Study your flashcards anywhere!

Download the official Cram app for free >

  • Shuffle
    Toggle On
    Toggle Off
  • Alphabetize
    Toggle On
    Toggle Off
  • Front First
    Toggle On
    Toggle Off
  • Both Sides
    Toggle On
    Toggle Off
  • Read
    Toggle On
    Toggle Off

How to study your flashcards.

Right/Left arrow keys: Navigate between flashcards.right arrow keyleft arrow key

Up/Down arrow keys: Flip the card between the front and back.down keyup key

H key: Show hint (3rd side).h key

A key: Read text to speech.a key


Play button


Play button




Click to flip

48 Cards in this Set

  • Front
  • Back
In the thyroid, hormones are ______ not ______.
stored; formed on demand
What does the thyroid follicle contain?
Colloidal iodinated thyroglobulin.
What hormone from the pituitary will cause thyroid enlargement?
What is colloid made of?
T3, T4, MIT, and DIT attached to Thyroglobulin.
What ion is essential for thyroid hormone synthesis? What purpose does it serve?
Iodide (I-).
Makes thyroid hormones more soluble.
What are symptoms of Iodide deficiency in infants?
Mental and growth impairment, increased infant morbidity and mortality.
What are the 2 predominant thyroid hormones?
1) T3 - Tri-iodothyronine
2) T4 - Thyroxine
What is an "iodide trap"?
Na+/I- Symporters (NIS) found on the membranes of thyroid follicles, linked to Na/K ATPase.
What are the 3 competitive inhibitors of Na/I Symport?
1) Thiocyanate
2) Perchlorate
3) Pertechnate
*Cause thyroid follicles to rapidly release Iodide.
Why might a person suffering from depression also have hypothyroidism?
Lithium therapy is common as an anti-depressant, but it is also an inhibitor of Na+/I- Symport (NIS).
What is radioactive pertechnetate used for in the thyroid?
To visualize thyroid anatomy and measure iodide trapping.
How is thyroid hormone regulated at the follicular plasma membrane?
Increase of Iodide uptake (NIS activity) will result in negative feedback for T4/T3 production and also decreased "Iodide Trapping" (NIS activity).
What is the Wolf-Chaikoff effect?
The plasma membrane will begin to reject excessive Iodide and slow Thyroid Hormone production (basically negative feedback).
What hormone is released from the hypothalamus to stimulate the anterior pituitary release of thyroid hormone?
Thyroid Releasing Hormone (TRH).
What hormone is released from the anterior pituitary to stimulate thyroid hormone production?
TSH after TRH binds to receptors on the pituitary gland.
What effect does T3/T4 production have on the pituitary?
Primary negative feedback loop, inhibit the release of TSH.
What effect do dopamine and somatostatin have on the hypothalamus-pituitary-thyroid axis?
Dopamine and somatostatin from the hypothalamus tonically inhibit TSH secretion from pituitary.
TSH is a ________ glycoprotein synthesized in the ________.
dimeric; pituitary
Describe the pathway of T3/T4 production, beginning with TSH binding to thyroid gland receptors.
1) Iodide is taken in via NIS
2) Thyroglobulin (TG)is produced in the ER
3) Thyroid Peroxidase produces colloidal iodinated thyroglobulin (T3-T4-MIT-DIT, bound to TG) in the follicle lumen.
4) Colloidal iodinated thyroglobulin is endocytosed and proteolysed.
5) T3/T4 is secreted with some rT3 (non-hormone)
6) MIT, DIT are recycled by Deiodinase.
7) Thyroid gland size increases.
What is organification?
The formation of T3-T4-MIT-DIT complex bound to TG by Thyroid Peroxidase and H2O2.
What is Graves' Disease?
The formation of Ab's that mimic TSH, binding to TSH receptors causing thyroid hormone hypersecretion. This results in goiter formation.
What might cause constitutive activation of thyroid hormones?
Hypersecreting thyroid adenomas caused by mutant TSH receptors.
What would a defect in iodide trapping result in?
Decreased thyroid hormone synthesis, increase in TSH.
What would a defect in thyroid peroxidase result in?
Decreased thyroid hormone synthesis, increase in TSH, increase in iodide trapping (no negative feedback).
What would a defect in deiodinase result in?
No thyroid hormone synthesis, increase in TSH, increase in iodide trapping (no negative feedback), and INCREASE in MIT/DIT excretion. Inability to recycle I- by MIT/DIT.
What would a defect in organification/coupling result in?
No thyroid hormone synthesis, increase in TSH, increase in iodide trapping (no negative feedback).
Which thyroid hormone is the dominant secreted form?
Where is T3 formed, mostly?
In extra-thyroid tissues where T4 is deiodinated (kidney, liver, pituitary).
Why are transport proteins necessary for thyroid hormones?
Because they are highly lipophilic and water insoluble.
What are the three transport proteins of T3/T4?
Thyroxine Binding Globulin (TBG), Thyroid-Binding Pre-Albumin (TBPA), and Albumin.
Which transport protein is primarily responsible for thyroid hormone transport?
Thyroxine Binding Globulin (TBG).
How does T3 binding to its target receptor affect gene expression?
T3 binds to its target receptors (liver, kidney, pituitary) and becomes a transcription factor that usually activates gene transcription.
T3-bound Thyroid Receptors dimerize with ___ to form a ______ dimer that ________ ____________.
RXR; hetero; activates; gene transcription.
Unbound Thyroid Receptors dimerize with ___ will form a ______ dimer that ________ _____________.
RXR; hetero; suppress; gene transcription.
What converts T4 to T3?
How does direct T3 activity affect the mitochondria?
Activate mitochondrial oxidative genes.
What is the heterodimer involved in gene expression by thyroid hormone?
TR-RXR (T3 bound or unbound)
What is hyperthyroidism?
Overproduction of thyroid hormone resulting in increased metabolic activity.
What is hypothyroidism?
Underproduction of thyroid hormone resulting in decreased metabolic activity.
What are the similar symptoms between hyperthyroidism and hypothyroidism?
Goiter, muscle weakness, increased infections, increase number of mitochondria in the cell.
How does thyroid hormone affect the cardiovascular system?
Increases cardiac output and rate.
What developmental impairments are caused by thyroid deficit?
Bone age, height age, and mental age are all retarded. Thyroid replacement therapy will allow "catch up" in bone and height, but not mental age.
What is the primary cause of hyperthyroidism?
Graves' disease.
What are some risk factors associated with hyperthyroidism?
Female, family history, smoking.
What is the best way to assess hyperthyroidism?
Clinical exam, though many hyperthyroid patients will demonstrate decreased serum TSH and increased serum T4/T3.
What is subclinical hyperthyroidism?
Asymptomatic, but high risk for hyperthyroidism.
What is the best way to assess hypothyroidism?
Measure serum TSH, also T3/T4 if necessary. Serum TSH will be high while T3/T4 levels will be low.
What is subclinical hypothyroidism?
Asymptomatic, but may progress to overt hypothyroidism due to a damaged or poorly functioning thyroid.