Introduction to Homeostasis and Feedback Mechanisms

These vocabulary flashcards cover the core concepts of homeostasis, regulated versus nonregulated variables, the components of feedback loops, positive and negative feedback examples, and levels of physiological control in the human body.

Homeostasis

The maintenance of a relatively constant internal fluid environment within a small, acceptable range.

Set range for blood sugar

The body aims to keep blood sugar between $80$ and $100$, with $90$ being the neutral target point.

Normal core body temperature

In scientific terms, the body's internal temperature set point is $37^{\circ}C$.

Law of mass balance

The principle that to maintain homeostasis, the body's total input (what is eaten, drunk, or breathed in) should equal its total output (what is excreted, sweated, or breathed out).

Internal environment

The fluid environment inside the body; notably, substances in the digestive tube or lungs are not part of this until they cross a membrane.

Physiologic variable

A state or condition in the body that is monitored and can change, such as blood pressure or heart rate.

Regulated variable

A variable that the body is constantly monitoring and keeping track of, such as blood pressure.

Nonregulated variable

A variable not monitored by the body that changes in an attempt to stabilize a regulated variable, such as heart rate changing to fix blood pressure.

Normal human heart rate range

The standard set point range for a human heart rate is between $60$ and $100$ beats per minute.

Sensor

The component of a feedback loop that detects a change in a set point variable.

Integrator

Also known as the air detector or controller, this center receives sensory information and compares it to the set point to decide if a correction is needed.

Effector

An organ, gland, or tissue that produces an effect to influence the variable that was originally sensed.

Afferent

Sensory information that is arriving at an integration center.

Efferent

Information exiting the integration center to travel to an effector.

Negative feedback mechanism

The most common feedback loop in the body that negates or reverses the stimulus (e.g., shivering to increase temperature when a drop is sensed) to maintain homeostasis.

Thermoreceptors

Sensory receptors in the skin that detect changes in temperature.

Positive feedback loop

A non-homeostatic mechanism that stimulates, enhances, or amplifies a change until a specific outcome occurs; examples include blood clotting and childbirth.

Oxytocin

A hormone used in positive feedback loops to increase uterine contractions during labor and to cause the ejection of breast milk during nursing.

Feed forward mechanism

A process where the body anticipates a stimulus before it happens to prepare a system, such as salivating when seeing food.

Intracellular control

Regulation of functions that occurs at the level of individual cells.

Intrinsic control

Also called local control, this occurs when a tissue or organ regulates itself, usually through chemical signals.

Extrinsic control

Regulation at the system or organism level, primarily involving the nervous and endocrine (hormone) systems.

Carpal

A term referring to the wrist or the wrist bones.

Hallux

An anatomical term referring to the big toe.

Pollex

An anatomical term referring to the thumb.