Lecture Notes: The Heart (Part 2)

Introduction

• Focus on the structure of the heart itself.
• The heart is located in the mediastinum, a space in the thoracic cavity extending from the ribs to the diaphragm.
• The heart is slightly tilted, with the left side more posterior and right side more anterior.
• Described as an inverted pyramid:
  • Base is superior.
  • Apex is inferior, pointing towards the left side under the sternum.

Mediastinum

• Contains everything in the thoracic cavity except the lungs.
• Heart positioned within this space.

Heart Images

• Visual representation often uses color to distinguish oxygenated/deoxygenated blood.
• Real-life heart tissue appears more in shades of brown/beige.

Pericardium

• Protective tissue surrounding the heart.
• Two main divisions:
  1. Fibrous Pericardium: Tough, inelastic dense connective tissue.
  2. Serous Pericardium: More delicate, double-layered (parietal and visceral layers).
• Pericardial Cavity: Space with fluid between parietal and visceral layers, reducing friction.

Layers of the Heart Wall

1. Epicardium: Outer layer (visceral serous pericardium), smooth texture.
2. Myocardium: Thickest layer, cardiac muscle tissue, responsible for contraction.
3. Endocardium: Thin endothelial layer lining chambers and valves.

Heart Chambers

• Atria: Receiving chambers.
• Ventricles: Pumping chambers.
• Septum: Walls separating chambers.
  • Interatrial septum (between atria).
  • Interventricular septum (between ventricles).

Unique Structures in Atria

• Pectinate Muscles: Rough walls in atria.
• Fossa Ovalis: Remnant of fetal circulation opening.
• Coronary Sinus: Drains blood into right atrium.

Unique Structures in Ventricles

• Trabeculae Carneae: Rough walls in ventricles.
• Papillary Muscles: Project into ventricles, help operate AV valves.
• Chordae Tendineae: String-like structures attaching to AV valves.

Thickness of Heart Walls

• Ventricles thicker than atria, with left ventricle being the thickest due to systemic pumping.

Heart Valves

• Atrioventricular (AV) Valves:
  • Right AV (tricuspid) and Left AV (bicuspid/mitral) valves.
  • Operate with chordae tendineae and papillary muscles.
• Semilunar Valves:
  • Pulmonary and aortic valves, operate based on pressure changes.

The Myocardium

• Requires significant energy, relies on aerobic metabolism.
• Contains many mitochondria and intercalated discs for strength.

Coronary Circulation

• Provides blood supply to the heart.
• Coronary Arteries: Supply oxygenated blood.
  • Right coronary artery branches: Right marginal and posterior interventricular.
  • Left coronary artery branches: Circumflex and anterior interventricular (Widowmaker).
• Coronary Veins: Return deoxygenated blood to the heart.
  • Great cardiac, middle cardiac, and small cardiac veins.

Heart Conditions

• Atherosclerosis: Narrowing of coronary arteries.
• Angina Pectoris: Chest pain due to reduced blood flow.
• Myocardial Infarction (Heart Attack): Blockage leading to tissue death.
  • Symptoms: Chest pain, pain in arm/jaw, nausea, sweating.
• Coronary Angiogram: Diagnostic tool to check for blockages.
• Treatment options: Stents, bypass surgery, medication to thin blood.