The main functions of epithelia are protection from the environment, coverage, secretion and excretion, absorption, and filtration. Cells are bound together by tight junctions that form an impermeable barrier.
They can also be connected by gap junctions, which allow free exchange of soluble molecules between cells, and anchoring junctions, which attach cell to cell or cell to matrix. The different types of epithelial tissues are characterized by their cellular shapes and arrangements: squamous, cuboidal, or columnar epithelia. Single cell layers form simple epithelia, whereas stacked cells form stratified epithelia.
Very few capillaries penetrate these tissues. Glands are secretory tissues and organs that are derived from epithelial tissues. Exocrine glands release their products through ducts. Endocrine glands secrete hormones directly into the interstitial fluid and blood stream. Glands are classified both according to the type of secretion and by their structure.
Merocrine glands secrete products as they are synthesized. Apocrine glands release secretions by pinching off the apical portion of the cell, whereas holocrine gland cells store their secretions until they rupture and release their contents. In this case, the cell becomes part of the secretion. In observing epithelial cells under a microscope, the cells are arranged in a single layer and look tall and narrow, and the nucleus is located close to the basal side of the cell.
The specimen is what type of epithelial tissue? Which of the following is the epithelial tissue that lines the interior of blood vessels? Which type of epithelial tissue specializes in moving particles across its surface and is found in airways and lining of the oviduct?
The structure of a tissue usually is optimized for its function. Describe how the structure of the mucosa and its cells match its function of nutrient absorption. The mucosa of the intestine is highly folded, increasing the surface area for nutrient absorption. A greater surface area for absorption allows more nutrients to be absorbed per unit time. In addition, the nutrient-absorbing cells of the mucosa have finger-like projections called microvilli that further increase the surface area for nutrient absorption.
Skip to content The Tissue Level of Organization. Learning Objectives By the end of this section, you will be able to: Explain the structure and function of epithelial tissue Distinguish between tight junctions, anchoring junctions, and gap junctions Distinguish between simple epithelia and stratified epithelia, as well as between squamous, cuboidal, and columnar epithelia Describe the structure and function of endocrine and exocrine glands and their respective secretions.
The Epithelial Cell Epithelial cells are typically characterized by the polarized distribution of organelles and membrane-bound proteins between their basal and apical surfaces.
Cell to Cell Junctions Cells of epithelia are closely connected and are not separated by intracellular material. Types of Cell Junctions. The three basic types of cell-to-cell junctions are tight junctions, gap junctions, and anchoring junctions. Classification of Epithelial Tissues Epithelial tissues are classified according to the shape of the cells and number of the cell layers formed Figure.
Cells of Epithelial Tissue. Simple epithelial tissue is organized as a single layer of cells and stratified epithelial tissue is formed by several layers of cells. Goblet Cell. Stratified Epithelium A stratified epithelium consists of several stacked layers of cells. Summary of Epithelial Tissue Cells. Glandular Epithelium A gland is a structure made up of one or more cells modified to synthesize and secrete chemical substances.
Endocrine Glands The secretions of endocrine glands are called hormones. Exocrine Glands Exocrine glands release their contents through a duct that leads to the epithelial surface. Glandular Structure Exocrine glands are classified as either unicellular or multicellular. Types of Exocrine Glands. Modes of Glandular Secretion.
These glands secrete oils that lubricate and protect the skin. They are holocrine glands and they are destroyed after releasing their contents. New glandular cells form to replace the cells that are lost.
Chapter Review In epithelial tissue, cells are closely packed with little or no extracellular matrix except for the basal lamina that separates the epithelium from underlying tissue. Interactive Link Questions Watch this video to find out more about the anatomy of epithelial tissues. The inside of the mouth, esophagus, vaginal canal, and anus. 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. Blood Vessels and Endothelial Cells. Molecular Biology of the Cell. Anatomy and physiology. Types of Epithelial Tissue. Medicine Libretexts. Simple Squamous Epithelium. Epithelial cells. Systems Cell Biology at Yale.
Lumen, Boundless Anatomy and Physiology. Chapter 2. Mesothelium and Malignant Mesothelioma. Journal of developmental biology, 7 2 , 7. Diverse properties of the mesothelial cells in health and disease. Pleura and peritoneum, 1 2 , 79— Epithelial Pathology. Color Atlas of Oral and Maxillofacial Diseases. Epithelial tissues.
An Atlas of Comparative Vertebrate Histology. Mesothelial cells: Their Structure, Function and Role in serosal repair. Mesothelial cells. Encylopedia of Respiratory Medicine. What is the Mesothelium. Osmoregulation is the regulation of water concentrations in the bloodstream, effectively controlling the amount of water..
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Table of Contents. Biology definition: Simple squamous epithelium is a type of simple epithelium made up of squamous epithelial cells that lines the outer layer of the skin, endothelium, and secretory parts of the small glands. It also lines the glomeruli in the kidney and the pulmonary alveoli where passive diffusion occurs. Synonyms: simple squamous epithelial tissue; pavement epithelium.
Quiz Choose the best answer. What is a simple squamous epithelium? An epithelial tissue composed of several layers of epithelial cells. For example, cilia are extensions of the apical cell membrane that are supported by microtubules. These extensions beat in unison, allowing for the movement of fluids and particles along the surface. Such ciliated epithelia line the ventricles of the brain where it helps circulate cerebrospinal fluid and line the respirtatory system where it helps sweep particles of dust and pathogens up and out of the respiratory tract.
Epithelial cells in close contact with underlying connective tissues secrete glycoproteins and collagen from their basal surface which forms the basal lamina. The basal lamina interacts with the reticular lamina secreted by the underlying connective tissue, forming a basement membrane that helps anchor the layers together. Cells of epithelia are closely connected with limited extracellular material present. Three basic types of connections may be present: tight junctions, anchoring junctions, and gap junctions Figure 4.
Epithelial cells are held close together by cell junctions. The three basic types of cell-to-cell junctions are tight junctions, gap junctions, and anchoring junctions. A Tight junction restricts the movement of fluids between adjacent cells due to the presence of integral proteins that fuse together to form a firm seal. Tight junctions are observed in the epithelium of the urinary bladder, preventing the escape of fluids comprising the urine. An anchoring junction provides a strong yet flexible connection between epithelial cells.
There are three types of anchoring junctions: desmosomes, hemidesmosomes, and adherens. Desmosomes hold neighboring cells together by way of cadherin molecules which are embedded in protein plates in the cell membranes and link together between the adjacent cells. Hemidesmosomes , which look like half a desmosome, link cells to components in the extracellular matrix, such as the basal lamina.
While similar in appearance to desmosomes, hemidesmosomes use adhesion proteins called integrins rather than cadherins. Adherens use either cadherins or integrins depending on whether they are linking to other cells or matrix. These junctions are characterized by the presence of the contractile protein actin located on the cytoplasmic surface of the cell membrane. These junctions influence the shape and folding of the epithelial tissue.
In contrast with the tight and anchoring junctions, a gap junction forms an intercellular passageway between the membranes of adjacent cells to facilitate the movement of small molecules and ions between cells.
These junctions thus allow electrical and metabolic coupling of adjacent cells. Epithelial tissues are classified according to the shape of the cells composing the tissue and by the number of cell layers present in the tissue. Figure 4. Similarly, cells in the tissue can be arranged in a single layer, which is called simple epithelium, or more than one layer, which is called stratified epithelium. Transitional describes a form of specialized stratified epithelium in which the shape of the cells, and the number of layers present, can vary depending on the degree of stretch within a tissue.
Epithelial tissue is classified based on the shape of the cells present and the number of cell layers present. Watch this video to find out more about the anatomy of epithelial tissues. Where in the body would one find non-keratinizing stratified squamous epithelium?
The cells in a simple squamous epithelium have the appearance of thin scales. The nuclei of squamous cells tend to appear flat, horizontal, and elliptical, mirroring the form of the cell. Simple squamous epithelium, because of the thinness of the cells, is present where rapid passage of chemical compounds is necessary such as the lining of capillaries and the small air sacs of the lung.
This epithelial type is also found composing the mesothelium which secretes serous fluid to lubricate the internal body cavities. 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 involved in the secretion and absorptions of molecules requiring active transport. 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.
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