7-Thyroid gland Flashcards
What does it control
Metabolism and body weight, development and growth
Structure
Butterfly like
Under Adam’s apple
Across trachea
Below larynx
Only 20-30% have pyramidal lobe
Thyroid follicle is one cells thick
Parafollicular C cells secrete calcitonin
Thyroglobulin-filled follicular lumen (colloid)
PT gland found under
Thyroid follicles are dynamic
Thyroglobulin contains enough iodide to supply thyroid hormones for 90 days
Can change from columnar epithelial shape
Hormones
T3 and T4
T3 more active
Diurnal release of TRH
Stress causes a decrease in release
TSH is 15% carbohydrate
alpha unit identical to TSH, LH, FSH and hCG
Beta units have glycoproteins attached
Low T3
Increase in thyroid production
Pituitary thyrotropes increase synthesis of TSH
High TSH activates the thyroid gland
leads to enlargement
Pull in thryoglobulin from lumen so cells change shape to columnar cells
TSH causes production of pseudopodia on apical cell surface
pull in as much thyroglobulin as possible
Increase in blood supply
T3 production
High T3
Thyrotropic activity decreased
Low TSH so thyroid shrinkage
Thyroglobulin accumulates
Cells back to cuboidal shape
T3 and T4 synthesis
Sodium Iodide Transporter NIS
NaK pump ensures Na moves in down gradient
Takes I against its gradient
Pendrin to follicular lumen
Constant secretion of thyroglobulin from ER
Thyroid peroxidase (TPO) situated on apical membrane
Responsible for iodination of thyroglobulin
Adds iodine to tyrosine in 2 positions
2 added if lots of iodine
T3 and T4
T3 has on tyrosine with one iodine and one with 2
T4 has 2 sets of 2
Not active yet
Take off thyroglobulin
90% T4 10 % T3
Thyroglobulin endocytosed back into epithelia cells and undergoes proteolysis
Any tyrosines not iodified are recycled
TSH binding
Binds GPCR Gs
Adenylate cyclase, cAMP and PKA
Increased iodine uptake
Increased thyroglobulin synthesis
Increased iodination by TPO
Differentiation of apical surface pseudopodia
Goitre
Severe iodine deficiency
Hypothyroidism
Weight gain
Can also be due to gland being unresponsive to TSH
Eating goitrogens inhibits TPO (cabbage, almonds)
Contain thiocynate
Latrogenic (surgery or radiotherapy)
Autoimmune destruction of the thyroid gland
Hyperthyroidism
Pituitary tumour causes excess TSH
or receptor abnormality
gives signal even when not bound
or autoimmune stimulation of receptor by antibodies (Graves disease)
Antibodies attack fatty tissue at back of the eye
Eyes protrude
Can have thyroid gland removed
Makes person hypothyroid
Use radioactive iodide treatment
Accumulation of radioactivity damages cells and stops hormone secretion
Weight loss
