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"Shaped like a shield"
Very important in early development, particularly neural


Rim of cells that form Thyroid Follicles
Make, secrete and store thyroid hormone


Precursor to thyroid hormones (T3, T4)

Thyroglobulin Molecular Structure

Tyrosine (amino acid) + Iodine


Amino acid
Non-essential: can be made from phenol alanine

Tyrosine Molecular Structure

Diiodotyrosine can be made by adding 2 I on each side of OH group

Phenol Alanine Hydroxylase

Makes tyrosine from phenol alanine

Sodium Potassium Symport

◦Symports move particles in the same direction
◦Responsible for moving iodide to thyrocyte

Thyroid Binding Globulin (TBG)

Carrier protein that transports thyroid hormone

Thyroid Hormone (T4) Molecular Structure


T4 (Tetraiodothyronine)

Half life: 15 days


Process by which T4 becomes T3

T4 Effects

Mitochondria proliferates in presence of hormone and mitochondrial hypertrophy (enlargement) occurs (individual mitochondrion become bigger)

Thyrotropin/Thyroid-Stimulating Hormone (TSH)

"Thyroid growth"
Hormone from pituitary gland that controls thyrocytes

What Controls Thyrocytes?







Encouragement of mitosis


Get smaller

How Does TSH Control Thyrocytes?

◦Hypertrophy = enlarges thyrocytes, allows it to make and secrete more T4
◦Hyperplasia = increase in number of cells, thyrocytes proliferate, mitogenic

What Controls the Pituitary Gland?


Thyrotropin-Releasing Hormone (TRH)

Neurohormone from small gland attached to the base of the brain that regulates pituitary gland by stimulating it to secrete TSH

What Controls the Brain in the Secretion of TRH?

Secretion of T4 reduces number of TRH receptors on
pituitary gland (fewer receptors, lower pituitary response to TRH)
• Down-Regulation of receptors


Hypertrophied thyroid

Graves Disease

◦Type of hyperthyroidism
◦Thyrocytes poisoned by abnormal antibodies (IgG) which compete with TSH for the same protein receptor and functions like TSH only more excessively
◦Increase in metabolic and heart rate (palpitations, arrhythmia), and oxygen consumption, exophthalmos, transplacental
◦High T4 levels will cause positive feedback on the brain, causing it to produce lower levels of TRH and therefore lower TSH
•Treatment 1: Radioactive iodine
•Treatment 2: Immunosuppression (Higher mortality rate)
•Treatment 3: Synthroid
•Treatment 4: Subtotal Thyroidectomy
•Treatment 5: Thiouracil
•Treatment 6: Thiocyanates


Found naturally in cabbage, inhibit sodium iodide transport


A membrane transport process that carries two substances in the same direction across the membrane.

Sodium Iodide Symports

Mechanism by which thyrocytes to take up iodine


Inhibits thyroperoxidase which contributes to synthesis of thyroid hormone

Subtotal Thyroidectomy

Partial removal of the thyroid


Will be passed from mother to child

Radioactive Iodine Treatment

"Hot" or radioactive iodine will compete with the "cold" or regular iodine and cell that intakes radioactive iodine will be destroyed by the radiation
◦Sodium iodide symports can get thyrocytes to take up
radioactive iodine
◦Iatogenic: patient will emit gamma radiation and will be unsafe for a while

Thyroid Stimulating Immunoglobin (IgG)

Abnormal antibody that competes with TSH for the same protein receptor and functions like TSH only more excessively, causing Graves Disease


Eyes bulge because of eyeball volume increase so that
eyeball cannot fit in orbital cavity which will cause deteriorating vision


Epithelial cancer


Secretory epithelial cancer


Condition of hyposecretion of the thyroid gland causing low thyroid levels in the blood that result in sluggishness, slow pulse, and often obesity


Condition of hypersecretion of the thyroid gland characterized by exophthalmia, tachycardia, goiter, and tumor

Hashimoto's Thyroiditis

7x greater incidence than Graves disease
‣ Primary and Secondary Diagnosis
◦Symptoms: Puffy eyes, apparent obesity (redistribution of polysaccharide), lethargy and stupor, low consumption of oxygen, decrease in metabolic rate
‣ Hashimoto antibody destroys TSH receptors, causes atrophy in thyroid > Insufficient T4 levels (brain is un-suppressed) elevation of both TRH and TSH
◦Treatment: Synthroid

Synthroid Treatment

Treatment with T4 when thyroid destroyed
Used to treat Hashimoto's Thyroiditis

Primary Diagnosis

Trouble found directly in thyroid

Secondary Diagnosis

Trouble found elsewhere, thyroid not directly responsible


Characteristic to a region

Endemic Goiter

-Mostly found in inland populations
-Cause: dietary deficiency of iodine
‣ Adequate T4 cannot be made > brain un-suppressed by loss of T4 > elevated TRH > elevated TSH
• Still binds to TSH receptors and will cause hypertrophy and induce mitosis in thyrocytes
◦Treatment: iodine

Relationship Between TRH, TSH and T4

TRH > +TSH > +T4
•T4 will then act in positive feedback to inhibit TRH and TSH


A disease that results from the adverse affects of treatment or surgery

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