(i) Exocrine gland, is a gland that pours its secretion on the surface or into a particular region by means of ducts for performing a metabolic activity, e.g., Sebaceous glands, sweat glands, salivary glands, etc.
(ii) Endocrine gland, is a gland that pours its secretion into blood or lymph for reaching the target organ because the gland is not connected with the target organ by any duct. It is also known as ductless gland.
(iii) Hormones are non-nutrient chemicals which act as intercellular messengers and are produced in trace amount.