Cardiovascular system consists of: • Muscular pump—the heart • Series of conduits—blood vessels • Fluid—bloodHeart • Function  Generates blood pressure to move blood through vessels  Regulates blood supply— changes in rates and force to meet demands  Routes blood through systemic or pulmonary circulationThe human heart has four chambers—two atria and two ventricles. The atria receive blood from the body and deliver it to the ventricles. The ventricles then pump the blood out to the body. The right ventricle pumps blood through the pulmonary circuit. The left ventricle pumps blood through the systemic circuit. Rt ventricle Rt atrium pulmonary vein Systemic circuit Pulmonary circuitValves prevent backflow of blood: • Atrioventricular (AV) valves lie between the atria and ventricles and prevent backflow when ventricles contract • The pulmonary valve and aortic valve (SL valves) lie between the ventricles and the major arteries and prevent backflow when ventricles relax Tricuspid valve Bicuspid valveThe right atrium receives deoxygenated blood from the body through large veins: • Superior vena cava—blood from upper body • Inferior vena cava—blood from lower body Rt ventricle Rt atrium pulmonary vein Systemic circuit Pulmonary circuitBlood passes from the right atrium through Rt AV (tricuspid) valve into the right ventricle. The atrium contracts, then the ventricle—the AV valve closes and blood is pumped through the pulmonary artery to the lungs where it is oxygenated. Rt ventricle Rt atrium pulmonary vein Systemic circuit Pulmonary circuitOxygenated blood returns to the left atrium of the heart through the pulmonary veins. The ventricle fills as blood enters through Left AV (bicuspid) valve. The left atrium contracts, then the ventricle—the aortic valve opens and blood circulates through the aorta. Rt ventricle Rt atrium pulmonary vein Systemic circuit Pulmonary circuit1 Blood returning to heart fills atria, putting pressure against AV valves; AV valves are forced open. 1 Ventricles contract, forcing blood against atrioventricular valve cusps. 2 As ventricles fill, AV valve flaps hang limply into ventricles. 2 Atrioventricular valves close. “Lub” 3 Atria contract, forcing additional blood into ventricles. 3 Papillary muscles contract and chordae tendineae tighten, preventing valve flaps from everting into atria. (a) AV valves open; atrial pressure greater than ventricular pressure (b) AV valves closed; atrial pressure less than ventricular pressure Direction of blood flow Atrium Ventricle Cusp of atrioventricular valve (open) Chordae tendineae Papillary muscle Atrium Blood in ventricle Cusps of atrioventricular valve (closed)As ventricles contract and Intraventricular pressure rises, blood is pushed up against semilunar valves, forcing them open As ventricles relax and intraventricular pressure falls, blood flows back from arteries, filling the cusps of semilunar valves and forcing them to close. “Dupp” (a) Semilunar valves open (b) Semilunar valves closed Aorta Pulmonary trunkfirst the two atria contract, then the two ventricles contract. Two phases: • Diastole—when ventricles relax • Systole—when ventricles contract  Creates pressure gradient that causes blood to flow Cardiac cycle p pBlood pressure changes are measured with a sphygmomanometer and a stethoscope. • Systolic value— pressure at which blood begins to flow after being compressed; pulsing sound • Diastolic value—pressure at which blood flows freely; pulsing sound stops Pressure at which blood starts to flow is the systolic P; Pressure at which blood flows freely is diastolic P. Ests of how hard the heart has to work to get blood flowing.Conduction system: • Cardiac muscles cells are in close contact with each other through desmosomes and gap junctions— spread of action potentials result in coordinated contraction • Cardiac muscles cells have the capacity to generate action potentials (electrical signals), independent of the nervous system. Some cells are pacemaker cells and generates the electrical signals for the heartbeat• An action potential is generated in the sinoatrial (SA) node; pacemaker cells • The action potential spreads in the atria (through gap junctions) and they contract together. The action potential in the atria are picked up by the atrioventricular node and passes it down through the bundle of His after a short delay. Purkinje fibers SA node AV node Bundle of His The bundle divides into right and left bundle branches that run to the tips of the ventricles.Purkinje Fibers carry impulses to heart apex and up the walls of both ventricles. A contraction spreads through ventricles, upward from apex. Ventricles contract in a “wringing” motion Purkinje fibers SA node AV node Bundle of HisBlood is a connective tissue: cells in a liquid extracellular matrix, called plasma. Most of the cells in blood are erythrocytes (or red blood cells), that transport gases. The hematocrit is the percentage of blood made up of RBC. 1 Withdraw blood and place in tube. 2 Centrifuge blood sample, separation based on density. Plasma • 55% of whole blood Buffy coat • Leukocytes,platelets Erythrocytes: RBC • 45% of whole blood Formed elements• 90% water • Proteins: mostly produced by the liver – E.g., albumin, globulin, fibrinogen • Respiratory gasses, hormones, nitrogenous by- products, nutrients, and electrolytes Plasma • 55% of whole blood Buffy coat • Formed elements Erythrocytes Blood PlasmaFormed elements • WBCs– only complete cells in blood • RBCs-- have no nuclei or organelles • Platelets-- cell fragments • Most formed elements survive in blood for ~few days • Most blood cells originate in bone marrow Platelets RBC WBC Plasma • 55% of whole blood Buffy coat • Formed elements ErythrocytesErythropoiesis: formation of red blood cells Erythropoietin, a hormone released in the kidney in response to hypoxia, stimulates erythropoiesis. Red blood cells are produced in bones (red marrow) They lose their organelles (eg., nucleus) and are released into blood. Immature RBCs mature in blood; turn white to red as they accumulate Hb. Circulate ≈ 120 days and then rupture.Red marrow also produces megakaryocytes that break off into cell fragments called platelets. Platelets initiate blood clotting when activated by collagen exposed in damaged blood vessels. •