• Form large complexes, both to other proteoglycans, to hyaluronan, and collagen. • Involved in binding cations (Na, K, Ca) and water • Regulating the movement of molecules through the matrix. • Can affect the activity and stability of proteins and signalling molecules within the matrix • Allows connective tissues of the Extracellular Matrix (ECM) to be able to withstand compressional forces through hydration and swelling pressure to the tissue. Examples of common glycosaminoglycans are • chondroitin 6-sulfate, • keratan sulfate • heparin • dermatan sulfate • hyaluronate. Hydrated proteoglycans form the highly viscous fluid of mucus and the matrix of the intercellular ground substance of connective tissue (mucopolysaccharide). Epithelium is devoid from blood (avascular tissue) and thus supplied by diffusion
Functions of epithelial tissue 1. Covering and lining 2. Absorption 3. Secretion 4. Sensation (neuro-epihelium) 5. Contraction (myo-epithelium) Embryonic origin of epithelial tissue It is derived from the three embryonic germ layers, 1. Ectoderm: skin, nose, mouth, and anus are derived 2. Endoderm: respiratory, digestive systems, and glandular epithlium are derived 3. Mesoderm: blood vessels are derived
Types of epithelial tissue Based on structure and function 1. Covering and lining epithelium 2. Glandular epithelium 1. Covering and lining epithelium Can be sub-classified according to the 1 . Number of cell layers a. Simple epithelium (single layer of cells) b. Stratified epithelium (more than one layer of cells) 2. Cell morphology (shape) a. Squamous b. Cuboidal c. Columnar
B. Stratified epithelium B. Stratified epithelium Further sub-classified into: 1. Stratified squamous epithelium: a. Keratinized: skin b. Non-keratinized: esophagus 2. Stratified cuboidal epithelium: lining the large duct of sweat gland 3. Stratified columnar epithelium: lining mammary gland duct 4. Transitional epithelium: lining urinary tract and urinary bladder
2. Glandular epithelium It is a modified secretory epithelium A. Endocrine epithelium (ductless glands) • Unicellular: entero-endocrine cells • Multicellular: pituitary gland B. Exocrine epithelium (ductile glands) • unicellular: goblet cells • Multicellular (simple coiled ): intestinal gland • Compound branched tubular: sweat glan • Compound tubulo alveolar: mammary gland
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- Fall '16