Thyroid Gland Flashcards
What does thyroid gland contain
Follicles
What are follicles made up of
Follicular cells surround
Colloid in middle
C-cells
What does colloid contain
Thyroglobulin
2-3 months supply
What do C-cells do
Secrete calcitonin to decrease Ca
What do follicular cells do
Support hormone synthesis and thyroglobulin
Actively concentrate iodide and transport to colloid
What happens to thyroglobulin
Thyroglobulin (rich in tyrosine) package into vesicle with thyroid peroxidase
Stays in colloid
Where do we get tyrosine and iodide
Diet
How does iodide enter follicular cells and what happens
Via Na / I transporte
Na down conc gradient coupled to iodide
Then transported to colloid
What inhibits transport into colloid
Thiocynates in smoke
What happens when iodine enters colloid
Thyroid peroxidase catalyses addition of iodide to tyrosine
Iodide loses electron = iodine (oxidation)
Iodine + tyrosine = MIT
Iodine + MIT = DIT
How are thyroid hormones produced
DIT + MIT = T3 (2 tyrosine + 3 iodine)
DIT + DIT = T4 (2 tyrosine + 4 iodine)
What stimulates release of hormones
TSH
Released into plasma by AP bound to thyroxine binding globulin
What has higher affinity for binding globulin
T4 so released slowly into plasma and longer half life
Most thyroid circulates as T4
What is needed to exert an effect on cells
T3 as receptors inside cell have higher affinity so more active
T4 deiodinates to T3
What is there a continuous secretion of
TRH
What increases secretion
Cold
Exercise
Pregnancy
What is inhibitory
Glucocorticoid - prevent conversion to T3
Somatostatin (GHIH) - inhibits TSH
What do thyroid hormones do
Raise metabolic rate Promote thermogenesis Increase hepatic gluconeogenesis Increase proteolysis Increase lipolysis
How is thyroid critical for growth even though above actions are catabolic
Permissive to GH
Very important for growth in children
What do factors affecting thyroid binding globulin do
Affects thyroid levels as most bound to this
If suspecting thyroid condition what is used as screening test
TSH = screen Individual hormones free T3 and T4 if abnormal Serum thyroidglobulijn Bloofd Ab Imaging
What Ab do you look for and what can they suggest
Anti-thyroid peroxidase (Grave’s + Hashimoto)
Anti-thyroid globulin (Graves + Hashimoto + Cancer)
TSH receptor Ab = Graves
What imaging
USS
Radioisotope
FNA Cytology
Use of USS
Differentiate between nodule / cyst / solid
Guide biopsy
Use of Radioisotope scan
More active cells take up iodine and release gamma If diffuse = Graves If patchy = toxic If focal=. TMN / adenoma If cold = cancer / thyroiditis
Where do most issues come from
Thyroid gland itself
Rare to be due to hypothalamus / pituitary issue
Who would be screened for thyroid
Patients with AF Patients with hyperlpidaemi Patients with DM Patients on amiodarone or lithium Patients with Down's, Turner's or Addison's
What bloods
FBC- normocytic anaemia / neutropenia of Rx
ESR - certain conditions
Ca / LFT may be raised
