The thyroid is one of the largest endocrine glands in the body. This butterfly-shaped gland is found in the neck, wrapped around the trachea, as shown in Figure. The thyroid is controlled by the pituitary.
The main thyroid hormone is thyroxine (T4). It controls the pace of all of the processes in the body. This pace is related to your metabolism. If there is too much thyroid hormone, every function of the body tends to speed up. As thyroxine controls how quickly the body burns calories, the thyroid gland regulates the body temperature by secreting more or less hormones.
The element iodine is very important for making thyroxine. If a person’s diet does not have enough iodine, their thyroid cannot work properly and the person develops an iodine deficiency disease called goiter. The addition of small amounts of iodine to table salt, has helped reduce the occurrence of iodine-deficiency in developed countries
As a result, problems with the under secretion (Hypothyroidism) or over secretion (Hyperthyroidism) of thyroid hormones affect many body systems.
The pancreas is both an exocrine gland as it secretes pancreatic juice containing digestive enzymes, and an endocrine gland as it produces several important hormones. It is located just below and behind the stomach, as shown in Figure. The endocrine cells of the pancreas are grouped together in areas called islets of Langerhans, shown in Figure. The islets produce the hormones insulin and glucagon. Insulin and glucagon are both involved in controlling blood glucose levels. Insulin causes excess blood glucose to be taken up by liver and muscle cells, where it is stored as glycogen, a polysaccharide. Glucagon stimulates liver cells to break down stores of glycogen into glucose which is then released into the blood.
- Insulin reduces blood glucose concentration
- Glucagon raises blood glucose concentration