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
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, oesophagus, 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.
- Immune system: protects the organism from foreign bodies
- 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.
The notion of system (or apparatus) relies upon the concept of vital or organic function: a system is a set of organs with a definite function. This idea was already present in Antiquity (Galen, Aristotle), but the application of the term "system" is more recent. For example, the nervous system was named by Monro (1783), but Rufus of Ephesus (c. 90-120), clearly viewed for the first time the brain, spinal cord, and craniospinal nerves as an anatomical unit, although he wrote little about its function, nor gave a name to this unit.
The enumeration of the principal functions - and consequently of the systems - remained almost the same since Antiquity, but the classification of them has been very various, e.g., compare Aristotle, Bichat, Cuvier.
The notion of physiological division of labor, introduced in the 1820s by the French physiologist Henri Milne-Edwards, allowed to "compare and study living things as if they were machines created by the industry of man." Inspired in the work of Adam Smith, Milne-Edwards wrote that the "body of all living beings, whether animal or plant, resembles a factory ... where the organs, comparable to workers, work incessantly to produce the phenomena that constitute the life of the individual." In more differentiated organisms, the functional labor could be apportioned between different instruments or systems (called by him as appareils).
- Biological network
- Artificial life
- Biological systems engineering
- Systems biology
- Systems ecology
- Systems theory
- Systems Biology: An Overview by Mario Jardon: A review from the Science Creative Quarterly, 2005.
- Synthesis and Analysis of a Biological System, by Hiroyuki Kurata, 1999.
- It from bit and fit from bit. On the origin and impact of information in the average evolution. Includes how life forms and biological systems originate and from there evolve to become more and more complex, including evolution of genes and memes, into the complex memetics from organisations and multinational corporations and a "global brain", (Yves Decadt, 2000). Book published in Dutch with English paper summary in The Information Philosopher, http://www.informationphilosopher.com/solutions/scientists/decadt/
- Schmidt-Rhaesa, A. 2007. The Evolution of Organ Systems. Oxford University Press, Oxford, .