The Heart

Pulmonary Circuit (Right Side): Responsible for pumping deoxygenated blood to the lungs for oxygenation.
Systemic Circuit (Left Side): Responsible for pumping oxygenated blood to the body.
**Chambers: **
- Top Chambers/Atria: Receive blood into the heart.
- Bottom Chambers/Ventricles: Pump blood out of the heart.
Capillary Beds: Connect the arteries and veins, facilitating nutrient and gas exchange.
Valves: Prevent backflow of blood to ensure unidirectional flow.

Fibrous Pericardium: Anchors the heart to the diaphragm and the major blood vessels.
Serous Pericardium: Reduces friction between the heart and surrounding structures, composed of:
- Parietal Layer: Lines the fibrous pericardium.
- Visceral Layer (Epicardium): Covers the heart muscle.
Pericardial Sac: Composed of fibrous pericardium and parietal pericardium containing serous fluid, which lubricates the heart.

Epicardium: The outermost layer, consisting of visceral pericardium and areolar connective tissue with fat.
Myocardium: The thick middle layer composed of cardiac muscle responsible for heart contractions.
Endocardium: The innermost layer, made up of simple squamous epithelium and areolar connective tissue, lining the heart chambers.

Structures include:
  - Auricles: Flaps on the atria that increase capacity.
  - Sulci: Grooves on the surface of the heart that indicate boundaries between chambers.
  - Left Common Carotid Artery
  - Left Subclavian Artery
  - Arch of Aorta
  - Right and Left Pulmonary Arteries
  - Superior Vena Cava
  - Inferior Vena Cava
Structures observed from various angles, such as Anterior (sternocostal) and Posterior (diaphragmatic) surfaces.

Four Chambers:
- Atria: Right and Left.
- Ventricles: Right and Left.
Valves: Include:
  - Atrioventricular Valves:
    - Right Atrioventricular (Tricuspid) Valve
    - Left Atrioventricular (Bicuspid or Mitral) Valve
  - Semilunar Valves:
    - Pulmonary Semilunar Valve
    - Aortic Semilunar Valve

vena cavas--right atrium--right

atrioventricular valve-right ventricle--pulmonary

semilunar valve-pulmonary arteries-lungs-

pulmonary veins-left atrium-left atrioventricular

valve-left ventricle-aortic semilunar valve-aorta

Systole (Contraction): A chamber empties.
Diastole (Relaxation): A chamber relaxes and fills.
Cycle Breakdown:
  - Atrial Systole: Atria contract, AV valves open.
  - Early Ventricular Systole: Ventricles contract; AV valves close, semilunar valves closed.
  - Late Ventricular Systole: Atria relax; semilunar valves open.
  - Early Ventricular Diastole: Atria relax; AV valves opened, ventricles filling with blood.
  - Late Ventricular Diastole: Atria fill passively as AV valves open.

"Lubb" Sound: Produced during ventricular contraction and closure of AV valves.
"Dubb" Sound: Produced during ventricular relaxation and closure of semilunar valves.

Initiation of Contracting:
- The sinoatrial (SA) node serves as the pacemaker.
- Impulses are conducted to the atrioventricular (AV) node, followed by the atrioventricular bundle, bundle branches, and Purkinje fibers throughout the ventricles.
Delay at AV Node: A brief 100-millisecond delay occurs before atrial contraction.

Waves Representing Heart Activity:
  - P Wave: Impulse spreads across atria, eliciting contractions.
  - QRS Complex: Impulse spreads to ventricles, triggering contractions.
  - T Wave: Represents the return of ventricles to resting state.
Importance: Displays depolarization and repolarization of cardiac muscle.

Oxygenation of Heart Tissue:
- The coronary arteries branch off from the ascending aorta, bringing oxygenated blood to the myocardium.
- Cardiac veins drain deoxygenated blood into the coronary sinus, which then deposits it into the right atrium.