Human body

The human body is the structure of a human being. It is composed of many different types of cells that together create tissues and subsequently organ systems. They ensure homeostasis and the viability of the human body.

It comprises a head, neck, trunk (which includes the thorax and abdomen), arms and hands, legs and feet.

The study of the human body involves anatomy, physiology, histology and embryology. The body varies anatomically in known ways. Physiology focuses on the systems and organs of the human body and their functions. Many systems and mechanisms interact in order to maintain homeostasis, with safe levels of substances such as sugar and oxygen in the blood.

The body is studied by health professionals, physiologists, anatomists, and by artists to assist them in their work.

Human Body 02
Female and male human bodies


201 Elements of the Human Body-01
Elements of the human body by mass. Trace elements are less than 1% combined (and each less than 0.1%).

The human body is composed of elements including hydrogen, oxygen, carbon, calcium and phosphorus.[1] These elements reside in trillions of cells and non-cellular components of the body.

The adult male body is about 60% water for a total water content of some 42 litres. This is made up of about 19 litres of extracellular fluid including about 3.2 litres of blood plasma and about 8.4 litres of interstitial fluid, and about 23 litres of fluid inside cells.[2] The content, acidity and composition of the water inside and outside cells is carefully maintained. The main electrolytes in body water outside cells are sodium and chloride, whereas within cells it is potassium and other phosphates.[3]


The body contains trillions of cells, the fundamental unit of life.[4] At maturity, there are roughly 30[5]–37[6] trillion cells in the body, an estimate arrived at by totaling the cell numbers of all the organs of the body and cell types. The body is also host to about the same number of non-human cells[5] as well as multicellular organisms which reside in the gastrointestinal tract and on the skin.[7] Not all parts of the body are made from cells. Cells sit in an extracellular matrix that consists of proteins such as collagen, surrounded by extracellular fluids. Of the 70 kg weight of an average human body, nearly 25 kg is non-human cells or non-cellular material such as bone and connective tissue.[5]

Cells in the body function because of DNA. DNA sits within the nucleus of a cell. Here, parts of DNA are copied and sent to the body of the cell via RNA.[8] The RNA is then used to create proteins which form the basis for cells, their activity, and their products. Proteins dictate cell function and gene expression, a cell is able to self-regulate by the amount of proteins produced.[9] However, not all cells have DNA – some cells such as mature red blood cells lose their nucleus as they mature.


External video
2120 Major Systemic Artery
Human Body 101, National Geographic, 5:10

The body consists of many different types of tissue, defined as cells that act with a specialised function.[10] The study of tissues is called histology and often occurs with a microscope. The body consists of four main types of tissues – lining cells (epithelia), connective tissue, nervous tissue and muscle tissue.[11]

Cells that lie on surfaces exposed to the outside world or gastrointestinal tract (epithelia) or internal cavities (endothelium) come in numerous shapes and forms – from single layers of flat cells, to cells with small beating hair-like cilia in the lungs, to column-like cells that line the stomach. Endothelial cells are cells that line internal cavities including blood vessels and glands. Lining cells regulate what can and can't pass through them, protect internal structures, and function as sensory surfaces.[11]


Organs, structured collections of cells with a specific function,[12] sit within the body. Examples include the heart, lungs and liver. Many organs reside within cavities within the body. These cavities include the abdomen and pleura.


Diagram of the human heart (cropped)

Circulatory system

The circulatory system consists of the heart and blood vessels (arteries, veins and capillaries). The heart propels the circulation of the blood, which serves as a "transportation system" to transfer oxygen, fuel, nutrients, waste products, immune cells and signalling molecules (i.e., hormones) from one part of the body to another. The blood consists of fluid that carries cells in the circulation, including some that move from tissue to blood vessels and back, as well as the spleen and bone marrow.[13][14][15]

Stomach colon rectum diagram-en

Digestive system

The digestive system consists of the mouth including the tongue and teeth, esophagus, stomach, (gastrointestinal tract, small and large intestines, and rectum), as well as the liver, pancreas, gallbladder, and salivary glands. It converts food into small, nutritional, non-toxic molecules for distribution and absorption into the body.[16]

Illu endocrine system

Endocrine system

The endocrine system consists of the principal endocrine glands: the pituitary, thyroid, adrenals, pancreas, parathyroids, and gonads, but nearly all organs and tissues produce specific endocrine hormones as well. The endocrine hormones serve as signals from one body system to another regarding an enormous array of conditions, and resulting in variety of changes of function.[17]


Immune system

The immune system consists of the white blood cells, the thymus, lymph nodes and lymph channels, which are also part of the lymphatic system. The immune system provides a mechanism for the body to distinguish its own cells and tissues from outside cells and substances and to neutralize or destroy the latter by using specialized proteins such as antibodies, cytokines, and toll-like receptors, among many others.[18]

Skin-no language

Integumentary system

The integumentary system consists of the covering of the body (the skin), including hair and nails as well as other functionally important structures such as the sweat glands and sebaceous glands. The skin provides containment, structure, and protection for other organs, and serves as a major sensory interface with the outside world.[19][20]

Sobo 1909 605

Lymphatic system

The lymphatic system extracts, transports and metabolizes lymph, the fluid found in between cells. The lymphatic system is similar to the circulatory system in terms of both its structure and its most basic function, to carry a body fluid.[21]


Musculoskeletal system

The musculoskeletal system consists of the human skeleton (which includes bones, ligaments, tendons, and cartilage) and attached muscles. It gives the body basic structure and the ability for movement. In addition to their structural role, the larger bones in the body contain bone marrow, the site of production of blood cells. Also, all bones are major storage sites for calcium and phosphate. This system can be split up into the muscular system and the skeletal system.[22]

Human brain NIH

Nervous system

The nervous system consists of the central nervous system (the brain and spinal cord) and the peripheral nervous system consists of the nerves and ganglia outside the brain and spinal cord. The brain is the organ of thought, emotion, memory, and sensory processing, and serves many aspects of communication and controls various systems and functions. The special senses consist of vision, hearing, taste, and smell. The eyes, ears, tongue, and nose gather information about the body's environment.[23]

Male anatomy

Reproductive system

The reproductive system consists of the gonads and the internal and external sex organs. The reproductive system produces gametes in each sex, a mechanism for their combination, and in the female a nurturing environment for the first 9 months of development of the infant.[24]


Respiratory system

The respiratory system consists of the nose, nasopharynx, trachea, and lungs. It brings oxygen from the air and excretes carbon dioxide and water back into the air.[25]


Urinary system

The urinary system consists of the kidneys, ureters, bladder, and urethra. It removes toxic materials from the blood to produce urine, which carries a variety of waste molecules and excess ions and water out of the body.[26]


Body cavities
Cavities of human body

Human anatomy is the study of the shape and form of the human body. The human body has four limbs (two arms and two legs), a head and a neck which connect to the torso. The body's shape is determined by a strong skeleton made of bone and cartilage, surrounded by fat, muscle, connective tissue, organs, and other structures. The spine at the back of the skeleton contains the flexible vertebral column which surrounds the spinal cord, which is a collection of nerve fibres connecting the brain to the rest of the body. Nerves connect the spinal cord and brain to the rest of the body. All major bones, muscles, and nerves in the body are named, with the exception of anatomical variations such as sesamoid bones and accessory muscles.

Blood vessels carry blood throughout the body, which moves because of the beating of the heart. Venules and veins collect blood low in oxygen from tissues throughout the body. These collect in progressively larger veins until they reach the body's two largest veins, the superior and inferior vena cava, which drain blood into the right side of the heart. From here, the blood is pumped into the lungs where it receives oxygen and drains back into the left side of the heart. From here, it is pumped into the body's largest artery, the aorta, and then progressively smaller arteries and arterioles until it reaches tissue. Here blood passes from small arteries into capillaries, then small veins and the process begins again. Blood carries oxygen, waste products, and hormones from one place in the body to another. Blood is filtered at the kidneys and liver.

The body consists of a number of different cavities, separated areas which house different organ systems. The brain and central nervous system reside in an area protected from the rest of the body by the blood brain barrier. The lungs sit in the pleural cavity. The intestines, liver, and spleen sit in the abdominal cavity

Height, weight, shape and other body proportions vary individually and with age and sex. Body shape is influenced by the distribution of muscle and fat tissue.[27]


Human physiology is the study of how the human body functions. This includes the mechanical, physical, bioelectrical, and biochemical functions of humans in good health, from organs to the cells of which they are composed. The human body consists of many interacting systems of organs. These interact to maintain homeostasis, keeping the body in a stable state with safe levels of substances such as sugar and oxygen in the blood.[28]

Each system contributes to homeostasis, of itself, other systems, and the entire body. Some combined systems are referred to by joint names. For example, the nervous system and the endocrine system operate together as the neuroendocrine system. The nervous system receives information from the body, and transmits this to the brain via nerve impulses and neurotransmitters. At the same time, the endocrine system releases hormones, such as to help regulate blood pressure and volume. Together, these systems regulate the internal environment of the body, maintaining blood flow, posture, energy supply, temperature, and acid balance (pH).[28]


Baby-256x385 1839565 640(1)
baby (infant)

Development of the human body is the process of growth to maturity. The process begins with fertilisation, where an egg released from the ovary of a female is penetrated by sperm. The egg then lodges in the uterus, where an embryo and later fetus develop until birth. Growth and development occur after birth, and include both physical and psychological development, influenced by genetic, hormonal, environmental and other factors. Development and growth continue throughout life, through childhood, adolescence, and through adulthood to senility, and are referred to as the process of ageing.

Society and culture

Professional study

Anatomical Male Figure Showing Heart, Lungs, and Main Arteries
Anatomical study by Leonardo da Vinci

Health professionals learn about the human body from illustrations, models, and demonstrations. Medical and dental students in addition gain practical experience, for example by dissection of cadavers. Human anatomy, physiology, and biochemistry are basic medical sciences, generally taught to medical students in their first year at medical school.[29][30][31]


Corinth stehender Mädchenakt
Figure drawing by Lovis Corinth (before 1925)

Anatomy has served the visual arts since Ancient Greek times, when the 5th century BC sculptor Polykleitos wrote his Canon on the ideal proportions of the male nude.[32] In the Italian Renaissance, artists from Piero della Francesca (c. 1415–1492) onwards, including Leonardo da Vinci (1452–1519) and his collaborator Luca Pacioli (c. 1447–1517), learnt and wrote about the rules of art, including visual perspective and the proportions of the human body.[33]

History of anatomy

Externarvm hvmani corporis sedivm partivmve, 1543.
Two facing pages of text with woodcuts of naked male and female figures, in the Epitome by Andreas Vesalius, 1543

In Ancient Greece, the Hippocratic Corpus described the anatomy of the skeleton and muscles.[34] The 2nd century physician Galen of Pergamum compiled classical knowledge of anatomy into a text that was used throughout the Middle Ages.[35] In the Renaissance, Andreas Vesalius (1514–1564) pioneered the modern study of human anatomy by dissection, writing the influential book De humani corporis fabrica.[36][37] Anatomy advanced further with the invention of the microscope and the study of the cellular structure of tissues and organs.[38] Modern anatomy uses techniques such as magnetic resonance imaging, computed tomography, fluoroscopy and ultrasound imaging to study the body in unprecedented detail.[39]

History of physiology

The study of human physiology began with Hippocrates in Ancient Greece, around 420 BC, and with Aristotle (384–322 BC) who applied critical thinking and emphasis on the relationship between structure and function. Galen (c. 126–199) was the first to use experiments to probe the body's functions.[40] The term physiology was introduced by the French physician Jean Fernel (1497–1558).[41] In the 17th century, William Harvey (1578–1657) described the circulatory system, pioneering the combination of close observation with careful experiment.[42] In the 19th century, physiological knowledge began to accumulate at a rapid rate with the cell theory of Matthias Schleiden and Theodor Schwann in 1838, that organisms are made up of cells.[41] Claude Bernard (1813–1878) created the concept of the milieu interieur (internal environment), which Walter Cannon (1871–1945) later said was regulated to a steady state in homeostasis. In the 20th century, the physiologists Knut Schmidt-Nielsen and George Bartholomew extended their studies to comparative physiology and ecophysiology.[43] Most recently, evolutionary physiology has become a distinct subdiscipline.[44]


Theology of the body of John Paul II

20th c. saw a rise of interest in reflection about human body in the light of Christian faith. One of the most significant contributions was that given by pope John Paul II in his catecheses held at the Vatican during Wednesday general audiences. It received the name of the Theology of the Body. In his catecheses John Paul II presented an interpretation of the fundamental significance of the body, and in particular of sexual differentiation and complementarity, one which aims to challenge common contemporary philosophical views.[45] In his approach to the subject, the pope used personalistic phenomenology but also was "echoing what he learned from St. John of the Cross"[46] and was "in harmony with St. Thomas Aquinas".[47]

See also


  1. ^ "Chemical Composition of the Human Body". About education. Retrieved 2 September 2016.
  2. ^ "Fluid Physiology". Anaesthesiamcq. Retrieved 2 September 2016.
  3. ^ Ganong's 2016, p. 5.
  4. ^ "The Cells in Your Body". Science Netlinks. Retrieved 2 September 2016.
  5. ^ a b c Ron Sender; Shai Fuchs; Ron Milo (2016). "Revised estimates for the number of human and bacteria cells in the body". PLOS Biology. 14 (8): e1002533. bioRxiv 036103. doi:10.1371/journal.pbio.1002533. PMC 4991899. PMID 27541692.
  6. ^ Bianconi, E; Piovesan, A; Facchin, F; Beraudi, A; Casadei, R; Frabetti, F; Vitale, L; Pelleri, MC; Tassani, S; Piva, F; Perez-Amodio, S; Strippoli, P; Canaider, S (5 July 2013). "An estimation of the number of cells in the human body". Annals of Human Biology. 40 (6): 463–471. doi:10.3109/03014460.2013.807878. PMID 23829164.
  7. ^ David N., Fredricks (2001). "Microbial Ecology of Human Skin in Health and Disease". Journal of Investigative Dermatology Symposium Proceedings. 6: 167–169. doi:10.1046/j.0022-202x.2001.00039.x. Retrieved 7 February 2017.
  8. ^ Ganong's 2016, p. 16.
  9. ^ "Gene Expression | Learn Science at Scitable". Retrieved 29 July 2017.
  10. ^ "tissue – definition of tissue in English". Oxford Dictionaries | English. Retrieved 17 September 2016.
  11. ^ a b Gray's Anatomy 2008, p. 27.
  12. ^ "organ | Definition, meaning & more | Collins Dictionary". Retrieved 17 September 2016.
  13. ^ "Cardiovascular System". U.S. National Cancer Institute. Archived from the original on 2 February 2007. Retrieved 16 September 2008.
  14. ^ Human Biology and Health. Upper Saddle River, NJ: Pearson Prentice Hall. 1993. ISBN 0-13-981176-1.
  15. ^ "The Cardiovascular System". SUNY Downstate Medical Center. 8 March 2008.
  16. ^ "Your Digestive System and How It Works". NIH. Retrieved 4 September 2016.
  17. ^ "Hormonal (endocrine) system". Victoria State Government. Retrieved 4 September 2016.
  18. ^ Zimmerman, Kim Ann. "Immune System: Diseases, Disorders & Function". LiveScience. Retrieved 4 September 2016.
  19. ^ Integumentary+System at the US National Library of Medicine Medical Subject Headings (MeSH)
  20. ^ Marieb, Elaine; Hoehn, Katja (2007). Human Anatomy & Physiology (7th ed.). Pearson Benjamin Cummings. p. 142.
  21. ^ Zimmerman, Kim Anne. "Lymphatic System: Facts, Functions & Diseases". LiveScience. Retrieved 4 September 2016.
  22. ^ Moore, Keith L.; Dalley, Arthur F.; Agur Anne M.R. (2010). Moore's Clinically Oriented Anatomy. Phildadelphia: Lippincott Williams & Wilkins. pp. 2–3. ISBN 978-1-60547-652-0.
  23. ^ "Nervous System". Columbia Encyclopedia (6th ed.). Columbia University Press. 2001. ISBN 978-0-7876-5015-5.
  24. ^ "Introduction to the Reproductive System". Epidemiology and End Results (SEER) Program. Archived from the original on 2 January 2007.
  25. ^ Maton, Anthea; Hopkins, Jean Susan; Johnson, Charles William; McLaughlin, Maryanna Quon; Warner, David; LaHart Wright, Jill (2010). Human Biology and Health. Prentice Hall. pp. 108–118. ISBN 0-13-423435-9.
  26. ^ Zimmerman, Kim Ann. "Urinary System: Facts, Functions & Diseases". LiveScience. Retrieved 4 September 2016.
  27. ^ Gray, Henry (1918). "Anatomy of the Human Body". Bartleby. Retrieved 4 September 2016.
  28. ^ a b "What is Physiology?". Understanding Life. Retrieved 4 September 2016.
  29. ^ "Introduction page, "Anatomy of the Human Body". Henry Gray. 20th edition. 1918". Retrieved 27 March 2007.
  30. ^ Publisher's page for Gray's Anatomy. 39th edition (UK). 2004. ISBN 0-443-07168-3. Archived from the original on 20 February 2007. Retrieved 27 March 2007.
  31. ^ "Publisher's page for Gray's Anatomy. 39th edition (US). 2004. ISBN 0-443-07168-3". Archived from the original on 9 February 2007. Retrieved 27 March 2007.
  32. ^ Stewart, Andrew (November 1978). "Polykleitos of Argos," One Hundred Greek Sculptors: Their Careers and Extant Works". Journal of Hellenic Studies. 98: 122–131. doi:10.2307/630196. JSTOR 630196.
  33. ^ "Leonardo". Dartmouth College. Retrieved 2 September 2016.
  34. ^ Gillispie, Charles Coulston (1972). Dictionary of Scientific Biography. VI. New York: Charles Scribner's Sons. pp. 419–427.
  35. ^ Hutton, Vivien. "Galen of Pergamum". Encyclopædia Britannica 2006 Ultimate Reference Suite DVD.
  36. ^ "Vesalius's De Humanis Corporis Fabrica". Retrieved 29 August 2010.
  37. ^ "Andreas Vesalius (1514–1567)". Ingentaconnect. 1 May 1999. Retrieved 29 August 2010.
  38. ^ "Microscopic anatomy". Encyclopædia Britannica. Retrieved 14 October 2013.
  39. ^ "Anatomical Imaging". McGraw Hill Higher Education. 1998. Retrieved 25 June 2013.
  40. ^ Fell, C.; Griffith Pearson, F. (November 2007). "Thoracic Surgery Clinics: Historical Perspectives of Thoracic Anatomy". Thorac Surg Clin. 17 (4): 443–448, v. doi:10.1016/j.thorsurg.2006.12.001.
  41. ^ a b Newman, Tim. "Introduction to Physiology: History And Scope". Medicine News Today. Retrieved 2 September 2016.
  42. ^ Zimmer, Carl (2004). "Soul Made Flesh: The Discovery of the Brain – and How It Changed the World". J Clin Invest. 114 (5): 604–604. doi:10.1172/JCI22882. PMC 514597.
  43. ^ Feder, Martin E. (1987). New directions in ecological physiology. New York: Cambridge Univ. Press. ISBN 978-0-521-34938-3.
  44. ^ Garland, Jr, Theodore; Carter, P. A. (1994). "Evolutionary physiology" (PDF). Annual Review of Physiology. 56 (1): 579–621. doi:10.1146/ PMID 8010752.
  45. ^ Waldstein, Michael (2006). A Theology of the Body: Translation, Introduction, and Index. Boston, MA: Pauline Books & Media. pp. 17, 34–55, 94–99. ISBN 0-8198-7421-3.
  46. ^ West, Christopher (2003). Theology of the Body Explained: A Commentary on John Paul II's "Gospel of the Body". Gracewing Publishing. ISBN 0852446004.:43
  47. ^ "Waldstein Links Pope John Paul II to St. John of the Cross". Christendom College. 28 September 2004.


  • Ganong's Review of Medical Physiology. 2016. ISBN 978-0-07-182510-8.
  • Gray's anatomy: the anatomical basis of clinical practice. Editor-in-chief, Susan Standring (40th ed.). London: Churchill Livingstone. 2008. ISBN 978-0-8089-2371-8.CS1 maint: others (link)

External links

Anatomical terminology

Anatomical terminology is a form of scientific terminology used by anatomists, zoologists, and health professionals such as doctors.

Anatomical terminology uses many unique terms, suffixes, and prefixes deriving from Ancient Greek and Latin. These terms can be confusing to those unfamiliar with them, but can be more precise, reducing ambiguity and errors. Also, since these anatomical terms are not used in everyday conversation, their meanings are less likely to change, and less likely to be misinterpreted.

To illustrate how inexact day-to-day language can be: a scar "above the wrist" could be located on the forearm two or three inches away from the hand or at the base of the hand; and could be on the palm-side or back-side of the arm. By using precise anatomical terminology such ambiguity is eliminated.An international standard for anatomical terminology, Terminologia Anatomica has been created.

Aura (paranormal)

An aura or human energy field is, according to New Age beliefs, a colored emanation said to enclose a human body or any animal or object. In some esoteric positions, the aura is described as a subtle body. Psychics and holistic medicine practitioners often claim to have the ability to see the size, color and type of vibration of an aura.In New Age alternative medicine, the human aura is seen as a hidden anatomy that affect the health of a client, and is often understood to comprise centers of vital force called chakra. Such claims are not supported by scientific evidence and are pseudoscience. When tested under controlled experiments, the ability to see auras has not been shown to exist.

Body cavity

A body cavity is any fluid-filled space in a multicellular organism other than those of vessels (such as blood vessels and lymph vessels). The human body cavity normally refers to the ventral body cavity, because it is by far the largest.

Body louse

The body louse (Pediculus humanus humanus, sometimes called Pediculus humanus corporis) is a louse that infests humans. The condition of being infested with head lice, body lice, or pubic lice is known as pediculosis. Body lice are vectors for the transmission of the human diseases epidemic typhus, trench fever, and relapsing fever. The body louse genome sequence analysis was published in 2010.


A cadaver is a dead human body that is used by medical students, physicians and other scientists to study anatomy, identify disease sites, determine causes of death, and provide tissue to repair a defect in a living human being. Students in medical school study and dissect cadavers as a part of their education. Others who study cadavers include archaeologists and artists.The term cadaver is used in courts of law to refer to a dead body, as well as by recovery teams searching for bodies in natural disasters. The word comes from the Latin word cadere ("to fall"). Related terms include cadaverous (resembling a cadaver) and cadaveric spasm (a muscle spasm causing a dead body to twitch or jerk). A cadaver graft (also called “postmortem graft”) is the grafting of tissue from a dead body onto a living human to repair a defect or disfigurement. Cadavers can be observed for their stages of decomposition, helping to determine how long a body has been dead.Cadavers have been used in art to depict the human body in paintings and drawings more accurately.

Composition of the human body

Body composition may be analyzed in various ways. This can be done in terms of the chemical elements present, or by molecular type e.g., water, protein, fats (or lipids), hydroxylapatite (in bones), carbohydrates (such as glycogen and glucose) and DNA. In terms of tissue type, the body may be analyzed into water, fat, connective tissue, muscle, bone, etc. In terms of cell type, the body contains hundreds of different types of cells, but notably, the largest number of cells contained in a human body (though not the largest mass of cells) are not human cells, but bacteria residing in the normal human gastrointestinal tract.

Development of the human body

Human development is the process of growth to maturity. The process begins with fertilisation, where an egg released from the ovary of a female is penetrated by a sperm cell from a male. The egg then lodges in the uterus, where an embryo and later fetus develop until birth. Further growth and development continues after birth, and includes both physical and psychological development, influenced by genetic, hormonal, environmental and other factors. This continues throughout life, through childhood, and adolescence into adulthood.

Effect of spaceflight on the human body

Venturing into the environment of space can have negative effects on the human body. Significant adverse effects of long-term weightlessness include muscle atrophy and deterioration of the skeleton (spaceflight osteopenia). Other significant effects include a slowing of cardiovascular system functions, decreased production of red blood cells, balance disorders, eyesight disorders and changes in the immune system. Additional symptoms include fluid redistribution (causing the "moon-face" appearance typical in pictures of astronauts experiencing weightlessness), loss of body mass, nasal congestion, sleep disturbance, and excess flatulence.

The engineering problems associated with leaving Earth and developing space propulsion systems have been examined for over a century, and millions of hours of research have been spent on them. In recent years there has been an increase in research on the issue of how humans can survive and work in space for extended and possibly indefinite periods of time. This question requires input from the physical and biological sciences and has now become the greatest challenge (other than funding) facing human space exploration. A fundamental step in overcoming this challenge is trying to understand the effects and impact of long-term space travel on the human body.

In October 2015, the NASA Office of Inspector General issued a health hazards report related to space exploration, including a human mission to Mars.On 12 April 2019, NASA reported medical results, from the Astronaut Twin Study, where one astronaut twin spent a year in space on the International Space Station, while the other twin spent the year on Earth, which demonstrated several long-lasting changes, including those related to alterations in DNA and cognition, when one twin was compared with the other.

Gray's Anatomy

Gray's Anatomy is an English language textbook of human anatomy originally written by Henry Gray and illustrated by Henry Vandyke Carter. Earlier editions were called Anatomy: Descriptive and Surgical, Anatomy of the Human Body and Gray's Anatomy: Descriptive and Applied, but the book's name is commonly shortened to, and later editions are titled, Gray's Anatomy. The book is widely regarded as an extremely influential work on the subject, and has continued to be revised and republished from its initial publication in 1858 to the present day. The latest edition of the book, the 41st, was published in September 2015.

Human body temperature

Normal human body temperature, also known as normothermia or euthermia, is the typical temperature range found in humans. The normal human body temperature range is typically stated as 36.5–37.5 °C (97.7–99.5 °F).Individual body temperature depends upon the age, exertion, infection, sex, and reproductive status of the subject, the time of day, the place in the body at which the measurement is made, and the subject's state of consciousness (waking, sleeping or sedated), activity level, and emotional state. It is typically maintained within this range by thermoregulation.

Human body weight

Human body weight refers to a person's mass or weight. Body weight is measured in kilograms, a measure of mass, throughout the world, although in some countries such as the United States it is measured in pounds, or as in the United Kingdom, stones and pounds. Most hospitals, even in the United States, now use kilograms for calculations, but use kilograms and pounds together for other purposes.

Strictly speaking, body weight is the measurement of weight without items located on the person. Practically though, body weight may be measured with clothes on, but without shoes or heavy accessories such as mobile phones and wallets and using manual or digital weighing scales. Excess or reduced body weight is regarded as an indicator of determining a person's health, with body volume measurement providing an extra dimension by calculating the distribution of body weight.

Human skeleton

The human skeleton is the internal framework of the body. It is composed of around 270 bones at birth – this total decreases to around 206 bones by adulthood after some bones get fused together. The bone mass in the skeleton reaches maximum density around age 21. The human skeleton can be divided into the axial skeleton and the appendicular skeleton. The axial skeleton is formed by the vertebral column, the rib cage, the skull and other associated bones. The appendicular skeleton, which is attached to the axial skeleton, is formed by the shoulder girdle, the pelvic girdle and the bones of the upper and lower limbs.

The human skeleton performs six major functions; support, movement, protection, production of blood cells, storage of minerals, and endocrine regulation.

The human skeleton is not as sexually dimorphic as that of many other primate species, but subtle differences between sexes in the morphology of the skull, dentition, long bones, and pelvis exist. In general, female skeletal elements tend to be smaller and less robust than corresponding male elements within a given population. The human female pelvis is also different from that of males in order to facilitate childbirth. Unlike most primates, human males do not have penile bones.

List of bones of the human skeleton

The human skeleton of an adult consists of 206-208 bones, depending on the counting of the sternum (which may alternatively be included as the manubrium, body of sternum, and the xiphoid process) It is composed of 270 bones at birth, but later decreases to 80 bones in the axial skeleton and 126 bones in the appendicular skeleton. Many small accessory bones, such as some sesamoid bones, are not included in this count.

List of distinct cell types in the adult human body

There are many different types of cell in the human body.

List of skeletal muscles of the human body

This is a table of skeletal muscles of the human anatomy.

There are over 600 skeletal muscles within the typical human body. Almost every muscle constitutes one part of a pair of identical bilateral muscles, found on both sides, resulting in approximately 320 pairs of muscles, as presented

in this article. Nevertheless, the exact number is difficult to define because different sources group muscles differently, e.g. regarding what is defined as different parts of a single muscle or as several muscles.

The muscles of the human body can be categorized into a number of groups which include muscles relating to the head and neck, muscles of the torso or trunk, muscles of the upper limbs, and muscles of the lower limbs.

The action refers to the action of each muscle from the standard anatomical position. In other positions, other actions may be performed.

These muscles are described using anatomical terminology.

List of systems of the human body

The main systems of the human body are:

Circulatory system:

Circulates blood around the body via the heart, arteries and veins, delivering oxygen and nutrients to organs and cells and carrying their waste products away.

Keeps the body's temperature in a safe range.

Digestive system and Excretory system:

System to absorb nutrients and remove waste via the gastrointestinal tract, including the mouth, esophagus, stomach and intestines.

Eliminates waste from the body.

Endocrine system:

Influences the function of the body using hormones.

Integumentary system / Exocrine system:

Skin, hair, nails, sweat and other exocrine glands

Immune system and lymphatic system:

Defends the body against pathogens that may endanger the body.

The system comprising a network of lymphatic vessels that carry a clear fluid called lymph.

Muscular system:

Enables the body to move using muscles.

Nervous system:

Collects and processes information from the senses via nerves and the brain and tells the muscles to contract to cause physical actions.

Renal system and Urinary system

The system where the kidneys filter blood to produce urine.

Reproductive system:

The sex organs required for the production of offspring.

Respiratory system:

Brings air into and out of the lungs to absorb oxygen and remove carbon dioxide.

Skeletal system:

Bones maintain the structure of the body and its organs.

Mineral (nutrient)

In the context of nutrition, a mineral is a chemical element required as an essential nutrient by organisms to perform functions necessary for life.

However, the four major structural elements in the human body by weight (oxygen, hydrogen, carbon, and nitrogen), are usually not included in lists of major nutrient minerals (nitrogen is considered a "mineral" for plants, as it often is included in fertilizers). These four elements compose about 96% of the weight of the human body, and major minerals (macrominerals) and minor minerals (also called trace elements) compose the remainder.

Minerals, as elements, cannot be synthesized biochemically by living organisms. Plants get minerals from soil. Most of the minerals in a human diet come from eating plants and animals or from drinking water. As a group, minerals are one of the four groups of essential nutrients, the others of which are vitamins, essential fatty acids, and essential amino acids. The five major minerals in the human body are calcium, phosphorus, potassium, sodium, and magnesium. All of the remaining elements in a human body are called "trace elements". The trace elements that have a specific biochemical function in the human body are sulfur, iron, chlorine, cobalt, copper, zinc, manganese, molybdenum, iodine and selenium.Most chemical elements that are ingested by organisms are in the form of simple compounds. Plants absorb dissolved elements in soils, which are subsequently ingested by the herbivores and omnivores that eat them, and the elements move up the food chain. Larger organisms may also consume soil (geophagia) or use mineral resources, such as salt licks, to obtain limited minerals unavailable through other dietary sources.

Bacteria and fungi play an essential role in the weathering of primary elements that results in the release of nutrients for their own nutrition and for the nutrition of other species in the ecological food chain. One element, cobalt, is available for use by animals only after having been processed into complex molecules (e.g., vitamin B12) by bacteria. Minerals are used by animals and microorganisms for the process of mineralizing structures, called "biomineralization", used to construct bones, seashells, eggshells, exoskeletons and mollusc shells.

Radio wave

Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Radio waves have frequencies as high as 300 gigahertz (GHz) to as low as 30 hertz (Hz). At 300 GHz, the corresponding wavelength is 1 mm, and at 30 Hz is 10,000 km. Like all other electromagnetic waves, radio waves travel at the speed of light. They are generated by electric charges undergoing acceleration, such as time varying electric currents. Naturally occurring radio waves are emitted by lightning and astronomical objects.

Radio waves are generated artificially by transmitters and received by radio receivers, using antennas. Radio waves are very widely used in modern technology for fixed and mobile radio communication, broadcasting, radar and other navigation systems, communications satellites, wireless computer networks and many other applications. Different frequencies of radio waves have different propagation characteristics in the Earth's atmosphere; long waves can diffract around obstacles like mountains and follow the contour of the earth (ground waves), shorter waves can reflect off the ionosphere and return to earth beyond the horizon (skywaves), while much shorter wavelengths bend or diffract very little and travel on a line of sight, so their propagation distances are limited to the visual horizon.

To prevent interference between different users, the artificial generation and use of radio waves is strictly regulated by law, coordinated by an international body called the International Telecommunications Union (ITU), which defines radio waves as "electromagnetic waves of frequencies arbitrarily lower than 3 000 GHz, propagated in space without artificial guide". The radio spectrum is divided into a number of radio bands on the basis of frequency, allocated to different uses.

Vitruvian Man

The Vitruvian Man (Italian: Le proporzioni del corpo umano secondo Vitruvio, which is translated to "The proportions of the human body according to Vitruvius"), or simply L'Uomo Vitruviano (Italian pronunciation: [ˈlwɔːmo vitruˈvjaːno]), is a drawing made by the Italian polymath Leonardo da Vinci around 1490. It is accompanied by notes based on the work of the architect Vitruvius. The drawing, which is in ink on paper, depicts a man in two superimposed positions with his arms and legs apart and inscribed in a circle and square. The drawing and text are sometimes called the Canon of Proportions or, less often, Proportions of Man. It is kept in the Gabinetto dei disegni e stampe of the Gallerie dell'Accademia, in Venice, Italy, under reference 228. Like most works on paper, it is displayed to the public only occasionally, so it is not part of the normal exhibition of the museum.The drawing is based on the correlations of ideal human body proportions with geometry described by the ancient Roman architect Vitruvius in Book III of his treatise De architectura. Vitruvius described the human figure as being the principal source of proportion among the classical orders of architecture. Vitruvius determined that the ideal body should be eight heads high. Leonardo's drawing is traditionally named in honor of the architect.

Human systems and organs
Circulatory system
Nervous system
Integumentary system
Immune system
Respiratory system
Digestive system
Urinary system
Reproductive system
Endocrine system
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