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Body structure and homeostasis review

Key terms

HomeostasisThe tendency to resist change in order to maintain a stable, relatively constant internal environment
Negative feedback loopFeedback loop that acts to oppose the triggering stimulus
Positive feedback loopFeedback loop that amplifies the starting signal
CellSmallest unit of life
TissueMade of a group of similar cells that work together on a specific task
OrganStructure made up of two or more tissues, organized to carry out a specific function
Organ systemGroups of organs with related functions

Maintaining homeostasis

The body maintains homeostasis for many factors. Some of these include body temperature, blood glucose, and various pH levels.
Homeostasis is maintained at many levels, not just the level of the whole body as it is for temperature. For instance, the stomach maintains a pH that's different from that of surrounding organs, and each individual cell maintains ion concentrations different from those of the surrounding fluid. Maintaining homeostasis at each level is key to maintaining the body's overall function.

Feedback loops

Homeostasis typically involves negative feedback loops that counteract changes of various properties from their target values. An example of a negative feedback loop is body temperature regulation.
Example of negative feedback loop
The maintaining of body temperature is an example of a negative feedback loop. When body temperature increases, there are mechanisms that work to decrease temperature, and vice versa.
In contrast to negative feedback loops, positive feedback loops amplify their initiating stimuli, in other words, they move the system away from its starting state.
Example of positive feedback loop
The ripening of fruit is an example of a positive feedback loop, as ethylene continues to trigger ripening in neighboring fruit.

Body structure

The body has levels of organization that build on each other. Cells make up tissues, tissues make up organs, and organs make up organ systems.
From left to right: single muscle cell, multiple muscle cells together forming muscle tissue, organ made up of muscle tissue (bladder), and organ system made up of kidneys, ureter, bladder and urethra.
Image credit: modified from Levels of structural organization of the human body by OpenStax College, Anatomy & Physiology, CC BY 4.0
At each level of organization (cells, tissues, organs, and organ systems), structure is closely related to function.

Common mistakes and misconceptions

  • Negative feedback is not bad for the body. Although the term "negative" is included, these feedback loops are essential and helpful to the body. In this instance, "negative" simply means that the feedback loop works to counter the stimulus, or cue, not that the feedback loop is detrimental.
  • Homeostasis is more than just "keeping things normal, and the body doesn't always know what is best for itself. " The body is constantly regulating itself and the mechanisms to maintain homeostasis are always in play. Sometimes, however, these homeostatic mechanisms can fail. If the conditions are not corrected, a disease or disorder can result. For example, if the amount of calcium in your blood is not properly regulated and becomes too low, you could develop hypocalcemia.

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