chapter 19

Part 2 of Heart Lecture - Detailed Study Notes

Overview of the Heart's Location

• The heart is situated in the mediastinum, a space within the thoracic cavity.

  • Mediastinum extends from the top of the ribs to the diaphragm, excluding the lungs.

  • The heart is slightly tilted:

  • The left side is positioned more posteriorly.

  • The right side is positioned more anteriorly.

• The heart resembles an inverted pyramid:

  • Base: Superior/top part of the heart.

  • Apex: Inferior/conical end, pointing slightly left, located below the left lower part of the sternum.

• Visual Imagery:

  • Images illustrate oxygenated (red) and deoxygenated (blue) blood, though actual heart tissue appears in shades of brown and beige.

Heart Structure

• The heart is surrounded by a protective tissue known as the pericardium:

  • The prefix peri- means around; cardi- refers to the heart.

• Two Main Divisions of Pericardium:

  1. Fibrous Pericardium:

  • Tough, inelastic, dense irregular connective tissue.

  • Anchors the heart to the diaphragm and closes off near the top.

  1. Serous Pericardium:

  • Delicate tissue similar to Saran Wrap, has two layers:

    • Parietal Layer: Outer layer of the serous pericardium.

    • Visceral Layer: Inner layer, also known as epicardium.

• The pericardial cavity lies between the parietal and visceral layers, containing a small amount of fluid that reduces friction during heart movement.

Visualization of Pericardium and Heart Layers

• Visual Representation: A balloon model can illustrate how the pericardium works:

  • The balloon represents the pericardial cavity (visceral layer touches the heart).

  • Parietal layer represented by the outer part of the balloon.

• Three Layers of the Heart Wall:

  1. Epicardium (Visceral Layer of the Serous Pericardium):

  • Composed of fibroelastic and adipose tissue, provides a smooth texture.

  1. Myocardium:

  • Thickest layer, comprises about 95% of the heart wall.

  • Made of cardiac muscle tissue, which is striated (like skeletal muscle) but involuntary.

  • Responsible for heart contraction.

  1. Endocardium:

  • Thin layer of endothelial tissue lining the heart chambers and valves, ensuring continuity with blood vessels.

Heart Chambers

• Chambers of the Heart:

  • Atria (Two receiving chambers):

  • Right Atrium: Contains deoxygenated blood.

  • Left Atrium: Contains oxygenated blood.

  • Ventricles (Two inferior pumping chambers):

  • Right Ventricle: Pumps blood to the lungs.

  • Left Ventricle: Pumps blood to the rest of the body.

• Interventricular Septum: Wall separating the two ventricles; Interatrial Septum separates the two atria.

  • Fossa Ovalis: Previously an opening (foramen ovale) in the fetal heart, allowing blood to bypass the lungs.

  • Pectinate Muscles: Roughened walls found in the atria to assist with blood turbulence.

Coronary Structures

• Structures on the Heart's Surface:

  • Coronary Sulcus: Groove separating atria from ventricles, houses coronary vessels.

• Layers of the Heart Wall Revisited:

  • Myocardium: Thickest layer, crucial for pumping action.

• Unique Ventricular Features:

  • Trabeculae Carneae: Ridges found in the ventricles.

  • Papillary Muscles: Projections that assist in valve operation.

  • Chordae Tendineae: String-like structures attaching to AV valves; absent in semilunar valves.

Heart Valves

• General Functions:

  • Ensure one-way flow of blood through pressure changes upon heart contraction/relaxation.

• Types of Valves:

  1. Atrioventricular (AV) Valves:

  • Tricuspid Valve (Right AV Valve): Three flaps; ensures blood flows from right atrium to right ventricle.

  • Bicuspid Valve (Left AV Valve): Two flaps, also known as the Mitral Valve; allows blood flow from left atrium to left ventricle.

  1. Semilunar Valves:

  • Pulmonary Valve: Between right ventricle and pulmonary trunk, allowing deoxygenated blood to flow to lungs.

  • Aortic Valve: Between left ventricle and aorta, pumping oxygenated blood to body.

Myocardium Characteristics

• Myocardium Structure:

  • High energy requirement due to constant pumping action.

  • Relies on aerobic metabolism, hence needs sufficient oxygen supply for ATP production.

• Cardiac Muscle Tissue:

  • Contains many mitochondria and unique intercalated discs that enhance structural integrity and function.

Coronary Circulation

• Coronary Circulation:

  • Composed of coronary arteries and veins, supplying blood to the heart muscle.

  • Coronary Arteries (Oxygenated Blood):

  • Right Coronary Artery branches into:

    • Right Marginal Branch: Supplies right border of the heart.

    • Posterior Interventricular Artery: Supplies the posterior part of the ventricles.

  • Left Coronary Artery branches into:

    • Circumflex Artery: Supplies left heart structures roundabout.

    • Anterior Interventricular Artery (Widowmaker): Major supplier of blood, often associated with heart attacks.

• Coronary Veins (Deoxygenated Blood):

  • Drain blood off the heart's surface into the coronary sinus, which then empties into the right atrium.

  • Key cardiac veins include:

  • Great Cardiac Vein: Near anterior interventricular artery.

  • Middle Cardiac Vein: Near the posterior interventricular artery.

  • Small Cardiac Vein: Drains adjacent to the right marginal artery.

Pathophysiology: Atherosclerosis

• Atherosclerosis:

  • Narrowing of coronary arteries due to plaque buildup, leading to insufficient blood supply.

  • Can result in Angina Pectoris, severe chest pain from heart ischemia.

  • May lead to Myocardial Infarction (heart attack) when blood flow is critically obstructed.

• Symptoms:

  • Chest pain or discomfort, potential radiating pain down the arms or jaw, nausea, sweating.

• Diagnostics:

  • Coronary Angiogram: Medical imaging that visualizes coronary arteries and identifies blockages.

  • Interventions may include stents, bypass surgery, or medication to restore blood flow.

Conclusion

• Understanding the heart's anatomy, blood supply, and valve function is essential for comprehending cardiovascular health and disease.