Human body | Organs, Systems, Structure, Diagram, & Facts

Prime Questions

What’s the chemical composition of the human physique?

Chemically, the human physique consists primarily of water and natural compounds—i.e., lipids, proteins, carbohydrates, and nucleic acids. The human physique is about 60 % water by weight.

What are the 4 foremost sorts of tissue within the human physique?

What are the 9 main organ techniques within the human physique?

The 9 main organ techniques within the human physique are the integumentary system, the musculoskeletal system, the respiratory system, the circulatory system, the digestive system, the excretory system, the nervous system, the endocrine system, and the reproductive system.

human physique, the bodily substance of the human organism, composed of residing cells and extracellular supplies and arranged into tissues, organs, and techniques.

Human anatomy and physiology are handled in many alternative articles. For detailed discussions of particular tissues, organs, and techniques, see human blood; cardiovascular system; digestive system, human; endocrine system, human; renal system; pores and skin; human muscle system; nervous system; reproductive system, human; respiration, human; sensory reception, human; skeletal system, human. For an outline of how the physique develops, from conception by outdated age, see getting old; development; prenatal growth; human growth.

For detailed protection of the physique’s biochemical constituents, see protein; carbohydrate; lipid; nucleic acid; vitamin; and hormone. For data on the construction and performance of the cells that represent the physique, see cell.

Many entries describe the physique’s main constructions.

For instance, see stomach cavity; adrenal gland; aorta; bone; mind; ear; eye; coronary heart; kidney; giant gut; lung; nostril; ovary; pancreas; pituitary gland; small gut; spinal wire; spleen; abdomen; testis; thymus; thyroid gland; tooth; uterus; vertebral column.

People are, after all, animals—extra notably, members of the order Primates within the subphylum Vertebrata of the phylum Chordata. Like all chordates, the human animal has a bilaterally symmetrical physique that’s characterised sooner or later throughout its growth by a dorsal supporting rod (the notochord), gill slits within the area of the pharynx, and a hole dorsal nerve wire. Of those options, the primary two are current solely throughout the embryonic stage within the human; the notochord is changed by the vertebral column, and the pharyngeal gill slits are misplaced fully. The dorsal nerve wire is the spinal wire in people; it stays all through life.

Attribute of the vertebrate kind, the human physique has an inside skeleton that features a spine of vertebrae. Typical of mammalian construction, the human physique exhibits such traits as hair, mammary glands, and extremely developed sense organs.

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Past these similarities, nonetheless, lie some profound variations. Among the many mammals, solely people have a predominantly two-legged (bipedal) posture, a undeniable fact that has drastically modified the final mammalian physique plan. (Even the kangaroo, which hops on two legs when shifting quickly, walks on 4 legs and makes use of its tail as a “third leg” when standing.) Furthermore, the human mind, notably the neocortex, is way and away essentially the most extremely developed within the animal kingdom. As clever as are many different mammals—equivalent to chimpanzees and dolphins—none have achieved the mental standing of the human species.

Chemical composition of the physique

Chemically, the human physique consists primarily of water and of natural compounds—i.e., lipids, proteins, carbohydrates, and nucleic acids. Water is discovered within the extracellular fluids of the physique (the blood plasma, the lymph, and the interstitial fluid) and inside the cells themselves. It serves as a solvent with out which the chemistry of life couldn’t happen. The human physique is about 60 % water by weight.


mainly fat, phospholipids, and steroids—are main structural parts of the human physique. Fat present an vitality reserve for the physique, and fats pads additionally function insulation and shock absorbers. Phospholipids and the steroid compound ldl cholesterol are main parts of the membrane that surrounds every cell.


additionally function a significant structural element of the physique. Like lipids, proteins are an essential constituent of the cell membrane. As well as, such extracellular supplies as hair and nails are composed of protein. So is also collagen, the fibrous, elastic materials that makes up a lot of the physique’s pores and skin, bones, tendons, and ligaments. Proteins additionally carry out quite a few practical roles within the physique. Notably essential are mobile proteins referred to as enzymes, which catalyze the chemical reactions essential for all times.


are current within the human physique largely as fuels, both as easy sugars circulating by the bloodstream or as glycogen, a storage compound discovered within the liver and the muscle mass. Small quantities of carbohydrates additionally happen in cell membranes, however, in distinction to vegetation and lots of invertebrate animals, people have little structural carbohydrate of their our bodies.

Nucleic acids

make up the genetic supplies of the physique. Deoxyribonucleic acid (DNA) carries the physique’s hereditary grasp code, the directions in keeping with which every cell operates. It’s DNA, handed from dad and mom to offspring, that dictates the inherited traits of every particular person human. Ribonucleic acid (RNA), of which there are a number of sorts, helps perform the directions encoded within the DNA.

Together with water and natural compounds,

the physique’s constituents embody varied inorganic minerals. Chief amongst these are calcium, phosphorus, sodium, magnesium, and iron. Calcium and phosphorus, mixed as calcium-phosphate crystals, kind a big a part of the physique’s bones. Calcium can be current as ions within the blood and interstitial fluid, as is sodium. Ions of phosphorus, potassium, and magnesium, then again, are considerable inside the intercellular fluid. All of those ions play important roles within the physique’s metabolic processes. Iron is current primarily as a part of hemoglobin, the oxygen-carrying pigment of the crimson blood cells. Different mineral constituents of the physique, present in minute however essential concentrations, embody cobalt, copper, iodine, manganese, and zinc.

Group of the physique

The cell is the essential residing unit of the human physique—certainly, of all organisms. The human physique consists of trillions of cells, every able to development, metabolism, response to stimuli, and, with some exceptions, copy. Though there are some 200 various kinds of cells within the physique, these could be grouped into 4 fundamental lessons. These 4 fundamental cell sorts, along with their extracellular supplies, kind the elemental tissues of the human physique: (1) epithelial tissues, which cowl the physique’s floor and line the interior organs, physique cavities, and passageways; (2) muscle tissues, that are able to contraction and kind the physique’s musculature; (3) nerve tissues, which conduct electrical impulses and make up the nervous system; and (4) connective tissues, that are composed of extensively spaced cells and enormous quantities of intercellular matrix and which bind collectively varied physique constructions. (Bone and blood are thought-about specialised connective tissues, during which the intercellular matrix is, respectively, exhausting and liquid.)

The subsequent stage of group within the physique is that of the organ. An organ is a gaggle of tissues that constitutes a definite structural and practical unit. Thus, the guts is an organ composed of all 4 tissues, whose perform is to pump blood all through the physique. After all, the guts doesn’t perform in isolation; it’s a part of a system composed of blood and blood vessels as nicely. The best stage of physique group, then, is that of the organ system.

The physique consists of 9 main organ techniques,

every composed of varied organs and tissues that work collectively as a practical unit. The chief constituents and prime capabilities of every system are summarized beneath.


The integumentary system, composed of the pores and skin and related constructions, protects the physique from invasion by dangerous microorganisms and chemical compounds; it additionally prevents water loss from the physique.


The musculoskeletal system (additionally referred to individually because the muscle system and the skeletal system), composed of the skeletal muscle mass and bones (with about 206 of the latter in adults), strikes the physique and protectively homes its inside organs.


The respiratory system, composed of the respiration passages, lungs, and muscle mass of respiration, obtains from the air the oxygen essential for mobile metabolism; it additionally returns to the air the carbon dioxide that varieties as a waste product of such metabolism.


The circulatory system, composed of the guts, blood, and blood vessels, circulates a transport fluid all through the physique, offering the cells with a gentle provide of oxygen and vitamins and carrying away waste merchandise equivalent to carbon dioxide and poisonous nitrogen compounds.


The digestive system, composed of the mouth, esophagus, abdomen, and intestines, breaks down meals into usable substances (vitamins), that are then absorbed from the blood or lymph; this technique additionally eliminates the unusable or extra portion of the meals as fecal matter.


The excretory system, composed of the kidneys, ureters, urinary bladder, and urethra, removes poisonous nitrogen compounds and different wastes from the blood.


The nervous system, composed of the sensory organs, mind, spinal wire, and nerves, transmits, integrates, and analyzes sensory data and carries impulses to impact the suitable muscular or glandular responses.


The endocrine system, composed of the hormone-secreting glands and tissues, gives a chemical communications community for coordinating varied physique processes.


The reproductive system, composed of the male or feminine intercourse organs, permits copy and thereby ensures the continuation of the species.

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