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
Biochemistry of primary HPTH
High PTH
High Ca
Low PO4
Normal VitD
Raised urinary Ca
Biochemistry of secondary HPTH
Low Ca
High PTH
High PO4
Causes- renal failure and vid D def
Renal failure- high phosphate which inhibits Vid d synthesis
Or Failure of 1a production
Biochemistry of tertiary HPTH
High Ca
High PTH
High PO3- due to original renal failure
Developed after longstanding secondary HPTH
Effects of calcitonin
Decrease bone resorption
Increase renal exretion of Ca and PO4
Factors increasing calcitonin secretion
B adrenergic agonists
Glucagon
Gastrin
CCK
Oestrogens
High Ca
Sx of hypocalcaemia
Tetany
Numbness
Prolonged QT
Chvostek- contraction of facial muscle when tapping on angle of jaw
Trousseau- wrist flexion and fingers drawn together in extension when BP cuff inflated
Why does low Ca cause tetany
Low Ca increases neuronal permeability
Hypercalcaemia sx
Constipation
Increases uriantion
Bone pain
Abdo pain
Mental health
Renal stones
Causes of high Ca
Primary HPTH
Malignancy- breast, lung, SCC
Multiple myeloma
Renal failure
Thiazide use
Effect of surgery or trauma on thyroid hormones
Decrease for a few days
Sick euthyroid syndrome biochemistry
Low T3
Normal T4 and TSH- may be high
Medications that effect levothyroixine absorption
Iron
Ca
PPI
Statins
Oestrogens
