Health & Medicine

The study of the human mind and body, how these function, and how they interact—not only with each other but also with their environment—has been of utmost importance in ensuring human well-being. Research on potential treatments and preventive medicine has expanded greatly with the development of modern medicine, and a network of disciplines, including such fields as genetics, psychology, and nutrition, aims to facilitate the betterment of our health.

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  • pregnancy
    Pregnancy
    Pregnancy, process and series of changes that take place in a woman’s organs and tissues as a result of a developing fetus. The entire process from fertilization to birth takes an average of 266–270 days, or about nine months. (For pregnancies other than those in humans, see gestation.) A new…
  • human chromosomes
    Heredity
    Heredity, the sum of all biological processes by which particular characteristics are transmitted from parents to their offspring. The concept of heredity encompasses two seemingly paradoxical observations about organisms: the constancy of a species from generation to generation and the variation…
  • ebolavirus; Ebola virus disease
    Ebola
    Ebola, contagious disease caused by a virus of the family Filoviridae that is responsible for a severe and often fatal viral hemorrhagic fever. Outbreaks in primates—including gorillas, chimpanzees, and humans—and domestic pigs have been recorded. The disease is characterized by extreme fever,…
  • HIV/AIDS; retrovirus
    AIDS
    AIDS, transmissible disease of the immune system caused by the human immunodeficiency virus (HIV). HIV is a lentivirus (literally meaning “slow virus”; a member of the retrovirus family) that slowly attacks and destroys the immune system, the body’s defense against infection, leaving an individual…
  • invertebrate: nervous system
    Nervous system
    Nervous system, organized group of cells specialized for the conduction of electrochemical stimuli from sensory receptors through a network to the site at which a response occurs. All living organisms are able to detect changes within themselves and in their environments. Changes in the external…
  • mitochondria and cellular respiration
    Metabolism
    Metabolism, the sum of the chemical reactions that take place within each cell of a living organism and that provide energy for vital processes and for synthesizing new organic material. Living organisms are unique in that they can extract energy from their environments and use it to carry out…
  • Death
    Death, the total cessation of life processes that eventually occurs in all living organisms. The state of human death has always been obscured by mystery and superstition, and its precise definition remains controversial, differing according to culture and legal systems. During the latter half of…
  • cocaine
    Drug use
    Drug use, use of drugs for psychotropic rather than medical purposes. Among the most common psychotropic drugs are opiates (opium, morphine, and heroin), hallucinogens (LSD, mescaline, and psilocybin), barbiturates, cocaine, amphetamines, tranquilizers, and cannabis. Alcohol and tobacco are also…
  • SARS
    SARS
    SARS, highly contagious respiratory illness characterized by a persistent fever, headache, and bodily discomfort, followed by a dry cough that may progress to great difficulty in breathing. SARS appeared in November 2002 in Guangdong province, China, where it was first diagnosed as an atypical…
  • Aedes mosquito; mosquito-borne disease
    Zika fever
    Zika fever, infectious mosquito-borne illness, typically mild in humans but capable in utero of causing brain anomalies in newborns, including a severe deformity known as microcephaly (abnormal smallness of the head). Zika fever is caused by Zika virus, a type of flavivirus closely related to the…
  • inherited reflex
    Human behaviour
    Human behaviour, the potential and expressed capacity for physical, mental, and social activity during the phases of human life. Humans, like other animal species, have a typical life course that consists of successive phases of growth, each of which is characterized by a distinct set of physical,…
  • The routine monitoring of blood pressure levels is an important part of assessing an individual's health. Blood pressure provides information about the amount of blood in circulation and about heart function and thus is an important indicator of disease.
    Human disease
    Human disease, an impairment of the normal state of a human being that interrupts or modifies its vital functions. Before human disease can be discussed, the meanings of the terms health, physical fitness, illness, and disease must be considered. Health could be defined theoretically in terms of…
  • influenza virus
    Influenza
    Influenza, an acute viral infection of the upper or lower respiratory tract that is marked by fever, chills, and a generalized feeling of weakness and pain in the muscles, together with varying degrees of soreness in the head and abdomen. Influenza is caused by any of several closely related…
  • body mass index for adults
    Nutritional disease
    Nutritional disease, any of the nutrient-related diseases and conditions that cause illness in humans. They may include deficiencies or excesses in the diet, obesity and eating disorders, and chronic diseases such as cardiovascular disease, hypertension, cancer, and diabetes mellitus. Nutritional…
  • diabetes
    Diabetes mellitus
    Diabetes mellitus, disorder of carbohydrate metabolism characterized by impaired ability of the body to produce or respond to insulin and thereby maintain proper levels of sugar (glucose) in the blood. Diabetes is a major cause of morbidity and mortality, though these outcomes are not due to the…
  • MERS; coronavirus
    MERS
    MERS, acute viral respiratory illness that is characterized primarily by cough, fever, and shortness of breath and is sometimes associated with severe and potentially fatal complications such as pneumonia and kidney failure. The illness was first observed in June 2012 in Jiddah, Saudi Arabia, and…
  • Edward Jenner: smallpox vaccination
    History of medicine
    History of medicine, the development of the prevention and treatment of disease from prehistoric and ancient times to the 21st century. Unwritten history is not easy to interpret, and, although much may be learned from a study of the drawings, bony remains, and surgical tools of early humans, it is…
  • Freud, Sigmund
    Mental disorder
    Mental disorder, any illness with significant psychological or behavioral manifestations that is associated with either a painful or distressing symptom or an impairment in one or more important areas of functioning. Mental disorders, in particular their consequences and their treatment, are of…
  • second pandemic of the Black Death in Europe
    Pandemic
    Pandemic, outbreak of infectious disease that occurs over a wide geographical area and that is of high prevalence, generally affecting a significant proportion of the world’s population, usually over the course of several months. Pandemics arise from epidemics, which are outbreaks of disease…
  • human lungs
    Human respiratory system
    Human respiratory system, the system in humans that takes up oxygen and expels carbon dioxide. The human gas-exchanging organ, the lung, is located in the thorax, where its delicate tissues are protected by the bony and muscular thoracic cage. The lung provides the tissues of the human body with a…
  • Structure of a typical bacterial cell, showing the cell wall, a plasmid, and other components that are susceptible to modifications contributing to the development of antibiotic resistance.
    Antibiotic resistance
    Antibiotic resistance, loss of susceptibility of bacteria to the killing (bacteriocidal) or growth-inhibiting (bacteriostatic) properties of an antibiotic agent. When a resistant strain of bacteria is the dominant strain in an infection, the infection may be untreatable and life-threatening.…
  • coronary artery; fibrolipid plaque
    Cardiovascular disease
    Cardiovascular disease, any of the diseases, whether congenital or acquired, of the heart and blood vessels. Among the most important are atherosclerosis, rheumatic heart disease, and vascular inflammation. Cardiovascular diseases are a major cause of health problems and death. Life depends on the…
  • Hookworm (Ancylostoma).
    Digestive system disease
    Digestive system disease, any of the diseases that affect the human digestive tract. Such disorders may affect the esophagus, stomach, small intestine, large intestine (colon), pancreas, liver, or biliary tract. A prevalent disorder of the digestive system is gastroesophageal reflux disease (i.e.,…
  • birth: premature
    Childhood disease and disorder
    Childhood disease and disorder, any illness, impairment, or abnormal condition that affects primarily infants and children—i.e., those in the age span that begins with the fetus and extends through adolescence. Childhood is a period typified by change, both in the child and in the immediate…
  • nervous system
    Human nervous system
    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…
  • The human digestive system as seen from the front.
    Human digestive system
    Human digestive system, the 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…
  • Measles
    Measles, contagious viral disease marked by fever, cough, conjunctivitis, and a characteristic rash. Measles is most common in children but may appear in older persons who escaped it earlier in life. Infants are immune up to four or five months of age if the mother has had the disease. Immunity to…
  • Chemoreception enables animals to respond to chemicals that can be tasted and smelled in their environments. Many of these chemicals affect behaviours such as food preference and defense.
    Chemoreception
    Chemoreception, process by which organisms respond to chemical stimuli in their environments that depends primarily on the senses of taste and smell. Chemoreception relies on chemicals that act as signals to regulate cell function, without the chemical necessarily being taken into the cell for…
  • Structure of the human ear.
    Human ear
    Human ear, organ of hearing and equilibrium that detects and analyzes sound by transduction (or the conversion of sound waves into electrochemical impulses) and maintains the sense of balance (equilibrium). The human ear, like that of other mammals, contains sense organs that serve two quite…
  • Aedes aegypti mosquito
    Dengue
    Dengue, acute, infectious, mosquito-borne fever that is temporarily incapacitating but rarely fatal. Besides fever, the disease is characterized by an extreme pain in and stiffness of the joints (hence the name “breakbone fever”). Complication of dengue fever can give rise to a more severe form,…
  • A horizontal cross section of the human eye, showing the major parts of the eye, including the protective covering of the cornea over the front of the eye.
    Human eye
    Human eye, in humans, specialized sense organ capable of receiving visual images, which are then carried to the brain. The eye is protected from mechanical injury by being enclosed in a socket, or orbit, which is made up of portions of several of the bones of the skull to form a four-sided pyramid,…
  • precancerous growth in a human colon
    Cancer
    Cancer, group of more than 100 distinct diseases characterized by the uncontrolled growth of abnormal cells in the body. Though cancer has been known since antiquity, some of the most significant advances in scientists’ understanding of it have been made since the middle of the 20th century. Those…
  • epilepsy
    Nervous system disease
    Nervous system disease, any of the diseases or disorders that affect the functioning of the human nervous system. Everything that humans sense, consider, and effect and all the unlearned reflexes of the body depend on the functioning of the nervous system. The skeleton and muscles support and…
  • Heart disease
    Heart disease, any disorder of the heart. Examples include coronary heart disease, congenital heart disease, and pulmonary heart disease, as well as rheumatic heart disease (see rheumatic fever), hypertension, inflammation of the heart muscle (myocarditis) or of its inner or outer membrane…
  • Prozac
    Therapeutics
    Therapeutics, treatment and care of a patient for the purpose of both preventing and combating disease or alleviating pain or injury. The term comes from the Greek therapeutikos, which means “inclined to serve.” In a broad sense, therapeutics means serving and caring for the patient in a…
  • striated muscle; human biceps muscle
    Muscle
    Muscle, contractile tissue found in animals, the function of which is to produce motion. Movement, the intricate cooperation of muscle and nerve fibres, is the means by which an organism interacts with its environment. The innervation of muscle cells, or fibres, permits an animal to carry out the…
  • vaccine
    Vaccine
    Vaccine, suspension of weakened, killed, or fragmented microorganisms or toxins or of antibodies or lymphocytes that is administered primarily to prevent disease. A vaccine can confer active immunity against a specific harmful agent by stimulating the immune system to attack the agent. Once…
  • blue-ringed octopus
    Poison
    Poison, in biochemistry, a substance, natural or synthetic, that causes damage to living tissues and has an injurious or fatal effect on the body, whether it is ingested, inhaled, or absorbed or injected through the skin. Although poisons have been the subject of practical lore since ancient times,…
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