"Anatomy of the human body" redirects here.
For the textbook, see Gray's Anatomy.
The human body is the structure of a human being.
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.
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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 (9.2 imp gal; 11 US gal).
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.
The content, acidity and composition of the water inside and outside cells is carefully maintained.
The body contains trillions of cells, the fundamental unit of life.
Not all parts of the body are made from cells.
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.
Main article: Genome
See also: Genetics
Cells in the body function because of DNA.
DNA sits within the nucleus of a cell.
Proteins dictate cell function and gene expression, a cell is able to self-regulate by the amount of proteins produced.
However, not all cells have DNA; some cells such as mature red blood cells lose their nucleus as they mature.
The body consists of many different types of tissue, defined as cells that act with a specialised function.
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.
See also: List of organs of the human body
Many organs reside within cavities within the body.
See also: List of systems of the human body
Main article: Circulatory system
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.
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.
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.
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.
Main article: Immune 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.
Main article: Integumentary system
The skin provides containment, structure, and protection for other organs, and serves as a major sensory interface with the outside world.
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.
Main article: Musculoskeletal system
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.
Main article: Nervous system
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.
The nervous system is subject to many different diseases.
There are also many other diseases of the nervous system.
Main article: Human reproductive system
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.
Main article: Respiratory system
It brings oxygen from the air and excretes carbon dioxide and water back into the air.
Air is briefly stored inside small sacs known as alveoli (sing.
- alveolus) before being expelled from the lungs when the diaphragm contracts again.
For the respiratory system to function properly, there need to be as few impediments as possible to the movement of air within the lungs.
Main article: Urinary system
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 anatomy is the study of the shape and form of the human body.
Nerves connect the spinal cord and brain to the rest of the body.
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.
From here, the blood is pumped into the lungs where it receives oxygen and drains back into the left side of the heart.
Here blood passes from small arteries into capillaries, then small veins and the process begins again.
The body consists of a number of body cavities, separated areas which house different organ systems.
The lungs sit in the pleural cavity.
Human physiology is the study of how the human body functions.
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.
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.
Together, these systems regulate the internal environment of the body, maintaining blood flow, posture, energy supply, temperature, and acid balance (pH).
Main article: Development of the human body
Development of the human body is the process of growth to maturity.
Growth and development occur after birth, and include both physical and psychological development, influenced by genetic, hormonal, environmental and other factors.
Society and culture
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.
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.
History of anatomy
Main article: History of anatomy
The 2nd century physician Galen of Pergamum compiled classical knowledge of anatomy into a text that was used throughout the Middle Ages.
Anatomy advanced further with the invention of the microscope and the study of the cellular structure of tissues and organs.
History of physiology
Main article: History of physiology
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.
Galen (ca. 126–199) was the first to use experiments to probe the body's functions.
The term physiology was introduced by the French physician Jean Fernel (1497–1558).
Most recently, evolutionary physiology has become a distinct subdiscipline.
- Medicine – Science and practice of the diagnosis, treatment, and prevention of physical and mental illnesses
- Glossary of medicine – List of definitions of terms and concepts commonly used in the study of medicine
- Anatomical model – Three-dimensional representation of human or animal anatomy
- Body image – A person's perception of the aesthetics or sexual attractiveness of his or her own body
- Cell physiology
- Comparative physiology
- Comparative anatomy – Study of similarities and differences in the anatomy of different species
- Development of the human body – Processes of growth from a zygote to an adult human
- Outline of human anatomy
- organ system
Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Human body.