For the anatomy of plants, see Plant anatomy.
For other uses, see Anatomy (disambiguation).
Anatomy is a branch of natural science which deals with the structural organization of living things.
It is an old science, having its beginnings in prehistoric times.
Anatomy is inherently tied to developmental biology, embryology, comparative anatomy, evolutionary biology, and phylogeny, as these are the processes by which anatomy is generated, both over immediate and long-term timescales.
Gross anatomy also includes the branch of superficial anatomy.
Methods have also improved dramatically, advancing from the examination of animals by dissection of carcasses and cadavers (corpses) to 20th century medical imaging techniques including X-ray, ultrasound, and magnetic resonance imaging.
Derived from the Greek ἀνατομή anatomē "dissection" (from ἀνατέμνω anatémnō "I cut up, cut open" from ἀνά aná "up", and τέμνω témnō "I cut"), anatomy is the scientific study of the structure of organisms including their systems, organs and tissues.
It includes the appearance and position of the various parts, the materials from which they are composed, their locations and their relationships with other parts.
For example, an anatomist is concerned with the shape, size, position, structure, blood supply and innervation of an organ such as the liver; while a physiologist is interested in the production of bile, the role of the liver in nutrition and the regulation of bodily functions.
Anatomy can be studied using both invasive and non-invasive methods with the goal of obtaining information about the structure and organization of organs and systems.
Methods used include dissection, in which a body is opened and its organs studied, and endoscopy, in which a video camera-equipped instrument is inserted through a small incision in the body wall and used to explore the internal organs and other structures.
The term "anatomy" is commonly taken to refer to human anatomy.
However, substantially the same structures and tissues are found throughout the rest of the animal kingdom and the term also includes the anatomy of other animals.
The term zootomy is also sometimes used to specifically refer to non-human animals.
The structure and tissues of plants are of a dissimilar nature and they are studied in plant anatomy.
Metazoans do not include the sponges, which have undifferentiated cells.
Vacuoles, when present, are more in number and much smaller than those in the plant cell.
All of the different cells of an animal are derived from the embryonic germ layers.
Those simpler invertebrates which are formed from two germ layers of ectoderm and endoderm are called diploblastic and the more developed animals whose structures and organs are formed from three germ layers are called triploblastic.
Connective tissue gives shape to organs and holds them in place.
Collagen plays a major part in organizing and maintaining tissues.
The matrix can be modified to form a skeleton to support or protect the body.
An endoskeleton is internal and present in all developed animals, as well as in many of those less developed.
Epithelial cells can be squamous (flat), cuboidal or columnar and rest on a basal lamina, the upper layer of the basement membrane, the lower layer is the reticular lamina lying next to the connective tissue in the extracellular matrix secreted by the epithelial cells.
There are many different types of epithelium, modified to suit a particular function.
The epithelial cells on the external surface of the body typically secrete an extracellular matrix in the form of a cuticle.
In simple animals this may just be a coat of glycoproteins.
In more advanced animals, many glands are formed of epithelial cells.
Muscle cells (myocytes) form the active contractile tissue of the body.
Muscle tissue functions to produce force and cause motion, either locomotion or movement within internal organs.
Smooth muscle has no striations when examined microscopically.
It contracts slowly but maintains contractibility over a wide range of stretch lengths.
Skeletal muscle contracts rapidly but has a limited range of extension.
It is found in the movement of appendages and jaws.
Obliquely striated muscle is intermediate between the other two.
The filaments are staggered and this is the type of muscle found in earthworms that can extend slowly or make rapid contractions.
In higher animals striated muscles occur in bundles attached to bone to provide movement and are often arranged in antagonistic sets.
See also: Neuroanatomy
In some slow-moving radially symmetrical marine animals such as ctenophores and cnidarians (including sea anemones and jellyfish), the nerves form a nerve net, but in most animals they are organized longitudinally into bundles.
In simple animals, receptor neurons in the body wall cause a local reaction to a stimulus.
Neurons can be connected together in ganglia.
The peripheral nervous system is divided into the somatic nervous system which conveys sensation and controls voluntary muscle, and the autonomic nervous system which involuntarily controls smooth muscle, certain glands and internal organs, including the stomach.
See also: Comparative anatomy
All vertebrates have a similar basic body plan and at some point in their lives, mostly in the embryonic stage, share the major chordate characteristics; a stiffening rod, the notochord; a dorsal hollow tube of nervous material, the neural tube; pharyngeal arches; and a tail posterior to the anus.
At the posterior end is a tail which continues the spinal cord and vertebrae but not the gut.
The mouth is found at the anterior end of the animal, and the anus at the base of the tail.
Jawed vertebrates are typified by paired appendages, fins or legs, which may be secondarily lost.
The limbs of vertebrates are considered to be homologous because the same underlying skeletal structure was inherited from their last common ancestor.
Main article: Fish anatomy
The body of a fish is divided into a head, trunk and tail, although the divisions between the three are not always externally visible.
The main skeletal element is the vertebral column, composed of articulating vertebrae which are lightweight yet strong.
The ribs attach to the spine and there are no limbs or limb girdles.
They are supported by the muscles which compose the main part of the trunk.
The heart has two chambers and pumps the blood through the respiratory surfaces of the gills and on round the body in a single circulatory loop.
The eyes are adapted for seeing underwater and have only local vision.
There is an inner ear but no external or middle ear.
Low frequency vibrations are detected by the lateral line system of sense organs that run along the length of the sides of fish, and these respond to nearby movements and to changes in water pressure.
Their bodies tend to be dorso-ventrally flattened, they usually have five pairs of gill slits and a large mouth set on the underside of the head.
The dermis is covered with separate dermal placoid scales.
Cartilaginous fish produce a small number of large, yolky eggs.
The bony fish lineage shows more derived anatomical traits, often with major evolutionary changes from the features of ancient fish.
They have a bony skeleton, are generally laterally flattened, have five pairs of gills protected by an operculum, and a mouth at or near the tip of the snout.
The dermis is covered with overlapping scales.
Bony fish have a swim bladder which helps them maintain a constant depth in the water column, but not a cloaca.
They mostly spawn a large number of small eggs with little yolk which they broadcast into the water column.
Main article: Amphibian anatomy
They are tetrapods, but the caecilians and a few species of salamander have either no limbs or their limbs are much reduced in size.
Their main bones are hollow and lightweight and are fully ossified and the vertebrae interlock with each other and have articular processes.
Their ribs are usually short and may be fused to the vertebrae.
Their skulls are mostly broad and short, and are often incompletely ossified.
These are then closed and the air is forced into the lungs by contraction of the throat.
They supplement this with gas exchange through the skin which needs to be kept moist.
In frogs the pelvic girdle is robust and the hind legs are much longer and stronger than the forelimbs.
The feet have four or five digits and the toes are often webbed for swimming or have suction pads for climbing.
Frogs have large eyes and no tail.
Salamanders resemble lizards in appearance; their short legs project sideways, the belly is close to or in contact with the ground and they have a long tail.
Caecilians superficially resemble earthworms and are limbless.
They burrow by means of zones of muscle contractions which move along the body and they swim by undulating their body from side to side.
Main article: Reptile anatomy
Their bones are better ossified and their skeletons stronger than those of amphibians.
The teeth are conical and mostly uniform in size.
The surface cells of the epidermis are modified into horny scales which create a waterproof layer.
Reptiles are unable to use their skin for respiration as do amphibians and have a more efficient respiratory system drawing air into their lungs by expanding their chest walls.
The heart resembles that of the amphibian but there is a septum which more completely separates the oxygenated and deoxygenated bloodstreams.
The reproductive system has evolved for internal fertilization, with a copulatory organ present in most species.
The bladder is small as nitrogenous waste is excreted as uric acid.
Turtles are notable for their protective shells.
These are formed from bony plates embedded in the dermis which are overlain by horny ones and are partially fused with the ribs and spine.
The neck is long and flexible and the head and the legs can be drawn back inside the shell.
Turtles are vegetarians and the typical reptile teeth have been replaced by sharp, horny plates.
In aquatic species, the front legs are modified into flippers.
There is one living species, Sphenodon punctatus.
The skull has two openings (fenestrae) on either side and the jaw is rigidly attached to the skull.
There is one row of teeth in the lower jaw and this fits between the two rows in the upper jaw when the animal chews.
The teeth are merely projections of bony material from the jaw and eventually wear down.
The brain and heart are more primitive than those of other reptiles, and the lungs have a single chamber and lack bronchi.
The tuatara has a well-developed parietal eye on its forehead.
This results in the jaws being less rigidly attached which allows the mouth to open wider.
Lizards are mostly quadrupeds, with the trunk held off the ground by short, sideways-facing legs, but a few species have no limbs and resemble snakes.
Lizards have moveable eyelids, eardrums are present and some species have a central parietal eye.
The skeleton consists of a skull, a hyoid bone, spine and ribs though a few species retain a vestige of the pelvis and rear limbs in the form of pelvic spurs.
The bar under the second fenestra has also been lost and the jaws have extreme flexibility allowing the snake to swallow its prey whole.
Snakes lack moveable eyelids, the eyes being covered by transparent "spectacle" scales.
They do not have eardrums but can detect ground vibrations through the bones of their skull.
Their forked tongues are used as organs of taste and smell and some species have sensory pits on their heads enabling them to locate warm-blooded prey.
Crocodilians are large, low-slung aquatic reptiles with long snouts and large numbers of teeth.
The head and trunk are dorso-ventrally flattened and the tail is laterally compressed.
It undulates from side to side to force the animal through the water when swimming.
The tough keratinized scales provide body armour and some are fused to the skull.
The nostrils, eyes and ears are elevated above the top of the flat head enabling them to remain above the surface of the water when the animal is floating.
Valves seal the nostrils and ears when it is submerged.
Unlike other reptiles, crocodilians have hearts with four chambers allowing complete separation of oxygenated and deoxygenated blood.
Main article: Bird anatomy
The long bones are thin, hollow and very light.
Air sac extensions from the lungs occupy the centre of some bones.
The sternum is wide and usually has a keel and the caudal vertebrae are fused.
There are no teeth and the narrow jaws are adapted into a horn-covered beak.
The eyes are relatively large, particularly in nocturnal species such as owls.
They face forwards in predators and sideways in ducks.
The feathers are outgrowths of the epidermis and are found in localized bands from where they fan out over the skin.
Large flight feathers are found on the wings and tail, contour feathers cover the bird's surface and fine down occurs on young birds and under the contour feathers of water birds.
The only cutaneous gland is the single uropygial gland near the base of the tail.
This produces an oily secretion that waterproofs the feathers when the bird preens.
There are scales on the legs, feet and claws on the tips of the toes.
Main article: Mammal anatomy
Mammals are a diverse class of animals, mostly terrestrial but some are aquatic and others have evolved flapping or gliding flight.
They mostly have four limbs but some aquatic mammals have no limbs or limbs modified into fins and the forelimbs of bats are modified into wings.
The legs of most mammals are situated below the trunk, which is held well clear of the ground.
The bones of mammals are well ossified and their teeth, which are usually differentiated, are coated in a layer of prismatic enamel.
They are clothed in hair and their skin contains glands which secrete sweat.
Some of these glands are specialized as mammary glands, producing milk to feed the young.
The mammalian heart has four chambers and oxygenated and deoxygenated blood are kept entirely separate.
Nitrogenous waste is excreted primarily as urea.
Most other mammals have a placenta through which the developing foetus obtains nourishment, but in marsupials, the foetal stage is very short and the immature young is born and finds its way to its mother's pouch where it latches on to a nipple and completes its development.
Humans have the overall body plan of a mammal.
Generally, students of certain biological sciences, paramedics, prosthetists and orthotists, physiotherapists, occupational therapists, nurses, podiatrists, and medical students learn gross anatomy and microscopic anatomy from anatomical models, skeletons, textbooks, diagrams, photographs, lectures and tutorials and in addition, medical students generally also learn gross anatomy through practical experience of dissection and inspection of cadavers.
Human anatomy, physiology and biochemistry are complementary basic medical sciences, which are generally taught to medical students in their first year at medical school.
Human anatomy can be taught regionally or systemically; that is, respectively, studying anatomy by bodily regions such as the head and chest, or studying by specific systems, such as the nervous or respiratory systems.
The major anatomy textbook, Gray's Anatomy, has been reorganized from a systems format to a regional format, in line with modern teaching methods.
Academic anatomists are usually employed by universities, medical schools or teaching hospitals.
They are often involved in teaching anatomy, and research into certain systems, organs, tissues or cells.
Invertebrates constitute a vast array of living organisms ranging from the simplest unicellular eukaryotes such as Paramecium to such complex multicellular animals as the octopus, lobster and dragonfly.
They constitute about 95% of the animal species.
By definition, none of these creatures has a backbone.
The cells of single-cell protozoans have the same basic structure as those of multicellular animals but some parts are specialized into the equivalent of tissues and organs.
Locomotion is often provided by cilia or flagella or may proceed via the advance of pseudopodia, food may be gathered by phagocytosis, energy needs may be supplied by photosynthesis and the cell may be supported by an endoskeleton or an exoskeleton.
Some protozoans can form multicellular colonies.
Metazoans are multicellular organism, different groups of cells of which have separate functions.
The most basic types of metazoan tissues are epithelium and connective tissue, both of which are present in nearly all invertebrates.
The outer surface of the epidermis is normally formed of epithelial cells and secretes an extracellular matrix which provides support to the organism.
Other invertebrates may have no rigid structures but the epidermis may secrete a variety of surface coatings such as the pinacoderm of sponges, the gelatinous cuticle of cnidarians (polyps, sea anemones, jellyfish) and the collagenous cuticle of annelids.
The outer epithelial layer may include cells of several types including sensory cells, gland cells and stinging cells.
Marcello Malpighi, the father of microscopical anatomy, discovered that plants had tubules similar to those he saw in insects like the silk worm.
He observed that when a ring-like portion of bark was removed on a trunk a swelling occurred in the tissues above the ring, and he unmistakably interpreted this as growth stimulated by food coming down from the leaves, and being captured above the ring.
Arthropods comprise the largest phylum in the animal kingdom with over a million known invertebrate species.
There is considerable variation between species and many adaptations to the body parts, especially wings, legs, antennae and mouthparts.
Spiders have no wings and no antennae.
They have mouthparts called chelicerae which are often connected to venom glands as most spiders are venomous.
They have a second pair of appendages called pedipalps attached to the cephalothorax.
These have similar segmentation to the legs and function as taste and smell organs.
At the end of each male pedipalp is a spoon-shaped cymbium that acts to support the copulatory organ.
Other branches of anatomy
- Superficial or surface anatomy is important as the study of anatomical landmarks that can be readily seen from the exterior contours of the body. It enables physicians or veterinary surgeons to gauge the position and anatomy of the associated deeper structures. Superficial is a directional term that indicates that structures are located relatively close to the surface of the body.
- Comparative anatomy relates to the comparison of anatomical structures (both gross and microscopic) in different animals.
- Artistic anatomy relates to anatomic studies for artistic reasons.
Main article: History of anatomy
In 1600 BCE, the Edwin Smith Papyrus, an Ancient Egyptian medical text, described the heart, its vessels, liver, spleen, kidneys, hypothalamus, uterus and bladder, and showed the blood vessels diverging from the heart.
The Ebers Papyrus (c. 1550 BCE) features a "treatise on the heart", with vessels carrying all the body's fluids to or from every member of the body.
Ancient Greek anatomy and physiology underwent great changes and advances throughout the early medieval world.
Over time, this medical practice expanded by a continually developing understanding of the functions of organs and structures in the body.
Phenomenal anatomical observations of the human body were made, which have contributed towards the understanding of the brain, eye, liver, reproductive organs and the nervous system.
Alexandria not only housed the biggest library for medical records and books of the liberal arts in the world during the time of the Greeks, but was also home to many medical practitioners and philosophers.
Great patronage of the arts and sciences from the Ptolemy rulers helped raise Alexandria up, further rivalling the cultural and scientific achievements of other Greek states.
Some of the most striking advances in early anatomy and physiology took place in Hellenistic Alexandria.
These two physicians helped pioneer human dissection for medical research.
They also conducted vivisections on the cadavers of condemned criminals, which was considered taboo until the Renaissance—Herophilus was recognized as the first person to perform systematic dissections.
Herophilus became known for his anatomical works making impressing contributions to many branches of anatomy and many other aspects of medicine.
Some of the works included classifying the system of the pulse, the discovery that human arteries had thicker walls than veins, and that the atria were parts of the heart.
Herophilus's knowledge of the human body has provided vital input towards understanding the brain, eye, liver, reproductive organs and nervous system, and characterizing the course of disease.
Erasistratus accurately described the structure of the brain, including the cavities and membranes, and made a distinction between its cerebrum and cerebellum During his study in Alexandria, Erasistratus was particularly concerned with studies of the circulatory and nervous systems.
He was able to distinguish the sensory and the motor nerves in the human body and believed that air entered the lungs and heart, which was then carried throughout the body.
His distinction between the arteries and veins—the arteries carrying the air through the body, while the veins carried the blood from the heart was a great anatomical discovery.
Erasistratus was also responsible for naming and describing the function of the epiglottis and the valves of the heart, including the tricuspid.
During the third century, Greek physicians were able to differentiate nerves from blood vessels and tendons and to realize that the nerves convey neural impulses.
It was Herophilus who made the point that damage to motor nerves induced paralysis.
Herophilus named the meninges and ventricles in the brain, appreciated the division between cerebellum and cerebrum and recognized that the brain was the "seat of intellect" and not a "cooling chamber" as propounded by Aristotle Herophilus is also credited with describing the optic, oculomotor, motor division of the trigeminal, facial, vestibulocochlear and hypoglossal nerves.
Great feats were made during the third century in both the digestive and reproductive systems.
Herophilus was able to discover and describe not only the salivary glands, but the small intestine and liver.
He showed that the uterus is a hollow organ and described the ovaries and uterine tubes.
He recognized that spermatozoa were produced by the testes and was the first to identify the prostate gland.
The anatomy of the muscles and skeleton is described in the Hippocratic Corpus, an Ancient Greek medical work written by unknown authors.
He compiled existing knowledge and studied anatomy through dissection of animals.
He was one of the first experimental physiologists through his vivisection experiments on animals.
Galen's drawings, based mostly on dog anatomy, became effectively the only anatomical textbook for the next thousand years.
Medieval to early modern
Anatomy developed little from classical times until the sixteenth century; as the historian Marie Boas writes, "Progress in anatomy before the sixteenth century is as mysteriously slow as its development after 1500 is startlingly rapid".
Mondino's Anatomy of 1316 was the first textbook in the medieval rediscovery of human anatomy.
It describes the body in the order followed in Mondino's dissections, starting with the abdomen, then the thorax, then the head and limbs.
It was the standard anatomy textbook for the next century.
He made use of his anatomical knowledge in his artwork, making many sketches of skeletal structures, muscles and organs of humans and other vertebrates that he dissected.
In England, anatomy was the subject of the first public lectures given in any science; these were given by the Company of Barbers and Surgeons in the 16th century, joined in 1583 by the Lumleian lectures in surgery at the Royal College of Physicians.
Further information: History of anatomy in the 19th century
In the United States, medical schools began to be set up towards the end of the 18th century.
Classes in anatomy needed a continual stream of cadavers for dissection and these were difficult to obtain.
Philadelphia, Baltimore and New York were all renowned for body snatching activity as criminals raided graveyards at night, removing newly buried corpses from their coffins.
A similar problem existed in Britain where demand for bodies became so great that grave-raiding and even anatomy murder were practised to obtain cadavers.
Some graveyards were in consequence protected with watchtowers.
The practice was halted in Britain by the Anatomy Act of 1832, while in the United States, similar legislation was enacted after the physician William S. Forbes of Jefferson Medical College was found guilty in 1882 of "complicity with resurrectionists in the despoliation of graves in Lebanon Cemetery".
He was responsible for setting up the system of three years of "pre-clinical" academic teaching in the sciences underlying medicine, including especially anatomy.
This system lasted until the reform of medical training in 1993 and 2003.
From 1822 the Royal College of Surgeons regulated the teaching of anatomy in medical schools.
Medical museums provided examples in comparative anatomy, and were often used in teaching.
He noticed that the frequently fatal fever occurred more often in mothers examined by medical students than by midwives.
The students went from the dissecting room to the hospital ward and examined women in childbirth.
Semmelweis showed that when the trainees washed their hands in chlorinated lime before each clinical examination, the incidence of puerperal fever among the mothers could be reduced dramatically.
It was the advent of microscopy that opened up an understanding of the building blocks that constituted living tissues.
Technical advances in the development of achromatic lenses increased the resolving power of the microscope and around 1839, Matthias Jakob Schleiden and Theodor Schwann identified that cells were the fundamental unit of organization of all living things.
Study of small structures involved passing light through them and the microtome was invented to provide sufficiently thin slices of tissue to examine.
Staining techniques using artificial dyes were established to help distinguish between different types of tissue.
About the same time, in the 1950s, the use of X-ray diffraction for studying the crystal structures of proteins, nucleic acids and other biological molecules gave rise to a new field of molecular anatomy.
Equally important advances have occurred in non-invasive techniques for examining the interior structures of the body.
Magnetic resonance imaging, computed tomography, and ultrasound imaging have all enabled examination of internal structures in unprecedented detail to a degree far beyond the imagination of earlier generations.
Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Anatomy.