Organ
An organ is a structure composed of two or more tissue types working together to perform a specific function. The heart is an organ: cardiac muscle tissue pumps blood, connective tissue provides structural support, epithelial tissue lines the chambers, and nervous tissue regulates the rhythm. No single tissue type could accomplish what the heart does — the organ is the functional unit.
Organ systems
Organs are grouped into systems that carry out major physiological functions:
| System | Major organs | Primary function |
|---|---|---|
| Nervous | Brain, spinal cord, peripheral nerves | Sensation, integration, motor control, cognition |
| Cardiovascular | Heart, blood vessels | Circulation of blood; oxygen and nutrient delivery |
| Respiratory | Lungs, airways, diaphragm | Gas exchange; oxygen in, carbon dioxide out |
| Musculoskeletal | Bones, skeletal muscles, joints, tendons, ligaments | Support, movement, protection |
| Digestive | Mouth, esophagus, stomach, intestines, liver, pancreas | Nutrient breakdown, absorption, drug metabolism |
| Immune/Lymphatic | Lymph nodes, spleen, thymus, white blood cells | Defense against infection; inflammation |
| Endocrine | Pituitary, thyroid, adrenals, pancreas, gonads | Hormone production; systemic regulation |
| Urinary | Kidneys, ureters, bladder | Filtration; waste and drug elimination |
| Integumentary | Skin, hair, nails | Barrier; temperature regulation; sensation |
| Reproductive | Gonads, uterus, associated structures | Reproduction |
These systems do not operate independently. The cardiovascular system delivers oxygen that the respiratory system acquires. The digestive system absorbs nutrients that the cardiovascular system distributes. The nervous system regulates all of them. Disease in one system affects others — which is why traditional Chinese medicine describes organs not as isolated structures but as functional systems defined by their relationships (Zang-Fu).
The organ concept in TCM
The distinction between the Western anatomical organ and the TCM functional organ is significant. In Western medicine, “the liver” is a physical structure in the right upper abdomen with specific histological features, identifiable on imaging, and removable by surgery. In TCM, “the Liver” (肝) is a functional system governing the smooth flow of Qi, the storage of blood, and the regulation of emotional and somatic tension. The Western liver and the TCM Liver overlap but are not identical — they are defined by different frameworks asking different questions.
This does not mean one framework is right and the other wrong. It means that what counts as an “organ” depends on what you are trying to describe. If you are planning a surgery, the anatomical organ is what matters. If you are trying to understand why a patient’s irritability, menstrual irregularity, and rib-side distension form a single clinical pattern, the TCM functional system offers a vocabulary that anatomical description does not.
Related terms
- Tissue — the components that make up organs
- Cell — the units that make up tissues
- Homeostasis — the stable conditions that organ systems maintain