Transport in Humans – Quick Review

Blood

  • Functions: transport substances & immune defence
  • Components
    • Plasma: water + dissolved nutrients, hormones, wastes (urea, CO_2), plasma proteins (prothrombin, fibrinogen), antibodies
    • Red blood cells (RBC): contain haemoglobin; form oxyhaemoglobin in lungs, release O_2 in tissues. Higher altitude → more RBC produced
    • White blood cells (WBC)
    • Phagocytes: lobed nucleus, amoeboid; perform phagocytosis
    • Lymphocytes: large spherical nucleus; secrete antibodies (lyse membranes, neutralise toxins, agglutinate pathogens)
    • Platelets: cell fragments; clotting cascade—damaged tissue releases thrombokinase → \text{Prothrombin} \xrightarrow[]{Ca^{2+}} \text{Thrombin} → fibrinogen → insoluble fibrin threads → clot
  • Tissue rejection: lymphocytes’ antibodies & phagocytes attack non-matching grafts; minimise by close genetic match + immunosuppressive drugs

ABO Blood Group Compatibility

  • Antigens on RBC: A, B, both (AB), none (O)
  • Plasma antibodies:
    • A → anti-b
    • B → anti-a
    • AB → none
    • O → anti-a & anti-b
  • Transfusion rule: consider recipient’s plasma vs donor RBC
    • O = universal donor (no antigens)
    • AB = universal recipient (no antibodies)

Blood Vessels

  • Arteries: thick elastic/muscular walls, narrow lumen, no valves (except aorta & pulmonary); carry blood away at high pressure
  • Veins: thin less-elastic walls, wide lumen, valves; return blood at low pressure. Upward flow aided by heart pump, skeletal muscle contraction, valves
  • Capillaries: one-cell-thick, highly branched, narrow lumen (single-file RBC); site of exchange with tissue fluid
  • Tissue fluid: plasma forced out at arterial end (high pressure); carries O_2, nutrients, wastes between cells & capillaries; large molecules remain in blood

Heart

  • Four chambers separated by median septum (prevents mixing of oxygenated & deoxygenated blood)
    • Atria: thin walls
    • Ventricles: thick walls; left > right (pumps to whole body vs lungs)
  • Valves: tricuspid (RA→RV), bicuspid/mitral (LA→LV), pulmonary (RV→pulmonary artery), aortic (LV→aorta); chordae tendineae prevent backflow into atria
  • Major vessels: vena cava → RA; RV → pulmonary artery; pulmonary veins → LA; LV → aorta

Cardiac Cycle (one heartbeat)

  1. Atrial diastole fills atria (vena cava, pulmonary veins)
  2. Atrial systole → blood into ventricles (AV valves open)
  3. Ventricular systole → AV valves close ("lub"), blood forced into aorta & pulmonary artery (SL valves open)
  4. Ventricular diastole → SL valves close ("dub"); cycle repeats
  • Pulse: arterial wall stretch during ventricular systole; pulses/min = heartbeats/min

Coronary Heart Disease (CHD)

  • Atherosclerosis: cholesterol & saturated fat deposits narrow coronary arteries → higher pressure, rough walls, clots
  • Reduced O_2 & glucose to cardiac muscle → less aerobic respiration → possible heart attack
  • Risk factors: high-fat/salt diet, smoking (CO, nicotine), genetics, age, sedentary lifestyle, stress
  • Prevention: balanced diet (less saturated fat), regular exercise, no smoking/vaping, manage stress