prostate cancer Malignant tumour of the prostate gland. Prostate can¬ cer commonly occurs in men over age 50. Symptoms include frequent or painful urination, blood in the urine, sexual dysfunction, swollen lymph nodes in the groin, and pain in the pelvis, hips, back, or ribs. The like¬ lihood of developing prostate cancer doubles if there is a family history. Treatment may include surgery, radiation therapy, hormone therapy, che¬ motherapy, or a combination of two or more of these approaches.
prostate gland Vpras-,tat\ Chestnut-shaped male reproductive organ, located under the bladder, which adds secretions to the sperm during ejacu¬ lation of semen. It surrounds the urethra (see urinary system) and is rounded at the top, narrowing to a blunt point. The prostate consists of 30-50 glands, supported by connective tissue, that discharge fluids into the ure¬ thra and two ejaculatory ducts. Those ducts, which also carry sperm and fluid discharged by the seminal vesicles, join the urethra inside the pros¬ tate. The prostate contributes 15-30% of the seminal fluid. It reaches its mature size at puberty. Around age 50, it commonly shrinks and decreases its secretions; an increase in size after midlife may be due to inflamma¬ tion or malignancy. See also prostatic disorder.
prostatic disorder \pra-'sta-tik\ Abnormality or disease of the pros¬ tate gland. About half of all men over 60 have some nonmalignant enlarge¬ ment, or benign prostatic hyperplasia (BPH). The gland may eventually compress the urethra, causing problems urinating. Severe cases can lead
to infection, bladder stones, obstruction, and kidney failure. Prostate can¬ cer, also found mainly in older men, can be deadly but usually grows so slowly that most patients die of something else before the cancer spreads. Since surgery and radiation therapy often lead to incontinence and impo¬ tence, many cases are monitored (through prostate-specific antigen, or PSA, tests) and treated only if necessary. Gonorrhea and other bacterial infections involving the prostate are treated with antibiotics.
prosthesis \pras-'the-s3s\ Artificial substitute for a missing part of the body, usually an arm or leg. Prostheses have evolved from wooden legs and hooks that replaced hands to sophisticated plastic, fibreglass, and metal devices designed to fit limbs amputated at different points. They may have working joints and allow motion either by amplification of electric current generated by muscle contractions or by actual attachment to the muscles. Arm prostheses usually allow some degree of grasping and manipulation. External or implanted breast prostheses are used after mastectomy.
prostitution Practice of engaging in sexual activity, usually with indi¬ viduals other than a spouse or friend, in exchange for immediate payment in money or other valuables. Prostitutes may be of either sex and may engage in either heterosexual or homosexual activity, but historically most prostitution has been by females with males as clients. Prostitution is a very old and universal phenomenon; also universal is condemnation of the prostitute but relative indifference toward the client. Prostitutes are often set apart in some way. In ancient Rome they were required to wear distinctive dress; under Hebrew law only foreign women could be pros¬ titutes; in prewar Japan they were required to live in special sections of the city. In medieval Europe prostitution was licensed and regulated by law, but by the 16th century an epidemic of venereal disease and post- Reformation morality led to the closure of brothels. International coop¬ eration to end the traffic in women for the purpose of prostitution began in 1899. In 1921 the League of Nations established the Committee on the Traffic in Women and Children, and in 1949 the UN General Assembly adopted a convention for the suppression of prostitution. In the U.S. pros¬ titution was first curtailed by the Mann Act (1910), and by 1915 most states had banned brothels (Nevada being a notable exception). Prostitu¬ tion is nevertheless tolerated in most U.S. and European cities. In The Netherlands many prostitutes have become members of a professional service union, and in Scandinavia government regulations emphasize hygienic aspects, requiring frequent medical examination and providing free mandatory hospitalization for anyone found to be infected with vene¬ real disease. Prostitutes are very often poor and lack skills to support themselves; in many traditional societies there are few other available money-earning occupations for women without family support. In devel¬ oping African and Asian countries, prostitution has been largely respon¬ sible for the spread of AIDS and the orphaning of hundreds of thousands of children.
Protagoras \pro-'tag-o-r3s\ (b. 485, Abdera, Greece—d. c. 410 bc) Greek philosopher, first and most famous of the sophists. He spent most of his life at Athens, where he considerably influenced contemporary thought on moral and political questions. Plato named one of his dialogues after him. Protagoras claimed to teach men “virtue” in the conduct of their daily lives. He is best known for his dictum, “Man is the measure of all things” (see relativism; ethical relativism). Though he adopted conventional moral ideas, his work Concerning the Gods advocated agnosticism regard¬ ing religious belief. He was accused of impiety, his books were publicly burned, and he was exiled from Athens c. 415 bc.
protectionism Policy of protecting domestic industries against foreign competition by means of tariffs, subsidies, import quotas, or other handi¬ caps placed on imports. The chief protectionist measures, government- levied tariffs, raise the price of imported articles, making them less attractive to consumers than cheaper domestic products. Import quotas, which limit the quantities of goods that can be imported, are another pro¬ tectionist device. Wars and economic depressions historically have resulted in increases in protectionism, while peace and prosperity have tended to encourage free trade. Protectionist policies were common in Europe in the 17th—18th centuries under mercantilism. Britain abandoned many of its protectionist laws in the 19th century, and by World War I tariffs were low throughout the Western world. Economic and political dislocation led to rising customs barriers in Europe in the 1920s, and the Great Depression produced a spate of protectionist measures; world trade shrank drastically as a result. The U.S. had a long history of protection¬ ism, with tariffs reaching high points in the 1820s and the Great Depres-
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sion, but in 1947 it became one of 23 nations to sign the General Agreement on Tariffs and Trade (GATT), which substantially reduced customs tariff's while reducing or eliminating quotas. Despite trade agreements such as GATT and NAFTA, calls for protectionism are still heard in many coun¬ tries when industries suffer severely from foreign competition. See also trade agreement; World Trade Organization.
protectorate Relationship in which one country exercises some deci¬ sive control over another country or region. The degree of control may vary from one in which the protecting state guarantees the safety of the other to one that is a disguised form of annexation. Though the relation¬ ship is an ancient one, the use of the term dates only from the 19th cen¬ tury. In modern times most protectorates have been established by treaties requiring the weaker state to surrender management of its international relations, thus losing part of its sovereignty.
protein Any of numerous organic compounds, complex polymers of amino acids that are involved in nearly every aspect of the physiology and biochemistry of living organisms. Twenty different amino acids are com¬ mon to proteins, linked in chains of hundreds to thousands of units. An active protein molecule has three important levels of structure: primary (the amino acid sequence), determined by the genes; secondary (the geo¬ metric shape, often a helix), determined by the angles of the covalent bonds between and within amino acids; and tertiary (the looped and folded overall shape), determined largely by attraction between oppositely charged groups (and repulsion between like charged groups) on amino- acid side chains and especially by hydrogen bonding. The tertiary struc¬ ture, which can be globular or sheetlike with ridges, crevices, or pockets, often holds the key to a protein’s biological activity. Proteins can serve, e.g., as structural material (as in connective tissue and hair; see collagen; keratin), as enzymes and hormones, as transporters of essential substances such as oxygen (see hemoglobin), as antibodies, or as regulators of gene expression. Some proteins are simple (amino acids only), some conju¬ gated (see conjugation) to other groups, often vitamins or metal atoms needed in tiny amounts in the diet (see coenzyme; cofactor). Rhodopsin and hemoglobin are conjugated proteins. Proteins may be covalently linked to other atoms or molecules, as to sugars (glycoproteins), phosphate groups (phosphoproteins), or sulfur (sulfoproteins). Proteins are an essen¬ tial human nutrient, obtained from both plant and animal foods. Their greatest commercial use is in food products; they are also employed in adhesives, plastics, and fibres.