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CALCIUM AND PHOSPHOROUS
METABOLISM
-DR. SUHASINI. G P
Lecturer
Dept. of Oral Pathology & Microbiology
Dr. Suhasini GP, Subharti Dental College, SVSU
INTRODUCTION
• Metabolism (Greek, Metabote= change)
• Sum of the chemical and physical changes in tissue consisting of anabolism (reactions that convert small molecules into large) & catabolism (reactions that convert large molecules into small)
Dr. Suhasini GP, Subharti Dental College, SVSU
Functions of Calcium
• Most abundant mineral
• Most important inorganic cation in
mineralised tissue- structural role
• [Ca10(PO4)6(OH)2] in bone, dentin,
cementum & enamel
Dr. Suhasini GP, Subharti Dental College, SVSU
Functions
Formation of bone and teeth
Controls secretion of glandular cells
Muscle contraction
Clotting of blood
Neuromuscular excitability
Cell-cell adhesion, cell integrity
Intracellular second messenger in harmonal actions
Dr. Suhasini GP, Subharti Dental College, SVSU
Dietary requirements
• Adults- 0.8 gms/day
• Children & pregnant and lactating women-
additional 1gm of Ca supplements/day
• Postmenopausal women
Dr. Suhasini GP, Subharti Dental College, SVSU
Sources • Milk & its products
• Green leafy veg (oxalic acid and phytic acid- reduces absorption)
• Raagi
• Egg yolk
• Legumes
• Nuts
• Dried fish
• Pan chewing with slacked lime
• Drinking water
Dr. Suhasini GP, Subharti Dental College, SVSU
Distribution of Ca++`
• Essentially distributed extracellularly
• 1.2-1.4 kg in 70kg adult
• 99%-skeleton
• 1%- soft tissue+ body fluids
Dr. Suhasini GP, Subharti Dental College, SVSU
Bone Ca++
Exists in 2 forms-
• Readily exchangeable form- simple exchange b/n newly deposited bone & exctracellular Ca++
• Stable form- constant formation & resorption of bone-
–Controlled by PTH, calcitonin & vit.D
Dr. Suhasini GP, Subharti Dental College, SVSU
Blood Ca++
• Plasma, little in RBC
• 9-11mg/dl- constant
• In plasma-
1. Diffusible
o Ionised
o Non-ionised
2. Non diffusible
Dr. Suhasini GP, Subharti Dental College, SVSU
• Ionised diffusible form- physiologically active form
• Non ionised diffusible form- in the form of complexes as citrates, phosphates n bicarbonates
• Protein bound (albumin in plasma)- physiologically inactive
Dr. Suhasini GP, Subharti Dental College, SVSU
Calcium balance
• Calcium absorption-
• Active transport- against conc. gradient- duodenum
• Passive diffusion- proximal jejunum & ileum
• Normal secretion of HCL is necessary for optimal absorption
• Achlorhydria, hypochlorhydria— decreased absorption.
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L U M E N C E L L B L O O D
d ie ta ry C a2 +
C B P
C a C B P
C a2 +
F a c ilita te d
D iffu s io n
N a+
/C a2 +
E x c h a n g e
C a2 +
N a+
N a+
C B P = c a lc iu m b in d in g p ro te in
4
1,25-dihydroxycholecalciferol
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Intake, Uptake and Excretion
D ie t
1 0 0 0 m g
G U T
8 0 0 m g
e x c re te d
a b s o rb s
3 5 0 m g
s e c re te s
1 5 0 m g
C a2 +
P o o l
B o n e
5 0 0 m g
5 0 0 m g
K id n e y 2 % f i l te re d
lo a d
2 0 0 m g
e x c re te d
C A L C IU M
5 Dr. Suhasini GP, Subharti Dental College, SVSU
• Positive Ca++ balance
• Negative Ca++ balance
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FACTORS AFFECTING Ca ABSORPTION
(a) Factors affecting mucosal cells
♣ Vit D- increases absorption
♣ D2(ergocalciferol)- yeast bread
♣ D3- fish liver oils
Dr. Suhasini GP, Subharti Dental College, SVSU
• 1,25 dihydroxycholecalciferol- active form
• Acts as a hormone
• Acts by promoting synthesis of Ca binding protein (CaBP) in epithelium of intestinal villi
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(b) precipitating anions • Ca soluble form- absorbed • Contents- stomach Intestine- alkaline
digestive juices- pH insoluble Ca salts- absorption
• Acidic conditions in small intestine- favor absorption
• Phosphate & long chain fatty acids, bile & bile salts are such anions
• Very high or low Ca/P ratio or too high levels of both absorption
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(c) Complexing agents • Fat+ Ca – colloidal complexes- absorbed through
intestinal wall (d) Carbohydrates &proteins • Disaccharide- lactose- absorption and bone
calcification • Proteins- absorption (e) Hormones • Parathyroid hormone- stimulate intestinal transport • Controls formation of 1,25 dihydroxycholicalciferol • GH increases the absortion
Dr. Suhasini GP, Subharti Dental College, SVSU
(f) Seasonal & unexplained effects-
• Max- July & august
• Min- Feb & March
• Emotional factors- Stress
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PARATHYROID HARMONE
VIT D
CALCITONIN
bone
kidney
intestine
Action on
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Role of PTH
• Stimulates renal reabsorption of calcium
• Stimulates bone resorption
• Inhibits bone formation and mineralization
• Stimulates synthesis of calcitriol- increased absorption from intestine
Net effect of PTH ↑ serum calcium
Dr. Suhasini GP, Subharti Dental College, SVSU
Regulation of PTH
Low serum [Ca+2] Increased PTH secretion
High serum [Ca+2] Decreased PTH secretion
Dr. Suhasini GP, Subharti Dental College, SVSU
Role of Calcitriol
• Stimulates GI absorption of calcium
• Stimulates renal reabsorption of calcium
• Stimulates bone resorption • (INCREASES SYNTHETIC ACTIVITY OF OSTEOBLASTS,
NECESSARY FOR NORMAL CALCIFICATION
• IN LARGE QUANTITIES- CAUSE RESORPTION OF BONE)
Net effect of calcitriol ↑ serum calcium
Dr. Suhasini GP, Subharti Dental College, SVSU
Regulation of Calcitriol
INTESTINE KIDNEY BONE
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Calcitonin
• Secreted by the type C cells(parafollicular) of thyroid.
• CT reduces Ca2+ by reducing transfer of Ca2+ to the blood and inhibiting bone resorption by decreasing the osteoclastic activity
• Used in the treatment of Paget’s disease & osteoporosis
Dr. Suhasini GP, Subharti Dental College, SVSU
Other harmones
• GROWTH HARMONE-increases intestinal absorption
• GLUCOCORTICOIDS-initially- inhibit osteoclstic activity- decreasing the plasma conc. Over prolonged periods- increases bone resorption and decreased bone formation
• THYROID HARMONES- T3, T4- hypercalemia and hypercalciuria- osteoporosis
• TESTOSTERONE-increases bone density & bone growth
• ESTROGEN- inhibits osteoclastic activity, prevents osteoporosis.
Dr. Suhasini GP, Subharti Dental College, SVSU
APPLIED ASPECTS
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Hypercalcemia
• Fatigue, lethargy
• Anorexia, nausea, vomitting
• Constipation (muscle hypotonia)
• Cardiac abnormality
• Peptic ulcer
• Metastatic calcification etc
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Tetany
• Ca++ <6mg/dl
• Chvostek’s sign-tapping of facial nerve- spasm of muscles
• Trousseau’s sign- application of torniquet of sphygmomanometer on arm- carpopedal spasm
• Accoucher’s hand-flexion of metacarpophalangeal joints while fingers remain extended
• Laryngeal stridor
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Hyperparathyroidism
• Primary- adenomas of PTH glands
• Secondary- renal diseases, rickets, osteomalacia, acromegaly, malabsorption syndrome
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Hypoparathyroidism
• Postoperative
• Functional
• Idiopathic
• Hypomagnesemia
• Pseudohypoparathyroidism- PTH level high, serum Ca++ low- defect in target cell receptor or CBP
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RICKETS
Rickets can be caused by lack of sunlight, but also from insufficient calcium. Vitamin D linked to calcium absorption.
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• RENAL RICKETS
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Pathologic calcification
• Dystrophic Calcification
• Metastatic calcification
• Calcinosis
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Dystrophic Calcification
• Calcification of dead and dying tissues.
• The level of calcium in blood is usually normal. (There is no hypercalcemia).
• In mouth- gingiva, tongue, cheek, pulp
Dr. Suhasini GP, Subharti Dental College, SVSU
Pulp calcification Calcifications in pulp:
Three types-
I. Denticles - Denticles are formed as a result of an epitheliomesenchymal interaction within the developing pulp.
II. Pulp stones- pulp stones are developed around the central nidus of pulp tissue
III. Diffuse linear calcifications- they exhibit areas of fine, fibrillar, irregular calcification that often parallel the vasculature.
Dr. Suhasini GP, Subharti Dental College, SVSU
• Classification by Hill-
• 1st - Nodular type- result of calcification of hyalinized CT
– perivascular, perineural, associated with fibrosis
• 2nd type- Found in and around the necrotic cells
• Inflammatory process
Dr. Suhasini GP, Subharti Dental College, SVSU
Local metabolic dysfunction
Hyalinization of injured cells
fibrosis
Trauma
Vascular damage
Mineralization
PULP STONE
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Clinical & radiographic features
denticles and pulp stones are detected on intraoral radiographs
as radioopaque enlargements within the pulp chamber or
canals
May interfere with root formation leading to early periodontal
destruction and tooth loss
Histopath features
• Denticles –consist of tubular dentin surrounding a
nest of epithelium , central epithelium degenerates
with time and tubules undergo sclerosis.
• Pulp stones –a central amorphous mass of irregular
calcification surrounded by concentric, lamellar rings
of regular calcified material.
• Diffuse linear calcification – consist entirely of fine,
fibrillar and irregular calcification that develop in the
pulp chambers and canals
Dr. Suhasini GP, Subharti Dental College, SVSU
Metastatic calcification
It is deposition of calcium salts in many tissues which may be normal. It is associated with disorders of calcium metabolism and there is hypercalcemia.
• Metastatic calcification may occur in organ throughout the body. It is commonly observed in:
• Organs which secrete or excretes acids like stomach, kidneys and lungs.
• Calculi or stones in salivary glands, intestine, urinary tract, gall bladder etc
Dr. Suhasini GP, Subharti Dental College, SVSU
• Aetiology:
– Increased PTH » Hyperparathyroidism
– Bone destruction » Tumour (MM, Leukaemia), Skeletal Mets (Breast Ca.)
» Increased bone turnover (Pagets), Immobilisation.
– Vitamin D related disorders » Excess Vitamin D
» Sarcoidosis
– Renal Failure » Retention of Phosphate, (secondary HyperPTH)
Dr. Suhasini GP, Subharti Dental College, SVSU
Calcinosis cutis
• Presence of calcifications in or under the skin
• Calcinosis circumscripta
• Calcinosis universalis- scleroderma and dermatomyositis
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PHOSPHOROUS
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Distribution and Requirements
Phosphate
• 80% of Pi is in mineralized tissue
• The remainder is mostly intracellular
• RDA = 800-900 mg
2 Dr. Suhasini GP, Subharti Dental College, SVSU
Intake, Uptake and Excretion
D ie t
9 0 0 m g
G U T
3 0 0 m g
e xc re te d
P i
P o o lB o ne
2 5 0 m g
K id ne y
6 0 0 m g
e xc re te d
P H O S P H A T E
6 0 0 m g
2 5 0 m g
S o ft T is s u e
la rge and
rap id
6 Dr. Suhasini GP, Subharti Dental College, SVSU
DIGESTION
• Phosphorous- Organic esters- broken down in stomach
• Plant sources- phytates- liberated by phytate from intestinal bacteria
• High protein diet- meat, milk, eggs & legumes
Dr. Suhasini GP, Subharti Dental College, SVSU
• Absorbed from small intestine (jejunum)
• Active system
• Interferes with Ca absorption- insoluble CaPO4
• Fe & Al- form insoluble phosphates like some other
cations- absorption
Dr. Suhasini GP, Subharti Dental College, SVSU
• One third ingested phosphate- gut (unabsorbed)- lost with feces
• Of the absorbed phosphate- major part excreted through kidney
• Certain amount- secreted- digestive juice, and unabsorbed part appears with the feces
Dr. Suhasini GP, Subharti Dental College, SVSU
• PTH- principal factor controlling renal excretion of phosphate
• Inj of PTH into blood- increases excretion of phosphate- Decreased level in blood
• Vit D- affects renal phosphate excretion
• Deficiency of vitamin- increases excretion
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Functions
• 70 kg adult- 700 gms of phosphorous
• 15% is present in soft tissue (100gm)
• Component of many compounds essential to cellular processes
Eg: Nucleic acids, ATP, Co- enzymes, phospholipids- cell membrane
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• Mineralized tissue • Phosphorylated metabolites (ATP) Degradation of glucose- glucose 6-phosphate, creatine
phosphate, etc.)
• DNA, RNA (part of genetic material) • Phospholipids • Free ortho- & pyro- phosphates • Phosphoenzymes (Enzymes, many are regulated,
activated by phosphorylating/dephosphorylating)
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HORMONAL INFLUENCE OF PHOSPHOROUS METABOLISM
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Role of PTH
• Inhibits renal reabsorption of phosphate
(Increased phosphate excretion in urine - decreases reabsorption of PO4 in the proximal tubule
Increased reabsorption of Ca in distal tubules)
• Stimulates bone resorption
• Stimulates synthesis of calcitriol
Net effect of PTH ↓ serum phosphate
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Actions of Vit D (Calcitriol)
• Stimulates GI absorption of both calcium and phosphate
• Stimulates renal reabsorption of both calcium and phosphate
• Stimulates bone resorption (Mobilization of P from bone)
Net effect of calcitriol ↑ serum phosphate
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Overview of Calcium-Phosphate Regulation
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Etiologies of Hyperphosphatemia
Increased GI Intake
Phospho-Soda
Decreased Urinary Excretion
Renal Failure
Low PTH (hypoparathyroidism)
thyroidectomy
I131 treatment for Graves disease of thyroid cancer
Autoimmune hypoparathyroidism
Cell Lysis
Rhabdomyolysis
Tumor lysis syndrome
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Hyperphosphatemia
• Rhabdomyolysis
• Cardiomyopathy
• Respiratory insufficiency (P depletion)
• Erythrocyte dysfunction
• Nervous dysfunction
• Phosphate trapping
• Metabolic acidosis etc
Dr. Suhasini GP, Subharti Dental College, SVSU
Etiologies of Hypophosphatemia Decreased GI Absorption
Decreased dietary intake (rare in isolation)
Diarrhea / Malabsorption
Phosphate binders (calcium acetate, Al & Mg containing antacids)
Decreased Bone Resorption / Increased Bone Mineralization
Vitamin D deficiency / low calcitriol
Osteoblastic metastases
Increased Urinary Excretion
Elevated PTH (as in primary hyperparathyroidism)
Vitamin D deficiency / low calcitriol
Fanconi syndrome
Internal Redistribution (due to acute stimulation of glycolysis)
Refeeding syndrome (seen in starvation, anorexia, and alcholism)
During treatment for DKA
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Hypophosphatemia
• Interference with renal reabsorption of metabolites- ca, P, H20- interfers with matrix mineralisation- rickets/ osteomalcia
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REFERENCES
• Textbook of medical physiology by Guyton & Hall; 10th Edition
• The physiology & biochemistry of the mouth by G Neil Jenkins; 4th Edition
• Textbook of physiology by Prof. A. K. Jain
• Shafers.Textbook of oral pathology.Ed 6th
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Thank you
Dr. Suhasini GP, Subharti Dental College, SVSU