External View

Generalities.

    The human body is a wonderful machine. It is so efficient and robust, and yet, at the same time, it is so complex with so many interdependent processes that 'a little grain of sand in the gears' can disable it. Each part of your body has its role; each organ, each cell, each molecule play a particular function for your body to work as a whole.

    Even though our body seems solid, more than half of its weight (about 56 %) is water. And this water has a composition close to sea water, just a little less salty.

    There is about 75 billions cells in our body. At the surface, though, you don't see living cells. Indeed, the external layer of our skin, hair and nails is made of dead cells and keratin.

    The external appearance of our body depends on multiple traits. Differences in the color of our skin, hairs and eyes, the size and length of our bones, the development of our muscles and our fat accumulation give each one of us a different look. Most of these traits are primarily ruled by genetic factors. If your parents and tall and slim, with black eyes, there is a good chance that you will look alike. But nothing is black and white in genetics: there are so many possible combinations and some mutations. After birth, surrounding environment, behavior, eating, exercise and diseases will mold a growing and aging body and change its appearance. We do not get born as a marathonist, but we need the genetic aptitude, the will and a lot of sweat to become one.

Orientation.

    We need to adopt a common terminology in order to orient ourselves when we want to describe our body. When we talk about spatial orientation, we need a point of reference. In anatomy, this point is the center of your body. In the following table, you will find a list of common terms used to orient ourselves, and the figure illustrate those terms (click for higher resolution). For example, the proximal end of your tibia is the one closest to the center of your body (at the level of the knee for the tibia), whereas the distal end of the tibia is the one closest to your extremity (at the level of the foot for the tibia).

Links.

    Here are some interesting links. They will help to improve your knowledge about the anatomy and physiology of the human body, and about science in general.