Hyperthyroidism vs Hypothyroidism: Signs & Symptoms
Hyperthyroidism vs hypothyroidism symptoms explained! Thyroid disease chart and thyroid hormone function, synthesis, feedback pathway, and effects on the body reviewed.
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Thyroid Hormone and Diseases
Thyroid hormone is important in regulating many functions of the human body including metabolism, growth, and development.
Problems can occur when thyroid hormone levels are too high (hyperthyroidism) or too low (hypothyroidism).
In this lecture, we will compare and contrast the signs and symptoms of hyperthyroidism vs hypothyroidism.
We will also review the thyroid hormone synthesis pathway and the effects thyroid hormone has on the body.
There is a simple cheat sheet summarizing everything above. Make sure to get your copy today!
There is also a table at the bottom of this post summarizing everything, so make sure to read until the end!
Thyroid Hormone Synthesis
Let’s briefly review the pathway in which thyroid hormone is produced and regulated.
The pathway involves the hypothalamus, anterior pituitary gland, and thyroid gland.
This pathway is called the hypothalamic-pituitary-thyroid axis (HPT axis) as a result.
The HPT axis is a self-regulatory circuit that balances thyroid hormone levels in the blood and maintains thyroid homeostasis in the body.
For a great step-by-step review of the HPT axis and how thyroid hormone is produced, make sure to check out the thyroid hormone synthesis lecture!
Thyroid Hormone Synthesis and Feedback Loop: The hypothalamic-pituitary-thyroid axis produces and regulates thyroid hormone levels in the body
Hypothalamus
The pathway starts with the hypothalamus, which is located in the center of the brain below the thalamus.
The hypothalamus releases a hormone called thyrotropin-releasing hormone (TRH).
Anterior Pituitary Gland
Located below the hypothalamus is the pituitary gland.
TRH acts on the pituitary gland and stimulates the anterior pituitary gland to release a hormone called thyroid-stimulating hormone (TSH).
TSH is released from the anterior pituitary gland into the bloodstream.
Thyroid Gland
TSH binds to another gland called the thyroid gland.
The thyroid gland is a butterfly shaped structure located at the base of the anterior neck.
TSH activates the thyroid gland to synthesize or produce thyroid hormone.
Thyroid hormone is then released from the thyroid gland into the bloodstream where it acts on many tissues and organs in the body, which we will discuss next.
The main thyroid hormones are triiodothyronine or T3 and thyroxine or T4.
Negative Feedback Loop
T3 and T4 levels in the blood create a negative feedback loop on the hypothalamus and anterior pituitary gland.
The negative feedback loop is to help regulate thyroid hormone levels in the blood and maintain thyroid homeostasis in the body.
High levels of thyroid hormone in the blood will inhibit the hypothalamus and anterior pituitary gland from releasing TRH and TSH respectively.
The opposite is true when thyroid hormone are low.
There will be decreased inhibition to the hypothalamus and anterior pituitary gland when thyroid hormone levels are low.
The hypothalamus and anterior pituitary gland will increase TRH and TSH release to stimulate more thyroid hormone production as a result.
Memory Tricks
The easy way to remember the order of the structures involved in thyroid hormone synthesis is to go in alphabetical order.
H = Hypothalamus
P = Pituitary Gland
T = Thyroid Gland
These structures create the HPT axis (alphabetical order).
It can also be easy to confuse TRH and TSH, and which comes first.
The trick is to go in alphabetical order again.
Use the “R” in TRH and the “S” in TSH.
“R” comes before “S”, which will help you remember the releasing hormone (TRH) is first followed by the stimulating hormone (TSH).
Thyroid Hormone Function
Thyroid hormone has many different target tissues and effects on the body.
Let’s focus on the main functions of thyroid hormone below.
Once you know the major effects thyroid hormone has on the body, then figuring out the symptoms of hyperthyroidism and hypothyroidism is simple.
Thyroid Hormone Function and Effects: Thyroid hormone has physiological effects on body metabolism, the heart, the brain, the GI tract, and the skin, hair, and nails.
Cells
The overall effect thyroid hormone has on the body is it “ramps or speeds things up”.
At a cellular level, thyroid hormone increases protein synthesis and metabolic activity within the cell.
The increased cellular metabolic activity will increase overall metabolism in the body.
Increased metabolism also generates body heat, a process known as thermogenesis.
The increased metabolic activity of cells will have different effects on the body depending on which organ system the cell is a part of.
Let’s look at some of the thyroid hormone effects on various organs.
Heart
Thyroid hormone acts on the heart to increase the number and sensitivity of beta-1 receptors.
We know from our lecture on beta receptors that the beta-1 adrenergic receptors are primarily located in the heart.
Beta receptors bind epinephrine and norepinephrine, which are involved in our “fight or flight” sympathetic response.
Activation of beta-1 receptors increases heart rate and cardiac contraction.
Increased cardiac contraction increases stroke volume.
Increased heart rate and stroke volume increases cardiac output.
Increased cardiac output increases blood pressure.
Thyroid hormone increases the expression and sensitivity of beta-1 adrenergic receptors which can increase heart rate, stroke volume, cardiac output, and blood pressure.
GI System
Thyroid hormone also acts on the GI system to increase GI motility and secretions.
Central Nervous System (CNS)
Thyroid hormone is able to cross the blood-brain barrier and has effects on the central nervous system, especially with prenatal brain development.
Thyroid hormone increases neurogenesis, which is the formation of new neurons.
Thyroid hormone also increases myelination.
Myelin is a sheath that forms around axons to help increase the conduction speed of an electrical impulse.
Thyroid hormone also increases synaptogenesis, which is the formation of more synapses or junctions between neurons.
Synapses are how neurons communicate with each other.
Thyroid hormone also helps increase dendrite formation.
Dendrites are the branches on a nerve cell that receive electrical impulses from other nerve cells.
Lastly, thyroid hormone increases the overall activity of the sympathetic nervous system.
The above effects play an important role in nervous system and brain development, particularly during the prenatal period, but they also play a role in mood and mental cognition in adults.
Skin, Hair, Nails
Thyroid hormone can also increase cutaneous blood flow and act on the skin, hair, and nails to maintain skin homeostasis, stimulate the proliferation of different skin cells in the epidermis and dermis, maintain sweat gland and oily secretions in the skin, stimulate hair growth, and stimulate nail growth.
Hyperthyroidism Definition
We can define hyperthyroidism by breaking down the word.
We know from our medical terminology lecture on prefixes that the prefix “hyper” means above normal, excess, high, or increased.
We also know from our medical terminology lecture on root words that the root word “thyroid” pertains to the thyroid gland or thyroid hormone.
Lastly, we know from our medical terminology lecture on suffixes that the suffix “ism” refers to a medical condition, disease, or process.
Therefore, hyperthyroidism is a condition in which the thyroid gland is overactive and produces too much thyroid hormone.
There will be increased levels of thyroid hormone in the blood as a result.
Hyperthyroidism can also be a result of exogenous thyroid hormone use, but most of the time it is from an overactive thyroid gland.
Hyperthyroidism Definition: A condition in which the thyroid gland is overactive resulting in high levels of thyroid hormone in the blood
Hyperthyroidism Symptoms
We already know the major effects thyroid hormone has on the body and how thyroid hormone “ramps or speeds things up”.
So the easiest way to think about the symptoms of hyperthyroidism is to amplify or “ramp up” those effects even more.
Signs and symptoms of hyperthyroidism include:
Weight Loss
Increased Appetite
Increased Body Temperature (Fever - In extreme cases)
Heat Intolerance
Increased Sensitivity to Heat
Tachycardia
Palpitations
Arrhythmias
Hypertension
Diarrhea
Anxiety
Nervousness
Irritability
Restlessness
Insomnia
Tremors
Hyperreflexia
Increased Sweating and Oily Secretions
Hair Growth
Fine, Soft Hair
Nail Growth
Onycholysis (Separation of the nail from the nail bed)
Myopathy
Osteoporosis
This is not a complete list, but some of the main symptoms that we will discuss below.
Hyperthyroidism Symptoms: High levels of thyroid hormone can have effects on metabolism, weight loss, heat intolerance, heart, GI system, mood, and skin or hair.
Metabolic Symptoms
Major metabolic symptoms include:
Weight Loss
Increased Appetite
Increased Body Temperature (Fever - In extreme cases)
Heat Intolerance
Increased Sensitivity to Heat
Individuals with hyperthyroidism are in a hypermetabolic state, which means they will be showing signs of increased metabolic activity.
Remember we mentioned how thyroid hormone increases the metabolic activity within cells.
If thyroid hormone levels are high in the blood, then there will be increased metabolic activity in the cells.
As a result, individuals with hyperthyroidism have increased body metabolism and a higher basal metabolic rate.
This is why weight loss is a symptom of hyperthyroidism.
It is also why there may be an increased appetite to try to restore the energy that is being used up.
We also mentioned above that body heat is generated with metabolism, a process known as thermogenesis.
If there is increased metabolism, then there will be increased body heat production.
This is why increased body temperature, heat intolerance, and increased sensitivity to heat are symptoms of hyperthyroidism as well.
Cardiovascular Symptoms
Major cardiovascular symptoms include:
Tachycardia
Palpitations
Arrhythmias
Hypertension
We previously mentioned how thyroid hormone increases beta-1 receptor expression and sensitivity in the heart, which increases heart rate and cardiac contraction.
These effects will be amplified in hyperthyroidism.
As a result, tachycardia (fast heart rate) may be present.
Individuals may also experience palpitations, which are sensations of the heart racing or skipping a beat.
Abnormal heart rates and rhythms are called arrhythmias, which may be present in hyperthyroidism.
The increased heart rate and cardiac contraction will also increase cardiac output, which is why hypertension (high blood pressure) may be present.
The increased sympathetic activity (see below) also contributes to the hypertension and tachycardia.
GI Symptoms
Major GI symptoms include:
Diarrhea
Frequent, Loose Stools
We also mentioned how thyroid hormone can act on the GI system to increase GI motility and secretions.
This can lead to symptoms of diarrhea and frequent loose stools in hyperthyroidism.
Neuropsychiatric Symptoms
Major neuropsychiatric symptoms include:
Anxiety
Nervousness
Irritability
Restlessness
Insomnia
Tremors
Hyperreflexia
We know from above that thyroid hormone plays an important role in the development and function of the central nervous system, particularly during the prenatal period.
Thyroid hormone also acts to increase sympathetic nervous system activity.
Individuals who have high levels of thyroid hormone may experience overstimulation of neuronal and sympathetic activity.
This can lead to symptoms of anxiety, nervousness, irritability, restlessness, insomnia, tremors, and hyperreflexia.
The increased sympathetic activity also contributes to the above cardiovascular symptoms of tachycardia and hypertension, as well as the increased sweating which we will discuss next.
Cutaneous Symptoms
Major cutaneous symptoms include:
Increased Sweating (Diaphoresis)
Increased Oily Secretions
Hair Growth
Fine, Soft Hair
Nail Growth
Onycholysis (Separation of the nail from the nail bed)
We also know thyroid hormone increases cutaneous blood flow and acts on the skin, hair, and nails.
The increased cutaneous blood flow, sympathetic activity, and body temperature in hyperthyroidism will cause increased sweating (diaphoresis).
As a reminder, sweat glands are innervated by the sympathetic nervous system.
Other symptoms of hyperthyroidism include hair growth, fine/soft hair, and nail growth.
The increased nail growth may cause onycholysis, which is separation of the nail from the nail bed.
Other Symptoms
In summary, we can see how hyperthyroidism will “ramp things up”.
The above symptoms are some of the main symptoms, but not a complete list.
Other general symptoms include shortness of breath, fatigue, muscle weakness, osteoporosis, among others.
Hypothyroidism Definition
We can define hypothyroidism by breaking down the word.
We know from our medical terminology lecture on prefixes that the prefix “hypo” means above normal, excess, high, or increased.
We also know from our medical terminology lecture on root words that the root word “thyroid” pertains to the thyroid gland or thyroid hormone.
Lastly, we know from our medical terminology lecture on suffixes that the suffix “ism” refers to a medical condition, disease, or process.
Therefore, hypothyroidism is a condition in which the thyroid gland is underactive and does not produce enough thyroid hormone.
There will be decreased levels of thyroid hormone in the blood as a result.
Hypothyroidism Definition: A condition in which the thyroid gland is underactive resulting in low levels of thyroid hormone in the blood (thyroid deficiency)
Hypothyroidism Symptoms
We already know the major effects thyroid hormone has on the body and how thyroid hormone “ramps or speeds things up”.
We also know hyperthyroidism will amplify these effects.
Hypothyroidism will have the opposite effects, which is why its symptoms are essentially the opposite of hyperthyroidism.
The easiest way to think about the symptoms of hypothyroidism is it “slows things down”.
Signs and symptoms of hypothyroidism include:
Weight Gain
Decreased Appetite
Decreased Body Temperature
Cold Intolerance
Increased Sensitivity to Cold
Bradycardia
Hypertension
Constipation
Fatigue
Depression
Impaired Memory
Impaired Cognition
“Mental Fog”
Delayed Deep Tendon Reflexes
Dry, Pale Skin
Hair Loss
Thin, Brittle Nails
Myopathy
This is not a complete list, but some of the main symptoms that we will discuss below.
Hypothyroidism Symptoms: Low levels of thyroid hormone (deficiency) can have effects on metabolism, weight gain, cold intolerance, heart, GI system, mood, hair loss, etc.
Metabolic Symptoms
Major metabolic symptoms include:
Weight Gain
Decreased Appetite
Decreased Body Temperature
Cold Intolerance
Increased Sensitivity to Cold
Individuals with hypothyroidism are in a hypometabolic state, which means they will be showing signs of decreased metabolic activity.
Remember we mentioned how thyroid hormone increases the metabolic activity within cells.
If thyroid hormone levels are low in the blood, then there will be decreased metabolic activity in the cells.
As a result, individuals with hypothyroidism have decreased body metabolism and a lower basal metabolic rate.
This is why weight gain is a symptom of hypothyroidism.
It is also why there may be decreased appetite.
Since energy is not being used up as quickly, there is no need to restore it with food.
We also mentioned above that body heat is generated with metabolism, a process known as thermogenesis.
If there is decreased metabolism, then there will be decreased body heat production.
This is why decreased body temperature, cold intolerance, and increased sensitivity to cold are symptoms of hypothyroidism as well.
Cardiovascular Symptoms
Major cardiovascular symptoms include:
Bradycardia
Hypertension
We previously mentioned how thyroid hormone increases beta-1 receptor expression and sensitivity in the heart, which increases heart rate and cardiac contraction.
In hypothyroidism, there will be less beta-1 receptor expression and sensitivity and the beta-1 adrenergic effects will be decreased.
Bradycardia (slow heart rate) may be present as a result.
Bradycardia is also a result of decreased sympathetic activity (see below).
Decreased heart rate and cardiac contraction can decrease cardiac output.
You would think this would lead to hypotension.
However, individuals with hypothyroidism often have hypertension like we saw with hyperthyroidism.
Why is this?
In addition to increasing beta receptors, thyroid hormone can also decrease alpha receptors.
So in a hypothyroidism, the opposite occurs.
There is a decrease in beta receptors and an increase in alpha receptors, particularly alpha-1 receptors.
We know from our alpha receptor lecture that alpha-1 receptors are located on blood vessels and lead to vasoconstriction when activated.
As a result, hypothyroidism can lead to vasoconstriction and increased peripheral vascular resistance, which can cause hypertension.
The decreased body temperature in hypothyroidism can also lead to vasoconstriction and increased peripheral vascular resistance, which can contribute to hypertension as well.
Lastly, the decreased cardiac output in hypothyroidism can potentially lead to compensatory vasoconstriction and increased peripheral vascular resistance as a result.
In summary, both hypothyroidism and hyperthyroidism can cause hypertension.
Hyperthyroidism usually causes tachycardia and hypertension, whereas hypothyroidism typically causes bradycardia and hypertension.
GI Symptoms
Major GI symptoms include:
Constipation
Less Frequent, Hard Bowel Movements
We also mentioned how thyroid hormone can act on the GI system to increase GI motility and secretions.
This can lead to symptoms of constipation and less loose stools in hypothyroidism.
Neuropsychiatric Symptoms
Major neuropsychiatric symptoms include:
Fatigue
Depression
Impaired Memory
Impaired Cognition
“Mental Fog”
Delayed Deep Tendon Reflexes
We know from above that thyroid hormone plays an important role in the development and function of the central nervous system, particularly during the prenatal period.
Thyroid hormone also acts to increase sympathetic nervous system activity.
Individuals who have low levels of thyroid hormone may experience a decrease in mental cognition, mood, and sympathetic activity.
This can lead to symptoms of fatigue, depression, impaired memory, impaired cognition, “mental fog”, and delayed deep tendon reflexes.
Low thyroid hormone during the prenatal period can also be detrimental to brain and central nervous system development.
The decreased sympathetic activity also contributes to the above cardiovascular symptoms of bradycardia, as well as the decreased sweating and dry skin which we will discuss next.
Cutaneous Symptoms
Major cutaneous symptoms include:
Dry, Pale Skin
Hair Loss
Coarse, Brittle Hair
Thin, Brittle Nails
We also know thyroid hormone increases cutaneous blood flow and acts on the skin, hair, and nails.
The decreased cutaneous blood flow, sympathetic activity, and body temperature in hypothyroidism can cause dry, pale skin.
Other symptoms of hypothyroidism include hair loss, coarse/brittle hair, and thin/brittle nails.
Other Symptoms
In summary, we can see how hypothyroidism will “slow things up”.
The above symptoms are some of the main symptoms, but not a complete list.
Other general symptoms include voice changes, hoarse voice, muscle cramps, joint pain, among others.
Hyperthyroidism v. Hypothyroidism
Below is a table comparing and contrasting hyperthyroidism vs hypothyroidism and summarizing everything discussed above.
Again we can see how hyperthyroidism generally increases and speeds things up, while hypothyroidism decreases and slows things down.
Hyperthyroidism vs Hypothyroidism Symptoms: Thyroid disease chart when thyroid hormone levels are too high or too low (deficiency)
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Referenceshttps://www.frontiersin.org/articles/10.3389/fendo.2018.00474/fullhttps://www.ncbi.nlm.nih.gov/books/NBK537053/https://www.ncbi.nlm.nih.gov/books/NBK519536/https://www.ncbi.nlm.nih.gov/books/NBK500006/https://www.ncbi.nlm.nih.gov/books/NBK499850/https://bsd.biomedcentral.com/articles/10.1186/s13293-021-00367-2#:~:text=Alteration%20of%20thyroid%20hormone%20level,disorder%2C%20anxiety%2C%20and%20depression.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3219173/