Thyroid Hormones and their control

Thyroid Hormonesand their control

Thyroid hormones control your metabolic rate. But what controls

your thyroid hormone levels?

In this thyroid tutorial, you should learn to:

– Explain how thyroid activity is regulated– Predict and explain hormone levels in differen

t 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.

Hypothalamus detects low thyroid hormones

What’s the next step?

Hypothalamus secretes TRH (thyrotropin

releasing hormone)

Hypothalamus secretes TSH

(thyroid stimulating hormone)

Thyroid secretes T3 and T4

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.

Hypothalamus releases TRH



TRH travels to anterior pituitary

Hypothalamus secretes TSH

(thyroid stimulating hormone)

Hypothalamus secretes T3 and

T4

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.





anterior pituitary

releases TSH (thyroid

stimulating hormone)

pituitary secretes T3 & T4

Thyroid secretes T3 and T4

Good work!

When it receives the Thyrotropin Releasing hormone, the anterior pituitary releases a

thyrotropin, or thyroid stimulating hormone.



anterior pituitary releases TSH



Thyroid stimulated by

TSH

pituitary secretes T3 & T4

Thyroid stimulated by

TRH

Good work!

Thyroid stimulating hormone does just what its name says – stimulate the thyroid.




Thyroid stimulated by TSH



Thyroid produces T3 &

T4

Thyroid produces only

T3

Thyroid produces TRH

Good work!

The thyroid produces 2 hormones.

T3 is tri-iodothyronine – 3 iodine atomsT4 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.





Thyroid produces T3 & T4



Hypothalamus and pituitary

detect T3 & T4; stop secreting TRH and TSH.

Hypothalamus and pituitary

detect T3 & T4; secrete more TRH and TSH.

Thyroid measures T3 &

T4, stops making them when there is

enough

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.






Hypothalamus and pituitary detect T3 & T4; stop

secreting TRH and TSH.









The thyroid is the PRIMARY organ making the thyroid hormones.









The anterior pituitary is the SECONDARY organ responsible for

making thyroid hormones.










The anterior pituitary is the SECONDARY organ responsible for

making thyroid hormones.


The hypothalamus is the TERTIARY organ responsible for making thyroid

hormones.


A man has high T3 & T4 levels, because of a problem with his thyroid. What’s his diagnosis?

Primary hyperthyroidism

Secondary hypothyroidism

Tertiary hyperthyroidism

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.





Thyroid produces Excess T3 & T4




A man has high T3 & T4 levels, because of a problem with his anterior pituitary. What’s his diagnosis?

Secondary hyperthyroidism



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





A man has primary hyperthyroidism. What will his levels of TSH be like?

LowHighNormal

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.









A man has secondary hyperthyroidism. What will his TSH levels be like?

High Low Normal

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.









A man has secondary hyperthyroidism. What will his TRH levels be like?

Low HighNormal

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.









A man has tertiary hypothyroidism. What will his TRH levels be like?

Low HighNormal

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.









A man has low T3 & T4 levels, but high TSH levels. What’s his diagnosis?

Primary hypothyroidism


Tertiary hypothyroidism

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.








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?

Tertiary hypothyroidism



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.








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?

Primary hyperthyroidism



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.








Hypothyroid: low thyroid hormones What is most likely to happen to someone who is

hypothyroid?

Decreased temperature

Elevated WBC count Hypertension

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.

Decreased aerobic metabolism



hypothyroid?

Weight gainWeight lossFatty stools

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.



Weight gain


hypothyroid?

ConstipationDiarrheaFast reflexes

Good work!

When metabolic rate decreases, muscles are less active. Bowel movement decreases.



Weight gain

Constipation


hypothyroid?

Weak heartbeatStrong heartbeat

Wide pulse pressure

Good work!

When metabolic rate decreases, muscles are less active. Heart movement decreases, weakening the

heartbeat.



Weight gain

Constipation

Weak heartbeat

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.



Weight gain

Constipation

Weak heartbeat

Dry, puffy skin

Enlarged tongue

Croaking voice

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


Weak heartbeat

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

Dry, puffy skin

Enlarged tongue

Croaking voice

Hyperthyroid: high thyroid hormones What is most likely to happen to someone who is

hyperthyroid?

Increased appetite

Elevated WBC count


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!

Increased aerobic metabolism

Increased appetite

What is most likely to happen to someone who is hyperthyroid?

Weight lossWeight gainFatty stools

Good work!

When metabolic rate increases, more food is burned to make ATP.

Weight loss

Hyperthyroid: high thyroid hormones


Increased appetite


Sweating Decreased temperatureConstipation

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.

Weight loss



Increased appetite

Sweating


Tremor Hypotension Lethargy

Good work!

When metabolic rate increases, muscles and nerves make more ATP and are more active. This can

present as tremor and anxiety.

Weight loss



Increased appetite

Sweating

Tremor


Tachycardia Anorexia Somnolence

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.

Weight loss



Increased appetite

Sweating

Tremor

Tachycardia

Weight loss



Increased appetite

Sweating

Tremor

Tachycardia

Exophthalmos

Which of the signs and symptoms listed is most likely to cause a severe complication? Click on the

one that worries you most.

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.

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 differen

t 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.

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Thyroid Hormones and their control