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Epithelia (S+T)
| Question | Answer |
|---|---|
| What causes breast cancer? | Abnormal proliferation of the epithelial cells (1 in 8 women). |
| What causes cystic fibrosis? | Defective epithelial chloride transport ion transport (1 in 2500 live births). |
| What causes cholera? | Enhanced activation of epithelial chloride ion transport in gastrointestinal tract. |
| What causes atherosclerosis? | Superficial injury to the epithelial lining of blood vessels causes cardiovascular disease (40% of the UK population will die due to associated complications with atherosclerosis). |
| What are epithelia? | Cells that cover or line all the body surfaces, tubes and cavities. Cells that form interfaces between different physiological fluid compartments. |
| What connects epithelia? | Cells are in intimate contact with each other and may be connected by tight junctions. |
| What separates the epithelial cells from underlying tissues? | The basement membrane. |
| How is the epithelial layer maintained? | Cells undergo rapid division to replace those continually lost from the surface. |
| What are the three shapes of epithelial cells | Columnar, Cuboidal and Squamous. |
| What is the structure of a columnar cell? | Apex- of the cell-next to the lumen. Base-basal part of the cell-next to the BM. |
| What is the shape of squamous cells? | Sheets of flattened cells. |
| What is the structure of simple epithelia? | One layer of cells. All cells in direct contact with the lumen and BM. They are found in sites in the body where there is: diffusion, absorption or secretion. |
| What is the structure of stratified epithelia? | Multiple layers of cells. Cells in contact with BM= basal. Cells in contact with lumen= apical. They are found in sites in the body where there is need for protection. |
| Why are stratified epithelia used for protection? | The thicker the epithelium the greater the protection from abrasion, infection or caustic content. |
| Why are simple epithelium thin? | The thinner the epithelium, the quicker diffusion or absorption can occur. |
| What type of epithelium do blood vessels have? | Simple squamous. |
| What type of epithelium does the kidney tubule have? | Simple cuboidal. |
| What type of epithelium does the GI tract have? | Simple columnar. |
| What type of epithelium does the skin have? | Stratified squamous. |
| What type of epithelium does the reproductive system have? | Stratified cuboidal. |
| What type of epithelium does the respiratory system have? | Pseudostratified columnar. |
| What type of epithelium does the bladder have? | Transitional. |
| Describe the structure of an exchange surface. | One cell layer. Squamous cells. Pores between cells permit easy passage of molecules. |
| Describe the structure of a transport surface. | One cell layer. Cuboidal or columnar cells. Tight junctions limit movement between cells. |
| Describe the structure of a ciliated surface. | One cell layer. Cuboidal or columnar cells. Cilia move fluid across the surface. |
| Describe the structure of a protective surface. | Many cell layers. Squamous on the surface: polygonal in deeper layers. Cells tightly connected by many desmosomes (an area of contact between two cells). |
| Describe the structure of a secretory surface. | One up to many cell layers. Columnar or polygonal cells. Extensive RER (proteins) or SER (steroids). |
| What are the features of a simple squamous epithelium? | Single layer of flattened cells. Individual cells are very thin with a central nucleus. Irregular shape. Close proximity to each other. |
| What is a mesothelium? | The single layer of cells that lines serous membranes. |
| What is a serous membrane? | A smooth transparent membrane, consisting of mesothelium and underlying elastic fibrous connective tissue. |
| What is the function of simple columnar epithelium? | Lining of the small intestine: 1. to increase surface area for absorption. 2. mucus secretion to lubricate gut contents. |
| What forms the brush border of a simple columnar epithelium? | Apical surface of each cell is covered by several hundred microvilli forming the brush border mucus adheres to. |
| What is the function of Goblet cells in the simple columnar epithelium? | Release intensely staining mucus to lubricate gut contents. |
| What is the function of the basement membrane in the simple columnar epithelium? | Separates the epithelial cells from the underlying tissues. |
| What does the pseudostratified ciliated columnar epithelium consist of? | Columnar cells, Goblet cells and Basal cells. |
| What is the structure of the stratified squamous epithelium? | Flattened cells that are worn off and shed from the surface- desquamation. Basal cells on the BM divide and move upwards to the surface. |
| What is the function of the stratified squamous epithelium? | It protects underlying tissues from abrasion. |
| Where would you find a stratified squamous epithelium? | Mouth, vagina and anal canal. |
| Define desquamation. | The process in which the outer layer of the epidermis of the skin is removed by scaling. |
| Where is the apical membrane? | Bordering the lumen. |
| Where is the basolateral membrane> | In between epithelium cells. |
| Where is the basal membrane? | Bordering the BM. |
| What membrane proteins are in a tight junction? | Claudin and occludin. |
| Which cytoskeleton fibre is in a tight junction? | Actin. |
| What is paracellular movement? | Secretion and absorption in adjacent tight junctions. |
| What are the roles of tight junctions? | Barriers, fences and gates. |
| How does a tight junction act as a barrier? | Separates one compartment from another. |
| How does a tight junction act as a fence? | Maintain the asymmetric distribution of lipids and proteins in the apical and basal membrane. |
| How does a tight junction act as a gate? | Allow some molecules to flow more easily than others. |
| What does a tight junction create? | Apical and basal membrane domains. |
| How does epithelial transport enable compartments with different compositions? | Differential distribution of transport systems enables trans-epithelial vectorial transport. Trans-epithelial vectorial transport creates compartments with different compositions. |
| In summary, tight junctions... | 1. create a barrier between different compartments. 2. allow the processes of absorption and/or secretion to create compartments with different molecular compositions. |