Regulation of Calcium and Phosphate Metabolism Flashcards
What are the processes in which Ca is involved?
- neurotransmission
- learning and memory
- muscle contraction
- mitosis
- mobility
- secretion
- fertilization
- blood clotting
- structure of bones and teeth
What makes up the regulatory system to maintain extracellular fluid levels of Ca and P?
- vitamin D
- parathyroid hormone
- calcitonin
Describe extracellular Ca levels.
- higher Ca concentration
- 50% ionized (free), 40% bound, 10% complexed in other forms(anions)
Describe intracellular Ca levels.
- lower Ca concentration
- cystolic Ca can be increased as needed
- some Ca bound to proteins
Explain Ca balance.
If Ca intake goes down, body adjusts by increasing percentage of Ca absorbed
Ca-sensing is done by what receptors involved in Ca homeostasis?
Ca receptors on endocrine cells
What is hypocalcemia and its effects?
- decrease in plasma Ca (ionized Ca)
- causes twitching/cramping of skeletal muscle
- can cause numbness/tingling (paresthesia), seizures if extreme
What can cause hypocalcemia?
- lactation
- parathyroid disorders
- vitamin D disorders
- gut malabsorption of Ca
- renal failure
- ethylene glycol toxicity
What is hypercalcemia and its effects?
- increase in plasma Ca (ionized Ca)
- causes constipation, polyuria, polydipsia, lethargy, coma, death
What can cause hypercalcemia?
- parathyroid disorders
- vitamin D toxicity
What can result in altering forms of Ca in plasma?
- changes in plasma protein concentration
- changes in complexing anion concentration
- acid-base disutrbances
What occurs during acidemia?
- more H ions in blood
- more H ions bind to albumin
- free ionized Ca increases which leads to hypercalcemia
What occurs during alkalemia?
- less H ions in blood
- more Ca bind to albumin
- ionized Ca in blood decreases which leads to hypocalcemia
Intestinal absorption of Ca is regulated by what?
vitamin D
Kidney reabsorption of calcium is refulated by what?
PTH
Why can Ca be released into or absorbed from blood?
Because bone is constantly remodeled
Describe calcium homeostasis.
interaction of bone, kidney, and intestine, plus parathyroid hormone, calcitonin, and vitamin D
What substances stimulate bone reabsorption of Ca?
- parathyroid hormone
- vitamin D
What substance inhibits bone reabsorption of Ca?
- calcitonin
Where is phosphate stored?
muscle
What ion has a fairly constant absorption from diet?
phosphate
Which substance is necessary for neuromuscular transmisison?
magnesium
What substance is a cofactor in enzyme reactions?
magnesium
Dietary megnesium absorbed by the gut is enhances by what?
vitamin D
What hormone regulates plasma Ca and P?
Parathyroid hormone
What cells are the source of PTH from the parathyroid glands?
chief cells
What are stimulators of PTH release?
- decreased blood Ca
- increased blood phosphate
- decreased Mg
PTH stimulates what, which ultimately feeds back and decreases PTH secretion?
vitamin D
What inihbits PTH release?
increased blood Ca
PTH targets what tissues?
- bone
- kidneys
- intestines
What are the actions of PTH?
- increases bone resorption to release Ca and P into blood
- stimulates Ca reabsorption in distal convoluted tubule of kidney
- inhibits phosphate reabsorption in proximal convoluted tubules of kidneys, thus causing P excretion in urine
- increases Mg reabsorption in kidneys
- stimulates vitamin D synthesis in kidneys
- increases Ca absorption from intestine via vitamin D
The primary form of hyperparathyroidism is caused by what?
caused by benign tumor or hyperplasia of one or both parathyroid glands
What are clinical signs of primary hyperparathyroidism?
- increased PTH
- hypercalcemia
- hypophosphatemia
- renal calculi
- bone pain and fractures
The secondary form of hyperparathyroidism is caused by what?
caused by increased phosphate in blood, which precipitates Ca and results in hypocalcemia which then causes secondary increase in PTH
Secondary hyperparathyroidism may result from what?
renal failure or increased dietary phosphate
Hypoparathyroidism may be caused by what?
- accidental surgical removal
- autoimmune destruction
- idiopathic
Hypoparathyroidism results in what?
- decreased PTH
- hypocalcemia
- hyperphosphatemia
How does calcitonin decrease blood Ca and P?
- inhibiting bone resorption
- increasing urinary P excretion
- inihbiting renal reabsorption of Ca
What are stimulators of calcitonin?
- increased blood Ca
- vitamin D (via feedback)
- ingested food
What sustance is required for bone formation and increases Ca absorption from GIT?
vitamin D
Where is vitamin D synthesized and what form is it synthesized as?
synthesized in skin as precursor 7-dehydrocholesterol
After synthesis or absorption in the gut, what happens to vitamin D in the liver?
- converted to 25-hydroxyvitamin D
- goes to kidney – most converted to 1,25-hihydroxyvitamin D
Intermediates and active vitamin D are bound to what?
protein carriers
What are the actions of vitamin D?
- stimulates Ca absorption via calbindin in intestine
- stimulates absorption of phosphate and Mg in intestine
- weakly stimulates Ca and P reabsorption in kidney
- stimulates bone resorption in presence of PTH
- increases Ca transport and uptake by SR in skeletal muscle cells
- decreases PTH synthesis
When Ca intake is low, Ca absorption is an ____ process.
active
When Ca intake is high, Ca absorption is a ______ process.
passive
