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

Function

Main Components

Cardiovascular

Transports substances

Heart, blood, vessels

Respiratory

Gas exchange

Lungs, trachea

Digestive

Breaks down food, absorbs nutrients

Mouth, stomach, intestines

Nervous

Fast control & coordination

Brain, nerves

Endocrine

Long-term regulation via hormones

Glands (e.g., pituitary, adrenal)

Muscular

Movement, heat

Skeletal, cardiac, smooth muscle

Skeletal

Structure, protection, blood cell production

Bones, joints

Reproductive

Produces offspring

Testes, ovaries, uterus

Urinary

Waste removal, fluid balance

Kidneys, bladder

Integumentary

Protection, temperature control

Skin, hair, nails

Lymphatic/Immune

Defense

Lymph nodes, white blood cells

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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