Thyroid Basics

Question 1

What is essential for thyroid hormone production?
How is thyroid hormone stored?
Why is thyroid hormone released?

Answer 1

Iodine

• actively transported into thyroid
• undergoes organification via thyroid peroxidase system to produce thyroid hormone

Thyroid hormone stored in colloid of thryoid gland follicles i.e. central gelatinous material
-colloid formed from thyroglobulin= inactive storage form of thyroid hormone

Released from surface of thyrocyte in response to TSH

Question 2

Is the majority of thyroid hormone protein bound or not?

Which is the biologically active version?

Answer 2

Majority is PROTEIN BOUND

Free unbound thyroid hormone is biologically active and able to act as thyroid hormone

Question 3

What are the 2 forms of thyroid hormone circulating?

What is the difference?

Answer 3

T4 and T3

T4 (thyroxine)
-prohormone

T3

• active hormone
• T4->T3 via liver, kidney and thyroid
• enters the cell and binds to THR on the nucleus
• has direct effect on transcription

Question 4

How is thyroid homeostasis maintained?

Answer 4

Negative feedback loop

TRH secreted from hypothalamus and acts on anterior pituitary to release TSH

TSH released from anterior pituitary and stimulates release of T4/3 from thyroid

When sufficient free T4/3 in circulation, hypothalamus and ant pituitary stop secretion of TRH and TSH to prevent excess T4/3 release

Question 5

What are the 3 main functions of the thyroid hormone?

Answer 5

Increased metabolism

Growth and development

Increased catecholamine affect