Q: Which of the following equations represents the conversion of T4 to T3 at target tissues?

$$\mathrm{T}_4 \xrightarrow{\text{deiodinase}} \mathrm{T}_3$$

Question 1

Which of the following best describes the role of thyroglobulin in thyroid hormone synthesis?

Accepted Answer

It is a glycoprotein produced by follicular cells and serves as the precursor for thyroid hormone synthesis within the colloid.

Question 2

A patient presents with low metabolic rate, dry skin, and puffy eyes. Laboratory tests reveal low levels of thyroid hormone and elevated TSH. Which condition is most likely responsible for these findings?

Accepted Answer

Adult hypothyroidism due to iodine deficiency

Question 3

Which of the following steps occurs FIRST in the synthesis of thyroid hormone?

Accepted Answer

Synthesis and transport of thyroglobulin into the follicle lumen

Question 4

Thyroid hormone (TH) increases basal metabolic rate and heat production. This effect is known as:

Accepted Answer

Calorigenic effect

Question 5

Which of the following equations correctly represents the formation of monoiodotyrosine (MIT) during thyroid hormone synthesis?

Accepted Answer

$$\mathrm{Tyrosine} + \mathrm{I}_2 \rightarrow \mathrm{Monoiodotyrosine\ (MIT)}$$

Question 6

Which of the following statements about T3 and T4 is CORRECT?

Accepted Answer

T4 is converted to T3, which is 10 times more active, at target tissues.

Question 7

A patient with Graves' disease is likely to exhibit which of the following symptoms?

Accepted Answer

Elevated metabolic rate, sweating, and exophthalmos

Question 8

Which hormone is produced by parafollicular cells of the thyroid gland, and what is its primary effect at high doses?

Accepted Answer

Calcitonin; inhibits osteoclast activity and promotes calcium incorporation into bone

Question 9

Which of the following best explains why a goiter may develop in response to iodine deficiency?

Accepted Answer

Low iodine decreases TH levels, increasing TSH secretion, which stimulates the thyroid to enlarge and produce more unusable thyroglobulin.

Question 10

Which of the following equations represents the conversion of T4 to T3 at target tissues?

Accepted Answer

$$\mathrm{T}_4 \xrightarrow{	ext{deiodinase}} \mathrm{T}_3$$

Question 11

Which hormone is responsible for stimulating the release of thyroid-stimulating hormone (TSH) from the anterior pituitary?

Accepted Answer

Thyrotropin-releasing hormone (TRH)

Question 12

A newborn presents with poor feeding, weak cry, and prolonged jaundice. Which hormone deficiency is most likely responsible, and what is the long-term treatment?

Accepted Answer

Thyroid hormone deficiency; lifelong TH replacement

Question 13

Which of the following is a permissive effect of thyroid hormone?

Accepted Answer

It increases the number of adrenergic receptors in blood vessels, allowing normal responses to epinephrine and norepinephrine.

Question 14

Which of the following best describes the feedback regulation of thyroid hormone release?

Accepted Answer

Falling TH levels stimulate TSH release, while rising TH levels inhibit TSH release.

Question 15

Which of the following equations represents the formation of T4 from its precursors?

Accepted Answer

$$\mathrm{DIT} + \mathrm{DIT} \rightarrow \mathrm{T}_4$$

Question 16

Which of the following is NOT a function of thyroid hormone?

Accepted Answer

Direct inhibition of parathyroid hormone secretion

Question 17

Which of the following best explains why thyroid hormone must travel in the bloodstream bound to carrier proteins?

Accepted Answer

TH is lipid-soluble and requires carrier proteins for transport in the aqueous environment of blood.

Question 18

Which of the following is a plausible consequence of untreated congenital hypothyroidism?

Accepted Answer

Critical impairment of growth and brain development

Question 19

Which of the following best describes the autoimmune mechanism in Graves' disease?

Accepted Answer

Antibodies mimic TSH, stimulating the thyroid to grow and secrete excess TH.

Thyroid and Parathyroid Glands: Structure, Function, and Homeostatic Imbalances

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