Human body

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"Anatomy of the human body" redirects here. Human body_sentence_0

For the textbook, see Gray's Anatomy. Human body_sentence_1

The human body is the structure of a human being. Human body_sentence_2

It is composed of many different types of cells that together create tissues and subsequently organ systems. Human body_sentence_3

They ensure homeostasis and the viability of the human body. Human body_sentence_4

It comprises a head, neck, trunk (which includes the thorax and abdomen), arms and hands, legs and feet. Human body_sentence_5

The study of the human body involves anatomy, physiology, histology and embryology. Human body_sentence_6

The body varies anatomically in known ways. Human body_sentence_7

Physiology focuses on the systems and organs of the human body and their functions. Human body_sentence_8

Many systems and mechanisms interact in order to maintain homeostasis, with safe levels of substances such as sugar and oxygen in the blood. Human body_sentence_9

The body is studied by health professionals, physiologists, anatomists, and by artists to assist them in their work. Human body_sentence_10

Composition Human body_section_0

Human body_table_general_0

Elements of the human body by mass. Trace elements are less than 1% combined (and each less than 0.1%).Human body_table_caption_0
Human body_cell_0_0_0 ElementHuman body_cell_0_0_1 SymbolHuman body_cell_0_0_2 percent massHuman body_cell_0_0_3 percent atomsHuman body_cell_0_0_4
OxygenHuman body_cell_0_1_0 OHuman body_cell_0_1_1 65.0Human body_cell_0_1_2 24.0Human body_cell_0_1_3
CarbonHuman body_cell_0_2_0 CHuman body_cell_0_2_1 18.5Human body_cell_0_2_2 12.0Human body_cell_0_2_3
HydrogenHuman body_cell_0_3_0 HHuman body_cell_0_3_1 9.5Human body_cell_0_3_2 62.0Human body_cell_0_3_3
NitrogenHuman body_cell_0_4_0 NHuman body_cell_0_4_1 3.2Human body_cell_0_4_2 1.1Human body_cell_0_4_3
CalciumHuman body_cell_0_5_0 CaHuman body_cell_0_5_1 1.5Human body_cell_0_5_2 0.22Human body_cell_0_5_3
PhosphorusHuman body_cell_0_6_0 PHuman body_cell_0_6_1 1.0Human body_cell_0_6_2 0.22Human body_cell_0_6_3
PotassiumHuman body_cell_0_7_0 KHuman body_cell_0_7_1 0.4Human body_cell_0_7_2 0.03Human body_cell_0_7_3
SulfurHuman body_cell_0_8_0 SHuman body_cell_0_8_1 0.3Human body_cell_0_8_2 0.038Human body_cell_0_8_3
SodiumHuman body_cell_0_9_0 NaHuman body_cell_0_9_1 0.2Human body_cell_0_9_2 0.037Human body_cell_0_9_3
ChlorineHuman body_cell_0_10_0 ClHuman body_cell_0_10_1 0.2Human body_cell_0_10_2 0.024Human body_cell_0_10_3
MagnesiumHuman body_cell_0_11_0 MgHuman body_cell_0_11_1 0.1Human body_cell_0_11_2 0.015Human body_cell_0_11_3
Trace elementsHuman body_cell_0_12_0 Human body_cell_0_12_1 < 0.1Human body_cell_0_12_2 < 0.3Human body_cell_0_12_3

The human body is composed of elements including hydrogen, oxygen, carbon, calcium and phosphorus. Human body_sentence_11

These elements reside in trillions of cells and non-cellular components of the body. Human body_sentence_12

The adult male body is about 60% water for a total water content of some 42 litres (9.2 imp gal; 11 US gal). Human body_sentence_13

This is made up of about 19 litres (4.2 imp gal; 5.0 US gal) of extracellular fluid including about 3.2 litres (0.70 imp gal; 0.85 US gal) of blood plasma and about 8.4 litres (1.8 imp gal; 2.2 US gal) of interstitial fluid, and about 23 litres (5.1 imp gal; 6.1 US gal) of fluid inside cells. Human body_sentence_14

The content, acidity and composition of the water inside and outside cells is carefully maintained. Human body_sentence_15

The main electrolytes in body water outside cells are sodium and chloride, whereas within cells it is potassium and other phosphates. Human body_sentence_16

Cells Human body_section_1

See also: List of distinct cell types in the adult human body Human body_sentence_17

The body contains trillions of cells, the fundamental unit of life. Human body_sentence_18

At maturity, there are roughly 30–37 trillion cells in the body, an estimate arrived at by totaling the cell numbers of all the organs of the body and cell types. Human body_sentence_19

The body is also host to about the same number of non-human cells as well as multicellular organisms which reside in the gastrointestinal tract and on the skin. Human body_sentence_20

Not all parts of the body are made from cells. Human body_sentence_21

Cells sit in an extracellular matrix that consists of proteins such as collagen, surrounded by extracellular fluids. Human body_sentence_22

Of the 70 kg (150 lb) weight of an average human body, nearly 25 kg (55 lb) is non-human cells or non-cellular material such as bone and connective tissue. Human body_sentence_23

Genome Human body_section_2

Main article: Genome Human body_sentence_24

See also: Genetics Human body_sentence_25

Cells in the body function because of DNA. Human body_sentence_26

DNA sits within the nucleus of a cell. Human body_sentence_27

Here, parts of DNA are copied and sent to the body of the cell via RNA. Human body_sentence_28

The RNA is then used to create proteins which form the basis for cells, their activity, and their products. Human body_sentence_29

Proteins dictate cell function and gene expression, a cell is able to self-regulate by the amount of proteins produced. Human body_sentence_30

However, not all cells have DNA; some cells such as mature red blood cells lose their nucleus as they mature. Human body_sentence_31

Tissues Human body_section_3

Human body_table_infobox_1

External videoHuman body_header_cell_1_0_0

The body consists of many different types of tissue, defined as cells that act with a specialised function. Human body_sentence_32

The study of tissues is called histology and often occurs with a microscope. Human body_sentence_33

The body consists of four main types of tissues – lining cells (epithelia), connective tissue, nerve tissue and muscle tissue. Human body_sentence_34

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. Human body_sentence_35

Endothelial cells are cells that line internal cavities including blood vessels and glands. Human body_sentence_36

Lining cells regulate what can and can't pass through them, protect internal structures, and function as sensory surfaces. Human body_sentence_37

Organs Human body_section_4

See also: List of organs of the human body Human body_sentence_38

Organs, structured collections of cells with a specific function, mostly sit within the body, with the exception of skin. Human body_sentence_39

Examples include the heart, lungs and liver. Human body_sentence_40

Many organs reside within cavities within the body. Human body_sentence_41

These cavities include the abdomen (which contains the stomach, for example) and pleura, which contains the lungs. Human body_sentence_42

Systems Human body_section_5

See also: List of systems of the human body Human body_sentence_43

Circulatory system Human body_section_6

Main article: Circulatory system Human body_sentence_44

The circulatory system consists of the heart and blood vessels (arteries, veins and capillaries). Human body_sentence_45

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. Human body_sentence_46

Paths of blood circulation within the human body can be divided into two circuits: the pulmonary circuit, which pumps blood to the lungs to receive oxygen and leave carbon dioxide, and the systemic circuit, which carries blood from the heart off to the rest of the body. Human body_sentence_47

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. Human body_sentence_48

Digestive system Human body_section_7

Main article: Digestive system Human body_sentence_49

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. Human body_sentence_50

It converts food into small, nutritional, non-toxic molecules for distribution and absorption into the body. Human body_sentence_51

These molecules take the form of proteins (which are broken down into amino acids), fats, vitamins and minerals (the last of which are mainly ionic rather than molecular). Human body_sentence_52

After being swallowed, food moves through the gastrointestinal tract by means of peristalsis: the systematic expansion and contraction of muscles to push food from one area to the next. Human body_sentence_53

Digestion begins in the mouth, which chews food into smaller pieces for easier digestion. Human body_sentence_54

Then it is swallowed, and moves through the esophagus to the stomach. Human body_sentence_55

In the stomach, food is mixed with gastric acids to allow the extraction of nutrients. Human body_sentence_56

What is left is called chyme; this then moves into the small intestine, which absorbs the nutrients and water from the chyme. Human body_sentence_57

What remains passes on to the large intestine, where it is dried to form feces; these are then stored in the rectum until they are expelled through the anus. Human body_sentence_58

Endocrine system Human body_section_8

Main article: Endocrine system Human body_sentence_59

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. Human body_sentence_60

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. Human body_sentence_61

Immune system Human body_section_9

Main article: Immune system Human body_sentence_62

The immune system consists of the white blood cells, the thymus, lymph nodes and lymph channels, which are also part of the lymphatic system. Human body_sentence_63

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. Human body_sentence_64

Integumentary system Human body_section_10

Main article: Integumentary system Human body_sentence_65

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. Human body_sentence_66

The skin provides containment, structure, and protection for other organs, and serves as a major sensory interface with the outside world. Human body_sentence_67

Lymphatic system Human body_section_11

Main article: Lymphatic system Human body_sentence_68

The lymphatic system extracts, transports and metabolizes lymph, the fluid found in between cells. Human body_sentence_69

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. Human body_sentence_70

Musculoskeletal system Human body_section_12

Main article: Musculoskeletal system Human body_sentence_71

The musculoskeletal system consists of the human skeleton (which includes bones, ligaments, tendons, and cartilage) and attached muscles. Human body_sentence_72

It gives the body basic structure and the ability for movement. Human body_sentence_73

In addition to their structural role, the larger bones in the body contain bone marrow, the site of production of blood cells. Human body_sentence_74

Also, all bones are major storage sites for calcium and phosphate. Human body_sentence_75

This system can be split up into the muscular system and the skeletal system. Human body_sentence_76

Nervous system Human body_section_13

Main article: Nervous system Human body_sentence_77

The nervous system consists of the body's neurons and glial cells, which together form the nerves, ganglia and gray matter which in turn form the brain and related structures. Human body_sentence_78

The brain is the organ of thought, emotion, memory, and sensory processing; it serves many aspects of communication and controls various systems and functions. Human body_sentence_79

The special senses consist of vision, hearing, taste, and smell. Human body_sentence_80

The eyes, ears, tongue, and nose gather information about the body's environment. Human body_sentence_81

From a structural perspective, the nervous system is typically subdivided into two component parts: the central nervous system (CNS), composed of the brain and the spinal cord; and the peripheral nervous system (PNS), composed of the nerves and ganglia outside the brain and spinal cord. Human body_sentence_82

The CNS is mostly responsible for organizing motion, processing sensory information, thought, memory, cognition and other such functions. Human body_sentence_83

It remains a matter of some debate whether the CNS directly gives rise to consciousness. Human body_sentence_84

The peripheral nervous system (PNS) is mostly responsible for gathering information with sensory neurons and directing body movements with motor neurons. Human body_sentence_85

From a functional perspective, the nervous system is again typically divided into two component parts: the somatic nervous system (SNS) and the autonomic nervous system (ANS). Human body_sentence_86

The SNS is involved in voluntary functions like speaking and sensory processes. Human body_sentence_87

The ANS is involved in involuntary processes, such as digestion and regulating blood pressure. Human body_sentence_88

The nervous system is subject to many different diseases. Human body_sentence_89

In epilepsy, abnormal electrical activity in the brain can cause seizures. Human body_sentence_90

In multiple sclerosis, the immune system attacks the nerve linings, damaging the nerves' ability to transmit signals. Human body_sentence_91

Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease, is a motor neuron disease which gradually reduces movement in patients. Human body_sentence_92

There are also many other diseases of the nervous system. Human body_sentence_93

Reproductive system Human body_section_14

Main article: Human reproductive system Human body_sentence_94

The reproductive system consists of the gonads and the internal and external sex organs. Human body_sentence_95

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. Human body_sentence_96

Respiratory system Human body_section_15

Main article: Respiratory system Human body_sentence_97

The respiratory system consists of the nose, nasopharynx, trachea, and lungs. Human body_sentence_98

It brings oxygen from the air and excretes carbon dioxide and water back into the air. Human body_sentence_99

First, air is pulled through the trachea into the lungs by the diaphragm pushing down, which creates a vacuum. Human body_sentence_100

Air is briefly stored inside small sacs known as alveoli (sing. Human body_sentence_101

alveolus) before being expelled from the lungs when the diaphragm contracts again. Human body_sentence_102

Each alveolus is surrounded by capillaries carrying deoxygenated blood, which absorbs oxygen out of the air and into the bloodstream. Human body_sentence_103

For the respiratory system to function properly, there need to be as few impediments as possible to the movement of air within the lungs. Human body_sentence_104

Inflammation of the lungs and excess mucus are common sources of breathing difficulties. Human body_sentence_105

In asthma, the respiratory system is persistently inflamed, causing wheezing and/or shortness of breath. Human body_sentence_106

Pneumonia occurs through infection of the alveoli, and may be caused by tuberculosis. Human body_sentence_107

Emphysema, commonly a result of smoking, is caused by damage to connections between the alveoli. Human body_sentence_108

Urinary system Human body_section_16

Main article: Urinary system Human body_sentence_109

The urinary system consists of the kidneys, ureters, bladder, and urethra. Human body_sentence_110

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. Human body_sentence_111

Anatomy Human body_section_17

Main articles: Outline of human anatomy and Anatomy Human body_sentence_112

Human anatomy is the study of the shape and form of the human body. Human body_sentence_113

The human body has four limbs (two arms and two legs), a head and a neck which connect to the torso. Human body_sentence_114

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. Human body_sentence_115

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. Human body_sentence_116

Nerves connect the spinal cord and brain to the rest of the body. Human body_sentence_117

All major bones, muscles, and nerves in the body are named, with the exception of anatomical variations such as sesamoid bones and accessory muscles. Human body_sentence_118

Blood vessels carry blood throughout the body, which moves because of the beating of the heart. Human body_sentence_119

Venules and veins collect blood low in oxygen from tissues throughout the body. Human body_sentence_120

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. Human body_sentence_121

From here, the blood is pumped into the lungs where it receives oxygen and drains back into the left side of the heart. Human body_sentence_122

From here, it is pumped into the body's largest artery, the aorta, and then progressively smaller arteries and arterioles until it reaches tissue. Human body_sentence_123

Here blood passes from small arteries into capillaries, then small veins and the process begins again. Human body_sentence_124

Blood carries oxygen, waste products, and hormones from one place in the body to another. Human body_sentence_125

Blood is filtered at the kidneys and liver. Human body_sentence_126

The body consists of a number of body cavities, separated areas which house different organ systems. Human body_sentence_127

The brain and central nervous system reside in an area protected from the rest of the body by the blood brain barrier. Human body_sentence_128

The lungs sit in the pleural cavity. Human body_sentence_129

The intestines, liver, and spleen sit in the abdominal cavity. Human body_sentence_130

Height, weight, shape and other body proportions vary individually and with age and sex. Human body_sentence_131

Body shape is influenced by the distribution of muscle and fat tissue. Human body_sentence_132

Physiology Human body_section_18

Main articles: Outline of physiology and Physiology Human body_sentence_133

Human physiology is the study of how the human body functions. Human body_sentence_134

This includes the mechanical, physical, bioelectrical, and biochemical functions of humans in good health, from organs to the cells of which they are composed. Human body_sentence_135

The human body consists of many interacting systems of organs. Human body_sentence_136

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. Human body_sentence_137

Each system contributes to homeostasis, of itself, other systems, and the entire body. Human body_sentence_138

Some combined systems are referred to by joint names. Human body_sentence_139

For example, the nervous system and the endocrine system operate together as the neuroendocrine system. Human body_sentence_140

The nervous system receives information from the body, and transmits this to the brain via nerve impulses and neurotransmitters. Human body_sentence_141

At the same time, the endocrine system releases hormones, such as to help regulate blood pressure and volume. Human body_sentence_142

Together, these systems regulate the internal environment of the body, maintaining blood flow, posture, energy supply, temperature, and acid balance (pH). Human body_sentence_143

Development Human body_section_19

Main article: Development of the human body Human body_sentence_144

Development of the human body is the process of growth to maturity. Human body_sentence_145

The process begins with fertilisation, where an egg released from the ovary of a female is penetrated by sperm. Human body_sentence_146

The egg then lodges in the uterus, where an embryo and later fetus develop until birth. Human body_sentence_147

Growth and development occur after birth, and include both physical and psychological development, influenced by genetic, hormonal, environmental and other factors. Human body_sentence_148

Development and growth continue throughout life, through childhood, adolescence, and through adulthood to old age, and are referred to as the process of aging. Human body_sentence_149

Society and culture Human body_section_20

Professional study Human body_section_21

Further information: History of anatomy, History of medicine, and History of physiology Human body_sentence_150

Health professionals learn about the human body from illustrations, models, and demonstrations. Human body_sentence_151

Medical and dental students in addition gain practical experience, for example by dissection of cadavers. Human body_sentence_152

Human anatomy, physiology, and biochemistry are basic medical sciences, generally taught to medical students in their first year at medical school. Human body_sentence_153

Depiction Human body_section_22

Main articles: Human figure (aesthetics) and Figure drawing Human body_sentence_154

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. Human body_sentence_155

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. Human body_sentence_156

History of anatomy Human body_section_23

Main article: History of anatomy Human body_sentence_157

In Ancient Greece, the Hippocratic Corpus described the anatomy of the skeleton and muscles. Human body_sentence_158

The 2nd century physician Galen of Pergamum compiled classical knowledge of anatomy into a text that was used throughout the Middle Ages. Human body_sentence_159

In the Renaissance, Andreas Vesalius (1514–1564) pioneered the modern study of human anatomy by dissection, writing the influential book De humani corporis fabrica. Human body_sentence_160

Anatomy advanced further with the invention of the microscope and the study of the cellular structure of tissues and organs. Human body_sentence_161

Modern anatomy uses techniques such as magnetic resonance imaging, computed tomography, fluoroscopy and ultrasound imaging to study the body in unprecedented detail. Human body_sentence_162

History of physiology Human body_section_24

Main article: History of physiology Human body_sentence_163

The study of human physiology began with Hippocrates in Ancient Greece, around 420 BCE, and with Aristotle (384–322 BCE) who applied critical thinking and emphasis on the relationship between structure and function. Human body_sentence_164

Galen (ca. 126–199) was the first to use experiments to probe the body's functions. Human body_sentence_165

The term physiology was introduced by the French physician Jean Fernel (1497–1558). Human body_sentence_166

In the 17th century, William Harvey (1578–1657) described the circulatory system, pioneering the combination of close observation with careful experiment. Human body_sentence_167

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. Human body_sentence_168

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. Human body_sentence_169

In the 20th century, the physiologists Knut Schmidt-Nielsen and George Bartholomew extended their studies to comparative physiology and ecophysiology. Human body_sentence_170

Most recently, evolutionary physiology has become a distinct subdiscipline. Human body_sentence_171

See also Human body_section_25

Human body_unordered_list_0


Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Human body.