Calcium Flashcards
calcium :-
quantity
source
RDA
1-1.5 KG
99% - bone 1%- ECF
good source - milk
medium sources - egg fish vegetables
small amt in - cereals
RDA - adult - 1000mg/day
child - 750mg/day
pregnancy and lactation - 1500mg/day
after age of 50 - 1500mg/day (+vit d - 20µg /day)
ABSORPTION OF CALCIUM
AND FACTORS
1. INCREASE
2.DECREASE
Occurs in the 1st and 2nd part of duodenum
active transport ( by Ca ATPase )
500g intake - 400g(feces)+ 100g(urine)
1. INCREASE -
1) VIT.D - ↑ calbindin production in intestine epithelial cells
2) PTH - ↑ca absorption from intestine
3) acidity 4)amino acids - Lys and Arg
2. DECREASE-
1)phytic acid - hexaphosphate of inositol (in cereals)
2)oxalates 3)malabsorption syndrome of fatty acids
4)high phosphate content - form insoluble ca-phosphate salts
Ca:P = 1:2/2:1 - for max. absorption (in milk)
CALCIUM IN CELLS
mainly in extracellular compartment
membrane is generally impermeable
influx - transport by Na+-Ca+2 exchange (low affinity for Ca)
uniport system for entry into mitochondria
Calcium pump:- exit of ca by na-ca antiport which inturn dependent on na-h atpase
other channels - Voltage gated , secondary messenger mediated and hormone receptor channels
CALMODULIN
ca binding regulatory protein
MW- 17000 dalton
1 can bind to 4 Ca atoms at a time
is a part of various regulatory kinases
active kinase converts the enzyme into phosphorylated enzyme and carries out the function
FUNCTIONS OF CALCIUM
- Activation of enzymes - either with use of calmodulin or without
- Muscle contraction and excitation
trigger of muscle contraction - binding of ca with troponinC
Calquestrin - active transport system utilising ca binding
protein - nerve impulse conduction
4.secretion of hormones - PTH, Insulin,calcitonin,vasopressin
5.vascular permeability - ↓ relaese of serum into spaces
6.coagulation - Factor -4
7.myocardium - prolongs systole (↑ca - cardiac arrest)
ca given very slowly intravenously - bone and teeth
CALPAINS
- ca dependent cysteine proteases
functions - fusion of myoblasts , potentiation of neurons , cell cycle progression , cell mobility
two isoforms - 1&2
mammalian calpain 3 - responsible of limb girdle muscular dystrophy
calapin 10 - susceptibility gene for diabetes mellitus (type-2)
calpain 9 - tumor supressor for gastric cancer
Calpastatin - endogenous calpain specific inhibitor
CALCIUM CONTENT
normal level - 8.5-10.5 mg/dl (10mg/dl=5meq/dl)
diffusible forms :-
1) 5mg/dl - ionised form (metabolically active)
2)1mg/dl - as complexes ( P , h2co3 , citrates)
nondiffusible forms :-
combined to proteins in blood - 4mg/dl
ESTIMATION OF CALCIUM
use of serum or lithium heparin plasma √ EDTA / oxalates ×
acidification of sample
↓
release of ca from protein complexes
↓
analysis by cresolphthalein complexone or by arsenzo(III)dye
commercial analysers - ISE (ion selective electrode)
HYPERCALCEMIA
ca level > 10.5mg/dl
Reasons- mainly hyperparathyroidism bcs of parathyroid adenoma or ectopic PTH secreting tumour
Results - osteoporosis , may cause pathological fracture
Mechanism :- Ca↑ → ALKP↑ → P↓
urine → ca released →cl not released →hyperchloremic acidosis
in urine ca precipitation may occur → recurrent bilateral urinary canaliculi
Ectopic calcification may occur - pancreas , arterial walls, renal tissue , muscle
Bone resorption and hypercalcemia occuring diseases
multiple myeloma , pagets’s disease , metastatic carcinoma of bone
HYPOCALCEMIA
Ca <8.5mg/dl – mild tremors
Ca<7.5 mg/dl – tetany
Causes :- def. of vit.D , PTH, albumin ,calcium
↑ in calcitonin , Mg , phosphorous ,
TETANY
Reasons :- accidental removal of PTH glands / autoimmune
NOT CAUSED BY VIT.D DEFICIENCY
Manifestations :- ↑ neuromuscular irritability , carpopedal spasms , laryngismus , stridor , increased QT interval , urinary excretions of both ca and p are ↓ ,
Signs :- +ve Chovestek’s sign - touching of facial erves causes facial contractions
+ve trousse’s sign - buff cuff inflation for 3mins → carpopedal spasms
Treatment - intravenous injections of Ca+2 ions
OSTEOCALCIN
-unique protein found in bone and dentine
- 1% of total proteins found in bone
secreted by - osteoblasts
function - role in mineralisation and Ca homeostasis
-acts as a BIOMARKER for the bone formation process
-during bone formation , 10-30% of it produced is released into circulation
