5.3 Thyroid Gland

Question 0

T3 and t4 can regulate levels of TRH and TSH via \_\_\_\_\_\_\_\_ :
A. Positive feed back
B. ultra short loop negative feedback
C.  short loop negative feedback
D.  Long loop negative feedback

Answer 0

D. Long loop negative feedback

Question 1

Inhibits T3 and T4 secretion

Answer 1

Dopamine and somatostatin

Question 2

Steps of thyroid hormone synthesis occur
A. Colloid
B. lumen
C. Apical membrane
D. Basal membrane

Answer 2

A. Colloid - where most thyroid hormones are STORED
B. lumen - steps of thyroid hormone synthesis occur Correct answer
C. Apical membrane - lines the lumen
D. Basal membrane - separates cytoplasm and capillary network

Question 3

Enumerate steps of thyroid hormones synthesis by TSH in correct order

Answer 3

Iodide trapping - organification - retrieval of stored hormone - proteolysis - secretion of t3 and t4 - deiodination

Question 4

Inhibits iodide trapping

Answer 4

Thiocyanate and perchlorate anions

Question 5

Inhibits organification

Answer 5

Propylthyrouracil - reduce thyroid hormone synthesis so it is used for tx of hyperthyroidism

Question 6

Iodinated thyroglobulin is taken back by
A. Endocytosis
B. Exocytosis

Answer 6

A. Endocytosis - Megalin

Question 7

Majority of T3 and T4 are
A. Bound
B. Unbound (free)

Answer 7

A. Bound

Question 8

Which is considered to be active
A. Bound
B. Unbound (free)

Answer 8

B. Unbound (free)
Which is why for lab measurement, free hormone levels are best appreciated since binding hormone levels may produce falsely high it low results

Question 9

Which is more tightly bound to TBG? T3 or t4

Answer 9

T4.
It has higher affinity for TBG, meaning it is more TIGHTLY BOUND and slowly liberated giving them a LONGER half life and LONGER duration of action compared to T3.

Question 10

Arrange the following as to highest affinity by T3 and T4

TBG, Transthyretin, Albumin

Answer 10

TBG > Albumin > Transthyretin

Question 11

Which is considered as the biologically active form of thyroid hormone? T3 or T4? Why?

Answer 11

T3 is the biologically active form since it has 10x greater affinity to THR (Thyroid Hormone Receptor).

NOTE: T4 has longer half life and longer duration of action since it has greater affinity to TBG (Thyroxine Binding Globulin).

Question 12

Considered as the major secretory product of the thyroid gland?
T3 or t4

Answer 12

T4 is considered as the major secretory product of the thyroid gland. Since it is the RESERVOIR of T3, t4 is eventually converted to T3.

Question 13

All are DIRECT effects of thyroid hormones except
A. Increased ventricular contractility
B. Increased G protein stimulatory/ inhibitory ratio
C. Increased CO2 and heat production
D. None of the above. All are direct effects.

Answer 13

C. Increased CO2 and heat production - INDIRECT EFFECT

Question 14

Synergistic effects of thyroid hormones

Answer 14

Heat production
Cardiac output
Lipolysis
Gluconeogenesis

Question 15

Which of the following CANNOT BE MEASURED
a. Free t3
B. Free t4
C. TRH
D. TSH

Answer 15

C. TRH

Question 16

In primary hypothyroidism, levels of TSH is
A. Low
B. Normal
C. High

Answer 16

In hypothyroidism T3 and T4 are LOW, TSH levels are HIGH.

Question 17

Kind of goiter characterized by normal T3 and T4
A. Toxic
B. Non toxic

Answer 17

A. Toxic - increased thyroid hormones

B. Non toxic - normal thyroid hormones Correct answer

Question 18

To treat hypothyroidism, what should be given

T3 or T4?

Answer 18

T4 should be given to treat hypothyroidism since T4 will be converted to T3.

Question 19

Which statement/s is/are true?

1. All hyperthyroid patients will end up having thyrotoxicosis
2. Not all thyrotoxic patients have hyperthyroidism

Answer 19

BOTH ARE TRUE.