Parathyroid And Thyroid Gland Flashcards
What is a parathyroid adenoma
Mass of chief cells distrusting Ca metabolism
What do chief and oxyphil cells:
- do and how
- look like
- Chief cells secrete PTH allowed by tons of Golgi apparatus and ER
They look smaller but more abundant with a paler stain - oxyphil cells increase with age- cause unknown
They are larger but less abundant with a darker stain
Where does PTH synthesis begin
How much aa does it start out with
Where does it go and what happens to it
What element is a co factor
- starts RER where pre- pro- PTH is produced which is 115 aa long (biologically active sequence, signal and pro sequence)
- the signal is cleaned within ER lumen leaving pro- PTH
- transferred to Golgi appertains where pro sequenced is cleaned to make PTH
- Mg is a co factor
Explain the humural synthesis that allows PTH to increase Ca
Increases RANKL production on osteoblasts which induce cytokines to act on osteoclasts which increase bone reabsorption and increase Ca resorption in the loop of henle and DCT and increase phosphate excretion in the PCT which prevents kidney stones
What does PTH do when it stimulates 1- alpha- hydroxylase
- increases calcitriol which induces calbindin D- 28K (Ca binding protein) in the intestine which is vital D depended and is how 1, 25- dihydroxycholecalcifiol increases Ca and phosphate absorption
- Vit increases mineralisation of bone as well as
How is vit d (25 hydroxycholecalcifiol) formed and what is it bound to in plasma and how does it become 1,25 dihydroxycholecalcifiol
- formed from cholecalciferol (D3)n in the liver
- bound to alpha globulin in plasma
- 1 alpha hydroxylase hydroxylases it
What is the negative feedback of Ca via chief cells and vit D
Chief cells have unique G protein CaR on surface which Ca binds ot when in excess which leads to phosphinositide production which prevents PTH secretion
- vit D/ calcitriol acts on parathyroid gland to decrease PTH gene transcription so less PTH synthesised
What is the action of calcitonin and is it short or long term
- only long term
- inhibits osteoclast bone resorption
What is the thyroid gland supplied and drained by
- supplied by superior thyroid aa from ECA and inferior thyroid aa from SCA and thyrocervical aa
- drained via superior and middle vv from IJV and inferior thyroid vv from brachiocephalic trunk
Where is calcitonin that decreases blood Ca secreted and where are they
Spaces between colloid filled follicles have parafollicular cells which secrete calcitonin which inhibits osteoclasts
What does follicle cells look like in hyper/ hypothyroidism
- hyper look columnar with little colloid
- hypo look flattened with large lumen of colloid
What is the function of thyroid gland with examples
Via what hormones acting on what receptors on target tissues
How is the desired effect achieved
- metabolic regulators, gluconeogenesis, protein synthesis, lipogenesis
- via T3 and T4 acting on nuclear receptors
- achieved by increasing size and number of mitochondria within cells, increasing Na-K pump activity and presence on beta receptors in cardiac muscle
How does iodide get into follicular cells and then to colloid and what can act as competitive inhibitors
- active transport via Na-I symportot thats more active with lower Iodide levels and is maintained via Na-KATPase
- then to colloid via pendrin
- comp inhibit is thiocyanase and penchorase
What os thyroglobulin, where is it formed and where does it go and what is it stored as
- large protein rich in tyrosine and formed in follicular ribosomes and placed in secretory vesicles
- exocytosis of thyroglobulin into follicle lumen where it is stored as colloid which acts as the scaffold of hormone synthesis
What happens to thyroglobulin as colloid and what enzyme helps and what happens to the products
What inhibits
- Iodination and oxidation, making it reaction by TPO or thyroid peroxide into MIT (I at position 3) and DIT (I at position 3 and 5) mono/ dityrosine
- MIT and DIT make T3 and DIT and DIT make T4
- inhibited by I- (wolff chaikoff)
