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The Heart: Structure, Circuits, and Function

Learn about the structure of the heart, its location in the thorax, the pulmonary and systemic circuits, and how blood flows through the heart. Understand the different chambers, walls, and coverings of the heart, and discover the heartbeat and its significance.

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The Heart: Structure, Circuits, and Function

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  1. PART 2 The Heart

  2. The Heart • A muscular double pump • Pulmonary circuit – takes blood to and from the lungs • Systemic circuit – vessels transport blood to and from body tissues • Atria – receive blood from the pulmonary and systemic circuits • Ventricles – the pumping chambers of the heart

  3. The Pulmonary and Systemic Circuits Figure 18.1

  4. Location and Orientation within the Thorax • Heart – typically weighs 250–350 grams (healthy heart) • Largest organ of the mediastinum • Located between the lungs • Apex lies to the left of the midline • Base is the broad posterior surface

  5. Location and Orientation within the Thorax Figure 18.2

  6. Four “Corners” of the Heart • Superior right • At costal cartilage of third rib and sternum • Inferior right • At costal cartilage of sixth rib lateral to the sternum • Superior left • At costal cartilage of second rib lateral to the sternum • Inferior left • Lies in the fifth intercostal space at the midclavicular line

  7. Location and Orientation within the Thorax Figure 18.2

  8. Structure of the Heart – Coverings • Pericardium – two primary layers • Fibrous pericardium • Strong layer of dense connective tissue • Serous pericardium • Formed from two layers • Parietal pericardium • Visceral pericardium

  9. Structure of the Heart – Coverings Figure 18.3

  10. Structure of the Heart – Layers of the Heart Wall • Epicardium • Visceral layer of the serous pericardium • Myocardium • Consists of cardiac muscle • Muscle arranged in circular and spiral patterns • Endocardium • Endothelium resting on a layer of connective tissue • Lines the internal walls of the heart

  11. Structure of the Heart – Layers of the Heart Wall Figure 18.4

  12. Heart Chambers • Right and left atria • Superior chambers • Right and left ventricles • Inferior chambers • Internal divisions • Interventricular septa • Interatrial septa • External markings • Coronary sulcus • Anterior interventricular sulcus • posterior interventricular sulcus PLAY Rotatable Heart

  13. Heart Chambers Figure 18.5b

  14. Right Atrium • Forms right border of heart • Receives blood from systemic circuit • Pectinate muscles • Ridges inside anterior of right atrium • Crista terminalis • Landmark used to locate veins entering right atrium • Fossa ovalis • Depression in interatrial septum • Remnant of foramen ovale

  15. Right Ventricle • Receives blood from right atrium through the tricuspid valve • Pumps blood into pulmonary circuit via • Pulmonary trunk • Internal walls of right ventricle • Trabeculae carneae • Papillary muscles • Chordae tendineae

  16. Left Atrium • Makes up heart’s posterior surface • Receives oxygen-rich blood from lungs • Opens into the left ventricle through • Mitral valve (left atrioventricular valve)

  17. Left Ventricle • Forms apex of the heart • Internal walls of left ventricle • Trabeculae carneae • Papillary muscles • Chordae tendineae • Pumps blood through systemic circuit via • Aortic semilunar valve (aortic valve) PLAY Rotatable Heart Section

  18. Heart Chambers Figure 18.5e

  19. Inferior View of the Heart Figure 18.5d

  20. Pathway of Blood Through the Heart • Beginning with oxygen-poor blood in the superior and inferior venae cavae • Go through pulmonary and systemic circuits • A blood drop passes through all structures sequentially • Atria contract together • Ventricles contract together

  21. Blood Flow Through the Heart Figure 18.6

  22. Pathway of Blood Through the Heart Figure 18.6b

  23. Heartbeat • 70 – 80 beats per minute at rest • Systole – contraction of a heart chamber • Diastole – expansion of a heart chamber • Systole and diastole also refer to • Stage of heartbeat when ventricles contract and expand

  24. Structure of Heart Wall • Walls differ in thickness • Atria – thin walls • Ventricles – thick walls • Systemic circuit • Longer than pulmonary circuit • Offers greater resistance to blood flow

  25. Structure of Heart Wall • Left ventricle – three times thicker than right • Exerts more pumping force • Flattens right ventricle into a crescent shape Figure 18.7

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