Wednesday, February 17, 2016

Hierarchical Engineering Model of the Human Body [1]


Som Karamchetty, PHD [2]

Abstract

     Through modeling and simulation, engineers understand the behavior of complex engineering systems, such as air & space systems, chemical refineries, nuclear plants, high performance computers, and autonomous robots. They divide a complex system into several hierarchical levels; each level is modeled in sufficient detail by engineers and scientists well-versed in those disciplines; and an integrated model is realized. Such modeling approach can be applied to the human body. A representative model would have six levels: the whole body as a system, system of systems in the body, organs, tissues, cells, and molecules. We can identify several systems in the body that deal with energy conversion and storage, transportation, pumping, electrical, chemical, biochemical, sensing, communications, and so on. Digestive system is the body’s typical energy system with inputs of food and conversion of food into intermediate forms that are readily used by the muscles to generate mechanical energy, forces, and moments to enable various internal functions as well as external activities of humans. The circulation system, the respiratory system, and a number of other systems are similar to transportation systems that move various materials from their sources to destinations.
    Following the engineering practice, faults can be inserted into models and the behavior of the body studied to see if certain known and unknown diseases can be modeled and simulated. Ultimately, such modeling will assist the medical, pharmaceutical, and nutritional specialists to provide humans with healthy living and appropriate healthcare when they fall ill.

Summary

      Engineers are able to understand the behavior of complex engineering systems, such as air & space systems, chemical refineries, nuclear plants, and high performance computers, through modeling and simulation. They divide a complex system into several hierarchical levels; each level is modeled in sufficient detail by engineers and scientists well versed in those disciplines; and an integrated model is realized.
     A hierarchical engineering model of the human body is suggested in a white paper by this author. Such a model would have six levels: the whole body as a system, system of systems in the body, organs, tissues, cells, and molecules. In order to implement the engineering modeling method, we first identify several systems in the body that deal with energy, transportation, pumping, electrical, chemical, biochemical, sensing, communications, and so on. Digestive system is the body’s typical energy system with inputs of food and conversion of food into intermediate forms that are readily used by the muscles to generate mechanical energy, forces, and moments to enable various internal functions as well as external activities of humans. The circulation system, the respiratory system, and a number of other systems are similar to transportation systems that move various materials from their sources to destinations. Again, like in an engineering system, as the materials are moved from one location to another, several mechanical transformations and chemical reactions occur. Hence, thermodynamic systems analyses are applied at each level. Just as we do with engineering components, mechanical and material analyses and modeling of various components and tissues in the body can be done.
    It is the author’s view that engineering modeling of the human body will throw light on various functions of a normally healthy body and may explain a variety of illnesses and diseases.
    Following the engineering practice, faults can be inserted into the models and the behavior of the body studied to see if certain known and unknown diseases can be modeled and simulated. Ultimately, such modeling will assist the medical, pharmaceutical, and nutritional specialists to provide humans with healthy living and great healthcare when they fall ill.
    The author suggests the development of a hierarchical model of the human body as such a model will lead to greater understanding of the healthy human and likely causes for diseases. It will lead to far reaching benefits to the medical and engineering fields.

 Outline

 1. Summary
2. Introduction
3. Human Body and Complex Systems
4. Engineering Functions Performed by the Human Body
5. Previous Efforts in Engineering Modeling of the Human Body
6. Hierarchies for Modeling Effort
7. Benefits and Prospects from Engineering Modeling

List of Figures

Figure 1: Human Body and a Jet Plane are Complex Systems
Figure 2: Human Body Exchanges Material, Forces, and Energy with Surroundings.
Figure 3: Human Body in a Dynamic posture.
Figure 4: Suggested Hierarchical Model.
Figure 5: Level 1 of the Hierarchical Model.
Figure 6: System of Systems in the Human Body.
Figure 7: Representation of Open and Closed Systems
Figure 8: Engineering Model of a Generic Open System.
Figure 9: A Simple Representation of the Digestive System with the Open System Model.
Figure 10: Human Body as an Energy Conversion Engine.
Figure 11: A Generic Model of an Organ.
Figure 12: Suggested Model Format for an Organ Along with Electrical Signals.
Figure 13: Example Model of the Heart.
Figure 14: Generic Model Format for a Tissue.
Figure 15: More Details Added to the Generic Model Format for a Tissue.
Figure 16: Template for the Model of a Cell.

1. Summary

    Engineers are able to understand the behavior of complex engineering systems, such as air & space systems, chemical refineries, nuclear plants, and high performance computers, through modeling and simulation. The system is divided into several hierarchical levels; each level is modeled in sufficient detail by engineers and scientists well versed in those disciplines; and an integrated model is realized.
     A hierarchical engineering model of the human body is suggested. Such a model would have six levels: the whole body as a system, system of systems in the body, organs, tissues, cells, and molecules. In order to implement the engineering modeling method, we first identify several systems in the body that deal with energy, transportation, pumping, electrical, chemical, biochemical, sensing, communications, and so on. Digestive system is the body’s typical energy system with inputs of food and conversion of food into intermediate forms that are readily used by the muscles to generate mechanical energy, forces, and moments to enable various internal functions as well as external activities of humans. The circulation system, the respiratory system, and a number of other systems are similar to transportation systems that move various materials from their sources to destinations. Again, like in an engineering system, as the materials are moved from one location to another, several mechanical transformations and chemical reactions occur. Hence, thermodynamic systems analyses are applied at each level. Just as we do with engineering components, mechanical and material analyses and modeling of various components and tissues in the body can be done.
    Controlled by the brain, the sensor systems and control systems in the body ensure that the organs and systems do their work and maintain activities to sustain life. Based on the commands of the brain, systems work to enable a human to perform external mechanical activities through interactions with the surroundings. 
  The human body performs three main categories of functions, namely, physical, intellectual, and procreative. The physical activities allow the various organs and systems to perform internal and external activities as described above. Similar to and perhaps far superior to a highly intelligent computer, the brain performs many intellectual activities and enables organs to perform very skilled activities. The third activity of the human body is procreation of offspring. 
     In engineered systems, repair, maintenance, and manufacturing are activities external to the system. In the case of the human body, the system does its own manufacturing starting with an egg, growing into a baby, and finally maturing into a fully functioning grown up adult. For the most part, the body maintains and repairs itself. It has several sensors throughout the body that convey the conditions and deviations to the brain, which orders restorative measures to be performed by the appropriate organs.
    It appears that the body engages itself actively in manufacturing activities during the early life. Later on, such manufacturing activities diminish and perhaps cease completely. In engineering, the phenomenon of fatigue is used to explain the failure of components. When a component fails, engineers replace it by repairing it through rebuilding or remanufacturing and the component attains full fatigue life freshly. Human body appears to go through such a process automatically as the cells build tissues and organs as they are used. For example, people are told that those parts of the body which are exercised well grow and build strength and stamina. In the latter stages of life, as the body’s growth phase ends, such replenishment or rebuilding or renewal of fresh full life to components appears to cease and the count-down of component life (fatigue life) seems to start. That is when bones appear to become weak and muscles (including heart muscles and brain) generate weaker forces and lose their ability to sustain strain.
    It is the author’s view that engineering modeling of the human body will throw light on various functions of a normally healthy body and may explain a variety of illnesses and diseases. Hence a modeling project is recommended. The high degree of complexity of the human body makes it nearly impossible to build one whole model. Hence a model with six hierarchical levels is suggested. Such a modeling frame work allows modelers to develop dispersed models and integrate results into the whole body model. Modelers can communicate from one level to another and higher level models can suggest to lower level modelers for data and process requirements thus encouraging new research. Whenever new research results are available at lower levels, they can be fed to the higher level models to enhance their close resemblance to the real human body behavior.
     Engineering systems are rated in terms such as efficiency, capacity per unit weight or volume, and design and off-design performance. If we apply such measures to human bodies, one may ask if a human should consume food (or different foods) in some proportion to the physical activity rather than the capacity of the digestive system. This aspect may give clues to obesity.
    Furthermore, following the engineering practice, faults can be inserted into the models and the behavior of the body studied to see if certain known and unknown diseases can be modeled and simulated. Ultimately, such modeling will assist the medical, pharmaceutical, and nutritional specialists to provide humans with healthy living and great healthcare when they fall ill.
     Lately, there has been great emphasis on genomics and other -omics. Genomics assists in letting us know that the right cells are doing the right tasks. But it is the body’s engineering infrastructure, namely the systems, organs, and tissues that assures that the pathways are clear and functioning properly for the genes to do their job of keeping a person healthy, fit, and active.
Modeling might tell us if a disease is due to inadequacies in the transportation system or in the organs not generating the required materials. By gaining knowledge of paths of specific materials from a source to destination, we can determine why certain deficiencies show up and cause diseases. With a good model, we should be able to follow the path of an element (material) from its origin to its intended or unintended destination. If a certain material is not reaching a particular organ, it can be a problem with the transportation system or with the specific organ that should be generating that material. If a material takes a wrong path it can cause other problems in the body. Models can reveal the issues via symptoms that result in each case.
     It appears that the body has numerous sensors embedded in tissues that generate signals somewhat like strain gages telling engineers about stresses and forces in engineering structures. When these stresses and forces exceed thresholds, the body appears to feel pains and aches as a warning sign of impending failure of tissues or organs.
    In reverse, engineers may also learn techniques that can be beneficial in the design of engineering systems from the human body’s behavior. For example, fatigue life of systems can be increased by exploring the potential for incorporating renewal mechanisms into the components.
    Hierarchical modeling of the human body suggested in this document can lead to far reaching benefits to the medical and engineering fields.

2. Introduction

      Humans are highly intelligent and spiritual beings. There are many medical models, systems biology models of how various systems and organs in the body work. Biologists and medical professionals had developed qualitative models, which explained the operation of the human body in great detail. Engineering contributions have been in the areas of advanced machinery for diagnostics and device developments to assist medical professionals in curing people of illnesses. In the recent past, engineers and scientists have been building analytical models to understand and explain the operation of various components of the body.
     Dr. Hans Peter Fischer (2008) [3] compares the human body to a passenger jet plane (Figure 1).  According to Dr. Fischer, “both consist of many individual parts—whereas the body is made up of billions of individual molecules and cells, a plane may include thousands of screws, cables, wheels, and other diverse elements.” Dr. Fischer notes that, although it is not possible to understand the workings of a jet plane without a catalog of these parts, simply identifying them will not describe how a jet plane works. “Only by exploring how they interact—how the mechanical parts are connected by wires with electronic components and how flipping one switch affects the movement of different parts—is it possible to understand complex processes such as takeoff, navigation, communication, or landing, or problems with these processes.”




Figure 1: Human Body and a Jet Plane are Complex Systems (Picture Source: Dr. Fischer, as above)

     In a jet engine, air enters the compressor and is compressed as it passes through various stages of the compressor. Air passes through the combustion chamber where fuel is injected and the air and fuel mixture undergoes combustion. Now, the working fluid becomes carbon dioxide intensive and attains high temperature; such combustion products enter the turbine and generate mechanical energy; and finally, the gases pass through a convergent divergent nozzle generating thrust that pushes the aircraft. Auxiliary fluids such as lubricating oil and cooling air streams enter the system at designated points. Aircraft carriers propelled by nuclear power plants and petroleum refineries are other examples of complex engineering systems. One might be surprised to learn that the internal processes in the human body are similar in several respects as we will discuss them in later sections.
    In designing and building engineering systems, engineers set themselves three main objectives: 1) systems performance of intended functions, 2) systems operation at a high efficiency, and 3) continued maintenance-free operation. Hence, the development of a comprehensive engineering and science model of the human body will be a great platform as it allows engineers, scientists, biological, and medical researchers to gain detailed interdisciplinary and quantitative knowledge of the body, leads to optimal healthcare interventions, such as advanced drug discoveries, medical procedures, and engineered devices for epochal health improvement of people, and provides insights into continued research needs. Such an engineering model with representational frameworks is suggested in this document.

3. Human Body and Complex Systems

      Human activities are of three principal types: Physical, Cerebral, and Procreative. The impression of force and motion on the surroundings falls in to the physical interaction category. Sensing, controlling, processing, communication, creativity, and enjoyment fall in to the cerebral category. Finally, producing offspring belong in the procreative category.
     The biological and medical communities have analyzed and defined several systems that make up the human body. Physiologists have described various systems [4] in the human body and they are:
·                     Circulatory System
·                     Digestive System
·                     Endocrine System
·                     Integumentary System
·                     Immune System
·                     Lymphatic System
·                     Nervous System
·                     Musculoskeletal System
·                     Reproductive System
·                     Respiratory System
·                     Endocannabinoid System
·                     Vestibular System
·                     Respiratory System, and
·                     Urinary System.
     Like a mobile and autonomous force generating system with a heat engine, human body receives solid, liquid, and gaseous resources, converts inputs through a series of processes, and develops mechanical work for its own operation and to impress forces on the surroundings (Figure 2). It receives various signals from the surroundings and reacting to those signals automatically and at the human’s accord, the body exchanges materials, forces, and energy with the surroundings.


Figure 2: Human Body Exchanges Material, Forces, and Energy with Surroundings.

    When we look at it as an engineering system, the human body obeys of the laws of conservation of mass, energy, and force and momentum balance. Mechanical work is generated by several hundred muscles which convert intermediate forms of chemical energy into mechanical energy to generate forces, torques, moments, and motions that are strong, precise, and delicate. Electrical signals, traveling waves, and periodic electric impulses activate internal muscles into periodic or occasional actions necessary to sustain life and to cause intentional external actions. Human body utilizes chemical energy to grow the body, to keep the body working, to enable external physical activities, and to maintain the necessary body temperature.
     The body has internal sensors to monitor its own elements and external sensors to discern external impacts on it. It has actuators that attend to internal functionality and to exert its influence on the surrounding environment. The human body also receives radiations, some intentional and others unintentional, and reacts to them in specific ways.
     Above all, the human body has the brain, which is its computational and control system to operate organs and systems as well as to perform functions that bring pleasure and esteem to humans. Human body’s control engineering functionality includes diagnostics through sensing of the state of the organs, components, and operational parameters, maintenance of subsystem parameters in proper balance and in working order, and vigorous defense of organs and subsystem components from external and internal living and non-living attackers. The body swings into action based on the commands given by the brain – the CPU of the system. Sensors in the human body pick up external events and cues. Interpreting the information from the sensors, the brain instructs various muscles to act and they follow the commands. This is a simple dynamic model of the human body (Figure 3).



Figure 3: Human Body in a Dynamic posture.

     The principal attributes of the human body are a super structure (skeleton) to hold the body in
the environment, structures to contain and house organs, mechanisms to facilitate movements (joints), means to generate motions and flows (muscles), flows to supply materials to sustain and grow the body (air, water, food, blood, urine, feces, etc.), reactors to enable mechanical and chemical processing of materials, and sensors, signal processors, communication channels, memory, and computations.
    Through interaction and exchange of specific material with other human beings, it perpetuates the species. The manufacturing functionality of the human body is evident when we see how the body grows from an egg in the mother’s womb taking the materials needed from the mother’s body through the umbilical cord. Once delivered, the human body receives liquid and solid food, breathes oxygen and continues to grow various organs and systems.
     The similarities between the human body and an engineering system are evident when we recognize that the body is essentially a system of systems, each system performing its functions rhythmically. Systems consist of organs with dedicated functionality. The organs are made up of tissues which are comparable to engineering components such as structures, cables, mechanisms, containers, tubes, working fluids, and so on. Tissues are made up of cells, which are composed of molecules. Thus, we see a hierarchy comprising the whole body, systems, organs, tissues, cells, molecules, and atoms. This hierarchy is a good guide to develop a hierarchical engineering model. Generic model formats are suggested for each hierarchical level in later sections of this document.

4. Engineering Functions Performed by the Human Body

     The suggestion that the human body should be modeled as an engineering system is intuitive as the body has several systems akin to engineering systems, such as,
•            Pumping systems
•              Transportation systems
•              Conversion systems
•              Filtering systems
•              Flow systems
•              Diffusions systems
•              Chemical reacting systems
•              Lubrication systems
•              Electrical systems
•              Sensor systems
•              Actuator systems, and
•              Information processing systems.
     The functioning and performance of organs and tissues also correspond to engineering components and structural elements.

5. Previous Efforts in Engineering Modeling of the Human Body

    Several models have been attempted or developed before. But depending on the sponsor’s requirements, the models had limited objectives. Some models focused on the strength of the body structure to withstand battlefield impacts. Many researchers are actively working on analysis of fluid flow through organs and in the circulation system, respiratory system, digestive system, and other systems. There are research reports on structures which support the flows. Many researchers are working on the causes for blockages and the failure of flow passages especially in the circulation system. Approximate models of the operation of various organs in the human body which handle complex chemical, biochemical, and electrochemical reactions are in progress. Researchers have been attempting static as well as dynamic and thermodynamic models of the operation of muscles to convert chemical energy into mechanical work.
     While there have been several simple (component level) modeling attempts, the Digital Human Consortium (DHC) [5] had proposed a program with the goal, “An accurate simulation of the human body from molecules to cells, tissues, organ systems and the entire body.” The DHC model is a major attempt in this direction. It lays emphasis at the cell level as it tries to emulate the genomics program. While genomics and DNA research have taken great strides during the last half a century, not all problems will be addressable or approachable at that level. The critical lesson should be that instead of one huge model that tries to drive everything from the cell level, there should be models at different hierarchical levels that collaborate by dovetailing into one another.
     As Mario Jardon [6] stated, “… biological information operates on multiple levels of organization (molecular, cellular, organic, systemic, etc.) and is processed in complex networks, which happen to be considerably robust (single perturbations will rarely cause systemic failure).”  The hierarchical level model suggested in this document takes this approach.

6. Hierarchies for Modeling Effort

Whole Body as a System:

     Based on the engineering functionality described in previous sections, we suggest a hierarchical model (Figure 4), which follows the engineering practice with complex physical systems.


Figure 4: Suggested Hierarchical Model.

There will be models at various hierarchical levels with models at each level feeding into the other as appropriate. It is expected that the higher level models will take data and behavior information from lower level models while they identify the data requirements from lower level models so that a comprehensive model of the whole body can be built.     At the topmost level (Level 1), by considering the human body as a simple force and energy generator, we would be interested in defining its ability to generate power, energy, and forces relative to the size, i.e. physical characteristics such as height, weight, and so on (Figure 5). The body also operates at a certain efficiency, which may be defined as the energy output per unit input of food. Bodies exhibit different capacities and efficiencies over time and relative to one another.

Figure 5: Level 1 of the hierarchical Model.
System of Systems:
     At Level 2 of the hierarchy, the human body is depicted as a network or system of systems (Figure 6). This can be set as the ultimate model that connects all systems and components within each system. It may be compared to the full network diagram of a complex engineering system. But, we should first begin to model individual systems with larger fluid flows and add other smaller networks, thus progressively enhancing the network to build the complete network.

Figure 6: System of Systems in the Human Body.

     When we compare these anatomical systems, they fall into two main types of engineering systems, viz., open systems and closed systems (Figure 7). Digestive system is an example of an open system where solid and liquid food products are inducted into the system and solid, liquid, and gaseous products exit the system. Several mechanical and chemical processes take place along the way. Other auxiliary systems connect at various points into the digestive system exchanging products with the digestive system. Respiration system is also an open system that receives air from the environment and outputs CO2 to the environment.
Figure 7: Representation of Open and Closed Systems.

     Circulation system is an example of a closed system in that it does not directly receive inputs from and provide outputs to the environment external to the body. The circulation system also has connections with other systems of the body. Although we may classify the circulation system as a closed system, it is not a hermetically sealed system as in a home refrigerator.
     An engineering model of a generic open system with mass flows of various components at various points along the system and energy exchanges is shown in Figure 8. Working fluid undergoes changes at each component as the flow moves on its way. Thermodynamic changes and chemical reactions occur in the components that contribute to changes of state and composition of the working fluid. In general, it will be a multi-component, multi-phase flow thermodynamic system with chemical, biochemical, and electrochemical reactions occurring at various points along the flow path.


Figure 8: Engineering Model of a Generic Open System.

      Figure 9 shows a simple representation of the digestive System with the open system model. In the case of the digestive system, solid and liquid foods enter via the mouth. Food is pulverized by the grinding action between the teeth. Salivary glands add secretions to begin the digestion process. Food items proceed down the esophagus and into the stomach through the action of local muscles maintaining the motion as well as mixing of the food. Digestive juices produced in other collaborative organs enter the stomach. As the food passes through the small and large intestines, glucose, fructose, lactose, amino acids, fats, vitamins, and hormones produced in the various organs of the digestive system pass into the blood stream. Heat is also released during these processes going on in the stomach. The figure shows how we may represent the system, the boundary, and the surroundings. Sensors and controls are not shown in this figure to keep it simple for the present description.



Figure 9: A Simple Representation of the Digestive System with the Open System Model.

      Figure 10 shows the major systems that directly participate in enabling the human body to digest the food intake and generate the capacity to exert force and energy on the surroundings.


Figure 10: Human Body as an Energy Conversion Engine.
Organs:
     Each system consists of several organs, whose models are represented at Level 3. Organs have definite roles and perform specific functions. A generic model of an organ is presented in Figure 11. An organ will have a structure made of certain materials, geometric shape, volume, and mass. It contains a fluid or a mixture of fluids with state properties such as pressure, volume, temperature. An organ will be part of one or more systems and accordingly it will have connections to other organs in the same or other systems. An organ exhibits growth, steadiness, or decline over time. An organ itself consists of components such as organelles or tissues. From an engineering modeling point of view, an organ is enclosed in a control volume with various material inflows and outflows. There can be chemical, biochemical, and electrochemical reactions taking place in an organ. There are sensing mechanisms in an organ that monitor the thermodynamic and structural states of the organ. Similarly, there are mechanical, electrical, chemical, or thermal control points in an organ that prod the organ to act in certain ways. An organ produces some materials through chemical or biochemical reactions and/or other mechanical actions. The materials produced are stored in the organ and transported to other organs via the outlet channels.

Figure 11: A Generic Model of an Organ.

      Figure 12 shows a suggested model format for an organ along with electrical signals while the body is in mechanical motion with respect to the surroundings. In general, the model of an organ would have its static functional representation as well as a representation with its sensors and controls. Figure 13 shows the example model of a heart where electrical signals control the functioning of the heart by means of the muscles in the heart. The heart’s functionality is to act as a pump pumping good oxygenated blood and CO2 rich blood to other distinct organs. Heart valves operate in a specific sequence to make the pump work. In that sense, the heart valves operate like the inlet and exhaust valves of an internal combustion engine in the automobile.


Figure 12: Suggested Model Format for an Organ Along with Electrical Signals. [7]


Figure 13: Example Model of the Heart. [8]
Tissues:
     Tissues play the role in a human body that a variety of materials and manufactured components play in engineering construction of structures, systems, and infrastructures. As structural entities, tissues serve different functions. For example, skin acts as a covering fabric. Esophagus acts as a specially shaped tube that also pushes food down into the stomach. Intestines act as a long tube passing soft to hard mass. Blood vessels act as tubes that pass mostly liquid with dissolved gases. The tissues in the muscles act in a manner somewhat similar to linear hydraulic or pneumatic motors. Figure 14 shows a generic model format for a Tissue. Figure 15 shows the generic model with more details added to show the various properties and characteristics of tissues and the functions they perform.

Figure 14: Generic Model Format for a Tissue.


Figure 15: More Details Added to the Generic Model Format for a Tissue.

      As the skeletal structure forms the stable shape of the body, the tissue in the bones should provide rigidity and structural stiffness. Besides rigidity at one level, there is also flexibility, agility, and maneuverability provided by joints and tendons. Hence some of the tissues may be modeled as tension members somewhat like the guy wires in engineering structures. In general, biomechanical engineering methods have addressed such modeling issues.
    Since a large number of fluids pass through various ducts in the body, the corresponding tissues should be modeled as tubes. These flow passages in the human body are not entirely rigid but are very flexible and are laid in soft matrixes. Hence, when fluids flow from one part of the body to another under fluid pressure, or due to pumping action caused by the application of mechanical work by other organs, the structure of the tubes also undergo deformation. In some cases, the structure of the tubes is not impervious but porous to allow certain fluids to cross the walls. In that sense, these tubes operate somewhat similar to soaker hoses used in gardens.
     Connective tissues are similar to highly complex engineering materials used to interface components while providing elasticity, viscoelastic buffering, voids, filler space, and so on. [9]
Since tissues play a variety of distinct roles, the model suggested above may be modified appropriately to represent special categories of tissues.

Cells:
     Just as engineering materials are manufactured, used in the construction of engineering components, structures, and systems, repaired and reinforced as their ability to support full functionality of the structures deteriorates with use, and ultimately dumped as the structure and system deteriorate beyond repair, tissues also undergo a similar cycle from beginning to end. Most of these functions (creation, growth, constant repair, continual reconstruction, and dumping) are carried out by cells in the human body. Most of the carbohydrates, fats, and proteins from the food that humans eat, is broken down into smaller molecules, which enter cells to be used for energy and building materials. Hence, at the Level 5, cells should be modeled as mobile construction workforce and resources of the human body. For example, human life depends on oxygen and its transportation from the lungs to all the tissues and organs where it is used to generate energy; cells play a critical role in this phenomenon. [10]
     As cells play a crucial role in our lives and good health, modeling of the behavior of cells  (birth, growth, action, death, and renewal) should be critically important in the chain of research efforts. Cells carry various chemicals to enable tissues to work their best, such as to build tissues at the right place by the right amount. As tissues over work, there will be breakage of parts and cells get signals to build those parts. This may be the method by which muscles grow; people develop stamina; and muscles develop memory.
     Figure 16 shows the template for the model of a cell. The model represents characteristic functionality of cells, such as, growing, developing, reproducing, and building up the material of specific tissues. Cells have interesting and perhaps complex structures for themselves in order to perform their functions. Since they carry materials at the molecular level, they undergo intense chemical reactions. At stages, they mine and seek the chemicals they need; they store those chemicals, as they move within the blood stream or other fluid streams or across boundaries of tissues and organs; they hide the chemicals from being dropped at the wrong locations; and finally deliver them at the right location where they are direly needed. Cells perform all these tasks in response to chemical and electrical signals, mechanical forces, and thermal influences.



Figure 16: Template for the Model of a Cell.

      Cells also are of various types as they perform different functions. [11] There are about 200 different kinds of specialized cells in the human body (a comparison with workers with different technical skills may be drawn). When many identical cells are organized together it is called a tissue (such as muscle tissue, nervous tissue, etc.). Various tissues organized together for a common purpose are called organs (e.g. the stomach is an organ, and so are the skin, the brain, and the uterus). [12]

Molecules:
    Oxygen, carbon dioxide, and molecules from food are broken down into smaller molecules in the digestive tract and are then carried to or from cells of the body by means of the circulatory system by way of capillaries located in the lining of the digestive tract. In that sense, the body acts a complex molecular factory and this forms the Level 6 in the suggested hierarchical modeling effort. Inside the cells, various chemical reactions take place producing and storing the chemicals needed by the tissues and organs. Carbon-containing (organic) molecules, water, and inorganic ions constitute cells. Water is the most abundant molecule in cells, accounting for 70% or more of total cell mass. The basic chemistry of cells can thus be understood in terms of the structures and functions of four major classes of organic molecules, namely, carbohydrates, lipids, nucleic acids, and proteins. Molecules are responsible for the structure, movement, communication, and chemical reactions in the cells. [13]
     The human body is a complex and thriving ecosystem. It contains about 1013 human cells and also about 1014 bacterial, fungal, and protozoan cells, which represent thousands of microbial species. [14] It is normal for humans to live in such close intimacy with a wide variety of microbes, while only some of them are capable of causing us illness or death. Molecular biologists study these systems and have developed sophisticated models. Although there are trillions of cells in the human body, their number should not bother a modeler. For example, digital electronic circuits carry millions to billions of gates that are similar. They are represented by just one model for one gate. Different models are formulated only when the structure and functionality of gates or components differ.
    In order to interpret the enormous amounts of data generated by –omics technologies, systems biologists can incorporate these data into mathematical equations that model how parts of the cell interact. Using these equations, researchers are attempting to predict how a biological system functions under various conditions, or how it would respond, for example, to a potential new drug. The complexity of the equations and the extent nature of data necessitate the use computer simulations, or models, to solve them. This subject area is extensively discussed in literature. [15]

7. Benefits and Prospects from Engineering Modeling

     Engineering model of the human body leads to a better understanding of the body as a system with subsystems and their mutual dependence, functionality of healthy organs, and influence of inputs on functioning of organs. It establishes mass and energy balance, force and momentum balance of organs, interconnections and interactions of organs, and effects on one part of the body due to actions and interactions on another party of the body. When studied in isolation, one is likely to miss the effects on one part of the body due to actions and interactions by and on other parts of the body.
     Manufacturing companies in the medical, pharmaceutical, and engineering fields have developed various medicines, devices, sensors, and instruments to cure illnesses and enable people to lead healthy, enjoyable, and productive lives. The proposed modeling platform would allow the professionals to specify the necessary measurements to identify the symptoms as well as the source causes for ineffective operation of the components of the body, i.e. illnesses.
     Medical professionals have been assisting humans when bodies fail in certain functions or self-repair. Healthcare has been progressing from an art form to science and is lately getting help from bioengineers, and biomechanical engineers. Human well-being can have a bright future through engineering modeling in direct collaboration with medical and biological sciences.
The whole body modeling will facilitate the understanding of mutual and synergistic effects. Following from the model of a healthy or a normal human body, various (sets of) deficiencies can be added into the model at various levels and their effects on the normal functioning of other organs and the whole human body may be discerned and conditions for and symptoms of several illnesses may be simulated. Hence, it is essential to develop a model of the human body as a system of systems. As modeling progresses down to the cell level and molecular level, connections up and down the levels should be established. Thus the model discovers research problems and research results refine the successive versions of the model. Such models will lead to modeling of diseases in the body or its malfunctioning.
     Human performance factors vary between humans and even in one person, changes occur with age and periodically. Modeling can help to determine the factors that contribute to such variations. Modeling is likely to be very effective in isolating the causes for the degradation of performance when the body does not behave well or what we identify as the body suffering from ill health. The performance of the human body is best explained by examining the engineering functionality of the systems that make up the body together with the medical analytics.
     Modeling has benefited the engineering field with a better understanding of systems, components, and materials. It allowed analytical model studies and minimized the need for testing of actual systems. In the case of high performance digital systems, modeling and simulation have allowed advanced designs and prediction of their performance prior to building systems. Engineering systems models follow a hierarchical modeling paradigm so that expertise at the various levels can be accurately modeled and comprehensive benefits achieved.
     In a similar manner, in the case of human body modeling, a beginning with a hierarchical engineering modeling framework might yield benefits at various stages of its progress.  At the top level we can be looking at modeling human’s capabilities, strength, output, health, and variations between individuals. The framework captures the functioning of human body’s systems, organs, and progressively goes down to lower level modeling of tissues, cells, and molecules. At each level, the functioning closely resembles engineering systems, assemblies, components, materials, and their behaviors. Starting with engineering approximations, the various models in the framework can be refined and fine-tuned as researchers from diverse backgrounds make contributions to this modeling effort.
     Modeling of the human body will tell us how various systems and organs in the healthy body function. Following the modeling methods of engineering systems, especially, those from digital electronics, incorporation of malfunctioning components and systems, illnesses can be represented or realized in models.
     As described earlier, by looking at the body as a complex multi-modal transportation system, we find that it is a highly featured transportation system transmitting and distributing the necessary nutrients, energy materials where and when they are needed. The materials travel at various speeds obeying the laws of fluid mechanics. It may be observed that the materials flow through the digestion system at a slow pace allowing for various chemical and biochemical reactions to take place. The rates of blood flow in the circulation system and the oxygen flow in the respiration system adjust to the demands placed on them by the muscles when they are pressed into action. When people ingest tablets or liquid medicines orally, they travel at moderate speeds while a doctor administers intravenous or intramuscular injections, the medicines travel faster. We feel the fast effect when a person suffers a snake bite or bee sting or mosquito bite.
     In engineered mobility systems, the capacity of the energy generator is selected to suit the requirements of the task the main system is expected to perform. In the case of the human body, it is hoped that as the body grows, the energy generator, viz., respiratory system, circulation system, and muscular systems grow in the right proportion. As we see people of various shapes, this hope is not realized. Modeling might help in the understanding of the causes and methods of balanced growth.
     An interesting comparison surfaces when we investigate the sensors in the body. In engineering structures, strain gages are emplaced on structures to measure strains and calculate stresses imposed on a structure. Such sensors tell us if the structure is safe under the imposed forces or if it is likely to fail. Human body appears to have numerous sensors telling us if we are subjecting a body part (a bone, or a muscle, or a duct, or skin) to too much strain. Such strain (or corresponding stress) appears to be converted to electrical signal (like in a strain gage), transmitted to the brain, and the body feels it as pain and aches. Pain is perhaps, the method used by human body to alert us to such use and abuse of the body components.
     Collaborative research work will explain the detailed operation of the muscles to assist medical and pharmaceutical professionals as they develop new drugs to help people to have healthy and strong lives late into their lives.
    Parts of the human body grow for a certain time in life and then they stop growing. While this phenomenon may be the result of the way it is programmed by human DNA (somewhat akin to firmware and software in physical systems), it may be verified as relevant research is undertaken based on insights gained from modeling. Similarly, as organs (muscles, in particular) are subjected to greater use, they tend to grow bigger and stronger and gain effectiveness. Once we gain an understanding of the mechanisms of growth, development of methods to gain longevity with good health are perhaps possible.
    Even in physically healthier individuals, functions of the brain may impede proper functioning of the otherwise healthier organs of the body (e.g. Alzheimer’s, Parkinson). Perhaps, the linkages can be discovered when the models connecting the functioning of the sensors, the brain, and control signals are represented and exercised as modeling advances.
     In subsequent stages of model development, by incorporating faults (ill health or dysfunctional units) into the model, effects on various components, systems, and the whole body can be evaluated. When fully implemented, the suggested modeling effort would reveal why an organ does not work the way it should; what factors cause it to be dysfunctional; and what medical, surgical, biochemical, electrochemical, cellular, sensory, or psychological remedies would restore full functionality.
     Referring to Figure 4, (Hierarchical Model), engineering models for Levels 5 and 6 are more intensive in molecular interactions, chemistry, and nano-level thermodynamics and would reveal more information about cell behavior, and the consequential health effects.
     Genomics methods assist medical professionals in ensuring that the right cells are doing their right tasks. But it is the body’s engineering infrastructure, namely the systems, organs, and tissues that assures that the pathways are clear and functioning properly for the genes to do their job of keeping a person healthy, fit, and active. With a good model, we should be able to follow the path of an element (material) from its origin to its intended or unintended destination. The answers may be obtained through experimentation and by empirical and statistical compilation.
     When we compare the human body to engineering systems, we observe that the later work at idling, normal operating, and peak levels. Furthermore, engineering systems are designed for a certain design level but they operate at part load most of the time. For engineering systems, (fuel) inputs depend on the operating level and not on the capacity. If we apply this view, humans should have intakes (of food and water) at the level necessary for the operating level and not to fill the capacity (of the stomach). This view might give us a new outlook on the human body and life.
     When we investigate the functioning of a healthy human body and an unhealthy human body, such a model can be queried in two ways. Model levels 1 to 4 will tell us if the systems and organs are working properly or not. Levels 5 and 6 will tell us if the right materials are being produced, transported, and delivered at the right quantities and at the right times.
     Human bodies appear to go through three major stages. In the first stage, various organs and systems of the body grow. In the second stage, growth ceases. During both of these phases, cells in the body will also respond to the maintenance needs of the body, i.e. they attend to necessary repairs to parts of the body affected by internal and external negative influences. In the final stage, parts of the body decline leading to its end. An interesting comparison can be made with material based mechanical systems.
     When mechanical components are subjected to stress cycles, they have a finite life based on the stress level. When a component at the end of its life or near such an end is melted and the component is manufactured afresh, it gets full life again. In the case of human body components, as the cells renew the components continuously, the fatigue life is perhaps renewed constantly during childhood and adult life. But during the old age, cells may not be continuing the renewal process. In that case, the fatigue life is not renewed and components reach their end of life. This may explain why organs fail (e.g. osteoporosis and cerebral atrophy) as people reach old age.
     The digestion system presents an interesting feature. In this system, food enters as a mixture of solid and liquid. As this mixture is pushed through by mechanical forces generated by the muscles in the system, chemical and mechanical changes occur. When chemical engineers design and develop chemical reactors, they try to optimize the flow rate, heat and mass transfers, and the rates of various reactions. In the human digestion system, various chemicals enter at various points to effect certain reactions to digest the food consumed by a person and to transfer some intermediate products during the passage of the reacting mixture. The first question a scientist might ask is if the system (built by the body) is optimal or not. Even if the system was built for optimal processing, the human may consume wrong foods at the wrong time intervals and the optimal operation of the system may be impaired. Modeling alone can tell us how the system is functioning. For example, it may be possible to get models to verify if the human body was originally built to cope with consumption of alcohol and ingestion of tobacco smoke.
     We may define some key performance factors for the human body at the top level, such as, material inputs versus growth of body (height, waist, and weight), material intake versus energy and force outputs (horse power per pound of bodyweight, speed per foot of height, latency (time relationship between inputs and outputs), sensitivity of sensors, potency of actuators, transmission of characteristics to offspring, capacity of brain and intellectual and emotional inputs and reactions.
     Constant refinement of model information and data will improve the model as more features are represented in the constituent models. Medical and engineering researchers can work on their niches and the overall model can incorporate newer results as they become available.
    The suggested modeling effort helps the engineering field also. As stated in the goal statement of the DARPA Program [16] “Living Foundries seeks to transform biology into an engineering practice by developing the tools, technologies, methodologies, and infrastructure to speed the biological design-built-test-learn cycle and expand the complexity of systems that can be engineered.  The tools and infrastructure developed as part of this program are expected to enable the rapid and scalable development of transformative products and systems that are currently too complex to access.”
    Hierarchical modeling of the human body suggested in this document can lead to far reaching benefits to both the medical and engineering fields.

References and End Notes: [17]

 [1] Humans are spiritual and highly intelligent beings. The suggestion to develop an engineering model of the human body is not an attempt at trivializing the amazing capabilities of humans and the bodies. The functioning of the body is very complex. But we can start with the engineering functionality to begin to understand and explain how the body does the extraordinary actions.
[2] Som Karamchetty is a retired engineering researcher, manager, and business counselor.
 somkdsr@verizon.net, (240) 328-6513, www.karamchetty.net
[3] Dr. Hans Peter Fischer (2008) http://pubs.niaaa.nih.gov/publications/AA75/AA75.htm
Fischer, H.P. Mathematical modeling of complex biological systems: From parts lists to understanding systems behavior. Alcohol Research & Health 31(1):49–59, 2008. http://pubs.niaaa.nih.gov/publications/arh311/49-59.htm
[4] http://en.wikipedia.org/wiki/List_of_systems_of_the_human_body
[5] http://fas.org/press/news/2004/2004jun_digitalhuman.html and
http://fas.org/faspir/2004/v57n3/dh.htm
[6] http://www.scq.ubc.ca/systems-biology-an-overview/
[7] Picture source: N/A
[8] Picture source: N/A
[9] http://www.highlands.edu/academics/divisions/scipe/biology/labs/rome/histology.pdf


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