Q.Thyroxine is secreted from

Thyroid Gland Hormones — A First Look

Think of your body as a finely tuned engine. Every cell burns fuel, generates heat, and performs work. That engine needs a throttle — something that tells every cell, "speed up" or "slow down." The thyroid gland, a butterfly-shaped organ wrapped around your windpipe, makes that throttle. It produces two hormones, T4 (thyroxine) and T3 (triiodothyronine), that set the metabolic pace of almost every tissue in your body.

But the thyroid does something else too. It also makes a completely different hormone, thyrocalcitonin (calcitonin), that has nothing to do with metabolism. This one is a calcium manager — it helps keep your blood calcium from climbing too high.

So the thyroid is really two glands in one: a metabolic throttle and a calcium brake.

The Metabolic Hormones: T4 and T3

The thyroid follicle cells (the main cells of the gland) take up iodine from your blood and attach it to the amino acid tyrosine. Depending on how many iodine atoms get attached, you get either:

• T4 (thyroxine) — four iodine atoms. This is the main product, about 90% of what the thyroid releases.
• T3 (triiodothyronine) — three iodine atoms. This is the much more active form, about 10% of release.

Here's the key: T4 is mostly a prohormone. It circulates in the blood, but most cells convert it into T3 right where they need it. T3 then binds to receptors inside the cell nucleus and directly turns genes on or off — ramping up the production of enzymes that control oxygen consumption, heat production, and energy use.

What does this actually do? A higher T3 level means your cells burn more calories, produce more heat, and work faster. Your heart beats faster, your gut digests quicker, your brain stays alert. Too little (hypothyroidism) and everything slows down — fatigue, weight gain, cold intolerance. Too much (hyperthyroidism) and the engine races — weight loss, sweating, anxiety, rapid pulse.

The Calcium Hormone: Thyrocalcitonin (Calcitonin)

Now switch gears entirely. Scattered between the thyroid follicles are different cells called parafollicular cells (or C-cells). These make thyrocalcitonin, often just called calcitonin.

Calcitonin's job is to lower blood calcium when it gets too high. It does this by:

• Stopping bone breakdown — it tells osteoclasts (the cells that dissolve bone) to slow down, so calcium stays locked in bone.
• Increasing calcium loss in urine — the kidneys excrete more calcium.