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CHAPTER 11

CHAPTER 11. Cardiovascular System. The Cardiovascular System. A closed system of the heart and blood vessels The heart pumps blood Blood vessels allow blood to circulate to all parts of the body

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CHAPTER 11

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  1. CHAPTER 11 Cardiovascular System

  2. The Cardiovascular System • A closed system of the heart and blood vessels • The heart pumps blood • Blood vessels allow blood to circulate to all parts of the body • The function of the cardiovascular system is to deliver oxygen and nutrients and to remove carbon dioxide and other waste products

  3. Blood • Transports gases, nutrients, hormones, and wastes • Carries oxygen from blood and nutrients from digestive organs to all body cells • Transports hormones from endocrine glands to target cells • Carries wastes from body cells to excretory organs

  4. Heart • Hollow, cone-shaped, muscular pump • Located within the mediastinum of the thoracic cavity, resting on diaphragm, between lungs • Apex extends downward and left • Average size is 14 cm long, 9 cm wide – approximately the size of a fist • Weighs less than a pound

  5. The Heart: Coverings • Pericardium – a double serous membrane • Visceral pericardium – part of heart wall • Next to heart • Parietal pericardium – dense, fibrous tissue • Outside layer • Serous fluid fills the space between the layers of pericardium • Figure 11.2 b

  6. The Heart: Heart Wall • Composed of three layers – Figure 11.2 b • Epicardium • Outside layer • This layer is actually the visceral pericardium covering • Connective tissue layer • Myocardium – “skeleton of the heart” • Middle layer • Mostly cardiac muscle • Endocardium – lines the chambers of the heart • Inner layer • Endothelium

  7. Heart Chambers 4 chambers – 2 left, 2 right • Superior chambers – atria • Thin walls, receive blood returning to heart • Receiving chambers • Inferior chambers – ventricles • Receive blood from atria and contract to force blood out of heart into circulation • Discharging chambers

  8. Septum – wall that separates right & left sides of heart • ***blood from 1 side never mixes with blood from other side • Interventricular septum • Interatrial septum

  9. Pulmonary Circuit • Right side of heart • Receives oxygen poor blood from veins • Blood enters heart through superior and inferior vena cavae • Leaves the heart through pulmonary trunk • Pulmonary trunk splits into right and left pulmonary arteries • Carried to lungs to pick up oxygen and remove CO2 • Returns to left side of heart through pulmonary veins

  10. Pulmonary circuit = blood from right side of heart, to lungs, to left side of heart • Functions to carry blood to lungs for gas exchange and back to heart • Figure 11.2 c, 11.3 - blue

  11. Systemic Circuit • Left side of heart • Supplies oxygen and nutrient rich blood to body organs • Pumped out of heart into aorta • Aorta branches into arteries which supply body tissues with oxygen and nutrients • Oxygen poor blood empties into veins which empty into superior or inferior vena cava

  12. Left ventricle needs to pump blood over a longer pathway through the body • Walls of left ventricle are thicker and more powerful than the right ventricle walls

  13. Heart Valves • 4 valves which allow blood to flow in only one direction, from artia through ventricles and out the arteries leaving the heart • Atrioventricluar valves – AV valves • Between atrial and ventricular chambers on each side • Left AV valve – bicuspid or mitral valve • Right AV valve – tricuspid valve

  14. Bicuspid valve • Between left atrium and left ventricle • Permits blood to flow from left atrium to left ventricle ONLY • Chordae tendineae prevent blood from backing up • fibrous strings that attach to the valve on the ventricle side and muscle tissue on the wall of ventricle

  15. Tricuspid valve • Between right atrium and right ventricle • Permits blood to flow from right atrium to right ventricle ONLY - blood cannot back up • Chordae tendineae – prevent blood from backing up

  16. Operation of AV Valves • Figure 11.4 • Blood enters atria, valves are forced open and ventricle fills – valves hang into ventricle • Atria contracts to fill ventricle • Filled ventricle contracts to empty forcing blood against AV valve which closes • Chordae tendineae prevent valves from opening

  17. Semilunar valves • Between ventricular chambers and arteries that leave the heart • Pulmonary semilunar valve • Aortic semilunar valve

  18. Pulmonary semilunar valve • When right ventricle contracts, pressure inside pushes on tricuspid valve & closes it • Only exit for blood is pulmonary trunk which divides into right & left pulmonary arteries • Pulmonary semilunar valve (3 cusps) is at base of pulmonary trunk & allows blood to leave right ventricle & not back up

  19. Aortic semilunar valve • When left ventricle contracts, pressure inside pushes on bicuspid valve & closes it • Only exit for blood is large artery called aorta • Aortic semilunar valve (3cusps) is at base of aorta and allows blood to leave left ventricle and not back up

  20. Each set of valves operates at a different time • During heart relaxation • AV valves are open • Semilunar valves are closed • During ventricle contraction • AV valves are closed • Semilunar valves are open

  21. The Heart: Associated Great Vessels • Aorta • Leaves left ventricle • Pulmonary arteries • Leave right ventricle • Vena cava • Enters right atrium • Pulmonary veins (four) • Enter left atrium

  22. Coronary Circulation • Blood in the heart chambers does not nourish the myocardium • The heart has its own nourishing circulatory system • Coronary arteries – branch from aorta, encircle the heart in the coronary sulcus • Cardiac veins – empty into coronary sinus • Blood empties into the right atrium via the coronary sinus

  23. Contractions of heart muscle • Heart pushes 6 liters of blood through the blood vessels over 1000 times in one day • Cardiac muscle cells contract spontaneously and independently without nerve impulses • Contractions are regulated by autonomic nervous system and the intrinsic conduction system

  24. Intrinsic conduction system • Built into heart tissue, sets the basic rhythm of the heart • Causes heart muscle depolarization – action potential • Composed of tissue unique to the heart, a cross between muscle and nervous tissue • Provides for a heart rate of 75 beats per minute • Heart beats as a coordinated unit

  25. Special tissue sets the pace • Sinoatrial (SA)node– in the right atrium • Pacemaker • Atrioventricular (AV) node – junction of atria and ventricles • Atrioventricular bundle – interventricular septum • Bundle branches - septum • Purkinje fibers – ventricle walls

  26. Sa node initiates depolarization • Depolarization passes through the atrial myocardium to AV node • Impulse is delayed so atria finishes contracting • Impulse passes to the AV bundle, the bundle branches, and the Purkinje fibers of the ventricular walls • Impulse begins at apex and moves toward atria

  27. Heart Contractions Figure 11.5

  28. Electrocardiogram - ECG • Traces the flow of current through the heart • Page 356 • P wave – depolarization of atria • QRS complex – depolarization of ventricles • T wave – repolarization of ventricle • When atria repolarize, ventricles are depolarized, therefore repolarization of atria is hidden by large QRS complex

  29. Abnormalities in shape or timing of ECG indicates that something is wrong with intrinsic conduction system • Myocardial infarct – area of heart tissue where cells have died due to ischemia – lack of adequate blood (oxygen) supply • Fibrillation – rapid, uncoordinated shudder of heart muscle

  30. Tachycardia – rapid heart rate, over 100 beats/min • Bradycardia – slower than normal heart rate, less than 60 beats/min

  31. Cardiac cycle • Refers to the events that occur during one heartbeat • Heartbeat refers to the contraction and relaxation of both the atria and ventricles • Atria contract simultaneously, then relax • When atria relax, ventricles contract • Heart beats 75 times/min • Cardiac cycle lasts about 0.8 second

  32. Systole – contraction of ventricles • Diastole – relaxation of ventricles • Figure 11.6 – 3 events in the cardiac cycle: • Mid-to-late diastole • Ventricular systole • Early diastole

  33. Mid-to-late diastole • Heart is in complete relaxation • Blood from both pulmonary and systemic circuit is filling atria and flowing passively into ventricles • AV valves are open, semilunar valves are closed • Atria contract to push remaining blood into ventricles (still relaxed)

  34. Ventricular systole • Ventricles contract and pressure closes AV valves • As pressure in ventricles increases, semilunar valves open and blood rushes into arteries leaving the heart • At the same time, atria are relaxed and begin to fill with blood again

  35. Early diastole • At end of systole, ventricles relax • Semilunar valves shut • Pressure in ventricles is low, atria are filling with blood and pressure in atria is high • The difference in pressure forces the AV valves to open and blood begins to fill the ventricles

  36. Heart sounds • “lub” “dup” • Sounds are heard through stethoscope • Lub – caused by the AV valves closing • Dup – caused by semilunar valves closing • Abnormal heart sounds are called murmurs • Usually indicate valve problems - when valve does not close properly or valve is too narrow

  37. Cardiac Output • Amount of blood pumped out of each ventricle in one minute • CO = heart rate x stroke volume • Heart rate – normally 75 beats/min • Stroke volume – volume of blood pumped out by a ventricle with each heart beat, about 70 mL/min • CO = 75 x 70 = 5250 mL/min

  38. Normal adult blood volume is about 5000 (6000) mL • Entire blood supply passes through the body once each minute • Cardiac output varies with the demands of the body – Figure 11.7 • CO rises if stroke vol is increased or heart beats faster • CO drops if either factor is decreased

  39. Changes in Stroke Volume • Stroke vol is increased by 1) stronger cardiac contractions or 2) increased venous return – the amount of blood entering the heart • Stroke vol is decreased by low venous return • Resulting from severe blood loss or rapid heart rate

  40. Changes in Heart Rate • Heart rate increases in order to maintain CO if stroke vol decreases • Heart rate is influenced by sympathetic and parasympathetic divisions of the autonomic nervous system • Heart rate does not depend on ANS, but can be temporarily changed • Heart rate is modified by hormones and ions • Age, gender, exercise, body temperature influence heart rate

  41. ANS controls • Sympathetic division • Physical or emotional stress stimulate SA and Av nodes • Heart rate increases • Parasympathetic division • Vagus nerve slow down heart rate and make in more steady in noncrisis situations

  42. Hormone & ion controls • Epinephrine and thyroxine increase heart rate • Low levels of Ca slow down heart rate, increased levels prolong contraction • Variations in Na and K levels can change heart rate

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