Contains the full lesson along with a supporting toolkit, including teachers’ notes.
What Is The Thyroid Gland?
The thyroid gland is a butterfly-shaped gland about the size of a 50 cent coin located in the front of the neck [not the throat – that is the inside of the neck below the larynx.
It is an endocrine or ductless gland i.e. the hormones it produces diffuse directly into the bloodstream rather than being discharged through a tube as happens to the products of exocrine glands. The thyroid produces two hormones - (i) calcitonin which helps control calcium levels in the blood and is produced by C cells and (ii) thyroxinewhich is produced by follicular cells and is needed for normal growth and nervous system development. It also increasesmetabolic rate, particularly the rate of aerobic respiration.
What Can Go Wrong?
Hypothyroidism, a condition in which the thyroid gland is underactive, leads to a deficiency of thyroxine. There are two main causes of this: either (i) a malfunction of the thyroid or (ii) a lack of iodine in the diet. The symptoms are different in adults and children. In children it results in reduced growth and poor brain development, which can lead to a condition called cretinism. In adults hypothyroidism produces extreme tiredness, weight gain, poor resistance to disease, coldness and a low heart rate. Iodine is an important component of thyroxine and in many countries all table salt is iodised i.e. it has trace amounts of iodine added as a safeguard against deficiency. The usual treatment of underactive thyroid is a thyroxine supplement.
An overactive thyroid leads to an excess of thyroxine and is called hyperthyroidism. This results in an increased metabolic rate. Common symptoms are weight loss, sweating and increased heart and breathing rates. Treatment includes surgically removing some of the thyroid, giving radioactive iodine to kill off cells in the most active part of the gland or giving medication to block the activity of thyroxine.