Lecture Outline - Chapter 13

13.1. Blood Vessels (p. 226)

1. The circulatory system consists of three types of blood vessels. (Fig. 13.1)
   • a. Arteries and Arterioles
     • i. Structure:
       - consists of an inner membranous endothelium of squamous epithelial cells;
       - thick middle layer is composed of elastic and smooth muscle fibers;
       - has an outer fibrous connective tissue layer.

       ii. Function to transfer blood away from the heart.

       iii. Arteries are able to expand after each heartbeat to accommodate increased blood volume.

       iv. Arteries regulate blood pressure.

       - Constriction increases blood pressure.

       - Dilation decreases blood pressure.
   • b. Capillaries
     • i. Structure:
       - Arterioles branch into capillaries.
       - Capillaries are very narrow, composed of one layer of endothelial cells.
       - Capillary beds (networks) open and close to shunt blood from one body system to another (digestion vs. exercise). (Fig. 13.2)
       - arteriovenous shunt allows blood to flow more directly from artery to vein.

       ii. Function as site of exchange of nutrients and waste between blood and body cells.
   • c. Veins and Venules (p. 227)
     • i. Structure:
       - Venules drain blood from capillaries; then join to form a vein.
       - Veins have same three layers as an artery but wall is much thinner.
       - Veins often have valves that allow blood to flow only in one direction.

       ii. Function:

       - to return blood from capillary beds to the heart.

       - as a reservoir of more than half of blood volume.

1. External Structure
   • a. Cone-shaped muscular organ.
   • b. About size of a fist.
   • c. Located behind sternum (breastbone).
   • d. Myocardium is major middle layer; consists largely of cardiac muscle tissue that is branched and tightly joined to each other.
2. Internal Structure
   • a. Consists of four chambers:
     • i. Two thin-walled atria;
     • ii. Two thick-walled lower, stronger ventricles.
     • iii. Left and right side are separated by a septum.
     • iv. Upper atria and lower ventricle chambers are separated by two atrioventricular valves:
       - tricuspid on right side.
       - bicuspid or mitral valve on left side of heart.
   • b. Valves are supported by chordae tendineae, fibrous strings that anchor the valves and prevent them from inverting.
   • c. Semilunar valves, resembling half moons, are found between the ventricles and their attached vessels.
3. Path of Blood Through the Heart (Fig. 13.4) (p. 229)
   • a. Superior and inferior vena cava carry deoxygenated blood low in oxygen and high in carbon dioxide, which enters the right atrium.
   • b. Right atrium sends blood through atrioventricular valve (tricuspid valve) to right ventricle.
   • c. Right ventricle sends blood through pulmonary semilunar valve into pulmonary trunk and two pulmonary arteries leading to lungs.
   • d. Four pulmonary veins carry oxygenated blood high in oxygen and low in carbon dioxide from the lungs, and enter left atrium.
   • e. Left atrium sends blood through atrioventricular valve (bicuspid or mitral valve) to left ventricle.
   • f. Left ventricle sends blood through aortic semilunar valve into aorta to body.
   • g. Heart is a double pump with two separate circular paths where oxygenated and deoxygenated blood never mixes; walls of left ventricle are thicker since it must pump blood to entire body.
4. Heartbeat
   • a. Each heartbeat equals a cardiac cycle. (Fig. 13.5)
   • b. First both atria contract, then both ventricles contract, then heart relaxes.
   • c. Systole is contraction of heart muscle.
   • d. Diastole is relaxation of heart muscle.
   • e. Average heart contracts 70 times a minute; each heartbeat lasts 0.85 seconds.
   • f. Normal healthy heartbeat variation is from 60 to 100 beats per minute.
   • g. Heart Sounds
     • i. "Lub-dup" sound occurs as valves of heart close.
     • ii. "Lub" sound is due to closing of the atrioventricular valves.
     • iii. "Dup" sound is caused by closing of the semilunar valves.
     • iv. Heart murmur is slush after the lub; often due to ineffective AV-valves that allow blood to pass back into atria.
     • v. Rheumatic fever results from bacterial infection causing faulty valve, usually bicuspid; may require operation to replace with artificial valve.
   • h. Pulse is alternating expansion and recoil of arterial wall due to blood surging with heartbeat in arteries.
     • i. Often measured on radial artery near outer border of palm side of wrist.
     • ii. Carotid artery at side of trachea in neck also provides strong pulse.
     • iii. Arterial wall pulse whenever left ventricle contracts.
5. Conduction System: Intrinsic Control of Heartbeat (Fig. 13.6) (p. 230)
   • a. SA (Sinoatrial) Node
     • i. Called "pacemaker" because it keeps the heartbeat regular.
     • ii. Found in the upper dorsal wall of the right atrium.
     • iii. Initiates the heartbeat by sending excitation impulse every 0.85 seconds to cause the atria to contract.
   • b. AV (Atrioventricular) Node
     • i. Found at the base of the right atrium near the septum.
     • ii. When receives stimulation from SA node, AV node signals ventricles to contract by way of Purkinje fibers.
   • c. Implantation of artificial pacemaker provides regular 0.85 second stimulus.
   • d. Electrocardiogram (ECG or EKG) (Fig. 13.6b) (p. 230)
     • i. Records ionic changes that occur with contraction of heart muscle.
     • ii. P wave represents excitation prior to contraction of the atria.
     • iii. QRS wave occurs prior to ventricular contraction.
     • iv. T wave shows repolarization of ventricles causing recovery of the ventricles.
   • e. Ventricular Fibrillation
     • i. Uncoordinated contraction of ventricles.
     • ii. Can be caused by injury or drug overdose.
     • iii. Ventricles must be defibrillated by applying strong electric current allowing SA node to reestablish coordinated beat.
6. Nervous Control of Heartbeat: Extrinsic Control
   • a. Cardiac center in medulla oblongata can alter heartbeat through autonomic nervous system.
   • b. Parasympathetic system promotes normal responses including slowing down heartbeat.
   • c. Sympathetic system promotes stress responses including speeding up heartbeat.
   • d. Need for oxygen, increase in blood pressure, etc. may activate systems.
7. Blood Pressure and Swiftness of Flow (p. 233)
   • a. Blood pressure is pressure of blood against wall of blood vessel.
   • b. Systolic blood pressure is highest arterial pressure when ventricles are contracting.
   • c. Diastolic pressure is lowest arterial pressure when ventricles are relaxing.
   • d. Blood pressure decreases with distance from left ventricle. (Fig. 13.7)
   • e. Normal pressure in brachial artery of young adult is 120/80 representing 120 mm of mercury (Hg) systolic over 80 mm diastolic.
   • f. Blood pressure is highest in aorta, drops sharply in arterioles and again in capillaries, correlating with an increase in total cross-sectional area of vessels.
   • g. In arteries, blood velocity is accounted for by blood pressure; as pressure decreases due to increased cross-sectional area, so does velocity.
   • h. In capillaries, blood velocity is slowest due to greatest total cross-sectional area.
   • i. Slow capillary velocity allows more time for exchange of nutrients, gases, and waste products with tissues.
   • j. In the veins, blood velocity increases due to:
     • i. Compression of the veins during skeletal muscle contraction aided by valves in veins.
     • ii. Reduction in cross-sectional area as small venules join to form veins.
     • iii. Decreased blood pressure during inspiration whenever chest expands.

1. Pulmonary circuit circulates blood through lungs; pathway involves:
   • a. Blood from all regions collects in right atrium, passes to right ventricle.
   • b. Right ventricle pumps deoxygenated, high carbon dioxide blood to pulmonary arteries.
   • c. Right and left pulmonary arteries branch into lungs.
   • d. Pulmonary capillaries are site where oxygen is picked up and carbon dioxide is given off.
   • e. Pulmonary veins leave lungs with oxygenated, low carbon dioxide blood and enter left atrium of heart. (Fig. 13.8)
   • f. Pulmonary veins carry oxygenated blood, pulmonary arteries carry deoxygenated blood--just opposite of systemic circuit.
2. Systemic circuit circulates blood through rest of body.
   • a. Pathway to and from body organs begins with the left ventricle.
   • b. Aorta is largest artery, carries oxygenated blood.
   • c. Vena cava is largest vein; superior vena cava collects blood from head, chest and arms; inferior vena cava collects blood from lower body.
   • d. For example, path for kidneys is: left ventricle --> aorta --> renal artery --> capillaries --> venules --> renal vein --> vena cava --> right atrium.
   • e. Coronary arteries:
     • i. nourish heart.
     • ii. are first branch off aorta just above aortic semilunar valve.
     • iii. lie on the exterior surface of heart.
     • iv. cardiac veins converge to empty into right atrium.
     • v. coronary arteries are small diameter; blockage may require bypass surgery.
3. Hepatic Portal System
   • a. System begins in capillaries of villi of small intestine.
   • b. Intestinal capillaries converge into venules and hepatic portal vein running to liver.
   • c. Hepatic portal vein divides into capillaries in liver.
   • d. Hepatic vein finally leaves liver and enters inferior vena cava.

1. Blood helps maintain homeostasis.
   • a. Blood transports molecules to and from capillaries.
   • b. Blood guards body against microbial invasion.
   • c. Blood reduces blood loss by clotting.
2. Plasma and Cells (Fig. 13.10)
   • a. Blood can be divided into two layers: plasma and formed elements (including red blood cells, white blood cells and platelets).
   • b. Plasma
     • i. Upper liquid portion (55% by volume of whole blood).
     • ii. Water: suspends or dissolves inorganic/organic substances
     • iii. Plasma proteins form 8- 9% of plasma; functions include:
       - transporting organic molecules including bilirubin transported by albumin and globulins transporting cholesterol as lipoproteins.
       - maintain blood volume; since protein molecules are too large to pass through capillary walls,
       - water automatically diffuses into capillaries.
       - blood clotting due to protein fibrinogen.
       - immunoglobulins are antibodies that help fight infection.
   • c. Red Blood Cells Carry Oxygen (p. 237)
     • i. Red blood cells are known as erythrocytes; also abbreviated as RBCs.
     • ii. Continuously formed in red bone marrow of skull, ribs, vertebrae, and ends of long bones.
     • iii. Normally 4- 6 million red blood cells per mm³ of whole blood.
     • iv. Each red blood cell contains about 200 million hemoglobin molecules.
     • v. Hemoglobin provides red color of blood.
     • vi. Hemoglobin has four polypeptide chains forming protein globin.
     • vii. Each chain has an iron-containing heme associated; this iron molecule acquires oxygen in lungs, yields oxygen to tissues.
     • viii. Whole blood carries 20 ml of oxygen per 100 ml compared to plasma that carries only 0.3 ml of oxygen; hemoglobin increases oxygen- carrying capacity 60 times.
     • ix. RBC numbers increase when there is reduced oxygen concentration; kidneys produce erythropoietin that stimulates RBC formation in stem cells in red bone marrow. (Fig. 13.12)
     • x. During RBC formation, they lose nucleus and acquire hemoglobin.
     • xi. Lifespan is about 120 days until destroyed by phagocytic cells in liver and spleen.
     • xii. Iron from broken down hemoglobin is recovered and reused.
     • xiii. Heme is excreted by liver to ultimately become bile pigments that color feces dark.
     • xiv. Anemia occurs when there is insufficient numbers of RBCs or not enough hemoglobin per RBC.
       - Iron-deficiency anemia occurs when hemoglobin count is low due to low iron intake.
       - Pernicious anemia results from not enough vitamin B₁₂ absorbed in digestive tract;
         leads to immature RBCs in large quantity.
   • d. White Blood Cells Fight Infection (Fig. 13.13) (p. 239)
     • i. Called leukocytes; abbreviated WBCs.
     • ii. WBCs are:
       - larger in size than RBCs.
       - have a nucleus.
       - are white in color since they lack hemoglobin.
       - are less numerous (5,000- 11,000/mm³) than RBCs.
       - are really translucent (unless stained) and not white.

       iii. Granular leukocytes:

       - have more granules.

       - have a many-lobed nucleus (are "polymorphonuclear").

       - neutrophils are most abundant WBCs and phagocytize microbes.

       iv. Agranular leukocytes:

       - have fewer granules.

       - monocytes are largest of WBCs; they become macrophages in tissues and phagocytize bacteria.

       - lymphocytes have two types (B and T); each is important in immunity.

       v. Leukemia is a form of cancer characterized by uncontrolled production of abnormal WBCs.

       vi. Infectious mononucleosis is caused by the Epstein-Barr virus; result is an excessive number of B- lymphocytes.

       vii. AIDS results in an abnormally low number of T-lymphocytes.

       viii. WBCs are also produced in the bone marrow; may live from days to years.
3. Platelets Assist Blood Clotting
   • a. Platelets, also called thrombocytes, result from fragmentation of large megakaryocytes.
   • b. Fibrinogen and prothrombin are proteins manufactured and deposited in blood by liver.
   • c. Vitamin K is necessary to produce prothrombin; lack of vitamin K results in hemorrhagic disorders.
   • d. Serum is plasma that lacks prothrombin and fibrinogen; serum forms above a clot in a test tube.
   • e. Blood Clotting Steps
     • i. When blood vessel is damaged, platelets clump at site and partially seal leak.
     • ii. Injured tissues plus platelets release clotting factor called prothrombin activator that converts prothrombin to thrombin in reaction requiring calcium ions (Ca⁺⁺).
     • iii. Thrombin acts as enzyme that severs amino acid chains from fibrinogen; activated fragments join end-to-end forming threads of fibrin.
     • iv. Fibrin threads wind around platelet plug; trapped red blood cells give red color. (Fig. 13.14)
     • v. When tissues are repaired, an enzyme called plasmin destroys fibrin clot and restores fluidity of plasma.
4. Exchanges Between Blood and Tissue Fluid (Fig. 13.15) (p. 241)
   • a. Two forces control fluid movement across capillary walls.
     • i. Osmotic pressure causes water to move from tissue fluid to blood.
     • ii. Blood pressure causes water to move from blood to tissue.
   • b. At arterial end of capillary, blood pressure (40 mm Hg) is higher than osmotic pressure (25 mm Hg); fluid exits capillary carrying the oxygen and nutrients.
   • c. Arterial process is termed filtration because large red blood cells and plasma proteins stay in blood, water and small molecule nutrients leave.
   • d. Osmotic pressure is created by presence of salts and plasma proteins in blood.
   • e. Midway in capillaries, blood pressure and osmotic pressures are about equal; solutes diffusing along concentration gradients with nutrients (glucose and oxygen) moving into tissues and wastes (including carbon dioxide) diffusing into capillary blood.
   • f. Tissue fluids contain all components of plasma except large proteins.
   • g. In venule, osmotic pressure is greater than blood pressure; water moves into capillary.
   • h. Water that returns to venule-end capillary is about equal to water that left in arteriole-end capillary minus small amount collected by lymphatic vessels. (Fig. 13.16)
   • i. Lymph is returned to venous blood when lymph vessels join subclavian veins in shoulder region.

1. Cardiovascular disease is leading cause of death in Western countries.
2. Hypertension: Silent Killer
   • a. Hypertension is the technical name for high blood pressure.
   • b. Twenty percent of Americans have higher than normal blood pressure.
   • c. For women at any age, 160/95 or above indicates hypertension.
   • d. For men under age 45, 130/90 is hypertensive; for men over 45, above 140/95 indicates hypertension.
   • e. Diastolic pressure reading is emphasized when considering medical treatment.
   • f. "Silent killer" because may not be detected until stroke or heart attack occurs.
   • g. Genetic basis is suspected involving two genes; one gene codes for angiotensinogen, a plasma protein converted to a vasoconstrictor by a product of second gene; this open possibility of gene therapy in future.
   • h. Regular blood pressure checkups and healthy life-style lower risk.
3. Atherosclerosis: Fatty Arteries (p. 243)
   • a. Atherosclerosis (formerly called arteriosclerosis) is narrowing of arteries due to accumulation of cholesterol in plaques beneath inner lining of arteries.
   • b. A diet low in saturated fat and cholesterol is recommended to prevent its onset and development.
   • c. Plaque can cause clot to form on irregular arterial walls.
     • i. If clot remains stationary, it is called a thrombus.
     • ii. If clot is dislodged and moves with blood, it is termed an embolus.
4. Stroke and Heart Attack: Lack of Oxygen
   • a. Both strokes and heart attack are associated with hypertension.
   • b. A stroke or cardiovascular accident (CVA) occurs when a portion of brain dies due to a lack of oxygen. Two causes are:
     • i. a ruptured arteriole from high blood pressure.
     • ii. an embolus blocks blood flow.
   • c. Stroke results in paralysis or death; early symptoms include numbness in hands or face, difficulty speaking, or temporary blindness in one eye.
   • d. Heart attack, also called a myocardial infarction, occurs when a portion of heart dies due to lack of oxygen.
     • i. If coronary artery is partially blocked, one may suffer from angina pectoris, radiating pain in the left arm.
     • ii. Angina is relieved by nitroglycerin which dilates blood vessels.
     • iii. If coronary artery is completely blocked, perhaps by thromboembolism, a heart attack occurs.
5. Dissolving Blood Clots
   • a. Medical treatment for thromboembolism involves dissolving blood clots.
   • b. Two drugs usually used:
     • i. Streptokinase produced by bacteria.
     • ii. tPA (tissue plasminogen activator), produced by genetic engineering but also the body's natural agent.
   • c. Both drugs convert plasminogen found in blood into plasmin, an enzyme that dissolves a blood clot; must be used immediately to prevent permanent damage.
   • d. Aspirin is an anticoagulant given to inhibit the stickiness of platelets; used for angina and thrombolytic stroke.
6. Clearing Clogged Arteries
   • a. Angioplasty is use of a plastic tube, inserted into an artery and inflated at plaque site to open the vessel; problems include the vessel re-closing due to smooth muscle cells growing in response to the trauma; future gene therapy may involve delivering a virus to site at same time as angioplasty. (Fig. 13.3)
   • b. Coronary bypass surgery involves splicing a segment of another blood vessel to bypass blood around a blocked coronary artery; it may also be possible to use gene therapy to cause new bypass vessels to grow.
7. Donated and Artificial Hearts (p. 246)
   • a. Congestive heart failure occurs when heart can no longer pump blood adequately; blood backs up in heart and lungs.
   • b. Heart donor transplants face two difficulties:
     • i. shortage of donor hearts.
     • ii. donated heart is rejected as foreign organ.
   • c. Alternatives:
     • i. back muscle can be wrapped around a weak heart.
     • ii. cardiac cell transplants involve injecting cardiac muscle cells that will contribute to pumping of heart.
   • d. Artificial hearts attempt to fulfill heart function with machinery.
     • i. Jarvik-7 was first experimental artificial heart; first used on December 2, 1982 with Barney Clark.
     • ii. Newer artificial heart models must overcome problems with continuous reliable power and limited size.
8. Veins: Dilated and Inflamed
   • a. Varicose veins are abnormal and irregular dilations in surface veins.
     • i. Usually found in the lower legs.
     • ii. Varicose veins in the rectum are termed hemorrhoids or piles.
     • iii. Develop when the valves become weak and blood backs up and expands vein; may be aggravated by crossing legs or otherwise constricting blood flow.
   • b. Phlebitis is inflammation of a vein.
     • i. Inflamed deep vessels may cause blood to clot.
     • ii. Resulting embolus may break off and come to rest in lungs; termed pulmonary embolism, it can result in death.