Connective Tissue PDF

CONNECTIVE TISSUE Dr Matthew Valentine BVMS MRCVS PhD Dipl ACVP Lecture overview 1. Characteristics, functions, relevance 2. Components of connective tissue A. Cells B. Fibers C. Ground substance • Interstitial fluid 3. Classification Characteristics of Connective Tissue (CT) • Supports epithel...

CONNECTIVE TISSUE Dr Matthew Valentine BVMS MRCVS PhD Dipl ACVP Lecture overview 1. Characteristics, functions, relevance 2. Components of connective tissue A. Cells B. Fibers C. Ground substance • Interstitial fluid 3. Classification Characteristics of Connective Tissue (CT) • Supports epithelia • Vascularised • Cells lack polarity • Less cohesive • No basement membrane Functions of Connective Tissue • Joins tissues together • Gives form, subdivides organs • Physical support of body (bone tissue) • Thermoregulation (adipose and vascular effects) • Nutrition & storage (adipose) • Defense & repair mechanisms (inflammatory and immune cells) Relevance • Basic understanding of tissue organization, development and functioning. • • • • Trauma and healing Inflammation Edema Tumor terminology and development – Malignant tumors: SARCOMAS (Gr. Sarcos – flesh) 2. Components of Connective Tissue A. Cells: • Resident • Transient B. Fibers: • Collagen • Elastic • Reticular C. Ground Substance • Macromolecules • Interstitial (tissue) fluid A. Resident Cells: Fibroblasts • • The most numerous cell population of CT They synthetize the fibers of the CT: collagenous, elastic, and reticular Active Fibroblasts vs Inactive Fibroblasts (a.k.a. Fibrocytes) Source: Junqueira Resident Cells: Reticular cells - Special fibroblasts that synthesize a fine type of collagen fibers that offer scaffolding to the parenchyma (specialized epithelial cells) of various organs (lymph nodes, liver, spleen, etc.). Parenchymatous organs need support for their internal organization but are not subjected to high mechanical stress. Lymph node, HE 400x Serial Electronic Microscopy (SEM) Resident Cells: Adipocytes • Cells specialized in depositing lipids. • Can be of 2 types: multilocular – contain multiple droplets (“brown fat”); unilocular – a single big round drop of lipids (“white fat”) Brown adipose tissue, 1000x, HE Subcutaneous white adipose tissue, 400x, HE Resident Cells: Macrophages • Resident phagocytic cell of CT (yellow arrow) • May be named by location. Example: Kupffer cells are macrophages in the liver; osteoclasts are macrophages in bone. http://www.doctorc.net/Labs/Lab5/lab5.htm Resident Cells: Mast Cells • Cells filled with basophilic granules (stained blue with H&E) • They are involved in inflammatory and allergic reactions SEM of mast cells isolated from nasal cavity of a patient suffering from ‘hay fever’. Mast cells in CT, Light Microscopy (LM) Degranulation (activation) of mast cells causes release of histamine and other chemical mediators that trigger symptoms of allergy. Transient CT Cells = White Blood Cells Neutrophil Basophil Eosinophil Lymphocyte B. Fibers of Connective Tissue 1. Collagen Fibers • The most numerous fibers of CT • Are white; a large number of collagen fibers gives a white color to collagen rich tissue: tendons, tunica albuginea, sclera of the eye, etc. • Very high tensile strength, very strong, can only stretch 5% of initial length. • Collagen fibers (C, yellow arrows) stain pink with HE • Black arrows point to fibrocyte nuclei Collagen (as a substance) • The most abundant protein in the body representing 30% of its dry weight in humans • Many cells synthesize collagen – fibroblasts, chondroblasts, osteoblasts, odontoblasts, etc. • Procollagen is formed in the fibroblast, transported outside the cell, and then assembled into collagen fibrils. • Vitamin C is an important cofactor in collagen synthesis. FYI - Main collagen types (there are over 25): • Type 1 – 90% of body’s collagen, found in skin, bone, dentin, tendons, fibrocartilage; resists tensile forces • Type 2 – found in cartilage; resists compression • Type 3 – reticular fibers found in the stroma of expandable organs – spleen, lymph node, liver, cardiovascular system, lymphatics, etc. • Type 4 – basal lamina of epithelia FYI: What happens when collagen isn’t properly synthesized? E.g. : Deficiency of Collagen Type III can result in fragile skin syndromes • • • • • 2. Elastic Fibers Individual, branching and anastomosing fibers Produced by many cell types including fibroblast Pale yellow grossly Can stretch 2 ½ times original length, and recoil Found in aorta and elastic arteries, lungs, vocal cords, dermis, pinna of ear, epiglottis, etc. Special stains can be used to highlight elastic fibres resorcin-fuchsin in (b), and orcein in (c) 3. Reticular Fibers • Form a fine network (reticulum) that can be stained by silver → aka argentaffin fibers • synthesized by reticular cells, liver cells, smooth muscle cells and skeletal muscle cells. • Serve as a scaffolding to cells or cell groups of various organs. Reticular fibers Lymph node 250X, Silver stain https://www.gettyimages.com/detail/photo/reticular-connective-tissuelymph-node-250x-high-res-stock-photography/139821619 C. Ground Substance • Amorphous, gel-like; bathed in interstitial fluid • Produced by resident cells • Composed of: • Glycosaminoglycans (GAGs) • e.g.hyaluronic acid; chondroitin sulfate; keratan sulfate; dermatan sulfate; heparan sulfate • GAGs link to core protein to make proteoglycans • Properties of these molecules allow for binding of water, resisting compressive forces, cell adhesion to fibers, cell migration, barrier to bacterial/ venom penetration Ross’Histology ‘Bristles’ are GAGs Core protein Tissue fluid Proteoglycan Interstitial (Tissue) Fluid • A solution of nutrients and dissolved gases derived from plasma • Bathes the cells, fibers and ground substance, aids in removing waste • Fluid dynamics maintain proper balance in CTs • Tissue fluid determines skin turgor; a decrease in skin turgor is a late sign of dehydration • Lymphatics are important in fluid movement and prevention of edema • Not visible on slides Edema= Abnormal accumulation of tissue fluid https://www.urdogs.com/a-dog-recovered-after-found-strangled-with-a-6-pound-chain/ Edema due to inflammation https://www.dog-on-it-parks.com/blog/bee-safe-how-to-prevent-and-treat-bee-stings/ Dog stung by a bee. Increased vascular permeability (Inflammation) “Potato”. Dog stung by a centipede. Antonella Guerra© Gross Appearance of Edema at Post Mortem Horse, edema, connective tissue of gastric wall. Adipose connective tissue • Composed of adipocytes: fatty cells • Functions: – Energy storage – Endocrine: adipocytes produce leptin, which has regulatory effect on body fat. Leptin levels are proportional to body fat. It signals to the brain (satiety center) that the body has had enough to eat. – Protection (absorbs forces in digital fat pad – Insulation • When adipocytes outnumber other cell types → adipose tissue White Adipose Tissue • Morphology: Unilocular fat cells – one lipid droplet • Functions: • Energy storage • Insulation • Endocrine = hormone “leptin” secretion Subcutaneous adipose tissue, 400x, HE Brown Adipose Tissue • Morphology: Multilocular fat cells – several lipid droplets; many mitochondria • Found in hibernating and newborn animals • Function: heat generation Brown AdiposeTissue 400x, HE • ADD PHOTO FYI: Unilocular adipocytes can generate very common benign tumors called LIPOMAS