The thyroid is an important endocrine gland that makes and releases certain hormones. Your thyroid's main job is to control your metabolism — how your body uses energy.

It's a part of your endocrine system and controls many of your body's important functions by producing and releasing (secreting) certain hormones. Your thyroid's main job is to control the speed of your metabolism (metabolic rate), which is the process of how your body transforms the food you consume into energy. Your thyroid hormones affect the following bodily functions:
How your body uses energy (metabolism).
Heart rate.
Breathing.
Digestion.
Body temperature.

Brain development.
Mental activity.

Skin and bone maintenance.
Fertility.

The four main conditions that affect your thyroid include:
Hypothyroidism (underactive thyroid).
Hyperthyroidism (overactive thyroid).
Goiter (enlarged thyroid).
Thyroid cancer.