Thus, these epithelia do not need to keratinize to avoid desiccation. The lubrication provided by mucus helps to protect against abrasion. Again, cell morphology changes from base to apex of the epithelium, the outermost being "squamous" in appearance whereas the basal cells appear more cuboidal or low-columnar. The orientation of the tissue can be confusing because of connective tissue projections that push up into the epithelium.
Epithelial tissue covers surfaces with an uninterrupted layer of cells. Epithelial tissue comprises an uninterrupted layer of cells. Epithelium covers nearly all external and internal body surfaces.
Even when an epithelial surface seems to be penetrated by a hole such as a the pore of a gland that hole is really just an invagination of the epithelium i. Special devices intercellular junctions, tonofilaments provide for structural integrity of the epithelium.
There are several types of cell junctions. Keratinocytes are joined to one another by many adhering junctions. Tight occluding junctions block diffusion; they typically form a seal or gasket around the apical end of cells comprising simple epithelia i.
This junction helps assure adequate separation between different fluid compartments i. Gap junctions provide direct intercytoplasmic communication between joined cells. That is, ions or small molecules can pass through gap junctions directly from the cytoplasm of one cell into the cytoplasm of an adjacent cell, without passing into intercellular space.
Intercellular spaces in epithelium are small. Within the epithelium, the narrow spaces between cells are sealed off from the external environment by cell junctions near the free surface of the cells. Compared to ordinary connective tissue, epithelial tissue has very little interstitial fluid.
Epithelial tissue is polarized. An epithelium has a free surface, the apical surface, exposed to the outside, and an attached surface, the basal surface, resting on the underlying connective tissue.
In a simple single-layered epithelium, each cell is polarized. The base of each cell is attached to an underlying basement membrane while the apical end faces free space.
Lateral surfaces are attached to neighboring epithelial cells. Polarization of epithelial cell structure is particularly evident in secretory and absorptive cells where the arrangement of intracellular organelles reflects the directional transport of material.
Less visible but equally important is the localization of membrane proteins, which confer special properties to the membrane i. Epithelial cells are separated from the underlying tissue by a basement membrane.
The basement membrane is a thin sheet of collagen and glycoproteins produced in part by the epithelial cells themselves and in part by underlying connective tissue cells specifically, fibroblasts.
The basement membrane serves to regulate cell behavior and can limit the spread of some neoplasms. In certain places, the basement membrane assumes major significance.
For example, in glomeruli of the kidney it serves as a filter for blood plasma on its way to becoming urine. In other places, the absence of a basement membrane is notable and functionally significant. For example, the absence of a basement membrane in the liver permits blood plasma to contact hepatocytes directly.
These common features confer a characteristic appearance upon most epithelial tissues, no matter how various their cells may be. In nearly all epithelia, cells are attached to one another and thus evenly spaced, in distinct contrast with connective tissue cells which are scattered and not attached.
Many support cells and immune cells are typically unpolarized and quiescent, with little cytoplasm and with nuclei containing condensed chromatin. I n contrast, because many epithelial cells are actively manufacturing, secreting, absorbing or dividing, epithelial cells usually have conspicuous cytoplasm and large, relatively euchromatic nuclei with finely granular chromatin and with prominent nucleoli.
Each of the following examples illustrates the distinct difference between epithelial tissue and connective tissue. Click on a thumbnail image for an annotated enlargement.This web site was created for students at Austin Community College who are enrolled in Biology / Human Anatomy.
Lab time is limited, and there is never enough time to become really familiar with all of the histology slides. Start studying Characteristics of Epithelial Tissues. Learn vocabulary, terms, and more with flashcards, games, and other study tools.
A comprehensive, fun and entertaining site devoted exclusively to histology. Learning histology was never so easy! This site includes histology quizzes, histology games, slides, mnemonics, histology puzzles and tons of information about histology. One of the best histology sites on the internet! Be able to classify epithelial tissues. Know the structure and function of junctions. Know the structure of apical specializations and their functions. Welcome to lab classes in basic histology. 33 Introducing lab class (in spanish) The aim of these lab classes is to provide students with educational resources to acquire basic practical skills of each subject, recognize, locate and describe cell types and basic tissues. Each of these practical sessions are structured around three main elements: .
A comprehensive, fun and entertaining site devoted exclusively to histology. Learning histology was never so easy! This site includes histology quizzes, histology games, slides, mnemonics, histology puzzles and tons of information about histology.
One of the best histology sites on the internet! Histology of tumor tissue remains the bedrock upon which diagnosis is established and is the basis for selecting appropriate testing to guide treatment.
Histologic diagnosis, although simple in concept, is extremely complex in practice and crucially depends on the expertise of the examining pathologist.
Tissue: Tissue, in physiology, a level of organization in multicellular organisms; it consists of a group of structurally and functionally similar cells and their intercellular material. By definition, tissues are absent from unicellular organisms.
Even among the simplest multicellular species, such as. Epithelia are tissues consisting of closely apposed cells without intervening intercellular substances. Epithelia are avascular, but all epithelia "grow" on an underlying layer of vascular connective tissue. The connective tissue and the epithelium are separated by a basement membrane.