Psychology Study Material: Thyroid Gland, Calcitonin and Iodine Deficiency

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Thyroid Gland

Thyroid Gland

Type, Location and Lobes

  • Very vascular organ and is located in the neck.
  • Consists of two parts/lobes, one on each side of the trachea, just below the larynx or voice box.
  • These two lobes are connected by a narrow band of tissue, called the ‘isthmus’ .
  • This gland consists of follicles, which produce thyroxin and triiodothyronine hormones.
  • These hormones contain iodine about 95 % of most functioning hormone is thyroxin and the remaining 5 % is triiodothyronine both require iodine for their synthesis.
  • Secretion is regulated by a negative feedback mechanism.


  • Secreted by Para follicular cells of the thyroid gland.
  • Opposes the action of the parathyroid glands by reducing the calcium level in the blood.
  • If calcium level in the blood becomes too high, calcitonin is secreted until calcium ion levels decreases to normal.

Iodine Deficiency

  • Thyroid enlargement is called “goiter” or “iodine deficiency goiter” .
  • If there is a deficiency of iodine in the body, then thyroid produce insufficient hormones required by the body causing the thyroid- stimulating hormone of the pituitary gland (anterior lobe) to secrete its hormone. This results in the increase in size of the thyroid gland, but it is unable to make enough hormones, because it is lacking the raw material for production i.e.. iodine.

Parathyroid Gland

Location, Type, Amount, Hormone

  • Parathyroid gland consists of four small masses of epithelial tissue that are embedded in the connective tissue capsule, on the posterior side of the thyroid glands.
  • Secretes ‘parathyroid hormone’ or ‘parathormone’ .
  • Most important regulator of blood calcium levels, secreted in response to low blood calcium levels, and its function is to increase calcium levels in the body.

Deficiency/Insufficient Secretion of Parathyroid Gland

  • Insufficient secretion of parathyroid hormone ‘hypoparathyroidisms’ , leads to increased nerve excitability.
  • Low blood calcium level in the body triggers spontaneous and continuous nerve impulses, which in turn stimulate muscle contraction.

Pancreas Islets of Langerhans

  • long, soft organ that lies transversely along the posterior abdominal wall, posterior to the stomach, and extends from the region of the duodenum to the spleen. a. Exocrine portion of this hormone secretes digestive enzymes that are carried by a duct to the duodenum
  • The endocrine portion consists of the pancreatic islets, and
  • secretes glucagons and insulin.

Alpha Cells in Pancreatic Islets

  • Secrete hormone called ‘glucagons’ when there is a low concentration of glucose in the blood.
  • Beta Cells in the Pancreatic Islets
  • After the alpha cells, beta cells secrete hormone called ‘insulin’ as a result of high concentration of glucose in the blood.