Lecture Notes: The Heart and Circulatory System

Introduction

• The circulatory system, also known as the cardiovascular system, circulates blood throughout the body.
• Comprised of the heart, arteries, veins, and capillaries.
• Focus of this lecture: Anatomy and function of the heart.

Role of the Heart

• The heart functions purely as a pump, not as a center of thought or emotion.
• Located in the mediastinum cavity of the thorax.

Circuits of the Heart

• The heart participates in two circuits:
  1. Pulmonary Circuit:
     • Blood enters the right side of the heart, goes to the lungs, gets oxygenated, and returns to the left side of the heart.
  2. Systemic Circuit:
     • Oxygenated blood leaves the left side of the heart, travels throughout the body, delivers oxygen and nutrients, and returns to the right side of the heart.

Chambers of the Heart

• Four Chambers:
  • Right Atrium
  • Left Atrium
  • Right Ventricle
  • Left Ventricle
• Atria are receiving chambers; ventricles are pumping chambers.
• Separated by the interatrial septum and interventricular septum.

Structure of the Heart

• Pericardium:
  • Protects the heart and maintains its position.
  • Composed of fibrous pericardium and serous pericardium.
  • Epicardium, myocardium, and endocardium make up the heart wall layers.
• Myocardium: Mostly cardiac muscle, supported by the cardiac skeleton.
• Endocardium: Lines heart chambers with endothelium.

Blood Flow Through the Heart

• Right Atrium: Receives oxygen-poor blood via:
  • Superior vena cava
  • Inferior vena cava
  • Coronary sinus
• Left Atrium: Receives blood from lungs through pulmonary veins.
• Right Ventricle: Sends blood to the lungs via the pulmonary trunk.
• Left Ventricle: Sends blood into the aorta.

Heart Valves

• Ensure unidirectional blood flow.
• Atrioventricular Valves (AV Valves):
  • Right atrioventricular valve: Tricuspid (three flaps)
  • Left atrioventricular valve: Mitral/Bicuspid (two flaps)
• Semilunar Valves:
  • Aortic valve
  • Pulmonary valve

Cardiac Muscle

• Unique to the heart, similar to skeletal muscle with striations.
• Cardiac fibers are short, fat, branched, with one or two nuclei.
• Connected via intercalated discs with desmosomes and gap junctions.
• Capable of automaticity (self-excitation).
• Long refractory period ensures proper function.

Intrinsic Cardiac Conduction System

• Pacemaker cells initiate and coordinate heart contractions.
• Specialized cells distribute impulses throughout the heart.
• Issues can lead to arrhythmias and fibrillation.

Coronary Circulation

• The heart is supplied with blood by coronary arteries and veins.

Conclusion

• Introduction to the heart completed.
• Further discussions on heart rate and other phenomena to follow in future lectures.