What Does Thyroid Hormone Do?

It occupies a receptor. T4 and T3 bind to thyroid receptor in nucleus (receptor for steroid hormones is in cytoplasm whereas receptor for thyroid hormone is in nucleus). You then get increases mRNA and a host of reactions for example:

1. Increased proteins for growth and maturation (hypothyroid kids are small)

2. Increased mitochondrial and respiratory enzymes which increase oxygen consumption and metabolic rate (hyperthyroid people are hypermetabolic, but it is possible to be hypermetabolic-euthyroid)

3. Increased thermogenesis/heat production. This leads to increased sweating

4. Increased CO2 production and increased respiration

5. Regulates protein and fat metabolism (decreased muscle mass if you have too much). Hypothyroid patients are fat.

6. Increases appetite and increases mobilization of endogenous carbohydrates, protein and fat. Hypothyroidism can thus lead to diabetes

7. Increases cardiac output. So older people can get angina if they are hypothyroid

Category: Physiology Notes