🦋 How the Thyroid Works

This page explains the basic job of the thyroid gland, how TSH, T4, and T3 hormones work together, and why the thyroid is so important for overall health and metabolism. 

Your thyroid is small – but it has a big job.

Understanding how it works makes everything else about thyroid problems much easier to understand.

📍 Where Is the Thyroid? 

⚙️ What Does the Thyroid Actually Do? 

The thyroid’s main job is to control your body’s metabolism.

Metabolism is basically how fast or slow your body runs.

Think of the thyroid like:

• A thermostat
  
  

• An engine speed controller
  
  

• A volume knob for your body
  
  

If the thyroid turns things up too high, your body runs too fast.
If it turns things down too low, your body slows way down.

🧬 The Hormones the Thyroid Makes 

The thyroid makes two main hormones:

• T4 (thyroxine)
  
  

• T3 (triiodothyronine)
  
  

These hormones travel through your bloodstream and affect almost every part of your body.

What These Hormones Control

Thyroid hormones help control:

• Energy levels
  
  

• Body temperature
  
  

• Heart rate
  
  

• Weight
  
  

• Mood
  
  

• Digestion
  
  

• Hair and skin
  
  

• Brain function
  
  

• Growth and development
  
  

That’s why thyroid problems can cause so many different symptoms.

🧠 The Thyroid Works With Your Brain 

Your thyroid does not work alone.

It is part of a system that includes:

• The hypothalamus (in the brain)
  
  

• The pituitary gland (also in the brain)
  
  

• The thyroid gland (in your neck)
  
  

This system works like a feedback loop.

Here’s How It Works – Step by Step 

1. Your brain checks how much thyroid hormone is in your blood.
   
   

2. The pituitary gland releases a hormone called TSH (Thyroid Stimulating Hormone).
   
   

3. TSH tells your thyroid how much hormone to make.
   
   

4. The thyroid releases T4 and T3 into your body.
   
   

5. Your body uses those hormones to run normally.
   
   

If levels get too high or too low, the brain adjusts TSH to fix it.

🧪 Why TSH Is So Important 

Because of this feedback loop:

• High TSH usually means the thyroid is too slow
  
  

• Low TSH usually means the thyroid is too fast
  
  

That’s why TSH is often the first blood test doctors check.

We’ll explain TSH in detail on another page.

🔄 T4 and T3 – What’s the Difference? 

• T4 is the main hormone the thyroid makes
  
  

• T3 is the active form your body actually uses
  
  

Most T4 gets converted into T3 inside your body.

If this system doesn’t work correctly, you can have thyroid symptoms even if some tests look normal.

🧂 Why Iodine Matters 

Your thyroid needs iodine to make thyroid hormones.

Most people get enough iodine from:

• Iodized salt
  
  

• Dairy products
  
  

• Seafood
  
  

• Certain breads and grains
  
  

Too little iodine can cause thyroid problems, but in the United States this is less common because iodine is added to many foods.

❗ When the System Goes Wrong 

Problems can happen at different points:

• The thyroid might not make enough hormone
  
  

• It might make too much hormone
  
  

• The immune system might attack it
  
  

• Nodules might grow in it
  
  

• The brain signals (TSH) might be off
  
  

All of these lead to different thyroid conditions, which we will cover one by one.

🧩 The Big Picture 

Here’s the simple takeaway:

• The thyroid controls your body’s speed
  
  

• It does this using T3 and T4 hormones
  
  

• The brain controls the thyroid using TSH
  
  

• When any part of this system is off, symptoms happen

👉 What Usually Happens Next 

If you’re learning about this because of symptoms or test results, the next steps are usually:

1. Blood tests (TSH, Free T4, sometimes Free T3)
   
   

2. Possibly thyroid antibody tests
   
   

3. Sometimes an ultrasound
   
   

4. A discussion with your doctor about treatment if needed

Coming Up Next 

Now that you know how the thyroid works, the next page will explain:

➡ Common Thyroid Symptoms

This will help you connect what you’re feeling with how the thyroid affects the body.