62 Questions
What is the primary function of the thyroid gland?
Secrete thyroid hormones to maintain metabolism
What are the consequences of hypothyroidism in adults?
Body wasting and poor resistance to cold
What hormone controls the function of the thyroid gland?
Thyroid-stimulating hormone (TSH)
What is a consequence of excess thyroid secretion?
Tremor
Which protein binds most of the circulating T4?
Thyroxine-binding globulin (TBG)
What is the half-life of transthyretin?
2 days
How much of the circulating T3 is formed by deiodination of T4?
87%
What serves to catabolize the thyroid hormones T4 and T3?
Liver, kidneys, and many other tissues
What is the primary regulator of thyroid function?
Pituitary TSH
Which hormone inhibits TSH secretion in a negative feedback manner?
Free T4
What happens to the thyroid gland with prolonged TSH stimulation?
Cells hypertrophy
What is the term used to describe enlargement of the thyroid gland?
Goiter
What is the main function of the thyroid gland?
To secrete calcitonin
How is thyroglobulin secreted into the colloid?
By exocytosis of granules
What enzyme mediates the oxidation and reaction of iodide with thyroglobulin?
Thyroid peroxidase
How does the secretion of thyroid hormone get controlled?
By negative feedback control from high thyroid hormone levels
Which protein has the smallest capacity to bind T4 in plasma?
Thyroxine-binding globulin (TBG)
What is the approximate daily secretion of T3 by the human thyroid in nmol?
7
In plasma, what is the approximate level of total T4 in adults in nmol/L?
103
Which type of thyroid hormones are considered physiologically active in plasma?
Free forms
What is the mechanism of action of propylthiouracil and methimazole in treating hyperthyroidism?
Inhibit the iodination of tyrosine by competing for iodine
Which compound is responsible for reducing the conversion of T4 to T3 in extrathyroidal tissues?
Propylthiouracil
What is the treatment approach for severe cases of hyperthyroidism that leads to partial destruction of the thyroid gland?
Infusion of radioactive iodine
Why does Hashimoto thyroiditis initially present with excess thyroid hormone secretion and thyrotoxicosis?
Inflammation causes excess thyroid hormone secretion
What is the main mechanism by which thyroid hormones exert their effects?
Entering cells and binding to nuclear receptors
What are the primary physiological effects of thyroid hormones in the body?
Increasing metabolic rate and cardiac function
What are the consequences of hypothyroidism in neonatal life?
Mental retardation and dwarfism
What effect does an increased proportion of α-myosin heavy chain have on the heart?
Increased ATPase activity
Which tissue experiences a catabolic effect due to stimulated lipolysis?
Adipose tissue
What is the metabolic effect on the gut as a result of thyroid hormone action?
Increased rate of carbohydrate absorption
Which tissue benefits from the promotion of normal growth and skeletal development by thyroid hormones?
Bone
What is the primary hormone responsible for regulating thyroid function?
TSH
What is the consequence of prolonged TSH stimulation on the thyroid gland?
Thyroid atrophy
Which hormone inhibits TSH secretion as part of a negative feedback mechanism?
T4
What is the syndrome of adult hypothyroidism generally called?
Myxedema
Which protein has the smallest capacity to bind T4 in plasma?
TBG
What is the approximate daily secretion of RT3 by the human thyroid in nmol?
3.5 nmol
Which compound is responsible for reducing the conversion of T4 to T3 in extrathyroidal tissues?
RT3
What is the normal total plasma T3 level in adults approximately?
0.15 μg/dL (2.3 nmol/L)
What is the recommended treatment approach for addressing iodide deficiency in developed countries?
Adding iodized salt to the diet
In cases of congenital hypothyroidism, what synthetic form of the thyroid hormone is typically given?
Levothyroxine
What are the characteristic symptoms of hyperthyroidism?
Nervousness and weight loss
What is the primary factor determining the severity of mental deficiency in cases of iodine deficiency during pregnancy?
The mother's thyroid condition
What effect does an increased rate of carbohydrate absorption in the gut as a result of thyroid hormone action have on metabolism?
Enhancing calorigenesis
How do thyroid hormones primarily influence the heart's function?
By enhancing responses to circulating catecholamines
What is the main regulatory hormone responsible for stimulating the synthesis and secretion of thyroid hormones?
Thyroid-stimulating hormone (TSH)
Which tissue is negatively affected by an increased metabolic rate due to stimulated oxygen consumption as a result of thyroid hormone action?
Adipose tissue
Thyroid peroxidase is not involved in the coupling as well as iodination of thyroid hormones.
False
In the normal human thyroid, the average distribution of iodinated compounds is 3% MIT, 33% DIT, 35% T4, and 7% T3.
True
RT3 is formed by condensation of two DIT molecules.
False
T3 is formed by condensation of MIT with DIT.
True
Hypothyroidism can only be caused by diseases of the thyroid gland.
False
When dietary iodine intake is inadequate, the thyroid hypertrophies.
True
Drugs can never inhibit thyroid function.
False
Iodide itself never inhibits thyroid function.
False
Graves disease is the most common cause of hypothyroidism.
False
Antibodies to the TSH receptor stimulate the receptor in Graves disease.
True
Plasma TSH levels are typically high in patients with Graves disease.
False
Exophthalmos is a common symptom of Graves disease.
True
Thyroid hormones only exert their effects by binding to thyroid receptors on the cell membrane.
False
Hypothyroidism in neonatal life can lead to mental retardation and dwarfism.
True
Overactivity of the thyroid gland caused by autoantibodies may result in body wasting, nervousness, and bradycardia.
False
Learn about the different proteins that bind to T4 (Thyroxine) in the plasma and their affinities. Understand the role of Thyroxine-binding globulin (TBG), Transthyretin (TBPA), and Albumin in binding to T4 under physiologic conditions.
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