Epithelium Chapter BUE 2020 PDF

.1"- Cell membrane ~~------- Secretory. vesicles Nucleus ~~ft--- Nucleolus...

.1"- Cell membrane ~~------- Secretory. vesicles Nucleus ~~ft--- Nucleolus Rough. "+-- I etidoplasn lie reticulum Ribosomes ~~-MilO- cliondrion. DIagram ofa protem. synthesizing cell at EM level 38  H. ----- __ Cell membrane :-.l. ----- __..Secretory. vesicles Golgi ~-- apparatus Nucleus Nucleolus ~~~~ Rough. ?"or- - endoplasmic reticulum Ribosomes Mi/o- ""-'>7"- cltondrion DIagram. of a protem. syn thesizing eel ItEM a level 38  CHAPTER 3 EPITHELIAL TISSUE Intended Learning Outcomes (ILOs) By the end of this chapter the student should: Understand the general characters and classifications of epithelial tissue. Know the main functions and sites for each type of epithelium.. Gain skills of identifying and drawing each type of epithelium at LM level GENERAL CHARACTERISTICS OF EPITHELIUM 1. It is formed of continuous sheets of cells in one layer or more. 2. Intercellular substance is nearly absent (cement substance) and the cells could be joined at their margins by cell junctions. 3. All the cells in the basal layer are resting on a basement membrane. 4. Blood vessels and lymphatics are not present between epithelial cells. 5. Nutrients reach the cells by diffusion from the capillaries located in the underlying loose connective tissue. 6. Nerve fibers can pass in-between epithelial cells. 7. These sheets of cells cover body surfaces, line body openings and line body cavities (covering or lining). 8. Some cells are modified to produce secretions and form glandular epithelium. 9. Some cells are modified to contract and form myoepithelium. 10. Some cells are modified to receive stimulation (receptors) and form neuroepithelium. 11. Epithelium can develop from all the embryonic germinal layers (ectoderm, endoderm, and mesoderm). 12. Most epithelial cells have the ability for regeneration (continuous wear and tear). 13. The epithelial tissues have many functions The most important functions are protection (skin), secretion (hormones and enzymes), lubrication (mucus), excretion (urine and sweat), absorption (digestive tract), contraction (basket cells), special sensations (taste, smell and hearing) and reproduction (ovaries and testes). 39  TYPES AND CLASSIFICATION OF EPITHELIAL TISSUE According to the major functions, epithelium is divided into: 1. Surface Epithelium (Epithelial membranes) II. Glandular Epithelium ill. Myoepithelium IV. Neuroepithelium I. SURFACE EPITHELIUM (EPITHELIAL MEMBRANES) It is formed of sheets of cells that cover body surfaces or line body cavities. According to the number of layers (sheets) it is classified into, simple (a single sheet of cells) and stratified epithelium (two or more sheets of cells). A. SIMPLE EPITHELIUM Simple epithelium is formed of a single sheet of cells. It is further sub classified according to the shape of cells into: 1. Simple squamous epithelium 2. Simple cuboidal epithelium 3. Simple columnar epithelium 4. Pseudostratified columnar epithelium 1. SIMPLE SQUAMOUS EPITHELIUM Simple squamous epithelium is formed of a single layer of flat thin cells with flat nuclei. The cytoplasm is hardly seen. Sites and functions. 1. Simple squamous epithelium lines the blood vessels, the heart and the lymphatic vessels. This type is called endothelium. Simple squamous cells provide smooth lining of these vessels. 2. It forms lining of peritoneal, pleural and pericardial cavities. This type is called mesothelium. It gives smooth covering of those organs that need a degree of freedom of movements. Alveoli of the lungs and glomeruli of the kidneys are also lined with simple squamous epithelium. The thin flat cells are ideal to perform the function of diffusion and filtration. 40 Simple squ,_am::J0u.s~ epitheUunt-· ::;::'-=::iliia::~-=:;Siliiii.====r;~3iI_~~. ;.....~.r: "'\'(" ),(.'~Jr--.'"., r: ( ,-'- '1,-. " "r»... r » '",'/,'"".\'"