Diabetes mellitus is caused by insulin deficiency or resistance. Goitre is a swelling in the neck due to iodine deficiency. Gigantism is caused by a tumour in the pituitary gland that leads to hypersecretion of growth hormone.
When an individual consumes a large volume of water than the body requirements, then large volumes of dilute urine is produced to maintain water balance. On the other hand, when the intake of water is inadequate or heavy sweating occurs then the blood solute concentration increases. This is detected by the osmoreceptors present in the hypothalamus. They send a large number of impulses to the neurohypophysis inducing the release of the anti-diuretic hormone (ADH) or vasopressin. The kidneys produce a reduced amount of urine concentrated with the salts.
Higher the level of ADH in the blood, greater is the reabsorption of the water and more concentrated the urine is. The lack of ADH due to the malfunctioning of neurohypophysis results in the failure of reabsorption of water through collecting tubules. This is turn results in the production of a large volume of dilute urine. This condition is called polyuria and the disease is called Diabetes insipidus.