In: Anatomy and Physiology
Jim, a 25 years old male, presents with hyperthyroidism because of tumor of the parathyroid glands. Jim was told by his doctor that he has a thyroid gland and four parathyroid glands, so image his confusion when his was told that a tumor of his parathyroid glands causes his hyperthyroidism (5pts)
(i) Explain to a very baffled Jim, why tumor of the parathyroid glands can cause hyperthyroidism
(ii) Explain to the Jim the effects of his disease on the hormones that control his bone homeostasis. Your explanation must address specifically the hormone(s) involved and their effect (s) on the bones.
i) The tumor of parathyroid glands causes hyperparathyroidism due to excess secretion of parathyroid hormones. The effect of hyperparathyroidism is increasing calcium levels in the blood thereby causing hypercalcemia. To maintain homeostasis, the antagonist hormone is secreted as a feedback due to hypercalcemia. Here antagonistic hormone is calcitonin which is released from C cells of the thyroid gland. Thereby hypercalcemia stimulates thyroid gland to secrete calcitonin. Along with the calcitonin due to excessive stimulation of thyroid gland also increases the secretion of thyroid hormones thereby causing hyperthyroidism in those patients.
ii) Parathyroid hormone usually increases the osteoclastic activity of the bone thereby increasing the calcium levels in blood due to resorption of bone. To maintain homeostasis hypercalcemia as a feedback stimulate secretion of calcitonin from C cells of the thyroid gland. This calcitonin has an osteoblastic activity and prevent the resorption of bone thereby decreasing the blood calcium levels. On the other hand vitamin D is a hormone synthesized by skin causes increase in blood calcium levels by absorption from GIT and reabsorption from kidney. This hormone thereby utilizes this calcium to stimulate bone formation. So, Jim has excess parathyroid hormone due to tumor of the gland increasing osteoclastic activity, thereby increasing blood calcium levels. This leads to excess demineralization of the bone and renal stone formation.