[Endocrinology] The thyroid gland

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Physiology 

The thyroid makes two hormones that it secretes into the blood stream.

• Thyroxine; this hormone contains four atoms of iodine and is often called T4. 
• Triiodothyronine, which contains three atoms of iodine and is often called T3.

In the cells and tissues of the body the T4 is converted to T3. So there are two sources of T3, secretion from the thyroid itself, and conversion from T4 in the peripheries.

T3 is biologically active and influences the activity of all cells and tissues in the body.

 

Pathophysiology 

• Hypothyroidism (underactive thyroid) - not enough thyroxine is produced for the body’s needs. This is more far common.
• Hyperthyroidism (overactive thyroid) - too much thyroxine is produced for the body’s needs.
• Thyroitidis 

 

Hormones

• Stimulated by: Thyroid stimulating hormone (TSH)
• Output: T3 hormone and T4 hormone