Thyroid Hormones and their control

1. Thyroid Hormonesand their control Thyroid hormones control your metabolic rate. But what controls your thyroid hormone levels?

2. In this thyroid tutorial, you should learn to: • Explain how thyroid activity is regulated • Predict and explain hormone levels in different thyroid imbalances • Predict and explain signs and symptoms of hyper- and hypo-thyroidism • Identify the emergency complications of hyper- and hypo-thyroidism. • To start, just click the forward arrow. To return to this menu at any time, click the home button.

3. Hypothalamus detects low thyroid hormones What’s the next step? Thyroid secretes T3 and T4 Hypothalamus secretes TSH (thyroid stimulating hormone) Hypothalamus secretes TRH (thyrotropin releasing hormone) Hypothalamus releases TRH Good work! The hypothalamus secretes RELEASING hormones. In this case, the hypothalamus is trying to stimulate the thyroid – so it secretes Thyrotropin releasing hormone. Thyrotropin means ‘thyroid growth-causer.’ So TRH is going to tell some other organ to RELEASE a THYROID GROWTH-CAUSER. Click on the forward arrow to go on.

4. Hypothalamus detects low thyroid hormones What’s the next step? TRH travels to anterior pituitary Hypothalamus secretes TSH (thyroid stimulating hormone) Hypothalamus secretes T3 and T4 Hypothalamus releases TRH TRH travels to anterior pituitary Good work! The hypothalamus secretes RELEASING hormones. to tell some other organ to RELEASE a THYROID GROWTH-CAUSER. The organ that releases stimulating hormones for the hypothalamus is the anterior pituitary - just about an inch below it. The TRH travels from the hypothalamus to the pituitary through a tiny portal system of blood vessels.

5. Hypothalamus detects low thyroid hormones What’s the next step? anterior pituitary releases TSH (thyroid stimulating hormone) pituitary secretes T3 & T4 Thyroid secretes T3 and T4 Hypothalamus releases TRH TRH travels to anterior pituitary Good work! When it receives the Thyrotropin Releasing hormone, the anterior pituitary releases a thyrotropin, or thyroid stimulating hormone. anterior pituitary releases TSH

6. Hypothalamus detects low thyroid hormones What’s the next step? pituitary secretes T3 & T4 Thyroid stimulated by TSH Thyroid stimulated by TRH Hypothalamus releases TRH TRH travels to anterior pituitary Good work! Thyroid stimulating hormone does just what its name says – stimulate the thyroid. anterior pituitary releases TSH Thyroid stimulated by TSH

7. Hypothalamus detects low thyroid hormones What’s the next step? Thyroid produces only T3 Thyroid produces T3 & T4 Thyroid produces TRH Hypothalamus releases TRH TRH travels to anterior pituitary Good work! The thyroid produces 2 hormones. T3 is tri-iodothyronine – 3 iodine atoms T4 is tetra-iodothyronine – 4 iodine atoms T3 is the active form. T4 is an inactive backup form; your tissues can convert it into T3 by taking off an iodine atom. anterior pituitary releases TSH Thyroid stimulated by TSH Thyroid produces T3 & T4

8. Hypothalamus detects low thyroid hormones What’s the next step? Thyroid measures T3 & T4, stops making them when there is enough Hypothalamus and pituitary detect T3 & T4; secrete more TRH and TSH. Hypothalamus and pituitary detect T3 & T4; stop secreting TRH and TSH. Hypothalamus releases TRH TRH travels to anterior pituitary Good work! When T3 & T4 levels return to normal, the hypothalamus and pituitary no longer need to stimulate the thyroid. That is, T3 & T4 exert negative feedback on the hypothalamus and pituitary. anterior pituitary releases TSH Thyroid stimulated by TSH Thyroid produces T3 & T4 Hypothalamus and pituitary detect T3 & T4; stop secreting TRH and TSH.

9. Hypothalamus detects low thyroid hormones Hypothalamus releases TRH TRH travels to anterior pituitary anterior pituitary releases TSH The thyroid is the PRIMARY organ making the thyroid hormones. Thyroid stimulated by TSH Thyroid produces T3 & T4 Hypothalamus and pituitary detect T3 & T4; stop secreting TRH and TSH.

10. Hypothalamus detects low thyroid hormones Hypothalamus releases TRH TRH travels to anterior pituitary The anterior pituitary is the SECONDARY organ responsible for making thyroid hormones. anterior pituitary releases TSH The thyroid is the PRIMARY organ making the thyroid hormones. Thyroid stimulated by TSH Thyroid produces T3 & T4 Hypothalamus and pituitary detect T3 & T4; stop secreting TRH and TSH.

11. Hypothalamus detects low thyroid hormones The hypothalamus is the TERTIARY organ responsible for making thyroid hormones. Hypothalamus releases TRH TRH travels to anterior pituitary The anterior pituitary is the SECONDARY organ responsible for making thyroid hormones. anterior pituitary releases TSH The thyroid is the PRIMARY organ making the thyroid hormones. Thyroid stimulated by TSH Thyroid produces T3 & T4 Hypothalamus and pituitary detect T3 & T4; stop secreting TRH and TSH.

12. Hypothalamus detects low thyroid hormones A man has high T3 & T4 levels, because of a problem with his thyroid. What’s his diagnosis? Tertiary hyperthyroidism Secondary hypothyroidism Primary hyperthyroidism Hypothalamus releases TRH TRH travels to anterior pituitary Good work! It’s called hyperthyroidism because there is too much T3 & T4. It’s called primary because the problem is in the primary organ making T3 & T4 – the thyroid itself. anterior pituitary releases TSH Thyroid stimulated by TSH Thyroid produces Excess T3 & T4 Hypothalamus and pituitary detect T3 & T4; stop secreting TRH and TSH.

13. Hypothalamus detects low thyroid hormones A man has high T3 & T4 levels, because of a problem with his anterior pituitary. What’s his diagnosis? Tertiary hyperthyroidism Secondary hyperthyroidism Secondary hypothyroidism Hypothalamus releases TRH TRH travels to anterior pituitary Good work! It’s called hyperthyroidism because there is too much T3 & T4. It’s called secondary because the problem is in the secondary organ stimulating T3 & T4 production – the anterior pituitary. anterior pituitary releases Excess TSH Thyroid overstimulated by excess TSH Thyroid produces Excess T3 & T4 Hypothalamus and pituitary detect T3 & T4; stop secreting TRH and TSH.

14. Hypothalamus detects low thyroid hormones A man has primary hyperthyroidism. What will his levels of TSH be like? Normal High Low Hypothalamus releases TRH TRH travels to anterior pituitary Good work! With primary hyperthyroidism, this man has too much T3 & T4 because of a problem with his thyroid. The hypothalamus and anterior pituitary are still working. They will detect these high levels of T3 & T4, and stop secreting TRH and TSH. Therefore, the levels of TRH and TSH will be lower than normal. anterior pituitary releases TSH Thyroid stimulated by TSH Thyroid produces Excess T3 & T4 Hypothalamus and pituitary detect T3 & T4; stop secreting TRH and TSH.

15. Hypothalamus detects low thyroid hormones A man has secondary hyperthyroidism. What will his TSH levels be like? Low Normal High Hypothalamus releases TRH TRH travels to anterior pituitary Good work! In secondary hyperthyroidism, the T3 & T4 levels are elevated because the anterior pituitary is producing too much TSH, over-stimulating the thyroid. TSH levels are higher than normal. anterior pituitary releases TSH Thyroid stimulated by TSH Thyroid produces T3 & T4 Hypothalamus and pituitary detect T3 & T4; stop secreting TRH and TSH.

16. Hypothalamus detects low thyroid hormones A man has secondary hyperthyroidism. What will his TRH levels be like? Normal Low High Hypothalamus releases TRH TRH travels to anterior pituitary Good work! In secondary hyperthyroidism, the T3 & T4 levels are elevated because the anterior pituitary is producing too much TSH, over-stimulating the thyroid. But there is nothing wrong with the hypothalamus, so it will still detect the high T3 & T4 levels, and stop producing TRH. TRH levels will be low. anterior pituitary releases TSH Thyroid stimulated by TSH Thyroid produces T3 & T4 Hypothalamus and pituitary detect T3 & T4; stop secreting TRH and TSH.

17. Hypothalamus detects low thyroid hormones A man has tertiary hypothyroidism. What will his TRH levels be like? Normal Low High Hypothalamus releases TRH TRH travels to anterior pituitary Good work! Hypothyroidism means the thyroid hormone levels are low. Tertiary means the organ at fault is the hypothalamus. It isn’t creating enough TRH to stimulate the thyroid. anterior pituitary releases TSH Thyroid stimulated by TSH Thyroid produces T3 & T4 Hypothalamus and pituitary detect T3 & T4; stop secreting TRH and TSH.

18. Hypothalamus detects low thyroid hormones A man has low T3 & T4 levels, but high TSH levels. What’s his diagnosis? Tertiary hypothyroidism Secondary hyperthyroidism Primary hypothyroidism Hypothalamus releases TRH TRH travels to anterior pituitary Good work! It’s called hypothyroidism because there is too little T3 & T4. you can tell it’s primary because the pituitary is doing its job – making TSH to stimulate the thyroid. But the thyroid isn’t responding! The problem must be with the thyroid itself. anterior pituitary releases TSH Thyroid stimulated by TSH Thyroid produces T3 & T4 Hypothalamus and pituitary detect T3 & T4; stop secreting TRH and TSH.

19. Hypothalamus detects low thyroid hormones A man has low T3 & T4 levels, and low TSH levels. When he is given an injection of TRH, his T3 & T4 go back to normal. What’s his diagnosis? Hypothalamus releases TRH Tertiary hypothyroidism Secondary hypothyroidism Tertiary hyperthyroidism TRH travels to anterior pituitary anterior pituitary releases TSH Good work! It’s called hypothyroidism because there is too little T3 & T4. you can tell it’s tertiary - involving failure of the hypothalamus - because when you give him the hormone the hypothalamus should be making, you fix his problem. Thyroid stimulated by TSH Thyroid produces T3 & T4 Hypothalamus and pituitary detect T3 & T4; stop secreting TRH and TSH.

20. Hypothalamus detects low thyroid hormones In Grave’s disease, antibodies shaped like TSH attach to TSH receptors on the thyroid and cause it to make excess T3 & T4. What kind of imbalance results? Hypothalamus releases TRH Primary hyperthyroidism Secondary hyperthyroidism Tertiary hyperthyroidism TRH travels to anterior pituitary anterior pituitary releases TSH Good work! It’s called hyperthyroidism because there is too much T3 & T4. It’s called primary because there’s nothing wrong with the pituitary or the hypothalamus. They are just doing their jobs as usual. Thyroid stimulated by TSH Thyroid produces T3 & T4 Hypothalamus and pituitary detect T3 & T4; stop secreting TRH and TSH.

21. Hypothyroid: low thyroid hormones What is most likely to happen to someone who is hypothyroid? Decreased aerobic metabolism Decreased temperature Elevated WBC count Hypertension Decreased temperature Good work! Your body is warm because heat is produced as a byproduct of aerobic metabolism. If you are doing less aerobic metabolism, your temperature will decrease.

22. Hypothyroid: low thyroid hormones What is most likely to happen to someone who is hypothyroid? Decreased aerobic metabolism Fatty stools Weight loss Weight gain Decreased temperature Weight gain Good work! When metabolic rate decreases, less food is burned to make ATP. The unused food is stored in the body – leading to weight gain.

23. Hypothyroid: low thyroid hormones What is most likely to happen to someone who is hypothyroid? Decreased aerobic metabolism Fast reflexes Diarrhea Constipation Decreased temperature Weight gain Constipation Good work! When metabolic rate decreases, muscles are less active. Bowel movement decreases.

24. Hypothyroid: low thyroid hormones What is most likely to happen to someone who is hypothyroid? Decreased aerobic metabolism Strong heartbeat Wide pulse pressure Weak heartbeat Decreased temperature Weight gain Constipation Good work! When metabolic rate decreases, muscles are less active. Heart movement decreases, weakening the heartbeat. Weak heartbeat

25. Hypothyroid: low thyroid hormones Hypothyroidism also causes a condition called myxedema, or mucusy edema. In myxedema, mucus builds up under the skin, giving it a dry, puffy look. The myxedema may also affect the tongue, making it larger. The vocal cords may swell, making the voice croaky. Decreased aerobic metabolism Decreased temperature Weight gain Constipation Weak heartbeat Dry, puffy skin Enlarged tongue Croaking voice

26. Hypothyroid: low thyroid hormones Which of the signs and symptoms listed is most likely to cause a severe complication? Click on the one that worries you most. Decreased aerobic metabolism Decreased temperature Good work! When metabolic rate decreases, muscles are less active. Heart movement decreases, weakening the heartbeat. If somebody with hypothyroidism catches an additional illness, their condition may get worse. Their heart might slow so much that it causes vascular collapse. This is called myxedema coma. Weight gain Constipation Weak heartbeat Dry, puffy skin Enlarged tongue Croaking voice

27. Hyperthyroid: high thyroid hormones What is most likely to happen to someone who is hyperthyroid? Increased aerobic metabolism Increased appetite Elevated WBC count Decreased temperature Increased appetite Good work! A person with a high metabolism is always hungry – the food is being burned up to make ATP as fast as the person can eat it!

28. Hyperthyroid: high thyroid hormones What is most likely to happen to someone who is hyperthyroid? Increased aerobic metabolism Fatty stools Weight gain Weight loss Increased appetite Weight loss Good work! When metabolic rate increases, more food is burned to make ATP.

29. Hyperthyroid: high thyroid hormones What is most likely to happen to someone who is hyperthyroid? Increased aerobic metabolism Constipation Sweating Decreased temperature Increased appetite Weight loss Sweating Good work! When metabolic rate increases, more food is burned to make ATP. This produces more heat, which means the person will be overheated and sweating.

30. Hyperthyroid: high thyroid hormones What is most likely to happen to someone who is hyperthyroid? Increased aerobic metabolism Lethargy Tremor Hypotension Increased appetite Weight loss Sweating Good work! When metabolic rate increases, muscles and nerves make more ATP and are more active. This can present as tremor and anxiety. Tremor

31. Hyperthyroid: high thyroid hormones What is most likely to happen to someone who is hyperthyroid? Increased aerobic metabolism Somnolence Anorexia Tachycardia Increased appetite Weight loss Sweating Good work! When metabolic rate increases, cardiac muscles make more ATP and are more active. This can present as tachycardia, a strong pulse, and a widened pulse pressure. Tremor Tachycardia

32. Hyperthyroid: high thyroid hormones Which of the signs and symptoms listed is most likely to cause a severe complication? Click on the one that worries you most. Increased aerobic metabolism Increased appetite Good work! If somebody with hyperthyroidism catches an additional illness, their condition may get worse. Their heart might speed up so much that there isn’t time for it to fill between beats. This causes vascular collapse. At the same time, their fever might soar to dangerous levels. This is called thyroid storm. Weight loss Sweating Tremor Tachycardia Exophthalmos

33. This is the end of the thyroid tutorial. • You should be able to: • Explain how thyroid activity is regulated • Predict and explain hormone levels in different thyroid imbalances • Predict and explain signs and symptoms of hyper- and hypo-thyroidism • Identify the emergency complications of hyper- and hypo-thyroidism. • Not sure? Just click on the topic you want to review.