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Circulation Chapter 32 Circulatory System Basics • Three major parts – Blood – Blood vessels – Heart Two Types of Systems • Open circulatory system: space within the body cavity (hemocoel) – Found in arthropods and most mollusks – Circulates hemolymph – Similar to interstitial fluids – Used to transport nutrients, wastes, hormones, rarely used for O2 Two Types of Systems • Closed circulatory system: blood confined within continuous vascular network with a pumping heart – Found in some invertebrates and all vertebrates Diverse Functions 1. Transport of O2 and CO2 2. Distribution of nutrients 3. Transport of waste 4. Distribution of hormones 5. Regulation of body temperature 6. Prevent blood loss 6. Protect against disease Evolution of the Vertebrate Heart • Vertebrate hearts have muscular chambers called atria and ventricles • Can have 2, 3, or 4 chambers – Atria collect blood from body • Contract and deposit blood in ventricles – Ventricles contract and discharge blood to body Evolution of the Vertebrate Heart • Two chambered hearts – Earliest vertebrate hearts with one atrium and one ventricle – Example: fish hearts – Conus arteriosus (aorta) carries blood away from ventricle – Sinus venosus – carries blood to the atrium Evolution of the Vertebrate Heart • Three chambered hearts – Have two atria and one ventricle – Examples: amphibian and most reptile hearts – Double circulation – blood moves thru heart twice while completing a circuit. Systemic & pulmonary circulation – No separation of right & left sides (mixing of oxygenated & deoxygenated blood) Evolution of the Vertebrate Heart • Four chambered hearts – Most advanced – Have two atria and two ventricles – Separation of O2-rich and O2-poor blood maximizes O2 levels in blood – Examples: bird and mammal hearts Human Heart Function • Two types of blood vessels connect to heart chambers: – Veins: carry blood to atria – Arteries: carry blood away from ventricles Human Heart Function • Made of two separate pumps – Right pump: made of right atrium and right ventricle – Left pump: made of left atrium and left ventricle – Right atrium receives O2-poor blood from body by superior and inferior vena cavae – Right ventricle ejects O2-poor blood into pulmonary arteries to be oxygenated by lungs Human Heart Function – Left atrium receives O2-rich blood from lungs by pulmonary veins – Left ventricle ejects O2-rich blood into aorta to be distributed to body tissues – Pumps separated by ventricular septum Heart Valves • Heart valves insure one-way flow of blood through heart – Insures that O2-poor blood is sent to lungs and O2-rich blood is sent to body tissues – Atrioventricular valves: allow blood to flow from atria to ventricles, prevent back flow – Semilunar valves: allow blood to flow from ventricles to arteries, prevent back flow Cardiac Muscle • The heart is composed of cardiac muscle tissue • Cardiac muscle cells are – Small, branched, and striated – Linked to one another via intercalated discs containing gap junctions – Gap junctions allow the electrical signals that trigger contractions to spread directly and rapidly from one muscle cell to the next • This results in the coordinated, synchronous contraction of heart muscle The Cardiac Cycle • The heart beats in a coordinated fashion: – Both atria contract and pump blood into ventricles – Both ventricles contract and pump blood into arteries – All chambers relax briefly before the cycle repeats – This cardiac cycle lasts less than 1 second Blood Pressure • Heart chamber contractions generate blood pressure that drives blood flow: – Systolic pressure: blood pressure during ventricular contraction – Diastolic pressure: blood pressure during ventricular relaxation – Pulse – expansion & contraction of artery walls during heartbeat High Blood Pressure • High blood pressure (hypertension) is caused by the constriction of arterioles • Causes resistance to blood flow and strain on the heart • Borderline reading for high blood pressure is 140/90 • Hypertension interacting with hardened arteries can lead to blood clot formation • Blood clots can block arteries, leading to – Heart attack – Stroke Coordination of Contractions • Pacemaker cells coordinate cardiac cycle – Heart cells that regularly produce spontaneous electrical impulses – Impulses spread throughout heart muscle cells and stimulate them to contract • Sinoatrial (SA) node is the primary pacemaker – In upper wall of right atrium – Generates impulses that spread throughout cardiac muscle cells of atria – Atrial cells contract in unison and finish emptying blood Coordination of Contractions • Atrioventricular (AV) node: second pacemaker cell cluster – In floor of right atrium – Stimulated by SA node impulse – After a 0.1 second delay, sends impulse to ventricles by excitable fibers – Ventricles contract when stimulated Control of Heart Rate • SA node maintains heart rate of 100 beats per minute (bpm) • Nervous system modifies heart rate: – At rest, parasympathetic nervous system slows heart rate to ~70 bpm – During exercise and stress, sympathetic nervous system increases heart rate • Endocrine system modifies heart rate – Under stress, the hormone epinephrine is released – Stimulates SA node and increases heart rate Two Major Blood Components • Plasma: fluid portion of blood – 55-60% of blood volume • Cellular components: made of red blood cells, white blood cells, and platelets – 40-45% of blood volume • Plasma – ~90% water • Other components – – – – – – Hormones Nutrients Gases Salts Wastes Proteins Plasma Proteins • Three major types – Albumins: maintain osmotic pressure of blood – Globulins: transport nutrients and act in immunity – Fibrinogen: involved with blood clotting Red Blood Cells • • • • Also called erythrocytes Make up 99% of all blood cells Carry oxygen from lungs to tissues Human erythrocytes have a biconcave disk shape • Red color caused by pigment hemoglobin – Composed of four polypeptide chains and four ironcontaining heme groups – Each heme group binds to O2 in lung and turns hemoglobin cherry red – Hemoglobin releases O2 and picks up some CO2 at tissues Red Blood Cell Life Span • • • • Formed in red bone marrow During formation, nucleus is removed Red blood cells live ~ 4 months 2 million red blood cells die per second and are replaced by bone marrow – Removed by liver and spleen – Iron recycled and used to form more hemoglobin Red Blood Cell Life Span • When blood O2 levels are low, erythropoietin is released by kidneys – Stimulates additional red blood cell formation by bone marrow – Controlled by negative feedback White Blood Cells • Also called leukocytes • Make up < 1% of all blood cells • Most protect body against disease Example: lymphocytes – Can produce antibodies used in immunity • Example: macrophages – Mobile and amoeba-like – Engulf foreign particles and bacteria Platelets • Fragments of megakaryocytes formed in the red bone marrow – Pieces pinched off and enter circulation • Called thrombocytes • Involved in clotting • Last 10-12 days Blood Clotting • Keeps animals from bleeding to death • Blood clot – Formed from sticky fibrin protein threads, platelets, and other cells forming patch over wound site • Results from interaction among circulating plasma proteins, particularly thrombin and fibrinogen Blood Clot Formation • Aggregated platelets in clot constrict after ~ 30 minutes – Tightens fibrin web and forces liquid out of clot – Results in denser, tougher clot • On skin surface, called a scab Pattern of Blood Flow • Blood flows through blood vessels • From heart Arteries arterioles capillaries venules veins back to heart Arteries • Thick walled vessels – Contain smooth muscle and elastic tissue to withstand high pressure • Elastic recoil maintains blood pressure during diastole • Carry oxygenated blood (except pulmonary arteries) Arterioles • Branch off of arteries • Smaller in diameter • Help control distribution of blood flow Capillaries • Tiniest vessels—thin, single-cell thick for easy diffusion • Allow exchange of materials between blood, interstitial fluids, and body cells – Nutrients – Gases – Hormones • Blood pressure drives fluid leakage out of capillaries and into spaces surrounding tissue cells (i.e., interstitial fluid) Venules • Capillaries merge to form larger venules • Venules merge to form veins Veins • Contain smooth muscle and elastic tissue – Wider, thinner walled than arteries – Contain one-way valves that allow blood to flow only to heart – Skeletal muscle contractions compress veins and drive blood movement towards heart Distribution of Blood Flow • Muscular arteriole walls contract and relax to redirect blood flow and regulate blood pressure • Controlled by nerves, hormones, and nearby chemicals The Lymphatic System • Includes lymphatic vessels, lymphatic capillaries, lymph nodes, thymus, and spleen • Functions – (1) Returns excess interstitial fluid to bloodstream – (2) Transports fats from small intestine to bloodstream – (3) Contributes to immunity Lymphatic Capillaries • “Dead-end” lymphatic capillaries collect excess interstitial fluid from tissues – Lymph: fluid in lymphatic system • Lymphatic capillary cells overlap – Act as one-way valves – Allow fluid and particles to drain into lymphatic capillaries – Merge to form lymphatic vessels Lymphatic Vessels • Similar in structure to veins, including oneway valves • Muscle contractions drive lymph flow Return of Fluid to the Blood • 3 to 4 liters of excess interstitial fluid are generated per day – Collected by lymphatic system and deposited into general circulation where thoracic duct joins with vena cava • Elephantiasis: a disease caused when parasitic roundworms colonizes lymphatic vessels – Prevent draining of lymph and causes extreme swelling (edema) Transport of Dietary Fats • Small intestine has many lymphatic capillaries • Lymph is composed of ~1% of fattransporting particles – Too large to diffuse into blood capillaries – Travel in lymph until introduced into general circulation Defense Against Disease • Tonsils: patches of connective tissue containing many lymphocytes – Destroy bacteria and viruses • Lymph nodes: kidney-shaped structures found connecting lymph vessels – Contain many macrophages and lymphocytes – Destroy foreign particles in lymph Defense Against Disease • Thymus: found above heart – Important site of lymphocyte development • Spleen: found in abdominal cavity – Functionally similar to a lymph node, but filters blood instead of lymph – Destroys old red blood cells