Calcium Metabolism Flashcards
Identify where most of the Ca and PO4 is stored in the body
Bone
List and describe the major sites of regulation for blood calcium
Kidney- Out: renal excretion
Gut- In: intestinal absorption, Out: fecal excretion
Bone- In: bone resorption, Out: bone formation (Ca incorporation into bone)
Describe the major pathway for loss of Ca++ in the body
Sites of calcium loss are in the gut (fecal excretion), kidneys (urine output), and in the bones (Ca incorporation into bone)
List hormones that are significant in Ca homeostasis
Parathyroid hormone, Calcitonin
Describe general effects of PTH on calcium and phosphate in blood, urine, and bone
Calcium:
Blood- increases
Urine- decrease
Bone- decrease
Phosphate:
Blood- decrease
Urine- increase
Bone- decrease
Describe the general effects of PTH on vitamin D synthesis
activates vitamin D in kidneys to calcitrol
Describe the source and effects of calcitonin.
Source: Perifollicular āCā cells of the thyroid produce calcitonin
inhibits bone resorption, decreases tubular calcium reabsorption
Describe, without using structure, the sites of synthesis of active vitamin D3 and the role of PTH
skin, liver, kidney (PTH)
Describe effects of vitamin D3 on the gut, bone and kidney
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Gut: stimulate transepithelial transport of calcium and phosphate in the small intestine
Bone: stimulates terminal differentiation of osteoclasts, stimulate osteoblasts to stimulate osteoclasts to mobilize calcium
Kidney: synthesizes vitamin D to calcitrol , induced by PTH
Describe effects of PTH on bone, gut, and kidney.
Gut- calcitrol increases intestinal absorption of calcium
Bone- increases bone resorption, moves calcium and phosphate from bones into extracellular fluid
Kidney- stimulates activation of Vitamin D, converts 25(OH)vitamin D to calcitrol; increases tubular calcium reabsorption, decreases tubular phosphate reabsorption
Describe effect of varying Ca and PO4 levels in the serum on parathormone secretion and calcitonin secretion.
CaxPO4 = K
K> 60-70, Ca salts are deposited
K< 30, bone resorption occurs
Calcitonin acts to lower serum levels of Ca/PO4
PTH acts when Ca gets too low/decreases PO4
Distinguish primary from secondary hyperparathyroidism
Primary: high PTH and high Ca; not feedback sensitive
Secondary: high PTH, low to normal Ca
Name one cause of secondary hyperparathyroidism
Chronic renal failure
Poor nutrition
Describe how you would differentiate hypervitaminosis D from primary hyperparathyroidism
primary hyperparathyroidism- high PTH, high Ca
hypervitaminosis D- high Ca, low PTH
Describe what typically triggers soft tissue mineralization, and organs affected.
commonly triggered by hypercalcemia; when product of CaxPO4 > 60-70, CaPO4 is deposited in the skin as a salt in a variety of soft tissues
kidney, skin, GI tract, cardiac and skeletal muscle, tendons and ligaments are common sites of deposition
structural and functional abnormalities result
basically irreversible
Define: Hypocalcemia
can be seen in postparturient paresis (milk fever) and c-cell carcinoma
Define: Hypercalcemia
high level of calcium in the blood, can be caused by Primary Hyperparathyroidism
Define: calcitonin
small protein, functions to lower serum levels of Ca and PO4 by inhibiting bone resorption, decreases tubular calcium reabsorption, may not be physiologically significant
Functions of phosphorus
ATP, buffer, enzyme activation, DNA/RNA, membrane structure, second messengers; loss is primarily seen through the kidneys
Define: calcitrol, 1,25 -dihydroxyvitamin D
form of vitamin D that increases intestinal absorption of calcium
Define: milk fever
hypocalcemic disorder associated with initiation of lactation in dairy cows: loss of calcium in milk
Define: hyperparathyroidism
Primary common in dogs, seen in cats
Usually do to adenoma, not feedback sensitive
high PTH, high Ca, low PO4; extensive bone loss
no treatment except surgery
Secondary chronic renal disease cases, nutritional: occurs do to hypocalcemia, overstimulation of PTH and bone loss (high PTH, low to normal Ca)
Define: hypoparathyroidism
rare
can be of autoimmune origin or caused by surgery for hyperthyroidism
young adults, 1-4 years old
symptoms- neuromuscular problems, focal muscle twitching, rear limb cramping, generalized muscle spasms, convulsions
emergency treatment: IV injection of Ca
oral treatment (maintenance): calcium lactate/carbonate and dihydrotachysterol
Define: hypervitaminosis D
causes hypercalcemia and PTH suppression; high Ca and PO4 levels due to increased GI absorption and bone breakdown
Define: malignancy
presence of tumor can cause hypercalcemia and low PTH levels; cannot be distinguished from hypervitaminosis D by just measuring PTH and Ca; some tumors produce a protein with effects similar to PTH,
Define: cholecalciferol
in skin it is Vitamin D3, can also be provided in diet; sometimes used in rodenticides because it can cause hypervitaminosis D
