pp 6 calcium

7/30/2019 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

pp 6 calcium

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