GHM L8 Flashcards
sDescribe the anatomy of thyroid gland
Butterfly-shaped, bilateral
2 lobes joined by isthmus
Front of neck, around cartilages of larynx
DIAGRAM
Functional units of thyroid gland - Follicles
Follicles contain follicular cells - produce colloid
Colloid (gelatinous proteins) - made of thyroglobulin (Tg), precursor to thyroid hormones (T3 and T4)
Tg facilitates assembly of thyroid hormones
T4 - Thyroxine
T3 - Triiodothyronine
This happens in thyroid follicular lumen
In thyroglobulin, its the tyrosine molecule that becomes modified, tyrosine is modified into T3 and T4
State the function of C cells in the thyroid gland follicles
C cells secrete CALCITONIN
State the function of follicular cells
Secrete
Tg into colloid with IODINE
Describe the process of TSH stimulation
TSH secreted from anterioir pituitary
Stimulates thyroid gland to secrete T3 and T4 - bloodstream
(Follicular cells reabsorb iodinated Tg, degreade it, releasing T3 and T4)
State the functions of T3 and T4
- Homeostasis
-Cell differentation
-Growth
-Metabolism
Describe the process of iodine trapping
- Iodine from diet (e.g. spinach), travels through bloodstream in form an iodide ion (I-)
- I- accumulate in thyroid via active transport
- Na+ cotransported with iodide from basolateral membrane
- Concentrated in thyroid follicles
What stimulates iodine trapping ?
TSH
What region of the thyroid contains the most iodide ions?
FOLLICLE
State examples of iodine sources
- Cow’s milk
- DIARY PRODUCTS yoghurt etc
- Meat
Describe the function of TPO
TPO: thyroperoxidase
- TPO found outer-membrane of follicular cells
- Catalyses oxidation of I- by H2O2 (adds H2O2) to a reactive iodine intermediate
- This intermediate iodises tyrosine - (iodine added to tyrosine to form T3 and T4, t3 - 3 iodines, t4 - 4 iodines)
This whole process is controlled by TSH (upregulates TPO expression)
Where is thyroglobulin synthesised and secreted?
ER
Secreted in colloid by exocytosis
Describe the proteolysis of Tg with release of T3 and T4
T4 and T4 synthesised + stored within thyroglobulin
Protelysis of modifed thyroglubulin occurs
Modified thyroglublin (Tg) taken back into the folicular cell via endocytosis (phagacytosis), then undergoes proteolytic cleavage (proteolysis) to release + produce the mature T3 and T4 hormones which are then secreted into circulation
State the name of the transporter on the apical side of follilcular cell membrane
PENDRIN (I-/Cl-)
State the name of the transporter on the apical side of follilcular cell membrane
Na+/I- symporter
What stimulates endocytosis of iodinated Tg back into the cell?
Megalin binding to iodinated thyrogloblin
TSH
Which thyroid hormone is more abundant in the body?
T4
Where in the body is T4 produced?
ONLY THYROID Gland