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Coverings of the heart Enclosed in a layered pericardium Pericardial space between layers is fluid filled Wall of heart Endocardium – inner layer Myocardium – middle; mostly cardiac muscles Epicardium (visceral pericardium) – outer layer Heart Chambers, Valves & Blood Flow Heart is divided into 4 chambers – 2 atria, 2 ventricles R. chambers and valves – O2 poor blood R. atrium receives blood from superior & inferior vena cava & coronary sinus Blood passes through tricuspid valve to R. ventricle Blood passes through pulmonary semilunar valve to L. & R. pulmonary arteries ***only arteries to carry O2 poor blood*** Heart Chambers, Valves & Blood Flow L. chambers and valves – O 2 rich Blood returns from lungs via L. & R. pulmonary veins ***only veins to carry O2 rich blood*** O2 rich blood dumps into L. atrium Blood passes through bicuspid valve into L. ventricle Blood passes through aortic semilunar valve to aorta Distributed to the rest of body (systemic circulation) http://www.youtube.com/watch?v=mH0QT WzU-xI (blood flow through the heart) http://vimeo.com/8321006 (animation - blood flow) Cardiac Cycle Pressure within chambers rises & falls in repeated cycles Contraction of heart – systole Relaxation of heart – diastole When atria are relaxes (atrial diastole) blood flows into them from veins (about 70% of blood flows directly into ventricles) When atria contract (atrial systole) the remaining 30% of blood flows into ventricles As ventricles contract (ventricular systole) bicuspid/tricuspid valves are pressed closed; blood flows either to lungs or body Stroke volume = volume of blood ejected from ventricles http://www.youtube.com/watch?v=jLTdgrhpDCg Heart Sounds Described as lub-dub Due to the vibrations produced by the blood & valve movements Lub – occurs as A-V valves are closing/ventricles contract Dub – occurs as semilunar valves are closing/ventricles relax http://www.youtube.com/watch?v=te_SY3MeWys Cardiac Conduction System – Fig. 12-7 Composed of specialized cardiac muscle tissue and functions to initiate and conduct depolarization waves through the myocardium Signal is initiated by S-A node located in upper part of R. atrium (known as the pace maker of the heart). Ability to excite themselves Impulses spread into surrounding myocardium Atria contract Cardiac Conduction System – Fig. 12-7 Impulses travel slowly from S-A node (so atria have time to contract) to A-V node located in lower part of R. atrium Impulses now travel quickly to A-V bundle (bundle of His) and then to Purkinje fibers Ventricles contract – muscle fibers in ventricular walls are arranged in whorls that “wring” blood out of ventricles Regulation of the Cardiac Cycle Heartbeat is affected by physical exercise, body temp. and concentration of various ions Parasympathetic impulses cause a decrease in heart rate Sympathetic impulses cause an increase in heart rate Arteries & Arterioles Adapted to carry relatively high pressure blood AWAY from the heart Arterioles are branches of arteries Walls of arteries consist of layers of endothelium, elastic membrane, smooth muscle, and connective tissue ***walls of arteries are thicker than walls of veins or capillaries*** Capillaries – form connections between arterioles & venules Consist of a single layer of cells that forms a semipermeable membrane Capillary density varies directly with tissue metabolic rates Muscle & nerve – rich supply Cartilaginous, epidermis, cornea (low metabolic rates) lack capillaries Capillaries – form connections between arterioles & venules Capillary flow is regulated by opening & closing of precapillary sphincters Open when cells are low in O2 Close when cellular needs are met Capillaries – form connections between arterioles & venules Gasses, nutrients, and metabolic by-products are exchanged between capillary blood & tissue fluid Diffusion provides the most important means of transport Filtration due to the hydrostatic pressure of blood causes outward movement of fluid at the arterial end of capillary Osmosis causes a net inward movement of fluid at the venule end of a capillary Capillaries – form connections between arterioles & venules Capillaries – form connections between arterioles & venules Veins & venules Venules continue from capillaries and merge to form veins Veins carry blood TOWARD the heart Contain valves to keep blood moving toward the heart Venous walls are similar to arterial walls, but are thinner and contain less muscle and elastic tissue. http://www.youtube.com/watch?v=HNuPW dfjDoc Blood pressure is the force exerted by blood against the insides of the blood vessels – Fig. 12-16 (also see – Clinical Application pg. 327) http://www.youtube.com/watch?v=0L3hVPLlC4 (how to take blood pressure) Arterial blood pressure Produced primarily be heart action; rises & falls with phases of the cardiac cycle Systolic pressure occurs when the ventricles contract; diastolic pressure occurs when the ventricles relax Factors that influence arterial blood pressure Blood Volume An increase in volume causes an increase in pressure A decrease in volume causes a decrease in pressure Factors that influence arterial blood pressure Heart Action Volume of blood discharged from L. ventricle with each contraction is called stroke volume (70ml – 75ml) Cardiac output = volume discharged in 1 minute Cardiac output = stroke volume x heart rate (ex. 75ml x 70 beats/min. = 5250 ml/min) If stroke volume increases & heart rate stays the same the cardiac output increases causing an increase in blood pressure Factors that influence arterial blood pressure Peripheral Resistance – friction between the blood and the walls of the blood vessels An increase in PR causes an increase in bp A decrease in PR causes a decrease in bp Viscosity – physical property – thickness An increase in viscosity causes an increase in bp A decrease in viscosity causes a decrease in bp Control of Blood Pressure – heart rate is regulated by different portions of medulla oblongata Venous Blood Flow Not a direct result of heart action; it depends on skeletal muscle contraction, breathing movements, and venoconstriction Many veins contain flaplike valves that prevent blood from backing up Central Venous Pressure – pressure in the R. atrium Influenced by factors that alter flow of blood into R. atrium Ex. – A weak heart causes an increase in pressure in R. atrium which causes the flow of blood to slow which causes pressure to increase in peripheral veins Pulmonary Circulation Composed of vessels that carry blood from R. ventricle to lungs and back to l. atrium Pulmonary capillaries contain lower pressure than systemic capillaries (R. ventricle contracts with less force than L. ventricle Exchange of oxygen and carbon dioxide; tightly joined epithelial cells of alveoli prevent most substance from entering alveoli Pulmonary Circulation Systemic Circulation http://www.youtube.com/watch?v=0jznS5psypI Vessels that carry blood from L. ventricle to body cells and back to R. atrium Includes aorta & branches & system of veins Hepatic portal – the route of blood flow through the liver (fig. 12-14); blood passes through 2 capillary beds before returning to the heart Renal circulation – the route of blood through kidneys (fig. 17-3 pg. 443); blood passes through 2 capillary beds before returning to the heart Coronary Circulation – The delivery of oxygen & nutrients and the removal of carbon dioxide & wastes from cardiac muscle tissue Hepatic Portal Circulation Renal Circulation Coronary Circulation Blood is carried between the placenta and the fetus by umbilical vessels Fetal blood carries more O2 than maternal blood Blood enters fetus through umbilical vein (O2 rich) and partially bypasses the liver by means of the ductus venosus Blood enters R. atrium & partially bypasses the lungs by means of the foramen ovale Blood entering the pulmonary trunk partially bypasses the lungs by means of the ductus arteriosus Blood enters umbilical arteries from the internal iliac arteries (O2 poor) http://www.youtu be.com/watch?v= OV8wtPYGE-I http://www.mhhe.com/biosci/genbio/virtual _labs_2K8/labs/BL_14/index.html (Virtual Blood Pressure Lab)