A biological system is a complex network of biologically relevant entities. As biological organization spans several scales, examples of biological systems are populations of organisms, or on the organ- and tissue scale in mammals and other animals, the circulatory system, the respiratory system, the nervous system, etc.
On the micro- to the nanoscopic scale, examples of biological systems are cells, organelles, macromolecular complexes and regulatory pathways.
A biological system is not to be confused with a living system, which is commonly referred to as life. For further information see e.g. definition of life or synthetic biology.
Organ and tissue systems
An example of a system: The nervous system. This basic diagram shows that this system is made up of 4 different basic organs: the brain
, the cerebellum
, the spinal cord
, and the nerves
These specific systems are widely studied in Human anatomy. "Human" systems are also present in many other animals.
- Circulatory system: pumping and channeling blood to and from the body and lungs with heart, blood and blood vessels.
- Integumentary system: skin, hair, fat, and nails.
- Skeletal system: structural support and protection with bones, cartilage, ligaments and tendons.
- Reproductive system: the sex organs, such as ovaries, fallopian tubes, uterus, vagina, mammary glands, testes, vas deferens, seminal vesicles and prostate
- Digestive system: digestion and processing food with salivary glands, esophagus, stomach, liver, gallbladder, pancreas, intestines, rectum and anus.
- Urinary system: kidneys, ureters, bladder and urethra involved in fluid balance, electrolyte balance and excretion of urine.
- Respiratory system: the organs used for breathing, the pharynx, larynx, bronchi, lungs and diaphragm.
- Endocrine system: communication within the body using hormones made by endocrine glands such as the hypothalamus, pituitary gland, pineal body or pineal gland, thyroid, parathyroid and adrenals, i.e., adrenal glands.
- Lymphatic system: structures involved in the transfer of lymph between tissues and the blood stream; includes the lymph and the nodes and vessels. The lymphatic system includes functions including immune responses and development of antibodies.
- Muscular system: allows for manipulation of the environment, provides locomotion, maintains posture, and produces heat. Includes skeletal muscles, smooth muscles and cardiac muscle.
- Nervous system: collecting, transferring and processing information with brain, spinal cord and peripheral nervous system.