11. ENDOCRINE SYSTEM

Endocrine system is the collection of glands in the body that produce hormones. These glands are the thyroid gland, pancreas, testes, ovaries, and adrenal glands. Their hormones are responsible for numerous bodily processes, including growth, metabolism, sexual development and function, and response to stress. Any increase or decrease in the production of a specific hormone interferes with the process it controls. To prevent underor overproduction, hormone secretion from many endocrine glands is regulated by the pituitary gland, which is influenced by the hypothalamus in the brain according to a feedback mechanism.

Thyroid gland is one of the main endocrine glands, which helps to regulate the rate of all the body?s internal processes. The thyroid gland is situated in the front of the neck, just below the larynx (voice box). It consists of 2 lobes, one on each side of the windpipe, joined by a portion of tissue called the isthmus. Thyroid tissue is composed of follicular cells, which secrete the iodine-containing hormones thyroxine (T4) and triiodothyronine (T3), and parafollicular cells (or C cells), which secrete the hormone calcitonin. T4 and T3 are important in controlling the body?s metabolism. Calcitonin helps to regulate calcium balance in the body.

Pancreas is a tapered gland that lies across the back of the abdomen, behind the stomach. The head (the broadest part) is on the right-hand side. The body (main part) tapers from the head and extends horizontally. The tail (the narrowest part) is on the left near the spleen. The pancreas has a digestive and a hormonal function. It mostly consists of exocrine tissue, which secretes digestive enzymes into the duodenum via the pancreatic duct. The pancreas secretes sodium bicarbonate; it neutralizes stomach acid entering the duodenum. The pancreas also contains groups of endocrine cells, called the islets of Langerhans, which secrete the hormones insulin and glucagon. These hormones regulate the level of glucose in the blood.