Welcome to the most useful manual you will read. Self-programming, self-regenerating carbon units come without a manual, which often leads to more malfunctioning than necessary.
Thanks to the resilient base design of the human body, functioning in survival mode doesn’t require knowledge of this manual. Human cultures integrated some of the essentials as well, which allowed the development of society as we know it today.
Your curiosity for this manual is living proof of the need for its existence. Maybe a malfunctioning body and failed attempts to “fix it” brought you here. Or the idea “I have a body, I know how it works, let me show you where you’re wrong”. Maybe a bunch of serendipities made it unavoidable to have a closer look.
Even without this manual, you have already managed to make your self home in a human body, and acquired the skills required to access this manual. And many more. Congratulations.
This manual uses a system perspective to explain the human body and some of its subsystems. As mentioned, you already made some important steps in operating a complex entity with amazing features.
Your body consists of trillions of very similar structured units, cells. Each cell has a life of its owns, and goes through the same cycles the whole organism does. We define a unit or entity by having a boundary. A membrane encloses a cell to distinguish between interior and exterior, just like the skin creates the physical border of the human body.
The boundary of carbon based units acts as interface between in- and outside, allowing nutrients to enter the organism and metabolic waste to leave it. This process of exchange and elimination happens nearly automatically while being dependent of the environment.
Once something nutritious has passed through the interface, it needs processing to fuel life. Molecules get broken up and reassembled, assimilating the useful bits and discarding the rest. A bunch of generic molecules transform into very specific ones capable of fulfilling the internal needs of the cell.
The assimilated food can then be converted to power the engine, or integrated to repair faulty components or build new ones. As energy source it provides vitality, as spare part it maintains the purity of the system.
A self-regulating system requires a bit of regulation to facilitate protection. If the membrane can’t react to toxins in its environment, or can’t circulate its essentially needed molecules to the right part of the cell, it can’t survive.
Not everything a cell needs is permanently available, nutrients converted to physical energy will be stored, and can be distributed to achieve the next goal. In an abundant environment, using energy for reproduction makes more sense than moving around. In a toxic environment, getting out of there serve survival best.
Just like any building block of your human body, you need food entering the system, digest it, extract nutrients, integrate and convert them into needed bits, use those bits for vitality and integrity, circulate them around, protect the system, store some energy and choose how to use it.
The subsystems achieving this functionality in a human body appear very complex. Describing any system from an unsuitable perspective makes it look complex, and like fish in water, humans many made some clumsy attempts of understanding their own existence, and how bodies work.
While many people talk about the cycle of life, they often simplify it to “get born, survive, propagate, die”. Life has many rhythms, and understanding the life cycle of a cell has much more relevance to our day to day existence than the life time perspective.
As any decent instruction manual, it starts with a description of the system, important components, features and specifications. This ends the first lesson.