Human body, abundance elements

Oxygen is the most abundant element on earth The earths crust is rich in carbonate and sili cate rocks the oceans are almost entirely water and oxygen constitutes almost one fifth of the air we breathe Carbon ranks only fourteenth among the elements in natural abundance but trails only hydro gen and oxygen in its abundance in the human body It IS the chemical properties of carbon that make it uniquely suitable as the raw material forthe building blocks of life Let s find out more about those chemi cal properties... 

Calcium. Calcium, the most abundant mineral element in mammals, comprises 1.5- -2.0 wt % of the adult human body, over 99 wt % of which... 

Phosphorus. Eighty-five percent of the phosphoms, the second most abundant element in the human body, is located in bones and teeth (24,35). Whereas there is constant exchange of calcium and phosphoms between bones and blood, there is very Httle turnover in teeth (25). The Ca P ratio in bones is constant at about 2 1. Every tissue and cell contains phosphoms, generally as a salt or ester of mono-, di-, or tribasic phosphoric acid, as phosphoHpids, or as phosphorylated sugars (24). Phosphoms is involved in a large number and wide variety of metaboHc functions. Examples are carbohydrate metaboHsm (36,37), adenosine triphosphate (ATP) from fatty acid metaboHsm (38), and oxidative phosphorylation (36,39). Common food sources rich in phosphoms are Hsted in Table 5 (see also Phosphorus compounds). 

The elements occur in widely varying quantities on earth. The 10 most abundant elements make up 98% of the mass of the crust of the earth. Many elements occur only in traces, and a few are synthetic. Fortunately for humanity, the elements are not distributed uniformly throughout the earth. The distinct properties of the different elements cause them to be concentrated more or less, making them more available as raw materials. For example, sodium and chlorine form salt, which is concentrated in beds by being dissolved in bodies of water which later dry up. Other natural processes are responsible for the distribution of the elements which now exist on earth. It is interesting to note that the different conditions on the moon—for example, the lack of water and air on the surface—might well cause a different sort of distribution of the elements on the earth s satellite. 

Mg2+ is one of the most abundant elements in the earth s crust and in the human body, and is the most abundant divalent cation within cells. Around 50% of total Mg2+ resides in bone, the remainder essentially within cells 50% of cytosolic Mg2+ is bound to ATP, and most of the rest, together with K+, is bound to ribosomes. The intracellular concentration of free Mg2+ is around 0.5 mM. Less than 0.5% of the total body Mg2+ is in plasma, where its concentration is maintained within fairly strict limits. 

After iron, zinc is the second most abundant trace element in the human body an average adult has 3 g of Zn, corresponding to a concentration of about 0.6 mM. Some 95% of zinc is intracellular. It is essential for growth and development in all forms of life, and has been proposed to have beneficial therapeutic and preventative effects on infectious diseases, including a shortening of the length of the common cold in man. 

There are 81 stable elements in nature. Fifteen of these are present in all living things, and a further 8-10 are only found in particular organisms. The illustration shows the first half of the periodic table, containing all of the biologically important elements. In addition to physical and chemical data, it also provides information about the distribution of the elements in the living world and their abundance in the human body. The laws of atomic structure underlying the periodic table are discussed in chemistry textbooks. 

The human body is composed of 60 to 70 percent water, and water contains twice as many hydrogen atoms as oxygen atoms. If two-thirds of every water molecule is hydrogen and if water makes up 60 percent of the body, it seems logical to conclude that hydrogen makes up 40 percent of the body. Yet hydrogen is only the third most abundant element in the body by mass. What gives ... 

Calcium. Calcium, ihe most abundant mineral element in mammals, comprises 1.5-2.0 w1 G of Ihe adult human body, over 99 wt (i of which is present in bones nnd teeth. About 48 of scrum calcium is ionic, ca 46G is bound nr hlood proteins, the rest is present as diffusible complexes, e.g.. of citrate. The calcium ion level must he maintained within definite limits... 

FIGURE 1.1 Estimated elemental composition (by mass percent) of (a) the earth s crust and (b) the human body. Oxygen is the most abundant element in both. Only the major constituents are shown in each case small amounts of many other elements are also present. 

FIGURE 19.1 The 10 most abundant elements by mass (a) in the earth s crust and (b) in the human body. All are main-group elements except iron and titanium. 

The group 4A elements—carbon, silicon, germanium, tin, and lead—are especially important, both in industry and in living organisms. Carbon is present in all plants and animals, accounts for 23% of the mass of the human body, and is an essential constituent of the molecules on which life is based. Silicon is equally important in the mineral world It is present in numerous silicate minerals and is the second most abundant element in the earth s crust. Both silicon and germanium are used in making modern solid-state electronic devices. Tin and lead have been known and used since ancient times. 

How many of the four most abundant elements in the earth s crust and in the human body can you identify without consulting Figure 19.1 ... 

Two of the four most abundant elements in living systems, hydrogen (H) and oxygen (O), combine to form water, H20. Without water there would be no life as we know it. The human body is largely made up of water. Water dissolves other life-supporting substances and transports them into and around cells. It is also a liquid in which important biochemical reactions take place. 

Elemental iron, the major element in Earth s core, is the fourth most abundant element in Earth s crust (about 5.0% by mass overall, 0.5%-5% in soils, and approximately 2.5 parts per billion in seawater.) In the crust, iron is found mainly as the oxide minerals hematite, Fe203, and magnetite, Fe304. Other common mineral forms are siderite, FeC03, and various forms of FeO(OH). Iron is an essential element in almost all living organisms. In the human body, its concentration ranges between 3 and 380 parts per million (ppm) in bone, 380-450 ppm in blood, and 20-1,400 ppm in tissue. 

Copper is the third most abundant metallic element in the human body, following iron and zinc. It also occurs in all other forms of life and it plays a role in the action of a multitude of enzymes that catalyze a great variety of reactions. There are two cross-cutting ways to classify the copper-containing enzymes (1) According to the structural and spectroscopic characteristics of the copper complex at the active site. (2) According to the function of the enzyme. We shall base discussion on the first of these, with allusions to function as we go along. 

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