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Home >>Biology Dictionary >> Thread Cell - Tissue Culture
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Thread cell. (nematoblas; cnidoblast). A specialized cell found only in the ectoderm of the Coelenterata. It contains a nematocyst, a fluid filled sac within which lies a long hollow coiled thread. When a small sensory projection (cnidocil)on the surface of the thread cell is touched, e.g. by prey, the thread is shot out and adhered to the prey, coils round it or injects poison into it. Numerous thread cells on the tentacles of jellyfish produce their sting.
Threadworms. Nematoda.
Threshold. That intensity of stimulus below which there is no response by a givln irritable tissue.
Thrombin. See Blood Clotting.
Thrombocyte. See Blood Platelet.
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Tymocyte. A lymphocyte in the thymus.
Thymonucleic acid. DNA. First extracted from thymus, which is rich in nuclei.
Thymus. Organ of vertebrates, usually in pharyngeal or neck region, formed embryologically from gill prouches or gillclefts. In mammals it lies in chest, and the cells from gillprouches are mixed up with masses of lymphotes; the organ reaches maximum size at puberty, and thereafter slowly diminishes.
Tylakoid. In photosyntheric organisms, vesicle, wall of which bears photosynthetic pigments. Thylakoids vary in form and arrangement in different groups of organisms.
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Thyroglobulin. A protein containing and storing thyroxine and triod – thyroxine in the thyroid gland.
Thyrotropic. (Thyrotrophic) hormone (Tsh). Hormone secreted by anterior lobe of pituitary, stimulating secretory activity and, in high doses, growth of thyroid gland.
Thysanoptera. The insect order containing the trips, major pests of corals and furits.
Tibial. Of or in the region of the Tiba.
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Tissue. Cellular fabric, of many varieties, of which organisms are made. Each consists mainly of cells of the same sort associated in large numbers in characteristic arrangement, bound together by cell-walls or by intercellular material or the numerous striped muscle fibres, bound together by collagen with associated blood and tymph vessel, nerves and connective tissue cells, which make up muscle tissue.
A collection of similar cells organized to carry out one or more particular functions. For example, in animals nervous tissue is specialized to perceive and transmit stimuli. An organ, such as a lung or kidney, contains many different types of tissues.
Tonsil. Mass of lymphoid tissue in mouth or pharynx of tetrapods. It lies underneath mucous membrane, deep crevices of which may communicate with interior of tonsil. Man has a pair of palatine tonsils (at junction of mouth and pharynx) and a single paryngeal tonsil.
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Tissue Culture. The growth of the tissue of living organisms outside the body in a suitable culture medium. Culture (or nutrient) media contain a mixture of nutrients either in solid form (e.g. in agar) or in liquid form (e.g. in physiological saline). Tissue culture has proved to be invaluable for gaining information about factors that control the growth and differentiation of cells.
Tomentum. The dense covering of short cottony hair on some plant structures.
Tongue. A muscular organ of vertebrates that in most species is attached to the floor of the mouth. It plays an important role in manipulating food during chewing and swallowing and in terrestrial specie sit bears numerous taste buds on its upper surface. In some advanced vertebrates the tongue is used in the articulation of sounds, particularly in human speech.
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Tonus (Tone). Continuous but moderate, physiological activity of a tissue or organ; e.g. striped muscle, as a result of the continuous nervous stimulation, is normally in a state of moderator contraction (tonus), by which the posture of the animal is maintained.
Thyroid gland. A bilobed endocrine gland in vertebrates, situated in the base of the neck. It secretes two iodine containing hormones, thyroxine and triiodoyrosine, which control the rate of all metabolic processes in the body and influence physical development. Growth and activity of the thyroid is controlled by a hormonene, thyrotrophin (or thyroid-stimulating hormone), secreted by the anterior pituitary gland.
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