calcium homeostasis - copy
TRANSCRIPT
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CALCIUM HOMEOSTASIS
New insight : BIVEK SINGH
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OBJECTIVE OF SESSION• Calcium• Body distribution of calcium• Function of calcium• Absorption and excretion of calcium• Calcium homeostasis -hormonal regulation 1. Parathyroid hormone (PTH) 2. Vitamin D (Calcitriol) 3. Calcitonin
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Calcium
Alkaline earth metal Atomic weight 20
Most abundant mineral in the human body
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Body distribution•Total content inadult body is 25000mmol (approx. 1kg)•99% of calcium is found in bone•extracellular fluid is 22.5 mmol
Plasma calcium
1.protein bound fraction- 4-5mg/dl
2.complex with citrate and phosphate- 1mg/dl
3.ionised form- 4-5mg/dl
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Major functions
•Calcification of bone and teeth
•Muscle contraction
•Role in neuromuscular transmission
•Role in blood coagulation
•Calcium as second messenger
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Absorption of calcium
• Calcium is taken in diet principally as calcium-phosphate,carbonate or tartarate
• About 40% of the average daily dietary intake of calcium is absorbed in gut.
• Absorption of calcium by gut mucosa occur by energy dependent active transport process.
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Excretion of calcium
• Partly through kidney and mostly through intestine
• Renal threshold for serum calcium is 10mg/dl
• Excretion is increased in vitamin D deficiency
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CALCIUM HOMEOSTATSIS
• Calcium homeostasis refers to the regulation of concentration of calcium ions in extracellular matrix
• Calcium homostasis is regulated by:
1. vitamin D (calcitriol)
2. parathyroid hormone (PTH)
3. calcitonin
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Vitamin D (Calcitriol)
• Vitamin D has two sources i.e. skin and diet
• 25-hydroxy cholecalciferol is the storage form of vitamin D in liver
• 1,25-hydroxy cholecalcitriol is the active form of vitamin D
• Activated by PTH and hypophosphptemia through 1-alpha hydroxylase enzyme in kidney
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VITAMIN D SYNTHESIS
SKIN LIVER KIDNEY
7-DEHYDROCHOLESTEROL
VITAMIN D3
VITAMIN D3
25(OH)VITAMIN D
h25-HYDROXYLASE
25(OH)VITAMIN D
1,25(OH)2 VITAMIN D
(ACTIVE METABOLITE)
1-HYDROXYLASE
TISSUE-SPECIFIC VITAMIN D RESPONSES
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Action of Calcitriol on intestine
• Calcitriol stimulates the absorption of dietary calcium and phosphate .
• Calcitriol induces the synthesis of calcium binding proteins(Calbindin D) in the enterocytes. Thus increases the uptake of calcium by intestine.
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Action of calcitriol on bone
• Calcitriol along with parathyroid hormone stimulates the osteoclastic bone resorption
• thus,mobilization of calcium and phosphate from bone.
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Action of Calcitriol on the Kidney
•Calcitriol reduces the excretion of calcium and phosphate through the kidney.
• Increase reabsorption.
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Parathyroid hormne• 4 parathyroid glands
• Release PTH in response to drop in serum calcium
• Magnesium needed to activate PTH release
• Effects on bone, kidney and indirectly on intestines
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Action of PTH on bone• PTH causes resorption of bone by osteoclastic activity
• Due to increased stimulation of pyrophosphatase and collagenase
• This causes the mobilization of calcium from bone
• Increase blood calcium level
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Action of PTH on kidney
• Increased reabsorption of calcium from kidney tubule
• Reduce the excretion of calcium
• Helps in synthesis of calcitriol by 1-alpha hydroxlase
enzyme
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Action of PTH on intestine
• Indirectly
• By promoting synthesis of calcitriol
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CALCIUM, PTH, AND VITAMIN D FEEDBACK LOOPS
NORMAL BLOOD Ca
RISING BLOOD Ca
FALLING BLOOD Ca
SUPPRESS PTH
STIMULATE PTH
BONE RESORPTION
URINARY LOSS
1,25(OH)2 D PRODUCTION
BONE RESORPTION
URINARY LOSS
1,25(OH)2 D PRODUCTION
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Calcitonin
• Secreted by parafollicular cells of thyroid gland
• Metabolism is antagonistic to PTH hormone
• Normal concentration in plasma is 10-20 pg/ml
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Action of calcitonin on bone & kidney
• Mainly acts on osteoclasts
• Reduces osteoclastic activities by reducing number and size of osteoclasts.Thus, inhibits bone resorption
• On kidney, it decreases calcium reabsorption from kidney
• Causes calciuria
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CALCIUM HOMEOSTASIS
DIETARY CALCIUM
INTESTINAL ABSORPTIONORGAN PHYSIOLOGY
ENDOCRINE PHYSIOLOGY
DIETARY HABITS,
SUPPLEMENTSBLOOD CALCIUM
BONE
KIDNEYS
URINE
THE ONLY “IN”
THE PRINCIPLE “OUT”
ORGAN PHYS.
ENDOCRINE PHYS.
ORGAN, ENDOCRINE
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Questions !!!!!!!!!Questions !!!!!!!!! oror suggestions ??????suggestions [email protected]
BIVEK SINGHBIVEK SINGHKIST MEDICAL COLLEGEKIST MEDICAL COLLEGELALITPUR,NEPALLALITPUR,NEPAL