Human Skin

WRITTEN BYF. John G. EblingSee All ContributorsProfessor of Zoology, 1968–82; Independent Research Worker in Dermatology, University of Sheffield, England. Coeditor of and contributor to Textbook of Dermatology.See Article History

Human skin, in human anatomy, the covering, or integument, of the body’s surface that both provides protection and receives sensory stimuli from the external environment. The skin consists of three layers of tissue: the epidermis, an outermost layer that contains the primary protective structure, the stratum corneum; the dermis, a fibrous layer that supports and strengthens the epidermis; and the subcutis, a subcutaneous layer of fat beneath the dermis that supplies nutrients to the other two layers and that cushions and insulates the body.

Human Renal system

WRITTEN BYJames Scott RobsonSee All ContributorsEmeritus Professor of Medicine, University of Edinburgh; Consultant Physician, Edinburgh Royal Infirmary. Author of numerous articles on acid-base and electrolyte metabolism and renal disorders.See Article History

Renal system, in humans, organ system that includes the kidneys, where urine is produced, and the ureters, bladder, and urethra for the passage, storage, and voiding of urine.

Human Cardiovascular system

WRITTEN BYStanley W. JacobSee All ContributorsGerlinger Professor of Surgery, Oregon Health Sciences University, Portland. Author of Structure and Function in Man.See Article History

Human cardiovascular system, organ system that conveys blood through vessels to and from all parts of the body, carrying nutrients and oxygen to tissues and removing carbon dioxide and other wastes. It is a closed tubular system in which the blood is propelled by a muscular heart. Two circuits, the pulmonary and the systemic, consist of arterial, capillary, and venous components.

Human Digestive system

WRITTEN BYWilliam T. KeetonSee All ContributorsLiberty Hyde Bailey Professor of Biology, Cornell University, Ithaca, New York, 1969–80. Author of Biological Science; Elements of Biological Science.Last Updated: Nov 4, 2020 See Article History

Human digestive system, system used in the human body for the process of digestion. The human digestive system consists primarily of the digestive tract, or the series of structures and organs through which food and liquids pass during their processing into forms absorbable into the bloodstream. The system also consists of the structures through which wastes pass in the process of elimination and other organs that contribute juices necessary for the digestive process.

Human evolution

WRITTEN BYRussell Howard TuttleRussell H. Tuttle is an active Professor of Anthropology, Evolutionary Biology, History of Science and Medicine and the College at the University of Chicago. He conducted pioneering functional morphological…See Article History

Human evolution, the process by which human beings developed on Earth from now-extinct primates. Viewed zoologically, we humans are Homo sapiens, a culture-bearing upright-walking species that lives on the ground and very likely first evolved in Africa about 315,000 years ago.

Human Nervous system

WRITTEN BYCharles R. NobackSee All ContributorsEmeritus Professor of Anatomy and Cell Biology, College of Physicians and Surgeons, Columbia University. Coauthor of The Human Nervous System and others.See Article History

Human nervous system, system that conducts stimuli from sensory receptors to the brain and spinal cord and conducts impulses back to other parts of the body. As with other higher vertebrates, the human nervous system has two main parts: the central nervous system (the brain and spinal cord) and the peripheral nervous system (the nerves that carry impulses to and from the central nervous system). In humans the brain is especially large and well developed.

Human Respiratory system

WRITTEN BYRobert A. KlockeSee All ContributorsProfessor of Medicine and Physiology; Chief, Pulmonary Division, State University of New York at Buffalo. Coauthor of Normal and Abnormal Lung Function.See Article History

Human respiratory system, the system in humans that takes up oxygen and expels carbon dioxide.

Human Sensory reception

WRITTEN BYCarl PfaffmannVincent and Brooke Astor Professor of Physiological Psychology, Rockefeller University, New York City, 1980–83. Editor of Olfaction and Taste, proceedings of the Third International Symposium on…See Article History

Human sensory reception, means by which humans react to changes in external and internal 

Ancient philosophers called the human senses “the windows of the soul,” and Aristotle described at least five senses—sight, hearing, smell, taste, and touch. Aristotle’s influence has been so enduring that many people still speak of the five senses as if there were no others. Yet the modern sensory catalog now includes receptors in the muscles, tendons, and joints, which give rise to the kinesthetic sense (that is, the sense of motion), and receptors in the vestibular organs in the inner ear, which give rise to the sense of balance.

Within the circulatory system, sensory receptors are found that are sensitive to carbon dioxide in the blood or to changes in blood pressure or heart rate, and there are receptors in the digestive tract that appear to mediate such experiences as hunger and thirst. Some brain cells may also participate as hunger receptors. This is especially true of cells in the lower parts of the brain (such as the hypothalamus) where some cells have been found to be sensitive to changes in blood chemistry (water and other products of digestion) and even to changes in temperature within the brain itself.

Human Skeleton

WRITTEN BYWarren AndrewProfessor of Anatomy, Indiana University, Indianapolis, 1958–82. Author of Textbook of Comparative Histology.See Article History

Human skeleton, the internal skeleton that serves as a framework for the body. This framework consists of many individual bones and cartilages. There also are bands of fibrous connective tissue—the ligaments and the tendons—in intimate relationship with the parts of the skeleton. This article is concerned primarily with the gross structure and the function of the skeleton of the normal human adult.

Human body

WRITTEN BYThe Editors of Encyclopaedia BritannicaEncyclopaedia Britannica’s editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree….See Article History

Human body, the physical substance of the human organism, composed of living cells and extracellular materials and organized into tissues, organs, and systems.