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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.
Contents
·
1Composition
o
1.1Cells
o
1.2Tissues
o
1.3Organs
o
1.4Systems
·
2Anatomy
·
3Physiology
·
4Development
·
5Society and culture
o
5.1Professional study
o
5.2Depiction
o
5.3History of anatomy
o
5.4History of physiology
·
6See also
·
7References
o
7.1Books
·
8External links
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 elementsincluding hydrogen, oxygen, carbon, calciumand 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]
Cells[edit]
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.
Tissues[edit]
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[edit]
See also: List of organs of the
human body
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.
Systems[edit]
See also: List of systems of the
human body
Circulatory system[edit]
Main article: Circulatory system
The circulatory system comprises
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]
Digestive system[edit]
Main article: 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]
Endocrine system[edit]
Main article: 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[edit]
Main article: 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]
Integumentary system[edit]
Main article: 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]
Lymphatic system[edit]
Main article: 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[edit]
Main article: 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]
Nervous system[edit]
Main article: 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]
Reproductive system[edit]
Main article: Human 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[edit]
Main article: 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[edit]
Main article: 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]
Cavities of
human body
Main
articles: Outline of human anatomy and Anatomy
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 skeletonmade 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. Nervesconnect 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]
Main articles: Outline of physiology and Physiology
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 (infant)
Main
article: Development of the human
body
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.
See also: History of beliefs about
the human body
Professional study[edit]
Anatomical study
by Leonardo da Vinci
Further
information: History of anatomy, History of medicine, and History of physiology
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]
Depiction[edit]
Figure drawing
by Lovis Corinth (before
1925)
Main
articles: Human figure (aesthetics) and Figure drawing
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[edit]
Two facing pages
of text with woodcuts of naked male and female figures, in the Epitome by Andreas Vesalius, 1543
Main
article: History of anatomy
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[edit]
Main article: History of physiology
The study of human physiology began with Hippocrates in Ancient
Greece, around 420 BC,[40] 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.[41][42] The term
physiology was introduced by the French physician Jean Fernel (1497–1558).[43] In the
17th century, William Harvey(1578–1657) described the circulatory system, pioneering the
combination of close observation with careful experiment.[44] 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.[43] 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.[40] In the
20th century, the physiologists Knut Schmidt-Nielsen and George Bartholomew extended
their studies to comparative physiology and ecophysiology.[45] Most
recently, evolutionary physiology has become
a distinct subdiscipline.[46]
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Development of the human
body
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^ Moore, Keith L.; Dalley,
Arthur F.; Agur Anne M.R. (2010). Moore's
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^ Maton, Anthea; Hopkins, Jean Susan; Johnson, Charles William;
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Books[edit]
·
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.
·
The Book of Humans (from the late 18th and early 19th centuries)
·
Inner Body
·
Anatomia 1522–1867: Anatomical
Plates from the Thomas Fisher Rare Book Library
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![Circulatory system[edit]](https://trwelling.org/File:Diagram_of_the_human_heart_(cropped).svg){kind=link}
![Digestive system[edit]](https://trwelling.org/File:Stomach_colon_rectum_diagram-en.svg){kind=link}
![Endocrine system[edit]](https://trwelling.org/File:Illu_endocrine_system.png){kind=link}
![Immune system[edit]](https://trwelling.org/File:PBNeutrophil.jpg){kind=link}
![Integumentary system[edit]](https://trwelling.org/File:Skin-no_language.PNG){kind=link}
![Lymphatic system[edit]](https://trwelling.org/File:Sobo_1909_605.png){kind=link}
![Musculoskeletal system[edit]](https://trwelling.org/File:Skelett-Mensch-drawing.jpg){kind=link}
![Nervous system[edit]](https://trwelling.org/File:Human_brain_NIH.jpg){kind=link}
![Reproductive system[edit]](https://trwelling.org/File:Male_anatomy.png){kind=link}
![Respiratory system[edit]](https://trwelling.org/File:Heart-and-lungs.jpg){kind=link}
![Urinary system[edit]](https://trwelling.org/File:Gray1120.png){kind=link}
.jpg){kind=link}
