Medicine

CHEMISTRY BIOGENIC ELEMENTS

Chemistry biogenic elements.

 

All matter in the Universe occurs in the form of atoms of a small number of elements. There are 92 naturally occurring chemical elements in the Universe.

Almost every one of the chemical elements plays some role in Earth's living systems, however, ~20 elements account for the vast majority of material in living systems.

Minerals are inorganic substances. Minerals are present in all body tissues and fluids. Unlike carbohydrates, fats and proteins, mineral elements do not furnish energy.

Unlike vitamins, the minerals are not destroyed in food preparation. However, they are soluble in water so that some loss will occur if cooking liquids are discarded.

In contrast to the organic substances, which can be considered as energy sources, the inorganic substances do not supply any energy. Their presence is necessary for the maintenance of certain physiochemical conditions which are essential for life.

The mineral element in the body is classified as principal (macronutrients) and trace elements.

For the chemical standpoint of view the living beings two types of constituents:

1.Organic compounds (proteins, carbohydrates, fats) which, though derived from inorganic elements (C, H, O and N), is the chief constituent. These components of about 90 % of the solid matter, remaining 10 % being the inorganic.

2. Inorganic component which, although constitutes a relatively small amount of the total body, is not less important than organic component to maintain the vital activities of a living being.

Elements can be divided into two main groups: essential and non essential elements.

Essential elements are defined as those elements which are indispensable to maintain the normal living state of a tissue or the whole of the body. Those elements divided into macroelements and microelements.

Macroelements are those elements which are required to be present in the diet in amounts more then 1 mg. these elements constitute 60–80 % of all the inorganica minerals in the body. These are 12 elements including carbon, hydrogen, oxygen, nitrogen, sodium, potassium, calcium, magnesium iron, phosphorus, sulphur, and chlorine. Out of these, the first four elements are present in substantial amounts in every body tissue and are derived from dietary carbohydrates, lipids and the proteins. The oxygen is derived directly from the atmosphere also. About 85% of the total oxygen and about 70% of the total hydrogen are present together in the form of water which makes roughly 3/5th of the total body weight. The remaining amount of oxygen and hydrogen, all nitrogen, most of the carbon and some of sulphur are the main components of the substances (carbohydrates, lipids and proteins) which fulfill the basic requirement of tissue structure, and the synthesis of various biochemical substances within these structures. The remaining eight elements are discussed in detail in this chapter.

Microelements are required in very small amounts, nenograms, by the body. These are also oligoelements and include copper, molybdenum, iodine, and fluorine. are those elements which almost in micrograms or called as trace elements or zinc, cobalt, manganese,

Non-essential elements: The remaining elements are not actually non-essential, but as their function in the body is yet unknown, these are called as non-essential elements. These include bromine, boron, silicon, arsenic, nickel, aluminium, lead, stannic, vanadium and titanium.

Principal minerals required by the body are sodium, potassium, calcium, magnesium, phosphorus, sulfur and chlorine.

These comprise 70 percent of the total mineral of the body contents. In addition, copper, zinc, cobalt, manganese, molybdenum, iodine, fluorine.

Basic functions performed by the minerals are:

1. As structural components of body tissues.

2. In the maintenance of acid-base balance.

3. In the regulation of body fluids.

4. In transport of gases.

5. In muscle contractions.

These biogenic elements are divided into:

­       six major biogenic elements (elements found in almost all of Earth's living systems, often in relatively large quantities);

­       five minor biogenic elements (elements found in many of Earth's living systems, and/or in relatively small quantities);

­       trace elements (essential elements necessary only in very small quantities to maintain the chemical reactions on which life depends, or elements found only a very few of Earth's living systems).

­       Highly toxic elements ! Hg, Cd, Cr, Arsenic (As), Lead (Pb)  As all heavy metals, they accumulate throughout the food chain, affecting more strongly higher organisms, including man at the top of the food "pyramid" Mercury and Arsenic tend to appear in the nature quite spontaneously, originating from some anthropogenic (human) sources as well as from geologic formations and released by local chemical conditions.

CALCIUM

Calcium is present in the body in the largest amount of all the minerals present in the body. Calcium comprises 2 percent of the body weight. RBC is devoid of calcium. The normal serum level is 9 – 11 mg percent.

Calcium is present in three forms:

1. Ionized form.

This form is physiologically active form.

2. Protein bound fraction.

On the far right we see some lamellar bone, looking like strata of geologic layers of earth. Into such bone, cones of cutting blood vessels penetrate. They then organize bone around their path of penetration forming bone in long layered tubes. We see those in cross section on the left. They are called Haversian Tubules (take a wild guess who they are named after).

 Cells are seen in layers around a central canal (Haversian Canal). Radiating micro tubules reach out intercommunicating.

Cells within bone (osteo) can make ("blast") or degrade and remove ("clast") bone substance. Osteoblasts lay down bone and osteoclasts digest bone. How active is all this? Well, depending on who you are, roughly one third of the bone you had yesterday isn't the bone you have today.

The layering and bundles of layered tubes are of cells and sheets of tissue made of very tough fiber called bone collagen. A bone with all of its calcium leached out can be tied in a knot. On and through that structure, a very special crystalline form of calcium is formed called hydroxyappetite. That stiffens the bone to make it hard.

Bone gets strength from two things.

1) What it is made from (kind of bone), and

2) How it is shaped and organized.

Hydroxyappetite figures in both aspects of strength. The first is kind of obvious. Some stuff is tougher than other stuff. But shape is very important. Tubes are stronger than rods. Tension and compression struts vastly support structures (look at power towers). As with certain crystals - such as those used in phonographs (remember those) - when pressure is placed on them, they polarize and exhibit an electric charge. A needle jiggling in a plastic track while pressing against a crystal will reflect the jiggling as a fluctuating charge which magnified gives us music - and we listen.

The compression of forces of daily activity on hydroxyappetite gives us zones of charge to which the osteoblasts listen. They respond by putting more bone substance where forces generate such charges. Where such charges fail to form, bone - always being dissolved - wheedles away. The form of bone follows function. In other words, as was spoken by Hypocrites a few years ago, "That which is not used, wastes away." The paraphrase is, "Use it or lose it."

This had to be rediscovered when perfected devices which held fractured bone pieces absolutely rigidly, better than ever before ... produced poorer healing. Without SOME movement, bone formation is not very good.

Body Distribution of Calcium and Phosphate

There are three major pools of calcium in the body:

Intracellular calcium: A large majority of calcium within cells is sequestered in mitochondria and endoplasmic reticulum. Intracellular free calcium concentrations fluctuate greatly, from roughly 100 nM to greater than 1 uM, due to release from cellular stores or influx from extracellular fluid. These fluctuations are integral to calcium's role in intracellular signaling, enzyme activation and muscle contractions.

Calcium in blood and extracellular fluid: Roughly half of the calcium in blood is bound to proteins. The concentration of ionized calcium in this compartment is normally almost invariant at approximately 1 mM, or 10,000 times the basal concentration of free calcium within cells. Also, the concentration of phosphorus in blood is essentially identical to that of calcium.

Bone calcium: A vast majority of body calcium is in bone. Within bone, 99% of the calcium is tied up in the mineral phase, but the remaining 1% is in a pool that can rapidly exchange with extracellular calcium.

As with calcium, the majority of body phosphate (approximately 85%) is present in the mineral phase of bone. The remainder of body phosphate is present in a variety of inorganic and organic compounds distributed within both intracellular and extracellular compartments. Normal blood concentrations of phosphate are very similar to calcium.

Fluxes of Calcium and Phosphate

Maintaining constant concentrations of calcium in blood requires frequent adjustments, which can be described as fluxes of calcium between blood and other body compartments. Three organs participate in supplying calcium to blood and removing it from blood when necessary:

The small intestine is the site where dietary calcium is absorbed. Importantly, efficient absorption of calcium in the small intestine is dependent on expression of a calcium-binding protein in epithelial cells.

Bone serves as a vast reservoir of calcium. Stimulating net resorption of bone mineral releases calcium and phosphate into blood, and suppressing this effect allows calcium to be deposited in bone.

This form is physiologically inert.

In combination with citrates.

Protein bound fraction is non-diffusible whereas other two fractions are diffusible.

Functions

1. Calcium along with phosphorus is essential for bones and teeth formation.

2. In blood coagulation.

Calcium activates the conversion of prothrombin to thrombin.

3. In milk clotting.

4. In enzyme activation.

Calcium activates large number of enzymes such as adenosine triphosphatase (ATPase), succinic dehydrogenase, lipase etc.

5. In muscle contraction.

6. In normal transmission of nerve impulses.

7. In neuromuscular excitability.

Regulation of Blood Calcium Level

1. Indirect factors. Those factors which have an effect on calcium absorption. Under this comes dietary factors which have been discussed in the absorption of calcium.

2. Direct factors. Those which have direct effect on blood calcium. These are:

а. Hormones

i. Parathyroid hormone regulates the concentration of ionized serum calcium

ii. Calcitonin lowers calcium level by inhibiting bone absorption and thus decreases the loss of calcium from bones.

b. Serum proteins

Decrease in serum proteins will result in decrease in total calcium level as most of the calcium bound to protein will be less.

с. А reciprocal relationship exists between calcium and phosphorus in the blood. Increase in serum phosphorus causes decrease in serum calcium and vice versa.

MAGNESIUM

Magnesium is an essential constituent of the tissues and body fluids, but little is known regarding its metabolism or requirements. It ranks next to potassium among the, cations of intracellular fluids.

Sources. Magnesium is widely distributed in vegetable (chlorophyll) and animal tissues. The important sources are almonds, cereals, beans, green vegetables, potatoes and cheese.

Absorption: The absorption of magnesium. from the bowl resembles that of calcium in many respects. Most of the absorption (about 44 % of the ingested Mg) takes place from the small intestine and little or none from the large intestine. An excessively high intake of fat, phosphate, calcium, and alkalies appear to diminish its absorption from the upper intestine by influencing the solubility of magnesium salts. Parathyroid hormone has little effect on the absorption as well as excretion of magnesium.

The role played by vitamin D in the absorption of magnesium is also not well known.

Distribution: The adult human body contains about 20 – 25 gm. (2000 – 2500 m. equiv.) of magnesium, which is distributed in different body

Magnesium, in contrast to calcium, shows а, tendency to remain inside the blood cells. About 70 to 85% of the serum magnesium is diffusible, the remainder being bound to plasma proteins. In certain respects, there exists а reciprocal relationship between magnesium and calcium, and magnesium and phosphate concentrations in the serum, е.g. in oxalate, poisoning, а decrease in serum calcium is accompanied by an increase in magnesium, whereas administration of vitamin D produces an increase in serum phosphate and а decrease in serum magnesium.

Functions:

1. Mg2+ ions serve as activators of important enzymes, including phosphorylase, phosphoglucomutase, enolase, peptidase, alkaline phosphatase, RNA polymerase, DNA polymerase acid several others.

2. It exerts an effect on neuromuscular irritability similar to that of Са2+, high levels inducing depression and low levels tetany.

3. In the body, magnesium and calcium act as antagonists to one other and counteract certain effects of one another. For instance, the marked depression of the central peripheral nervous system associated with hypermagnesium is reversed promptly by intravenous administration of calcium.

Excretion: Like ca1cium, magnesium is excreted in the faeces and urine. Under normal conditions about 50 to 80 per cent is excreted in the faeces (magnesium of food, bile and digestive secretions) and the remainder by the kidneys. The average urinary excretion is usually over 100 mg. or 10 m-equiv. per day. The amount depends very much on the intake, which may be between 17 and 34 m-equiv. per day. Administration of acidifying substances (e.g. NH4Cl) is followed by increased urinary elimination of magnesium (as of calcium).

Requirements: Minimal requirements recommended for magnesium in the diet are 300 mg./day for adult women and 350 mg./day for adult men. Several dietary substances which interfere with the retention of magnesium may increase the requirements as high as 700 to 800 mg/day. These substances include calcium, protein, vitamin D, alcohol, etc.

SODIUM

Sodium is the principle cation of the extracellular fluid.

Functions

1. In the regulation of acid base balance.

2. In the maintenance of osmotic pressure of the body fluids.

3. In the preservation of normal irritability of muscles and permeability of the cells.

The normal serum sodium level is 133-146 mEq/l.

Increased level of sodium in the serum is called Hypernatremia. Hypernatremia occurs in:

1. Gushing disease.

2. Administration of ACTH.

3. Administration of sex hormones.

4. Diabetes insipidous.

5. After active заеабпц.

Low levels of sodium in serum is called Hyponatremia. Hyponatremia occurs in:

1. Acute Addison's disease.

2. Vomiting, diarrhea.

3. Severe burns.

4. Intestinal obstruction.

5. Nephrosis.

6. Any situation where there is active sweating and we take

POTASSIUM

Potassium is the principal cation of the intracellular fluid.

Functions

1. Intracellular cation in acid-base balance.

2. In muscle contraction, particularly in cardiac muscle.

3. Conduction of nerve impulse.

4. Cell membrane function.

The normal concentration of potassium in the serum is 3.5 – 5.5 mEq /l.

Increased level of potassium in serum is called Hyperkalemia.

Hyperkalemia occurs in:

1. Addison's disease.

2. Advanced chronic renal failure.

3. Dehydration.

4. Shock.

Low levels of potassium in serum give to hypokalemia.

Hypokalemia occurs in:

1. Diarrhea.

2. Metabolic alkalosis.

3. Familial periodic paralysis.

Potassium is required during glycogenesis. This potassium is withdrawn from the extracellular fluid giving rise to hypokalemia.

IRON

Total iron content in the body is 3.5 gm. 70 percent of this iron is present in hemoglobin.

Biologically important compounds of iron are hemoglobin, myoglobin, cytochromes, catalases, peroxidase. In all these compounds iron is present as heme form or porphyrin form. In addition to these iron is present in non-heme form called non-heme iron.

Non-heme iron is present as ferritin (а stored form of iron) and transferring (а transport form of iron).

Functions of iron

1. As hemoglobin, in the transport of oxygen.

2. In cellular respiration, where it functions as essential component of enzymes involved in biological oxidation such as cytochromes с, с,, а,, etc.

Absorption of iron

The maximum absorption of iron is not more than 10 percent of the iron content of the diet.

In the food, iron is present in ferric form either as ferric hydroxides or in combination with ferric organic compounds, Acidity of gastric juice results in the liberation of ferric form. Ferric form is reduced to ferrous form by the reducing substances such as glutathione, vitamin С and cysteine present in the food absorption.

The regulation of iron absorption is governed by Mucosal block theory. According to this theory, ferrous ions on entering the mucosal epithelial cell are oxidized to ferric ions which combine with а protein called apoferritin to form Ferrritin (also known as siderophilin). Apoferritin is а glycoprotein containing sialic acid, galactose, and mannose as the carbohydrate moieties.

Each molecule of apoferritin combines with 2 atoms of ferric, iron to form ferritin. This ferritin is stored form of iron. The amount of apoferritin present in the mucosal cells is the controlling factor.

Factors which affect iron absorption are:

1. Low phosphate diet increases iron absorption whereas high phosphate diet decreases iron absorption by forming insoluble iron phosphates.

2. Iron in ferrous form is more soluble and is readily absorbed than the ferric form.

3. Phytic acid and oxalates decreases iron absorption by forming iron phytate and iron oxalate.

No absorption of iron takes place under following conditions:

1. Any condition of partial or total gastrectomy.

2. Dissertion of small intestine.

3. Achlorohydria.

4. Profuse diarrhea.

5. Malabsorption syndrome.

Iron is transported in the plasma as Fe3+ form in combination with b-globulin called transferrin also known as sidoferrin. The iron in this form is called protein bind iron (PBI). The entire iron in the plasma is in the protein bound iron.

The protein bound iron in:

Adults 120 — 140 mg per 100 ml of blood.

Females 90 — 120 mg per 100 ml of blood.

The plasma iron content is the net resultant of the following:

i. Rate of RBC destruction;

ii. Rate of iron absorption from intestines

iii. Rate of apoferritin synthesis

iv. Rate of erythropoisis

v. Extent of blood losses.

Iron is stored in the body as ferritin. Ferritin can bind up to 4000 iron atoms per molecule. If iron is taken in abnormally large amounts, the excess is deposited in liver as Hemosiderin.

Excessive accumulation of iron in liver, lungs, pancreas, heart are other tissues results in hemositderosis, when this is accompanied by bronze pigmentation of the skin, the condition is called hemochromatosls.

Sources

Meat, heart, kidney, spleen, egg yolk, fish, dates, nuts, legumes, molasses, spinach, cooking of food in iron vessels.

Daily Requirements 10 –15 mg.

PHOSPHORUS

Functions

1. Phosphorus along with calcium is essential for bones and teeth

2. Buffering action, i.е., phosphate buffers.

3. In the formation of high energy compounds, i.е., ATP.

4. In the synthesis of RNA and DNA.

5. In the synthesis of phospholipids.

6. In the synthesis of phosphoproteins.

Sulfur

Sulfur is present in three amino acids. Methionine, cystine and cysteine and thus it is present in all proteins in the body. Connective tissue, skin, hair and nails are especially rich in sulfur. Also thiamine and biotin (member of Vitamin В complex) and coenzyme А contain sulfur in these molecules.

Diet which is adequate in protein meets the daily requirement of sulfur.

COPPER

Total copper content in the human body is 100-150 mg. It is present in almost all the tissues of the body. Liver is the richest source of copper.

Functions

1. Copper is an important constituent of certain enzymes such as, cytochromes, cytochrome oxidase, cataiase, peroxidase, ascorbic acid oxidase, uricase, tyrosinase, cytosolic superoxide dimutase, etc.

2. Necessary for growth and bone formation.

3. Necessary for formation of myelin sheaths in the nervous systems.

4. Helps n the incorporation of iron in hemoglobin.

5. Helps in the absorption of iron from Gl tract.

6. Helps in the transfer of iron from tissues to the plasma.

Copper is present in the plasma as ceruloplasmin. The concentration of ceruloplasmin in plasma is 23 – 40 mg percent. The copper containing protein in RBC is erythrocuperin, in liver it is hepatocuperin, and in brain it is cerebrocuperin.

Like iron, copper is conserved and reutilized by the body.

Ceruloplasmjn.

It is а blue colored copper containing metalloprotein with a2- globulin. It contains 8 atoms of copper bourld per molecule. The reduced form is colorless. It is glycoprotein containing 8 – 10 units of sialic acid residues per molecule. About 90 — 95 percent of the total copper in the plasma is present in the ceruloplasmin molecule and remainder is bound to albumin.

Ceruloplasmin has oxidase activity and thereby facilitates the incorporation of ferric iron into transferrin. Vitamin С is utilized as hydrogen donor.

Increased levels are seen in acute infections. Chronic conditions such as rheumatoid artheritis, cirrhosis and in post operative stages. Malnutrition also has increased levels.

Wilson disease shows decrease serum levels in both copper and cerruloplasmin.

ZINC

Zinc is an important constituent of pancreas.

Functions

1. Zinc is а constituent of certain enzymes such as carbonic anhydrase, carboxypeptidase, alkaline phosphatase, lactate dehydrogenase, alcohol dehydrogenase, superoxide dimutase, retinene reducthse, DNA and RNA polymerase.

2. Necessary for taste buds.

3. Necessary for fertility of mice.

4. Necessary for tissue repair and wound healing.

5. Necessary for protein synthesis and digestion.

6. Necessary for optimum insulin action as zinc is the integral constituent of zinc.

FLUORIDE

Functions

1. It gives strength to enamel tissues.

2. It prevents the bacterial action to the teeth.

3. Necessary for the health of teeth.

Fluoride ions inhibits all those enzymes which needs Mg also, i.е., inhibition of glycolysis reactions. On enolase, it has the maximum inhibition activity.

Addition of fluoride salts in water is known as fluoridation.

Oddsei - What are the odds of anything.