Homeostasis: the state of equilibrium (balance or stability) within a system such as an organism or a cell. “Home-” refers to similar, and “stasis” means stable or balance.

This internal state of balance is self-regulated by various systems in the body such as the nervous system and endocrine system. Homeostasis requires that the body’s internal processes are balanced and functioning within parameters. Feedback mechanisms detect when something in the body needs to be changed in order to maintain homeostasis. These feedback mechanisms strive to keep the body’s systems, processes and outputs within established parameters and at optimal levels. Hormones, neurotransmitters and receptors are used to send and receive messages within the body and maintain homeostasis.

The body must also adapt and maintain homeostasis in response to external factors. For example, adapting to environmental changes such as changes in room temperature. In this example, the body can shiver in response to cold, or even change its rate of metabolism for long-term exposure to cold.

Terminology Related to Homeostasis

Feedback or a feedback loop occurs when the physiological outputs of body processes are detected by the source of the output.

Negative feedback loop: promotes equilibrium and homeostasis by creating a change in the opposite direction of the stimulus. For example, if glucose levels get too high, the body releases insulin (hormone) to bring the glucose level back to normal parameters. It glucose levels get too low, then the body releases a glucagon (hormone) to increase the blood glucose level.

Positive feedback loop: this is an amplification process that creates an even more unstable state within the body. It is like a chain reaction or snowball effect. For example, once labor contractions begin, they become stronger and occur at an increased frequency until the baby is born.

Hormone: chemical messengers that are produced by endocrine glands. Hormones signal other tissues in the body in order to regulate their physiological processes. Hormones are typically released into the bloodstream. Examples of hormones are cortisol, oxytocin, estrogen, testosterone, melatonin, and thyroxin.

Neurotransmitter: endogenous (made by the body) chemical messengers that transmit signals across a synaptic cleft to receptors on a target cell. Neurotransmitters can be excitatory, inhibitory, or modular. Examples include acetylcholine, glutamate, dopamine, serotonin, GABA, norepinephrine, histamine, adrenaline. *Some chemical messengers function as both a hormone and a neurotransmitter.

Examples of Homeostasis in the Body

The following are examples of human conditions in the body that must be kept relatively constant (state of homeostasis):

Core temperature (98.6 deg F.)
Blood component levels (oxygen, carbon dioxide, blood glucose, fluid balance, etc.)
Blood pH between 7.35 to 7.45
Electrolyte and mineral levels (potassium, calcium, salt…)
Maintaining blood pressure around 120/80 mmHg
Respiration rate to keep correct O2 and CO2 balance

Shivering is an involuntary response that the body can use to generate heat and raise the body’s core temperature if it drops below its threshold.

Negative feedback loop

They are both chemical messengers.

homeostasis

synaptic cleft (or synapse)

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