Key terms
Term Meaning
Homeostasis The tendency to resist change in order to maintain a stable, relatively constant internal environment
Negative feedback loop Feedback loop that acts to oppose the triggering stimulus
Positive feedback loop Feedback loop that amplifies the starting signal
Cell Smallest unit of life
Tissue Made of a group of similar cells that work together on a specific task
Organ Structure made up of two or more tissues, organized to carry out a specific function
Organ system Groups 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.

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.

The ripening of fruit is an example of a positive feedback loop, as ethylene continues to trigger ripening in neighboring fruit.

 

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

 

Fun facts
The human body contains nearly 100 trillion cells.
There are at least 10 times as many bacteria in the human body as cells.
The average adult takes over 20,000 breaths a day.
Each day, the kidneys process about 200 quarts (50 gallons) of blood to filter out about 2 quarts of waste and water
Adults excrete about a quarter and a half (1.42 liters) of urine each day.
The human brain contains about 100 billion nerve cells
Water makes up more than 50 percent of the average adult’s body weight