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Biology LibreTexts

10.2: Organization of the Body

  • Page ID
    22511
  • A Fantastic Machine

    This six-legged robot was created for research, but it looks like it might be fun to play with. It’s obviously a complex machine. Think about some other, more familiar machines, such as power drills, washing machines, and lawn mowers. Each machine consists of many parts, and each part does a specific job, yet all the parts work together to perform certain functions. Many people have compared the human body to a machine, albeit an extremely complex one. Like real machines, the human body also consists of many parts that work together to perform certain functions, which in the case of the human body include keeping the organism alive. The human body may be the most fantastic machine on Earth, as you will discover when you learn more about it in this concept.

    six-legged robot
    Figure \(\PageIndex{1}\): (By FZI Forschungszentrum Informatik Karlsruhe - Abteilung IDS [Copyrighted free use], via wikimedia.org)

    What the Human Machine Can Do

    Imagine a machine that has all of the following attributes. It can generate a “wind” of 166 km/hr (100 mi/hr), and it can relay messages faster than 400 km/hr (249 mi/hr). It contains a pump that moves about a million barrels of fluid over its lifetime, and it has a control center that contains billions of individual components. The machine in question can even repair itself if necessary and not wear out for up to a century or more. It has all these abilities, and yet it consists mainly of water. What is it? It is the human body.

    Organization of the Human Body

    Levels of Organization in Body
    Figure \(\PageIndex{2}\): This diagram shows the levels of organization of the human body, from atoms to the whole organism. (CC BY: on opentextbc.ca)

    The human body is a complicated, highly organized structure that consists of trillions of parts that function together to achieve all the functions needed to maintain life. The biology of the human body incorporates the body’s structure, the study of which is called anatomy, and the body’s functioning, the study of which is called physiology.

    The organization of the human body can be seen as a hierarchy of increasing size and complexity, starting at the level of atoms and molecules and ending at the level of the entire organism, which is an individual living thing. You can see the intervening levels of organization in Figure \(\PageIndex{2}\) and read about them in the figure and the sections that follow.

    Cells

    The basic units of structure and function of the human body, as in all living things, are cells — an amazing 37 trillion of them by the time the average person reaches adulthood! Each cell carries out basic life processes that allow the body to survive. In addition, most human cells are specialized in structure and function to carry out other specific roles. In fact, the human body may consist of as many as 200 different types of cells, each of which has a special job to do. Just a few of these different human cell types are pictured in the figure below. The cells in the figure have obvious differences in structure that reflect their different functions. For example, nerve cells have long projections sticking out from the body of the cell. These projections help them carry electrical messages to other cells.

    variety animal cells

    Figure \(\PageIndex{3}\): A few of the many different types of cells in the human body are illustrated here. Each type of cell is specialized for a particular role in the body. (Sunshineconnelly at en.wikibooks [CC BY 3.0]; via Wikimedia.org)

    Tissues

    After the cell, the tissue is the next level of organization in the human body. A tissue is a group of connected cells that have a similar function. There are four basic types of human tissues: epithelial, muscle, nervous, and connective tissues. These four tissue types, which are shown in the figure below, make up all the organs of the human body.

    Four types of tissue

    Figure \(\PageIndex{4}\): The human body contains these four types of tissues. (www.nlm.nih.gov [Public domain]; via Wikimedia.org)

    Organs and Organ Systems

    Six of the organ systems
    Figure \(\PageIndex{5}\): Six of the organ systems that make up the human body are presented here. (OpenStax College. Anatomy & Physiology, Connexions Web site. cnx.org [CC BY-SA 4.0; via Wikimedia.org])

    After tissues, organs are the next level of organization of the human body. An organ is a structure that consists of two or more types of tissues that work together to do the same job. Examples of human organs include the heart, brain, lungs, skin, and kidneys. Human organs are organized into organ systems, six of which are shown in the figure above. An organ system is a group of organs that work together to carry out a complex overall function. Each organ of the system does part of the larger job.

    A Well-Oiled Machine

    All of the organs and organ systems of the human body normally work together like a well-oiled machine. This is because they are closely regulated by the nervous and endocrine systems. The nervous system controls virtually all body activities, and the endocrine system secretes hormones that help to regulate these activities. Functioning together, the organ systems supply body cells with all the substances they need and eliminate their wastes. They also keep temperature, pH, and other conditions at just the right levels to support life.

    Summary

    • The organization of the human body is a hierarchy of increasing size and complexity, starting at the level of atoms and molecules and ending at the level of the entire organism.
    • Cells are the level of organization above atoms and molecules, and they are the basic units of structure and function of the human body. Each cell carries out basic life functions as well as other specific roles. Variations in cell function are generally reflected in variations in cell structure.
    • The next level of organization above cells is the tissue. A tissue is a group of connected cells that have a similar function. There are four basic types of human tissues: epithelial, muscle, nervous, and connective tissues. These four types of tissues make up all the organs of the human body.
    • The next level of organization above tissues is the organ. An organ is a structure that consists of two or more types of tissues that work together to do the same job. Examples include the brain and heart.
    • Human organs are organized into organ systems. An organ system is a group of organs that work together to carry out a complex overall function. For example, the skeletal system provides structure to the body and protects internal organs.

    Review

    1. How is the human body like a complex machine?
    2. Compare and contrast human anatomy and human physiology.
    3. Summarize the hierarchical organization of the human body.
    4. Relate cell structure to cell function, and give examples of specific cell types in the human body.
    5. Define tissue, and identify the four types of tissues that make up the human body.
    6. What is an organ? Give three examples of organs in the human body.
    7. Define organ system, and name five organ systems in the human body.
    8. True or False. How cells use oxygen is an example of physiology.
    9. The organ system that secretes hormones is called the _______________ system.
    10. A neuron is a:

      A. specialized cell       B. unspecialized cell

      C. an organ               D. an organ system

    11. Which organ system’s function is to provide structure to the body and protect internal organs?

    12. How is the human body regulated so all of its organs and organ systems work together
    13. True or False. Organs consist of one or more types of tissue.
    14. Give one example of how the respiratory and circulatory systems work together.

    15. The human body has as many as _________ types of cells

      A. 4     B. 20

      C. 137   D. 200

    Explore More

    The human body consists of more than just human cells, tissues, organs, and organ systems. It also includes a huge number of single-celled organisms that live inside the body and have a great and largely unexplored role in our health. You can learn more about the three pounds of microbes that you carry around with you by watching this eye-opening TED talk.

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