Chapter 20 notes (Heart)

From Biol557

Contents 1 Chapter 20: The heart 1.1 An introduction to the cardiovascular system 1.2 The heart is a four-chambered organ, supplied by the coronary circulation, that pumps oxygen-poor blood to the lungs and oxygen-rich blood to the rest of the body 1.2.1 The pericardium 1.2.2 Superficial anatomy of the heart 1.2.3 The heart wall 1.2.3.1 Cardiac muscle tissue 1.2.4 Internal anatomy and organization

Chapter 20: The heart

An introduction to the cardiovascular system

• There is a pulmonary circuit and a systemic circuit.
• Efferent vessels = arteries = away from the heart.
• Afferent vessels = veins = toward the heart.
• Capillaries = exchange vessels.
• The heart pumps 100k times per day, moving 8k liters!
• The right atrium receives blood from the systemic circuit; the left atrium receives blood from the pulmonary circuit.
• The ventricles pump at the same time and move the same volume of fluid into each circuit.

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The heart is a four-chambered organ, supplied by the coronary circulation, that pumps oxygen-poor blood to the lungs and oxygen-rich blood to the rest of the body

• The heart lies slightly to the left of center, behind the sternum.
• The inferior tip of the heart is called the apex.
• The mediastinum is the region between the two pleural cavities.
• The mediastinum holds the heart (in the pericardial sac) and the great vessels as well as the thymus, esophagus, and trachea.

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The pericardium

• The pericardial sac is like a balloon in which one's heart is depressed.
• The pericardial sac has two tissue layers:
  • The visceral pericardium (epicardium) covers and adheres to the surface of the heart.
  • The parietal pericardium lines the inner surface of the sac.
• Between the membranes, there is pericardial fluid which serves to reduce friction between the membranes and to protect the heart.
  • Pericarditis is the reduction of pericardial fluid and thus presents with a scratching noise that can be heard via stethoscope.
  • Cardiac tamponade occurs when fluid builds up in the pericardial sac (from infection or wounding, perhaps) and thus restructs the movements of the heart.
    • Tampon means plug in latin.

Superficial anatomy of the heart

• The atria have thin, muscular walls that are highly expandable.
• The atria have auricles that go limp and wrinkle after contracting blood out of the atria.
• The coronary sulcus is a deep grove that marks the boundary between the atrium and the ventricle.
• The anterior / posterior interventricular sulci are shallower depressions that mark the boundary between the left and right ventricles.
• The sulci also contain the coronary arteries / veins and substantial amounts of fat.

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The heart wall

• There are three layers to the wall of the heart:
  • The epicardium is the same as the visceral pericardium and has two sub layers: the exposed mesothelium and the areolar tissue which is connected to the myocardium.
    • Areolar: "Areolar tissue known as areis exhibits interlacing, loosely organized fibers, abundant blood vessels, and significant empty space. Its fiber run in random directions and are mostly collagenous, but elastic and reticular fibers are also present." [1]
  • The myocardium contains nerves, blood vessles, and muscle tissue that intricately wraps around the great vessels, the atria, and the ventricles with a figure-eight pattern. The myocardium has multiple layers of muscle fibers.
  • The endocardium is a simple squamous epithelium that covers the inside of the heart, including the valves, and is continuous with the endothelium of the vasculature.
    • Squamous: "In anatomy, squamous epithelium (from Latin squama, "scale") is an epithelium characterised by its most superficial layer consisting of flat, scale-like cells called squamous cell". [2]

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Cardiac muscle tissue

• Cardiac muscle fibers are connected with intercalated discs where the membranes of adjacent muscle cells interlock and are held together by desmosomes and gap junctions.
• These junctions allow for the fast propagation of action potentials.
• Note that cardiac muscle fibers can be differentiated in histological slides by:
  • their smaller size,
  • their single, centrally located nucleus,
  • their branching interconnections, and
  • the presence of intercalated discs.

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Internal anatomy and organization