Organ Systems

Summary: Human Body Systems and Organization

Key Concepts

• The human body is organized into levels: cells → tissues → organs → organ systems.

• Organ systems work together to perform essential life functions.

• Survival depends on the integration and coordination of all systems, regulated mainly by the nervous and endocrine systems.

Levels of Organization

1. Cells: Basic unit of life.

2. Tissues: Groups of similar cells performing a function.

3. Organs: Structures made of different tissues working together.

4. Organ Systems: Groups of organs performing complex functions.

Four Basic Tissue Types

• Epithelial: Covers surfaces and lines cavities.

• Connective: Supports and connects (includes bone, blood, fat).

• Muscle: Enables movement (skeletal, cardiac, smooth).

• Nervous: Sends and processes information (neurons, glia).

Major Organ Systems (Functions & Key Parts)

System Interdependence

• Digestive & Circulatory: Nutrient absorption and transport.

• Respiratory & Circulatory: Oxygen delivery and CO₂ removal.

• Excretory & Circulatory: Waste filtration.

• Endocrine & Nervous: Coordinate responses (fast vs. long-term).

Control Systems

• Endocrine: Hormones through blood, slower.

• Nervous: Nerve signals, fast.

• Together: Handle complex responses (e.g., fight or flight).

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