2. INTRODUCTION
Calcis meaning lime
In 1883 Sir Sydney Ringer demonstrated the biological significance
of calcium.
An important aspect of calcium metabolism is plasma
calcium homeostasis, the regulation of calcium ions in the blood
plasma within narrow limits
3. DISTRIBUTION OF BODY CALCIUM
Calcium is the most abundant mineral in the human body. The average adult body
contains in total approximately 1-1.5 kg, 99% in the skeleton in the form of calcium
phosphate salts, the remaining 1% is in the blood, body fluids and soft tissues.
Normal level of plasma calcium is 9-11gm/dl
4. SOURCES OF CALCIUM
The best source of Calcium rich foods is Milk, which is a natural source of Calcium for
both adults, Children and Calcium in it is easly digested.
5. DAILY REQUIREMENT OF CALCIUM
It is most important to note that the body does not produce its own Calcium, Adequate
calcium intake is required.
The recommended amounts of calcium for adults and children
6. Absorption of calcium
Calcium absorption across the intestinal wall into the blood occurs
by two major mechanisms includes
Active transport (transcellularly)
Passive diffusion (paracellularly)
7. Active transport of calcium is dependent on the action of calcitriol and the intestinal
vitamin D receptor (VDR)
Passive diffusion or paracellular uptake involves the movement of calcium between
mucosal cells and is dependent on luminal:serosal electrochemical gradients
8. FACTORS INCRESING THE CALCIUM ABSORPTION
Vitamin D – Calcitriol induces the synthesis of the carrier protein
(Calbindin) in the intestinal epithelial cells & so facilitates the
absorption of calcium.
Parathyroid hormones - Increases calcium transport from the
intestinal cells.
Amino acids - Especially lysine & arginine increase absorption.
Lactose :- Enhance passive Ca uptake; its effect is valuable because of
it presence in milk.
Low pH
9. FACTORS THAT DECREASES CALCIUM ABSOPTION
Phytates - Phytates are substances found in some plant foods that can bind calcium in
the intestine and decrease its absorption.
Oxalates are present in some leafy vegetables which cause formation of insoluble
calcium oxalates .
In malabsorption syndromes , fatty acid is not absorbed , causing formation of
insoluble calcium salt of fatty acid .
High phosphate content will cause precipitation as calcium phosphate.
Absorption is also decreased with increase intake of protein & fiber in diet.
High pH
10. Calcium metabolism in bone has two divisions:
Bone remodeling
Calcium homeostasis
11. BONE REMODELLING
Throughout life, small portions of bone is removed and replaced by
new bone deposition.
For bone remodeling - A set of locally acting chemicals like
interleukins, prostaglandins, estrogen and other hormones are
necessary.
Calcium acts as second messenger for initiation of formation of
bone cells namely,
osteoclasts and osteoblasts which are responsible for bone remodeling.
Eg. ln orthodontic tooth movement.
When the assimilation of calcium from dietary sources is less than the
metabolic requirements and the obligatory losses , then calcium is
withdrawn from the skeleton to maintain the critical concentration of
the element in the blood and tissue fluids.
12. The primary source of available calcium is trabecular bone, not cortical
bone.
The sites of trabecular bone which supply mobile calcium are the jaws,
ribs, bodies of the vertebrae, and the ends of the long bones.
Prolonged depletion results in disorganization and loss of trabeculae,
followed by cortical remodeling or structural failure.
13. CALCIUM HOMEOSTASIS
Calcium homeostasis is the mechanism by
which the body maintains adequate calcium levels.
CALCIUM BALANCE
This term is used to describe the amount of Ca++ either stored or lost by the body over a
specific period of time.
15. Factors regulating calcium level
Three Hormones
VITAMIN-D
PARATHORMONE
CALCITONIN
In humans, when the plasma calcium level rises above its set point, the thyroid gland
releases calcitonine, causing the plasma calcium level to return to normal.
When it falls below that set point, the parathyroid gland release parathyroid hormone
(PTH), causing the plasma calcium level to rise
16. 1. Parathormone -
is a protein hormone secreted by chief cells of the parathyroid gland
Its main function is to increase the blood calcium level by mobilizing
calcium from bone
The rate of formation & secretion of PTH are promoted by low Ca2+
concentration
17. 2. 1,25-dihydroxy cholecalciferol – Calcitriol
Calcitriol is a steroid hormone synthesized in kidney.
It is the activated form of vitamin D.
Its main action is to increase the blood calcium level by increasing
the calcium absorption from the small intestine.
18. 3. CALCITONIN
Calcitonin secreted by parafollicular cells of thyroid gland.
Calcitonin decreases serum calcium level
It inhibits resorption of bone
It decreases the activity of osteocalasts and increases that of osteoblasts
PTH & CALCITONIN are directly antagonistic
Effects of other hormones
Growth hormone –increases the blood calcium level by increasing the intestinal calcium
absorption.
It is also suggested that it increases the urinary excretion of calcium.
Glucocorticoids -Decrease blood calcium by inhibiting intestinal absorption and increasing
the renal excretion of calcium
19. Calcium Excretion
Calcium leaves the body mainly in urine and feces, but
also in other body tissues and fluids, such as sweat
Calcium is excreted partly through the kidneys and mostly
through the intestine. The renal threshold for serum
calcium is 10mg/dl. Calcium gets excreted into the urine
beyond this concentration
.
20. FUNCTIONS OF CALCIUM
1. Development of bones and teeth
2. Muscle contraction
3. Blood coagulation
4. Nerve transmission
5. Membrane integrity and permeability
6. Activation of enzymes
7. Calcium as intracellular messenger
8. Release of hormones
23. 3) Muscle contraction
For muscle contraction, myosin filament should get attached with actin
muscle filament - for this calcium ions are required.
Action potential on Sarcolemma
Ca+ Channels open up
Ca release (from ECF to lCF)
Ca acts as a coupling agent between AP and contraction.
24. Calcium play a vital roles in contraction of heart as well as skeletal
and smooth muscles.
Therefore drugs affecting calcium ion metabolism can be used to treat
hypertension or cardiac contractility.
Activation of enzymes:
Calmodulin is a calcium binding regulatory protein,
Calmodulin can bind with 4 calcium ions
Calcium binding leads to activation of enzymes
Calmodulin is part of various regulatory kinases
Enzymes activated by Ca2+ include pancreatic lipase, enzymes
of coagulation pathway, and rennin
25. Second messenger:
Calcium and cAMP are second messengers for hormones e.g. epinephrine in liver
glycogenolysis
Calcium serves as a third messenger for some hormones e.g, ADH acts through cAMP and
then Ca2+
Myocardium: Ca2+ prolongs systole
In hypercalcemia, cardiac arrest is seen in systole
