Calcium Metabolism Flashcards
Explain the significance of maintaining serum calcium levels within set limits
- Maintains bones teeth
- Reg HR
- Eases insomnia
- Regulates passage of nutrients in/out of the cells walls
- Lowers BP
- Reduces blood cholesterol levels
- Intracellular signalling pathways
Describe the hormonal regulation of serum calcium by PTH
PTH = active when serum [Ca2+] low
1) Stim osteoclast activity = release of Pi and Ca
2) Stim Ca reabsorption in kidney and excretion of phosphate (stops crystal formation)
3) Stim conversion of Vit D to active form = increase Ca absorption
Describe the hormonal regulation of serum calcium by calcitriol (active vit D)
High Ca = lowered calcitriol = less Ca2+ taken from gut
Describe the hormonal regulation of serum calcium by Vit D
Increased intestinal Ca absorption
Increases renal Ca reabsorption
Increases bone resorption
What reaction occurs to activate Vit D?
2 hydroxilation reactions
What is the role of calcitonin?
Counteracts effects of PTH
What is the feedback regulation for increased plasma [Ca]?
PTH lowers
Bone = increased bone building, decreased bone breakdown
Kidney = lowers calcitriol levels, lowers kidney Ca reabsorption
What cells prod PTH?
Chief cells in the parathyroid gland
Explain the regulation of parathyroid hormone
Low serum Ca up-reg gene transcription + prolongs survival of mRNA
High serum calcium down-reg gene transcription
Outline the secretion of PTH
GPCR
High [Ca] binds
Slows/inhibs release of PTH
What is the role of hydroxyapatite crystals?
Mineralises collagen matrix produced by osteoblasts
Explain the regulation of vit D
PTH stim amount of conversion of vit D to active form
Therefore increases the absorption of Ca2+
Explain the significance of renal function on calcium metabolism
Ascending limb/DCT = Ca reabsorption
Thick ascending limb = P inhibited reabsorption
What factor is Ca in the clotting cascade?
IV
What Ca chelator needs to be added to blood samples to inhibit clotting?
EDTA
What is added to donor blood packs to stop clotting, and what does this then mean?
Citrate chelates Ca ions
Massive blood transfusions therefore require IV Ca
What is the most common cause of hypercalcemia in a hospital setting?
Malignant osteolytic bone mets
Multiple myeloma
What cancers met to bone causing lytic lesions?
Breast, lung, renal, thyroid
= lytic and therefore cause hypercalcemia
What is the most common cause of osteoblastic bone met?
Prostate cancer
= osteoblastic therefore NO hypercalcemia
What are the common sites for bone mets?
Vertebrae, pelvis, proximal femur, ribs, proximal humerus, skull
Outline primary hyperparathyroidism
1 of the 4 glands devel adenoma
= prod excessive PTH = serum Ca rise and serum Phos to fall
Outline secondary hyperparathyroidism
All four glands hyperplastic = think no enough Ca
Vit D def = low Ca = high PTH = activates osteoclasts = mobilise Ca from bone = bone pain, osteomalacia
Vit D def due to chronic renal failure = renal osteodystrophy
What is serum alkaline phospatase?
Marker of high bone turnover
What are the symptoms of primary hyperparathyroidism?
Moans, groans, stones, bones
What are the symptoms of severe hypercalcemia?
High Ca in polyuria = dehydration = rehydration the main treatment
When is hypocalcemia most commonly seen?
Post total-thyroidectomy
What is the most dangerous concern regarding hypocalcemia?
Can kill due to laryngeal muscle tetany (spasm)
How does Ca change neuronal activity?
Hyper = suppression of neuronal activity: lethargy, confusion, coma
Hypo = excitable nerve: tingling, muscle tetany, epilepsy
What is osteoporosis?
Decreased bone density with normal ratio of mineral to matrix
= normal bone but not enough of it
What is osteomalacia?
Ratio of mineral to matrix is decreased
= soft bones that are prone to bending
What are the risk factors for osteoporosis?
Postmenopausal women, low BMI, long-term oral steroid use, heavy drinking, smoking, low BMI, prolonged inactivity
