WATER AND ELECTROLYTES

 

 

Water Is the Liquid of Life

Water is truly the liquid of life. Often, we dont think about the many ways it affects our lives. We use water each day for things like drinking, cooking, cleaning, manufacturing, irrigation, transportation, power generation, and recreation.

We must understand our part in protecting our water supplies. It is also important for us to know how water affects our lives and wellness.

Almost three-fourths of the world is covered with water, which may lead you to think we have plenty of usable water. Actually, only about 1 percent of the water on earth is in a place and form that we can use. Almost 97 percent of the earths water is salt water. This salt water is found in oceans, seas, salt lakes, and rivers.

That leaves only 3 percent fresh water on the earth. Most of this fresh water is frozen in the polar ice caps.

Waters Role in Our Health

The human body is approximately 65 percent water. This water performs a lot of functions that are critical to staying healthy. While we can live for a long time without food, we can survive only a few days without water or some other liquid to hydrate our bodies. Water is important in many of the bodys activities.

Water (H2O) is composed of two atoms of hydrogen and one of oxygen.

Each hydrogen atom is linked to the oxygen atom by a single covalent bond. Because oxygen is more electronegative than hydrogen, there is a separation of charge within the molecule. The electron distribution in oxygen-hydrogen bonds may therefore be described as polar or asymmetrical. If water molecules were linear, then the bond polarities would cancel each other out, and water would be nonpolar. However, water molecules have a bent geometry with a bond angle of 104.5

Molecules such as water, which have an unbalanced distribution of charge, are called dipoles. Such molecules have opposite charges on two points. When molecular dipoles are subjected to an electric field, they orient themselves in the direction opposite to that of the field.

Water's properties are directly related to its molecular structure.

One consequence of the large difference in electronegativity of hydrogen and oxygen is that the hydrogens of one water molecule are attracted to the unshared pairs of electrons of another water molecule. This noncovalent relationship is called a hydrogen bond. In addition to hydrogen bonds, three other types of noncovalent interactions play important roles in determining the capacity of water to interact with other types of molecules. These are electrostatic interactions, van der Waal's forces, and hydrophobic interactions. Because biological reactions take place in a water medium, an understanding of noncovalent bonding is important.

Covalent bonds between hydrogen (electropositive atoms) and oxygen are polar. For example, each of the two hydrogens in water molecules will be weakly attracted to oxygen atoms in other nearby water molecules. The resulting intermolecular "bonds" act as a bridge between adjacent molecules. Although considerably weaker than ionic and covalent bonds, hydrogen bonds are stronger than most other types of noncovalent bonds.

Electrostatic interactions occur between oppositely charged atoms or groups. An important aspect of all electrostatic interactions in aqueous solution is the hydration of ions that occurs. Because water molecules are polar, they are attracted to charged ions. Shells of water molecules, referred to as solvation spheres, cluster around both positive and negative ions. As ions become hydrated, the attractive force between them is reduced, and the charged species dissolves in the water.

Water, sometimes called the universal solvent.

Melting point of water 0 oC; boiling point 100 oC.

Water plays an important role in the thermal regulation of living organisms. Water's high heat capacity coupled with the high water content found in most organisms (between 50% and 95%, depending on species) contributes to the maintenance of an organism's internal temperature. The evaporation of water is used as a cooling mechanism, since it permits large losses of heat. For example, an adult human may eliminate daily as much as 1200 g of water in expired air, sweat, and urine. The associated heat loss may amount to approximately 20% of the total heat generated by metabolic processes.

Water is a remarkable solvent.

Water's ability to dissolve a large variety of ionic and polar substances is determined by its dipolar structure and its capacity to form hydrogen bonds. Salts such as sodium chloride (NaCI) are held together by ionic (or electrostatic) forces. They dissolve easily in water because dipolar water molecules are attracted to the Na+ and Cl- ions.

Organic molecules with ionizable groups and many neutral organic molecules with polar functional groups also dissolve in water. Their solubility is due primarily to the hydrogen bonding capacity of water. Nonpolar compounds are not soluble in water. Because they lack polar functional groups, such molecules cannot form hydrogen bonds.

Liquid water molecules have a limited capacity to ionize to form a hydrogen ion (H+) and a hydroxide ion (OH-). (H+ does not actually exist in aqueous solution. In water a proton combines with a water molecule to form the hydrated hydrogen ion, H3O+, commonly called a hydronium ion. For convenience, however, the hydrated proton is usually represented as H+.)

The state and distribution of water in the organism.

There are two water compartments in the body:

1.     Intracellular water

2.     Extracellular water

Extracellular fluid is divided into:

1.     interstitial fluid

2.     plasma

 

The intracellular fluid (ICF) is the fluid within cells. The interstitial fluid (IF) is part of the extracellular fluid (ECF) between the cells. Blood plasma is the second part of the ECF. Materials travel between cells and the plasma in capillaries through the IF.

 

 

Distribution of water in an adult man, weighing 70 kg

Compartment

Body weight (%)

Volume (l)

Total

60

42

ICF

40

28

ECF

20

14

Interstitial fluid

15

10,5

Plasma

5

3,5

 

Biological role of water:

1.     Water is an essential constituent of cell structures and provides the media in which the chemical reactions of the body take place and substances are transported.

2.     It has a high specific heat for which, it can absorb or gives off heat without any appreciable change in temperature.

3.     It has a very high latent heat. Thus, it provides a mechanism for the regulation of heat loss by sensible or insensible perspiration on the skin surface.

4. The fluidity of blood is because of water

5. Water is the most suitable solvent in human body

6. Dielectric constant : Oppositely charged particles can coexist in water. Therefore, it is a good ionizing medium. This increases the chemical reactions.

7. Lubricating action: Water acts as lubricant in the body to prevent friction in joints, pleura, conjunctiva and peritoneum

Water balance. Endogenous water.

Water balance is an equilibrium persists between the intake and output of water in the body. In addition to other factors, certain hormones, such as ADH, vasopressin, oxytocin and aldosterone influence the regulatory mechanism of body water.

A. Water intake : Water is supplied to the body by the following processes:

1. Water taken orally (1200-1300ml).

2. Along with food (1000ml).

3. Oxidation of foodstuffs : Fats, proteins and carbohydrates yield water after combustion. Fats produce 107 ml./lOO gm., proteins 41 ml./lOO gm. and carbohydrates 56 ml./100 gm. (metabolic water 300-400 ml).

B. Water losses :

Water is lost from the body by 4 routes:

1. Evaporation from skin and lungs.

2. Kidneys, as urine.

3. The intestines, in the the feces.

4. Perspiration.

C. Additional water losses in disease:

1. Water loss is more in diarrhea and vomiting and these losses can be fatal in infants.

2. In kidney disease, renal water loss is more.

3. In fever, insensible losses may rise much higher than normal.

4. Patients in high environmental temperatures also sustain extremely high extrarenal water losses.

Regulation of Water Metabolism

There are several factors which regulate the water metabolism in the body; they are as follows:

1. Antidiuretic hormone or Vasopressin:

Posterior pituitary releases ADH which has got the property to enhance water reabsorption in the distal tubules and collecting ducts. Water permeability gets increased.

2. Hypothalamus:

There is a centre in hypothalamus known as a thirst centre; whenever there is dehydration in the body, osmoconcentration of plasma takes place which eventually stimulates the thirst centre producing thirst as a result of which animal gets provoked to drink the required amount of water. Besides this, osmoconcentration of plasma also stimulates supraoptic and paraventricular nuclei of hypothalamus; nerve impulses from them are responsible to increase the release of vasopressin from neurohypophysis into the blood. Lesions in the supraopticoparaven-tricular region or in the neurohypophysis produce diabetes insipidus in which large volume of dilute (hypotonic) urine is passed, may be 10 litres or so a day. Diabetes insipidus is due to the abnormalities in the ADH secretion. In primary diabetes insipidus, there is less secretion of the ADH hormone which is usually due to the destruction of the hypothalamic-hypophyseal tract either from a basal skull fracture, or tumor, or infection. Besides, diabetes insipidus may be hereditary also.

3. Adrenal Cortex and Water loss:

Loss of electrolytes and the loss of water from the body are closely interlinked. Adrenal cortex plays a very important role in governing the reabsorption of water by the renal tubules. The excretion of sodium and potassium by the kidneys is controlled by a steroid hormone called aldosterone which is secreted by the zona glomerulosa of the adrenal cortex. In man, aldosterone first increases the elimination of potassium and hydrogen ion and then decreases the excretion of sodium without any change in GFR.

Aldosterone acts mainly at the distal tubule but its effect on sodium reabsorption may be partly at the proximal tubule. Apart from its action on the renal tubuie, aldosterone increases the reabsorption of sodium from the secretions of the intestinal mucosa and of the salivary and sweat glands. Thus, the body content of Na+ rises and that of K+ decreases.

Aldosterone is not the only cortical hormone affecting water balance. The diuretic response to a water load gets impaired in patients whose adrenal glands are destroyed by diseases like Addison's disease or are removed after operation. The ability to deal normally with water is, however, restored by the administration of cortisone or hydrocortisone.

4. Rennin-Angiotensin system:

This system is also involved in the regulation of blood pressure and electrolyte metabolism. The primary hormone involved is angiotensin II, an octapeptide formed from angiotensiongen. A decrease in circulating blood volume stimulates rennin secretion from kidneys which in turn promotes angiotensin formation in plasma. Angiotensin II stimulates the synthesis and secretion of aldosterone and the release of vasopressin, and thereby increases renal absorption of Na+ and H2O.

5. Prostaglandins:

They are also believed to help maintain glomerular filtration inspite of hypotension, by causing renal vasodilation. They may also increase urinary loss of water by inhibiting the antidiuretic effect of vasopressin and by increasing the urinary sodium.

6. Solutes:

Osmotic effect of Na+ helps to retain water in extracellular fluids. Elevation in plasma Na+ raises the ECF volume in primary aldosteronism while an increase in urinary Na+ raises the urinary water output in Addison's disease. K+ helps to retain water in the cells, whereas, plasma proteins do help to retain water in the body by their osmotic effects. Increase in urinary urea or excretion of glucose in urine increases osmotically the urinary loss of water (osmotic diuresis).

TRANSPORT IN AND OUT OF CELLS

Water and Solute Movement

 

Cell membranes act as barriers to most, but not all, molecules. Development of a cell membrane that could allow some materials to pass while constraining the movement of other molecules was a major step in the evolution of the cell. Cell membranes are differentially (or semi-) permeable barriers separating the inner cellular environment from the outer cellular (or external) environment.

Water potential is the tendency of water to move from an area of higher concentration to one of lower concentration. Energy exists in two forms: potential and kinetic. Water molecules move according to differences in potential energy between where they are and where they are going. Gravity and pressure are two enabling forces for this movement. These forces also operate in the hydrologic (water) cycle. Remember in the hydrologic cycle that water runs downhill (likewise it falls from the sky, to get into the sky it must be acted on by the sun and evaporated, thus needing energy input to power the cycle).

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The hydrologic cycle. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates and WH Freeman, used with permission.

 

Diffusion is the net movement of a substance (liquid or gas) from an area of higher concentration to one of lower concentration. You are on a large (10 ft x 10 ft x10 ft) elevator. An obnoxious individual with a lit cigar gets on at the third floor with the cigar still burning. You are also unfortunate enough to be in a very tall building and the person says "Hey we're both going to the 62nd floor!" Disliking smoke you move to the farthest corner you can. Eventually you are unable to escape the smoke! An example of diffusion in action. Nearer the source the concentration of a given substance increases. You probably experience this in class when someone arrives freshly doused in perfume or cologne, especially the cheap stuff.

Since the molecules of any substance (solid, liquid, or gas) are in motion when that substance is above absolute zero (0 degrees Kelvin or -273 degrees C), energy is available for movement of the molecules from a higher potential state to a lower potential state, just as in the case of the water discussed above. The majority of the molecules move from higher to lower concentration, although there will be some that move from low to high. The overall (or net) movement is thus from high to low concentration. Eventually, if no energy is input into the system the molecules will reach a state of equilibrium where they will be distributed equally throughout the system.

 The Cell Membrane

The cell membrane functions as a semi-permeable barrier, allowing a very few molecules across it while fencing the majority of organically produced chemicals inside the cell. Electron microscopic examinations of cell membranes have led to the development of the lipid bilayer model (also referred to as the fluid-mosaic model). The most common molecule in the model is the phospholipid, which has a polar (hydrophilic) head and two nonpolar (hydrophobic) tails. These phospholipids are aligned tail to tail so the nonpolar areas form a hydrophobic region between the hydrophilic heads on the inner and outer surfaces of the membrane. This layering is termed a bilayer since an electron microscopic technique known as freeze-fracturing is able to split the bilayer.

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Diagram of a phospholipid bilayer. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates and WH Freeman, used with permission.

 

Phospholipids and glycolipids are important structural components of cell membranes. Phospholipids are modified so that a phosphate group (PO4-) replaces one of the three fatty acids normally found on a lipid. The addition of this group makes a polar "head" and two nonpolar "tails".

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Structure of a phospholipid, space-filling model (left) and chain model (right). Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates and WH Freeman, used with permission.

 

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Diagram of a cell membrane. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates and WH Freeman, used with permission.

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Cell Membranes from Opposing Neurons (TEM x436,740). This image is copyright Dennis Kunkel at, used with permission.

 

Cholesterol is another important component of cell membranes embedded in the hydrophobic areas of the inner (tail-tail) region. Most bacterial cell membranes do not contain cholesterol.

Proteins are suspended in the inner layer, although the more hydrophilic areas of these proteins "stick out" into the cells interior as well as the outside of the cell. These integral proteins are sometimes known as gateway proteins. Proteins also function in cellular recognition, as binding sites for substances to be brought into the cell, through channels that will allow materials into the cell via a passive transport mechanism, and as gates that open and close to facilitate active transport of large molecules.

The outer surface of the membrane will tend to be rich in glycolipids, which have their hydrophobic tails embedded in the hydrophobic region of the membrane and their heads exposed outside the cell. These, along with carbohydrates attached to the integral proteins, are thought to function in the recognition of self. Multicellular organisms may have some mechanism to allow recognition of those cells that belong to the organism and those that are foreign. Many, but not all, animals have an immune system that serves this sentry function. When a cell does not display the chemical markers that say "Made in Mike", an immune system response may be triggered. This is the basis for immunity, allergies, and autoimmune diseases. Organ transplant recipients must have this response suppressed so the new organ will not be attacked by the immune system, which would cause rejection of the new organ. Allergies are in a sense an over reaction by the immune system. Autoimmune diseases, such as rheumatoid arthritis and systemic lupus erythmatosis, happen when for an as yet unknown reason, the immune system begins to attack certain cells and tissues in the body.

 

Cells and Diffusion

 

Water, carbon dioxide, and oxygen are among the few simple molecules that can cross the cell membrane by diffusion (or a type of diffusion known as osmosis ). Diffusion is one principle method of movement of substances within cells, as well as the method for essential small molecules to cross the cell membrane. Gas exchange in gills and lungs operates by this process. Carbon dioxide is produced by all cells as a result of cellular metabolic processes. Since the source is inside the cell, the concentration gradient is constantly being replenished/re-elevated, thus the net flow of CO2 is out of the cell. Metabolic processes in animals and plants usually require oxygen, which is in lower concentration inside the cell, thus the net flow of oxygen is into the cell.

Osmosis is the diffusion of water across a semi-permeable (or differentially permeable or selectively permeable) membrane. The cell membrane, along with such things as dialysis tubing and cellulose acetate sausage casing, is such a membrane. The presence of a solute decreases the water potential of a substance. Thus there is more water per unit of volume in a glass of fresh-water than there is in an equivalent volume of sea-water. In a cell, which has so many organelles and other large molecules, the water flow is generally into the cell.

Animated image/movie illustrating osmosis (water is the red dots) and the selective permeability of a membrane (blue dashed line).

Hypertonic solutions are those in which more solute (and hence lower water potential) is present. Hypotonic solutions are those with less solute (again read as higher water potential). Isotonic solutions have equal (iso-) concentrations of substances. Water potentials are thus equal, although there will still be equal amounts of water movement in and out of the cell, the net flow is zero.

 

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Water relations and cell shape in blood cells. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates and WH Freeman, used with permission.

 

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Water relations in a plant cell. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates and WH Freeman, used with permission.

One of the major functions of blood in animals is the maintain an isotonic internal environment. This eliminates the problems associated with water loss or excess water gain in or out of cells. Again we return to homeostasis. Paramecium and other single-celled freshwater organisms have difficulty since they are usually hypertonic relative to their outside environment. Thus water will tend to flow across the cell membrane, swelling the cell and eventually bursting it. Not good for any cell! The contractile vacuole is the Paramecium's response to this problem. The pumping of water out of the cell by this method requires energy since the water is moving against the concentration gradient. Since ciliates (and many freshwater protozoans) are hypotonic, removal of water crossing the cell membrane by osmosis is a significant problem. One commonly employed mechanism is a contractile vacuole. Water is collected into the central ring of the vacuole and actively transported from the cell.

 

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The functioning of a contractile vacuole in Paramecium. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates and WH Freeman, used with permission.

 

Active and Passive Transport

Passive transport requires no energy from the cell. Examples include the diffusion of oxygen and carbon dioxide, osmosis of water, and facilitated diffusion.

 

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Types of passive transport. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates and WH Freeman, used with permission.

 

Active transport requires the cell to spend energy, usually in the form of ATP. Examples include transport of large molecules (non-lipid soluble) and the sodium-potassium pump.

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Types of active transport. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates and WH Freeman, used with permission.

 

Carrier-assisted Transport

The transport proteins integrated into the cell membrane are often highly selective about the chemicals they allow to cross. Some of these proteins can move materials across the membrane only when assisted by the concentration gradient, a type of carrier-assisted transport known as facilitated diffusion. Both diffusion and facilitated diffusion are driven by the potential energy differences of a concentration gradient. Glucose enters most cells by facilitated diffusion. There seem to be a limiting number of glucose-transporting proteins. The rapid breakdown of glucose in the cell (a process known as glycolysis) maintains the concentration gradient. When the external concentration of glucose increases, however, the glucose transport does not exceed a certain rate, suggesting the limitation on transport.

In the case of active transport, the proteins are having to move against the concentration gradient. For example the sodium-potassium pump in nerve cells. Na+ is maintained at low concentrations inside the cell and K+ is at higher concentrations. The reverse is the case on the outside of the cell. When a nerve message is propagated, the ions pass across the membrane, thus sending the message. After the message has passed, the ions must be actively transported back to their "starting positions" across the membrane. This is analogous to setting up 100 dominoes and then tipping over the first one. To reset them you must pick each one up, again at an energy cost. Up to one-third of the ATP used by a resting animal is used to reset the Na-K pump.

 

Types of transport molecules

Uniport transports one solute at a time. Symport transports the solute and a cotransported solute at the same time in the same direction. Antiport transports the solute in (or out) and the co-transported solute the opposite direction. One goes in the other goes out or vice-versa.

 

Vesicle-mediated transport |

Vesicles and vacuoles that fuse with the cell membrane may be utilized to release or transport chemicals out of the cell or to allow them to enter a cell.

Exocytosis is the term applied when transport is out of the cell.

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This GIF animation is from Note the vesicle on the left, and how it fuses with the cell membrane on the right, expelling the vesicle's contents to the outside of the cell.

 

Endocytosis is the case when a molecule causes the cell membrane to bulge inward, forming a vesicle.

Phagocytosis is the type of endocytosis where an entire cell is engulfed. Pinocytosis is when the external fluid is engulfed. Receptor-mediated endocytosis occurs when the material to be transported binds to certain specific molecules in the membrane. Examples include the transport of insulin and cholesterol into animal cells.

Endocytosis and exocytosis. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates and WH Freeman, used with permission.

 

Dehydration

Dehydration may be defined as a state in which loss of water exceeds that of intake, as a result of which body's water content gets reduced. In this state, the body is in negative water balance.

Causes

1. Primary dehydration: There is purely water depletion and no salt depletion. It occurs in following states:

(a) Due to deprivation of water as generally happens during desert travelling.

(b) In mental patients who refuse to drink water/fluids.

(c) In those who keep such a 'fast' in which water/fluid is completely restricted.

(d) It occurs more quickly during fever or in the high temperature of the environment.

(e) Excessive water loss due to vomiting, prolonged diarrhoea, gastroenteritis.

(f) Due to excretion of large quantities of urine or sweat.

This type of dehydration raises the concentration and osmotic pressure of extracellular fluid as a result of which there is consequent outflow of the intracellular water to the ECF; thus, ECF volume gets largely restored but there becomes deficiency of water inside the cells as a result of which they suffer from osmoconcentration; symptoms of which include dry tongue, poor salivation, dry shrunken skin, nausea, reduced sweating and intense thirst.

When the blood becomes hypertonic, it lowers the urinary output and also makes the urine concentrated as a result of which there is less elimination of NPN and other acids which leads to acidosis and eventually coma. Death occurs in man due to renal failure, acidosis, intracellular hyperosmolality, circulatory collapse or neural depression, when body water falls by 20%.

Drinking of concentrated saline like sea-water or failure of Na+ excretion (e.g., in Cushing's syndrome and Primary aldosteronism) may cause hypertonicity of ECF which in turn is responsible for withdrawal of water from tissue cells, dehydration of tissues, but a rise in ECF volume. Mg2+ of sea-water may be responsible for an increased intestinal loss of water due to its osmotic effect in the intestinal lumen.

 

2. Secondary dehydration:

The concentration of the electrolytes of the body fluids is maintained constant either through The elimination or retention of water. The reduction or elevation in the total electrolytes, which affects the basic radicals chiefly i.e. Na (extracellular) and K (intracellular) and the acid radicals HCO3 and Cl are accompanied by a corresponding increase or decrease in the volume of body water which is eventually the cause of intracellular edema; as a result of which there is slowing of circulation and impairment of urinal functions. All this causes an individual to become weak bodily.

 

3. Dehydration due to injection of hypertonic solution:

When a highly concentrated solution of sugar or salt is injected into the body of an individual, the osmotic pressure of blood will increase which results in the flow of fluid from the tissues into the blood unless an equilibrium is reached. Consequently, the blood volume increases. This increased blood volume soon returns to normal by the loss of excess material through excretion which finally causes a net loss of body water producing dehydration.

 

 

Effects of dehydration

There are various side effects of dehydration as follows, which may be overcome as soon as the body gets hydrated; otherwise the consequences are serious and may even lead to death.

1. Disturbance in acid-base balance.

2. Loss of body weight due to the reduction in tissue water.

3. Rise in nonprotein nitrogen (NPN) of blood.

4. Dryness, wrinkling and looseness of the skin.

5. Elevation in the plasma protein concentration and chloride.

6. Rise in the temperature of body due to reduction of circulating fluid.

7. Increased pulse rate and reduced cardiac output.

8. Exhaustion and collapse i.e. death.

 

Correction of dehydration

1. Ordinarily, sodium chloride solution may be given parenterally to compensate the loss.

2. In several disorders like diarrhoea, gastroenteritis, pancreatic or biliary fistulas, etc., a mixture of two-thirds isotonic saline solution and one-third sodium lactate solution (M/6) should be administered intravenously.

3. Dehydration is a burning problem in several disorders like diabetes mellitus, Addison's disease, uremia, shock and extensive burns which is difficult to correct by the above two ways.

 

Water Intoxication

 

This condition is generally caused due to the retention of excess water in the body and can occur due to renal failure, excessive administration of fluids parenterally and hypersecretion of ADH. Symptoms of water intoxication include nausea, headache, muscular weakness, etc.

MINERALS

Minerals serve a variety of functions in our bodies. Structurally, minerals provide rigidity and strength to the teeth and skeleton; the skeletal mineral components also serve as a storage depot for other needs of the body. Minerals, allowing for proper muscle contraction and release, influence nerve and muscle functions. Other functions of minerals include acting as cofactors for enzymes and maintaining proper acid-base balance of body fluids. Minerals are also required for blood clotting and for tissue repair and growth.

Mineral Categories

Based on the amount of each mineral in the composition of our bodies, the 16 essential minerals are divided into two categories: major and trace minerals. To maintain body levels of major minerals, these minerals are needed daily from dietary sources in amounts of 100 mg or higher. In contrast, trace minerals are required daily in amounts less than or equal to 20 mg (Box 8-3). Although the required amounts differ greatly between the major and trace minerals, each is absolutely necessary for good health. The dietary reference intakes (DRIs) listed in this chapter for minerals are those for young adults ages 19 to 24. Levels for other groups are noted when special mention is needed. Keep in mind that because nutrition is a relatively young science, new functions of minerals as nutrients in the human body are still being discovered.

 

 

 

 

 

Food Sources

The prime sources of minerals include both plant and animal foods. Valuable sources of plant foods include most fruits, vegetables, legumes, and whole grains. Animal sources consist of beef, chicken, eggs, fish, and milk products. The discussions of individual minerals highlight the best food choices. In contrast to vitamins, minerals are stable when foods containing them are cooked. As inorganic substances, they are indestructible. Minerals may leach into cooking fluids but are still able to be absorbed if the fluid is consumed.

Although plants may contain an abundance of various minerals, some minerals in plants are not easily available to the human body. Bioavailability refers to the level of absorption of a consumed nutrient and is of nutritional concern. Binders such as phytic and oxalic acids may bind some minerals to the plant fiber structures. Binders are substances in plant foods that combine with minerals to form indigestible compounds, making them unavailable for our use. The amount of plant minerals available for absorption may depend on minerals in soils in which the plants are grown.

Minerals from animal foods do not have the same bioavailability issues. In fact, minerals from animal foods can be absorbed more easily than those from plants. However, fat content may be an issue for some animal foods. Lower fat sources of dairy and meat products are usually available and provide the same levels of minerals at a higher nutrient density. Liver is often cited as a good source of minerals such as iron and zinc. Liver is also high in cholesterol and saturated fats and may contain toxins to which the animal may have been exposed. These factors, combined with liver's somewhat unusual taste, often leaves the impression that good nutrient intake depends on eating healthy food that tastes bad. Other sources of each nutrient may be more appealing and equally as nutritious.

Food processing may reduce the amount of minerals available for absorption. Processing oranges into orange juice does not affect potassium levels naturally contained in oranges. However, processing whole wheat flour into white flour does cause significant losses of minerals because the whole grain is not used. Iron is the only mineral returned to white flour through enrichment; zinc, selenium, copper, and other minerals are permanently lost. Because we have difficulty obtaining high enough levels of some minerals naturally, fortification of manufactured foods has become commonplace. It is in this manner that food processing can serve the nutrient needs of consumers while still addressing the issues of convenience and taste appeal. Salt fortified with iodine is available; dry cereals have added minerals such as iron and an assortment of vitamins and other minerals.

 

Minerals as Nutrients within the Body

Structure

Minerals are inorganic substances. As elements, they are found in the rocks of the earth. Their tendency to gain or lose electrons makes them electrically charged. Thus they have special affinities for water, which itself carries positive and negative charges. As we consume plant and animal foods containing minerals, we can incorporate them into our body structures (bones), organs, and fluids.

Digestion and Absorption

During the process of digestion, minerals (as inorganic substances) are separated from the foodstuff in which they entered our bodies. Digestion does change the valence states of some minerals, which changes their ability to be absorbed. However, their structure is not changed, to prepare them for absorption. As noted earlier, bioavailability affects the level of minerals we actually absorb. Generally, consuming a variety of whole foods ensures an adequate intake of minerals. Mineral deficiencies for which Americans tend to be at risk are iron, calcium, and zinc. Concerns and strategies for consuming appropriate amounts of these nutrients are discussed later in this chapter.

Metabolism

Because minerals are inorganic and do not provide energy, they are not metabolized by the human body. Instead some minerals assist as cofactors of metabolic processes.

Biological role of potassium and sodium

Potassium ions promotes the protein synthesis by ribosomes;

number of enzymes require K+ for maximum activity (for example in the glycolitic sequence K+ is required for maximum activity of pyruvate);

metabolically supported gradients of Na+ and K+ across the cell membrane are involved in the maintenance of the membrane potential of excitable tissues, which is the vehicle for transmission of impulses in the form of an action potential;

K+ ions enhance the function of parasympathetic nervous system and acetylcholine action on the nervous terminals in muscles;

K+ ions reduce the exciting influence of ions on muscles;

a proper plasma K+ level is essential for the normal heart functioning more precisely for relaxation of miocardium (diastole);

 

 

Sodium ions play the main role in regulation of osmotic pressure and retention of water in an organism;

sodium chloridum of blood plasma is the main origin of hydrochloric acid formation;

Na+ ions take part in the formation of a short-term memory.

 

 

 

 

Regulation of the Na and K metabolism in organism.

 

Sodium content in blood plasma is 130-150 mmol/l. Potassium content in the blood is 3.4-5.3 mmol/l, this is only 2 % of all potassium content in the human body.

Kidneys are the main regulator of body Na+ and normally 98 % of the body loss of Na+ occurs in the urine. If more Na+ is ingested, its excretion in the urine increases. If less Na+ is ingested or if plasma Na+ falls due to any reason, Na+ may totally dissappear from the urine. This is brought about through the aldosteron which increases the tubular reabsorption of Na+ in the distal part of the nephrons.

 

The various factors can affect the urinary escretion of Na+:

 

1. When glomerular filtration is broken, the amount of Na+ filtered is smaal, the renal tubules reabsorb all the filtered Na+ resulting in Na+ retention and hypernatriemia.

2. When tubular reabsorption is broken (in chronic renal failure), it resulting in excessive urinary loss of Na+ and hyponatriemia.

3. Severe acidosis aggravates Na+ loss in the urine because the ranel tubules may fail to produce NH3 in sufficient amount to buffer H ions in the tubular lumen; in this way, there arises a defficiency of NH4 ions which could be excreted in the urine in exchange for Na+ ions.

4. Diuresis. Most Na+ is lost in diuretic conditions as diabetes mellitus, diabetes insipidus or after administration of mannitol or urea (osmotic diuretics).

5. Hormones. The main hormones, regulating Na+ metabolism, are mineralocorticoids and atrial natriuretic peptide (ANP). The mineralocorticoids, aldosterone and deoxycorticosterone, increase Na+ reabsorption from the tubular fluid and therefore their excess causes Na+ retention. In addition, these hormones increase the elimination of more K+ and Na+ in the urine. A greater formetion of aldosterone (primary aldosteronism or Conns syndrome) is associated with an increased Na+ retention in the body (hypernatriemia) with hypokaliemia and metabolic alkalosis. Conditions like congestive heart failure, cirrhosis of the liver and nephrotic syndrome also lead to a greater formation of aldosterone (secondary aldosteronism).

The atrial natriuretic peptide is produced y the atrial muscle fibers. It increases the urinary loss of Na+.

The severe decrease of Na+ in the extracellular space may lead to hypovolemia, hypotension, circulatory collapse and syncope.

Patients with Na+ excess show a raised venous pressure, peripheral and pulmonary edema with eventual respiratory failure. Cerebral symptoms may be seen due to hyperosmolality of the plasma.

The main causes of hyperkaliemia are:

1. Release of cellular K+ from muscle tissue (hard traumas), in intravascular hemolysis, after extensive surgical operations.

2. Renal failure the K+ secretion by the distal tubules is decreased and retention of K+ takes place.

3. Chronic dehydration and shock (associated with decreased formation of urine and K+ retention).

4. Acidosis H+ ions displace K+ ions from the cells.

5. Addisons disease.

Symptoms of hyperkaliemia are exerted mostly on the heart and nervous systems. When the serum K+ level is above 7 mmol/L, ECG changes are observed, bradycardia and arrhytmias appear. The heart becomes more susceptible to vagal stanstil, and heart may stop in diastole.

Hypokaliemia may be observed in decreased K+ intake (in starvation, malnutrition states such as kwashiorkor), in excessive renal loss (in metabolic alkalosis, using of some diuretics, such as furosemid, in renal tubular disorders, in hyperaldosteronism Iincreased production of aldosterone), in severe vomitting or diarrhea. Symptoms are: anorexia, nausea, muscle weakness and mental depression. Irregular pulse and a fall of blood pressure are observed.

 

Function of Na+, K+-ATP-ase

 

Most animal cells maintain intracellular K+ and extracellular Na+ at a relatively high concentration due to the operation of the special transmembrane enzyme which is called Na+, K+-ATP-ase. Na+, K+-ATP-ase use the energy derived from ATP to drive the transport of Na+ and K+ ions against the concentration gradient. The Na+, K+-pump is a prominent example of a primary transporter. Na+, K+-ATP-ase has the molecular weight of about 250000 to 300000 and contains two different types of subunits. The large subunit is the portion of the molecule that is phosphorylated as ATP is hydrolyzed. It has binding sites for Na+, K+ and appears to extend through the entire thickness of the cell membrane. The smaller subunit is a glycoprotein and contains sialic acid as well as glucose, galactose and other hexose residues.

 

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 Biological role of Calcium and Phosphorus

Calcium forms about 1% of adult body weight. It is the most abundant electrolyte in the human body due to its structural function for the skeleton. Normal serum or plasma calcium level is 2.3-2.75 mmol/l. More than 99% of calcium in the body occurs in bones as its phosphate and carbonate; only 0.03% of the total body calcium occurs in blood. The bone calcium is constantly exchanged with the calcium of interstitial fluid and this process is regulated primarily by the parathyroid hormone, active vitamin D and also by calcitonin.

Milk and milk products are the best dietary sources of calcium.

 

Other good sources are egg yolk, leafy vegetables and hard drinking water. In spite of their high calcium content, some vegetable foods such as spinach contain also oxalates and benzoates and are a poor source of calcium because calcium oxalate and benzoate thus formed are insoluble and are not absorbed.

Functions of calcium in the body:

1. Calcium salts take part in bone and tooth development. Deficient supply of calcium leads to rickets in children and osteomalacia in adults. Sufficient calcium intake must be ensured in early life to build up the skeletal reserves. If this is not done, then there occurs an increased incidence of osteoporosis in old age because at that time deficiency of sex hormones especially in females results in calcium mobilization from bones leading to osteoporosis.

2. The clotting of blood needs calcium ions.

3. By regulating the membrane permeability calcium ions control the excitability of nerves. If plasma ionized calcium level falls markedly, tetany results in which spasms of various muscle groups occur. Death may occur from convulsions or from laryngospasm. An excess of plasma calcium depresses nervous activity.

4. Calcium ions act as a cofactor or activator of certain enzymes. A protein namely calmodulin is present within cells, which can bind calcium. The calmodulin-calcium complex becomes attached to certain enzymes which ire activated. Such enzymes include adenylate cyclase, Ca2+ ATPase, phosphorylase kinase, myosin light chain kinase, phosphodiesterasc and phospholipase A; this mechanism also is required for the release of acetylcholine at the neuromuscular junctions.

5. Calcium ions take part in the contraction of muscle including heart muscle and are involved in the excitation-conraction coupling mechanism. In increased plasma calcium, heart stops in systole. In addition, a high plasma calcium decreases conduction of cardiac impulses and thus can produce heart block.

6. Calcium ions are responsible for initiating contraction in vascular and other smooth muscles. Calcium ions enter through specific channels just as is the case with cardiac muscle. Drugs that block these channels [Ca2+ channel blockers] have profound effect on the contractility of cardiac and smooth muscle as well as on the conduction of impulses within the heart. These drugs find use in the treatment of angina pectoris, cardiac arrhythmias and hypertension.

7. Calcium is essential for maintaining the integrity of capillary wall. In its deficiency, capillary walls become fragile and there is increased permeability of capillaries.

8. Calcium ions are involved in exocytosis and thus have an importrole in stimulus-secretion coupling in most exocrine and endocrine glands, e.g. the release of catecholamines from the adrenal medulla, neurotransmitters at synapses and histamine from mast cells is dependent upon Ca2+.

9. Some hormones exert their influence through Ca2+. For example, the effect of adrenaline on the liver cells to increase glycogenolysis is partly due to an increased Ca2+ within these cells which is independent of cAMP.

 

 

 

Osteoporosis is a disease affecting many millions of people around the world. It is characterized by low bone mass and micro-architectural deterioration of bone tissue, leading to bone fragility and a consequent increase in risk of fracture.

The incidence of vertebral and hip fractures increases exponentially with advancing age (while that of wrist fractures levels off after the age of 60 years). Osteoporosis fractures are a major cause of morbidity and disability in older people and, in the case of hip fractures, can lead to premature death. Such fractures impose a considerable economic burden on health services worldwide Worldwide variation in the incidence and prevalence of osteoporosis is difficult to determine because of problems with definition and diagnosis.

The most useful way of comparing osteoporosis prevalence between populations is to use fracture rates in older people. However, because osteoporosis is usually not life-threatening, quantitative data from developing countries are scarce. Despite this, the current consensus is that approximately 1.66 million hip fractures occur each year worldwide, that the incidence is set to increase four-fold by 2050 because of the increasing numbers of older people, and that the age-adjusted incidence rates are many times higher in affluent developed countries than in sub Saharan Africa and Asia

In countries with a high fracture incidence, rates are greater among women (by three- to four-fold). Thus, although widely regarded in these countries as a disease that affects women, 20% of symptomatic spine fractures and 30% of hip fractures occur in men.

In countries where fracture rates are low, men and women are more equally affected . The incidence of vertebral and hip fractures in both sexes increases exponentially with age. Hip-fracture rates are highest in Caucasian women living in temperate climates, are somewhat lower in women from Mediterranean and Asian countries, and are lowest in women in Africa. Countries in economic transition, such as Hong Kong Special Administrative Region (SAR) of China, have seen significant increases in age-adjusted fracture rates in recent decades, while the rates in industrialized countries appear to have reached a plateau.

 

Diet, physical activity and osteoporosis

Diet appears to have only a moderate relationship to osteoporosis, but calcium and vitaminDare both important, at least in older populations.

Calcium is one of the main bone-forming minerals and an appropriate supply to bone is essential at all stages of life. In estimating calcium requirements, most committees have used either a factorial approach, where calculations of skeletal accretion and turnover rates are combined with typical values for calcium absorption and excretion, or a variety of methods based on experimentally-derived balance data . There has been considerable debate about whether current recommended intakes are adequate to maximize peak bone mass and to minimize bone loss and fracture risk in later life, and the controversies continue Vitamin D is obtained either from the diet or by synthesis in the skin under the action of sunlight. Overt vitaminDdeficiency causes rickets in children and osteomalacia in adults, conditions where the ratio of mineral to osteoid inbone is reduced.Poor vitaminDstatus in the elderly, at plasma levels of 25-hydroxyvitamin D above those associated with osteomalacia, has been linked to age-related bone loss and osteoporotic fracture, where the ratio of mineral to osteoid remains normal.

Many other nutrients and dietary factors may be important for long-term bone health and the prevention of osteoporosis. Among the essential nutrients, plausible hypotheses for involvement with skeletal health, based on biochemical and metabolic evidence, can be made for zinc, copper, manganese, boron, vitamin A, vitamin C, vitamin K, the B vitamins, potassium and sodium. Evidence from physiological and clinical studies is largely lacking,and the data are often difficult to interpret because of potential size-confounding or bone remodelling transient effects.

Strength of evidence

For older people, there is convincing evidence for a reduction in risk for osteoporosis with sufficient intake of vitamin D and calcium together, and for an increase in risk with high consumption of alcohol and low body weight. Evidence suggesting a probable relationship, again in older people, supports a role for calcium and vitamin D separately, but none with fluoride.

Strength of evidence with fracture as outcome

There is considerable geographical variation in the incidence of fractures, and cultural variation in the intakes of nutrients associated with osteoporosis and the clinical outcome of fracture. In Table, where the evidence on risk factors for osteoporosis is summarized, it is important to note that the level of certainty is given in relation to fracture as the outcome, rather than apparent bone mineral density as measured by dual-energy X-ray absorptiometry or other indirect methods. Since the Consultation addressed health in terms of burden of disease, fractures were considered the more relevant end-point.

 

 

Disease-specific recommendations

In countries with a high fracture incidence, a minimum of 400--500 mg of calcium intake is required to prevent osteoporosis. When consumption of dairy products is limited, other sources of calcium include fish with edible bones, tortillas processed with lime, green vegetables high in calcium (e.g. broccoli, kale), legumes and by-products of legumes (e.g. tofu). The interaction between calcium intake and physical activity, sun exposure, and intake of other dietary components (e.g. vitamin D, vitamin K, sodium, protein) and protective phytonutrients (e.g. soy compounds), needs to be considered before recommending increased calcium intake in countries with low fracture incidence in order to be in line with recommendations for industrialized countries With regard to calcium intakes to prevent osteoporosis, the Consultation referred to the recommendations of the Joint FAO/WHO.

Expert Consultation on Vitamin and Mineral Requirements in Human Nutrition which highlighted the calcium paradox. The paradox (that hip fracture rates are higher in developed countries where calcium intake is higher than in developing countries where calcium intake is lower) clearly calls for an explanation. To date, the accumulated data indicate that the adverse effect of protein, in particular animal (but not vegetable) protein, might outweigh the positive effect of calcium intake on calcium balance.

The report of the JointFAO/WHOExpert Consultation on Vitamin and Mineral Requirements in Human Nutrition made it clear that the recommendations for calcium intakes were based on long-term (90 days) calcium balance data for adults derived from Australia, Canada, the European Union, the United Kingdom and the United States, and were not necessarily applicable to all countries worldwide. The report also acknowledged that strong evidence was emerging that the requirements for calcium might vary from culture to culture for dietary, genetic, lifestyle and geographical reasons. Therefore, two sets of allowances were recommended: one for countries with low consumption of animal protein, and another based on data from North America and Western Europes.

Biological role of phosphorus

An adult body contains 1 kg phosphate and it is found in every cell of the body. Most of it (about 80%) occurs in combination with calcium in the bones and teeth. About 10% of body phosphorus is found in muscles and blood in association with proteins, carbohydrates and lipids.

Biochemical functions:

1.                 Phosphorus is essential for the development of bones and teeth.

2.                 It plays a central role for the formation and utilization of high-energy phosphate compounds (ATP, GTP, creatine phosphate etc.).

3.                 Phosphorus is required for the formation of phospholipids, phosphoproteins and nucleic acids (DNA and RNA).

4.                 It is essential component of several nucleotide coenzymes eg. NAD, NADP, pyridoxal phosphate, ADP, AMP.

5.                 Several proteins and enzymes are activated by phosphorylation.

6.                 Phosphate buffer system is important for the maintenance of pH in the blood as well as in the cells.

 

Role of vitamins and hormones in regulation of phosphorous metabolism

The hormones calcitriol, parathyroid hormone and calcitonin are the major factors that regulate the plasma phosphorus within a narrow range (1.2-2.2mmol/l). Calcitriol is the biologically active form of vit.D. It acts at 3 different levels (intestine, kidneys and bone).

Calcitriol increases the intestinal absorption of calcium and phosphate. Calcitriol along with parathyroid hormone increases the mobilization of calcium and phosphorus from bone.

Calcitriol is also involved in minimizing the excretion of Ca and P through the kidney, by decreasing their excretion and enhancing reabsorption.

Calcitonin inhibits the reabsorption of phosphorus in kidneys. Thus, calcitonin decreases the phosphorus content in blood. Parathyroid hormone decreases serum phosphorus and increases urinary PO4 (increase phosphorus excretion in urine).

 

Biological role of magnesium.

Half of magnesium occurs in the inorganic matter of bones and the rest occurs in soft tissues and body fluids.

Blood plasma contains 0.8-1.2 mmol/l of Mg.

Nuts, legumes, chlorophyll and whole grains are very good sources of magnesium.

Functions of Mg in the body:

1. It takes part in the formation of complex salts of bones and teeth.

2. It acts as a cofactor for many enzymes.

3. It serves to decrease neuromuscular irritability.

Effects of a high serum Mg2 level - Experimentally, a serum Mg2+ level of 8 mmol/L produces immediate and profound anesthesia and paralysis of voluntary muscles. These effects can be reversed by an intravenous injection of a corresponding amount of Ca2+. Serum Mg2+ tends to rise in renal failure.

Deficiency of Mg may occur in the malabsorptive syndrome, increased renal losses (diuretics, gentamycin intake and primary renal disease), chronic alcoholism, diabetic acidosis, cirrhosis of the liver, primary aldosteronism, hyperparathyroidism, prolonged and severe losses of body fluid and prolonged administration of Mg-free intravenous fluids. Plasma Mg may be lowered after parathyroidectomy (along with hypocalcemia) due to avidity of bones for divalent ions. In acute pancreatitis, Mg may become bound as soaps thus decreasing its plasma level.

 

Symptoms and signs of hypomagnesemia.

1. Neuromuscular disorders - weakness, tremors, muscle fasciculations and sometimes tetany.

2. Central nervous system disorders - personality changes, delirium, psychosis and coma.

 

Biological role of iron.

Iron is part of the structure of many important body constituents, e.g. hemoglobin, myoglobin, enzymes like cytochromes, catalase, xanthine oxidase, mitochondrial α-glycerophosphate oxidase, etc. The iron content of hemoglobin is 0.34%.

Function

Iron is responsible for distributing oxygen throughout our bodies. Oxygen depends on the iron in hemoglobin of red blood cells (erythrocytes) to bring oxygen to all cells. Myoglobin holds oxygen in the muscle cells for quick use when needed.

Because of its ability to change ionic charges, iron also assists enzymes in the use f oxygen by all cells of the body. Iron is conserved and recycled by the body. When red blood cells are old or damaged, the spleen removes their iron component. Some iron is kept in the spleen for later use, and the rest is sent to the liver for processing. From the liver, iron is transported as transferrin to bone marrow and recycled for use in new red blood cells. Some iron is lost through the shedding of tissue cells in urine and sweat and when bleeding occurs; this lost iron must be replaced by dietary sources.

Dietary sources

Animal sources are the best and include liver, red meat and egg yolk. Of the vegetables, spinach and other leafy vegetables are good sources. Dried fruits also contain appreciable amounts of iron.

 

 

Iron is found in both plant and animal sources (Figure 8-5). Heme iron, found in animal sources of meat, fish, and poultry, is more easily absorbed than nonheme iron found in plant foods. Animal sources of iron also contain nonheme iron in ad dition to heme iron. Although egg yolks contain iron, the iron is not absorbed as well as other heme sources. Nonheme iron sources include vegetables, legumes, dried fruits, whole grain cereals, and enriched grain products, especially ironfortified dry cereals.

Increased absorption of iron occurs when dietary sources are consumed with foods containing ascorbic acid (vitamin C).

For example, drinking orange juice or eating slices of cantaloupe with meals increases the amount of nonheme iron absorbed. Absorption of nonheme iron increases in the presence of heme iron. This means that consuming iron from several sources improves absorption of the total iron amounts of heme and nonheme iron.

Factors that inhibit iron absorption include consumption of foods that contain binders (e.g., phytates) and oxalates that keep the dietary iron from separating from plant sources. Tannins in plants, most notably in teas and coffee, can also interfere with iron absorption. Continuous use of antacids and excessive intake of other minerals competes with the absorption sites for iron. Pica, the consumption of nonnutritive substances, creates health problems. When the nonnutritive substances are excreted from the body, minerals are also excreted, which decreases mineral absorption. Pica is discussed in the next section.

 

 

Plasma iron transport

Before iron can leave the intestinal mucosal cells, it is first converted to Fe2+ form. On entering the plasma, it is again oxidized to Fe3 form and is taken up by a pink colored protein called siderophilin or transferrin, having a mol. wt. about 80,000. The transfer of iron to the transferrin is catalyzed by a Cu-containing protein, namely ceruloplasmin. One molecule of siderophilin binds 2 atoms of iron. The absorbed iron is utilized to form products such as heme, etc. and the remaining portion is mostly stored in the body as ferritin in the reticuloendothelial cells and hepatocytes.

Ferritin is a conjugated protein; its iron is in combination with the protein part of the molecule called apoferritin. Apoferritin has a mol. wt. of about 450,000 and is composed of 24 polypeptide subunits; these form an outer shell within which resides a storage cavity for polynuclear hydrous ferric oxide phosphate.

Iron within ferritin molecule occurs as ferric hydroxide-ferric phosphate complex and its iron content may be upto 30%. Ferritin also is present in blood plasma where its level is a good index of iron stores of the body. If iron is in excess, then ferritin molecules aggregate forming hemosiderin (iron content upto 55%). Hemosiderin is stored as microscopically visible golden brown granules because it is insoluble due to its containing a characteristic arrangement of the micelles of Fe(OH)3.

Recently the genes for the human transferrin receptors and ferritin have been discovered and the mechanism of regulation of expression of transfcrrin receptors and intraccllular ferritin in response to the iron supply have been established. When iron is in excess, the synthesis of transferrin receptors is decreased and ferritin production is increased; this favors iron storage. When iron is deficient, then reverse changes occur which lead to a decreased ferritin production that decreases iron storage so that iron can be utilized in the body to a maximum.

 

 

Factors increasing iron absorption from the intestine:

1. Conditions associated with increased rate of erythropoiesis.

2. Low body stores of iron

3. Taking ascorbic acid, succinic add, fructose and sorbitol along with iron - Ascorbic acid favors reduction of Fe3+ to Fe2+; the latter is more readily absorbed. The other compounds make complexes with iron and increase its absorption.

4. Intake of inorganic iron.

Factors inhibiting iron absorption:

1. Malabsorption syndromes.

2. Diarrheal diseases.

3. An excess of phosphates, oxalates and phyfic acid - These form complexes with iron which are insoluble and cannot be absorbed. Vegetable foods have an excess of phosphates and interfere with iron absorption.

4. Subtotal gastrectomy.

5. Surgical removal of the upper small intestine.

6. Food intake along with iron.

7. Antacid therapy.

8. Chronic Infections.

The iron deficiency results in anemia - this is of hypochromic, microcytic type. It is the most common type of anemia being specially present in women of child-bearing age and infants below 1 year of age. The RBCs are smaller in size and have less hemoglobin as well as less mean corpuscular volume RBC count is low but hemoglobin level of blood is proportionately still lower. The color index which is hemoglobin as o of the normal divided by RBC count as % of the normal is therefore below one. In addition to the symptoms which are common to all anemias such as a pale appearance and breath lessness on minor exertion, the patient shows some characteristic features. These include a derangement of epithelial surface such as abnormal nail growth (spoon shaped nails or koilonychia), glossitis, fissures around the corners of the mouth and localized thickening of the mucous lining of the esophagus causing dysphagia (Plummer-Vinson syndrome)

 

 

Anaemia is commonly caused by a lack of iron. The most common cause of lack of iron in the UK is heavy menstrual periods. There are many other causes. Bleeding into the gut is a common cause in older people. Tests may be advised to find the cause of the anaemia. Treatment with iron tablets can correct the anaemia. Other treatments may be advised, depending on the cause.

Blood is made up of a fluid called plasma which contains:

                     Red blood cells - which take oxygen around the body.

                     White blood cells - which are part of the immune system and defend the body from infection.

                     Platelets - which help the blood to clot if we cut ourselves.

                     Proteins - and other chemicals that have various functions.

Red blood cells are made in the bone marrow. Millions of them are released into the bloodstream each day. A constant supply of new red blood cells is needed to replace old ones that break down. Red blood cells contain a chemical called haemoglobin. Haemoglobin transports oxygen from the lungs to all parts of the body. To keep making red blood cells and haemoglobin, you need a healthy bone marrow. Your diet is also important as a source of iron and certain vitamins that you need.

 

 

What is iron-deficiency anaemia?

Anaemia means:

                     You have fewer red blood cells than normal; OR

                     You have less haemoglobin than normal in each red blood cell.

In either case, a reduced amount of oxygen is carried around in the bloodstream. The most common cause of anaemia in the UK is a lack of iron. Iron is needed to make haemoglobin. Anaemia caused by a lack of iron is called iron-deficiency anaemia.

What are the causes of iron-deficiency anaemia?

A normal balanced diet will usually contain enough iron for your body's needs. A low level of iron, leading to anaemia, can result from various causes. Some are more serious than others, and include the following:

Heavy menstrual periods

Anaemia is common in women (of all ages) who have heavy periods. About 1 in 10 women will become anaemic at some point because of this. The amount of iron that you eat may not be enough to replace the iron that you lose during each period. Having heavy periods does not always lead to anaemia. Anaemia is more likely to develop if you have heavy periods and eat a diet that contains little iron.

Pregnancy

A growing baby needs iron and will take it from the mother. Anaemia is common in pregnant women. It is more likely to develop during pregnancy if you eat a diet that has little iron.

Poor absorption of iron

Some conditions of the gut (intestine) lead to poor absorption of various foods, including iron. Coeliac disease is an example.

Bleeding from the gut (intestine)

Several conditions of the gut can lead to bleeding. Sometimes this is sudden - for example, after a burst duodenal ulcer. Vomiting or passing blood is obvious then.

Sometimes the bleeding is not obvious. A constant trickle of blood into the gut can be passed unnoticed in the stools (faeces). The iron that you may lose with the bleeding may be more than you eat. Conditions causing this include: stomach or duodenal ulcers, colitis (inflammation of the large intestine), inflammation of the oesophagus (gullet), piles (haemorrhoids), cancers of the bowel and other rarer bowel disorders.

If you have one of these problems, you may have other gut symptoms such as stomach pains, constipation, or diarrhoea. However, in the early stages of these conditions, you may not have any symptoms and anaemia may be the first thing that is noticed. For example, iron-deficiency anaemia in an older person may be the first indication that bowel cancer has developed.

Medication

Some medicines can sometimes cause bleeding into the gut without causing symptoms. The most common example is aspirin. Other anti-inflammatory painkillers such as ibuprofen, naproxen, and diclofenac may also have this side-effect in some people. (Anti-inflammatory tablets may cause bleeding by irritating the stomach lining which may then lead to bleeding.)

Bleeding from the kidney

A small but regular trickle of blood from various diseases of the kidney or bladder, may not be noticed in the urine. However, enough may be lost to cause anaemia.

Dietary factors

Not eating foods with enough iron is sometimes the cause of iron-deficiency anaemia. This is uncommon in the UK as iron is in meat, liver, green vegetables, flour, eggs and other foods. Some people who have a poor diet with just enough iron to get by, may slip into anaemia if other factors develop. For example, a barely adequate diet combined with a growth spurt in children, or with a pregnancy or with heavy periods may lead to anaemia.

A restricted diet such as a vegan or a limited vegetarian diet sometimes does not contain enough iron.

Traditional diets in some parts of the world contain a high level of chemicals such as phytates and polyphenols. For example, certain types of flat breads (such as chapatis) may contain a high level or phytates. Tea can contain a high level of polyphenols. These chemicals interfere with the way iron is absorbed from the gut. So, if you eat a lot of these foods, it can lead to iron deficiency. For example, iron-deficiency anaemia is common in parts of India where chapatis are a staple food.

Biological role of iodine, fluoride, copper, zinc, selenium and cobalt.

Iodine

The total body contains about 20mg iodine, most of it (80%) being present in the thyroid gland. The only known function of iodine is its requirement for the synthesis of thyroid hormone mainly thyroxin (T4) and triiodothyronin (T3).

Dietary requirements: 100-150micrograms per day.

Sources: Sea food, drinking water, iodized salt.

 

 

Diseases states: Toxic goiter.

 

Fluoride

Functions:

1.It prevents the development of dental caries.

2.It is necessary for the proper development of bones .

3.It inhibits the activities of certain enzymes.

Dietary requirements: 1-2 mg per day.

Sources: Drinking water.

Diseases states: dental caries, fluorosis.

 

Copper

Roles in the Body:

--Absorption and Use of Iron in the Formation of Hemoglobin

Deficiency/Toxicity:

--Anemia/Bone Abnormalities

--Menkes Disease

--Wilsons Disease

Functions:

1.           Its an essential constituent of several enzymes (cytochrome oxidase, catalase, superoxide dismutase etc.)

2.           Its necessary for the synthesis of hemoglobin, melanin and phospholipids.

3.           Ceruplasmin has oxidase activity and thereby facilitates the incorporation of ferric iron into transferrin.

4.           Development of bone and nervous system (myelin requires Cu).

Dietary requirements:2-3 mg per day.

Sources: Liver, kidney, meat, egg yolk, nuts and green leafy vegetables.

Disease status:

1.           Copper deficiency (anaemia).

2.           Menkes disease (defect in the intestinal absorption of copper).

3.           Wilsons disease

Zinc

Functions:

1.           It is an essential component of several enzymes (carbonic anhydrase, alcohol dehydrase etc.)

2.           The storage and secretion of insulin from the beta cells of pancreas requires zinc.

3.           It is require for wound healing.

4.           It is essential for the proper reproduction.

Dietary requirements: 10-15g per day.

Sources: Meat , fish, eggs, milk, nutts.

Disease status:

Zinc deficiency: poor wound healing, anaemia, loss of appetite, loss of taste sensation.

Cobalt

Cobalt is only important as constituent of vit-B12. The functions of cobalt is same as that of vit B12.

 

Selenium

 

Functions:

1.           Selenium along with vit E, prevents the development of hepatic necrosis and muscular dystrophy.

2.           Selenium is involved in maintaining structure integrity of biological membranes.

3.           Selenium prevents lipid peroxidation and protect the cells against the free radicals.

4.           Selenium binds with certain heavy metals and protects the body from their toxic effects.

Dietary requirements: 60-250micrograms.

Sources: Liver, kidneys, seafood.

Toxicity: Selenosis is a toxicity due to very excessive intake of selenium. The manifestation of selenosis includes weight loss, emotional disturbances, diarrhea, hairloss and garlic odour in breath.

 

Chlorine is contained in all biological liquids of the organism.

Functions:

1. As a component of sodium chloride, it is essential in acid-base equilibrium:

2. As chloride ion, it is also essential in water balance and osmotic pressure regulation.

3. It is also important in the production of hydrochloric acid in the gastric juice.

4. Chloride ion is important as an activator of amylase

Sources: It is mainly available as sodium chloride

Daily requirement: 5 10 g

The requirements of NaCI depend on the climate and occupation and on the salt content of the diet. Foods of animal origin contain more NaCI than those of vegetable origin.

Disease state: chloride deficit also occurs when losses of sodium are excessive in diarrhea, sweating; loss of gastric juice by vomiting.

Excretion: it is chiefly eliminated in the urine. Also Cl is excreted in the sweat.

 

Sulphur

 

In the organism sulphur exists both as organic and inorganic compounds

 

Functions:

1. It is present primarily in the cell protein in the form of cysteine and methionine.

2. The cysteine is important in protein structure and in enzymic activity.

3. Methionine is the principal methyl group donor in the body .

4. Sulfur is a constituent of coenzyme A and lipoic acid which are utilized for the synthesis of acetyl-CoA and S-acetyl lipoate, respectively.

5. Sulfur is a component of other organic compounds, such as heparin, glutathione, thiamine, biotin, taurocholic acid, sulfocyanides, indoxyl sulfate, chondroitin sulfate, insulin, penicillin, anterior pituitary hormones and melanin.

Sources:

Sulfur intake is mainly in the form of cystine and methionine present in proteins. Other compounds present in the diet contribute small amounts of sulfur.

Disease state:

1. The serum sulfate concentration is increased in the presence of renal functional impairment, pyloric and intestinal obstruction and leukemia.

2. Marked sulfate retention in advanced glomerulonephritis cause the development of acidosis.

3. An increase in the blood indican concentration (indoxyl potassium sulfate) may occur in uremia.

Excretion: it is excreted in the urine