Term
Importance of Ca regulation |
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Definition
•Ca plays a key role in many physiological processes:
•Contraction of skeletal, cardiac and smooth muscles
•Transmission of nerve impulses
•Blood clotting
•Many others
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Term
1,25-dihydroxycholecalciferol |
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Definition
•Effects
–Prolonged effect (several week duration of CBP)
–Calcium binding protein
–Ca++ stimulated ATPase
–Alkaline phosphatase
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Term
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Definition
•Biologically active 1,25-hydroxycholecalciferol is synthesized in the kidney under PTH stimulation
•Synthesis of 1,25-hydroxycholecalciferol is stimulated by parathyroid hormone and inhibited by high plasma Ca and phosphate
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Term
Forms of Ca in the extracellular fluid |
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Definition
•1. Ionized free. 50%
•2. Ionized complexed with anions (phosphate, citrate). 9%
•3. Protein-bound. 41%. Non-diffusible thru the capillary wall.
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Term
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Definition
•HPO4- - and H2PO4-
•1.3 mmol/L
•4 mg/dL
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Term
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Definition
•Calcium and phosphate
•Hydroxyapatite
–Ca10(PO4)6(OH)12
–Platelike
•Also contain Mg, Na, K, CO3
Crystals stacked like bricks in a wall
And fibers run lengthwise like steel cables in concrete
Gives tremendous tensile strength combined with compresional strength from crystals
Actually stronger than reinforced concrete
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Term
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Definition
Osteoblasts lay down osteoid
Collagen
Ground substance
Some cells trapped – osteocytes
Calcium salts deposit
Initially amorphous crystals
Remodeled into hydroxyapatite
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Term
Ca exchange between bone and extracellular fluid |
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Definition
•Exchangeable Ca provides buffering tool to keep normal concentration of the ionized Ca
•Exchangeable Ca contains only 0.4–1% of the total bone Ca
•Bones are continually being deposited by osteoblasts and absorbed by osteoclasts
•Coordinated activity of osteoblasts and osteoclasts allows bones to respond to physiological challenges
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Term
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Definition
•Balance between deposition and reabsorption
–Localized mass of osteoclasts bore tunnel
–Osteoblasts invade tunnel and rebuild after about 3 weeks and remain for months
–Haversian canal remains
–Osteon
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Term
Reasons for Bone Remodeling |
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Definition
•Adjustments in bone strength and shape
–Athletes vs nonathletes
–Piezo-electric effect
•(-) potential at site of compression
•Replace degenerated organic matrix
–Maintains supportive collagen fibers
•Fracture
–Maximal stimulation of osteoblastic activity
•Progenitor cells
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Term
Effect of PTH on Ca and phosphate concentration in the extracellular fluid |
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Definition
•1. Increased Ca and phosphate absorption from the bone
•2. Decreased Ca secretion by the kidneys
•3. Increased renal phosphate secretion
•Net effect:
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extracellular Ca concentration
extracellular phosphate
concentration
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Term
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Definition
•Increased reabsorption of Ca
•Diminished reabsorption of phosphate, promoting phosphate secretion with urine
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Term
Control of parathyroid secretion |
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Definition
•PTH secretion is stimulated when Ca concentration in the blood falls down (pregnancy, lactation, rickets)
•PTH secretion is inhibited by:
•excess quantities of Ca in the diet
•bone absorption caused by factors other than PTH
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Term
How Parathyroid Hormone Works |
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Definition
•Bone
–Osteocytes and osteoblasts form osteocytic membrane system
•“bone fluid”
•Activation of calcium pump
–Osteoclasts
•Activation of present osteoclasts
•Formation of new osteoclasts
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Term
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Definition
•Secretion of calcitonin is stimulated by increased plasma Ca
•1. Immediate effect.
•Decreased activity of osteoclasts and bone absorption
•2. Prolonged effect.
•Decreased formation of new osteoclasts
•Calcitonin has a weak effect on plasma Ca concentration in adult humans
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Term
Pathophysiologies involving Ca++ Homeostasis |
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Definition
Parathyroid gland hypertropy
1.Rickets
2.Pregnancy
3.Lactation
Parathyroid gland atrophy
1.Excessive vitamin D
2.Excessive calcium
3.Bone absorption
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Term
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Definition
•Osteoclasts become almost dormant
•Plasma calcium depletes
–Tetany
–Laryngeal muscles (possibly lethal)
•Treatment
–PTH administration (expensive)
–Vitamin D and Calcium administration
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Term
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Definition
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•Lack of Calcium and/or phosphate in ECF
–Vitamin D deficiency
–Lack of adequate sunlight
•Condition may appear in spring after winter has allowed for depletion of stored Vit D precursors
–Months to become apparent
•Tetany may develop in late stages
•Treatment
–Dietary calcium and phosphate
–Vitamin D supplements
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Term
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Definition
•Old age
•Common
•Diminished organic matrix
–Reduced osteoblastic activity
–Sometimes caused by increased osteoclast activity (hyperparathyroidism)
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Term
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Definition
•Old age
–Loss of growth hormone and reduced protein function
•Malnutrition
•Inactivity
–No physical stress to stimulate bone deposition
•Loss of estrogen at menopause
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