5.6 Calcium Homeostasis Flashcards
Importance of calcium
Nerve and muscle excitability
Neurotransmitter release from axon terminals
2nd messenger in intracellular signaling
Major constituent of bone
Most of total body calcium is in ___
Bone
Importance of phosphorus
Enzyme activation/inactivation
Major constituent of DNA, RNA and other phosphoproteins
Major component of bone
Majority of phosphorus is in __
Bone
Contains the second most abundant storage of phosphorus
ICF
The most biologically important form of calcium
Free ionized form
Calcium RDA for adults
around 1000 mg
Major dietary source of calcium
Dairy products
Organ which is the major site of phosphorus homeostasis
Kidneys
The Bone forming cell responsible for secreting and depositing organic matrix that will form the new bone (osteoid)
Osteoblast
Cells that promote bone resorption
Osteoclast
Signals for activation and maturation of osteoclasts
RANK ligands
Various interleukins
Cytokines
A group of osteoclasts and osteoblasts that carries out the process of bone remodeling
BMU or Basic Multicellular Unit
Relative length of bone remodeling
3 months
Most important hormone in regulating ca
Parathyroid hormone
Primary regulator for secretion of PTH
Ionized calcium
Primary stimulus for secretion of PTH
Decreased plasma ionized calcium
in the presences of calcium, GPCR activates this effector which leads to the inhibitions of PTH secretion and synthesis
Protein Lipase C/phospholipase C
Hormone which inhibits gene expression of PTH
Calcitriol
___ terminal of PTH contains the biologically active sequence
Amino terminal
Net effect of PTH
Increase serum calcium
Decrease serum phosphorus
Effect of PTH on Bone
Stimulate both osteoblasts (directly) and osteoclasts (indirectly)
How PTH increases serum Ca via the kidneys
PTH increases Ca reabsorption at the thick ascending limb and early distal convoluted tubule
Effect of calcitriol on bone
Represses synthesis of type 1 collagen
induces synthesis of osteocalcin
Enzyme which acts upon 25 hydroxycholecalciferol to produce 1,25 dihydroxycholecalciferol (calcitriol; activated form of calcium)
1alpha-hydroxylase
Source of calcitonin
Thyroid gland, C cells or clear cells or parafollicular cells
Effect of calcitonin
Promote bone deposition and inhibits osteoclastic resorption
PTH and Ca levels in hypoparathyroidism
Low PTH, Low Ca
Signs and symptoms of hypocalcemia
Neuromuscular irritability: cramping, tetany, tingling, paresthesia, chvostek’s sign
