Cardiovascular System Notes

The Cardiovascular System

The Heart

• Cardiology: The study of the heart's anatomy, physiology, and diseases.
• Heart: A muscular organ, roughly the size of your fist.
  • Located in the middle of the thorax (between the lungs), deep to the sternum, extending from the ribs.
  • Cone-shaped, with a broad base (superiorly) and a pointed apex (inferiorly), the apex pointing towards the left.
  • Divided into 4 chambers; lower chambers separated by a muscular septum.
  • Upper chambers: Atria (singular: atrium).
  • Lower chambers: Ventricles.

Pericardial Sac

• A loose-fitting sac surrounding the heart, confining it to a certain position and reducing friction during contraction.
  • Attached only where blood vessels enter and leave.
  • Two layers:
    1. Fibrous Pericardium: The tough, outer layer.
    2. Serous Pericardium: Thinner, more delicate inner layer, divided into:
       • Parietal Layer: Adheres to the underside of the fibrous pericardium.
       • Visceral Layer: Adheres to the surface of the heart, also called the epicardium.
       • Pericardial Space: Between parietal and visceral layers, filled with pericardial fluid to reduce friction.

Heart Wall

• Three layers:
  1. Epicardium: Thin outer epithelial layer.
  2. Myocardium: Thick middle layer made of cardiac muscle cells.
     *Cardiac muscle cells are involuntary, striated, and branched allowing for rapid electrical impulse conduction and coordinated muscle fiber contraction; all cells in both atria contract at the same time, followed by all cells in the ventricles.
     *Cardiac fibers are autorhythmic & contract on their own and the rate of contraction can be affected by external innervation.
  3. Endocardium: Thin, smooth inner epithelial lining.

Chambers

• Atria: Receive blood from veins; pump blood into ventricles.

  • Have relatively thin walls.

• Ventricles: Receive blood from atria; pump blood into arteries.

  • Much thicker walls than atria.
  • Left ventricular wall is thicker than right ventricle wall because the Right ventricle pumps blood to the lungs, while the left ventricle pumps blood to the rest of the body.

Valves

• Prevent backflow of blood into atria or ventricles.
  • Atrioventricular (AV) Valves: Located between atria and ventricles.
    • Right = tricuspid valve: has three cusps.
    • Left = bicuspid (or mitral) valve: has two cusps.
  • Semilunar Valves: Located between ventricles and the arteries they pump blood into.
    • Right = pulmonary semilunar valve (opening into pulmonary trunk).
    • Left = aortic semilunar valve (opening into aorta).

General Circulation

• Heart pumps blood into two circuits:
  1. Pulmonary Circulation: To and from lungs; exchange of gases (O2 & CO2).
  2. Systemic Circulation: To and from rest of body; distribution of gases and nutrients.
     *Arteries transport blood away from the heart, while veins transport blood to the heart. Also arteries carry oxygenated blood and veins carry deoxygenated blood except for the pulmonary arteries & veins.
• Coronary Circulation: Blood supply to the heart muscle (a subdivision of systemic circulation).
  • As the aorta leaves the heart, the first two arteries that branch off immediately after the aortic semilunar valve are the left and right coronary arteries; branches of these two arteries supply the heart muscle with oxygenated blood.
  • Deoxygenated blood is drained from the heart muscle by cardiac veins, which empty into the coronary sinus on the posterior of the heart; the coronary sinus empties directly into the right atrium.
  • An obstruction in the coronary arteries leads to ischemia (lack of oxygen) in the affected heart cells, and could result in a myocardial infarction (= cell death), or