Tunica


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tunica

[′tü·nə·kə]
(biology)
A membrane or layer of tissue that covers or envelops an organ or other anatomical structure.

Tunica

 

(1) In animals, the peripheral layer of skin coverings of ascidians, salpids, and other animals of the subphylum Tunicata, phylum Chordata. The tunica is a thickened cuticle of cutaneous epithelium that is colonized by cells, a unique phenomenon in the animal kingdom. It serves to protect the internal organs.

The tunica is composed of tunicin, a carbohydrate closely related to cellulose. This substance has a gelatinous consistency, which makes possible the implantation in the tunica of cells that migrate from the cutaneous epithelium. In histological structure, the tunica resembles connective tissue with a gelatinous basal substance. Blood vessels may grow into the tunica. In appendicu-larians, the tunica separates from the body as the result of a process that resembles molting, forming a transparent gelatinous or chitinoid membrane, which serves as an outer covering of the animal or which is appended to the animal externally. This structure is adapted to filtering food particles out of seawater.

(2) In plants, one or more external layers of cells of formative tissue (meristem) covering the corpus of the growing point (apex) in the form of a vault. Dicotyledons have as many as five tunicae, while monocotyledons have as many as three.

Cell division in the tunica predominantly occurs anticlinally, or perpendicular to the surface of the organ; hence the surface of the tunica enlarges without change in the number of cell layers. The epidermis is usually formed from the outer layer of the tunica, which corresponds to the dermatogen according to the histogen theory of the German botanist J. von Hanstein; the primary cortex or part of it is formed from the inner layer of the tunica. The tunica-corpus theory was proposed by the German scientist A. Schmidt in 1924. Sometimes only the layers of cells located higher than the rudimentary leaves are called the tunica. The number of layers of the tunica sometimes increases gradually, but always remains a characteristic taxonomical feature of the plant.

References in periodicals archive ?
Also, the company mentioned that it acquired the operations of Resorts Casino Tunica, along with Bally's Casino Tunica (subsequently renamed "1st Jackpot"), in March 2017.
Tambien se observo una hipertension asintomatica con aumento del grosor de la tunica media en arterias pulmonares, con la capa muscular extendiendose hasta las arteriolas, aumentando la resistencia vascular pulmonar como una respuesta adaptativa (Penaloza, 2012).
In view of above facts, this study was designed to evaluate the effects of supplementation of oregano dried leaves powder in quail diet on the villus height, crypt depth and tunica muscularis thickness in the quail intestine, which directly influence the nutrient absorption and utilization leading to improved performance of broiler.
Tunica Airport said its partnership with Ashley Air and Travel will enhance the area's tourism industry by opening up its gaming and entertainment product to millions of consumers in four major markets.
Group A (24 patients) underwent Tunica Vaginalis Flap (TVF) repair as soft tissue cover after urethroplasty.
De estos principios se puede establecer que existen inconsistencias en la denominacion latina de Tunica y la traduccion al espanol que figura como Capa.
The tunica albuginea was circumferentially dismembered (Ruptured) and the testicle was seen as nearly two separate lobes.
The amount of decorin staining in subsinusoidal areas of tunica albuginea (SATA) and subsinusoidal areas of trabecular wall (SATW) are summarized in Table 1.
Tunica muscularis of esophagus of duck was made up of thick inner circular and narrow outer longitudinal smooth muscle fibers layers.
The lining of the testicles is known as the tunica vaginalis.
A tunica adventicia, nas regioes cranial e media, esta revestindo a tunica muscular, sendo constituida de tecido conjuntivo frouxo, celulas adiposas, vasos sanguineos e terminacoes nervosas (Figuras 1A e 1B).