Atlas of plant and animal histology

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Glossary: T


Tanyciyte: it is a type of glial cell found in the central nervous system. The tanycyte cell body is usually located among ependymal cells, although sometimes is far from them. Tanycytes have one apical process or the soma itself in contact with the cerebrospinal fluid, and a basal process that extends into the surrounding nervous tissue. This process generally ends at the blood vessel surface or at the pial membrane surface..

♣ Animal tissues: Epéndimo.

Taste bud: it is a sensory structure found in the oral cavity, mainly in the tongue papillae. Taste buds are responsible for sensing molecules that provide taste. Cells in the taste buds are organized resembling a head of garlic. There are three types of cells: subtentacular or support cells found in the periphery, sensory neuroepithelial cells situated innerly, and basal cells found basal and peripherally, near the basal lamina of the taste bud.

♣ Animal organs: Senses.

Tegmen: (in plants) it is the inner coat of the seed episperm. Tegmen is developed from the integument of the ovule.

♣ Plant organs: Seed.

Testa: (in plants) it is one layer of the seed coat. The testa is differentiated from a outer layer of the integument surrounding the embryo.

♣ Plant organs: Seed.

Tetrarch root: (in plants) it is a type of root with four rows, or poles, of protoxylem.

♣ Plant organs: Root: primary growth.

Thalamus: it is the p2 part of the diencephalon, one of the compartments of the brain. Except for the olfactory information, the thalamus modulates all sensory information projecting to the cerebral cortex, which in turn sends information back to the thalamus. The habenula is found in the dorsal part of the thalamus. The pineal gland, or epiphysis, is also associated with the thalamus.

Theca: (in plants) it is each of the compartments of the anther of the stamens in flowers.

♣ Plant organs: Flower, Flower: parts, Stamens.

Thermoreceptor: it is a type of sensory receptor that detects changes in temperature. Thermoreceptors are abundant in the skin as free nerve endings.

♣ Aninal organs: Senses.

Thymus: it is an organ of animals located just above the heart and before the large blood vessels. The thymus is derived from the endoderm that form the pharynx and develops its functions from the birth to puberty. The thymus is an organ where T lymphocytes mature. After puberty, the thymus is replaced by adipose tissue.

♣ Aniimal organs: Cardiovascular, Lymphatic system .

Thyroid: it is a gland found in the front part of the trachea, close to the laryngeal prominence (Adan's apple). Thyroid secretory cells are arranged in follicles and release thyroglobulin toward the follicle lumen. From thyroglobulin, the thyroid synthesizes and releases tyroxine (T4) and triiodotiroxine (T3) hormones into the blood stream.

♣ Animal tissues: Glandular epithelium, Thyroid .

Tight junction: it is a type of cell junction found in the apical domain of epithelial cells. They can be also found in other tissues like cardiac muscle. Tight junctions strongly adhere adjoining cells between each other, so much that occlude the intercellular space.

♣ Anical tissues: Epithelium, Cardiac muscle.

Tissue: (from latin texere = weave)it is a group of cells that work together to carry out one or several functions in organisms such as plants and animals.

♣ Plant tissues: Introduction.
♣ Animal tissues: Introduction.

Trabecular bone: it is a type of bone organization found in the deep part of bones, usually surrounded by compact bone. In the trabecular bone, there are bone lamellas organized in trabeculae that leave large and irregular cavities known as vascular cavities. That is why this type of bone tissue is also known as spongy bone. Bone cavities contain many blood vessels and hematopoietic cells that together with connective tissue form the bone marrow.

Trachea: (in plants) they are also known as vessels. Tracheae are the main conducting cells of the xylem of angiosperms. They are dead cells organized in rows that communicate between each other by perforated plates. The lateral cell walls of the tracheae cells show thickenings resembling rings, spirals and reticular structures.

♣ Plant tissuess: Vascular, Metaxylem, Xylem.

Tracheary elements: (in plants)they are the conducting cells of the xylem. Tracheary elements are the vessel elements and tracheids.

♣ Plant tissues: Vascular tissue , Metaxylem.

Tracheid: (in plants) it is a type of conducting cell of the xylem. The main role of tracheids is to conduct water and minerals from the roots to the rest of the plant body. Tracheids are also a mayor supporting cell. Tracheids are elongated cells, with lignified secondary wall showing pit areas. They are the only conducting cell type in gymnosperms.

Transitional epithelium: it is a type of covering epithelium consisting in non-uniform epithelial cells that are not organized in well-defined layers within the epithelial sheet. The thickness of the transitional epithelium may change dramatically to be adapted to the changes of the structure dimension. Transitional epithelium lines excretory structures like the urinary bladder.

Triarch root: (in plants) it is a type of root with three rows, or poles, of protoxylem.

♣ Plant organs: Root: primary grow.

Trichoma: (in plants) it is epidermal structure made up of one or several specialized epidermal cells. Trichomas are variable in number and shape, may be unicellular or multicellular, filaments or branched. They can protect against dehydration and herbivores, and many of them are glandular structures.

♣ Plant organs: Primary stem, Flower.

Tubular gland: it is a type of exocrine gland whit the secretory unit not wider than the excretory duct. Thus, the secretory and excretory parts are tube-like structures.

Tubulo-acinar gland: it is a type of exocrine compound gland where the secretory units can be either tubular or acinar. The excretory ducts of both types of secretory units drain into the same final excretory duct.

Tunica adventitia: see adventitia.

Tunica albuginea: it is a sheet of dense connective tissue that encloses the seminiferous tubules of testis, and also overlies the corpus cavernosum of the penis. The tunica albuginea forms septa toward the inner part of the testis that divide the seminiferous tubules into lobes.

♣ Tejidos animales: Conectivo denso irregular.

Tunica fibrosa: (or fibrous tunica) see sclerotica

Tunica íntima: it is the layer that lines the lumen of arteries and veins. Tunica intima is composed of endothelium and subendothelial tissue where the extracellular matrix plays a major role.

Tunica media: it is a sheet of tissue found between the tunica intima and the tunica adventitia in arteries and veins . The tunica media is very thick in large arteries and thin in veins. It is composed of smooth muscle cells and abundant extracellular matrix containing collagen and elastic fibers.

Tympanic cavity: it is a space in the temporal bone of the head where the middle ear is enclosed. Tympanic cavity is separated from the ear canal by the tympanic membrane. There are three bones (malleus, incus, and stirrup) and the muscles responsible for their movement in the typanic cavity.

♣ Animal organs: Senses.

Tympanic membrane: (or tympanum) it is the layer of tissue that separates the external from the internal ear. The tympanic membrane transmits the air vibrations, coming from the environment, to the ossicles of the middle ear.

♣ Animal organs: Senses .

Tympanum: (or tympanic membrane) it is a membrane of the auditory system that vibrates with the sound waves coming from the environment through the external auditory canal. These vibrations are directly transmitted to the hammer bone of the middle ear.

♣ Animal organs: Senses.
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