Thyroid Function Test

Question 1

The thyroid gland produces two related hormones

Answer 1

thyroxine (T4) and

triiodothyronine (T3)

Question 2

Acting through thyroid hormone

receptors α and β, these hormones play a critical role in

Answer 2

Cell differentiation
during development and help maintain thermogenic
and metabolic homeostasis in the adult

Question 3

Thyroid in Greek

Answer 3

(Greek thyreos, shield, plus eidos, form)

Question 4

The normal thyroid size

Answer 4

12–20 g in size, highly vascular, and soft in consistency.

Question 5

Structure traverse the lateral
borders of the thyroid gland and must be identified
during thyroid surgery to avoid injury and vocal cord
paralysis

Answer 5

The recurrent laryngeal nerves

Question 6

The thyroid gland develops from

Answer 6

the floor of the primitive pharynx
during the third week of gestation. The developing gland migrates
along the thyroglossal duct to reach its final location in the neck.

Question 7

Thyroid hormone

synthesis normally begins

Answer 7

11 weeks gestation

Question 8

Neural crest derivatives from the ultimobranchial body give rise to

Answer 8

Thyroid medullary C cells that produce calcitonin

Question 9

The C cells are interspersed throughout the thyroid gland, although their density is greatest in

Answer 9

the juncture of the upper one-third

and lower two-thirds of the gland.

Question 10

Plays a minimal role in

calcium homeostasis in humans

Answer 10

Calcitonin

Question 11

C-cells are important because

of their involvement in

Answer 11

Medullary thyroid cancer

Question 12

Thyroid gland development is orchestrated by the coordinated expression of several developmental transcription factors.

Answer 12

(TTF)-1, TTF-2, and paired homeobox-8 (PAX-8)

Question 13

The thyroid gland consists of numerous spherical follicles composed
of

Answer 13

thyroid follicular cells that surround secreted colloid, a proteinaceous fluid containing large amounts of thyroglobulin, the protein
precursor of thyroid hormones

Question 14

The thyroid follicular

cells are polarized

Answer 14

basolateral surface is apposed to the bloodstream

and an apical surface faces the follicular lumen.

Question 15

Increased demand for thyroid hormone is regulated by

Answer 15

thyroid-stimulating hormone (TSH), which binds to its receptor on the basolateral surface of the follicular cells

Question 16

TSH secreted by

Answer 16

thyrotrope cells of the anterior pituitary

Question 17

Deiodination leads to production

Answer 17

potent hormone triiodothyronine

(T3) or the inactive hormone reverse T3

Question 18

TSH is hormone composed of _subunits;

Answer 18

subunit is common to the other glycoprotein hormones (luteinizing hormone, folliclestimulating
hormone, human chorionic gonadotropin [hCG]), whereas the TSH β subunit is unique to TSH

Question 19

The extent and nature of carbohydrate

modification are modulated

Answer 19

by thyrotropin-releasing hormone

(TRH) stimulation and influence the biologic activity of the hormone.

Question 20

Thyroid hormones act via negative feedback predominantly through

Answer 20

thyroid hormone receptor β2 (TRβ2) to inhibit TRH and TSH production

Question 21

The “set-point” in thyroid axis is established by

Answer 21

TSH

Question 22

Peak TSH secretion occurs

Answer 22

15 min after administration of exogenous

TRH

Question 23

3 substance suppress TSH

Answer 23

Dopamine, glucocorticoids, and somatostatin

Question 24

Thyroid hormones are derived from

Answer 24

Tg

Question 25

Is a critical first step

in thyroid hormone synthesis

Answer 25

Iodide uptake

Question 26

characterized by mental and growth
retardation and occurs when children who live in iodine-deficient
regions are not treated with iodine or thyroid hormone to restore
normal thyroid hormone levels during early life. These children are
often born to mothers with iodine deficiency, and it is likely that
maternal thyroid hormone deficiency worsens the condition

Answer 26

Cretinism

Question 27

Concomitant deficiency may also contribute to the neurologic manifestations of cretinism

Answer 27

selenium

Question 28

Iodine deficiency

Answer 28

remains the most common cause of preventable mental deficiency

Question 29

The recommended average

daily intake of iodine

Answer 29

150–250 μg/d for adults, 90–120 μg/d for children,

and 250 μg/d for pregnant and lactating women. Urinary iodine is >10 μg/dL in iodine-sufficient populations

Question 30

TSH regulates thyroid gland function through the

Answer 30

TSHR, a seven-transmembrane G protein–coupled receptor (GPCR).

Question 31

Serum half-life of Thyroid hormones

Answer 31

T4 7 days

T3 2 days

Question 32

Fraction directly from the thyroid

Answer 32

T4 100%

T3 20%

Question 33

% Protein-bound

Answer 33

T4 99.98%

T3 99.7%

Question 34

Which is located primarily in thyroid, liver, and kidneys,

has a relatively low affinity for T4

Answer 34

Type I deiodinase

Question 35

has a higher affinity
for T4 and is found primarily in the pituitary gland, brain, brown fat,
and thyroid gland.

Answer 35

Type II deiodinase

Question 36

inactivates T4 and T3 and is the most important

source of reverse T3 (rT3), including in the sick euthyroid syndrome

Answer 36

Type III deiodinase

Question 37

In the sick euthyroid syndrome, especially with

hypoperfusion, inactivated in muscle and liver

Answer 37

type III deiodinase