The human body is made ??up of around 1,100 g of calcium ( 99 % found in bones and teeth ) . The rest is plasma in 3 fractions , ie free ionized calcium ( 50 % ) , protein -bound calcium ( 40 % ) , and complexed calcium ( 10 % ) .
Complexed fraction and ionized Ca 2+(about 60 % of the Ca 2+plasma ) can pass through the plasma membrane . 10-20 % protein -bound ? ? ? ? Ca 2 + binds to globulin . The rest , the majority ( 80-90 % ) binds to albumin ? , and sensitive to changes in pH .
- Acidosis - > protein -bound Ca 2+decreased , free or ionized Ca 2+increase in plasma .
- Alkalosis - > protein -bound Ca 2+increases, ionized Ca 2+decreased in plasma .
The concentration of Ca 2+at resting intracellular ( cytosolic ) approximately 100 nM , but can be increased to 1 ?M with the production of Ca 2+from intracellular suggestions or uptake Ca 2+from the extracellular . While the concentration of Ca 2+surrounding extracellular intracellular 10,000 -fold .
In addition to the intracellular messenger and enzyme cofactor , Ca ? ? ? ? 2 + also plays a role in extracellular functions such as in blood clotting, nerve stimulation , etc. . So Ca ? ? ? ? 2 + is very important in maintaining the normal function of the body . For example , when the Ca ? ? ? ? 2 + decreased, it can happen hipereksitabilitas neuromuscular causes numbness ( numbness ) , and tingling sense ( tingling ) or muscle cramp . Hipereksitabilitas nerve can cause Chovstek sign ( ipsilateral contraction of facial muscles when patted on the skin above the facial nerve ) or Trosseau ( induction stiffness at Karpal to inflate the blood pressure cuff to 20 mmHg above the systolic pressure of the patient for 3-5 minutes) .
Bone Interaction , Renal , and Intestinal Calcium Homeostasis in Babysitting
Calcium in the bones distributed through :
- Readily exchangeable pool - > keep plasma levels of Ca 2+to convert 550 mg of calcium between bone and extracellular matrix .
- Stable pool - > help the process of bone remodeling . After pertumbukan skeletal unified , cortical and trabecular bone remodeling persists .
In the kidney , almost all the Ca 2+that difiltrasi , will terreabsorpsi .
- 40 % direabsorpsi in distal tubular under the influence of PTH . At the distal tubular , reabsorption mediated by active cellular absorption stimulated by the binding of PTH to PTHR1 .
- Approximately 60 % ( almost all the rest ) direabsorpsi in proximal tubular without the influence of hormonal regulation .
- Transport ? ? ? ? Ca 2 + transelular facilitated by vitamin D through increased expression of calbindin - D28K and Ca ? ? ? ? 2 + transporter in the basolateral membrane .
Availability of calcium from food is very important for calcium homeostasis . Dietary calcium intake of about 1000 mg / d , and only 30 % in intestinal diabsorpsi . Diabsorpsi amount of calcium increased by vitamin D when growth , pregnancy , and lactation . Current period of growth, there is bone accretion . After completion of the growth phase , the rate of increase of calcium in the bones or reduced. Total Ca ? ? ? ? 2 + are removed through urine will equal the amount diabsorpsi .
Ca absorption ? ? ? ? 2 + in the intestinal occur in 2 ways :
- Paracellular pathway (non- saturable ) - > when supply is ? ? ? ? Ca 2 + excess
- Transcellular pathway ( saturable ) - > when supply is ? ? ? ? Ca 2 + is limited, vitamin - D dependent
Transport Ca ? ? ? ? 2 + transepitel on intestinal through 3 stages :
- Passing through the apical membrane passively
- Diffusion of terfasilitasi sitosolik vitamin D -dependent calcium -binding protein ( calbindin )
- Passing through the basolateral membrane with active ekstruksi , mediated Ca ? ? ? ? 2 + - ATPase and Na + / Ca ? ? ? ? 2 + exchanger .
Hormones regulation on Calcium Homeostasis
The reduction in free ionized Ca ? ? ? ? 2 + are known to the sensor ? ? ? ? Ca 2 + in the parathyroid chief cell , until the release of PTH increases. PTH then binds to receptors on osteoblasts and stimulates osteoclast production pengaktivasi factors to enhance bone resorption and release of Ca ? ? ? ? 2 + into the circulation .
In the kidney , PTH increase Ca reabsorption ? ? ? ? 2 + and Pi excretion in urine . PTH also stimulates hydroxylation of 25 - hydroxivitamin D3 at position 1 , to activate vitamin D ( calcitriol or 1,25 ( OH ) 2D3 ) . Vitamin D increases absorption ? ? ? ? Ca 2 + reabsorption in the intestinal and ? ? ? ? Ca 2 + in the kidneys .
In bone , vitamin D increase and stimulate osteoclast bone resorption , so the Ca ? ? ? ? 2 + in circulation increases. Increased Ca ? ? ? ? 2 + free in circulation causes decreased production of PTH by the parathyroid glands , decreased activation of vitamin D in the kidney , and thyroid stimulation in parafolikular cells for calcitonin secretion .
Calcitonin has the opposite effect with PTH , namely menginhibisi osteoclast activity , reducing bone resorption , and increases excretion of Ca ? ? ? ? ? ? ? 2 + in the kidneys , so the Ca ? ? ? ? 2 + -free drop. It can be concluded , that PTH , calcitriol , and calcitonin work together to keep calcium homeostasis in the body .
Factors involved in the regulation of the metabolism of Ca 2+and bone
PTH ? bone resorption of Ca2 + and plasma
? vitamin D intestinal absorption of Ca2 + , ?
Calcitonin ? bone resorption and plasma Ca2 +
Sex steroid - 1a activity hydroxilase ? , ? bone resorption , osteoprotegerin synthesis ?
Stimulation of GH and IGF synthesis and bone growth
Thyroid hormone, bone resorption ?
? prolactin and renal reabsorption of Ca2 + - 1a activity hydroxilase
Glucocorticoid ? bone resorption , bone synthesis ?
? bone resorption of inflammatory cytokine
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