Anatomy
From Encyclopædia
Anatomy is the branch of biology involving the structure of
plants, animals, and other forms of biological organisms. It is related to morphology, which is concerned with the description of organisms, and MORPHOGENESIS, concerned with their development. COMPARATIVE ANATOMY is concerned with the difference in structure of animal forms.Anatomy is divided into several subdisciplines. Gross anatomy involves studies on structures that can be seen with the naked eye. HISTOLOGY is the study of tissue structure and CYTOLOGY that of
cell structure; because histological and cytological studies require the use of a microscope, they are known together as microscopic anatomy. When the word functional is placed before any of these words, as in "functional anatomy," reference is being made to the subject of PHYSIOLOGY. Often anatomy cannot be discussed properly without introducing some physiology, and physiology can almost never be discussed properly without an anatomical background.Two other divisions of anatomy are EMBRYOLOGY and paleoanatomy. Embryology is commonly called developmental anatomy because it is concerned with the genesis and development of a fully differentiated tissue,
organ, or organism. Paleoanatomy is the study of the structure of extinct organisms.EARLY HISTORY OF ANATOMYAristotleThe first recorded attempts to study anatomy were made by
Aristotle (384-22 BC), although hieroglyphics and papyruses produced from 3000 to 1600 BC indicate that some
interest was taken in certain anatomical aspects, or appearances, in mummies.
Aristotle, the founder of biological
science, dissected
plants and animals, although neither he nor HIPPOCRATES (460-374 BC), the father of
medicine, dissected the human body. Both believed that the HEART is the seat of thought and of the
soul.Herophilus and ErasistratusSoon after the death of
Aristotle the Ptolemies, kings of
Egypt, encouraged dissections. Herophilus (335-280 BC) and his contemporary ERASISTRATUS (310-250 BC) were perhaps the most active practitioners.Herophilus dissected about 600 human bodies and wrote more than one treatise on anatomy, another on the eyes, and a handbook for midwives. His greatest contribution was to dispel the earlier erroneous notions of
Aristotle and Hippocrates about the mind, proving that the BRAIN is the center of the
nervous system and the seat of
intelligence by tracing nerves from the brain to the
spinal cord and classifying them as voluntary and involuntary.Erasistratus observed lymph carrying fat toward the heart, described the function of the epiglottis in closing the
larynx, identified the tricuspid valve of the heart, and was able to distinguish sensory nerves from motor nerves. He studied the
circulatory system intensively, but, like his predecessors, he held that the arteries contain air. This was a common belief, since the veins normally contain about 60 percent of the total BLOOD, and on death the arteries empty out into the
capillary beds and veins.GalenDespite many incorrect observations by the ancients, perhaps as many principles were known by the end of Cleopatra's reign (around 30 BC) as were to be discovered during the next 1,000 years. Shortly after Cleopatra's death, Alexandria became a Roman
city and one of the main centers of the Christian church. Its leaders then began to discourage dissections. Leaders in other parts of the
world, except Arabia, also denounced them. The fervor for achievement of anatomical knowledge did not die immediately, however, in spite of these difficulties.Most notable among those who strove to advance anatomical understanding was Claudius GALEN (AD 131-200), physician to the Roman
emperor Marcus Aurelius. Known historically as the founder of experimental physiology, Galen showed that urine is formed in the
kidneys, not in the bladder, and that sectioning of the
spinal cord results in paralysis to that part of the body below the cut. His monumental work, On the Use of the Parts of the Human Body, served as the standard medical text for 1,400 years.Despite some excellent contributions to experimental
medicine, however, Galen may have delayed anatomical progress. Because of religious prejudice and
superstition, he was not permitted to dissect human bodies, and many of his conclusions were based on dissections of oxen, dogs, swine, and apes. More important, he perpetuated false beliefs established by his predecessors and contemporaries--that cosmic life is taken into the body with each breath (pneuma) and that three separate spirits dwell in the body: a "natural" spirit in the
liver, a "vital" spirit in the heart, and an "animal" spirit in the brain. The first of these beliefs gained further credence in that it was established on Galen's experimental approaches. Although Galen's beliefs suited and pleased the leaders of both
church and state, they served to misinform the concerned portion of the populace who, although wishing to know the truth, had to accept a fallacious presentation until
William HARVEY would prove it wrong in the 17th century.Galen's view of the
circulatory system was also incorrect. Like his predecessors, and despite numerous studies on his own, Galen traced the passage of blood from the
liver--where, he maintained, it was formed--to the heart, where supposedly a breath of air was injected into it as a gaseous material from the LUNGS. One important contribution of his is that the arteries carry blood, not air. According to Galen, the blood then travels to the rest of the body rather than first going to the lungs and back into the heart. This view of the circulatory passage as one-way was also maintained as scientific thought until the 17th century.Avicenna and the ArabsMeanwhile, faced with increasing religious antipathy, anatomical pursuit was virtually abandoned, except for what work was done by the
Arabs. Un?ortunately, their studies were based on
Aristotle's and Galen's works, which the
Arabs had translated into their
language. AVICENNA (AD 980-1037) was perhaps the most famous of the Arab anatomists. His Canon of
medicine, published in AD 1000, contained information based on observations derived from studies on humans, apes, dogs, and other animals. Neither he nor his peers, however, carried out systematic studies. Dissections were sometimes performed, mainly in an attempt to learn the causes of death, and occasionally public authorities permitted physicians to dissect executed criminals.VesaliusGradually, as the
Renaissance became established, some individuals began to circumvent authoritarian restrictions, and the
number of anatomists increased rapidly. Perhaps the most important of these was Andreas VESALIUS (1514-64), who ushered in the modern era of anatomy. Rather than accept many of the incorrect observations of Galen and pursue the study of the topic through metaphysical dialectic, he took a straightforward scientific experimental approach. He compared the anatomy of various animals with humans and noted the fallacy of extrapolating from one to the other. His work culminated in On the Structure of the Human Body, which was published the same year (1543) as Copernicus's On the
revolution of Celestial Bodies. Vesalius's work was most significant in that it was the first to contain accurate depictions of the inner structure of the human body. Successors and contemporaries of Vesalius added important details to the basework he had created, and in less than a century they had completed much of the basic studies on gross anatomy.HarveyThis basic work culminated in the accomplishments of
William Harvey (1578-1657), an English physician who was the first to postulate that the blood moves in a circle from left heart to arteries to veins to right heart. He also postulated the existence of thousands of miles of microscopic blood capillaries, a theory that was proved correct after microscopes became available. At about this time anatomy began to become established as a full-fledged
science. Scientific societies were formed, textbooks and atlases began to appear, schools were established, and laws were enacted regulating the acquisition of human bodies for dissection and study.HISTORY OF MICROSCOPIC ANATOMYRapid strides were made as microscopic anatomy began to be established and, together with gross anatomy, merged with comparative and developmental anatomy. Marcello MALPIGHI (1628-94), a young contemporary of the elderly
William Harvey, demonstrated that blood went through capillaries in the lungs before reaching the left heart. He described many other important histological features, such as the germinal layer at the base of the outer layer (epidermis) of
skin and the structure of the functional units of the kidney (nephrons) through which blood is filtered in producing urine.Robert HOOKE (1635-1703) also was an outstanding physicist. In 1665 he reported in Micrographia his observations on
plant anatomy. Based on his microscopic observations of cork, he coined the word
cell. His observations later helped other investigators advance the concept that
cells are the unit structures of tissues. In particular, about a century later, Caspar Friedrich WOLFF (1733-94), as a result of intensive study in embryology, hinted that
cells are the building blocks of
organs. Later, Robert Brown (1773-1858) discovered the
cell nucleus, probably because staining techniques became available. Still later, M. J. Schleiden (1804-81) and Theodor SCHWANN (1810-82) in 1840 advanced the theory that all tissues, including bone, tendon, and ligament, are composed of
cells. In doing so, they brought cytology into existence as a separate, although interrelated, field of inquiry. This field now comprises the subspecialties of cytochemistry and cytogenetics.
