Physiology Thyroid Book Flashcards
How is iodide converted to iodine
Thyroid peroxidase
Process of making thyroid hormones
Iodide is absorbed from plasma by pump
Converted to iodine by TPO
Secreted into colloid where it is added to tyrosine by enzyme iodinate
These bind to protein- thyroglobulin
TSH causes them to be released back into thyroid follicular cell and released by proteolysis
Composition of thyroid hormones in blood
99% bound to TBP and albumin
T4 higher conc
Effects of thyroid hormones on body
Increase isotropic effect on heart
Increase protein breakdown
Increase carb absorption
Lipolysis
3 hormones produced by thyroid
Tetra- principle hormone
Tri- shorter duration but more potent
Calcitonin- parafollicullar C cells
Where does PTH act
Bone- resorption
DCT- reabsorption of Ca
PCT- excretion of PO4
Vit D formation
Overall net effect of hyperparathyroidism on Ca exrection
Net excreten despite absorption in DCT due to overwhelmed
Effect of thyroid hormone on PVR
Decrease due to raise in temp
Effect of thyroid hormones on cholesterol
Increase LDL receptors- increased removal of cholesterol from circulation
Where are thyroid receptors found
Intranuclear hormones
Which bind to DNA via zinc fingers
Types of thyroid receptors
TRB2- brain
TRa2, TRB1- widely distributed in Body
T3 unable to bind to a2
Factors inhibiting osteoclasts
Calcitonin, oestrogen, PGE2
What inhibits osteoblasts
Corticosteroids
How PTH causes action in cells
Binds to surface receptors
Increase cAMP
What cell is PTH released from
Chief cells