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Transcript

  • 1. The Heart Chapter 19
  • 2. Heart Anatomy
  • 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.  
  • 5. 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
  • 6. 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
  • 7. 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
  • 8. Layers of Heart
    • 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
  • 9.  
  • 10. Heart Chambers The heart has 4 chambers: 2 superior atria and 2 inferior ventricles
  • 11. 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.
  • 12.  
  • 13. 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.
  • 14. 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.
  • 15. 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
  • 16. 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.
  • 17. 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
  • 18. Pathway of Blood
  • 19.
    • Heart is two side-by-side pumps
    • Each side serves two different circuits:
      • Pulmonary Circuit
      • Systemic Circuit
  • 20.  
  • 21. 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.
  • 22. 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.
  • 23. 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
  • 24.  
  • 25. 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.
  • 26.  
  • 27. 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.
  • 28.  
  • 29. 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.
  • 30.  
  • 31. 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.
  • 32.  
  • 33. 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.
  • 34.  
  • 35. 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.
  • 36.  
  • 37. 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
  • 38. 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)
  • 39. Cardiac Cycle (con’t)
    • Two important points:
      • Blood flow through the hear tis controlled by pressure changes, and
      • Blood flow along a pressure gradient is always from higher pressure to lower pressure through any available opening.
  • 40. 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.
  • 41. 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.
  • 42. 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
  • 43. 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.