Topic 3.1: Maintaining the Internal Environment

Vocabulary-style flashcards covering the concepts of homeostasis, tolerance limits, the stimulus-response model, and feedback loops based on the lecture notes.

Homeostasis

The maintenance of a relatively constant internal environment to ensure the optimum conditions for the body to function.

Structural mechanisms

Physical features which help with tolerating changes, such as fur on animals that live in cold climates.

Physiological mechanisms

Internal processes that detect and respond to changes, such as the release of insulin when blood sugar is high.

Behavioural mechanisms

Things that organisms do to avoid or counteract changes, such as animals being active at dawn and dusk in hot climates.

Tolerance limit

The small range that variable factors can be within before an organism is adversely affected.

Hyperthermia

A condition occurring when the body temperature rises above the tolerance limit ($36-38^{\circ}\text{C}$), causing proteins to denature and cellular processes to become inefficient.

Hypothermia

A condition occurring when the body temperature is too low, causing chemical reactions and bodily processes to occur too slowly.

Isotonic solution

A solution where animal cells thrive because it prevents them from gaining too much water (lysing) or losing too much water (shrivelling); for blood plasma, this is about $0.9\%\, \text{NaCl}$.

Acidosis

A condition where too much carbonic acid in the blood lowers the pH, damaging proteins and altering other chemical reactions; caused by blood carbon dioxide levels exceeding $5-6\%$.

Hypoglycemia

A condition where blood glucose concentration is below the optimal range of $750-950\,\text{mg/L}$, resulting in cells having less access to energy.

Hyperglycemia

A condition where blood glucose concentration is too high, leading to damaged tissue and a high risk of infection.

Set point

The optimal value for a specific variable factor within an organism.

Stimulus

A variable factor in the internal or external environment that can be detected by the organism.

Receptors

Cells or tissues that detect a change in the external or internal environment.

Transmission

The relay of information via nerves and/or hormones to an effector.

Effector

Usually a gland or muscle that brings about a response after receiving information.

Response

An action which occurs due to the initial stimulus.

Feedback

The impact of the response on the initial stimulus, which can be positive or negative.

Control centre

The component that analyses information from the receptor and determines the appropriate response to a change.

Negative feedback loop

A response model that seeks to remove the initial stimulus and return the body to the set state.

Positive feedback loop

A response model where the body's response further increases the stimulus, used to sustain medium or long term physiological changes such as breastfeeding or immune response.