Epithelium in the context of "Blood vessel"

In biology, tissue is an assembly of similar cells and their extracellular matrix from the same embryonic origin that together carry out a specific function. Tissues occupy a biological organizational level between cells and a complete organ. Accordingly, organs are formed by the functional grouping together of multiple tissues.

The English word "tissue" derives from the French word "tissu", the past participle of the verb tisser, "to weave".

The cervix (pl.: cervices) or uterine cervix (Latin: cervix uteri) is a dynamic fibromuscular sexual organ of the female reproductive system that connects the vagina with the uterine cavity. The human female cervix has been documented anatomically since at least the time of Hippocrates, over 2,000 years ago. The cervix is approximately 4 cm (1.6 in) long with a diameter of approximately 3 cm (1.2 in) and tends to be described as a cylindrical shape, although the front and back walls of the cervix are contiguous. The size of the cervix changes throughout a female's life cycle. For example, females in the fertile years of their reproductive cycle tend to have larger cervixes than postmenopausal females; likewise, females who have produced offspring have a larger cervix than those who have not.

In relation to the vagina, the part of the cervix that opens into the uterus is called the internal os while the opening of the cervix into the vagina is called the external os. Between those extremes is the conduit commonly called the cervical canal. The lower part of the cervix, known as the vaginal portion of the cervix (or ectocervix), bulges into the top of the vagina. The endocervix borders the uterus. The cervical conduit has at least two types of epithelium (lining): the endocervical lining is glandular epithelia that lines the endocervix with a single layer of column-shaped cells; while the ectocervical part of the conduit contains squamous epithelium. Squamous epithelia line the conduit with multiple layers of cells topped with flat cells. These two linings converge at the squamocolumnar junction (SCJ). This junction changes location dynamically throughout a female's life. The cervix is the organ that allows epithelia to flow from a female's uterus and out through her vagina at menstruation. Menstruation releases epithelia from a female’s uterus with every period of her fertile years, unless pregnancy occurs.

The trachea (pl.: tracheae or tracheas), also known as the windpipe, is a cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all animals' lungs. The trachea extends from the larynx and branches into the two primary bronchi. At the top of the trachea, the cricoid cartilage attaches it to the larynx. The trachea is formed by a number of horseshoe-shaped rings, joined together vertically by overlying ligaments, and by the trachealis muscle at their ends. The epiglottis closes the opening to the larynx during swallowing.

The trachea begins to form in the second month of embryo development, becoming longer and more fixed in its position over time. Its epithelium is lined with column-shaped cells that have hair-like extensions called cilia, with scattered goblet cells that produce protective mucins. The trachea can be affected by inflammation or infection, usually as a result of a viral illness affecting other parts of the respiratory tract, such as the larynx and bronchi, called croup, that can result in a cough. Infection with bacteria usually affects the trachea only and can cause narrowing or even obstruction. As a major part of the respiratory tract, the trachea, when obstructed, prevents air from entering the lungs; thus, a tracheostomy may be required. Additionally, during surgery, if mechanical ventilation is required during anaesthesia, a tube is inserted into the trachea: this is called tracheal intubation.

Cnidaria (/nɪˈdɛəriə, naɪ-/ nih-DAIR-ee-ə, ny-) is a phylum under kingdom Animalia containing over 11,000 species of aquatic invertebrates found both in freshwater and marine environments (predominantly the latter), including jellyfish, hydroids, sea anemones, corals and some of the smallest marine parasites. Their distinguishing features are an uncentralized nervous system distributed throughout a gelatinous body and the presence of cnidocytes or cnidoblasts, specialized cells with ejectable organelles used mainly for envenomation and capturing prey. Their bodies consist of mesoglea, a non-living, jelly-like substance, sandwiched between two layers of epithelium that are mostly one cell thick. Many cnidarian species can reproduce both sexually and asexually.

Cnidarians mostly have two basic body forms: swimming medusae and sessile polyps, both of which are radially symmetrical with mouths surrounded by tentacles that bear cnidocytes, which are specialized stinging cells used to capture prey. Both forms have a single orifice and body cavity that are used for digestion and respiration. Many cnidarian species produce colonies that are single organisms composed of medusa-like or polyp-like zooids, or both (hence they are trimorphic). Cnidarians' activities are coordinated by a decentralized nerve net and simple receptors. Cnidarians also have rhopalia, which are involved in gravity sensing and sometimes chemoreception. Several free-swimming species of Cubozoa and Scyphozoa possess balance-sensing statocysts, and some have simple eyes. Not all cnidarians reproduce sexually, but many species have complex life cycles of asexual polyp stages and sexual medusae stages. Some, however, omit either the polyp or the medusa stage, and the parasitic classes evolved to have neither form.

Gastrulation is the stage in the early embryonic development of most animals, during which the blastula (a single-layered hollow sphere of cells), or in mammals, the blastocyst, is reorganized into a two-layered or three-layered embryo known as the gastrula. Before gastrulation, the embryo is a continuous epithelial sheet of cells; by the end of gastrulation, the embryo has begun differentiation to establish distinct cell lineages, set up the basic axes of the body (e.g. dorsal–ventral, anterior–posterior), and internalized one or more cell types, including the prospective gut.

The ureters are tubes composed of smooth muscle that transport urine from the kidneys to the urinary bladder. In adult humans, the ureters are typically 20–30 centimeters long and 3–4 millimeters in diameter. They are lined with urothelial cells, a form of transitional epithelium, and feature an extra layer of smooth muscle in the lower third to aid peristalsis.The ureters can be affected by diseases including urinary tract infections and kidney stones. Stenosis is the narrowing of a ureter, often caused by chronic inflammation. Congenital abnormalities can cause development of two ureters on the same side or abnormally placed ureters. Reflux of urine from the bladder into the ureters is common in children.

The ureters have been identified for at least two thousand years, with the word ureter stemming from the stem uro- relating to urinating and seen in written records since at least the time of Hippocrates. It is, however, only since the 16th century that the term "ureter" has been consistently used to refer to the modern structure, and only since the development of medical imaging in the 20th century that techniques such as X-ray, CT, and ultrasound have been able to view the ureters. The ureters are also seen from the inside using a flexible camera, called ureteroscopy, which was first described in 1964.