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Thyroid in Health and Disease
Richard B. Horenstein, MD
Assistant Professor
Department of Medicine
Division of Endocrinology Diabetes & Nutrition
Thyroid Microscopic
Anatomy: The thyroid
Follicle
Follicular cells
Colloid
The structural and functional
unit of the thyroid is the
follicle, a closed sac filled
with colloid, a protein rich
fluid which contains the
hormones (T4 and T3) made
by thyroid follicular cells.
Thyroid follicular cells line
the wall of the follicle and
secrete thyroid hormones
into the colloid.
Hormones Produced by the Thyroid
• Thyroxine (T4)
• Triiodothyronine (T3)
– “T” stands for Thyroid
– The numbers ‘4’ and ‘3’ refer to the number of iodine
residues which are found in each hormone
– We need iodine in our diet to make thyroid hormone
The Thyroid in Health
– Produces hormones (thyroid hormones)
which travel from the thyroid into the
blood stream
– Thyroid hormones bind to receptors in all
cells (like a key into a lock)
– Thyroid hormones help regulate
metabolism (energy use), and temperature
Thyroxine T4
Triiodothyronine T3
Normal Regulation of Thyroid Function
• The thyroid itself acts in response to a hormone
(Thyroid Stimulating Hormone) produced by a
part of the brain
• TSH (Thyroid Stimulating Hormone) levels are
what doctors measure most commonly to check
thyroid function
• If the thyroid is making too little hormone, TSH
levels rise; if the thyroid makes too much
hormone (or if one takes too much of a thyroid
hormone supplement), TSH levels falls
Thyroid Hormone Regulation
The hypothalamic – pituitary – thyroid axis
Thyroid Hormone Regulation
Thyroid Hormone Regulation
Iodine Deficiency and Goiter
• Prevalent in many mountainous regions, central
Africa, central South America, and norther Asia
• Goiter (enlargement of the thyroid) is found in
areas of relative iodine deficiency
• The thyroid is able to take up dietary iodine
efficiently
• To prevent iodine deficiency, our salt and bread
has iodine added (Wonder, Stroehman,
Pepperidge Farm); so do prenatal vitamins
US efforts to prevent iodine deficiency
Iodine and Development
• Decreased iodine in the diet, leading to
insufficient thyroid hormone, results in lower
IQ levels in children, pointing to the import of
iodine and thyroid hormone to normal
development
• When iodine deficiency is severe and
children are not treated with iodine or thyroid
hormones, cretinism, a disorder
characterized by mental and growth
retardation, results
Common Thyroid Diseases
• Hypothyroidism – the condition where the thyroid
does not make enough thyroid hormone
• Hyperthyroidism – the condition where the thyroid
makes too much thyroid hormone
• Thyroid Nodules – disordered growth of thyroid
follicles
• Thyroid Cancer – uncontrolled growth and spread of
thyroid follicular cells (most commonly)
Hyperthyroidism - Symptoms
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Fatigue
Heat intolerance
Sweating
Nervousness
Restlessness
Frequent bowel movements
Weight loss despite increased appetite
Hyperthyroidism - Signs
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Rapid Heart Rate
Warm moist skin
Tremor
Eye lid retraction
Proximal muscle weakness
Diffuse enlargement of the thyroid is possible
Eye Lid Retraction in Hyperthyroidism
Patients with Graves' Ophthalmopathy
Bahn RS. N Engl J Med 2010;362:726-738
Graves' Hyperthyroidism
Iraci GS, Fux-Otta C. N Engl J Med 2009;360:e31.
Hyperthyroidism - laboratory findings
• Elevated Free T4 and Free T3 levels
• Depressed TSH level
Hyperthyroidism - Causes
• Iodine excess
• Antibodies directed against the thyroid
(Graves’ Disease)
• Inflammation of the thyroid (thyroiditis) due
to infection or trauma
• Toxic Nodule (clone of thyroid cells which
produce too much thyroid hormone)
• Ingesting too much thyroid hormone
Hyperthyroidism - Treatment
• Use of medications which slow the incorporation
of iodine into new thyroid hormone
– Methimazole
– PTU (propylthiouracil)
• Use of radioactive iodine (I-131) to destroy
a focus of increased thyroid hormone
production
• Surgery to remove the overactive thyroid
• Stop use of excess thyroid hormone
Hyperthyroidism - Treatment
• Treat with methimazole or PTU until the
TSH levels rise into the normal range
• If the thyroid gland is removed in whole or
in part, treat with thyroid hormone
replacement (Synthroid, levothyroxine)
Hypothyroidism – Causes
• Inflammation due to immune factors
(autoimmune thyroid disease)
• Previous medical treatment with radiation to
the head and neck
• Congenital (birth without a thyroid gland)
• Previous treatment of hyperthyroidism with
radioactive iodine (I-131)
• Surgery to remove part or the entire gland
• Viral illness (thyroiditis)
• Infiltration of the gland by other proteins,
metals (iron) or by other cancers
• Drugs prescribed for other diseases (lithium,
amiodarone)
Hypothyroidism - Symptoms
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Being more sensitive to cold
Constipation
Depression
Fatigue or feeling slowed down
Lower extremity edema
Increased menstrual flow
Joint or muscle pain
Weakness
Thin, brittle hair or fingernails
Unintentional weight gain
Hypothyroidism - Signs
• Slow pulse
• Cool extremities
• Dry, coarse skin
• Puffy face, hands, and feet
• Lower extremity edema
• Delayed tendon reflex relaxation
Hypothyroidism - Treatment
• Provide the patient with thyroid hormone
supplementation
– Synthroid, levothyroxine
• Treat so that the TSH level falls into the
normal range (the brain senses that the
thyroid hormone levels are normal)
Imaging Techniques to Evaluate the Thyroid
• Nuclear medicine studies
• Radiology Studies
– Ultrasound
– MRI
– CT Scan
Image of normal thyroid on nuclear medicine iodine scan
Ultrasound image of well circumscribed thyroid nodule
Thyroid Cancer - Treatment
• Surgery to remove the entire thyroid
• Treatment with higher doses of radioactive
iodine (I-131) to destroy remaining thyroid
cells
• Treatment with Synthroid (levothyroxine) at
levels which are high enough to suppress
TSH
Questions?