Thyroid Gland

Question 1

What does thyroid gland contain

Answer 1

Follicles

Question 2

What are follicles made up of

Answer 2

Follicular cells surround
Colloid in middle
C-cells

Question 3

What does colloid contain

Answer 3

Thyroglobulin

2-3 months supply

Question 4

What do C-cells do

Answer 4

Secrete calcitonin to decrease Ca

Question 5

What do follicular cells do

Answer 5

Support hormone synthesis and thyroglobulin

Actively concentrate iodide and transport to colloid

Question 6

What happens to thyroglobulin

Answer 6

Thyroglobulin (rich in tyrosine) package into vesicle with thyroid peroxidase
Stays in colloid

Question 7

Where do we get tyrosine and iodide

Answer 7

Diet

Question 8

How does iodide enter follicular cells and what happens

Answer 8

Via Na / I transporte
Na down conc gradient coupled to iodide
Then transported to colloid

Question 9

What inhibits transport into colloid

Answer 9

Thiocynates in smoke

Question 10

What happens when iodine enters colloid

Answer 10

Thyroid peroxidase catalyses addition of iodide to tyrosine
Iodide loses electron = iodine (oxidation)
Iodine + tyrosine = MIT
Iodine + MIT = DIT

Question 11

How are thyroid hormones produced

Answer 11

DIT + MIT = T3 (2 tyrosine + 3 iodine)

DIT + DIT = T4 (2 tyrosine + 4 iodine)

Question 12

What stimulates release of hormones

Answer 12

TSH

Released into plasma by AP bound to thyroxine binding globulin

Question 13

What has higher affinity for binding globulin

Answer 13

T4 so released slowly into plasma and longer half life

Most thyroid circulates as T4

Question 14

What is needed to exert an effect on cells

Answer 14

T3 as receptors inside cell have higher affinity so more active
T4 deiodinates to T3

Question 15

What is there a continuous secretion of

Answer 15

TRH

Question 16

What increases secretion

Answer 16

Cold
Exercise
Pregnancy

Question 17

What is inhibitory

Answer 17

Glucocorticoid - prevent conversion to T3

Somatostatin (GHIH) - inhibits TSH

Question 18

What do thyroid hormones do

Answer 18

Raise metabolic rate
Promote thermogenesis
Increase hepatic gluconeogenesis
Increase proteolysis
Increase lipolysis

Question 19

How is thyroid critical for growth even though above actions are catabolic

Answer 19

Permissive to GH

Very important for growth in children

Question 20

What do factors affecting thyroid binding globulin do

Answer 20

Affects thyroid levels as most bound to this

Question 21

If suspecting thyroid condition what is used as screening test

Answer 21

TSH = screen
Individual hormones free T3 and T4 if abnormal 
Serum thyroidglobulijn 
Bloofd 
Ab
Imaging

Question 22

What Ab do you look for and what can they suggest

Answer 22

Anti-thyroid peroxidase (Grave’s + Hashimoto)
Anti-thyroid globulin (Graves + Hashimoto + Cancer)
TSH receptor Ab = Graves

Question 23

What imaging

Answer 23

USS
Radioisotope
FNA Cytology

Question 24

Use of USS

Answer 24

Differentiate between nodule / cyst / solid

Guide biopsy

Question 25

Use of Radioisotope scan

Answer 25

More active cells take up iodine and release gamma
If diffuse = Graves
If patchy = toxic 
If focal=. TMN / adenoma
If cold = cancer / thyroiditis

Question 26

Where do most issues come from

Answer 26

Thyroid gland itself

Rare to be due to hypothalamus / pituitary issue

Question 27

Who would be screened for thyroid

Answer 27

Patients with AF
Patients with hyperlpidaemi
Patients with DM
Patients on amiodarone or lithium 
Patients with Down's, Turner's or Addison's

Question 28

What bloods

Answer 28

FBC- normocytic anaemia / neutropenia of Rx
ESR - certain conditions
Ca / LFT may be raised