Chemical Coordination and IntegrationNEET Zoology · Class 11 · NCERT Chapter 19

You can expect 2 to 3 questions from Chemical Coordination in NEET 2027. The most reliable scoring topics are: anterior vs posterior pituitary hormones, the cause of common endocrine disorders (diabetes mellitus, diabetes insipidus, goiter, cretinism, Addison disease), insulin vs glucagon, and the difference between peptide and steroid hormone action.

The anterior pituitary (adenohypophysis) makes and releases its own hormones: Growth Hormone (GH), TSH, ACTH, FSH, LH, prolactin and MSH. The posterior pituitary (neurohypophysis) does NOT make hormones; it only stores and releases two hormones that are made by the hypothalamus: ADH (vasopressin) and oxytocin. This difference is a NEET-favorite.

Diabetes insipidus is caused by ADH (vasopressin) deficiency from the posterior pituitary. Without ADH, the kidneys cannot concentrate urine. Symptoms: very large volumes of dilute urine, extreme thirst. Blood sugar is normal. Diabetes mellitus is caused by insulin deficiency or resistance from the pancreas. Without insulin, blood glucose rises. Symptoms: high blood sugar, glucose in urine, weight loss, polyuria. The two are completely different disorders.

Two hormones working in opposite directions. Calcitonin (from thyroid C-cells) lowers blood calcium by promoting calcium deposition in bone. Parathyroid hormone (PTH, from parathyroid glands) raises blood calcium by mobilising calcium from bone and increasing intestinal absorption (with the help of vitamin D). PTH is the "hypercalcemic" hormone.

Peptide hormones (insulin, growth hormone, ADH) cannot cross the cell membrane because they are water-soluble and large. They bind to receptors on the cell surface and activate second messengers like cAMP. Their action is fast but short. Steroid hormones (cortisol, aldosterone, testosterone, estrogen) and thyroid hormones are lipid-soluble. They cross the cell membrane and bind to intracellular receptors. The hormone-receptor complex enters the nucleus and turns on specific genes. Their action is slow but long lasting.

The pituitary gland is often called the master gland because its hormones control most other endocrine glands. TSH controls the thyroid, ACTH controls the adrenal cortex, and FSH and LH control the gonads. However, the pituitary itself is controlled by the hypothalamus, so some textbooks call the hypothalamus the master.

Goiter is the swelling of the thyroid gland. The most common cause is iodine deficiency. Iodine is needed to make thyroid hormones (T3 and T4). Without iodine, the thyroid cannot make enough hormone, so the pituitary releases more TSH to push the thyroid harder. The thyroid grows bigger trying to make hormone, but still cannot. This swelling is goiter. The fix is iodised salt. In children, severe iodine deficiency in the womb causes cretinism (stunted growth, mental retardation).