| Criteria | Transcellular Transport | Paracellular Transport | Transcytosis | Remarks |
| Definition | Movement of molecules through the cell, crossing apical and basolateral membranes | Movement of substances between adjacent cells through intercellular junctions | Vesicle-mediated movement of macromolecules across the cell from one surface to another | Highlights directional differences and structural pathways used |
| Pathway | Crosses both plasma membranes and cytoplasm | Passes through tight junctions and intercellular clefts | Involves endocytosis, vesicular trafficking, and exocytosis | Transcellular and paracellular are structurally distinct; transcytosis adds vesicular complexity |
| Energy Requirement | May be passive or active, depending on transporter involved | Passive; driven by concentration and electrochemical gradients | Active; requires ATP for vesicle movement and fusion | Transcytosis is always energy-dependent, unlike others |
| Transported Molecules | Glucose, amino acids, ions, drugs, water | Water, ions (e.g., Na⁺, Cl⁻), small solutes | Antibodies (e.g., IgA), transferrin, insulin, nanoparticles | Transcytosis handles bulkier cargo |
| Barrier Interaction | Mediated by membrane proteins: channels, carriers, ATPases | Governed by tight junction integrity and claudin expression | Utilizes vesicle-coating proteins and receptor-mediated endocytosis | Transport regulation differs across the three pathways |
| Selectivity | High selectivity via specific transporters | Lower selectivity; governed by size and charge exclusion | Selective (receptor-mediated) or non-selective (fluid-phase) | Paracellular transport is more passive and less regulated |
| Biological Examples | Intestinal glucose uptake; renal sodium reabsorption | Intestinal water absorption; passive ion leakage in leaky gut | IgA secretion in intestinal epithelium; antibody delivery across endothelium | Widely used examples to illustrate physiological roles |
| Role in Physiology | Crucial for nutrient absorption, ion homeostasis | Supports passive diffusion and osmotic regulation | Delivers immune factors and nutrients across barriers | All are essential for maintaining barrier function and cellular communication |
| Clinical Relevance | Targeted by drugs affecting channels/transporters (e.g., diuretics) | Altered in IBD, inflammation, epithelial cancers | Basis for drug delivery strategies, nanomedicine, vaccine design | Clinical manipulation of these pathways is therapeutically significant |
| Remarks | Highly selective and adaptable; main route for solutes and small molecules | Passive but regulated by tight junction composition and inflammation | Specialized for large molecule passage; emerging in targeted therapy | Each plays a unique role depending on molecular size, transport direction, and cellular context |
