Thyroid Gland

Question 1

Parafollicular cells of thyroid gland secrete

Answer 1

Calcitonin

Question 2

Thyroid hormone synthesized by- and what is colloid

Answer 2

Follicular epithelial cells

Colloid is newly synthesized thyroid hormones attached to thyroglobulin

Question 3

Conversion of T4 to T3

Answer 3

Deodinase 1 or 2 converts T4 to active T3

Deodinase 3 converts T4 to inactive T3

Question 4

Synthesis of thyroid hormones

Answer 4

TG is transported into colloid lumen inside follicular cell
Iodide is cotransported into follicular cells with Na, and is then transported into colloid lumen and converted to I2 iodine
Peroxidase converts thyroglobulin + iodine to T3/T4
After stimulation, T3/T4-TG complex is transported into follicular cell, and T3/T4 are then released from TG and transported out of cell

Question 5

Intrathyroidal deoidinase

Answer 5

Recycles Iodide and TG inside follicular cells after T3/T4 is released

Question 6

Deodinase deficiency

Answer 6

This will mimic and iodine deficiency

When iodide is restricted, formation of T3 is favored

Question 7

Pendrin function/mutation

Answer 7

Chloride/iodide pump that pumps iodide into colloid lumen
If this gene is defective, it will cause hypothyroidism with goiter
Can also affect cochlea causing sensorineural hearing loss

Question 8

Perchlorate and thiocynate

Answer 8

Compete with the binding of iodide to Na/I transporter so it cannot get into cell
Will impair thyroid hormone synthesis

Question 9

Peroxidase defective/PTU/Wolf-Chaikoff effect

Answer 9

Defective thyroid hormone synthesis, hypothyroidism
Peroxidase is disrupted by PTU
This will cause Wolf-Chaikoff effect
PTU can be treatment for hyperthyroidism

Question 10

Graves disease vs normal hyperthyroidism in radioactive iodine test

Answer 10

Graves disease has faster uptake of radioactive iodine than someone with hyperthyroidism

Question 11

T3/T4 binding proteins and half life

Answer 11

T4- 6 day half life
T3- 1 day half life
Thyroxine binding globulin TBG- higher affinity for T4
Transthyretin TTR - brain
Albumin

Question 12

High/low TBG levels

Answer 12

High levels of TBG will mean lower levels of T3 resin uptake and higher levels of T4
Low TBG means lower T4 and higher T3 resin uptake

Question 13

Hepatic failure and pregnancy TBG/T3 resin uptake levels

Answer 13

Hepatic failure- Low TBG, High T3

Pregnancy- High TBG, Low T3

Question 14

TSH regulated by

Answer 14

TRH and free T3

TSH secretion occurs at a steady rate

Question 15

What stimulates thyroid hormone secretion besides TSH

Answer 15

Thyroid stimulating Igs
Increased TBG levels like during pregnancy
(decreased TBG such as during liver failure will inhibit)

Question 16

TSH stimulates what major protein in many tissues

Answer 16

Na/K ATPase

Question 17

Cadiovascular effects of thyroid hormone

Answer 17

Decreased diastolic pressure, may trigger Renin-AG-Ald system
Synthesis of B1 adrenergic receptors
Decreased peripheral vascular resistance
Increased cardiac output

Question 18

Deficient thyroid hormone during pregnancy/prenatal period

Answer 18

Abnormal development of synapses
Decreased myelination and branching of dendrites
Cretinism (congenital hypothyroidism)

Question 19

Sheehan syndrome

Answer 19

Postpartum hypopituitarism due to necrosis of the pituitary gland
Most patients present with difficulties in lactation
Amenorrhea
Some patients have hypothyroidism