Homeostasis

Tolerance Range

Difference between maximum and minimum tolerance limits.

Limiting Factor

A variable that, when in low supply, will limit a process or the growth of an organism. Shown as plateau on graph.

Examples of Factors for which Organisms have Tolerance Limits

• Body temperature.

• Water availability.

• Blood glucose level.

• Carbon dioxide concentration in blood and tissues.

Homeostasis

The maintenance of a relatively constant internal environment, ensuring the body optimum conditions to function. Keeps conditions in a tolerance range, does not keep conditions static.

Reasons Homeostasis is Important for Humans

• Maintaining optimal conditions for maximum function.

• Maintaining optimal conditions for metabolic processes, such as aerobic respiration.

• Keeping toxic substances, such as carbon dioxide, at low concentrations to prevent impacts on metabolic processes.

Stimulus

A detectable change in the internal or external environment.

Sensory Receptors

Parts of cells or groups of cells in the body that detect stimuli.

Sensory Receptor Types

Thermoreceptor

• Sensory nerve sensitive to temperature changes.

• Found in skin, muscle cells, liver, Hypothalamus.

Mechanoreceptor

• Sensory nerve that responds to mechanical stimuli, such as touch or sound.

• Found in muscle tissues, skin, ear.

Photoreceptor

• Specialised neurons in retina that convert light into nerve impulses.

Chemoreceptor

• Sensory nerve that translates chemical substances into biological signals.

• Found in Hypothalamus, tongue, central nervous system.

Stimulus Response Model (Negative Feedback Loop)

1. Stimulus causes imbalance in homeostasis.

2. Receptors of sensory neuron detect stimulus.

3. Input sent through interneurons to control centre (brain).

4. Output sent via interneurons to motor neurons.

5. Effector of motor neuron creates response to change.

6. Imbalance in homeostasis is corrected.

*Loops back to beginning here.

Hypothalamus

Small region in brain that acts as a control centre for various bodily functions and behaviours. Regulates activities such as hunger, thirst, body temperature, and sleep. Also plays role in hormone production and emotion regulation.