Lecture 1 Epithelium + Connective Tissue PDF

 Epithelia Connective tissue Human Tissues Muscle Tissue Nervous tissue Epithelium Genaral Characteristics: 1. It is formed of crowded cells with minimal intercellular substance. 2. It rests on a basement membrane & underlying connective tissue. 3. It is avasc...

 Epithelia Connective tissue Human Tissues Muscle Tissue Nervous tissue Epithelium Genaral Characteristics: 1. It is formed of crowded cells with minimal intercellular substance. 2. It rests on a basement membrane & underlying connective tissue. 3. It is avascular (=non vascularized). 4. It is rich in nerve endings. 5. It has a high power of regeneration. forms: a- sheets covering all surfaces &lining all cavities in the body (covering &lining epithelium) b- clusters of cells forming glands (glandular epithelium) c- modified structures acting as sensory receptors (sensory epithelium) It is the layer thet sparates the epithelium from the underlying connective tissue. By LM, it appears as a thin layer & can be stained with PAS & silver. By EM, it is formed of: 1. Cell coat of epithelial cells. 2. Basal lamina: is a homogenous layer composed of glycoproteins. 3. A layer of reticular fibers. Function: 1- acts as a barrier against diffusion of macromolecules. 2- support for the epithelial layer. 1. Simple squamous epithelium: Formed of one layer of flat cells with flat nuclei. Site: lining blood vessels &all body cavities.  2. Simple Cuboidal epithelium: Formed of one layer of cubical cells with central rounded nuclei. Site: lining renal tubules &thyroid follicles. 3. Simple Columnar epithelium: Formed of one layer of tall cells with oval basal nuclei. Site: lining the stomach, the intestines & gall bladder. 4. Pseudostratified Columnar epithelium Formed of one layer of cells. Some cells are tall & reach the surface of the epithelium and others are too short to reach the surface but all the cells rest on the basement membrane. The epithelium appears falsely stratified. Site: lining the trachea (pseudostratified columnar ciliated ep.) 1- Stratified Squamous Epithelium: Structure: Formed of several layers of cells. The basal cells are columnar, the following layers are polyhedral, the superficial cells are flattened squamous. Site: It has two types: 1. Stratified squamous non keratinized: lining the oral cavity & the oesophagus. 2 Stratified squamous keratinized: covers the skin 2. Transitional Epithelium: Means that the epithelium can change its form. Site: It lines organs which can expand greatly like the urinary bladder. Structure: a- When the epithelium is stretched (as in full bladder), it is similar to a stratified squamous non keratinized type. b- When the epithelium is relaxed (as in empty bladder): The basal cells are short columnar, the intermediate cells are polyhedral and the superficial cells are large rounded with convex upper surfaces &have one or two nuclei. Classification of Glandular Epithelium: There are several ways of classification of glandular epithelium: a. According to presence or absence of ducts: 1. Exocrine glands: have ducts that carry their secretion to the surface of the epithelium, e.g. salivary glands. 2. Endocrine glands: are ductless glands. They secrete hormones directly into blood, e.g. pituitary gland. Exocrine glands: are further classified according to: A- the nature of secretion into: 1. Serous glands secrete watery secretion rich in enzymes e.g. pancreas. 2. Mucous glands secrete viscid mucous secretion e.g. esophageal glands. 3. Muco-serous glands: secrete mucous &serous secretion e.g. submandibular salivary gland. B- the mode of secretion: 1. Merocrine glands: The secretion leaves the cell by exocytosis & the cell membrane is left intact. No part of the cell is lost e.g. salivary glands. 2. Apocrine glands: During secretion, there is loss of the apical part of the cell e.g. apocrine sweat glands. 3. Holocrine glands: The cells after being full of secretion, they burst &become totally included in the secretion e.g. sebaceous glands. It is epithelial tissue modified to act as a receptor. Structure: formed of three types of cells: 1. sensory cells. 2. supporting cells. 3. basal cells. Site: -taste buds in the tongue. -olfactory epithelium in the nose Connective tissue  It is one of the four basic tissues of the body. It consists of :  1- Connective tissue cells  2- Connective tissue fibers  3- Ground substance and tissue fluid.  Functions:  It is concerned with connecting and holding the other tissues together.  Nutrients are transported from capillaries that lie in the intercellular substance to the cells of other tissues.  Defense mechanism and immunity.  There are three types of fibers: Collagenic,  elastic and reticular fibers.  Collagen (white) fibers :  Are colourless elongated or wavy bundles, non- branching small fibrils. It is composed of the protein collagen  Collagenic fibers are acidophilic thus staining pink with H&E stain.  Function :  They provide strength to the tissue.  B) Elastic (yellow)fibers:  They are long, thin fibers which are branched and may unite and form irregular networks.  They are mainly composed of the protein elastin.  Elastic fibers are weakly acidophilic with Hx&E stain, with orcein stain they take a dark brown colour.  Function :  They provide elasticity and strength to the tissue.  C) Reticular fibers:  They are fine fibers which are arranged in the form of networks.  They are mainly formed of the protein collagen in addition to carbohydrate.  They are not visible in H&E preparations but with silver stains they take a black colour.  Function: They provide the frame work of the organs.  Connective Tissue Cells: Fixed cells: These are stable long – lived cells and include fibroblasts, fat (Adipose) cells and mesenchymal cells. Free (wandering) cells: These are short – lived cells that are changing population which include mast cells, plasma cells, macrophages and leukocytes.   Fibroblast  *It is the most common cell in connective tissue proper.  Origin: Mesenchymal cells divide and differentiate into fibroblasts which are active young cells. After getting old, fibroblasts are celled fibrocytes.  Structure: (L/M)  The active young cells appear as branched cells with abundant basophilic cytoplasm and oval pale nucleus with prominent nucleolus.  E.M: It contains numerous rough endoplasmic reticulum, several well developed Golgi stacks, ribosomes, mitochondria and transfer vesicles  Functions:  Formation of both components of the intercellular substance.  1) Secretion of mucopolysacharide (GAG) of the matrix  2) They secrete tropocollagen which is synthesized in the rough endoplasmic reticulum, forming the collagenic fibers.  3) Secretion of elastin which give elastic fibers.  4) Repair of wounds. Click to view full size  Plasma cells:  Origin: Plasma cells differ from other C.T. cells in that they are not developed from mesenchymal cells. They arise from B – lymphocytes that enter the loose C.T. from the blood stream.  Structure of plasma cells:  L/M  They are spherical or ovoid cells.The nucleus is eccentric in position and has a coarse pattern of heterochromatin (clock – face chromatin).  The cytoplasm is intensely basophilic except at an area close to the nucleus which appears pale and represents the site of Golgi apparatus and centriole (negative Golgi area).  EM  There are numerous RER and free ribosomes, well developed Golgi located beside the nucleus, and in this region there is a pair of centrioles and few mitochondria. Secretory vesicles containing immunoglobulin bud from the flattened vesicles of the Golgi to become secreted outside the cell. The cytoplasm contains rounded acidophilic bodies, (Russell bodies).  Function:  The formation of antibodies that circulate into the blood (humoral antibodies).  Mast cells: They are rounded or spindle shaped. The nucleus is rounded and central in position. The cytoplasm is studded with basophilic granules, only seen after staining with Toluidine blue where they stain metachromatically (they stain purple to red).  Function of mast cells:  Secretion of heparin and histamine  Macrophages (histiocytes ) Origin: From mesenchymal cells in prenatal life. From monocytes which come to loose C.T. from the blood in postnatal life. Appearance of macrophages: It has oval shape with eccentric condensed nucleus which is indented. The cytoplasm contains numerous lysosomes. Function Phagocytosis of foreign materials.  Ground substances of C.T  composed of:  Mainly hyaluronic acid which is a non sulphated acid mucopolysaccharidies glucosaminoglycans (GAG).  Sulphated acid mucopolysaccharids,  Glycoprotein. It functions in attaching cells to fibers.  Function: Transport of nutrients and oxygen from capillaries to other tissues. Classification of connective tissues: I- Connective tissue proper, which includes:  1. Loose C.T.  2. Dense white fiberous C.T.  3. Dense elastic C.T.  4. Reticular tissue.  5. Adipose tissue.  6. Mucous (Embryonic) C.T. II- specialized connective tissue  Cartilage. Bone. Blood