The Thyroid Gland
The thyroid is an endocrine gland which produces thyroid hormones. It is shaped like a butterfly and is located in the front of the lower neck. It has a right and a left lobe (half) connected by what an area called the isthmus.
Endocrine glands are organs that secrete proteins (called hormones) into the bloodstream which have an effect on the rest of the body.
Thyroid hormones are critical determinants of infant development and of metabolic activity in adults; they also affect the function of virtually every organ system.
A simple of way of thinking about what thyroid hormones do is to think of the thyroid as the body’s “speed dial”. If the thyroid is overactive, it is like turning the “speed dial” up 🡪 heart beats faster, the patient can feel anxious, can have a tremor (shaking), may lose weight, feel hot and have diarrhoea. If the thyroid is underactive, it is like turning the “speed dial” down 🡪 the heart may slow down, the patient may gain weight, suffer from constipation, feel cold and have slow mentation.
It makes thyroid hormones called T3 and T4.
Production of these hormones as well as growth of the thyroid gland is controlled by another gland in the head called the pituitary gland. This produces a hormone called TSH (Thyroid Stimulating Hormone) which does exactly as its name implies – it stimulates the thyroid gland to grow and make more hormones.
When the thyroid gland makes too much T3 & T4, the pituitary gland senses this and reduces its production of TSH. So, when the thyroid is overactive, the T3 & T4 go up and the TSH goes down.
On the other hand, if the thyroid is underactive (ie not making enough T3 & T4), the pituitary gland makes more TSH to stimulate the thyroid and therefore the TSH goes up.