Classification of glands (Based on presence or absence of ducts):
| Endocrine (ductless) glands | Exocrine (ducted) glands | ||
| 1. Hypothalamus 2. Pituitary 3. Pineal 4. Thyroid 5. Parathyroid 6. Thymus 7. Pancreas (Islets of Langerhans) 8. Adrenal 9. Gonads (Testes & Ovary) | Unicellular | Multicellular | |
| E.g. Chalice cells (Goblet cells) in the epithelial lining of the small intestine. | Simple | Compound | |
| 1. Non-coiled tubular: E.g. crypts of Lieberkuhn | 1. Tubular: E.g. Milk glands of egg-laying mammals, Brunner’s glands | ||
| 2. Coiled tubular: E.g. Sweat glands | 2. Alveolar: E.g. Mammary glands | ||
| 3. Branched tubular: E.g. Gastric glands, Brunner’s glands, Sweat glands of arm pit | 3. Tubule-alveolar: E.g. Salivary glands, pancreas | ||
| 4. Alveolar (Acinus): E.g. Mucus secreting glands in frog skin | | ||
| 5. Branched alveolar (Branched acinus): E.g. Sebaceous glands (oil glands) | |||
Classification of glands (Based on modes of secretion):
| Holocrine glands | The entire cells disintegrate to release secretions. E.g. Ceruminous glands, Sebaceous glands |
| Merocrine glands | Glands release secretions by simple diffusion (without the loss of cytoplasm). E.g. Sweat glands, Salivary glands |
| Apocrine glands | The contents and the free ends of glandular cells are pinched off during secretion. E.g. Mammary glands, certain sweat glands |