Anatomy 101: From Muscles and Bones to Organs and Systems, Your Guide to How the Human Body Works

THE CHEMISTRY OF CELLS

Nuclear Reactions and Why We Love Them

Everything in the universe—from the largest of stars in the sky to the smallest grain of sand on the beach—is made up of matter. To be more precise, everything that takes up space and has mass is made up of matter. That small grain of sand may not seem like it takes up any space or has any real mass, but wait until it gets in your shoe. Then you’ll know it as a physical object.

We might call matter “physical substance” (as opposed to that random thought you just had about what’s for lunch; random thoughts have no physical essence).

The study of the structure of matter, its properties, and how different kinds of matter interact is called chemistry, and an understanding of basic chemistry is crucial to learning the principles of anatomy and physiology.

The interaction of atoms—which you probably know as the building blocks of matter—has created the human body and the world it inhabits. Atoms together form elements, a type of matter that cannot be broken down by chemical means (that’s where the nuclear reaction comes in—elements can only be changed by nuclear means). Various elements combine together to create cells, which are the smallest structural units in the human body that perform a function. For example, your blood cells carry oxygen throughout your body. They have a distinct structure from cells that perform other functions, such as nerve cells or muscle cells. Chemistry rules not only how these cells are structured but also how they perform their functions.

The Most Important Elements

Just as the human body doesn’t have a single “most important” organ, several elements are essential for the creation of life. These are among the most important elements of all living things on earth:

· hydrogen (which is denoted by its chemical symbol, H)

· carbon (C)

· nitrogen (N)

· oxygen (O)

Whether in the air we breathe, the food we eat, or the materials that make up the physical structures of the human body, without these elements humanity would not exist. What makes these elements so essential to the formation of life is their ability to interact with other elements and then organize them into important molecules (matter that is composed of more than one atom) or compounds (molecules composed of two or more different elements). They can do this because of their subatomic structure and particles.

Anatomy of a Word

molecule

A molecule is a piece of matter consisting of more than one atom. A molecule can be made up of atoms that are all the same element (such as a molecule of oxygen) or it can be made up of different atoms, meaning that a molecule can be a compound (such as a molecule of water, which is a combination of hydrogen atoms and oxygen atoms).

Subatomic Particles

All atoms are made up of three basic subatomic (i.e., anything smaller than an atom) particles:

· protons (which have a positive electrical charge)

· neutrons (which have no charge)

· electrons (which carry a negative electrical charge)

The number and organization of these particles dictates whether an atom will readily interact with any other atom—and also defines what type of atom it is. If an atom has only 1 proton, it must be a hydrogen atom.

Positively charged protons are found in the nucleus of the atom.

Where do atomic numbers come from?

The number of protons present in an atom is the atomic number for that element. For example, carbon has an atomic number of 6 and oxygen has an atomic number of 8, which means carbon has 6 protons and oxygen has 8 protons in the nucleus.

Another particle found in the nucleus of an atom is the neutron. While neutrons don’t contribute any charge to the atom, they do contribute to the mass of the atom. Therefore, the atomic mass of an atom is the number of protons and neutrons present in the atom. So while carbon has an atomic number of 6 (6 protons), it has an atomic mass of 12 (which means there are also 6 neutrons in the nucleus).

However, while the nucleus is populated, there is an unequal charge for the atom. As with most things in the universe, atoms seek balance. To obtain this balance, atoms have negatively charged particles that orbit around the nucleus. These are called electrons. It is the electrostatic attraction between the electrons and the protons that keeps the electrons spinning in orbit around the nucleus, much like the moon is held close to the earth by gravity. In fact, to find a natural balance, atoms will have the same number of protons as electrons, leaving the atom with an overall net neutral charge.

Electrons, however, are not restricted to a single location, such as the nucleus. They are found in orbitals (shells) around the nucleus. An atom can have many orbitals. In illustrations, these will often be drawn as concentric circles with the first being closest to the nucleus. The first orbital of any atom (that is, the orbital closest to the nucleus) can contain up to 2 electrons. After this orbital is filled, if the atom has more electrons, they will be packed into the next orbital, which can contain up to 8 electrons. Once the next orbital is filled (if there are more electrons), then they are packed into the next and so on. All orbitals after the first can contain up to 8 electrons.

Orbitals by the numbers

For carbon, with an atomic number of 6 (meaning 6 protons and thus 6 electrons), 2 of the electrons will be in the first orbital and the remaining 4 will be in the second (and outermost) orbital.

With this basic understanding of atoms and subatomic particles, you can better understand how atoms will combine together to form molecules and compounds.

The real building blocks of matter

The fact that subatomic particles exist is why scientists cry out in despair when people say atoms are the building blocks of matter. Particles such as protons are smaller than atoms, and for many years scientists thought they were the building blocks of matter … until someone discovered quarks, which have itty bitty charges and combine to form protons and neutrons. No one has actually seen a quark, but experiments show they must exist. Thus it is quarks that are actually the building blocks of matter (and will continue to be until someone finds something smaller).

Periodic Table of Elements

In order to show the relationship of the various elements, scientists have arranged them into the periodic table of elements, which you probably remember from high-school chemistry class. The table of the elements begins with the element that has an atomic weight of 1 (hydrogen) and goes to—well, that depends on the table you’re looking at. There are 114 confirmed elements and several others are suspected to exist, such as 118 (ununoctium, a synthetic element no one knows much about, sort of like that weird neighbor down the street). Ninety-eight elements occur in nature; the others are only found in labs (where they are synthesized).

Each entry in the table includes the element’s atomic number and its chemical symbol. Some tables may also show the atomic mass. Color coding is often used to indicate groups of elements that share similar qualities.


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