Also found in: Dictionary, Thesaurus, Medical, Wikipedia.
Related to Tunica: tunica intima, tunica adventitia, tunica externa, tunica media, tunica albuginea


A membrane or layer of tissue that covers or envelops an organ or other anatomical structure.



(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 ?
4] Malignant mesothelioma originating from the tunica vaginalis is extremely rare.
It involves the pleura, less frequently the peritoneum and very rarely the pericardium or the tunica vaginalis of the testis.
In a review of the literature, there was one reported case (5) with a purely sarcomatoid pattern in a mesothelioma of the tunica vaginalis testis; however, such tumors have been more often described in pleural and peritoneal malignant mesotheliomas.
While the blues trail shines light on Mississippi's esteemed musical heritage, Tunica offers modern head-liners, including Reba McIntire, Rob Thomas, Billy Idol, and Vince Gill.
Tunica is now more well-positioned than ever to continue growing and contributing to Mississippi's economy, whereas 15 years ago, it was a drain on the economy.
Before the casinos opened up and provided employment, Tunica County had an odd distinction, said Susalla.
If outdoor recreation is what you need, try a round of golf at one of Tunica's two PGA Championship courses--Cottonwoods at Grand Casino Tunica, or River Bend Links at Casino Strip Resorts.
He added the responsibilities of Vice President of Non-Gaming Operations in March 2008 and held both roles until January 2010 when he was named Assistant General Manager of Harrah's Tunica.
The Tunica facility will produce MyCar, a two-seat Neighborhood Electric Vehicle (NEV) that produces zero emissions, provides segment-leading range per charge and can be recharged via a common 110V wall outlet, a 220V wall outlet or fast charging stations.
Just ask the over 15,000 people who now work and are moving to Tunica County, Mississippi.
Carlucci, most recently the Assistant General Manager at Penn National's Boomtown Biloxi property, fills the General Manager position at Hollywood Casino Tunica previously held by John Osborne, who was named the General Manager of Penn National's Hollywood Slots Hotel & Raceway in Bangor, Maine on September 28.
26, 2014 /PRNewswire/ -- The Fitz Casino & Hotel, Tunica is hosting, accepting and making the ALS Ice Bucket Challenge on September 5[sup.