Lecture on the Heart: Chapter 20 - Part 1

Introduction

• Transition from Chapter 19 (blood) to Chapter 20 (the heart).
• Heart Facts:
  • Beats ~100,000 times/day.
  • Pumps ~8,000 liters of blood/day.
  • Total blood volume circulates multiple times per day.

Heart Structure and Function

Dual Pump System

• Right Side:
  • Pumps blood to pulmonary circuit (lungs).
  • Flow: Right atrium ➜ Right ventricle ➜ Pulmonary trunk ➜ Pulmonary arteries ➜ Lungs.
  • Blood is oxygen-poor (blue).
• Left Side:
  • Pumps blood to systemic circuit (body tissues).
  • Flow: Lungs ➜ Left atrium ➜ Left ventricle ➜ Aorta ➜ Body tissues.
  • Blood is oxygen-rich (red).

Blood Vessel Color Code

• Systemic Arteries: Red (oxygen-rich).
• Systemic Veins: Blue (oxygen-poor).
• Pulmonary Arteries: Blue (oxygen-poor).
• Pulmonary Veins: Red (oxygen-rich).

Heart Location

• Located in the mediastinum, between lungs, behind sternum.
• Positioned slightly left of the midline.
• Surrounded by the pericardium.

Pericardium

• Fibrous Pericardium: Dense fibrous connective tissue, anchors heart.
• Serous Pericardium: Two layers with lubricating serous fluid.
  • Parietal Layer: Lines the fibrous pericardium.
  • Visceral Layer (Epicardium): Outer layer of the heart wall.

Heart Wall Layers

• Epicardium: Outer layer, same as visceral pericardium.
• Myocardium: Thick middle layer, cardiac muscle tissue.
• Endocardium: Inner layer, smooth endothelium.

Heart Anatomy

Chambers

• Atria:
  • Right atrium collects oxygen-poor blood (superior vena cava, inferior vena cava, coronary sinus).
  • Left atrium receives oxygen-rich blood from pulmonary veins.
• Ventricles:
  • Right ventricle pumps to pulmonary circuit.
  • Left ventricle pumps to systemic circuit, thicker wall.
• Apex & Base:
  • Apex: Point of the heart.
  • Base: Major blood vessels entry/exit.

Heart Valves

• Atrioventricular (AV) Valves:
  • Right (Tricuspid): Between right atrium and ventricle.
  • Left (Bicuspid/Mitral): Between left atrium and ventricle.
  • Anchored by chordae tendineae and papillary muscles.
• Semilunar Valves:
  • Pulmonary Valve: Between right ventricle and pulmonary trunk.
  • Aortic Valve: Between left ventricle and aorta.

Coronary Circulation

• Supplies blood to heart wall.
• Coronary Arteries: Originate from the aorta.
• Coronary Veins: Drain into coronary sinus ➜ Right atrium.
• Coronary Artery Disease: Narrowing due to cholesterol plaques, can lead to heart attack.

Cardiac Physiology: Electrical Conduction

• Cardiac Conducting System: Specialized cardiac muscle cells.
  • Includes SA node, AV node, bundle of His, Purkinje fibers.
  • Autorhythmic: Sets own rhythm.

Electrical Flow Through the Heart

1. SA Node: Pacemaker, initiates heartbeat.
2. Atria Activation:
   • Signal spreads through right and left atria.
3. AV Node: Delays signal (100 ms).
4. AV Bundle (Bundle of His): Only electrical connection between atria and ventricles.
   • Bundle Branches: Transmit signal through interventricular septum.
   • Moderator Band: Shortcut to right ventricle's papillary muscles.
5. Purkinje Fibers: Rapidly conduct signal through ventricles.

Conclusion

• Review of heart anatomy and physiology.
• Encourage questions and further reading in the textbook.

End of Lecture Notes

Note: For exam preparation, focus on understanding the flow of blood through the heart, structure of heart walls, and electrical conduction system.