Homeostasis and the Stimulus-Response Model

Vocabulary based on the introduction to Homeostasis, the Stimulus-Response Model, and feedback mechanisms.

Homeostasis

The maintenance of a stable internal environment within a narrow field/tolerance limits, allowing chemical reactions within cells to occur effectively.

Stimulus

An imbalance or change detected in the environment that triggers the stimulus-response model.

Receptors

Specialised structures used by organisms to detect changes in the environment (stimuli).

Exteroceptors

Receptors that receive signals from the external environment, such as changes to outside temperature, noises, or light levels.

Interoceptors

Receptors that receive signals from the organism’s internal environment, such as changes to internal temperature, sugar levels, or enzyme levels.

Afferent pathway

The pathway through which input is sent to the Control Centre after a change is detected.

Control Centre

Typically the brain, where information is integrated and processed for a decision to be made.

Efferent pathway

The pathway through which output is sent from the Control Centre to the effector.

Effector

Muscles or glands which produce a required response, such as the pancreas or skeletal muscles.

Extracellular fluid

The fluid outside of cells, which includes blood plasma, tissue fluid, lymph, and cerebro-spinal fluid.

Intracellular fluid

The fluid found inside of cells, also known as cytosol.

Negative Feedback

A control system that responds when conditions change from the ideal or set point and works to counteract the signal to return conditions to that set point.

Positive Feedback

A mechanism that drives a factor further away from its desired amount or set point rather than returning it (e.g., giving birth).

Vasodilation

The relaxation of smooth muscles in arterioles to maximise blood flow to the skin, allowing excess heat to radiate to surroundings.

Thermoreceptors

Specific receptors located in the skin and Hypothalamus that detect changes in temperature.

Homeostatic Blood Sugar Range

The ideal concentration of glucose in the blood, typically kept between $3.9-5.6\,mmol/L$.

Concentration of Ions

Factors maintained by homeostasis involving specific charged particles like $K^+$ and $Na^+$.

Homeostatic Temperature Range

The narrow range in which human body temperature is typically kept, defined as $37 \pm 2^{\circ}C$.