External Environment

Skin separates the internal and external environments.

Extracellular fluid, which differs in composition from the external environment, bathes all cells of the organism.

Foods, salts, and water

External Environment The Body

Some organs carry out the exchange of materials between the internal and external environments.

Cells of organs exchange materials with each other via the internal environment.

Some organs carry out the exchange of materials between the internal and external environments.

Cells of organs exchange materials with each other via the internal environment.

Other cells became specialized to provide nutrients, and still others to maintain appropriate levels of oxygen and carbon dioxide. As multicellular animals evolved to be larger and more complex, specialized cells formed specialized tissues, and different tissues became incorporated into organs and organs became incorporated into organ systems to control various properties of the internal environment (see Figure 41.1).

The composition of the internal environment is constantly being challenged by the external environment and by the activities of cells themselves. For example, during a race, the muscle cells in Lance Armstrong's legs are taking up oxygen and fuel molecules and releasing carbon dioxide and lactic acid. Their metabolism is contributing heat to the internal environment. Lance sweats to dissipate that heat and thereby loses water and salts from his internal environment. For Lance to continue in the race, his cells, tissues, and organs must continuously correct the physical and chemical composition of his internal environment so that his muscle cells can function optimally.

The maintenance of constant conditions in the internal environment is called homeostasis. Homeostasis is an essential feature of complex animals. If an organ fails to function properly, homeostasis is compromised, and as a result, cells become damaged and die—not just those of the malfunction ing organ, but the cells of other organs as well. To avoid loss of homeostasis, the activities of organs must be controlled and regulated in response to changes in both the external and internal environments.

Control and regulation require information; hence the organ systems of information—the endocrine and nervous systems—must be included in our discussions of every physiological function. For that reason, we treat the endocrine and nervous systems early in Part Seven. Subsequent chapters deal with the organ systems responsible for controlling various aspects of the internal environment. Although each chapter will focus on different organs, those organs are all made of the same tissue types. What are these tissue types, and what are their general features?

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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Responses

  • Dirk
    What type of tissue separates the internal from the external environment?
    8 years ago
  • belladonna labingi
    How the body exchanges materials between the internal and external environment.?
    8 years ago
  • natalia padovano
    What separates the internal environment of the body from the external environment?
    8 years ago
  • minto
    What are examples of external environment of plasma membrane?
    8 years ago
  • Karri
    What seperates the internal environment of the body from the external environment?
    8 years ago
  • alfredino
    Which body system seperates the internal and external enviorments?
    7 years ago

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