Clinical Pathology Presentation

Question 1

What is the primary trace element used in making thyroid hormones

Answer 1

Iodine

Question 2

What medication is iodine found in

Answer 2

Amiodarone

Used to treat certain iodine conditions

Question 3

If iodine intake drops below ….. μg daily, the thyroid gland is unable to manufacture adequate amounts of thyroid hormone and thyroid hormone deficiency—hypothyroidism—results

Answer 3

50

Question 4

What is the major component of colloid

Answer 4

Thyroglobulin

Question 5

Thyroglobulin is rich in what amino acid

Answer 5

Tyrosine

Question 6

On the outer side of the follicle, iodine is actively transported into the thyroid cell by the ………. located on the basement membrane.

Answer 6

Na+ /I - symporter

Question 7

Concentrated iodide is oxidized and bound with tyrosyl residues on thyroglobulin. This results in production of monoiodothyronine (MIT) and diiodothyronine (DIT)
What enzyme catalyses this reaction

Answer 7

Thyroxine peroxidase (TPO)

This same enzyme also aids in the coupling of two tyrosyl residues to form triiodothyronine (T3 ) (one MIT residue + one DIT residue) or thyroxine (T4 ) (two DIT residues)

Question 8

Which hormone signals the follicular cell to ingest a microscopic droplet of colloid by endocytosis. Inside the follicular cell, these droplets are digested by intracellular lysosomes into T4 , T3 , and other products. T4 and T3 are then secreted by the thyroid cell into the circulation

Answer 8

TSH

Question 9

What process takes T 4(5′-deiodination) and leads to the production of 3,5,3′-triiodothyronine (T3 ). T3 is three to eight times more metabolically active than T 4 and often considered to be the active form of thyroid hormone, while T 4 is the “pre” hormone (with thyroglobulin being the “prohormone”)

Answer 9

Outer ring deiodination

Question 10

How is inactive rT3 produced

Answer 10

Inner ring deiodination of T4 results in the production of metabolically inactive rT3

Question 11

What are the three forms of iodothyronine 5′-deiodinase

Answer 11

Type 1 iodothyronine 5′-deiodinase, the most abundant form, is found mostly in the liver and kidney and is responsible for the largest contribution to the circulating T3 pool

Type 2 iodothyronine 5′-deiodinase is found in the brain and pituitary gland. Its function is to maintain constant levels of T 3 in the central nervous system. Its activity is decreased when levels of circulating T4 are high and increased when levels are low

Question 12

Mention some drugs that can slow for type 1 deiodinase and are used from the treatment of severe hyperthyroidism

Answer 12

Propylthiouracil [PTU]
Glucocorticoids
Propranolol