| Category | Key Examples | Primary Route |
|---|
| Nutrients | Glucose, amino acids, fatty acids, vitamins, minerals | Intestine → portal vein → liver → systemic |
| Respiratory gases | O₂ (bound to Hb), CO₂ (dissolved, HCO₃⁻, carbamino-Hb) | Lungs ↔ tissues |
| Hormones | Insulin, glucagon, thyroid hormones, cortisol, sex steroids | Endocrine glands → target tissues |
| Electrolytes | Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, HCO₃⁻, PO₄³⁻ | Intake → distribution → renal regulation |
| Waste products | Urea, creatinine, uric acid, bilirubin | Tissues → kidneys/liver → excretion |
| Immune cells & factors | Leukocytes, antibodies, complement, cytokines | Bone marrow/lymphoid → sites of infection/inflammation |
| Heat | Thermal energy | Core → skin (thermoregulation) |
Transport Mechanisms
- Dissolved in plasma (gases, lipids on albumin, water-soluble substances).
- Bound to proteins (hormones, drugs, Fe on transferrin, Cu on ceruloplasmin).
- Intracellular (RBCs) – O₂ on hemoglobin; CO₂ as carbamino-Hb.
- Cellular transport – leukocytes migrate via diapedesis.
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