All subdivisions of the system called human body are arbitrary to a certain extend, most ‘components’ prove essential to the survival and well being of the organism. Beneath your skin lies a complex, interactive system requiring smooth interactions of every cell involved. This manual uses other systems that have been engineered as comparison to illustrate functions of the human body.
The cells of a human body differ slightly from a single cell organism, as they specialise to become part of other subsystems (eg flesh, bones, blood, organs, etc). The environment of a human body cell determines which function it will fulfil, yet it still has the same life cycle as the whole organism.
Unless you’re very young, none of your body cells from your birth is still around. It takes about seven years to replace all of your currently existing cells with new ones. Most of the cells you move through the world aren’t even yours, as you carry more micro-organisms on your skin and in your guts than those with your own DNA.
Your digestive system needs a microbiome to function – without bacteria living in your stomach and intestines you couldn’t process food. The human body compares well to a symbiotically living large community of autonomous entities, not so well to an army of obedient cells following the order of general brain.
Just after conception, unspecialised identical cells divide until there are enough to build a hollow sphere, the blastula. In the next stage of development, three different layers diversify the cells of an embryo into endo-, meso- and ectoderm.
The innermost layer, the endoderm will develop into most internal organs, the middle layer (mesoderm) gives rises to muscles, bones, connective tissue, heart, kidneys, gonads and the ectoderm ends up as skin, tooth enamel and the entire nervous system.
These three layers mix up thoroughly in the torso, while limbs and head only contain cells descending from the meso- and ectoderm. Several fractal interconnected networks within the whole body emerge: the nervous system, the fascia system and the circulatory system (blood vessels and lymphatic system).
The concept of morphogenetic fields offers the most plausible explanation to the magic of cells with identical DNA in the same environment suddenly diversifying and specialising. Don’t worry too much if you couldn’t follow the quite technical description so far. I will point out the essential parts for the how-to section of the manual.
Here’s what you need to know from this section. Several interconnected systems work within the human body: An electrical system, a plumbing system and a structural support system.