In biology, an organ is a group of tissues which perform some function. Common animal organs include the heart, lungs, brain, eye, stomach, spleen, pancreas, kidneys, liver, intestines, skin, uterus, bladder, bone, etc. Common plant organs include the stalk, stem, leaf, roots, and stamen. A group of related organs is an organ system.

Organelles are analogous sub-cellular structures.

• circulatory system
• digestive system
• endocrine system
• immune system
• integumentary system
• lymphatic system
• muscular system
• nervous system
• reproductive system

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• respiratory system
• skeletal system
• urinary system

See also

• Human anatomy
• transplant
• artificial organ