In biology and anatomy, an organ (Latin: organum, "instrument, tool", from Greek ὄργανον - organon, "organ, instrument, tool") is a tissue that performs a specific function or group of functions within an organism.
Usually there is a main tissue and sporadic tissues. The main tissue is the one that is unique for the specific organ. For example, main tissue in the heart is the myocardium, while sporadic are the nerves, blood, connective etc.. Functionally related organs often cooperate to form whole organ systems. Organs exist in all higher biological organisms, in particular they are not restricted to animals, but can also be identified in plants. In single-cell organisms like bacteria, the functional analogues of organs are called organelles.
Organ systems
A group of related organs is an organ system. Organs within a may be related in any number of ways, but relationships of function are most commonly used. For example the urinary system comprises organs that work together to produce, store, and carry urine.
The functions of organ systems often share significant overlap. For instance, the nervous and endocrine system both operate via a shared organ, the hypothalamus. For this reason, the two systems are combined and studied as the neuroendocrine system. The same is true for the musculoskeletal system, which involves the relationship between the muscular and the skeletal system.
Plant organs and organ systems
Organs of plants can be divided into vegetative and reproductive. Vegetative plant organs are root, stem and leaf. The reproductive organs are variable. In angiosperms, they are represented with the flower, seed and fruit. In conifers, the organ that bears the reproductive structures is called a cone. In other divisions of plants, the reproductive organs are called strobili (in Lycopodiophyta) or simply gametophores (in mosses).
The vegetative organs are essential for maintaining the life of a plant (they perform the vital functions, such as photosynthesis), while the reproductive organs are essential in reproduction. But, if there is asexual vegetative reproduction, the vegetative organs are those which create the new generation of plants (see clonal colony).
The two main organ systems in vascular plants are the root system and the shoot system.
Animal organs and organ systems
The organ level of organisation in animals can be first detected in flatworms and the more advanced phyla. The less-advanced taxons (like Placozoa, Porifera and Radiata) do not show consolidation of their tissues into organs.
List of major human organ systems
There are typically considered to be eleven major organ systems of the human body.
Humans have a variety of systems due to the complexity of the species' organism. These specific systems are widely studied in Human anatomy. "Human" systems are also present in many animals.
- Circulatory system: pumping and channeling blood to and from the body and lungs with heart, blood and blood vessels.
- Digestive system: digestion and processing food with salivary glands, esophagus, stomach, liver, gallbladder, pancreas, intestines, rectum and anus.
- Endocrine system: communication within the body using hormones made by endocrine glands such as the hypothalamus, pituitary or pituitary gland, pineal body or pineal gland, thyroid, parathyroids and adrenals, i.e., adrenal glands.
- Integumentary system: skin, hair and nails.
- Lymphatic system: structures involved in the transfer of lymph between tissues and the blood stream, the lymph and the nodes and vessels that transport it including the Immune system: defending against disease-causing agents with leukocytes, tonsils, adenoids, thymus and spleen.
- Muscular system: movement with muscles.
- Nervous system: collecting, transferring and processing information with brain, spinal cord, peripheral nerves and nerves.
- Reproductive system: the sex organs, such as ovaries, fallopian tubes, uterus, vagina, mammary glands, testes, vas deferens, seminal vesicles, prostate and penis.
- Respiratory system: the organs used for breathing, the pharynx, larynx, trachea, bronchi, lungs and diaphragm.
- Skeletal system: structural support and protection with bones, cartilage, ligaments and tendons.
- Urinary system: kidneys, ureters, bladder and urethra involved in fluid balance, electrolyte balance and excretion of urine.
Organs and organ systems in invertebrates
The animals without backbone are known as invertebrates. They possess many specific organs which are not found in vertebrates.
| Phylum | Notable organ / organ system | Function |
|---|---|---|
| Platyhelminthes | Protonephridia | Excretion and osmoregulation. |
| Nemertea | Rhynchocoel | Cavity which stores the proboscis. |
| Nematoda | Amphids and phasmids | Sensory structures. |
| Mollusca | Radula; Nidamental glands | Scraping, cutting and chewing food; secreting egg cases, found only in Cephalopoda. |
| Annelida | Metanephridia; trophosome | Excretion of metabolic wastes; habitat for symbiotic bacteria, found only in Siboglinidae. |
| Echiura | Anal vesicles | Probably excretion. |
| Phoronida, Bryozoa, Entoprocta, Brachiopoda | Lophophore | Collecting system for suspension feeding. |
| Arthropoda | Tracheae; Malpighian tubules | Transport of metabolic gasses to and from tissue; excretion and osmoregulation. |
| Echinodermata | Aristotle's lantern | Chewing organ, found only in sea urchins. |
See also
- Cloning
- Fascia
- Organ transplant
- Organelles, analogous sub-cellular structures
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