1. Calcium and Phosphorus Metabolism
Dr. Rajeev Sharma

2. Functions of Calcium 1. Acts as an external guard of Na+ channels.
2. Necessary for normal neuronal function.
3. An important intracellular second messenger.
4. Necessary for muscle contraction.
5. Necessary for blood coagulation.
So a very important cat ion for normal tissue function .

3. Functions of Phosphorus
1.Found in ATP,ADP,cAMP, 2,3-DPG, many proteins & vital compounds in the body.
2.Phosphorylation & dephosphorylation of proteins – involved in regulation of cell function.
3.Gives rigidity to bones & teeth.
So an important anion for normal tissue function.

4. MAIN ORGANS INVOLVED
They are :
1. G.I.T.
2. Kidneys.
3. Bones.

5. MECHANISM
A triangle :
G.I.T.
E.C.F.
BONES KIDNEYS

6. Distribution of calcium in human body
Total body calcium – 1100g
Plasma calcium –9.4 to10mg/dl (4.8 to meq./ L or 2.4 to 2.5 mmol./L).
98.9% of body calcium is in bones
1% intracellular
0.1% extracellular fluid

7. Distribution of calcium in plasma
41%
1.0 mmol/L
(Inactive)
Diffusible
50%
(1.2 mmol/L)
(Active form)
9%(Di.)
(0.2 mmol/L)
(Citrates,Po4)(Inactive)
Non Diffusible

8. ABSORPTION FROM G.I.T. 1.Occurs actively, mainly from duodenum.
2. Amount absorbed is exactly as much
as is needed by the body.
3. Divalent cations on their own are poorly
absorbed.
4. Under the influence of vit. D about 35%

9. Renal Handling of Calcium
A. : CALCIUM –
a. 59% of the plasma ca. is filtered.
b. 99% of the filtered amount is reabsorbed.
I.90% obligatory in :P.T.,L.H.,Early D.T.
II.10% Selective in :Late D.T.,C.T.,C.D.
( Increased by P.T.H.)

10. Calcium Metabolism Diet Bones 1,000gms Exchangable 20gms GI Tract ECF
(1000mg/day)
Calcium Metabolism
Bones
1,000gms GI
Tract
1000 +
600 mg
Vitamin D+ Absorption
700mg/day
Exchangable
20gms
ECF
1000 mg
Calcitonin,+Vit.D
Secretion
600mg/day
300mg
Resorption
(PTH,Vit.D +)
Stable
980 gms
9900 mg PTH,Vit.D +(Cal- ),
Glomerular Filtrate 10,000mg/ day
Feces
900 mg/day
Urine
100 mg/day

11. Distribution of BodyPhosphorus
Total body phosphorus, gm.
85% in skeleton,14-15% in I.C.F.,<1%
in E.C.F.
Total plasma phosphate 3 to 4mg/dl.

12. Intestinal absorption of phosphorus.
1. Some of it is lost in feces combined
with non absorbed Ca.
2. Rest is easily absorbed.

13. Renal handling of phosphorus
1.Above renal threshold of 1 m.mol./ L,
it is lost in urine.
2. It is strongly stimulated by P.T.H.

14. Phosphorus Metabolism
Diet
900mg/day
Phosphorus Metabolism
Duodenum
& SI
Active Transport/ Passive Diffusion
3mg /Kg/day
ECF
Bone
3mg /Kg/day
90% PT
Glomerular Filtrate
6oo mg./ day

15. BONES
STRUCTURE

16. A. Matrix : Type-1 Collagen Fibers. (90-95%,give tensile strength.)
COMPOSED OF : A. Organic matrix ( 30%) B. Deposits of calcium salts ( 70%)
A. Matrix : Type-1 Collagen Fibers.
(90-95%,give tensile strength.)
Ground substance
(5-10%)
B : Salts : Made of ECF and Proteoglycans, (Chondroitin sulphate & hyaluronicacid)
Salts –Mainly Calcium & Phosphate, (hydroxyapatite crystals ) also, Mg, Na, K, &.carbonate ions form bone salts.
Uranium, Plutonium, Lead, Gold.
Give compressional strength.

18. BONE CELLS

19. TYPES
1. OSTEOBLASTS- Found on outer surface and cavities,forms new bone &
brings about Ca and PO4 exchange
2. OSTEOCYTES-a.Found within osteoid.
b. Formed from osteoblasts.
c. Responsible for Ca & PO4 exchange.
3. OSTEOCLASTS- Found near osteoblasts, reabsorb bone.

21. Hormones which increase osteoblast activity:
Growth hormone
Estrogen
Growth factors
Calcitonin
Hormones which increase osteoclast activity:
Parathyroid Hormone.
Vit. D.in very high conc.

22. DEVELOPMENT OF BONE CELLS

24. BONE PHYSIOLOGY

25. BONE REMODELLING 1. Bone deposition and absorption occurs
continuously.
2. Normally in adults, deposition and absorption are equal.
3. In youngs,deposition> absorption.
4. In olds,absorption > deposition.

26. ADVANTAGES OF BONE REMODELLING
1.It adjusts the bone strength and shape with the stress put on it.
2. Old matrix degenerates gradually and
has to be replaced with a new one. This
maintains it’s strength.

28. Bone formation Osteoblasts secrete collagen & ground substance
Collagen monomers polymerize to form collagen fibers
Resulting cartilage like material that precipitates calcium salts is called Osteoid
Entrapped osteoblasts become quiescent osteocytes

29. Bone Growth

30. CALCIFICATION OF BONES
1. Ca.& Po4, do not precipitate elsewhere
due to inhibition by ? Pyrophosphates.
2. In bones :
PrecipitationofCa.&PO4,(?neutralization of Pyrophosphate) ( Some Amorphous, Most to Hydroxyapatite crystals)

31. 3. Amorphous part remains as such,
which is readily exchangeable with
E.C.F. Ca & PO4.
4. Abnormalities : Precipitation in,
a.Arteriosclerosis.
b.Degenerating tissues.
c.Old blood clots.

32. Calcium exchange between E.C.F and Bones.
1. Occurs within 30 min. to 1 hr.of a change in Ca++ conc. in E.C.F.
2. Buffering occurs between amorphous
Ca.&PO4 in bones on one side and ECF on the other.

33. MECHANISM 1. Osteocytes and Osteoblasts in bone
are in contact with each other, through
cell processes running in canaliculi.
2. Functionally they form one continuous
membrane called Osteocytic Membrane
system (OSM).

34. 3. This separates three different fluid
compartments, general ECF towards
the capillary, ICF within cells and the
bone fluid (B. F.) towards osteoid.
4. There is a Ca++ pump pr. in the membrane towards the ECF side, which pumps Ca from ICF to ECF.

35. 5.O.M.S. is permeable to Ca. & PO4 on
the bone fluid side.

36. Bone resorption Brought about by osteoclasts by :
a. Secretion of proteolytic enzymes, which will
dissolve collagen.
b. Secrete acids, like lactic and citric, which
dissolve minerals.

37. Osteoclast resorbing bone
Integrins
Bone resorbing compartment

38. Bone Diseases A. Osteopetrosis :
Defective osteoclasts – unable to resorb bone.
Steady increase in bone density,
narrowing / distortion of foramina Compression of nerves.
Hematologic abnormalities – crowding of bone marrow cavities.

39. Osteoporosis
1.Aetiology:relative excess of osteoclastic function Loss of bone matrix is marked.
3. Incidence of fracture increases in bones like distal forearm, vertebral body, hips.
4. Commonly seen in old age, post menopausal women, patients immobilized for any reason
5. Prevention: increase calcium intake,exercise.
6. Hormone Replacement Therapy (H.R.T.)

41. FRCTURE HEALING 1. Activation of Osteoblasts.
2. Conversion of Osteoprogenitor cells
to Osteoblasts.
3. Formation of new bone called callus.
4. Increases due to mechanical pressure.