Simple squamous epithelium cells are flat in shape and arranged in a single layer. This single layer is thin enough to form a membrane that compounds can move through via passive diffusion. This epithelial type is found in the walls of capillaries, linings of the pericardium, and the linings of the alveoli of the lungs.
Simple cuboidal epithelium consists of a single layer cells that are as tall as they are wide. The important functions of the simple cuboidal epithelium are secretion and absorption. This epithelial type is found in the small collecting ducts of the kidneys, pancreas, and salivary glands. Simple columnar epithelium is a single row of tall, closely packed cells, aligned in a row.
These cells are found in areas with high secretory function such as the wall of the stomach , or absorptive areas as in small intestine.
They possess cellular extensions e. These are simple columnar epithelial cells whose nuclei appear at different heights, giving the misleading hence pseudo impression that the epithelium is stratified when the cells are viewed in cross section. Pseudostratified epithelium can also possess fine hair-like extensions of their apical luminal membrane called cilia. In this case, the epithelium is described as ciliated pseudostratified epithelium.
Ciliated epithelium is found in the airways nose, bronchi , but is also found in the uterus and fallopian tubes of females, where the cilia propel the ovum to the uterus. Stratified epithelium differs from simple epithelium by being multilayered.
It is therefore found where body linings have to withstand mechanical or chemical insults. Stratified epithelia are more durable and protection is one their major functions. Since stratified epithelium consists of two or more layers, the basal cells divide and push towards the apex, and in the process flatten the apical cells. Stratified epithelia can be columnar, cuboidal, or squamous type.
However, it can also have the following specializations:. In keratinized epithelia, the most apical layers exterior of cells are dead and lose their nucleus and cytoplasm. They contain a tough, resistant protein called keratin. This specialization makes the epithelium waterproof, and it is abundant in mammalian skin. The lining of the esophagus is an example of a non-keratinized or moist stratified epithelium. Transitional epithelia are found in tissues that stretch and it can appear to be stratified cuboidal when the tissue is not stretched, or stratified squamous when the organ is distended and the tissue stretches.
It is sometimes called the urothelium since it is almost exclusively found in the bladder, ureters, and urethra. Privacy Policy. Skip to main content. Organization at the Tissue Level. Search for:. Epithelial Tissue. Characteristics of Epithelial Tissue The human body consists of four types of tissue: epithelial, connective, muscular, and nervous.
In both cases, the transported materials are usually swallowed, and end up in the acidic environment of your stomach. Epithelial tissues are classified according to the shape of the cells and number of the cell layers formed Figure 4. Cell shapes can be squamous flattened and thin , cuboidal boxy, as wide as it is tall , or columnar rectangular, taller than it is wide.
Similarly, the number of cell layers in the tissue can be one—where every cell rests on the basal lamina—which is a simple epithelium, or more than one, which is a stratified epithelium and only the basal layer of cells rests on the basal lamina.
Transitional describes a form of specialized stratified epithelium in which the shape of the cells can vary. The shape of the cells in the single cell layer of simple epithelium reflects the functioning of those cells.
The cells in simple squamous epithelium have the appearance of thin scales. Squamous cell nuclei tend to be flat, horizontal, and elliptical, mirroring the form of the cell. The endothelium is the epithelial tissue that lines vessels of the lymphatic and cardiovascular system, and it is made up of a single layer of squamous cells.
Simple squamous epithelium, because of the thinness of the cell, is present where rapid passage of chemical compounds is observed. The alveoli of lungs where gases diffuse, segments of kidney tubules, and the lining of capillaries are also made of simple squamous epithelial tissue. The mesothelium is a simple squamous epithelium that forms the surface layer of the serous membrane that lines body cavities and internal organs. Its primary function is to provide a smooth and protective surface.
Mesothelial cells are squamous epithelial cells that secrete a fluid that lubricates the mesothelium. In simple cuboidal epithelium , the nucleus of the box-like cells appears round and is generally located near the center of the cell.
These epithelia are active in the secretion and absorptions of molecules. Simple cuboidal epithelia are observed in the lining of the kidney tubules and in the ducts of glands. In simple columnar epithelium , the nucleus of the tall column-like cells tends to be elongated and located in the basal end of the cells.
Like the cuboidal epithelia, this epithelium is active in the absorption and secretion of molecules. Simple columnar epithelium forms the lining of some sections of the digestive system and parts of the female reproductive tract. Ciliated columnar epithelium is composed of simple columnar epithelial cells with cilia on their apical surfaces. These epithelial cells are found in the lining of the fallopian tubes and parts of the respiratory system, where the beating of the cilia helps remove particulate matter.
Pseudostratified columnar epithelium is a type of epithelium that appears to be stratified but instead consists of a single layer of irregularly shaped and differently sized columnar cells. In pseudostratified epithelium, nuclei of neighboring cells appear at different levels rather than clustered in the basal end.
The arrangement gives the appearance of stratification; but in fact all the cells are in contact with the basal lamina, although some do not reach the apical surface. Pseudostratified columnar epithelium is found in the respiratory tract, where some of these cells have cilia. Both simple and pseudostratified columnar epithelia are heterogeneous epithelia because they include additional types of cells interspersed among the epithelial cells.
A stratified epithelium consists of several stacked layers of cells. This epithelium protects against physical and chemical wear and tear.
The stratified epithelium is named by the shape of the most apical layer of cells, closest to the free space. Simple columnar epithelial cells are some of the most prolific cells in the body, mainly because they can fulfill so many functions. Wann, David. Simple columnar epithelial cells are longer than they are wide.
Characteristically, their nucleui are found at the base of the cell. The cells are connected by tight junctions. The cells receive nutrients through the basement membrane, which separates the cells from the capillary basal layer. The main function of simple columnar epithelial cells are protection.
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