Homeostasis is the property of a system in which variables are regulated so that internal conditions remain stable and relatively constant.

Negative feedback loop in maintenance of homeostasis

Homeostasis - negative feedback loop diagram

The importance of homeostasis in the human body

Healthy people share certain bodily constants:

  1. a blood glucose concentration that remains at about 100 mg/mL,
  2. a blood pH near 7.4,
  3. a blood pressure of about 160/106 KPa (120/80 mm Hg),
  4. a body temperature of approximately 37°C.

Maintenance of homeostasis means to keep different bodily constants in a dynamic equilibrium what is important to optimal functioning of the human body.

Dynamic equilibrium is a state of balance achieved within an environment as the result of internal control mechanisms that continuously oppose outside forces that tend to change that environment.

Most homeostatic mechanisms operate as negative feedback loops.

Positive and negative feedback loops in maintenance of homeostasis

Negative feedback in homeostasis

A negative feedback loop is a process that detects and reverses deviations from normal body constants.

To maintain homeostasis, negative feedback loops exist throughout the body.

These systems prevent blood sugar, blood pressure, temperature, and other body constants from becoming too high or too low.

Homeostasis and temperature regulation in humans

In 1775, Dr. Charles Blagden of the Royal Society of London tested the human body’s ability to withstand heat. 

He had a special room heated to 126°C, well above the boiling point of water. He then entered the room with a pet dog and a piece of raw meat.

After 45 minutes, he left the room with no ill effects other than a pulse rate that had increased to 144 beats per minute (about twice its normal rate). The dog, too, was fine, but the meat had been cooked.

Negative feedback loop in temperature homeostasis

Homeostasis mechanisms for regulation of body temperature in humans

Positive feedback in homeostasis

Positive feedback loops also exist, but they are usually associated with disease or change (for example, drug addiction).

An example of a positive feedback loop is high blood pressure.

Damage to arteries due to high blood pressure results in the formation of scar tissue. This scar tissue traps cholesterol, which impedes the flow of blood through the arteries and thereby increases blood pressure even more.

Another example of a positive feedback loop is an action of oxytocin hormone during childbirth

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