How does the human body power itself?

This query can be divided into sub-queries:

  1. What form/s of energy does the human body "run" on?
  2. Why/for what are these particular forms of energy required?
  3. From what can these types of energy be derived?
  4. How efficiently (less waste) does the body use energy?

Looking for a simple, effective answer with little to no jargon (distinction between pertinent use of terminology and showboating).

The question is broad and can hardly be fully answered in a single post. I will be very brief hoping it will help you and push you to seek for more knowledge.

Humans, like all other animals (or almost all) are chemo-organotroph. This mean we get our energy from the food we eat and we release this energy through oxydation. It is therefore chemical energy that we're using. We are then storing this energy into another chemical called ATP. Note that not only humans use ATP but any living thing on earth uses ATP (or GTP I think). ATP is then used (ATP loses one phosphate group and becomes ADP) to perform specific action (such as the use of a trans-membrane pump or the contraction of a muscle fiber).

You should have a look at wikipedia > Primary nutritional groups as well as wikipedia > chemotrophs and eventually this post.

For more information, please consider having a look at wikipedia and if you can't find feel free to ask your question in a new post. Always attempt to narrow your post down to a single, clearly defined question.

The Organization and Structure of the Human Body

The human body is made up of a complex structure of systems that all work together. There are several levels of organization to this structure, with each level more complex than the last.

smallest working part of a living organism.

series of organs and glands responsible for the ingestion, digestion, and absorption of food. Also called the alimentary canal.

tubular system in the human digestive system, which regulates elimination of waste products from the body.

cells, organs, and tissues including the brain and spine that respond to internal and external stimuli.

musical instrument made of pipes that release different sounds when a keyboard forces air through them.

cells that form a specific function in a living organism.

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Related Resources

Science 101: Human Body

How does the human body work? What roles do the digestive, reproductive, and other systems play? Learn about human anatomy and the complex processes that help your body function. This video contains depictions of the human body.

Introduction to Microbes and Human Body Systems

Students build a stronger understanding of how the human body is organized and interacts with microbes through a series of articles and videos and by creating a human body microbial map. Then they create a public service announcement on a specific microbe.

Icehouse 1

This earthen structure is one of four known icehouses that provided year-round ice supplies to the ancient city of Sultan Kala.

Related Resources

Science 101: Human Body

How does the human body work? What roles do the digestive, reproductive, and other systems play? Learn about human anatomy and the complex processes that help your body function. This video contains depictions of the human body.

Introduction to Microbes and Human Body Systems

Students build a stronger understanding of how the human body is organized and interacts with microbes through a series of articles and videos and by creating a human body microbial map. Then they create a public service announcement on a specific microbe.

Icehouse 1

This earthen structure is one of four known icehouses that provided year-round ice supplies to the ancient city of Sultan Kala.

How does the body heal itself from injury & illness?

The cells found in our physical bodies can heal themselves when they start getting damaged or unhealthy. They replicate to become new cells once they replace the damaged or destroyed cells. Using broken bones as an example, your body will immediately begin to produce new cells to heal all the damage that’s been done.

When your skin is cut, platelets in your blood clot to stop all the bleeding by forming a scab over the wound. White blood cells remove all the dead and injured cells while the healthy new cells repair the damaged tissue around the wound. This is one of the most important functions in our body! Could you imagine what life would be like if the daily cuts and bruises we experience never healed? Our bodies are always in a constant state of removing damaged cells and producing new, healthy tissue.

Biology KS3 & KS4: How humans heal themselves

Featuring ruptured blood cells, platelets and fibrin, this video covers all of the essential elements of clotting.

The wider immune system, and the role of macrophages in the bruise colour change, is also described.

This short film is from the BBC series, Inside the Human Body.

Teacher Notes

After viewing, students could investigate why not all body tissues are able to repair themselves like this, and thus the importance of stem cell research to enable body parts to heal themselves.

Their investigation could include a look into the ethical debate surrounding stem cell research, and case studies of how stem cell research has already helped patients.

Curriculum Notes

This short film will be relevant for teaching biology at KS3 and KS4/GCSE in England, Wales and Northern Ireland and National 4/5 in Scotland. Appears in AQA, OCR, EDEXCEL, CCEA, WJEC, SQA

The Anatomy Of Emotion

Emotions can be classified along two axes: valence and intensity. Valence has to do with the nature of an emotion, with how bad or good something makes us feel on a spectrum from avoidance to approach. Intensity refers to the strength of the emotion, the degree of arousal it evokes. We can actually map most emotions onto these two axes. Such a map doesn’t capture the entire essence of a particular emotion, but it does present it in a way that is useful when matching facial expressions to the brain systems that produce them.

Many structures in the brain are involved in emotion, but four of them are particularly important: the hypothalamus, which is the executor of emotion the amygdala, which orchestrates emotion the striatum, which comes into play when we form habits, including addictions and the prefrontal cortex, which evaluates whether a particular emotional response is appropriate to the situation at hand. The prefrontal cortex interacts with, and in part controls, the amygdala and striatum.

Many structures in the brain are involved in emotion, but four of them are particularly important.

We say the amygdala “orchestrates” emotion because it links the unconscious and conscious aspects of an emotional experience. When the amygdala receives sensory signals from the areas concerned with vision, hearing, and touch, it generates responses that are relayed onward, largely by the hypothalamus and other structures in the brain that control our automatic physiological responses. When we laugh or cry—when we experience any emotion—it is because these brain structures are responding to the amygdala and acting on its instructions. The amygdala is also connected to the prefrontal cortex, which regulates the feeling state, the conscious aspects of emotion, and its influence on cognition.

It goes without saying that our emotions need to be regulated. Aristotle argued that the proper regulation of the emotions was a defining feature of wisdom. “Anyone can become angry—that is easy,” he wrote in The Nicomachean Ethics. “But to be angry with the right person and to the right degree and at the right time and for the right purpose, and in the right way—that is not within everybody’s power and is not easy.”

Excerpted from The Disordered Mind: What Unusual Brains Tell Us About Ourselves by Eric R. Kandel, published in August by Farrar, Straus and Giroux. Copyright © 2018 by Eric R. Kandel. All rights reserved.

2 Answers 2

There is, I think, a problem with your question. The problem is that specifying total energy is not enough. Additionally, specifying power is not enough. Adding force is not enough. Adding speed is not enough. Let me explain.

Let's say energy is the only constraint. Then you can levitate rocks to high altitude and let them sit there, waiting for the command to drop. Making a modest assumption of 100 J/sec, you can lift a 1 pound rock about 20 meters in one second, do this for 50 seconds for a final height of 1 km, and it takes no energy to leave it there. Doing this for an 8-hour day will give you about 500 man-killers. Doing that for a month will give you a cloud of 15,000 rocks, enough to obliterate any village or small army.

Is this reasonable? Many don't think so, since it seems obvious that nobody can hold up 15,000 pounds. So applied force needs to be considered. And once you start considering force, how does magic deal with mechanical advantage? And how fast can a magician apply force? Consider throwing a rock. A major-league pitcher can throw a 5-ounce baseball 100 mph. That's 140 grams at 44 m/sec, or about 140 J. A 9 mm pistol slug has about 500 J, but is far more lethal than a baseball. Can a magician accelerate a small, dense body faster than a pitcher accelerate a baseball? Let's take a 1/3 oz flechette, a small dart about an inch long. At 140 J, it will have a speed of 140 m/sec, and will pierce a person's body all the way through. Remember those floating rocks? Replace each one with a 1 oz metal dart 3 or 4 inches long. Dropped from 1000 feet, one of these will punch all the way through a person - lengthwise. And a cloud of 320 of them will only weigh 20 pounds, and almost anybody can hold that weight indefinitely.

And then there's power density. Sunlight, with a power density of 1 kW/sq meter, can be focused by a 6-inch diameter magnifying glass to a spot size of less than 1 mm (as lots of kids have discovered, to the detriment of the local ant population). That's less than 20 watts to produce a nasty little burn. So it's clear that, if only power or energy is limited, 100 watts can do very bad things to one's enemies.

Finally, it gets worse if rather specialized knowledge is invoked. Creating light is a staple of magic. Knowing it's possible, what's to prevent the creation of coherent light? A laser beam of less than 100 mW is more than capable of temporarily blinding someone. Is there any good reason that a magician can't do it, rendering an attacker helpless at almost no energy cost? Focussed acoustic energy of a few watts is more than enough to destroy a person's eardrums. Is this allowed?

Why Your Biology Runs on Feelings

I have long been interested in human affect—the world of emotions and feelings—and have spent many years investigating it: why and how we emote, feel, use feelings to construct ourselves how feelings assist or undermine our best intentions why and how brains interact with the body to support such functions.

As for the idea, it is very simple: feelings have not been given the credit they deserve as motives, monitors, negotiators of human cultural endeavors. Humans have distinguished themselves from all other beings by creating a spectacular collection of objects, practices, and ideas, collectively known as cultures. The collection includes the arts, philosophical inquiry, moral systems and religious beliefs, justice, governance, economic institutions, and technology and science. Why and how did this process begin?

A frequent answer invokes an important faculty of the human mind—verbal language—along with distinctive features such as intense sociality and superior intellect. For those who are biologically inclined the answer also includes natural selection operating at the level of genes. I have no doubt that intellect, sociality, and language have played key roles in the process, and it goes without saying that the organisms capable of cultural invention, along with the specific faculties used in the invention, are present in humans by the grace of natural selection and genetic transmission. The idea is that something else was required to jump-start the saga of human cultures. That something else was a motive. I am referring specifically to feelings.

DO FISH HAVE FEELINGS?: “Once nervous systems entered the scene, the path for feelings was open,” writes Antonio Damasio. “That is why even humble nervous systems probably allow some measure of feeling.”

T o understand the origin and construction of feelings, and appreciate the contribution they make to the human mind, we need to set them in the panorama of homeostasis. The traditional concept of homeostasis refers to the ability, present in all living organisms, to continuously and automatically maintain their functional operations, chemical and general physiological, within a range of values compatible with survival. For numerous living creatures, however, and certainly for humans, this narrow usage of the term “homeostasis” is inadequate.

It is true that humans still make good use and greatly benefit from automatic controls: The value of glucose in the bloodstream can be automatically corrected to an optimal range by a set of complex operations that do not require any conscious interference on the part of the individual. The secretion of insulin from pancreatic cells, for example, adjusts the level of glucose. In humans and in numerous other species endowed with a complex nervous system, however, there is a supplementary mechanism that involves mental experiences that express a value. The key to the mechanism is feelings.

Nature could have evolved in another way and not stumbled upon feelings. But it didn’t.

Importantly, feelings are not an independent fabrication of the brain. They are the result of a cooperative partnership of body and brain, interacting by way of free-ranging chemical molecules and nerve pathways.

The alignment of pleasant and unpleasant feelings with, respectively, positive and negative ranges of homeostasis is a verified fact. Homeostasis in good or even optimal ranges expresses itself as well-being and even joy, while the happiness caused by love and friendship contributes to more efficient homeostasis and promotes health. The negative examples are just as clear. The stress associated with sadness is caused by calling into action the hypothalamus and the pituitary gland and by releasing molecules whose consequence is reducing homeostasis and actually damaging countless body parts such as blood vessels and muscular structures. Interestingly, the homeostatic burden of physical disease can activate the same hypothalamic-pituitary axis and cause release of dynorphin, a molecule that induces dysphoria.

The circularity of these operations is remarkable. On the face of it, mind and brain influence the body proper just as much as the body proper can influence the brain and the mind. They are merely two aspects of the very same being.

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Whether feelings correspond to positive or negative ranges of homeostasis, the varied chemical signaling involved in their processing and the accompanying visceral states have the power to alter the regular mental flow, subtly and not so subtly. Attention, learning, recall, and imagination can be disrupted and the approach to tasks and situations, trivial and not, disturbed. It is often difficult to ignore the mental perturbation caused by emotional feelings, especially in regard to the negative variety, but even the positive feelings of peaceful, harmonious existence prefer not to be ignored.

The roots for the alignment between life processes and quality of feeling can be traced to the workings of homeostasis within the common ancestors to endocrine systems, immune systems, and nervous systems. They go back in the mists of early life. The part of the nervous system responsible for surveying and responding to the interior, especially the old interior, has always worked cooperatively with the immune and endocrine systems within that same interior.

When a wound occurs, caused, for example, by an internally originated disease process or by an external cut, the usual result is an experience of pain. In the former case, the pain results from signals conveyed by old, unmyelinated C nerve fibers, and its localization can be vague in the latter case, it uses myelinated fibers that are evolutionarily more recent and that contribute to a sharp and well-localized pain.

Even humble nervous systems probably allow some measure of feeling.

However, the feeling of pain, vague or sharp, is only a part of what actually goes on in the organism and, from an evolutionary point of view, the most recent part of it. What else goes on? What constitutes the hidden part of the process?

The answer is that both immune and neural responses are engaged locally by the wound. These responses include inflammatory changes such as local vasodilation and a surge of leucocytes (white blood cells) toward the area. The leucocytes are called for to assist in combating or preventing infection and removing the debris of damaged tissue. They do the latter by engaging in phagocytosis—surrounding, incorporating, and destroying pathogens—and the former by releasing certain molecules. An evolutionarily old molecule—proenkephalin, an ancestral molecule and the first of its kind—can be cleaved, resulting in two active compounds that are released locally.

One compound is an antibacterial agent the other is an analgesic opioid that will act on a special class of opioid receptors—the δ class—located in the peripheral nerve terminals present at the site. The many signs of local disruption and reconfiguration of the state of the flesh are made locally available to the nervous system and gradually mapped, thus contributing their part to the multilayered substrate of the feeling of pain. But simultaneously, the local release and uptake of the opioid molecule helps numb the pain and reduces inflammation. Thanks to this neuro-immune cooperation, homeostasis is hard at work attempting to protect us from infection and trying to minimize the inconvenience, too.

But there is more to tell. The wound provokes an emotive response that engages its own suite of actions for example, a muscular contraction that one might describe as flinching. Such responses and the ensuing altered configuration of the organism are also mapped and thus “imaged” by the nervous system as part of the same event. Creating images for the motor reaction helps guarantee that the situation does not go unnoticed. Curiously, such motor responses appeared in evolution long before there were nervous systems. Simple organisms recoil, cower, and fight when the integrity of their body is compromised.

I n brief, the package of reactions to a wound that I have been describing for humans—antibacterial and analgesic chemicals, flinching and evading actions—is an ancient and well-structured response resulting from interactions of the body proper and the nervous system. Later in evolution, after organisms with nervous systems were able to map non-neural events, the components of this complex response were imageable. The mental experience we call “feeling pain” is based on this multidimensional image.

The point to be made is that feeling pain is fully supported by an ensemble of older biological phenomena whose goals are transparently useful from the standpoint of homeostasis. To say that simple life-forms without nervous systems have pain is unnecessary and probably not correct. They certainly have some of the elements required to construct feelings of pain, but it is reasonable to hypothesize that for pain itself to emerge, as a mental experience, the organism needed to have a mind and that for that to pass, the organism needed a nervous system capable of mapping structures and events. I suspect that life-forms without nervous systems or minds had and have elaborate emotive processes, defensive and adaptive action programs, but not feelings. Once nervous systems entered the scene, the path for feelings was open. That is why even humble nervous systems probably allow some measure of feeling.

Feelings have not been given the credit they deserve as motivators of human culture.

It is often asked, not unreasonably, why feelings should feel like anything at all, pleasant or unpleasant, tolerably quiet or like an uncontainable storm. The reason should now be clear: When the full constellation of physiological events that constitutes feelings began to appear in evolution and provided mental experiences, it made a difference. Feelings made lives better. They prolonged and saved lives. Feelings conformed to the goals of the homeostatic imperative and helped implement them by making them matter mentally to their owner as, for example, the phenomenon of conditioned place aversion appears to demonstrate. The presence of feelings is closely related to another development: consciousness and, more specifically, subjectivity.

The value of the knowledge provided by feelings to the organism in which they occur is the likely reason why evolution contrived to hold on to them. Feelings influence the mental process from within and are compelling because of their obligate positivity or negativity, their origin in actions that are conducive to health or death, and their ability to grip and jolt the owner of the feeling and force attention on the situation.

This distinctive account of feelings illustrates the fact that mental experiences do not arise from plain mapping of an object or event in neural tissue. Instead, they arise from the multidimensional mapping of body-proper phenomena woven interactively with neural phenomena. Mental experiences are not “instant pictures” but processes in time, narratives of several micro events in the body proper and the brain.

It is conceivable, of course, that nature could have evolved in another way and not stumbled upon feelings. But it didn’t. The fundamentals behind feelings are so integral a part of the maintenance of life that they were already in place. All that was needed in addition was the presence of mind-making nervous systems.

Ultimately, feelings can annoy us or delight us, but that is not what they are for. Feelings are for life regulation, providers of information concerning basic homeostasis or the social conditions of our lives. Feelings tell us about risks, dangers, and ongoing crises that need to be averted. On the nice side of the coin, they can inform us about opportunities. They can guide us toward behaviors that will improve our overall homeostasis and, in the process, make us better human beings, more responsible for our own future and the future of others.

Antonio Damasio is a university professor David Dornsife Professor of Neuroscience, Psychology, and Philosophy and director of the Brain and Creativity Institute at the University of Southern California. Awards he has received include the Prince of Asturias Prize in Science and Technology, the Grawemeyer Award, the Honda Prize, and the Pessoa and Signoret prizes. In 2017 he received the Freud Medal from the Royal Dutch Academy of Sciences. Damasio is a member of the National Academy of Medicine and a fellow of the American Academy of Arts and Sciences and the Bavarian Academy of Sciences. He is the author of Descartes’ Error, The Feeling of What Happens, Looking for Spinoza and Self Comes to Mind, all of which have been published in translation and are taught in universities throughout the world.

From the book The Strange Order of Things by Antonio Damasio, © 2018 by Antonio Damasio. Published by arrangement with Pantheon Books, a division of Penguin Random House LLC.

Human Organs

An organ is a collection of tissues joined in a structural unit to serve a common function. Organs exist in most multicellular organisms, including not only humans and other animals but also plants. In single-celled organisms such as bacteria, the functional equivalent of an organ is an organelle.

Tissues in Organs

Although organs consist of multiple tissue types, many organs are composed of the main tissue that is associated with the organ&rsquos major function and other tissues that play supporting roles. The main tissue may be unique to that specific organ. For example, the main tissue of the heart is the cardiac muscle, which performs the heart&rsquos major function of pumping blood and is found only in the heart. The heart also includes nervous and connective tissues that are required for it to perform its major function. For example, nervous tissues control the beating of the heart, and connective tissues make up heart valves that keep blood flowing in just one direction through the heart.

Vital Organs

The human body contains five organs that are considered vital for survival. They are the heart, brain, kidneys, liver, and lungs. The locations of these five organs and several other internal organs are shown in Figure (PageIndex<2>). If any of the five vital organs stops functioning, the death of the organism is imminent without medical intervention.

  1. The heart is located in the center of the chest, and its function is to keep blood flowing through the body. Blood carries substances to cells that they need and also carries away wastes from cells.
  2. The brain is located in the head and functions as the body&rsquos control center. It is the seat of all thoughts, memories, perceptions, and feelings.
  3. The two kidneys are located in the back of the abdomen on either side of the body. Their function is to filter blood and form urine, which is excreted from the body.
  4. The liver is located on the right side of the abdomen. It has many functions, including filtering blood, secreting bile that is needed for digestion, and producing proteins necessary for blood clotting.
  5. The two lungs are located on either side of the upper chest. Their main function is exchanging oxygen and carbon dioxide with the blood.

Anatomy and Physiology of Human Ribs

Both men and women have 12 pairs of ribs.1 These ribs extend from the vertebrae to form the wall of the thoracic cavity (where the lungs and heart reside). The first seven pairs of ribs are called true ribs and connect to the sternum. The remaining five pairs of ribs are called false ribs because they don’t attach directly to the sternum. Ribs 8–10 attach to cartilage that attaches the true ribs to the sternum, and ribs 11–12 are floating—they do not attach to the sternum or other ribs.

The function of ribs is threefold. First, they provide protection for the lungs and heart. The ribs more or less form a “cage” around these very important organs. Second, they are one of the few bones that continue to make red marrow (and thus blood cells) in the adult. Third, they serve as attachment points for chest muscles involved in respiration.

The rib cage can be thought of as a handle on a bucket. When we breathe in, the muscles attached to the ribs pull the ribs out just as when you lift the handle on a bucket from the side—it goes out and up. The lungs are coordinated with this movement, expanding and taking air in. The opposite occurs when we breathe out the muscles attached to the ribs relax, and the ribs go down and in (just like dropping a bucket handle)—and the lungs follow (become smaller), causing air to leave.

The absence of this latter function was known by our Savior during His crucifixion on the cross. In crucifixion the arms are stretched to the extent that the chest muscles connecting to the ribs are pulled tight. A person enduring crucifixion can breathe in, but they have a difficult time breathing out. The ribs remain in a fixed position because the muscles attached to the ribs can’t relax. Thus, the lungs can’t become smaller, which is necessary for air to leave.

Jesus would have had to lift Himself up (scraping a severely beaten back on the wooden cross) to allow the chest muscles to relax and the rib cage to move so He could breathe out. To think that He did this successfully for several hours and managed to say seven phrases during that time period should make us appreciate even more His sacrifice for us.

Biological Project Ideas


  • Does a person's BMI affect their blood pressure?
  • What is the average normal body temperature?
  • Which types of exercise are most effective for increasing muscle growth?
  • How do various types of acid (phosphoric acid, citric acid, etc.) affect tooth enamel?
  • How do heart rate and blood pressure vary during the day?
  • Does exercise affect lung capacity?
  • Does blood vessel elasticity affect blood pressure?
  • Does calcium impact bone strength?


  • Do food smells affect saliva production?
  • Does eye color affect a person's ability to distinguish colors?
  • Does light intensity affect peripheral vision?
  • Do different stressors (heat, cold, etc.) affect nerve sensitivity?
  • How is sense of touch affected by scar tissue?
  • What is the highest and lowest frequency that the average person can hear?
  • Does the heat of food impact the effectiveness of different types of taste (salty, sour, sweet, bitter, umami)
  • Is sense of smell or sense of touch more useful in effectively identifying unknown objects without the use of other senses?