Editor’s note: We are delighted to present this excerpt from Your Designed Body, the new book by engineer Steve Laufmann and physician Howard Glicksman.
To be alive, every cell in your body needs solutions to a complicated set of problems — containment, gates, controls, framing, transport, energy, information, and reproduction. Zooming out from a single cell, the human body as a whole is made up of around thirty trillion cells (a figure that varies widely with an individual’s size). It needs to solve all the same kinds of problems that a cell does, plus quite a few more. And it needs new ways to solve old problems, ways completely different from how the same problems were solved at the cellular level.
For example, a single-celled organism is like a microscopic island of life. The cell gets what it needs and gets rid of what it doesn’t need from its surrounding environment. In contrast, a large multi-cellular organism (like you) is more like a continent with a deep and dark interior. Most of the cells reside deep in the interior with no direct access to the body’s surrounding environment. For a multicellular organism, then, harvesting the raw materials its cells need and getting rid of toxic by-products becomes a major logistical problem.
Several hundred such problems must be solved for a complex body to be alive. And many of the solutions to these basic problems generate new problems that must also be solved, or that constrain other solutions in critical ways. The result is that for a complex body to be alive, thousands of deeply interconnected problems must be solved, and many of them solved at all times, or life will fail.
Additionally, many of the problems the body faces are much more complex than those solved in any individual cell. For example, while it takes impressive engineering for cells to sense their environment (a process not well understood), sensing poses a considerably greater engineering challenge for a human body, since it involves much more sophisticated forms of sensing — like vision, hearing, taste, smell, and the fine-touch sensing in your hands.
The bottom line is that, as hard as it is for a cell to maintain life, it’s much harder for an organism with a complex body plan like yours.
Hard Problems Take Clever Solutions
Together, the many thousands of problems the body must solve for survival and reproduction require many thousands of ingenious solutions. Most of these solutions need special-purpose equipment across all levels of the body plan, from specifically adapted molecular machinery (like hemoglobin molecules) to specialized cells (like red blood cells) to tissues (like bone marrow) to whole body systems (like the cardiovascular system). This may involve hundreds of thousands of parts, replicated in millions of places.
Solutions to this class of problems always exhibit four interesting characteristics:
It takes the right parts to make a working whole. Each part must perform a function with respect to the larger system. Each part must be made of the right materials, fine-tuned to precise tolerances, and equipped with suitable interfaces with the other parts. This is a design principle known as separation of concerns. Virtually every designed object in human experience is based on this design strategy. And this appears to be equally true in biological systems, including virtually every capability in the human body.
The parts must be in the right places, arranged and interconnected to enable the function of the whole. Each part must work with the other parts in an integrated way. The parts are often made of different materials, where a material is chosen for how its particular properties support the specific needs of that particular part and how it must function in light of the whole. This is a design principle known as the rule of composition. It counterbalances the separation of concerns principle. Separation of concerns breaks large problems into subproblems that are (slightly) easier to solve, while the rule of composition puts the solutions to the subproblems (the parts) together such that the function of the whole is achieved.
The parts must have exactly those interfaces that enable the parts to work together. With bones, this obviously involves their shapes, especially at their connection and articulation points (the joints). For other body systems this can involve structural support, alignment, shock absorption, gating and transport systems, electrical signaling, chemical signaling, exchange of complex information, and integrated logic.
The parts must be coordinated such that each performs its respective function or functions at the right time. This usually requires one or more control systems, either active or passive, and usually some form of sensing and communication between the parts and the controls. This property is achieved by orchestration or choreography, which differ in the ways the controls are achieved, the former by a more centralized approach and the latter by a more distributed approach. In an old Chevy pickup, this function for the engine is achieved by a camshaft. In ATP Synthase, this is also achieved by a camshaft.
In designing a complex system, all four of the above factors must be considered across the whole when designing each of the parts.
When a system has all the right parts, in all the right places, made of the right materials, with the right specifications, doing their respective functions, at all the right times, to achieve an overall, system-level function that none of the parts can do on its own, you have what is known as a coherent system. Coherence, in this sense, is a functional requirement for all non-trivial systems. Moreover, in life the systems are never standalone — there are always interdependencies between and among the various component systems and parts. The human body is composed of coherent, interdependent systems.
Of course, each part in a larger system may be a system itself, composed of specialized parts, which may also be systems composed of specialized parts, and so on, forming a hierarchy of design. As with most human-designed artifacts, living systems consist of layers of systems and subsystems — a system of systems. This is exemplified in the human body. See the figure below.
The Scope of the Body’s Solutions
It takes a lot of work to keep a sawmill running. Logs need to be obtained, sorted, and brought in. Cut lumber needs to be taken away for further processing. The motors need electricity. The saw blades need to be changed out and sharpened. The workers need coffee. Lots of coffee. All these require various systems within the larger system.
Similarly, to keep your cells alive and working properly, your body requires eleven major organ systems1 to distribute, dispose, defend, generate energy, and perform other crucial tasks. The systems and their roles:
- The respiratory system takes in the oxygen (O2) your cells need and gets rid of excess carbon dioxide (CO2).
- The gastrointestinal (digestive) system takes in the water, sugar, fat, protein, salt, vitamins, and minerals your cells need.
- The renal/urinary system rids your body of excess nitrogen (ammonia, urea) and helps maintain your blood pressure and control your body’s water and salt content.
- The cardiovascular system pumps blood throughout your body to provide “just in time” delivery of supplies to every organ no matter what you’re doing. It’s also critical for managing temperature, dissipating excess heat, and distributing chemical signals throughout the body.
- The integumentary system (skin) protects your body from the outside world while helping control your temperature through sweating. It continually replenishes itself from the inside out and is remarkably good at repairing itself when it gets cut or scraped.
- The skeletal system (bones) provides support and protection for many of your vital organs (like your brain, spinal cord, lungs, and heart) and is the framework for the muscles. Its structures, organization, and proportions enable an amazing range of movement and activity.
- The motor system (muscles) allows the body to move around, stay balanced, and handle things. It’s capable of a wide range of strength demands yet possesses extraordinarily fine controls.
- The nervous system (nerves and brain) allows the body to sense your surroundings, maintain your body’s vital functions, and control your activities. It also allows you to be awake and aware — to think, communicate, imagine, and create.
- The immune/lymphatic system protects you from invading pathogens.
- The endocrine system sends out hormones to regulate things like your metabolism and growth.
- The reproductive system, male and female, enables new human life.
Each of these is a specialized subsystem in the body. The body needs all of them, organized properly, and coordinated to remarkably fine tolerances. In turn, each of these subsystems is a complete system, itself composed of many specialized subsystems and parts, organized in specific ways, and precisely coordinated.
- While many sources count twelve major body systems, we’ve chosen to treat the immune and lymphatic systems as a single larger system because they operate so seamlessly together.