Monthly Archives: January 2023

Top Questions

What is the chemical composition of the human body?

Chemically, the human body consists mainly of water and organic compoundsi.e., lipids, proteins, carbohydrates, and nucleic acids. The human body is about 60 percent water by weight.

What are the four main types of tissue in the human body?

What are the nine major organ systems in the human body?

The nine major organ systems in the human body 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 body, the physical substance of the human organism, composed of living cells and extracellular materials and organized into tissues, organs, and systems.

Human anatomy and physiology are treated in many different articles. For detailed discussions of specific tissues, organs, and systems, see human blood; cardiovascular system; digestive system, human; endocrine system, human; renal system; skin; human muscle system; nervous system; reproductive system, human; respiration, human; sensory reception, human; skeletal system, human. For a description of how the body develops, from conception through old age, see aging; growth; prenatal development; human development.

For detailed coverage of the bodys biochemical constituents, see protein; carbohydrate; lipid; nucleic acid; vitamin; and hormone. For information on the structure and function of the cells that constitute the body, see cell.

Many entries describe the bodys major structures. For example, see abdominal cavity; adrenal gland; aorta; bone; brain; ear; eye; heart; kidney; large intestine; lung; nose; ovary; pancreas; pituitary gland; small intestine; spinal cord; spleen; stomach; testis; thymus; thyroid gland; tooth; uterus; vertebral column.

Humans are, of course, animalsmore particularly, members of the order Primates in the subphylum Vertebrata of the phylum Chordata. Like all chordates, the human animal has a bilaterally symmetrical body that is characterized at some point during its development by a dorsal supporting rod (the notochord), gill slits in the region of the pharynx, and a hollow dorsal nerve cord. Of these features, the first two are present only during the embryonic stage in the human; the notochord is replaced by the vertebral column, and the pharyngeal gill slits are lost completely. The dorsal nerve cord is the spinal cord in humans; it remains throughout life.

Characteristic of the vertebrate form, the human body has an internal skeleton that includes a backbone of vertebrae. Typical of mammalian structure, the human body shows such characteristics as hair, mammary glands, and highly developed sense organs.

Beyond these similarities, however, lie some profound differences. Among the mammals, only humans have a predominantly two-legged (bipedal) posture, a fact that has greatly modified the general mammalian body plan. (Even the kangaroo, which hops on two legs when moving rapidly, walks on four legs and uses its tail as a third leg when standing.) Moreover, the human brain, particularly the neocortex, is far and away the most highly developed in the animal kingdom. As intelligent as are many other mammalssuch as chimpanzees and dolphinsnone have achieved the intellectual status of the human species.

Chemically, the human body consists mainly of water and of organic compoundsi.e., lipids, proteins, carbohydrates, and nucleic acids. Water is found in the extracellular fluids of the body (the blood plasma, the lymph, and the interstitial fluid) and within the cells themselves. It serves as a solvent without which the chemistry of life could not take place. The human body is about 60 percent water by weight.

Lipidschiefly fats, phospholipids, and steroidsare major structural components of the human body. Fats provide an energy reserve for the body, and fat pads also serve as insulation and shock absorbers. Phospholipids and the steroid compound cholesterol are major components of the membrane that surrounds each cell.

Proteins also serve as a major structural component of the body. Like lipids, proteins are an important constituent of the cell membrane. In addition, such extracellular materials as hair and nails are composed of protein. So also is collagen, the fibrous, elastic material that makes up much of the bodys skin, bones, tendons, and ligaments. Proteins also perform numerous functional roles in the body. Particularly important are cellular proteins called enzymes, which catalyze the chemical reactions necessary for life.

Carbohydrates are present in the human body largely as fuels, either as simple sugars circulating through the bloodstream or as glycogen, a storage compound found in the liver and the muscles. Small amounts of carbohydrates also occur in cell membranes, but, in contrast to plants and many invertebrate animals, humans have little structural carbohydrate in their bodies.

Nucleic acids make up the genetic materials of the body. Deoxyribonucleic acid (DNA) carries the bodys hereditary master code, the instructions according to which each cell operates. It is DNA, passed from parents to offspring, that dictates the inherited characteristics of each individual human. Ribonucleic acid (RNA), of which there are several types, helps carry out the instructions encoded in the DNA.

Along with water and organic compounds, the bodys constituents include various inorganic minerals. Chief among these are calcium, phosphorus, sodium, magnesium, and iron. Calcium and phosphorus, combined as calcium-phosphate crystals, form a large part of the bodys bones. Calcium is also present as ions in the blood and interstitial fluid, as is sodium. Ions of phosphorus, potassium, and magnesium, on the other hand, are abundant within the intercellular fluid. All of these ions play vital roles in the bodys metabolic processes. Iron is present mainly as part of hemoglobin, the oxygen-carrying pigment of the red blood cells. Other mineral constituents of the body, found in minute but necessary concentrations, include cobalt, copper, iodine, manganese, and zinc.

The cell is the basic living unit of the human bodyindeed, of all organisms. The human body consists of trillions of cells, each capable of growth, metabolism, response to stimuli, and, with some exceptions, reproduction. Although there are some 200 different types of cells in the body, these can be grouped into four basic classes. These four basic cell types, together with their extracellular materials, form the fundamental tissues of the human body: (1) epithelial tissues, which cover the bodys surface and line the internal organs, body cavities, and passageways; (2) muscle tissues, which are capable of contraction and form the bodys musculature; (3) nerve tissues, which conduct electrical impulses and make up the nervous system; and (4) connective tissues, which are composed of widely spaced cells and large amounts of intercellular matrix and which bind together various body structures. (Bone and blood are considered specialized connective tissues, in which the intercellular matrix is, respectively, hard and liquid.)

The next level of organization in the body is that of the organ. An organ is a group of tissues that constitutes a distinct structural and functional unit. Thus, the heart is an organ composed of all four tissues, whose function is to pump blood throughout the body. Of course, the heart does not function in isolation; it is part of a system composed of blood and blood vessels as well. The highest level of body organization, then, is that of the organ system.

The body includes nine major organ systems, each composed of various organs and tissues that work together as a functional unit. The chief constituents and prime functions of each system are summarized below. (1) The integumentary system, composed of the skin and associated structures, protects the body from invasion by harmful microorganisms and chemicals; it also prevents water loss from the body. (2) The musculoskeletal system (also referred to separately as the muscle system and the skeletal system), composed of the skeletal muscles and bones (with about 206 of the latter in adults), moves the body and protectively houses its internal organs. (3) The respiratory system, composed of the breathing passages, lungs, and muscles of respiration, obtains from the air the oxygen necessary for cellular metabolism; it also returns to the air the carbon dioxide that forms as a waste product of such metabolism. (4) The circulatory system, composed of the heart, blood, and blood vessels, circulates a transport fluid throughout the body, providing the cells with a steady supply of oxygen and nutrients and carrying away waste products such as carbon dioxide and toxic nitrogen compounds. (5) The digestive system, composed of the mouth, esophagus, stomach, and intestines, breaks down food into usable substances (nutrients), which are then absorbed from the blood or lymph; this system also eliminates the unusable or excess portion of the food as fecal matter. (6) The excretory system, composed of the kidneys, ureters, urinary bladder, and urethra, removes toxic nitrogen compounds and other wastes from the blood. (7) The nervous system, composed of the sensory organs, brain, spinal cord, and nerves, transmits, integrates, and analyzes sensory information and carries impulses to effect the appropriate muscular or glandular responses. (8) The endocrine system, composed of the hormone-secreting glands and tissues, provides a chemical communications network for coordinating various body processes. (9) The reproductive system, composed of the male or female sex organs, enables reproduction and thereby ensures the continuation of the species.

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

HumanSkin

Range from pinkish-white to almost black

1.26m-2.4m (average 1.68m)

Brown, blue, grey, green, gold, hazel, and turquoise

Brown, black, blond, red, grayish-white to fully white

Humans (Na'vi name: tawtutemeaning "sky people") are a sapient, sentient, bipedal mammalian dominant species native to planet Earth, who by the 22nd century has become a technologically advanced species capable of interstellar travel and colonization.

Humanity is the first and only alien species known to the Na'vi, another sapient species native to Pandora, where the humans arrived in search for and to extract the rare mineral unobtanium. The Na'vi refer to humans as tawtute (pl. sawtute), meaning "sky person/people" in the Na'vi language, and derogatorily as "pinkskins".[1]

Humans are mid-sized hominid primates and the only extant species of the genus Homo, with an upright bipedal posture and prehensile forelimbs, each with a highly dexterous five-digit hand adapted for fine motor functions. Humans also display noticeable sexual dimorphism, with the male humans generally being taller and more muscular than the females.

The human skeletal structures are quite small and weak by Pandoran standards, and are prone to losing muscle strength in the lighter gravity of Pandora without constant exercise. In combat, humans tend to avoid melee combat and favor chemically powered range based projectile weapons such as firearms, and employ heavy use of aircraft and weaponized exoskeletons such as the AMP suit.

Like Pandoran animals, humans are oxygen-breathers, but can't survive in the high-carbon dioxide atmosphere of Pandora, and thus are heavily dependent on air filtration systems such as exopacks.

Humans have highly developed brains capable of abstract reasoning, advanced language, introspection, problem-solving, and organization, and over the millennia have accumulated vast quantities of knowledge and expertise. As well as countless wars on Earth since their founding of the first civilization. Although anatomically human brains are far less complex than the Na'vi brains, which are specially evolved for interspecies neural bonding, humans are far more capable of designing and building complex machinery and therefore are superior in terms of resources and technological sophistication.

Humanity began forays into the universe during the mid-20th century after their 2nd World War, first by launching 'primitive' satellites into low orbit, then sending human occupants to orbits. About 25 years after the first unmanned craft was launched from Earth, humans first made the journey to the nearest celestial body to Earth, the Moon. Trips to and from the Moon occurred for a decade. Humanity then set up an international coalition dedicated to funding and building an international space station in low earth orbit. After this, private corporations grouped together and built interstellar vessels like the ISV Venture Star, which allowed the human race to expand to other nearby star systems, particularly the Alpha Centauri System, and explore their planets and moons.

Following the ravaging of their home planet by pollution and war which left Earth largely unsuitable for life and in the midst of an energy crisis, the goal of humans shifted to venturing to Pandora to mine the mineral unobtanium, which is valued at 20 million United States dollars a kilogram. The Security Operations (SecOps) group, which is owned by the RDA, was installed at Hell's Gate to protect the interests of the RDA as they mine the valuable mineral from Pandora. SecOps also served to prevent any and all intrusions by Pandoran natives. The RDA also established the Science Operations (SciOps), a branch dedicated to researching Pandora, interacting with natives, and possibly synthesizing various flora and fauna for practical use on Earth; compared to SecOps and the Mining Operations, SciOps is largely underfunded.[2]

Though relations between the human and the Na'vi initially started peaceful, things eventually deteriorated. Tensions and conflicts escalated to the point where both sides were on the brink of war. Upon Jake Sully's arrival on Pandora, the RDA made one last attempt to find a diplomatic and peaceful agreement with the Na'vi, so they could mine the unobtanium from the moon without interference. However, this unfortunately failed and the RDA resorted to using full force against the Na'vi in order to get the resources they desired.

The RDA's plans were foiled by the Na'vi who defeated them during the Assault on the Tree of Souls with the help of like-minded humans. Most humans were exiled from Pandora, though a few were permitted to stay. The humans who stayed behind did not agree with the RDA's goals and worked with the Na'vi to rebuild, as well as sustain themselves. Despite this, relations between the humans who stayed and the Na'vi remained resentful. The remaining humans on Pandora were eventually able to build a suitable home for themselves where they could survive and even started to raise families of their own.

However, although the RDA was banished from Pandora, they eventually returned and established the Bridgehead complex to begin plundering the Pandoran oceans for their resources and create a colony as Earth's situation deteriorated to almost unhabitable level.

Generations after the RDA's chokehold presence on Pandora, they were finally expelled for good, and Alpha Centauri Expeditions set to work repairing the relationship between Na'vi and humans. After reaching peace with the nearby Omaticaya Clan, ACE set up a thriving ecotourism system in the Valley of Mo'ara so that humans could return to Pandora and learn about the Na'vi, as well as about the RDA's harmful practices. The Pandora Conservation Initiative helps to undo environmental destruction caused by the RDA and relaunched the Avatar Program to continue their research and allow guests to experience Pandora through avatar bodies. With these measures in place, Na'vi and humans largely live harmoniously.

Humans have created advanced technology over the centuries, including subliminal travel, which is required to travel between Earth and the Alpha Centauri system in a realistic time span. Since humans are unable to breathe Pandora's atmosphere, they must use exopacks (supplied to them by the RDA) when on the moon's surface. The Avatar Program technology enables the transfer of human consciousness into cloned human/Na'vi hybrids, known as avatars. Once transferred to an avatar body, a human can live comfortably on Pandora.

Even though humans have advanced technology, they have ravaged their planet, Earth, to the point of resource depletion. As such, the economies of Earth nations have become poor. The majority of power on Earth has been split up among powerful companies, corporations and organizations that enlist ex-military soldiers and civilians.

A list of notable human organizations, including those with substantial presence on Pandora, are as follows.

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Human | Avatar Wiki | Fandom