Organ systems: definition and examples

Organisation • Principles of organisation

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What causes nutritional supplies to cells to decrease despite normal digestion?

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Transport failure such as reduced blood flow prevents delivery of absorbed nutrients to tissues.

Key concepts

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Definition

An organ system is a group of organs that work together to carry out one or more major functions for an organism. The term limits scope to cooperating organs rather than single tissues or cells. Examples include the digestive, circulatory and respiratory systems .

Hierarchy of biological organisation

Cells form tissues, tissues form organs, and organs form organ systems. Higher-level functions arise when organs combine in systems; system failure often follows dysfunction in one or more component organs, reducing overall function and affecting the organism's state .

Cause → effect: organ cooperation

When organs share tasks and communicate, the system performs a complex function (cause). For example, the digestive system breaks down food into small molecules (cause), which enables absorption of nutrients into the blood (effect) and supplies cells with substrates for respiration and growth .

Homeostasis and organ systems

Multiple organ systems cooperate to maintain stable internal conditions. If sensory or control organs detect a change, endocrine or nervous system responses occur (cause) and corrective actions restore balance (effect). Disruption of any system can impair homeostasis and alter body functions .

Limiting factors and system performance

System performance depends on the health and capacity of individual organs, available energy, and communication between organs. A single failing organ or limited resource reduces overall system output (effect). For example, blocked blood vessels reduce oxygen transport despite healthy lungs and heart muscles.

Key notes

Important points to keep in mind

Organ systems are collections of specialised organs that act together to perform major life functions.

Hierarchy: cells → tissues → organs → organ systems → organism.

Cause → effect: organ cooperation produces system-level functions; organ failure reduces system output.

Homeostasis depends on multiple systems working together; disruption of one system affects internal stability .

Examples of limiting factors: organ damage, restricted blood flow, reduced surface area for exchange.

The pancreas is both an exocrine gland (digestive enzymes) and an endocrine gland (hormones).

Villi and alveoli increase surface area to maximise exchange rates in digestive and respiratory systems respectively .

Nervous control is rapid; hormonal control is slower but longer lasting.