Anatomy

History

Human anatomy

Anatomical nomenclature

Resources

Anatomy, a subfield of biology, is the study of the structure of living things. There are three main areas of anatomy: cytology studies the structure of cells; histology examines the structure of tissues; and gross anatomy deals with organs and organ systems. Comparative anatomy, which strives to identify general structural patterns in families of plants and animals, provides the basis for the classification of species. Human anatomy is a crucial element of the modern medical curriculum.

History

Modern anatomy, as a branch of Western science, was founded by the Flemish scientist Andreas Vesalius (1514–1564), who in 1543 published De humani corporis fabrica (Structure of the human body). In addition to correcting numerous misconceptions, Vesalius’s book was the first description of human anatomy that organized the organs into systems. Although initially rejected by many followers of classical anatomical doctrines, Vesalius’s systematic conception of anatomy eventually became the foundation of anatomical research and education throughout the world; anatomists still use his systematic approach.

Human anatomy

Human anatomy divides the body into the following distinct functional systems: cutaneous, muscular, skeletal, circulatory, nervous, digestive, urinary, endocrine, respiratory, and reproductive. This division helps the student understand the organs, their relationships, and the relations of individual organs to the body as a whole.

The cutaneous system consists of the integument— the covering of the body, including the skin, hair, and nails. The skin is the largest organ in the body, and its most important function is to act as a barrier between the body and the outside world. The skin’s minute openings (pores) also provide an outlet for sweat, which regulates the body temperature. Melanin, a dark pigment found in the skin, provides protection from sunburn. The skin also contains oil-producing cells.

The muscles of the muscular system enable the body to move and provide power to the hands and fingers. There are two basic types of muscles. Voluntary (skeletal) muscles enable movements under conscious direction (e.g., to walk, move an arm, or smile). Involuntary (smooth) muscles are not consciously controlled and operate independent of conscious direction. For example, they play an important role in digestion. The third type of muscle, cardiac muscle, is involuntary, but also is striated, as are skeletal muscles. Because cardiac muscle is self-contractile it allows the heart to pump blood throughout the body, without pause, from early in embryogenesis to death.

The skeletal system, or the skeleton, is the general supportive structure of the body. In addition, the skeletal system is the site of many important and complex physiological and immunological processes. The skeletal frame provides the support that muscles need in order to function. Of the 206 bones in the human body, the largest is the femur, or thighbone. The smallest are the tiny ear ossicles, three in each ear, named the hammer (malleus), anvil (incus), and stirrup (stapes). Often included in the skeletal system are the ligaments, which connect bone to bone; the joints, which allow the connected bones to move; and the tendons, which connect muscle to bone.

The circulatory system comprises the heart, arteries, veins, capillaries, blood and blood-forming organs, and the lymphatic subsystem. The four chambers of the heart allow the heart to act as a dual pump to propel blood to the lungs for oxygenation (pulmonary system) and to pump blood throughout the body (systemic circulation). From the heart, the blood circulates through arteries. The blood is distributed through smaller and smaller tubes until it passes into the microscopic capillaries that bathe every cell. The veins collect deoxygenated blood from the capillaries and return it to the heart.

The nervous system consists of the brain, spinal cord, and sensory organs that provide information to them. For example, our eyes, ears, nose, tongue, and skin receive stimuli and send signals that travel both electrically and chemically to the brain. The brain is an intricate system of complicated neurons (nerve cells) that allow us to process sensory information, visceral signals (e.g. regulating breathing, body temperature, etc.), and perform cognitive thought.

The digestive system is essentially a long tube extending from the mouth to the anus. Food entering the mouth is conducted through the stomach, small intestine, and large intestine, where accessory organs contribute digestive juices to break down the food, extracting the molecules that can be used to nourish the body. The unusable parts of the ingested food are expelled through the anus as fecal matter. The salivary glands (in the mouth), the liver, and the pancreas are the primary digestive glands.

The urinary system consists of the kidneys, the bladder, and the connecting tubules. The kidneys filter water and waste products from the blood and pass them into the bladder. At intervals, the bladder is emptied through the urinary tract, ridding the body of waste.

The endocrine system consists of ductless (endocrine) glands that produce hormones that regulate various bodily functions. The pancreas secretes insulin to regulate sugar metabolism, for example. The pituitary gland in the brain is the principal or “master” gland that regulates many other glands and endocrine functions.

The respiratory system includes the lungs, the diaphragm, and the tubes that connect them to the outside atmosphere. Respiration is the process whereby an organism absorbs oxygen from the air and returns carbon dioxide. The diaphragm is the muscle that enables the lungs to work.

Finally, the reproductive system enables sperm and egg to unite and the egg to remain in the uterus or womb to develop into a functional human.

Anatomical nomenclature

Over the centuries, anatomists developed a standard nomenclature, or method of naming anatomical structures. Terms such as “up” or “down” obviously have no meaning unless the orientation of the body is clear. When a body is lying on its back, the thorax and abdomen are at the same level. The upright sense of up and down is lost. Further, because anatomical studies and particularly embryological studies were often carried out in animals, the development of the nomenclature relative to comparative anatomy had an enormous impact on the development of human anatomical nomenclature. There were obvious difficulties in relating terms from quadrupeds (animals that walk on four legs) who have abdominal and thoracic regions at the same level as opposed to human bipeds in whom an upward and downward orientation might seem more obvious.

In order to standardize nomenclature, anatomical terms relate to the standard anatomical position. When the human body is in the standard anatomical position it is upright, erect on two legs, facing frontward, with the arms at the sides each rotated so that the palms of the hands turn forward.

In the standard anatomical position, superior means toward the head or the cranial end of the body. Inferior means toward the feet or the caudal end of the body. The body’s frontal surface is the anterior or ventral surface. Accordingly, the terms “anteriorly” and “ventrally” specify a position closer to—or toward—the front surface of the body. The body’s back surface is the posterior or dorsal surface, and the terms “posteriorly” and “dor-sally” specify a position closer to—or toward—the posterior surface of the body.

The terms superficial and deep relate to the distance from the exterior surface of the body. Cavities such as the thoracic cavity have internal and external regions that correspond to deep and superficial relationships in the midsagittal (vertical midline) plane.

The bones of the skull are fused by sutures that form important anatomical landmarks. Sutures are joints that run jaggedly along the interface between the bones. At birth, the sutures are soft, broad, and cartilaginous. Near the end of puberty or early in adulthood the sutures eventually fuse and become rigid and ossified.

The sagittal suture, which unites the parietal bones of the skull along the body’s midline, is used as a landmark in anatomical nomenclature to establish sagittal planes. The primary sagittal plane runs through the length of the sagittal suture. Planes that are parallel to the sagittal plane, but that are offset from the midsagittal plane are termed parasagittal planes. Sagittal planes run anteriorly and posteriorly and are always at right angles to the coronal planes (perpendicular to the midsagittal plane, divides the body into dorsal and ventral sections). The medial plane or midsagittal plane divides the body vertically into superficially symmetrical right and left halves.

The medial plane also establishes a centerline axis for the body. The terms medial and lateral relate positions relative to the medial axis. If a structure is medial to another structure, the medial structure is closer to the medial or center axis. If a structure is lateral to another structure, the lateral structure is farther away from the medial axis. For example, the lungs are lateral to the heart.

The coronal suture unites the frontal bone with the parietal bones. In anatomical nomenclature, the primary coronal plane designates the plane that runs through the length of the coronal suture. The primary coronal plane is also termed the frontal plane because it divides the body into dorsal and ventral (front and back) halves.

Planes that divide the body into superior and inferior portions, and that are at right angles to both the sagittal and coronal planes, are termed transverse planes. Anatomical planes that are not parallel to sagittal, coronal, or transverse planes are termed oblique planes.

The body is also divided into several regional areas. The most superior area is the cephalic region, which includes the head. The thoracic region is commonly known as the chest region. Although the celiac region more specifically refers to the center of the abdominal region, celiac is sometimes used to designate a wider area of abdominal structures. At the inferior end of the abdominal region lies the pelvic region or pelvis. The posterior or dorsal side of the body has its own special regions, named for the underlying vertebrae. From superior to inferior along the midline of the dorsal surface lie the cervical, thoracic, lumbar and sacral regions. The buttocks are the most prominent feature of the gluteal region.

The term upper limbs or upper extremities refers to the arms and hands; lower limbs or lower extremities refers to the legs and feet.

The proximal end of an extremity is at the junction of the extremity (i.e., arm or leg) with the trunk of the body. The distal end of an extremity is the point on the extremity farthest away from the trunk (e.g., fingers and toes). Accordingly, if a structure is proximate to another structure it is closer to the trunk (e.g., the elbow is proximate to the wrist). If a structure is distal to another, it is farther from the trunk (e.g., the fingers are distal to the wrist).

Structures may also be described as being medial or lateral to the midline axis of each extremity. Within the upper limbs, the terms radial and ulnar may be used synonymouly with lateral and medial. In the lower extremities, the terms fibular and tibial may be used as synonyms for lateral and medial.

Rotations of the extremities may de described as medial rotations (toward the midline) or lateral rotations (away from the midline).

Many structural relationships are described by combined anatomical terms (e.g., the eyes are ante-rio-medial to the ears).

There are also terms of movement that are standardized by anatomical nomenclature. Starting from the anatomical position, abduction indicates the movement of an arm or leg away from the midline or mid-sagittal plane. Adduction indicates movement of an extremity toward the midline.

The opening of the hands into the anatomical position is termed supination of the hands. Rotation so the dorsal side of the hands face forward is termed pronation.

The term flexion means movement toward the flexor or anterior surface. In contrast, extension may be generally regarded as movement toward the extensor or posterior surface. Flexion occurs when the arm brings the hand from the anatomical position toward the shoulder (a curl) or when the arm is raised over the head from the anatomical position. Extension returns the upper arm or lowers it to the anatomical position. Because of the embryological rotation of the lower limbs that rotates the primitive dorsal side to the adult form ventral side, flexion occurs as the thigh is raised anteriorly and superiorly toward the anterior portion of the pelvis. Extension occurs when the thigh is returned to anatomical position. Specifically, due to the embryological rotation, flexion of the lower leg occurs as the foot is raised toward the back of the thigh, and extension of the lower leg occurs with the kicking motion that returns the lower leg to anatomical position.

The term palmar surface (palm side) is applied to the flexion side of the hand. The term plantar surface is applied to the bottom sole of the foot. From the anatomical position, extension occurs when the toes are curled back and the foot arches upward and flexion occurs as the foot is returned to anatomical position.

Rolling motions of the foot are described as inversion (rolling with the big toe initially lifting upward) and eversion (rolling with the big toe initially moving downward).

See also Anatomy, comparative; Forensic science; Human evolution; Physiology, comparative; Physiology; Surgery.

Resources

BOOKS

Gray, Henry. Gray’s Anatomy. Philadelphia: Running Press, 1999.

Marieb, Elaine Nicpon. Human Anatomy & Physiology. 5th Edition. San Francisco: Benjamin/Cummings, 2000.

Netter, Frank H., and Sharon Colacino. Atlas of Human Anatomy. Yardley, PA: Icon Learning Systems, 2003.

OTHER

“Anatomy” MedLinePlus. (accessed October 14, 2006) <http://www.nlm.nih.gov/medlineplus/anatomy.html>.

“Anatomy of the Human Body” Bartleby.com. (accessed October 14, 2006) <http://www.bartleby.com/107>.

“Human Anatomy Online” Intellimed. (accessed October 14, 2006) <http://www.innerbody.com/htm/body.html>.

K. Lee Lerner
Larry Blaser

ANATOMY

ANATOMY . There is no systematic account of the anatomy of the human body in the Bible, although abundant use is made there of anatomical facts, metaphors, and expressions. Biblical anatomy is factual, empirical in the good sense of the word, and based on correct observation. Talmudic anatomy is inestimably richer; it is not free from fanciful distortions, but it reaches further and supplants the Greek theory of the "humors" with a rational explanation of the normal and pathological structure of the body. The details are sometimes astonishing in their accuracy, as in the description of the small cartilage rings in the structure of the trachea, discovered by Western anatomists only in the 18^th century. At the same time, talmudic anatomy is deficient by omission, apparently because the subject was not studied systematically but only incidentally as far as it was necessary for the solving of halakhic problems. Side by side with fanciful notions, there are to be found in the Talmud the beginnings of a scientific method using postmortem examination and dissection of the bodies of animals. Like Greek anatomy, talmudic anatomy shows lack of precision in terminology, which is sometimes expressed through analogy and figures of speech. Graphic illustration is also lacking, since drawing was introduced in the study of anatomy only during the period approaching the Renaissance.

As in all ancient anatomical works, numerous terms are cited in the Bible for the bones: the lower part of the spinal column is called aẓeh (Lev. 3:9); the upper part of the pelvis kesalim; the loins are given a plural (ibid. 3:4), in accordance with their dual structure; the upper (cervical) part of the spinal column is described as mafreket (i Sam. 4:18) with its anatomical location, explaining the sudden death resulting from its fracture. Joints mentioned are the berekh ("knee"); karsol ("ankle," "malleolus"; Ps. 18:37; ii Sam. 22:37); the term kaf ha-yarekh ("the hollow of the thigh") and its topographical connection with the gid ha-nasheh ("sinew of the thigh"; Gen. 32:33) have not been sufficiently defined. The term thigh entered Vesalius' Tabulae Anatomicae (Table 5), where it is labeled as the yarekh, femur, and also paḥad ha-yarekh (Table 6, according to Job 40:17). Even in Vesalius' time it was felt that the biblical word yarekh was used in various meanings and was not altogether clear.

The Bible makes frequent mention of internal organs of the body such as the pharynx (lo'a), the gullet (garon), the heart (lev), the liver (kaved) with the gallbladder (marah), the womb (reḥem), the stomach (kevah), the entrails (me'ayim), and the kidneys (kelayot). The yoteret ha-kaved or ha-yoteret al ha-kaved (in connection with the liver) is difficult to identify (Lev. 3:4), although the reference is probably to the mesentery, called by Tobias *Cohn the Physician "the covering membrane." The gidim ("sinews") in the Bible, as in Greek anatomy, denote both nerves and ligaments and sometimes even vessels. The gid ha-nasheh ("nerve of the thigh") is usually identified with the ischiadic nerve. The muscles are recognized as the parts furnishing power and movement: "his strength is in the muscles of his belly" (Job 40:16).

Talmudic scholars were much occupied with the regulations concerning ritually unclean meat, with physical disfigurement that disqualified a man for the priesthood, and with rules concerning the menstruous woman, defilement, and the like. This accounts for the anatomical knowledge so widespread among talmudists. The dissection of animal carcasses to ascertain their ritual fitness revealed important facts and prevented the development of fantastic notions. The Talmud even assumes the possibility of the investigation of the human body for forensic purposes (Ḥul. 11a). In Bekhorot 45a, Samuel relates that "the disciples of R. Ishmael boiled the corpse of a prostitute who had been condemned by the king to be burned; upon examination, they found that she had 252 [bones]." This investigation was carried out in order to ascertain the number of bones in the human body, since the remains of corpses defile an abode only if they constitute more than half the skeleton, i.e., most of the bones. The sages carried out the examinations themselves or relied on the testimony of a qualified physician (cf. Tosef. Oho. 4:2; Naz. 52a, "Todos the physician entered and all the physicians with him").

The Skeleton

The enumeration of 248 (רמ״ח) members (bones) in the human body is famous in rabbinic tradition (Oho. 1:8). This number does not correspond to the number of bones in the body of an adult, which amounts only to 200. From the number counted by Ishmael's pupils it may be inferred that the body they examined was that of a girl of 17. Supporting this explanation is the figure "six [members] of the key of the heart," i.e., the breastbone (sternum), of which there is only a single unit in an adult but which contains six points of ossification. The term "key of the heart" is to be explained by the inclusion of the two superior ribs in the morphological description of the breastbone: these two superior ribs are shorter and rounder, and their junction with the breastbone actually resembles a key. Accordingly, the rabbis of the Mishnah enumerate only 11 ribs instead of 12, the upper being already included in the "key of the heart." The figure 248 for the number of bones in the body also occurs in the writings of Abu-l-Qasim, the famous surgeon of the tenth century. It would seem that in this detail the Arabs were influenced by the Talmud rather than by the Greeks, since Hippocrates cites figures which are widely inaccurate (101, including the nails), while Galen gives no figure at all. The nomenclature of the bones in the Talmud is precise in its anatomical differentiation. The Mishnah distinguishes bet ween the foot (pissat ha-regel), the leg (shok), and the thigh or thighbone (yarekh, kulit). Corresponding to these are three joints by which the bones are joined to each other: the ankle (karsol), the knee joint (arkuvah), and the hip joint (katlit). Besides these precise anatomical details, mention is also made of the legendary bone known as the luz (the medieval os resurrectionis) said to be situated at the bottom of the spinal column. According to the legend, it could not be dissolved in water or burned by fire, "and from it man will blossom forth at the resurrection" (Eccles. R. 12:5, no. 1; Gen. R. 28:3).

The Digestive Organs

A remarkable passage is that which compares the salivary glands to springs of water and refers to them as "the conduit (ammat ha-mayim) that passes beneath the tongue" (Lev. R. 16:4). This is most interesting in view of the fact that the ducts of the salivary glands were not described with precision in scientific literature until the 16^th and 17^th centuries. The tongue (lashon) is described as enclosed by two walls – the jawbone (leset) and the flesh of the cheek (leḥi; Ar. 15b). The topography of the windpipe (kaneh) and the esophagus (veshet) is described correctly ("lest the food enter the windpipe before it reaches the esophagus" – Ta'an. 5b; Pes. 108a). In the esophagus two membranes were accurately distinguished: the outer or red muscular membrane, and the inner or white mucous one (Ḥul. 43a). Many structural details of the maw of the ruminants were also known to talmudists (Ḥul. 3:1). The digestive tract of the human being is described in a pseudo-scientific manner: "Ten organs minister to the body in the following phases of food absorption: from the mouth to the esophagus; from there to the first stomach where the food is ground; from there to the lower digestive tract of the maw; from there to the stomach; from there to the small intestine; from there to the colon ascendens; from there to the colon transversum; from there to the colon descendens; from there to the anus, and thence outward." This defective account, which is to be found in several midrashic versions (Lev R. 3:4; Eccles. R. 7:19, no. 3; et al.), is patently influenced by findings in animals. The liver was regarded as one of the ruling parts of the human body (Zohar, iv, 153a), the other two being the brain and the heart. The tarpesh above the liver, according to Maimonides, designates the diaphragm. The ḥaẓẓar ha-kaved ("courtyard of the liver"; Yoma 8:6) according to Preuss, is the part known as the lobus caudatus [?]. The eẓba ha-kaved ("finger of the liver"; Tam. 4:3) is identified by J.L. Katzenelsohn as the pancreas, although that structure was unknown in ancient anatomy as a special organ. The spleen is described in its various parts (Ḥul. 93a), its convex side being called dad ha-teḥol ("nipple of the spleen"). The membrane and the blood vessels of the hilus lienalis are also mentioned. The removal of the spleen by surgery is referred to in the Talmud (Sanh. 21b).

The Respiratory Organs

The upper part of the windpipe is called the gargeret (Ḥul. 3:1); the windpipe is composed of rings (ḥulyot), and sub-rings are also referred to, i.e., the ligaments joining the cartilage rings. There are descriptions of the ring cartilage called "the large ring," of the thyroid cartilage, called the kova ("helmet") together with its protruding part, ḥud ha-kova ("the point of the helmet"), and of its lower parts, shippu'ei kova ("the slopes of the helmet"). Identification was also made of the two small cartilages called ḥitin ("protuberances") at the end of the large ring. (These cartilages were not discovered in the West before Santorini in the 18^th century.) The talmudists also correctly recognized the existence of three lobes in the right lung and two in the left. (Hippocrates enumerated three on each side.) They also described the serous membranes of the lung and of the bronchial tubes.

The Heart

The Talmud contains few details on the anatomy of the heart, since a wound in the heart generally caused the death of the animal before slaughtering. The position of the heart is given as on the left side of the body (Men. 36b), in contrast to Galen's statement that it was in the exact center of the chest. The heart is divided into chambers (Ḥul. 45b), but there is no trace of Aristotle's erroneous view, supported by Avicenna, of the existence of three chambers in the heart. The aorta is mentioned under the name of keneh ha-lev ("pipe of the heart") in Ḥullin 45b, and Maimonides adds mizrak gadol ("the aorta is the great fountain"). The two auricles are mentioned in Tikkunei Zohar (69): "There are two houses (battim) and two ears (udenin) in the heart."

The Genital Organs

in the male

The special terms for the membrum virile are eiver (bm 84a), eẓba (Pes. 112b), gid, ammah (Shab. 108b), shammash (Nid. 60b), etc. The term atarah ("crown") designating the part projecting behind the glans of the penis passed to Western anatomy as corona glandis. The (erroneous) view that "there are two ducts in the male, one to emit urine and the other semen, separated by a thin tissue" (Bek. 44b) was widely held in the Middle Ages, also among the Arabs, and was corrected only in the 16^th century by Vesalius. The rabbis described the two membranes of the testicles (Ḥul. 45a) and the vas deferens (ḥutei beiẓah; Yev. 75b) and knew of the connection between erection of the penis (kishui) and the spinal cord, where disease prevents cohabitation.

in the female

Because of their attention to regulations concerning the menstruous woman, the talmudic scholars treated the female genitalia much more extensively. The language they used (for reasons of propriety) to designate them frequently causes great difficulty in understanding the anatomical details referred to. The Mishnah (Nid. 2:5) lists the chamber (ḥeder), antechamber (perozedor), upper chamber (aliyyah), and fallopian tube (adnexa). "The blood of the chamber defiles (the blood of the upper does not); that found in the antechamber defiles on account of uncertainty, since it is strongly probable that it comes from the source (uterus)." The Gemara (Nid. 17b) explains: "The chamber is within and the antechamber without, and the upper chamber is built over both and there is an open passage (lul) between the upper chamber and the antechamber; consequently, from the lul inward the blood in case of doubt (sefeko) is defiling; from the lul outward, it is in a state of purity." Ever since modern medical historiography came into existence, scholars have struggled to explain these halakhot. Abraham Hartog Israels identifies the "upper chamber" with the fallopian tube; Rosenbaum (see bibl.) identifies it with the adnexa uteri and the broad ligaments. Leibowitz' identification is that the "chamber" is the womb; the "antechamber" is the part nearest the cervix. But Preuss holds that the "antechamber" is the exterior portion of the female genitalia (vulva); the "upper chamber" is the vagina, which in present day Hebrew is called nartik. This conjecture is irreconcilable with the talmudic passage as a whole, since the vulva everywhere in the Talmud is called bet ha-toref, bet ha-setarim, bet ha-ḥiẓon (exterior chamber; hidden chamber; outer chamber), which also includes the labia. Katzenelson would identify the parts of the "antechamber" with the septum vesico-vaginale and the septum recto-vaginale. Nor is it at all clear what is meant by the term lul; it is perhaps to be identified with the cavity in the upper vagina: "from the lul inward" denotes the upper parts near the cervix; "from the lul outward," the lower parts of the vagina. In the anatomy of the female genitalia there is a place called in the Jerusalem Talmud bein ha-shinnayim ("between the teeth") or bet ha-shinnayim ("abode of the teeth"), which Rosenbaum identifies as the collum; Rashi says "within the womb are fleshy protuberances like teeth."

Other Organs

The Talmud does not deal much with the normal anatomy of the kidneys, but gives numerous accounts of kidney diseases. It contains descriptions of the membranes of the kidney, and refers to hilus renalis as ḥariẓ (Ḥul. 55b). It describes the outer and inner membranes (meninges) of the brain and recognizes the existence of motor centers in the spinal column. The Talmud records examinations of the spinal cord and of injuries to its membranes and marrow (Ḥul. 45b); it describes various kinds of morbid changes in the tissue and important details in its pathology such as softening (hamrakhah), dissolution (hamsasah), and softening (hitmazmezut) of the marrow; and mentions the fontanel: "the place where an infant's brain is soft" (rofes; Men. 37a). It recognized two hemispheres of the cerebellum over the large aperture at the base of the cranium "like two beans (polim) lying at the aperture of the cranium" (Hul. 45a–b). These are also described by R. Jeremiah in the case of a fowl: "He examined a fowl and found objects resembling two beans placed at the aperture of the cranium" – a fine example of comparative anatomy.

Middle Ages

In the Middle Ages and the Renaissance period, the Jewish physicians shared the anatomical opinions of their neighbors. Vesalius was, however, assisted in his work of the compilation of his Anatomical Tables in the 16^th century by the Jew Lazarus (Lazaro) de *Frigeis. The reluctance of Jews to submit bodies for dissection led to complications and ill-feeling in the universities (e.g., at *Padua in the 17^th–18^th centuries; Eastern Europe in the 20^th). The most outstanding Jewish physician of the Renaissance was *Amatus Lusitanus, who in the 16^th century participated in the teaching of anatomy at the university at Ferrara. He first described the valves of the veins, exemplified on the azygos vein. Lusitanus identified these valves through opening 12 bodies, although he did not show their connection with the circulation of the blood.

Modern

Outstanding in the modern study of anatomy was Friedrich Gustav Jacob *Henle (1809–1885) who did important research on the skin, the intestinal tract, and the kidneys. Another important figure was Benedict *Stilling (1810–1879) who did pioneer research on the spinal cord.

bibliography:

M. Perlmann, Midrash Refu'ah (1926); J.L. Katzenelson, Ha-Talmud ve-Ḥokhmat ha-Refu'ah (1928); A.H. Israels, Dissertatio historico-medica exhibens collectanea ex Talmude Babylonico (1845); R.J. Wunderbar, Biblisch-talmudische Medicin, 2 vols. (1850–60); J.L. Katznelson, Die normale und pathologische Anatomie des Talmuds (1896); E. Rosenbaum, L'anatomie et la physiologie des organes génitaux de la femme (1901); J. Preuss, Biblisch-talmudische Medizin (1911).

[Joshua O. Leibowitz]

Anatomy

Anatomy, a subfield of biology , is the study of the structure of living things. There are three main areas of anatomy: cytology studies the structure of cell ; histology examines the structure of tissues; and gross anatomy deals with organs and organ groupings called systems. Comparative anatomy , which strives to identify general structural patterns in families of plants and animals, provided the basis for the classification of species . Human anatomy is a crucial element of the modern medical curriculum.

History

Modern anatomy, as a branch of Western science, was founded by the Flemish scientist Andreas Vesalius (1514–1564), who in 1543 published De humani corporis fabrica (Structure of the human body). In addition to correcting numerous misconceptions about the human body, Vesalius's book was the first description of human anatomy that organized the organs into systems. Although initially rejected by many followers of classical anatomical doctrines, Vesalius's systematic conception of anatomy soon became the foundation of anatomical research and education throughout the world; anatomists still use his systematic approach.

Human anatomy

Human anatomy divides the body into the following distinct functional systems: cutaneous, muscular, skeletal, circulatory, nervous, digestive, urinary, endocrine, respiratory, and reproductive. This division helps the student understand the organs, their relationships, and the relations of individual organs to the body as a whole.

The cutaneous system consists of the integument—the covering of the body, including the skin, hair, and nails. The skin is the largest organ in the body, and its most important function is to act as a barrier between the body and the outside world. The skin's minute openings (pores) also provide an outlet for sweat, which regulates the body temperature . Melanin, a dark pigment found in the skin, provides protection from sunburn. The skin also contains oil-producing cells.

The muscles of the muscular system enable the body to move and provide power to the hands and fingers. There are two basic types of muscles. Voluntary (skeletal) muscles enable movements under conscious direction (e.g., to walk, move an arm, or smile). Involuntary (smooth) muscles are not consciously controlled, and operate independent of conscious direction. For example, they play an important role in digestion. The third type of muscle, cardiac muscle is involuntary, but also is striated, as in skeletal muscles. Because cardiac muscle is self-contractile it allows the heart to pumps blood throughout the body, without pause, from early in embryogenesis to death.

The skeletal system , or the skeleton, is the general supportive structure of the body. In addition, the skeletal system is the site of many important and complex physiological and immunological processes. The skeletal frame provides the support that muscles need in order to function. Of the 206 bones in the human body, the largest is the femur, or thigh bone. The smallest are the tiny ear ossicles, three in each ear, named the hammer (malleus), anvil (incus), and stirrup (stapes). Often included in the skeletal system are the ligaments, which connect bone to bone; the joints, which allow the connected bones to move; and the tendons, which connect muscle to bone.

The circulatory system comprises the heart, arteries , veins , capillaries , blood and blood-forming organs, and the lymphatic sub-system. The four chambers of the heart allow the heart to act as a dual pump to propel blood to the lungs for oxygenation (pulmonary system) and to pump blood throughout the body (systemic circulation). From the heart, the blood circulates through arteries. The blood is distributed through smaller and smaller tubes until it passes into the microscopic capillaries which bathe every cell. The veins collect the "used" blood from the capillaries and return it to the heart.

The nervous system consists of the brain , the spinal cord, and the sensory organs that provide information to them. For example, our eyes, ears, nose, tongue, and skin receive stimuli and send signals that travel both electrically and chemically to the brain. The brain is an intricate system of complicated neurons (nerve cells) that allow us to process sensory information, visceral signals (e.g. regulating breathing, body temperature, etc.), and perform cognitive thought.

The digestive system is essentially a long tube extending from the mouth to the anus. Food entering the mouth is conducted through the stomach, small intestine, and large intestine, where accessory organs contribute digestive juices to break down the food, extracting the molecules that can be used to nourish the body. The unusable parts of the ingested food are expelled through the anus as fecal matter . The salivary glands (in the mouth), the liver, and the pancreas are the primary digestive glands.

The urinary system consists of the kidneys, the bladder, and the connecting tubules. The kidneys filter water and waste products from the blood and pass them into the bladder. At intervals, the bladder is emptied through the urinary tract, ridding the body of unneeded waste.

The endocrine system consists of ductless (endocrine) glands that produce hormones that regulate various bodily functions. The pancreas secretes insulin to regulate sugar metabolism , for example. The pituitary gland in the brain is the principal or "master" gland that regulates many other glands and endocrine functions.

The respiratory system includes the lungs, the diaphragm, and the tubes that connect them to the outside atmosphere. Respiration is the process whereby an organism absorbs oxygen from the air and returns carbon dioxide . The diaphragm is the muscle that enables the lungs to work.

Finally, the reproductive system enables sperm and egg to unite and the egg to remain in the uterus or womb to develop into a functional human.

Anatomical nomenclature

Over the centuries, anatomists developed a standard nomenclature, or method of naming anatomical structures. Terms such as "up" or "down" obviously have no meaning unless the orientation of the body is clear. When a body is lying on it's back, the thorax and abdomen are at the same level. The upright sense of up and down is lost. Further, because anatomical studies and particularly embryological studies were often carried out in animals, the development of the nomenclature relative to comparative anatomy had an enormous impact on the development of human anatomical nomenclature. There were obvious difficulties in relating terms from quadrupeds (animals that walk on four legs) who have abdominal and thoracic regions at the same level as opposed to human bipeds in whom an upward and downward orientation might seem more obvious.

In order to standardize nomenclature, anatomical terms relate to the standard anatomical position. When the human body is in the standard anatomical position it is upright, erect on two legs, facing frontward, with the arms at the sides each rotated so that the palms of the hands turn forward.

In the standard anatomical position, superior means toward the head or the cranial end of the body.

The term inferior means toward the feet or the caudal end of the body.

The frontal surface of the body is the anterior or ventral surface of the body. Accordingly, the terms "anteriorly" and "ventrally" specify a position closer to—or toward—the frontal surface of the body. The back surface of the body is the posterior or dorsal surface and the terms "posteriorly" and "dorsally" specify a position closer to—or toward—the posterior surface of the body.

The terms superficial and deep relate to the distance from the exterior surface of the body. Cavities such as the thoracic cavity have internal and external regions that correspond to deep and superficial relationships in the midsagittal plane .

The bones of the skull are fused by sutures that form important anatomical landmarks. Sutures are joints that run jaggedly along the interface between the bones. At birth , the sutures are soft, broad, and cartilaginous. The sutures eventually fuse and become rigid and ossified near the end of puberty or early in adulthood.

The sagittal suture unties the parietal bones of the skull along the midline of the body. The suture is used as an anatomical landmark in anatomical nomenclature to establish what are termed sagittal planes of the body. The primary sagittal plane is the sagittal plane that runs through the length of the sagittal suture. Planes that areparallel to the sagittal plane, but that are offset from the midsagittal plane are termed parasagittal planes. Sagittal planes run anteriorly and posteriorly, are always at right angles to the coronal planes. The medial plane or midsagittal plane divides the body vertically into superficially symmetrical right and left halves.

The medial plane also establishes a centerline axis for the body. The terms medial and lateral relate positions relative to the medial axis. If a structure is medial to another structure, the medial structure is closer to the medial or center axis. If a structure is lateral to another structure, the lateral structure is farther way from the medial axis. For example, the lungs are lateral to the heart.

The coronal suture unites the frontal bone with the parietal bones. In anatomical nomenclature, the primary coronal plane designates the plane that runs through the length of the coronal suture. The primary coronal plane is also termed the frontal plane because it divides the body into frontal and back halves.

Planes that divide the body into superior and inferior portions, and that are at right angles to both the sagittal and coronal planes are termed transverse planes. Anatomical planes that are not parallel to sagittal, coronal, or transverse planes are termed oblique planes.

The body is also divided into several regional areas. The most superior area is the cephalic region that includes the head. The thoracic region is commonly known as the chest region. Although the celiac region more specifically refers to the center of the abdominal region, celiac is sometimes used to designate a wider area of abdominal structures. At the inferior end of the abdominal region lies the pelvic region or pelvis. The posterior or dorsal side of the body has its own special regions, named for the underlying vertebrae. From superior to inferior along the midline of the dorsal surface lie the cervical, thoracic, lumbar and sacral regions. The buttocks is the most prominent feature of the gluteal region.

The term upper limbs or upper extremities refers to the arms. The term lower limbs or lower extremities refers to the legs.

The proximal end of an extremity is at the junction of the extremity (i.e., arm or leg) with the trunk of the body. The distal end of an extremity is the point on the extremity farthest away from the trunk (e.g., fingers and toes). Accordingly, if a structure is proximate to another structure it is closer to the trunk (e.g., the elbow is proximate to the wrist). If a structure is distal to another, it is farther from the trunk (e.g., the fingers are distal to the wrist).

Structures may also be described as being medial or lateral to the midline axis of each extremity. Within the upper limbs, the terms radial and ulnar may be used synonymous with lateral and medial. In the lower extremities, the terms fibular and tibial may be used as synonyms for lateral and medial.

Rotations of the extremities may de described as medial rotations (toward the midline) or lateral rotations (away from the midline).

Many structural relationships are described by combined anatomical terms (e.g. the eyes are anterio-medial to the ears).

There are also terms of movement that are standardized by anatomical nomenclature. Starting from the anatomical position, abduction indicates the movement of an arm or leg away from the midline or midsagittal plane. Adduction indicates movement of an extremity toward the midline.

The opening of the hands into the anatomical position is supination of the hands. Rotation so the dorsal side of the hands face forward is termed pronation.

The term flexion means movement toward the flexor or anterior surface. In contrast, extension may be generally regarded as movement toward the extensor or posterior surface. Flexion occurs when the arm brings the hand from the anatomical position toward the shoulder (a curl) or when the arm is raised over the head from the anatomical position. Extension returns the upper arm and or lower to the anatomical position. Because of the embryological rotation of the lower limbs that rotates the primitive dorsal side to the adult form ventral side, flexion occurs as the thigh is raised anteriorly and superiorly toward the anterior portion of the pelvis. Extension occurs when the thigh is returned to anatomical position. Specifically, due to the embryological rotation, flexion of the lower leg occurs as the foot is raised toward the back of the thigh and extension of the lower leg occurs with the kicking motion that returns the lower leg to anatomical position.

The term palmar surface (palm side) is applied to the flexion side of the hand. The term plantar surface is applied to the bottom sole of the foot. From the anatomical position, extension occurs when the toes are curled back and the foot arches upward and flexion occurs as the foot is returned to anatomical position.

Rolling motions of the foot are described as inversion (rolling with the big toe initially lifting upward) and eversion (rolling with the big toe initially moving downward).

See also Anatomy, comparative; Forensic science; Human evolution; Physiology, comparative; Physiology; Surgery.

Resources

books

gray, henry. gray's anatomy. philadelphia: running press,1999.

Marieb, Elaine Nicpon. Human Anatomy & Physiology. 5th Edition. San Francisco: Benjamin/Cummings, 2000.

Netter, Frank H., and Sharon Colacino. Atlas of Human Anatomy. Yardley, PA: Icon Learning Systems, 2003.

K. Lee Lerner Larry Blaser

KEY TERMS

Dissection

—To cut apart or separate to reveal structures of the organism being studied.

anatomy The word ‘anatomy’ derives from the Greek ana (up) and tome (a cutting) — hence ‘dissection’ — and it can be defined as the science of the structure of a body learned by dissection. The word can thus be applied to any structure, and we can talk about the anatomy of a plant, an insect, or even a machine, but here the term will be restricted to the structure of the human being.

Since earliest times, man may have been curious about the inner structure and workings of his body. Certainly the ancient Egyptians, in performing mummification, which involved preliminary removal of the viscera, would have gained considerable information about the organs of the chest and abdomen. However, the practitioners of this art were not medical, and there is little evidence that the doctors of those times derived any knowledge from this potentially rich source of anatomical material. The first recorded school of anatomy, where dissection of the human body was performed, was in Alexandria, and it flourished between the first century bc and the second century ad. Here two Greeks, Herophilus and Erasistratus, were celebrated for their experience of anatomy acquired by the dissection of condemned criminals, and they described many structures of the human body. Herophilus recognized the brain as the central organ of the nervous system and the seat of intelligence, thus reversing the view of Aristotle, the Greek philosopher, of the primacy of the heart. Erasistratus observed the convolutions of the brain, noted that they were more marked in man than in lower animals, and associated this complexity with the higher intelligence of man. He also described the main parts of the brain, its coverings, and its cavities, the ventricles.

The most celebrated anatomist of the ancient world was undoubtedly Galen (129–216 ad). Born in Pergamon in Asia Minor, he studied in Smyrna and Alexandria before settling in Rome. He studied the human skeleton in Alexandria, but by then human dissection had virtually ceased, and much of his anatomy was based on animal studies.

Although Galen made many contributions to the subject, his work on bones and muscles being particularly good, and although many of the anatomical terms still in use today have their roots in his work, he also made errors and misinterpretations in his findings. In spite of this, his writings were regarded as definitive and beyond criticism over the next 1300 years. As a simple example, he described the kidneys as being lobulated, as they are in cattle, when the most casual glance would have shown that they are smooth in man. His statement that blood passed through pores between the left and right side of the heart again could have been refuted by simple observation. To make matters worse, continued copying of his writings and translations from one language to another led to further mistakes and faults creeping into his texts.

During the Middle Ages, human dissection was frowned upon by the Church. In the late fifteenth and early sixteenth centuries, a revival of learning and, with it, of anatomical observation took place, especially in Italy and more particularly in the University of Padua. It was there that a revolution in anatomy took place with the publication, in 1543, by Andreas Vesalius, then aged only 28, of his book De Fabrica Corporis Humani (The Structure of the Human Body). This was based on his personal observations of his own human dissections, and of studies of the human skeleton. It contained magnificent illustrations, taken directly from his dissections, which could be used today in any modern textbook of anatomy.

Over the next centuries dissection of the human body became a standard part of the training of medical students. Indeed, it provided more or less the only scientific subject in the curriculum. However, because of religious and social attitudes surrounding the acquisition of bodies, and because of the unpleasant nature of dissection on unpreserved and often decomposing material, both anatomy and practitioners followed a somewhat chequered course. Anatomies were usually made in winter months, when the process of putrefaction was delayed, and the timing in England was also made to correspond with the assizes, when the bodies of executed criminals would be available. The legitimate sources of bodies — executed criminals and unclaimed corpses of paupers — were often inadequate for the increasing numbers of medical schools and of medical students. In Britain in particular, there was the scandal of the grave robbers (or ‘resurrectionists’ as they were called), who would dig up a body shortly after burial and sell it to an anatomy school. Relatives would sit up, armed, at night to protect the grave, or secure the graves with iron cages known as ‘mort-safes’. Sometimes, indeed, because of the chronic shortage of bodies, criminals would resort to murder to obtain their material, as in the infamous case of Burke and Hare in Edinburgh, who committed no less than 16 murders. Hare turned King's evidence, but Burke was hanged and afterwards publicly dissected. The scandal of this case undoubtedly led to the Anatomy Act of 1832, which licensed premises for dissection and made legal the provision of bodies from workhouses or elsewhere which were unclaimed. The anatomy school was responsible for the subsequent burial or cremation of the body according to the religion of the deceased. These regulations have gradually been replaced by the bequests of individuals of their bodies for anatomical purposes after death so that today, in the UK, virtually all bodies are received at anatomy departments by these means.

The techniques of anatomical studies were improved by the injection of coloured materials into blood vessels and lymphatics, and by methods of embalming and preserving the body. Formalin, discovered in 1868 by Von Hoffman, rapidly replaced other preservative agents, and remains the basis of modern preservation methods.

The development of simple microscopes in the seventeenth century founded the important science of microscopic anatomy. A pioneer in this field was Malpighi, whose extensive studies demonstrated the blood capillaries, thus finally establishing the anatomical basis of the circulation of the blood. He also described red blood corpuscles, and the structure of the skin and of many other tissues. The modern achromatic compound microscope was invented in 1878, and it was this instrument that added the extra dimension of the microscopic study of tissues to anatomical teaching.

With the advent of anaesthesia in 1846, and the introduction of antiseptic surgery as a result of the work of Lister in 1867, the vistas of surgery were greatly increased and, with them, the importance of a detailed knowledge of anatomy to the surgeon. To most students, however, anatomical teaching was something of a sterile test of memory, with emphasis on exact topographical details of the finer ramifications of nerves and blood vessels. In the twentieth century, particularly in its second half, the subject of anatomy became much wider and of a more practical nature. It is true to say that there is little interest today in ‘pure’ topographical anatomy. The detailed mapping of the human body is now fully documented and is to be found in the major textbooks. Indeed, the name of Gray's Anatomy, the standard text, has passed into popular parlance. However, in its various sub-divisions, the subject is thriving and the most important of these need some separate descriptions.

Topographic anatomy

In this, the body is studied by regions rather than by organs. This is of importance to the surgeon who exposes different planes after the skin incision and who, of course, must be perfectly familiar with structures as he explores the limbs and body cavities. Once the sole preserve of the surgeon, this field has acquired immense significance today for the radiologist (see below). In this respect cross-sectional topographic anatomy has come into its own.

Endoscopic anatomy

With the development of fibreoptic instruments, the body's tubes and cavities are now being explored in life. The detailed anatomy, for example, of the bronchial tree as seen through the bronchoscope is now of great importance. The introduction of laparoscopic and thoracoscopic instruments to explore and operate in the abdomen and thorax respectively has also opened new vistas as surgeons require to learn their anatomical landmarks through these approaches.

Surface (living) anatomy

From the practical point of view, every medical practitioner needs to know the detailed structure of the tissues beneath the skin of his patient. This forms an important part of the teaching of medical students, who can practise on themselves the identification of bones, landmarks, muscles, and arterial pulses; the palpation of normal structures through the intact skin; and the range of movement of the joints.

Radiological and imaging anatomy

The discovery by Röntgen of X-rays a century ago opened new vistas of anatomical study. This was enhanced by the development of radiological techniques to outline viscera, for example by injecting radio-opaque solutions into blood vessels (angiography) or by swallowing barium paste in order to demonstrate the oesophagus and stomach. More recently, other imaging techniques, which include ultrasonography, computerized tomography, and, in particular, magnetic resonance imaging, have provided unrivalled information of three-dimensional anatomy in the living body. Indeed, today, the radiologist must possess a detailed knowledge of anatomy that certainly rivals that of his surgical colleagues.

Embryological anatomy

The complex changes in the growing fetus are studied because much of adult anatomy can only be understood by appreciating its prenatal development. More and more has been learned about the underlying causes of the numerous congenital abnormalities that may arise as aberrations of normal development.

Microscopic anatomy

is of fundamental importance in the understanding of pathological changes, and has advanced with the introduction of electron microscopy, which enables the finest details of the cells to be studied at an ultramicroscopic magnification of several thousands.

Kinesiology,

the study of joint and limb movement, has developed into a subject of immense importance, together with biomechanics and orthotics (the study and use of artificial limbs). Here, research has an immediate application in orthopaedic practice, for the study of joint prostheses, the measurement of forces acting on the skeleton, and choosing the strength of materials utilized in reconstructive surgery; also for the analysis of the causes of failures of artificial joint implants, or of the materials used in internal fixation of fractures.

Neuroanatomy,

the study of the brain, spinal cord, and nerves, forms an important part of the battery of approaches needed for neurobiological exploration, which today is complemented by physiology, pharmacology, molecular biology, and dynamic whole brain imaging.

All these topics are of obvious importance in the various expanding fields of medicine, but anatomy also impinges on other sciences. Examples are comparative anatomy — the comparison of structures in different animals and species; palaeoanatomy — the study of ancient remains — mainly, of course, of bones; and physical anthropology — the study of the different human races.

A recent development has been the appearance of a complete, sectioned human body appearing on the World Wide Web. The Visible Human Project presents transverse CT, MRI and cryosection images of two complete human cadavers, one male and one female, at an average of 1 mm intervals. These allow three-dimensional constructions to be ‘visualized’ from any angle on the computer screen.

Anatomy is thus a subject which encompasses a great variety of endeavours characterized by the study of the organization of the human body, and which impinges on many other sciences. In teaching anatomy to medical students, dissection of the cadaver remains fundamental, but the student also studies living, imaging, microscopic, and embryological anatomy. Anatomy forms an essential part of the scientific basis of medicine. All those concerned with disorders of the human body must start from a background of knowledge of its normal macroscopic and microscopic structure.

Harold Ellis

Anatomy

Anatomy is a branch of biology that deals with the structure of plants and animals. Comparative anatomy is a related field in which the structures of different animals are studied and compared. There are three main areas of anatomy: gross anatomy deals with organs and organ groupings called systems that are visible to the naked eye; cytology is the study of cell structure; and histology examines the structure of tissues. Microscopes are used in both cytology and histology to study cell and tissue structures.

History of anatomy

Attempts to understand the structure of living things go as far back as Aristotle (384–322 b.c.), the famous Greek philosopher and biologist. His dissection (cutting into pieces to examine the parts) and study of animals and plants led to his formation of a classification system that was used by scientists for almost 2,000 years.

Some of the first human dissections were carried out by Greek anatomists and physicians Herophilus (late fourth century b.c.) and his younger follower Erasistratus. Herophilus made many anatomical studies of the brain. He distinguished the cerebrum (larger portion) from the cerebellum (smaller portion), suggested that the brain was the seat of intelligence, and identified and named several structures of the brain, some of which still carry the names he gave them. He also discovered that nerves originate in the brain and noted the difference between motor nerves (those concerned with motion) and sensory nerves (those related to sensation). Together with Erasistratus, Herophilus established the disciplines of anatomy and physiology (the science that deals with the function of the body's parts and organs).

In his studies of the heart and blood vessels, Erasistratus came very close to working out the circulatory system of the blood. He understood that the heart served as a pump and he studied and explained the function of the heart valves. Erasistratus theorized that the arteries and veins both spread from the heart but incorrectly believed that the arteries carried air instead of blood.

After Erasistratus's time, the dissection of human bodies to study their anatomy ended due to the pressure of public opinion. Egyptians believed that a body needed to remain whole to enter the afterlife, and they engaged in the practice of mummification (treating a body with preservatives for burial).

Important contributions to the science of anatomy were made by the last and most influential of the great ancient medical practitioners, Greek physician Claudius Galen (a.d. 131–200). He expertly dissected and accurately observed all kinds of animals but sometimes mistakenly applied what he saw to the human body. Nevertheless, he was the first to observe that muscles work in opposing pairs: for every muscle that causes a joint to bend, there is an opposing muscle that restores the joint to its original position.

Through experiments, Galen observed and described two ground-breaking anatomical events: (1) paralysis resulting from the cutting of the spinal cord and (2) the process by which urine passes from the kidneys to the bladder. In his observations about the heart and blood vessels, however, Galen made critical errors that remained virtually unchallenged for 1,400 years. He mistakenly believed that blood was formed in the liver and was circulated throughout the body by the veins. When anatomical research stopped for many centuries, Galen's teachings remained the ultimate medical authority.

After human dissections resumed in the sixteenth century, the long-held teachings of Galen were overturned by the work of Flemish anatomist and physician Andreas Vesalius (1514–1564). Vesalius, who founded modern scientific anatomy, noted obvious conflicts between what he saw in his dissections of the human body and what Galen had described. He reasoned that Galen's errors resulted from only having done animal dissections, which often did not apply to human anatomy.

In 1543, Vesalius published one of the most important books in medical history and the world's first textbook of anatomy, On the Structure of the Human Body. The book contains detailed anatomical descriptions of all parts of the human body, directions for carrying out dissections, and meticulously drawn illustrations. Vesalius believed that accurate, basic knowledge of the human body could only be gained by performing human dissections. In his book, he set forth an objective, scientific method of conducting medical research that was to become the foundation of anatomical research and education throughout the world.

The correct description of the circulation of blood was provided by English physician William Harvey (1578–1657). In the course of many experimental dissections, he established the existence of pulmonary circulation (blood flowing from heart to lungs to heart) and noted the one-way flow of blood. He was the first to discover that blood flows in a continuous circle from the heart to the arteries to the veins and back to the heart. Harvey published this radical new concept of blood circulation in 1628.

The discovery of capillaries (small blood vessels) by Italian anatomist Marcello Malpighi (1628–1694) in 1661 provided the factual evidence to confirm Harvey's theory of blood circulation. Malpighi discovered the capillaries—the tiny connecting links between the veins and arteries—using the newly invented microscope.

The science of anatomy was further advanced by the work of English physicist Robert Hooke (1635–1703). His 1665 publication Micrographia describes the structures of insects, fossils, and plants in detail from his microscopic studies. While examining the porous structure of cork, Hooke coined the term "cells" to describe the tiny rectangular holes he observed. This led scientists to adopt the concept of cells as the unit

structures of tissues, which in turn led to the suggestion of cells as the building blocks of organs and to the discovery of the cell nucleus. A later theory proposing that all of the body's tissues are composed of cells was the basis for the science of cytology.

Histology, or the study of tissues (structured groups of specialized cells), began in earnest in the 1700s with the work of French scientist Xavier Bichat (1771–1802). Bichat found that organs were built up out of different types of simpler structures, and each of these simpler structures could occur in more than one organ. He further noted that different tissues have specific properties and are thereby vulnerable to tissue-specific diseases.

Until that time, general anatomy was a descriptive order, based upon obvious characteristics such as the location of organs. Bichat suggested adopting a systematic order for anatomy based upon structure and function. He specified 21 tissues (or systems) in the human body based on what he saw with his naked eye, distinguishing these different tissues by their composition and by the arrangement of their fibers. These include epithelial (skin and digestive), muscular, nervous, connective, and vascular (blood) types.

Histology began to take on its modern form with the introduction of cell theory in 1839. At that time tissues began to be understood not as the basic building blocks of living things but as unique systems of cells with their own stages of development within the embryo (early stage of an organism's growth before birth or hatching).

Modern anatomy

Anatomy today makes use of knowledge from many fields of science to explore and understand how the structure of an organism's cells, tissues, and organs relates to their function.

Human anatomy, a crucial element in the medical school curriculum, divides the body into separate functional systems. These consist of the skin, the muscles, the skeleton, the circulatory system (blood, blood vessels, and heart), the digestive system, the urinary system, the respiratory system (lungs and breathing), the nervous system (brain, spinal cord, and nerves), the endocrine system (glands and hormones), and the reproductive system.

[See also Circulatory system; Digestive system; Endocrine system; Muscular system; Nervous system; Reproductive system; Respiratory system; Skeletal system ]