AB

Week 2: Blood Flow Through the Heart

Vessel Types

  • Arteries: conduct blood away from the heart; systemic arteries usually carry oxygen-rich blood, pulmonary arteries carry oxygen-poor blood.
  • Veins: return blood to the heart; systemic veins usually carry oxygen-poor blood, pulmonary veins carry oxygen-rich blood.
  • Capillaries: thin-walled exchange vessels linking arterial and venous systems.
  • Lymphatic vessels: collect excess interstitial fluid and return it to the bloodstream.

Heart Chambers & Circuits

  • Right atrium and ventricle form the pulmonary circuit, moving oxygen-poor blood to the lungs.
  • Left atrium and ventricle form the systemic circuit, moving oxygen-rich blood to the body.
  • Coronary sinus empties venous blood from the myocardium into the right atrium.

Valves (One-Way Gates)

  • Right atrioventricular valve = tricuspid; mnemonic: “If you Tri you are Right.”
  • Left atrioventricular valve = bicuspid / mitral.
  • Semilunar valves: pulmonary (right side) and aortic (left side); prevent backflow from great vessels into ventricles.

Sequential Blood Flow

Oxygen-poor route:

  • Body tissues → superior vena cava, inferior vena cava, coronary sinus → right atrium → tricuspid valve → right ventricle → pulmonary valve → pulmonary trunk → pulmonary arteries → lungs.

Gas exchange in lungs: blood gains oxygen and releases carbon dioxide.

Oxygen-rich route:

  • Lungs → pulmonary veins → left atrium → mitral valve → left ventricle → aortic valve → aorta → systemic arteries → body tissues → systemic veins → right atrium (cycle repeats).

Key Vessels & Functions

  • Superior vena cava: drains head, neck, upper limbs, and thorax.
  • Inferior vena cava: drains structures below the diaphragm.
  • Pulmonary trunk and arteries: carry oxygen-poor blood to lungs (one of the two arterial exceptions).
  • Pulmonary veins: carry oxygen-rich blood to heart (one of the two venous exceptions).
  • Aorta: distributes oxygen-rich blood to every organ.
  • Coronary arteries: supply myocardium; coronary sinus returns myocardial venous blood.

Clinical Correlations (High-Yield)

  • Coronary artery disease: plaque narrows coronary arteries; may cause angina or myocardial infarction.
  • Congenital heart defects: structural abnormalities present at birth; may involve walls, valves, or vessels.
  • Valvular disease: stenosis or regurgitation disrupts forward flow.
  • Hypertension: chronically elevated arterial pressure stresses heart and vessels.
  • Heart failure: ventricular inability to pump sufficient blood to meet metabolic demands.

Quick Recall

  • Atrium = accepts blood; Ventricle = vacates blood.
  • Right side handles oxygen-poor blood; left side handles oxygen-rich blood.
  • AV valves separate atria from ventricles; semilunar valves separate ventricles from great arteries.
  • Pulmonary arteries and pulmonary veins are the primary exceptions to the usual oxygen content of arteries and veins.