They are tightly packaged and smaller than those of the upper layers. The adult stem cells that proliferate and differentiate to replace cells of the upper layers are found in this layer. As they detach from the basal layer and migrate toward the superficial layer, they increase in size and differentiated. The proliferative activity of the transitional epithelium is low under normal conditions, but it may be increased after injuries, when it shows a strong regenerative capability.
For example, when superficial cells are damaged, intermediate cells quickly differentiate to replace the superficial lost cells. It has been proposed that all cells of the transitional epithelium send processes that make physical contact with the basal lamina, at least in some species. Arrighi S. The urothelium: Anatomy, review of the literature, perspectives for veterinary medicine.
Annals of anatomy. Transitional epithelium. Connective tissue. Epithelial cells may be squamous, cuboidal, or columnar in shape and may be arranged in single or multiple layers. Simple cuboidal epithelium is found in glandular tissue and in the kidney tubules. Simple columnar epithelium lines the stomach and intestines. Pseudostratified columnar epithelium lines portions of the respiratory tract and some of the tubes of the male reproductive tract.
Epithelia tissue forms boundaries between different environments, and nearly all substances must pass through the epithelium. In its role as an interface tissue, epithelium accomplishes many functions, including:.
Epithelial tissue is composed of cells laid out in sheets with strong cell-to-cell attachments. These protein connections hold the cells together to form a tightly connected layer that is avascular but innervated in nature. The epithelial cells are nourished by substances diffusing from blood vessels in the underlying connective tissue. One side of the epithelial cell is oriented towards the surface of the tissue, body cavity, or external environment and the other surface is joined to a basement membrane.
The basement layer is non-cellular in nature and helps to cement the epithelial tissue to the underlying structures. Epithelial tissues are identified by both the number of layers and the shape of the cells in the upper layers. There are eight basic types of epithelium: six of them are identified based on both the number of cells and their shape; two of them are named by the type of cell squamous found in them. Epithelial tissue is classified based on the number of cells, the shape of those cells, and the types of those cells.
Air sacs of the lungs and the lining of the heart, blood vessels and lymphatic vessels Allows materials to pass through by diffusion and filtration, and secretes lubricating substances Simple cuboidal epithelium. In ducts and secretory portions of small glands and in kidney tubules Secretes and absorbs Simple columnar epithelium.
Ciliated tissues including the bronchi, uterine tubes, and uterus; smooth nonciliated tissues are in the digestive tract bladder Absorbs; it also secretes mucous and enzymes. Pseudostratified columnar epithelium.
Ciliated tissue lines the trachea and much of the upper respiratory tract Secrete mucous; ciliated tissue moves mucous Stratified squamous epithelium.
Lines the esophagus, mouth, and vagina Protects against abrasion Stratified cuboidal epithelium. Sweat glands, salivary glands, and mammary glands Protective tissue Stratified columnar epithelium. The male urethra and the ducts of some glands. Secretes and protects Transitional epithelium.
Lines the bladder, urethra and ureters Allows the urinary organs to expand and stretch Types of Epithelial Tissue Epithelial tissue is classified by cell shape and the number of cell layers. Most epithelial tissue is described with two names. The first name describes the number of cell layers present and the second describes the shape of the cells. For example, simple squamous epithelial tissue describes a single layer of cells that are flat and scale-like in shape.
Epithelial Tissue : There are three principal classifications associated with epithelial cells. Squamous epithelium has cells that are wider than they are tall. Cuboidal epithelium has cells whose height and width are approximately the same. Columnar epithelium has cells taller than they are wide. Simple epithelium consists of a single layer of cells. They are typically where absorption, secretion and filtration occur. The thinness of the epithelial barrier facilitates these processes.
Simple epithelial tissues are generally classified by the shape of their cells.
0コメント