Most of the body functions are regulated by hormone: like growth, vegetative and sexual development, thermoregulation, cellular oxidation, metabolism of carbohydrates, proteins, fats, etc. Hormones are needed in very small quantity to carry out these functions. Some hormones are proteinaceous, e.g., insulin (regulates sugar metabolism) growth hormone of pituitary, parathyroid hormone: parathormone (regulates $\mathrm{Ca}$ and phosphate transport).