Chapter 32 Circulation 32 1 What Are the Major Features and Functions of Circulatory Systems All circulatory systems have three major parts A pump the heart that keeps the blood A liquid blood that serves as a medium of circulating transport A system of tubes blood vessels that conduct the blood throughout the body The vertebrate circulatory system of humans and other vertebrates has diverse functions Transport of O2 from the lungs or gills to the tissues and transport of CO2 from the tissues to the lungs or gills Distribution of nutrients from the digestive system to all body cells Transport of waste products and toxic substances to the liver where many of them are detoxified and to the kidneys for excretion Distribution of hormones from the glands and organs that produce them to the tissues on which they act Regulation of body temperature by adjustments in blood flow Wound healing and blood clotting to prevent blood loss Protection against disease by circulating white blood cells and antibodies 32 2 How Does the Vertebrate Heart Work The vertebrate heart consists of muscular chambers capable of strong contractions Chambers called atria collect blood Atrial contractions send blood into ventricles chambers whose contractions circulate blood through the lungs and to the rest of the body During the course of evolution the heart has become increasingly complex with more separation between oxygenated blood and deoxygenated blood The hearts of fish the first vertebrates to evolve consist of two chambers a single atrium that empties into a single ventricle Evolution of the Vertebrate Heart gill capillaries ventricle atrium body capillaries a Fish Fig 32 2a As fish gave rise to amphibians and amphibians to reptiles a three chambered heart evolved which consists of two atria and one ventricle Evolution of the Vertebrate Heart lung capillaries atria ventricle body capillaries b Amphibians and some reptiles Fig 32 2b The four chambered hearts of some reptiles including crocodiles and their relatives and all birds and mammals have separate right and left ventricles that completely isolate oxygenated and deoxygenated blood Evolution of the Vertebrate Heart lung capillaries atria ventricles body capillaries c Mammals crocodiles and birds Fig 32 2c Helpful Circulation terminology Artery vessel that carries blood away from the Vein vessel that carries blood to the heart Pulmonary having to do with the lungs Systemic having to do with everywhere else in heart the body Vena Cava largest vein in the human body Aorta largest artery in the human body Four chambered hearts consist of two separate pumps One pump consisting of the right atrium and right ventricle deals with deoxygenated blood Oxygen depleted blood enters the right atrium through two large veins called the superior and inferior vena cava After filling with blood the right atrium contracts forcing blood into the right ventricle Contraction of the right ventricle sends the oxygen depleted blood to the lungs through the pulmonary arteries vessels that carry blood away from the heart and to the lungs The other pump consisting of the left atrium and left ventricle deals with oxygenated blood Oxygen rich blood from the lungs enters the left atrium through the pulmonary veins and is then squeezed into the left ventricle Contraction of the left ventricle sends the oxygenated blood through the aorta to the rest of the body Valves maintain the direction of blood flow When the ventricles contract blood must be prevented from flowing back into the atria Blood entering the pulmonary artery and aorta must also be prevented from flowing back into the ventricles as the heart relaxes The directionality of blood flow is maintained by one way valves Pressure in one direction opens them but reverse pressure forces them closed Atrioventricular valves allow blood to flow from the atria into the ventricles but not the reverse Semilunar valves allow blood to enter the pulmonary artery and the aorta when the ventricles contract but prevent blood from returning as the ventricles relax The Human Heart and Its Valves and Vessels aorta superior vena cava pulmonary artery to left lung left atrium pulmonary artery to right lung pulmonary veins from right lung right atrium atrioventricular valve pulmonary veins from left lung atrioventricular valve semilunar valves left ventricle thicker muscle of left ventricle Fig 32 3 inferior vena cava right ventricle descending aorta to lower body Cardiac muscle is present only in the heart Cardiac muscle cells are small branched and striated These cells are connected by intercalated discs which contain desmosomes that link cells together and prevent the strong heart contractions from pulling the muscle cells apart These cells also contain gap junctions that allow the electrical signals to spread from one muscle cell to another producing synchronous heart muscle contractions The Structure of Cardiac Muscle cell nucleus Intercalated discs containing desmosomes and gap junctions link adjacent cardiac muscle cells Fig 32 4 The coordinated contractions of atria and ventricles produce the cardiac cycle The heart beats in a coordinated fashion Both atria contract and pump blood into the ventricles Both ventricles contract and pump blood into the arteries that exit the heart All chambers relax briefly before the cycle repeats This cardiac cycle lasts less than 1 second The Cardiac Cycle Oxygenated blood is pumped to the body Deoxygenated blood is pumped to the lungs Deoxygenated blood from the body enters the right ventricle Oxygenated blood from the lungs enters the left ventricle Blood fills the atria and begins to flow passively into the ventricles Atria contract forcing 1 blood into the ventricles 3 The cycle ends as the heart relaxes 2 Then the ventricles contract forcing blood through the arteries to the lungs and the rest of the body Fig 32 5 The cardiac cycle generates the forces that are measured when blood pressure is taken Systolic pressure the higher of the two readings is measured during ventricular contraction Diastolic pressure is the minimum pressure in the arteries as the heart rests between contractions A blood pressure reading of less than 120 80 is considered healthy a pressure of 140 90 or higher is defined as high blood pressure High blood pressure or hypertension is caused by the constriction of small arteries which causes resistance to blood flow and strain on the heart Some people have a genetic tendency
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