60 Questions
What is the molecular weight of thyroglobulin?
660 kDa
What percentage of thyroglobulin is made up of carbohydrates by weight?
10%
How many tyrosine residues are normally incorporated into thyroid hormones?
4-8
What is the name of the enzyme that mediates the oxidation and reaction of iodide with thyroglobulin?
Thyroid peroxidase
What happens to the colloid when there is a need for thyroid hormone secretion?
It is internalized by the thyrocytes by endocytosis
What is the product formed when two DIT molecules undergo an oxidative condensation?
T4
What is the approximate percentage of iodinated compounds in the normal human thyroid that is T3?
7%
What is the main difference between the two theories of thyroglobulin coupling?
One theory involves intramolecular coupling while the other involves intermolecular coupling.
What is the approximate amount of T4 secreted by the human thyroid per day?
80 μg (103 nmol)
What is the function of free thyroid hormones in plasma?
To inhibit pituitary secretion of TSH.
What is the name of the protein that binds to thyroid hormones in plasma and tissues?
All of the above
What is the approximate normal total plasma T4 level in adults?
8 μg/dL (103 nmol/L)
What is the primary function of thyroid hormones in the body?
To stimulate O2 consumption by most of the cells in the body
What is the consequence of thyroid gland dysfunction during fetal and neonatal life?
Mental retardation and dwarfism
What is the hormone that regulates circulating levels of calcium?
Calcitonin
What is the hormone that stimulates the thyroid gland to produce thyroid hormones?
Thyroid-stimulating hormone (TSH)
What is the consequence of hypothyroidism in adults?
Mental and physical slowing and poor resistance to cold
What is the negative feedback control mechanism that regulates thyroid hormone production?
High circulating levels of thyroid hormones acting on the hypothalamus and the anterior pituitary
Which protein has the largest capacity to bind T4?
Albumin
What percentage of circulating T4 is normally converted to T3 in adult humans?
45%
What is the half-life of transthyretin?
2 days
What is the role of deiodination reactions in the liver, kidneys, and other tissues?
To catabolize and provide a local supply of T3
What is the primary mediator of the physiologic effects of thyroid secretion?
T3
What inhibits TSH secretion in a negative feedback manner?
Circulating free T4 and T3
What happens to iodide binding after the injection of TSH?
It increases within minutes
What is the effect of thyroid hormones on oxygen consumption?
It stimulates oxygen consumption
What is the result of prolonged TSH stimulation on the thyroid gland?
The gland becomes detectably enlarged
How do thyroid hormones regulate lipid metabolism?
By regulating lipid metabolism
What happens to the expression of genes when thyroid hormones bind to TR in the nuclei?
Gene expression is increased
What is the effect of thyroid hormones on the absorption of carbohydrates from the intestine?
They increase the absorption of carbohydrates
What is the approximate distribution of DIT in the normal human thyroid?
33%
Which of the following proteins has the smallest capacity to bind T4?
Albumin
What is the product formed when MIT condenses with DIT?
T3
What is the primary mechanism by which TBG binds to T4?
High-affinity binding
What is the approximate amount of T3 secreted by the human thyroid per day?
4 μg (7 nmol)
What percentage of circulating T4 is converted to RT3?
45%
What is the primary function of free thyroid hormones in plasma?
To inhibit pituitary secretion of TSH
Which hormone inhibits TSH secretion in a negative feedback manner?
Free T4 and T3
What is the result of the coupling of two DIT molecules?
Formation of T4
What is the main purpose of deiodination reactions in the liver, kidneys, and other tissues?
To catabolize thyroid hormones and provide a local supply of T3
What is the half-life of albumin?
13 days
What is the approximate weight percentage of carbohydrate in thyroglobulin?
10%
What is the percentage of circulating T3 that is secreted by the thyroid?
13%
How many tyrosine residues are normally incorporated into thyroid hormones?
4–8
What is the function of thyroid peroxidase in thyroid hormone synthesis?
To generate reactive iodine species that can attack thyroglobulin
What happens to the colloid when there is a need for thyroid hormone secretion?
It is internalized by the thyrocytes and directed toward lysosomal degradation
What is the product formed when two DIT molecules undergo an oxidative condensation?
T4
What is the molecular weight of thyroglobulin?
660 kDa
What is the primary function of thyroid hormones in maintaining optimal metabolism?
Influencing mentation and body mass
What is the consequence of thyroid gland dysfunction during fetal and neonatal life?
Mental retardation and dwarfism
What stimulates the thyroid gland to produce thyroid hormones?
Thyroid-stimulating hormone (TSH)
What is the effect of hypothyroidism in adults?
Mental slowing and physical slowing
What is the function of calcitonin?
Regulating circulating levels of calcium
What controls the secretion of thyroid-stimulating hormone (TSH)?
Thyroid hormones
What is the effect of TSH on thyroid function?
It increases iodide binding, synthesis of T3, T4, and iodotyrosines, and secretion of thyroglobulin into the colloid
What is the effect of thyroid hormones on lipid metabolism?
They increase lipid metabolism
What is the mechanism of action of thyroid hormones?
They enter cells and bind to receptors in the nuclei
What is the effect of thyroid hormones on oxygen consumption?
They increase oxygen consumption
What is the consequence of prolonged TSH stimulation on the thyroid gland?
The thyroid gland becomes detectably enlarged
What is the effect of thyroid hormones on the dissociation of oxygen from hemoglobin?
They increase the dissociation of oxygen from hemoglobin
Learn about the thyroid gland, its functions, and how it regulates metabolism, lipid and carbohydrate metabolism, and body mass. Explore the importance of thyroid hormones and their role in the body.
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