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  1. 1. The Heart Chapter 19
  2. 2. Heart Anatomy
  3. 3. Size and Location • About the size of the fist and weighs less than a pound • Enclosed within the mediastinum, medial cavity of the thorax • Rests on superior surface of diaphragm • Anterior to vertebral column and posterior to sternum • Lungs flank laterally and partially obscure it • ~ 2/3 of it lies to left • Broad, flat base or posterior surface
  4. 4. Coverings • Heart enclosed in double-wall sac called the pericardium • Loosely fitting superficial part of sac is the fibrous pericardium • The pericardium: – Protects heart – Anchors it to surrounding surfaces – Prevents overfilling of the heart with blood
  5. 5. Coverings (con’t) • Deep to fibrous pericardium is the serous pericardium, which is thin and slippery and composed of 2 layers. – The two layers have a film of serous fluid between them – Allows the hear to work in a relatively friction-free environment
  6. 6. Coverings (con’t) • Inflammation of the pericardium, pericarditis, hinders production of serous fluid and roughens the surfaces. • Creates a creaking sound that can be hear with a stethoscope and pain deep to the chest. • If persists, can cause adhesions and impede heart activity
  7. 7. Layers of Heart 1. Epicardium - visceral layer of the serous pericardium - often infiltrated with fat 2. Myocardium - composed mainly of cardiac muscle - forms bulk of heart - layer that contracts 3. Endocardium - glistening white sheet of endothelium - lines heart chambers and covers valves
  8. 8. Heart Chambers The heart has 4 chambers: 2 superior atria and 2 inferior ventricles
  9. 9. The internal partition that divides the heart is the interatrial septum when it separates the atria and the interventricular septum when it separates the ventricles.
  10. 10. Atria: The Receiving Chambers • The atrium has two basic parts: – A smooth-walled posterior part – An anterior part with ridged walls • The interatrial septum has a shallow depression called the fossa ovalis. This marks the spot where the foramen ovale existed in the fetal heart.
  11. 11. Atria (con’t) • Receiving chambers for blood returning to the heart from the circulation. • Contract minimally to push blood into the ventricles; therefore, they are relatively small and thin.
  12. 12. Atria (con’t) • Blood enters the right atrium through 3 veins: – Superior vena cava – returns blood from body regions superior to the diaphragm – Inferior vena cava – returns blood from body areas below the diaphragm, and – Coronary sinus – collects blood from the myocardium
  13. 13. Atria (con’t) • Four pulmonary veins enter the left atrium, which make up most of the heart’s base. • The pulmonary veins transport blood from the lungs back to the heart. • These vessels are best seen in a posterior view of the heart.
  14. 14. Ventricles: The Discharging Chambers • Make up most of the heart • Right ventricle forms heart anterior surface • Left ventricle forms inferior surface • When contracted, blood is propelled out of the heart into circulation. – Right ventricle pumps blood into pulmonary trunk  to the lungs for gas exchange – Left ventricle pumps blood into the aorta  to the body’s systems
  15. 15. Pathway of Blood
  16. 16. • Heart is two side-by-side pumps • Each side serves two different circuits: – Pulmonary Circuit – Systemic Circuit
  17. 17. Pulmonary Circuit Pump • Right side • Blood returns from body, which is oxygen- poor and carbon dioxide-rich and enters the right atrium. • Then, it passes into the right ventricle, which pumps it to the lungs via the pulmonary trunk. • In the lungs, blood unloads the carbon dioxide and pucks up oxygen. • Freshly oxygenated blood is carried to the left side of heart.
  18. 18. Systemic Circuit Pump • Left side of heart • Freshly oxygenated blood leaves lungs to return to left atrium and passes into left ventricle, which pumps into the aorta. • Blood is transported via smaller arteries to body tissues, where gases and nutrients are exchanged. • Blood loaded with carbon dioxide and oxygen depleted, returns through the systemic veins to right side of heart, where enters venae cavae.
  19. 19. Pathway (con’t) • Although equal volumes are pumped, 2 ventricles have unequal workloads. – Pulmonary circuit is short and low- pressure. – Systemic circuit is very long and high- pressure. •Encounters 5x’s as much friction •Walls are 3x’s as thick •Cavity is nearly circular
  20. 20. Coronary Circulation • Feeds the heart and is the shortest circulation of body • Actively delivers blood when heart is relaxed, but are ineffective when ventricles are contracting because: – They’re compressed by contracting myocardium, and – The entrances are partly blocked by flaps of valves.
  21. 21. Coronary Circulation (con’t) • Myocardial cells are weakened by temporary lack of oxygen, but don’t die. • Complete blockage of a coronary artery leads to tissue death and a myocardial infarction, or heart attack or coronary. • Cardiac muscle is amitotic, which is replaced by noncontractile scar tissue.
  22. 22. Heart Valves Blood flows through the heart in one direction: from atria to ventricles. One way traffic is enforced by heart valves. Valves open and close in response to changes in blood pressure.
  23. 23. Atrioventricular (AV) Valves • Located at each atrial-ventricular junction, preventing backflow into the atria when the ventricles are contracting. • Right AV valve, the tricuspid valve, has 3 flaps. Left AV valve, the bicuspid valve, has 2 flaps. • Attached to the valve flaps are tiny white collagen cords called chordae tendineae, or “heart strings,” anchor flaps to heart walls.
  24. 24. AV Valves • When heart is relaxed, AV flaps hang limply into ventricular chambers below; blood flows into atria and through open AV valves into ventricles. • When ventricles contract, blood is compressed into chambers, intraventricular pressure rises, forcing blood upwards against valve flaps. • Valve flap edges meet, closing valves. • Chordae tendineae serve as guidewires to anchor flaps in place.
  25. 25. Semilunar (SL) Valves • Aortic and pulmonary SL valves guard bases of large arteries that exit the ventricles. • When ventricles are contracting and intraventricular pressure rises, the SL valves are forced open and flaps flatten against the arterial walls and blood rushes by. • When ventricles relax, blood flows back toward the heart and closes the valves.
  26. 26. Cardiac Cycle • Heart writhes in the chest when it contracts • Forces blood out of chambers when it contracts and fills with blood when it relaxes. • Two terms are used to refer to heart contraction/relaxation: – Systole  contraction – Diastole  relaxation
  27. 27. Cardiac Cycle (con’t) • Includes all events associated with the flow of blood through the heart during one heartbeat. • Marked by a succession of pressure and blood volume change in heart. • Lasts about 0.8 seconds – Atrial systole  0.1 s – Ventricular systole  0.3 s – Total heart relaxation  0.4 s (quiescent period)
  28. 28. Cardiac Cycle (con’t) • Two important points: 1. Blood flow through the hear tis controlled by pressure changes, and 2. Blood flow along a pressure gradient is always from higher pressure to lower pressure through any available opening.
  29. 29. Heart Sounds • Two distinguishable sound during cardiac cycle can be heard. • Often described as “lub-dup”, which is associated with the closing of the heart valves. • Pause between lub-dup is the quiescent period.
  30. 30. Murmurs • An abnormal or unusual heart sound • Caused by obstruction along blood pathway • Fairly common in young children • Indicate valve problems (or possible hole in heart) • If a valve is incomplete, a swishing sound can be heard.
  31. 31. Cardiac Output (CO) • Amount of blood pumped out be each ventricle in 1 min. • Highly variable and increases in response to demands • Difference in resting and maximal CO is called the cardiac reserve. – Nonathletes’ reserve is 4-5x’s normal CO – Athletes’ reserve can be 7x’s the normal CO
  32. 32. Regulation of Heart Rate • With a healthy cardiovascular system the amount of blood pumped (stroke volume) is relatively constant. • When blood volume drops sharply or the heart is weakened, stroke volume declines and the heart maintains the CO by beating faster. • Also, the nervous system can affect heart rate. Fear, anxiety, stress, etc. causes an increase in norepinephrine, which causes the pacemaker to fire more rapidly and the heart beats faster.