Situated in the front of the windpipe, the thyroid’s primary objective in the endocrine system is to control metabolism (body’s ability to break down food and convert it to energy) levels through the release of hormone from Thyroid Gland. Thyroid cells are highly specialized in absorbing and using iodine and help the gland in extracting iodine from the blood.

Thyroid is controlled and managed by both hypothalamus and the pituitary gland. When thyroid hormone levels dip, the hypothalamus releases TRH (TSH Releasing Hormone) which signals the pituitary to make TSH (thyroid stimulating hormone). The thyroid responds with more production of hormones.

Hormones released by Thyroid gland
The thyroid gland is responsible for producing and releasing two major hormones T3 (tri-iodothyronine) and T4 (thyroxine). A normal functioning thyroid produces and releases 20% T3 and 80% T4 hormones, though T3 is firmer of the two. The thyroid also produces some amount of calcitonin which manages blood calcium levels.

Diseases associated with the thyroid gland
There are multiple diseases linked with the thyroid. There are no age restrictions to them and can occur due to other diseases, injury, malnutrition etc. But in most cases the problems are:

• Excess or limited production of thyroid hormone 
• Irregular thyroid growth
  
• Lumps within the thyroid 
• Thyroid cancer

1. Goiters: A goiter is an inflammation of the neck. A toxic goiter is linked to hyperthyroidism, and a non-toxic goiter is just an endemic goiter caused by iron deficiency.  
2. Hyperthyroidism: Too much release of thyroid hormone leads to hyperthyroidism. Patients suffering from this disease are responsive to heat, eat in large quantities and hyperactive. Sometimes, goiter is the side-effect of hyperthyroidism. This happens because of over-stimulated thyroid and swelled tissues.  
3. Hypothyroidism: Hypothyroidism occurs due to less production of thyroid hormone. Cretinism is the term used when it happens to infants. The side effects are severe including mental retardation and abnormal bone formation. In adults, receptiveness to cold, little appetite and sluggishness are some of the symptoms of hypothyroidism. Hypothyroidism can go unnoticed for years.  
4. Solitary Thyroid Nodules: Solitary nodules in the thyroid are very common. It is estimated that in future, half of the population will have this disease. Most of the nodules don’t possess a threat to life. However, FNA (Fine needle aspiration biopsy) is required to check for cancerous nodule. 
5. Thyroid Cancer: Thyroid Cancer is very common but patients can survive it. Symptoms include neck pain, enlarged lymph nodes and hoarseness. People of any age or sex can suffer from thyroid cancer, though man and women over 30 years of age are more likely to develop this condition. 
6. Thyroiditis: Thyroiditis is swelling of the thyroid gland that may be linked with unusual thyroid function. Swelling can kill thyroid’s cells affecting its ability to produce enough hormones to maintain the body's normal metabolism. There are five kinds of thyroiditis, treatment which differs from each other.