32 Questions
What is the function of thyrocytes in the thyroid gland?
Synthesizing thyroglobulin and expressing a TSH receptor
Where is the thyroid gland located?
At the base of the neck, just below the Adam's apple
What is the role of parafollicular cells or C cells in the thyroid gland?
Producing calcitonin, crucial for calcium metabolism
What is the main function of thyroglobulin in the thyroid gland?
Acting as a substrate for T4 and T3 biosynthesis
What is the size of the thyroid gland?
5 to 25 grams
What is the function of the thyroid gland hormones T4 and T3?
Regulating metabolism
Which hormone is more active than T4?
T3
What is the major component in T3 and T4 synthesis?
Iodine
Which medication competes with iodide for uptake, limiting iodination?
Thiocyanate
What process occurs in various peripheral tissues and in neural tissues for the conversion of T4 to T3?
Deiodination
What is the percentage of free T3 in the blood?
0.4%
Which enzyme mediates the coupling of DIT and DIT to produce T4?
Thyroid peroxidase (TPO)
What stimulates the release of T3 and T4?
$TSH$
Which medication blocks the sodium-iodide symporter (NIS), reducing the uptake of iodine by thyroid follicular cells?
Perchlorate
What inhibits the coupling of iodotyrosines, further reducing thyroid hormone synthesis?
Propylthiouracil (PTU)
What interacts with nuclear receptors in target cells, regulating gene expressions?
T3
What is the function of the parafollicular cells or C cells in the thyroid gland?
Production of calcitonin
What is the role of thyrocytes in synthesizing thyroglobulin?
Specialization in synthesizing thyroglobulin
What is the main function of the thyroid gland hormones T4 and T3?
Regulating gene expressions in target cells
What inhibits the coupling of iodotyrosines, further reducing thyroid hormone synthesis?
ReverseT3
Where is the thyroid gland located?
At the base of the neck, just below the Adam's apple
Which enzyme mediates the coupling of DIT and DIT to produce T4?
Thyroid peroxidase
Where does the conversion of T4 to T3 occur?
In various peripheral tissues, neural tissues, and the pituitary gland
What medication inhibits TPO, preventing the coupling and inhibiting the formation of MIT and DIT?
Propylthiouracil (PTU)
What is the main function of thyroglobulin in the thyroid gland?
Breaking down to release T3 and T4
Which medication competes with iodide for uptake, limiting iodination?
Thiocyanate
What is the percentage of free T4 in the blood?
0.04%
What process occurs within thyroid cells and in presence of H2O2 and TPO?
Iodine oxidation, tyrosine iodination, and organification
What stimulates the release of T3 and T4?
TSH
What inhibits the coupling of iodotyrosines, further reducing thyroid hormone synthesis?
What is the major component used for iodide transport or symport in thyroid hormone synthesis?
NIS
Which enzyme mediates the coupling of DIT and DIT to produce T4?
TPO
Study Notes
Thyroid Gland Structure and Function
- Thyrocytes are responsible for synthesizing thyroglobulin in the thyroid gland.
- The thyroid gland is located in the anterior neck, below the larynx.
- The thyroid gland is approximately 2 inches (5 cm) in length and weighs around 1 ounce (28 grams).
Thyroid Hormone Synthesis and Function
- Thyroglobulin is the main protein involved in thyroid hormone synthesis, providing a storage site for iodine.
- Parafollicular cells (C cells) produce calcitonin, which helps regulate calcium levels in the blood.
- Thyroid hormones T4 and T3 play a crucial role in regulating metabolism, growth, and development.
- T3 is more active than T4, with a shorter half-life.
- Iodine is the major component required for T3 and T4 synthesis.
- The enzyme thyroid peroxidase (TPO) mediates the coupling of DIT and DIT to produce T4.
Regulation of Thyroid Hormone Synthesis and Release
- The conversion of T4 to T3 occurs in peripheral tissues and neural tissues through a process called deiodination.
- The release of T3 and T4 is stimulated by thyroid-stimulating hormone (TSH) from the pituitary gland.
- Pharmaceuticals like perchlorate and thiocyanate compete with iodide for uptake, limiting iodination.
- Methimazole and propylthiouracil inhibit TPO, preventing the coupling of iodotyrosines and reducing thyroid hormone synthesis.
- The sodium-iodide symporter (NIS) is inhibited by perchlorate, reducing the uptake of iodine by thyroid follicular cells.
Thyroid Hormone Function and Levels
- T3 and T4 interact with nuclear receptors in target cells, regulating gene expressions.
- Only a small percentage of T3 (0.3%) and T4 (0.03%) are present in the free form in the blood, with the majority bound to proteins.
- The process of iodination occurs within thyroid cells in the presence of H2O2 and TPO.
This quiz covers the thyroid gland hormones, focusing on the production and secretion of T4 and T3. It discusses the microscopic structure and important functions of the thyroid gland.
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