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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
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
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.
Hypothalamus releases TRH
TRH travels to anterior pituitary
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
Good work!
When it receives the Thyrotropin Releasing hormone, the anterior pituitary releases a
thyrotropin, or thyroid stimulating hormone.
Hypothalamus releases TRH
TRH travels to anterior pituitary
anterior pituitary releases TSH
Hypothalamus detects low thyroid hormones
What’s the next step?
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.
Hypothalamus releases TRH
TRH travels to anterior pituitary
anterior pituitary releases TSH
Thyroid stimulated by TSH
Hypothalamus detects low thyroid hormones
What’s the next step?
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.
Hypothalamus releases TRH
TRH travels to anterior pituitary
anterior pituitary releases TSH
Thyroid stimulated by TSH
Thyroid produces T3 & T4
Hypothalamus detects low thyroid hormones
What’s the next step?
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 releases TRH
TRH travels to anterior pituitary
anterior pituitary releases TSH
Thyroid stimulated by TSH
Thyroid produces T3 & T4
Hypothalamus and pituitary detect T3 & T4; stop
secreting TRH and TSH.
Hypothalamus detects low thyroid hormones
Hypothalamus releases TRH
TRH travels to anterior pituitary
anterior pituitary releases TSH
Thyroid stimulated by TSH
Thyroid produces T3 & T4
Hypothalamus and pituitary detect T3 & T4; stop
secreting TRH and TSH.
The thyroid is the PRIMARY organ making the thyroid hormones.
Hypothalamus detects low thyroid hormones
Hypothalamus releases TRH
TRH travels to anterior pituitary
anterior pituitary releases TSH
Thyroid stimulated by TSH
Thyroid produces T3 & T4
Hypothalamus and pituitary detect T3 & T4; stop
secreting TRH and TSH.
The anterior pituitary is the SECONDARY organ responsible for
making thyroid hormones.
The thyroid is the PRIMARY organ making the thyroid hormones.
Hypothalamus detects low thyroid hormones
Hypothalamus releases TRH
TRH travels to anterior pituitary
anterior pituitary releases TSH
Thyroid stimulated by TSH
Thyroid produces T3 & T4
Hypothalamus and pituitary detect T3 & T4; stop
secreting TRH and TSH.
The anterior pituitary is the SECONDARY organ responsible for
making thyroid hormones.
The thyroid is the PRIMARY organ making the thyroid hormones.
The hypothalamus is the TERTIARY organ responsible for making thyroid
hormones.
Hypothalamus detects low 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.
Hypothalamus releases TRH
TRH travels to anterior pituitary
anterior pituitary releases TSH
Thyroid stimulated by TSH
Thyroid produces Excess T3 & T4
Hypothalamus and pituitary detect T3 & T4; stop
secreting TRH and TSH.
Hypothalamus detects low thyroid hormones
A man has high T3 & T4 levels, because of a problem with his anterior pituitary. What’s his diagnosis?
Secondary hyperthyroidism
Secondary hypothyroidism
Tertiary 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.
Hypothalamus releases TRH
TRH travels to 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.
Hypothalamus detects low thyroid hormones
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.
Hypothalamus releases TRH
TRH travels to anterior pituitary
anterior pituitary releases TSH
Thyroid stimulated by TSH
Thyroid produces Excess T3 & T4
Hypothalamus and pituitary detect T3 & T4; stop
secreting TRH and TSH.
Hypothalamus detects low thyroid hormones
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.
Hypothalamus releases TRH
TRH travels to anterior pituitary
anterior pituitary releases TSH
Thyroid stimulated by TSH
Thyroid produces T3 & T4
Hypothalamus and pituitary detect T3 & T4; stop
secreting TRH and TSH.
Hypothalamus detects low thyroid hormones
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.
Hypothalamus releases TRH
TRH travels to anterior pituitary
anterior pituitary releases TSH
Thyroid stimulated by TSH
Thyroid produces T3 & T4
Hypothalamus and pituitary detect T3 & T4; stop
secreting TRH and TSH.
Hypothalamus detects low thyroid hormones
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.
Hypothalamus releases TRH
TRH travels to anterior pituitary
anterior pituitary releases TSH
Thyroid stimulated by TSH
Thyroid produces T3 & T4
Hypothalamus and pituitary detect T3 & T4; stop
secreting TRH and TSH.
Hypothalamus detects low thyroid hormones
A man has low T3 & T4 levels, but high TSH levels. What’s his diagnosis?
Primary hypothyroidism
Secondary hyperthyroidism
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 releases TRH
TRH travels to anterior pituitary
anterior pituitary releases TSH
Thyroid stimulated by TSH
Thyroid produces T3 & T4
Hypothalamus and pituitary detect T3 & T4; stop
secreting TRH and TSH.
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
Secondary hypothyroidism
Tertiary hyperthyroidism
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 releases TRH
TRH travels to anterior pituitary
anterior pituitary releases TSH
Thyroid stimulated by TSH
Thyroid produces T3 & T4
Hypothalamus and pituitary detect T3 & T4; stop
secreting TRH and TSH.
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
Secondary hyperthyroidism
Tertiary 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.
Hypothalamus releases TRH
TRH travels to anterior pituitary
anterior pituitary releases TSH
Thyroid stimulated by TSH
Thyroid produces T3 & T4
Hypothalamus and pituitary detect T3 & T4; stop
secreting TRH and TSH.
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
Decreased temperature
Hypothyroid: low thyroid hormones What is most likely to happen to someone who is
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.
Decreased aerobic metabolism
Decreased temperature
Weight gain
Hypothyroid: low thyroid hormones What is most likely to happen to someone who is
hypothyroid?
ConstipationDiarrheaFast reflexes
Good work!
When metabolic rate decreases, muscles are less active. Bowel movement decreases.
Decreased aerobic metabolism
Decreased temperature
Weight gain
Constipation
Hypothyroid: low thyroid hormones What is most likely to happen to someone who is
hypothyroid?
Weak heartbeatStrong heartbeat
Wide pulse pressure
Good work!
When metabolic rate decreases, muscles are less active. Heart movement decreases, weakening the
heartbeat.
Decreased aerobic metabolism
Decreased temperature
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.
Decreased aerobic metabolism
Decreased temperature
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
Decreased temperature
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
Decreased temperature
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 aerobic metabolism
Increased appetite
What is most likely to happen to someone who is hyperthyroid?
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
Hyperthyroid: high thyroid hormones
Increased aerobic metabolism
Increased appetite
Sweating
What is most likely to happen to someone who is hyperthyroid?
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
Hyperthyroid: high thyroid hormones
Increased aerobic metabolism
Increased appetite
Sweating
Tremor
What is most likely to happen to someone who is hyperthyroid?
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
Hyperthyroid: high thyroid hormones
Increased aerobic metabolism
Increased appetite
Sweating
Tremor
Tachycardia
Weight loss
Hyperthyroid: high thyroid hormones
Increased aerobic metabolism
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.