn-out cells and protect us against invading microbes and foreign agents. b. There are several types of white blood cells. 1) Neutrophils, basophils, macrophages, and dendritic cells are phagocytes. 2) Lymphocytes, the “B” and “T” cells, are involved in the immune responses. 3) Natural killer cells directly kill body cells that have turned cancerous or have been infected by viruses. 5. Platelets a. These are fragments of megakaryocytes produced by bone marrow stem cells. b. They function in blood clotting. 33.3 Blood Disorders A. Red Blood Cell Disorders 1. Anemias are conditions in which there are too few, or deformed, RBCs. 2. Hemorrhagic (sudden) and chronic (slow) anemias follow blood loss. 3. Certain protozoans replicate in RBCs and cause hemolytic anemias (malaria). 4. Insufficient iron causes iron deficiency anemia. 5. Sickle-cell anemia and thalassemias arise from mutations that either alter the hemoglobin or stop its synthesis altogether. 6. Polycythemias (far too few RBCs) and blood doping make blood flow sluggish. B. White Blood Cell Disorders 1. Infectious mononucleosis is a viral disease in which too many monocytes and lymphocytes form; it may last several weeks with a gradual recovery. 2. Leukemias are cancers of the bone marrow, which impair WBC formation. 33.4 Blood Typing A. Blood transfusion can save lives. 1. Blood typing is necessary before a blood transfusion can be done. a. All cells have surface proteins and other molecules that serve as markers. b. Antibodies recognize markers on foreign cells. 2. If bloods of certain donors and recipients are mixed, agglutination (clumping) may occur. B. ABO Blood Typing 1. ABO blood typing is based upon surface markers on red blood cells. 2 Type A has A markers; type B has B markers; type AB has both markers; type O has neither marker. C. Rh Blood Typing 1. An Rh– person (lacks this marker) transfused with Rh+ blood (has this marker) will produce antibodies to the Rh marker. 2. There are risks in childbirth or pregnancy (erythroblastosis fetalis) if an Rh – woman bears a second Rh+ child. 3. Medical treatment (RhoGam) can inactivate the Rh antibodies. 33.5 Human Cardiovascular System A. The general route of blood circulation is: heart ——> arteries ——> arterioles ——> capillaries ——> venules ——> veins ——> heart. B. Blood circulates through two circuits. 1. The human heart is a double pump, propelling blood into the two cardiovascular circuits. a. In the pulmonary circuit, oxygen-poor blood is pumped to the lungs from the right side of the heart, and oxygen-rich blood is returned from the lungs to the left side. b. In the systemic circuit, oxygen-rich blood is pumped from the left side of the heart to all the body. 2. Usually a given volume of blood in either circuit passes through only one capillary bed; an exception is blood from the digestive tract that passes through the liver before entering the general circulation. 33.6 The Heart Is a Lonely Pumper A. Heart Structure 1. The heart tissue is layered. a. The outer covering of the heart is the pericardium, which is partially a fluid-filled sac and the outer part of the heart wall. b. The bulk of the heart wall is the heart muscle—myocardium—serviced by coronary circulation. c. The heart is lined with a smooth endothelium. 2. Nutrients and oxygen are delivered to the heart tissues by the coronary arteries. 3. The heart has four chambers and four valves. a. Each half of the heart consists of an atrium (receiving) and a ventricle (pumping) separated by an atrioventricular valve. b. Blood exits each ventricle through a semilunar valve. 4. The cardiac cycle consists of a sequence of contraction (systole) and relaxation (diastole). a. As the atria fill, the ventricles are relaxed. b. Pressure of the blood in the atria forces the atrioventricular valves to open; the ventricles continue to fill as the atria contract. c. The ventricles contract, the atrioventricular valves close, and blood flows out through the semilunar valves. d. The heart sound “lub” is made by the closing of the AV valves; the “dup” sound is the closure of the semilunar valves. B. How Does Cardiac Muscle Contract? 1. Cardiac muscle has orderly arrays of sarcomeres, which contract by a sliding-filament mechanism. 2. Because of the close junctions of cardiac muscle cells, they contract in unison. 3. Excitation for a heartbeat is initiated in the sinoatrial (SA) node (also known as the cardiac pacemaker) then passes to the atrioventricular (AV) node for ventricular contraction; this is the cardiac conduction system. 4. The nervous system adjusts rate and strength. 33.7 Pressure, Transport, and Flow Distribution A. Blood is distributed by means of arteries, arterioles, capillaries, venules, and veins. 1. Two key factors influence the rate of flow through each type of blood vessel. a. The flow rate is directly proportional to the pressure gradient between the start and end of the vessel. b. The flow rate is inversely proportional to the vessel’s resistance to flow. 2. Blood pressure drops along the way due to energy loss from resistance. B. Rapid Transport in Arteries 1. Arteries are large diameter vessels that present low resistance to flow as they conduct blood away from the heart. 2. Because of their elastic walls, arteries tend to “smooth out” the pulsations associated with the discontinuous pumping cycle of the heart. C. Distributing Blood Flow 1. Arteries branch into smaller arterioles, which offer greater resistance to flow and thus the greatest drop in blood pressure. 2. Neural and endocrine signals cause changes in arteriole diameter by stimulating the muscle cells in the walls. a. If the blood pressure increases, the arterioles are instructed to relax (vasodilation). b. If the pressure decreases, the diameter of the arterioles decreases (vasoconstriction). 3. Arterioles serve as control points where adjustments can be made in blood volume distribution. D. Controlling Blood Pressure 1. A special instrument with a cuff surrounding the upper arm is connected to a pressuremeasuring device. a. The peak pressure (systolic) is recorded when the ventricles are contracting—120mm is typical. b. The lowest pressure (diastolic) is reached when the ventricles are relaxing—80mm. 2. Baroreceptors in the carotid artery walls can detect blood pressure changes and signal the brain to alter the cardiac output and arteriole diameter. 33.8 Diffusion at Capillaries, Then Back to the Heart A. Capillary Function 1. Capillaries are diffusion zones for exchanges between blood and interstitial fluid. a. A capillary is the smallest tube (red blood cells travel single file) in the path of circulation. b. Total resistance is less than in arterioles so the drop in blood pressure is not as great. c. Its wall consists of a single layer of endothelial cells, which facilitates diffusion to and from the interstitial fluid. 2. Movement across the capillary is by several modes: diffusion (of oxygen and carbon dioxide), endocytosis and exocytosis (of proteins), between the cells (of ions), and bulk flow (of water). a. At the beginning of a capillary bed, there is a movement of plasma out into the interstitial fluid in a process known as ultrafiltration. b. Further on, some tissue fluid moves into the capillary through clefts between its endothelial walls in a process known as reabsorption. B. Venous Pressure 1. Capillaries merge into venules then into veins. a. Blood pressure and resistance to flow are both low; valves prevent backflow. b. Veins are blood volume reservoirs (50–60 percent of blood volume) because their walls can distend or contract. 2. The movement of skeletal muscles squeezes the veins and pushes the blood along against the forces of gravity. 33.9 Cardiovascular Disorders A. Good Clot, Bad Clot 1. Hemostasis is the process that stops blood loss when a vessel is damaged and constructs a framework for repairs. 2. There are several sequential steps. a. Spasm of the smooth muscle in the damaged blood vessel stops blood flow for a few minutes. b. Platelets clump to plug the rupture. c. The blood coagulates and forms a clot; the clot then retracts into a compact mass. B. A Silent Killer—Hypertension 1. Hypertension (high blood pressure) can affect a person without outward symptoms. 2. There is a gradual increase in resistance to flow in the smaller arteries. a. Heredity and/or diet may play roles. b. The heart may enlarge and fail; arterial walls may “harden.” C. Atherosclerosis 1. In this condition, lipids such as cholesterol build up in the arterial wall. a. Low-density lipoproteins (LDLs) infiltrate the walls, causing an atherosclerotic plaque to form. b. Platelets gather at the site and initiate clot formation. 2. Enlarging plaques and blood clots narrow or block arteries. a. A clot that stays in place is a thrombus; a dislodged, traveling clot is an embolus. b. The tiny coronary arteries are the most vulnerable, leading to the familiar signs of a heart attack. D. Rhythms and Arrhythmias 1. ECGs can reveal arrhythmias, an abnormal heartbeat. a. Bradycardia is a below average resting cardiac rate, which may be the result of ongoing exercise. b. Tachycardia, fast heartbeat, is caused by exercise or stress. 2. Atrial and ventricular fibrillation are repeated contractions that disrupt the normal cardiac cycle. E. Risk Factors [cardiovascular disorders] 1. Tobacco smoking tops the list. 2. Others include genetics, hypertension, cholesterol, obesity, diabetes, age, physical inactivity, and gender. 33.10 Connections with the Lymphatic System A. The lymphatic system returns excess fluid (lymph) to the bloodstream via transport tubes. B. Lymph Vascular System 1. The lymph vascular system includes lymph capillaries and lymph vessels. 2. It returns excess water and proteins, transports fats, and brings foreign materials to the lymph nodes for disposal. 3. Lymph capillaries begin blindly in the tissues of the body; they lead to lymph vessels, which in turn lead to ducts that return the fluid to the bloodstream. C. Lymphoid Organs and Tissues 1. They contain lymphocytes that help to fight infections. 2. The organs and functions include: a. The lymph nodes (with resident cells) located along the lymph vessels help remove bacteria and cellular debris. b. The spleen removes spent RBCs, holds macrophages, and produces red blood cells in human embryos. c. The thymus secretes hormones that regulate the activity of lymphocytes and is a site where they multiply and mature.