Stratified squamous epithelium
A stratified squamous epithelium consists of squamous epithelial cells arranged in layers upon a basal membrane. Only one layer is in contact with the basement membrane, the other layers adhere to one another to maintain structural integrity. Although this epithelium is referred to as squamous, many cells within the layers may not be flattened, in the deeper layers, the cells may be columnar or cuboidal. It forms the outermost layer of the skin and the lining of the mouth, esophagus. Non-keratinized surfaces must be kept moist by bodily secretions to prevent them drying out. Examples of non-keratinized stratified squamous epithelium include cornea, lining mucosa of oral cavity, anal canal, keratinized surfaces are protected from abrasion by keratin and kept hydrated and protected from dehydration by glycolipids produced in the stratum granulosum. Examples of keratinized stratified squamous epithelium include epidermis of the palm of the hand and sole of the foot, and the masticatory mucosa
Stratified cuboidal epithelium
Stratified cuboidal epithelium is a type of epithelial tissue composed of multiple layers of cube-shaped cells. Only the most superficial layer is made up of cells. This type of tissue can be observed in sweat glands, mammary glands, circumanal glands and they protect areas such as the ducts of sweat glands, mammary glands, and salivary glands. Overview at umdnj. edu Histology at KUMC epithel-epith17 Sweat Duct Histology image, 43_03 at the University of Oklahoma Health Sciences Center - Skin
If glands are categorized by shape, alveolar glands contrast with tubular glands. Alveolar glands have a saclike secretory portion, thus are termed saccular glands and they typically have an enlarged lumen, hence the name similar to alveoli, the smallest air sacs in the lungs. Branched alveolar glands are classified as follows, Some sources draw a distinction between acinar and alveolar glands, based upon the size of the lumen. A further complication in the case of the alveolar glands may occur in the form of still smaller saccular diverticuli growing out from the main sacculi, the term racemose gland is used to describe a compound alveolar gland or compound acinar gland
Transitional epithelium is a type of tissue consisting of multiple layers of epithelial cells which can contract and expand. It is so named because of this function in the transition of degree of distension and this tissue structure type is found in urothelium, including that of the renal pelvis, urinary bladder, the ureters, the superior urethra, and the prostatic and ejaculatory ducts of the prostate. The appearance of transitional epithelium depends on the layers in which it resides, cells of the basal layer are cuboidal, or cube-shaped, and columnar, or column-shaped, while the cells of the superficial layer vary in appearance depending on the degree of distension. These cells appear to be cuboidal with an apex when the organ or the tube in which they reside is not stretched. When the organ or tube is stretched, the tissue compresses, when this happens, the cells flatten, and they appear to be squamous and irregular. The transitional epithelium cells stretch readily in order to accommodate fluctuation of volume of the liquid in an organ, Transitional epithelium functions as barrier between the lumen, or inside hollow space, of the tract that it lines and the bloodstream.
To help achieve this, the cells of transitional epithelium are connected by tight junctions and this barrier prevents reabsorption of toxic wastes and pathogens by the bloodstream. Transitional epithelium is made up of three types of layers, basal and superficial. The basal layer fosters the epithelial cells in order to provide constant renewal of the epithelium. These cells cytoplasm is rich in tonofilaments and mitochondria, the tonofilaments play a role in the attachment of the basal layer to the basement membrane via desmosomes. The intermediate cell layer is highly proliferative and, provides for rapid cell regeneration in response to injury or infection of the organ or tube in which it resides and these cells contain a prominent Golgi apparatus and an array of membrane-bound vesicles. These function in the packaging and transport of proteins, such as keratin, the superficial cell layer, that which lines the lumen, is the only fully differentiated layer of the epithelium. It provides a barrier between the lumen and the bloodstream, so as not to allow the bloodstream to reabsorb harmful wastes or pathogens.
All transitional epithelial cells are covered in microvilli and a fibrillar mucous coat, the epithelium contains many intimate and delicate connections to neural and connective tissue. These connections allow for communication to tell the cells to expand or contract, the superficial layer of transitional epithelium is connected to the basal layer via cellular projections, such as intermediate filaments protruding from the cellular membrane. These structural elements cause the epithelium to allow distension, all cells touch the basement membrane. This impermeability is due to a highly keratinized cellular membrane synthesized in the Golgi apparatus, the membrane is made up of a hexagonal lattice put together in the Golgi apparatus and implanted into the surface of the cell by reverse pinocytosis, a type of exocytosis. The cells in the layer of the transitional epithelium are highly differentiated
Holocrine is a term used to classify the mode of secretion in exocrine glands in the study of histology. Holocrine secretions are produced in the cytoplasm of the cell and released by the rupture of the plasma membrane, holocrine secretion is the most damaging type of secretion, with merocrine secretion being the least damaging and apocrine secretion falling in between. Examples of holocrine glands include the sebaceous glands of the skin, the sebaceous gland is an example of a holocrine gland because its product of secretion is released with remnants of dead cells
Merocrine is a term used to classify exocrine glands and their secretions in the study of histology. Merocrine is the most common manner of secretion, the gland releases its product and no part of the gland is lost or damaged. The term eccrine is specifically used to designate merocrine secretions from sweat glands, salivary glands Pancreatic glands Certain sweat glands Diagram at uwa. edu. au
Pseudostratified columnar epithelium
A pseudostratified epithelium is a type of epithelium that, though comprising only a single layer of cells, has its cell nuclei positioned in a manner suggestive of stratified epithelia. As it rarely occurs as squamous or cuboidal epithelia, it is considered synonymous with the term pseudostratified columnar epithelium. The nuclei of cells, are disposed at different levels. Not all ciliated cells extend to the surface, such cells are capable of cell division providing replacements for cells lost or damaged. Pseudostratified epithelia function in secretion or absorption, if a specimen looks stratified but has cilia, it is a pseudostratified ciliated epithelium, since stratified epithelia do not have cilia. Ciliated pseudostratified columnar epithelia are found in the linings of the trachea as well as the respiratory tract. Non-ciliated pseudostratified columnar epithelia are located in the part of male vas deferens. Pseudostratified columnar epithelia with stereocilia are located in the epididymis, stereocilia of the epididymis are not cilia because their cytoskeleton is composed of actin filaments, not microtubules.
They are structurally and molecularly more similar to microvilli than to true cilia, pseudostratified columnar epithelia are found forming the straight, tubular glands of the endometrium in females