pp 6 calcium
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Calcium
Hertanto W Subagio
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Overview
The most abundant mineral in the body
The fifth most abundant elemen in the body
99% in the bones and teeth- as an integral part of bone structure
- as a Ca bank
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Physiological function
Structural component of bones and teeth
- hydroxyapatite
- will maintain calcemia at bones expense
Role in biochemical reactions- muscle contraction
- blood clotting
- enzymes and hormones activation- transmission of nerve impulses
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Sources
Milk and milk product
Sardines
Oysters
Cauliflowers
Brocolli
Legumes
Dried fruits
Ca carbonate (40%)
Ca citrate ( 21%)
Ca phosphate (8%)
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Bioavailability of Ca from selected foods
> 50% absorbedcauliflower, broccoli, ca-fortified foods and beverages
30% absorbed
milk, Ca-fortified soy milk, cheese, yogurt
20% absorbed
almonds, sesame seeds, beans
< 5 % absorbed
spinach
Also depends on the mixture of the foods
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Absorption
Occurs primarily in the upper part of the small intestine
because Ca requires a pH < 6 to stay in solution in an
ionic state.
Depends on the active vit D.
Human absorb about 25% ca in the food, however, when
the body needs extra Ca absorption might reach as high
as 60%.
Older people < young people
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Ca absorption
Enhancer
- Stomach acid
- Vit D (helps to make Ca binding protein)
- Lactose- Growth hormones
Inhibitor
- high P intakes
- high fiber diet ( phytate, oxalate)
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Transport, Storage, and Excretion
Each cell has a critical need for calcium, obtaining it fromthe blood stream.
This critical need is probably the reason humans have
such excellent hormonal systems to control blood
calcium. Normal blood Ca can be maintained despite an
inadequate Ca intake, as much is stored in in bones.
Blood Ca is a poor measure in Ca status.
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Ca Homeostatis
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Ca Homeostasis
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Functions of Calcium
Bone development and maintenance
Blood clotting
Transmission of nerve impulses Muscle contraction
Cell metabolism
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Bone development and maintenance
Bone contain osteoblasts and osteoclasts
Osteoblast secrete a collagen matrix, which form the supportstructures of the bone. They mature osteocytes and then secretebone mineral, which cause bone mineralization.
Osteoclast continually break down bone in areas where bone is not
needed. Bone turnover (bone remodelling) represent a cycle of bone
breadown by osteoclasts, followed by bone rebuilding byosteoblasts. More bone being build in areas put under high stress.
Most bone is built from infancy through the late adolescent
Bone loss begins in mid adulthood and increases significantly atmenopause in women. In men bone loss is slow and steady fromaround age 30.
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Promotion and Prevention of bone resorption
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Ca in bones
Ca salts form crystals (hydroxyapatite)on a matrix of the collagen
During mineralization give strength and
rigidity to the maturing bones
Types : cortical and trabecular (spongy)bones
Bones are gaining and losing minerals
continuously in an ongoing process of
remodelling. Turnover in teeth is not as rapid as in
bone
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Cortical and trabecular bone
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Blood clotting
Ca ions participate in in several reactions in thecascade that leads to the formation of fibrin, the
main protein component of blood clot.
For example in the conversion of prothrombin tothrombin.
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Mechanism of Blood clotting
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Transmission of nerve impulse
When a nerve impulse reaches its target site , the impulse is
transmitted across the junction between the nerve and its target
cell, called synapse
The arrival of the impulse at the target site stimulates an influxof Ca ions into the nerve from the extracellular medium.
The rise in intracellular Ca ions then triggers the release of
neurotransmitters from synaptic vesicles, which are
responsible for storing the neurotransmitter until needed.
The released neurotransmitter then carries the impulse across
the synapse to the target cells.
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The release of a neurotransmitter
Nerve impulses, by opening Ca2+ channels
Stimulate the fusion of synaptic
vesicles containing
neurotransmitters with the cell
membrane of the nerve
terminals
This leads to exocytosis and the
release of a neurotransmitter
that will bind to and stimulates
the postsynaptic membrane of
nearby cells
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Muscle contraction
When a skeletal muscle is stimulated by a nerve impulse
from the brain, Ca ions are released from intracellular
stores within the muscle cells.
The increased Ca ions permits the contractile proteins to
slide along each other, leads to muscle contraction.
To allow for subsequent relaxation, Ca ions are returned
to intracellular stores, and the contractile proteins slide
appart.
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Mechanism of muscle contraction
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Ca in cell metabolism
Ca ions help regulate
metabolism in the cell by
participating in the calmodulin
system.
When Ca enters a cell and
binds to the protein
calmodulin, the resulting
protein-calcium complex can
regulate the activity of various
enzymes, including one that
breaks down glycogen to manyunits of glucose 1-phosphate.
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Hypercalcemia
Hypertension
Anemia
Neurological disturbance Urolithiasis
Calcification of other tissues
Increased HCl secretionpeptic ulcer
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Hypocalcemia
Increased in membrane excitability (
hypocalcemic tetany).
Cardiac depression
- hypototension
- bradycardia
- heart block
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osteoporosis
Ca loss is the effect, not the cause
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Osteoporosis: Definition
A skeletal disorder characterized by compromised bone
strength predisposing to an increased risk of fracture.
Osteoporosis Prevention, Diagnosis, and Therapy. NIH Consensus Statement 2000 March 27-29; 17(1): 1-36.
Dempster, DW, et al., JBMR 2000; 15 (1): 20.
Normal Bone Osteoporotic Bone
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WHO, Guidelines for Preclinical Evaluation and Clinical Trials in Osteoporosis, 1998.
T-Score
World Health Organization (WHO)
Osteoporosis Guidelines
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Established Risk Factors for Osteoporosis
Genetic Female
White or Asian races
Thin or low peak bone
mass Family history of
fractures
Medical Menopause
Menstrual dysfunction orearly menopause
Glucocorticoid, thyroid
use
Lifestyle Smoking
Excessive alcohol use
Lack of exercise
Nutritional
Low calcium Vitamin D deficiency
Vitamin A excess