CALCIUM METABOLISM

DR NILESH KATE
MBBS,MD
ASSOCIATE PROF
ESIC MEDICAL COLLEGE, GULBARGA.
DEPT. OF PHYSIOLOGY
CALCIUM
METABOLISM

OBJECTIVES.
 Calcium, phosphorus & Magnesium
Metabolism.
 Calcium metabolism
 Phosphorus metabolism
 Magnesium metabolism.
 Bone physiology.
 Function and composition of Bone
 Structural considerations.
 Physiological considerations.

INTRODUCTION.
 Ca, P & Mg principal
elements constitute 60-
80% inorganic material.
 Imp –
 Ca & P for bones & teeth
 Ca & Mg for Neuro-
muscularexcitability.
Saturday, May 12, 2018

CALCITROPIC HORMONES.
 Parathyroid hormones, Calcitonin &
Cholecalciferol are concerned with ca, P & Mg
metabolism.
 Parathyroid hormone related protein (PTHrP) 4th
hormone acts on PTH receptors
 Other hormones – Glucocorticoids, Growth
hormones & Oestrogens.

CALCIUM METABOLISM
PHYSIOLOGICAL AND BIOCHEMICAL
FUNCTIONS.
 Development of bone & teeth.
 Neuromuscular excitation.
 Blood coagulation.
 Membrane integrity and
plasma membrane transport.
 Mediation of intracellular
action of hormones.
 Activation of Enzymes.
 Release of hormones
& neurotransmitters.
 Calmodulin mediated
action of calcium.
 Regulation of
secretory process.
 Contact inhibition.
 Action on heart.

CALCIUM DISTRIBUTION IN
THE BODY.
 Calcium in bones.
 Pool of stable calcium.
 Pool of readily
exchangeable calcium.
 Calcium in plasma.
(9-11 mg/dl)
 Diffusible (6 mg/dl)
 Non-diffusible.
(4mg/dl)
 Calcium balance.
 Absorption of calcium
– of daily intake of
1000 mg 35%
absorbed.
 Exchange of calcium
between bones and
extracellular fluid.
 Rapid exchange
 Slow exchange.

EXCRETION OF CALCIUM
 Faecal excretion of
calcium
 Unabsorbed fraction 650
mg
 Absorbed in the form of
bile, Pancreatic juice,
intestinal secretions 150
mg so total 800 mg/day.
 Urinary excretion of
calcium. – 200 mg/day.

TYPES OF CALCIUM BALANCE
 Neutral calcium
balance
 Positive calcium
balance.
 Negative calcium
balance.

HORMONAL REGULATION OF
PLASMA CALCIUM LEVEL.
 Calcitropic hormones
 Parathyroid hormones
 Active form of vit D
 Calcitonin.
 Parathyroid hormone related protein – acts on
PTH receptors & imp for skeletal development in
Utero.
 Other hormones – Growth hormone, sex hormones

PHOSPHORUS METABOLISM
 Physiological and
biochemical functions.
 Development of bone &
teeth.
 Structural part of
 ATP, GTP
 NAD, NADP
 Second messengers Camp, IP
 Nucleic acid – DNA,RNA
 Activation of enzymes.
 Role in carbohydrate
metabolism
 Phosphate buffer
system.
 Imp intracellular
Anions.

DISTRIBUTION OF
PHOSPHATE IN THE BODY.
 Blood phosphate.
 Plasma levels – 3-5
mg/dl
 3 forms
 Protein bound – 10%
 Free ions – 40%
 Complexed with
cations 50%
 Bones & teeth – 80%
 Muscle & blood – 10%
 Chemical compounds
– 10%.

PHOSPHORUS BALANCE
 Intake & absorption.
 Required - 800 mg/day
 Rich sources – milk,
cereals, leafy
vegetables, meat, eggs.
 Daily intake 1000 mg/d
 Vit D , PTH, Growth
hormone absorption.
 Cortisol & heavy metal

EXCRETION OF PHOSPHATE
 Fecal excretion – 300
mg (30% of Ingested).
 Urinary excretion –
7000 mg filtered /day
 90% reabsorbed.

PHOSPHORUS BALANCE
 Exchange of
phosphate between
extracellular fluid and
soft tissue.
 Exchange of
phosphate between
extracellular fluid and
bone.

REGULATION OF SERUM
PHOSPHATE LEVELS
 Response to Hypocalcaemia is more immediate than
hypophosphatemia.
 Hypophosphatemia is compensated by reduced
urinary loss.

MAGNESIUM METABOLISM
 Functions
 Role in bone & teeth
formation
 Co- factor several enzymes
 For proper Neuro-
muscular function.
 Required for release of
PTH in response to
Hypocalcaemia.

MAGNESIUM METABOLISM
 Distribution of Mg in
the body.
 Total – 25 mg
 10 % in bone with Ca & P
 50% in soft tissue &
body fluids.
 Plasma level- 1.8-2.4
mg/dl

MAGNESIUM BALANCE.
 Daily requirement – 300-500
mg
 Sources – leafy vegetables, nuts
& soyabean
 40% absorbed
 Increased by PTH
 Decreased by Ca, P & Alcohol
 Deficiency compensated by
decreased urinary excretion.

BONE PHYSIOLOGY
 Bone – specialized
tough connective
tissue that forms
skeleton of the body.

FUNCTIONS OF BONE
 Protective function
 Mechanical function
 Movements
 Metabolic function
 Haemopoietic
function.

COMPOSITION OF BONE
 Bone matrix (Osteoid)
 Collagen fibres –
arranged in laminae,
parallel to each other,
 90% of bone matrix – type
1 collagen
 Rich in Glycine, Proline &
Hydroxyproline.
 Ground substances
 Formed by ECF &
proteoglycans

COMPOSITION OF BONE
 Bone salts
 Inorganic component of
bone
 Contains mainly Ca & P
in the form of
Hydroxyappatite crystals
 It strengthen the bone
matrix.

STRUCTURE OF BONE
 Structure of compact
bone.
 Make outer layer of most
bones
 Made up of cylindrical
osteons or Haversion system
 Osteon – several collagen
lamellae concentrically
present arounf haversion
canal which contains blood
vessel, lymph vessel & nerve.

STRUCTURE OF BONE
 Structure of compact
bone.
 In between concentric
layers present
lacunnae contains
osteocytes.
 Haversion canals run
across long axis
connect with each
other also externally by
canals of Volkmann.

STRUCTURE OF BONE
 Structure of trabecular or
spongy bone.
 Present inside compact bone &
makes up 20% of bone
 Made up of thin trabecule
seperated by space
 Trabeculae are covered by
connective tissue – endosteum
containing osteoblasts,
osteoclasts & osteoprogenitor
cells.

CELLS OF BONE
 Osteoprogenitor cells
 Osteoblasts
 Osteocytes
 Osteoclasts.
 Bone lining cells.

CELLS OF BONE
 Osteoprogenitor cells –
stem cells of
mesenchymal origin that
can proliferate and
convert themselves into
osteoblasts
 In the fetus – at sites of
bone formation
 In adults- over periosteum
& endosteum.

CELLS OF BONE
 Osteoblasts – Bone
forming cells.
 Functions
 Role in laying down of the
organic matrix of bone
 Role in calcification.
 Role in bone resorption.
 Fate of osteoblasts.

CELLS OF BONE
 Osteocytes – cells of mature
bones, maintain Ca between
bone & ECF.
 Osteoclasts- Bone removing
cells, giant multinucleated
cells, derived from
monocytes
 Bone lining cells- flattened
cells forming epithelium like
layer on bone surface.

BONE GROWTH
 Ossification – Process
of bone formation.
 2 mechanisms
 Endochondral bone
formation.
 Intramembranous
bone formation.

BONE GROWTH
 Endochondral bone
formation – first
formation of cartilagenous
model replaced by bone
 Intramembranous bone
formation – formation of
bones directly in a fibrous
membrane without
cartilagenous model.

STEPS OF GROWTH OF LONG
BONES
 Formation of a cartilage
model
 Ossification and
calcification by
osteoblasts by at
primary center of
ossification.
 Growth in length & girth
by secondary centers of
ossification.

BONE FORMATION
 Osteoid fromation.
 Bone matrix
mineralization.
 Initiation of
mineralization or
nucleation
 Rapid calcification
after enucleation

BONE FORMATION
 Formation of trabecular
bone.
 Conversion of
trabecular bone to
compact bone.

BONE RESORPTION
 Osteoclasts
 Process of bone
resorption.
 Removal of unmyelinated
osteoid layers
 Attachement of osteoclasts
 Release of proteolytic
enzymes & acids
 Digestion & dissolution of
bone.

REGULATION OF BONE
RESORPTION
 Stimulated by PTH,
Calcitriol, EGF
(Epidermal growth
factor), PDGF,
 Its mediated through
PG, TGF-β, & IL-I

BONE REMODELLING
 Def – process of bone
resorption followed by bone
formation
 Bone remodelling unit
 Phases of bone remodelling
cycle
 Resorption phase
 Formation phase.

PHYSIOLOGICAL SIGNIFICANCE OF
CONTINIOUS BONE REMODELLING
 Bone adjusts its strength
according to stress
 So in athlete, soldiers
bones becomes heavy &
strong.
 Shape of bone rearranged
according to stress
 Old bone becomes
relatively weak & brittle.

CALCIUM METABOLISM

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