Epithelia - The tissue of the Human Body.pdf

Epithelia - The tissue of the Human Body Lect 2 What is the cytoskeleton? Cyto(cell), so basically cell skeleton - a skeleton is the backbone of the cell structures What is the cytoskeleton made-up of? Two components; 1) Microfilaments - Bundles of brown structure beneath cell membrane 7 transverse...

Epithelia - The tissue of the Human Body Lect 2 What is the cytoskeleton? Cyto(cell), so basically cell skeleton - a skeleton is the backbone of the cell structures What is the cytoskeleton made-up of? Two components; 1) Microfilaments - Bundles of brown structure beneath cell membrane 7 transverse through cytoplasm. - The microfilaments provide support for the cell, maintaining the shape of the cell by linking cytoplasm to the cell membrane. - Additional helps with muscle contraction - An example protein is actin. 2) Intermediate filaments - Responsible for strength - An example protein is keratin. Describe the general features of epithelial tissue Location of epithelial tissue - covers body surfaces, line hollow organs, cavities and ducts (tube) What is the epithelial tissue responsible for? The epithelium tissue is responsible for absorption, excretion, secretion, filtration and protection. The epithelium tissue also forms glands What are the key functions of epithelial tissue? - Selective barrier which limits or aids transfer of materials for the cells. Secretion onto free surfaces (as the tissues covers body surfaces, line hollow organs, cavities and ducts (tube)) Protection from abrasions (not easily scratched). How are the cells of the epithelium arranged? They are arranged in continuous sheets as single or multiple layers & are held together by cell junctions. Inorder for the tissues to be held together the cell junctions are an important factor. There are 5 types of cell junctions: desmosomes, hemidesmosomes, gap junctions, tight junctions and adherens junctions. Tight junction Description - As it says in the word tight junctions block the intercellular movement of the small solutes. Tight junctions are composed of the two main proteins occludins and claudins. The tight junctions connect the cytoskeleton of adjacent cells eg.via zo-1 to actin. - Tight junctions are found in the stomach, intestine and bladder. How are the tight junctions held together? There are individual sealing strands made up of transmembrane proteins called the occludin and claudin. The more stands the tighter the junctions. What is the cell polarity of the tight junctions? The tight junctions are present on the lateral surface - which keeps the cell polarity by preventing migration of proteins between the apical and basal surface. Adherens Junction/ belt junction - zonula adherens Description - Location of the adherens junction is more towards the basal surface of the epithelium cell. - Function, the adherens junction prevents cell separation from tension forces during contraction. What does “adhesion plaques” mean? Plaques (Plak) is a dense layer of proteins on the inside of the plasma membrane that attaches both membrane proteins and microfilaments to the cytoskeleton. If there is no presence of adherens junction or tight junctions in the cell-cell bond then adhesion plaques are present in areas where cells are less tightly bounded. What is the dense layer of proteins in adherens junction? The adherens junction is made of plaque layers of proteins on the inside of the cell. Two proteins are cadherins and catenins. There is a gap between the cells because of the protein's cadherins. As the cadherin passes through the cell membrane it joins other protein catenins. The catenin then locks the cadherin to the microfilament in the cell cytoplasm specifically to the protein actin. Desmosome Junction Description - Location: found in the lateral wall of the epithelial and cardiac tissue. - Resists sharing forces - withstand the mechanical stress - Present in skin epithelium and cardiac cells of the heart to prevent pulling apart. What is the plaque structure of the desomone junction? The cadherin protein spans the gap between the cell walls, passes through the wall and binds to desmoplakin. Which links to the intermediate filament, keratin. The keratin spans from one desomes to another on the other side of the cell structural integrity. Gap Junctions Description - Create direct connection between the cells. - Gap junctions enable nerve or muscle impulses to spread rapidly among cells. Important part of the nervous system and contraction of muscles. - Gap junctions allow 1KDA of molecule to pass through. How is the connection between the cells created by the gap junctions? - The plasma membranes of the gap junction are not fused together but are separated by a very narrow intercellular gap (space). - In the membrane proteins of the gap junction connexins, 6 connexin protein molecules form connexon or hemichannels, Which connect the neighbouring cells. How many hemichannels make up a gap junction? 2 hemichannels are at one gap junction. Hemidesmosome Description - Links the epithelia to the basement tissue - Links the intermediate filament to the basement membrane What do hemidesmosomes anchor cells too? Hemidesmosome anchor cells not to each other but to the basement membrane. The transmembrane glycoproteins in the hemidesmosomes are integrins. The integrins bind to the intermediate filaments (keratin) on the inside of the plasma membrane. On the outside of the plasma membrane the integrins attach to the protein laminin present in the basement membrane. Describe the general structure of the basement membrane and understand its functions The basement membrane composition is of extracellular matrix that is made up of two parts; Lamina = thin layer 1) Basal lamina - Connects the integrin in hemidesmosome to epithelial cells to the basement membrane. - Also contains other glycoproteins and proteoglycans 2) Reticular lamina - Close to the underlying connective tissue and contains proteins such as collagen produced by the connective tissues called the fibroblast. The major function of the basement membrane is to connect the epithelium tissue and connective tissue. But there are other functions that the basement membrane has.. - Basement membrane supports the overlying epithelium providing structural support to the epithelial cells. During tissue growth and wound healing the epithelia call need to migrate to repair or cover damaged areas, the basement membrane serves as a substrate. Acts as a physical barrier preventing large molecules between the epithelia and connective tissue. Participates in the filtration of substances from the kidney, the basement membrane crucial role in the filtration process of blood from urine. Give an example of basement membrane acting as a barrier Preventing the invasion of malignant melanoma. As once the barrier is broken the chance of metastasis occurring increases. What are the warning signs of melanoma? Using ABCD abbreviation Asymmetry; if one half of a mole doesn’t match the other half. Border irregularity; the edges of the mole are irregular Colour; there is a mix of colour within the mole Diameter; 6mm All are warning signs of melanoma What is the process of diffusion? Epithelia has its own nerve tissue but does not contain blood vessels, thus avascular. The epithelial tissue relies on the adjacent connective tissue’s blood vessel to bring in nutrients and remove water material. The process is called diffusion. Describe selected types of epithelial tissue and have an understanding of their classification, structure, location and function Epithelial tissue - Covering epithelia; outer covering and inner covering - Glandular epithelia; exocrine and endocrine