calcium phosphorus - aligarh muslim universityobjectives by the end of this session you should be...
TRANSCRIPT
CALCIUM & PHOSPHORUS DR. AKIF AHSAN Assistant Professor
Dept. of Biochemistry JNMC, AMU, Aligarh
OBJECTIVES By the end of this session you should be able to:
Define principal elements & trace elements. 1.
Enumerate the functions of Ca & P. 2.
Tell the normal levels of Ca & P in blood. 3.
Discuss the factors affecting the absorption of Ca.
4.
Discuss the role of Vit-D, PTH & Calcitonin in Ca-P homeostasis.
5.
Minerals
Required in relatively large quantities (>100 mg/day) - Principal elements or macronutrients
Required in minute quantities (<100 mg/day) - Trace elements or micronutrients
Ca, P, Mg, Na, K, Cl and S
Fe, I, Cu, Zn, Co, Mn, Mo, Cr, Se and F
CALCIUM
Calcium
Most abundant mineral in human beings.
Total Ca: 1000 grams » 99% is present in bones and teeth (Calcium phosphate)
Different forms of CALCIUM
Hydroxyapatite Ca10(PO4)6(OH)2
in Plasma
45% - free ionized form
45% - bound to proteins
10% - complexed with anions (citrate, sulfate, phosphate)
Typically measured in routine blood tests (9-11 mg/dL).
Physiologically active
Functions of Ca
Formation of bones & teeth
Nerve conduction
Neuromuscular transmission
Excitation & contraction of muscles
Coagulation of blood
Action of hormones
Activation of enzymes
Actin filaments
Synaptic vesicles containing Neurotransmitter molecules
Synapsin-I Reserve Pool
Ca2+
Calmodulin dependent kinase II
ATP
ADP P
Releasable Pool
Neurotransmitter molecules are released by exocytosis
Coagulation of Blood
Some clotting factors (II, VII, IX, and X) require Ca2+(Factor IV): » For their enzymatic action. » To bind with phospholipids (of platelets and
tissues).
Many of the anticoagulants used to prevent in vitro coagulation of blood (Oxalate, citrate & EDTA), act by binding Ca ions.
Action of Hormones
Ionized Ca acts as a second messenger for some of the hormones (Angiotensin, GnRH, TRH, oxytocin).
Moreover, the secretion of hormones which are stored in granular form also requires the presence of Ca ions (Insulin, calcitonin, vasopressin).
Activation of Enzymes
via Calmodulin » activates kinases
Direct activation » pancreatic lipase » enzymes of coagulation pathway
PHOSPHORUS
Phosphorus
Total P: 700 grams » 80% in bones & teeth » Remainder is distributed all over the body (nerves & muscles are particularly rich in P)
Different forms of PHOSPHATE
Hydroxyapatite Ca10(PO4)6(OH)2 in Plasma
Intracellular Phosphate (Phospholipids, DNA, RNA,
ATP, ADP)
Circulating Phospholipids
Inorganic Phosphates (HPO4
2- & H2PO4-)
Physiologically active and is typically measured in routine blood
tests (2.5-4 mg/dL)
Formation of bones & teeth
Formation of high energy compounds
Role in metabolism
Formation of nucleic acids
Formation of membranes
Formation of nervous tissues
Maintenance of pH
Functions of P
Role in Metabolism
P is a constituent of many co-enzymes: » FMN » FAD » NAD » NADP » Thiamine pyrophosphate » Pyridoxal phosphate » Coenzyme A
MCQ
a) Phosphorus b) Sulfur c) Magnesium d) Iron
Which is a trace element?
[KEY: d]
MCQ
a) Calcium phosphate b) Free ionized calcium c) Calcium bound to albumin d) Calcium bound to citrate
Which form of calcium is physiologically active?
[KEY: b]
MCQ
a) Insulin b) Angiotensin c) GnRH d) Oxytocin
Ca2+ acts as a second messenger for all the following hormones, except:
[KEY: a]
MCQ
a) Cycline b) Calmodulin c) Collagen d) Kinesin
A small Ca binding protein that modifies the activity of many enzymes and other proteins in response to
changes of Ca2+ concentration, is known as:
[KEY: b]
ABSORPTION of Calcium
and Phosphorus
Absorption of Ca
Absorption of Ca occurs by an active uptake system in the upper part of small intestine. » 10-20% of the dietary Ca is absorbed.
Ca absorption is affected by: » pH » Calcium : Phosphorus ratio » Proteins » Vitamin-D & Paratharmone
Vit-D & PTH
Active form of Vit-D: Calcitriol » Vit-D is converted into its active form with the help of PTH.
Calcitriol acts on intestinal mucosa and induces the synthesis of: » Ca-binding protein (Calbindin) » Ca-dependent ATPase » Alkaline phosphatase
These are required for the active absorption of Ca.
Cholecalciferol Calcidiol
Calcitriol
Liver
Kidney Hydroxylase Hydroxylase
Ca-binding protein Ca-dependent ATPase Alklaline phosphatase
Calcium absorption
Int. mucosa
Int. mucosa
Plasma Ca
Parathyroid gland
PTH
Released into circulation
Induction
pH
A relatively low pH increases solubility of Ca salts. » This increases Ca absorption.
Proteins
Presence of proteins and amino-acids (lysine & arginine) in the food facilitates the absorption of Ca.
Calcium : Phosphorus Ratio
Oxalic acid, phytic acid and malabsorption syndrome decreases Ca absorption.
The ideal ratio is 1:1 but the absorption may occur satisfactorily as long as the ratio lies between 1:2 and 2:1.
Absorption of P
P is absorbed from the small intestine along with Ca.
If Ca absorption is normal, so will be that of P.
MCQ
a) Calcitriol b) Low pH c) Oxalates d) Amino acids
All of the following factors increase calcium absorption, except:
[KEY: c]
Calcium-Phosphate HOMEOSTASIS
Normal Levels & Requirements
CALCIUM
9-11 mg/dL
1000 mg
Normal plasma level
Daily requirement
PHOSPHORUS
2.5-4 mg/dL
700 mg
Normal plasma level
Daily requirement
Calcium-Phosphate Homeostasis
Body’s property to maintain the normal plasma level of Ca & P.
Ca-P homeostasis is mediated by: » Vit-D (calcitriol) » PTH » Calcitonin
Cholecalciferol (Vitamin D3)
Ergocalciferol (Vitamin D2)
7-Dehydrocholesterol Calcidiol Calcitriol
Vitamin D 25- Hydroxylase
Vitamin D 1α- Hydroxylase
PTH
↓ Serum Phosphate
FGF23
↑ Serum Phosphate
Vitamin-D activation
GI System
Calcium
Phosphate
Renal System
Bones
Endocrine System
Food
Feces
Absorption
Filtration Reabsorption
Urine
Bone Turnover
(Mediated by Hormones)
Calcium, Phosphate
Calcium, Phosphate
Calcium, Phosphate
Calcium, Phosphate
Calcitriol
Calcitriol
PTH PTH, Calcitriol
Calcitonin
Calcitonin
Calcium Phosphate
PTH
GI Tract
Kidneys
Bones FGF-23
Net Effect
Calcitriol: ↑ calcium, ↑ phosphate PTH: ↑ calcium, ↓ phosphate Calcitonin: ↓ calcium, ↓ phosphate
Ca-P homeostasis
Summary
Calcitriol Intestine Kidneys Bones
PTH Intestine Kidneys Bones
Calcitonin Intestine Kidneys Bones
↑ absorption of Ca & P
↑ reabsorption of Ca & P ↑ bone resorption
↑ Ca (& ↓ P ) reabsorption ↑ resorption & ↓ mineralization
↓ reabsorption of Ca & P ↓ bone resorption
↑ Calcium
↑ Phosphate
↑ Calcium
↓ Phosphate
↓ Calcium
↓ Phosphate
Acts via calcitriol
Hormone Organ Action Net Effect
MCQ
a) Calcitriol b) FGF23 c) Decreased serum phosphate d) Increased serum phosphate
Which of the following factors increases the activity of 1α- hydroxylase?
[KEY: c]
MCQ
a) Calcitriol b) PTH c) FGF23 d) Calcitonin
Urinary excretion of phosphate is increased by all, except:
[KEY: a]
MCQ
a) Both A and R are true and R is the correct explanation of A.
b) Both A and R are true but R is NOT the correct explanation of A.
c) A is true but R is false. d) A is false but R is true. e) Both A and R are false
Assertion: PTH decreases serum P levels. Reason: PTH enhances bone resorption.
[KEY: b]
CAN YOU ??? Define principal elements & trace elements. 1.
Enumerate the functions of Ca & P. 2.
Tell the normal levels of Ca & P in blood. 3.
Discuss the factors affecting the absorption of Ca.
4.
Discuss the role of Vit-D, PTH & Calcitonin in Ca-P homeostasis.
5.