| 单词 | testis | |||
| 释义 | testistes·tisT0127300 (tĕs′tĭs)testis(ˈtɛstɪs)tes•tis(ˈtɛs tɪs)n., pl. -tes (-tēz). tes·tis(tĕs′tĭs)testis
Testistestis(tĕs`tĭs) ortesticle(tĕs`tĭkəl), one of a pair of glands that produce the male reproductive cells, or spermspermor spermatozoon , in biology, the male gamete (sex cell), corresponding to the female ovum in organisms that reproduce sexually. In higher animals the sperm is produced in the testis of the male; it is much smaller than the ovum and consists primarily of a head, ..... Click the link for more information. . In fetal life the testes develop in the abdomen, then descend into an external sac, the scrotum. A testis is composed of about 800 coiled seminiferous tubules whose linings contain cells that develop into sperm. These tubules merge into a larger tube called the epididymis that leads out of the testis into the vas deferens. Between the seminiferous tubules there is interstitial tissue that secretes the male sex hormone testosteronetestosterone , principal androgen, or male sex hormone. One of the group of compounds known as anabolic steroids, testosterone is secreted by the testes (see testis) but is also synthesized in small quantities in the ovaries, cortices of the adrenal glands, and placenta, usually ..... Click the link for more information. , which stimulates the development of the male reproductive system and secondary sex characteristics. Sometimes the testes do not descend normally before or shortly after birth and remain in the abdomen or groin. Such a condition requires medical attention or the gland will eventually become sterile. See also reproductive systemreproductive system, in animals, the anatomical organs concerned with production of offspring. In humans and other mammals the female reproductive system produces the female reproductive cells (the eggs, or ova) and contains an organ in which development of the fetus takes ..... Click the link for more information. . TestisThe organ of sperm production. In addition, the testis (testicle) is an organ of endocrine secretion in which male hormones (androgens) are elaborated. In the higher vertebrates (reptiles, birds, and mammals), the testes are paired and either ovoid or elongated in shape. In mammals, the testes are usually ovoid or round. In many species (for example, humans) they are suspended in a pouch (scrotum) outside the main body cavity; in other species they are found in such a pouch only at the reproductive season; in still others the testicles are permanently located in the abdomen (for example, in whales and bats). Within a firm and thick capsule of connective tissue, the tunica albuginea, the testis contains a varying number of thin but very long seminiferous tubules which are the sites of sperm formation. Essentially, these tubules are simple loops which open with both their limbs into a network of fine, slitlike canals, the rete testis. From this the sperm drains through a few, narrow ducts, the ductuli efferentes, into the epididymis, where sperm mature and are stored. The seminiferous tubules comprise most of the testis, and in different species vary greatly in complexity. Each tubule is surrounded by a layer of thin cells which is contractile and enables the tubules to wriggle slowly. The spaces between tubules are filled with connective tissue, blood vessels, an extensive network of very thin-walled lymph vessels, and secretory cells, the interstitial cells or cells of Leydig, which secrete male hormone. The sperm cells, spermatozoa, develop in the wall of the seminiferous tubules, either periodically, as in most vertebrates, or continually, as in humans. Most of the cells in the tubules are potential spermatozoa (spermatogenic or germ cells). Nursing cells (Sertoli cells) are interspersed at regular intervals between them. The Sertoli cells support and surround the developing spermatogenic cells and provide a specialized environment, which is absolutely necessary for normal sperm development. See Sperm cell Spermatogenesis in the testis is the result of a balance between proliferation and differentiation, and cell degeneration or apoptosis. Apoptosis of the spermatogenic cells is largely hormonally controlled, and specifically directed apoptosis occurs in conditions of testicular damage due to environmental insults such as heat, radiation, or chemical toxicants. Recovery of spermatogenesis is possible provided the stem cells are not depleted by these processes. See Spermatogenesis The functions of the testis are dependent on the secretion of gonadotropic hormones, the release of which from the pituitary gland is in turn regulated by the central nervous system. In mammals, male-hormone production resides in the Leydig cells, located in the intertubular tissue of the testes. The principal androgenic hormone released by the testis into the bloodstream is testosterone. The testis is able to form cholesterol and to convert this via a number of pathways to testosterone. Testosterone may be further metabolized into estrogens in the testis. The production of estrogens in the male varies quite widely among species, from relatively low in humans to very high, for example in stallions and boars. Estrogens are important in the development and proper function of the ducts which drain the testis (the rete testis and ductuli efferentes), even in species with relatively low levels of estrogens. See Androgen Testosterone synthesis is normally limited by the rate of pituitary gonadotrophin secretion: administration of the luteinizing hormone or of chorionic gonadotrophin results in increased testosterone synthesis and release within minutes. These hormones also stimulate growth and multiplication of Leydig cells. Hypophysectomy leads to cessation of androgen formation. See Adenohypophysis hormone, Pituitary gland At the ambisexual stage of embryonic development, the testis promotes the growth of the paired Wolffian ducts and their differentiation into the epididymis, vasa deferentia, and seminal vesicles; the fetal testis also causes masculinization of the urogenital sinus, fusion of the labioscrotal folds in the midline, and development of the genital tubercle into a phallus. See Embryology Toward puberty, increased secretion of testosterone stimulates the growth of the penis, scrotum, and male accessory glands responsible for the formation of the seminal plasma, for example, the prostate and seminal vesicles. The hormone brings about the appearance of secondary sex characters, such as the male-type distribution of hair and body fat and lowered pitch of voice in man, the growth of the comb and wattles in birds, the clasping pads of amphibians, or the dorsal spine of certain fishes. Unlike the ovary, the testis remains functional throughout life, with ongoing spermatogenic development. However, the efficiency of spermatogenesis falls away, and androgen levels begin to fall due to a declining Leydig cell activity. These events can lead to reduced fertility, and androgen insufficiency problems in later life in some men. See Reproductive system Testisin animals and man, the male gonad, which produces spermatozoa. The testes are usually a paired organ. In invertebrates the simplest testes are found in coelenterates and consist of a mass of sexual cells. Sperm is released to the outside in hydroids through a rupture in the body wall, and in scyphozoans, anthozoans, and ctenophorans through the gastrovascular cavity and then through the mouth opening. Platyhelminths have numerous testes, each with their own ducts; some trematodes have 30 to 200 testes, and tapeworms have as many as 1,000 testes in every body segment. The numerous testes of nemertines do not have permanent ducts and are arranged along the sides of the intestine. In nematodes the tubular testis enlarges into a sperm duct, which opens near the posterior end. In annelids many body segments have one pair of testes (polychaetes) or two or, less commonly, four pairs of testes (oligochaetes); sperm is excreted through special canals, or coelomoducts, which open into the coelom and do not communicate with the testes. In arthropods the paired testes, which vary in shape and structure, have ducts. The testes are paired in bivalves and unpaired in other mollusks. The testes of echinoderms usually are located in the interradii; for example, a starfish has ten testes, with two in each interradius. In enteropneusts numerous paired testes open on the dorsal side of the trunk. Among the tunicates, appendicularians have unpaired and ductless testes, Salpae have two testes with ducts, and ascidians have from one to 150 pairs of testes with ducts. Acraniates, for example, lance-lets, have approximately 25 pairs of ductless testes. In most vertebrates the testes are paired organs symmetrically arranged in the abdominal cavity. They form during the gestation period as thickenings in the abdominal wall. (In cyclostomes both rudimentary testes fuse together.) In most mammals, with the exception of monotremes, many insectivores and edentates, proboscidians, hyracoids, sirenians, pinnipeds, and cetaceans, the testes are located in the scrotum, a saccular process in the body wall. The testes descend into the scrotum from the abdominal cavity through the inguinal canal, usually during embryonic development. In some mammals, for example, in many rodents, the testes descend into the scrotum only during the breeding period, after which they are withdrawn into the abdominal cavity. Human testes are also called testicles. Testis(also testicle), either of the paired male gonads. The testes are organs of reproduction and internal secretion. They are responsible for the formation of male sex hormones, chiefly testosterone, in humans. The egg-shaped organs are situated in the scrotum and measure on the average 4 cm in length and 3 cm in diameter. The parenchyma consists of seminiferous tubules. Congenital disorders of the testis include cryptorchidism and anorchism. Injury, such as contusion or rupture, may cause sharp pain, swelling of the scrotum, and hemorrhaging. For contusion, it is necessary to prescribe rest, application of cold to the scrotum, the use of an athletic supporter, and antibiotics. Open injuries require surgery. The most frequent inflammatory disease of the testis is orchitis. Testicular tuberculosis usually results from tuberculosis of the prostate or appendix testis. The testis becomes thickened and tuberous and adheres to the scrotum, and purulent fistulas are observed. Treatment is surgical, involving complete or partial removal of the testis. Injury from syphilis or brucellosis is less common. Diagnosis is based on the results of special tests and reactions. Treatment is by medication. Testicular tumors mainly occur early in life. The most common type is seminoma, although teratoblastoma and choriocarcinoma also occur. Treatment is chiefly surgical. A. L. SHABAD testis[′tes·təs]testistestis[tes´tis] (L.) If the testes are removed (castration" >castration, bilateral orchiectomy) before puberty, the male is sterile and will never develop all the adult male characters" >secondary sex characters. If they are removed after puberty, the male becomes sterile and his secondary sex characters will diminish unless he receives injections of male hormones. With aging, there is a gradual decrease in the production of testosterone. In the fetus in utero, the testes lie close to the kidneys. During approximately the seventh month of fetal life, the testes begin to descend through the abdominal wall at the groin and enter the scrotum. As they descend they are accompanied by blood vessels, nerves, and ducts, all contained within the spermatic cord. The passageway through which the testis and spermatic cord descend is called the inguinal canal. Failure of a testis to descend into the scrotum is called cryptorchidism. The testis is divided internally into about 250 compartments or lobules, each of which contains one to three small tubules" >convoluted tubules, within which spermatozoa are produced. When mature, the spermatozoa leave the tubules and enter the epididymis (situated on top of and behind each testis), where maturation is completed. The spermatozoa are stored in the epididymis until such time as they are mixed in the semen and ejaculated during coitus. (See also reproduction and male reproductive organs.) In order to ensure early detection of cancer of the testis, men are urged to conduct a monthly self-examination of the testes. The self-examination involves the use of both hands to examine each of the testes. The index and middle fingers are placed below the testis and the thumbs on top. With a gentle motion each testis is rolled between the thumbs and fingers to discover any lump (usually about the size of a pea), thickening, or change in the consistency of the tissues. It is important that the man become familiar with the feel of the epididymis so that he doesn't confuse this normal structure with an abnormal lump. Should a lump or any other abnormality be found, a doctor should be consulted immediately. The American Cancer Society publishes several pamphlets that explain the procedure for testicular self-examination and give additional information on testicular cancer. Diagnosis of testicular cancer is confirmed by biopsy of the suspect testis. There are three stages of classification for malignancy of the testis: Stage I: the tumor is confined to the affected testis; Stage II: the malignancy has spread to the regional lymph nodes; and Stage III: there is metastasis to other organs, such as the lung and liver. Treatment of testicular cancer (simple orchiectomy for Stage I malignancy) may or may not render the patient impotent and sterile. If there is no metastasis, only the affected testis need be removed. The remaining testis will retain its normal function and the patient should be able to have normal sexual intercourse and be fertile. However, if more radical surgery and radiation therapy are called for and both testes and the lymph nodes are dissected, and if there has been no damage to nerves during surgery, the patient may be able to have sexual intercourse but no seminal fluid will be emitted. A young man who is looking forward to having children may consider banking his sperm prior to surgery so that he might father children by artificial insemination.  tes·tis, pl.tes·tes(tes'tis, -tēz), [TA]See also: appendix testis. testis(tĕs′tĭs)testisEither of the pair of male sexual organs, which are located in the scrotum and produce sperm—beginning in puberty and then throughout life—as well as testosterone.tes·tis, pl. testes (tes'tis, -tēz) [TA]See also: appendix of testis Synonym(s): orchis [TA] , didymus, testicle. testis(tes'tis) plural.testes [L.] AnatomyEach is an ovoid body about 4 cm long and 2 to 2.5 cm in width and thickness, enclosed within a dense inelastic fibrous tunica albuginea. The testis is divided into numerous lobules separated by septa, each lobule containing one to three seminiferous tubules within which the spermatozoa are produced by meiosis. The lobules lead to straight ducts that join a plexus, the rete testis, from which 15 to 20 efferent ducts lead to the epididymis. The epididymis leads to the ductus deferens, through which sperm are conveyed to the urethra. Between the seminiferous tubules are the interstitial cells (cells of Leydig), which secrete testosterone. Within the tubules are sustentacular cells, which secrete inhibin. The testes are suspended from the body by the spermatic cord, a structure that extends from the inguinal ring to the testis and contains the ductus deferens, testicular vessels (spermatic artery, vein, lymph vessels), and nerves. DisordersHyperfunction (hypergonadism) may cause early maturity such as large sexual organs with early functional activity and increased growth of hair. Hypofunction (hypogonadism) is indicated by undeveloped testes, absence of body hair, high-pitched voice, sterility, smooth skin, loss of sexual desire, low metabolism, and eunuchoid or eunuch body type. descent of testisdisplaced testisfemoral testisinverted testisperineal testisundescended testisCryptorchidism..testisOne of the two male gonads, suspended in the scrotum by the spermatic cord. The testis, or testicle, contains the long, coiled seminiferous tubules in which the SPERMATOZOA are formed. Between the tubules are cells that secrete testosterone and other masculinizing steroid hormones and oestrogens.testis(pl. testes) the organ of the male animal, producing the male gametes, or sperms. It also produces ANDROGENS - male Dictionary of Biology 2005 9.5 2/6 /05 3:46 pm Page 465 sex hormones. See SCROTUM, SEMINIFEROUS TUBULES, GERMINAL EPITHELIUM, SERTOLI CELLS.Patient discussion about testisQ. Has anyone ever had Epididymitis? I was just diagnosed with it and want to know what to expect. Thanks testis
Synonyms for testis
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testis - one of the two male reproductive glands that produce spermatozoa and secrete androgens; "she kicked him in the balls and got away"