Organ system

Components and common examples

Each organ system is defined by the role it plays and the primary organs it contains. Typical systems in vertebrates include:

• Circulatory system: heart, blood, and vessels
• Respiratory system: lungs and airways
• Digestive system: stomach, intestines, liver
• Nervous system: brain, spinal cord, nerves
• Musculoskeletal, endocrine, urinary, reproductive, immune/lymphatic, and integumentary systems

Function and integration

Organ systems do not act in isolation. They exchange chemical signals, blood flow, and neural inputs to maintain homeostasis. Feedback mechanisms—hormonal and neural—allow systems to adjust activity in response to internal or external changes. For example, the respiratory and circulatory systems cooperate to deliver oxygen and remove carbon dioxide.

Development and evolution

Organ systems develop during embryogenesis from primary germ layers (ectoderm, mesoderm, endoderm). Across evolutionary history, systems have diversified: simpler animals may have few specialized systems, while vertebrates have elaborate, highly integrated systems that arose through adaptation to ecological niches.

Importance and distinctions

Understanding organ systems is essential in medicine, physiology, and comparative anatomy. Diseases are often described by the system they affect (e.g., cardiovascular disease, respiratory infection). Note the distinction between a single organ, a tissue, and an organ system: tissues compose organs, and organs combine to form systems whose collective function exceeds the abilities of parts alone.