Hormonal Regulation of Calcium and Phosphate

What does arachidonic acid pathway do to parathyroid hormone?

How does it do this (explain pathway)

• inhibits secretion of PTH

• calcium binds to receptor

• activates signalling pathway = arachidonic acid

• arachidonic acid inhibits PTH secretion

• reduced calcium levels inhibit this signalling pathway, allowing PTH secretion

What are the main targets for PTH?

• bone and kidney

What do osteoblasts do?

• mediate bone formation

What do osteoclasts do?

• mediate bone resorption

What is osteoprotegerin?

• a decoy receptor that RANKL binds to protect bone (regulates RANKL and RANK so bone not always being broken down)

What happens when PTH gets sent to osteoblasts?

• increased production of RANKL, decreased production of osteoprotegerin

What does RANK and RANKL do?

• RANKL binds to RANK on osteoclast precursor (immature osteoclast)

• signals osteoclast differentiation (cells mature) and activation (start breaking down bone)

• bone breakdown causes calcium and phosphate to enter bloodstream

What happens when bone breaks down?

• calcium and phosphate level in bloodstream increases

What happens to calcium and phosphate in the kidneys?

• increased calcium reabsorption, decreased phosphate reabsorption (excreted in urine)

What does 1,25-dihydroxyvitamin D do (explain in detail)?

• increases calcium and phosphate absorption from the intestines

• vitamin D enters cell

• activates receptor in nucleus

• activates gene expression of calcium transporter proteins

• leads to increased absorption of calcium

Does 1,25-dihydroxyvitamin D have an affect on PTH?

• yes (not on purpose), as vit D causes increase of calcium but PTH only secreted when calcium levels low, so RANK and RANKL lowkey get inhibited

What is calcitonin?

• a peptide hormone secreted by C cells in thyroid gland

What does calcitonin do?

• lowers calcium and phosphate levels by inhibiting activity of osteoclasts