Connective Tissue Histology Notes PDF

CONNECTIVE TISSUE Dr Diana Bochynska DVM dipECVP (previous instructor Drs Matthew Valentine I. Irimescu C. Fuentealba) Lecture overview 1. Definition, origin, functions, relevance 2. Components of connective tissue A. Cells B. Fibers C. Ground substance Interstitial fluid 3. Classification of connec...

CONNECTIVE TISSUE Dr Diana Bochynska DVM dipECVP (previous instructor Drs Matthew Valentine I. Irimescu C. Fuentealba) Lecture overview 1. Definition, origin, functions, relevance 2. Components of connective tissue A. Cells B. Fibers C. Ground substance Interstitial fluid 3. Classification of connective tissue (CT) Embryonic Adult (connective tissue proper) Special (will be studied in following lectures) Low vs High Cellular Density Connective tissue Lots of intercelllular matrix Few cells 1000x H&E stain 1000x Hepatic tissue (glandular epithelium) Little intercellular matrix High cellular density Definition of Connective Tissue (CT) Tissue made up of few cells loosely embedded in a complex extracellular matrix. Is well vascularized and innervated (most types of CT) Cells lack polarity (no apical or basolateral surface) Origin (derived from mesoderm) Special CT will be studied separately Mesenchyme is embryonic connective tissue Functions of Connective Tissue Connects other tissues Gives form, subdivides organs Physical support of body (bone tissue) Thermoregulation Nutrition & storage Defense & repair mechanisms Relevance Basic understanding of tissue organization, development and functioning. Trauma and healing Inflammation Edema Vitamin C deficiency Tumor terminology and development – Malignant tumors: SARCOMAS (Gr. Sarcos – flesh) 2. Components of Connective Tissue A. Cells: Resident Transient B. Fibers: Collagen Elastic Reticular Others (fibronectin, laminin) 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 Lipids: red Omentum, stained by Sudan red, 1000x Resident Cells: Macrophages Resident phagocytic cell of CT (fixed or mobile) (yellow arrow) Monocytes from blood cross the vessel walls into CT, becoming macrophages Tissue macrophages can proliferate locally; they survive for months 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 NOTE: These will be studied in the Blood & Hematopoiesis segment of this course Neutrophil Eosinophil Basophil Lymphocyte B. Fibers of Connective Tissue 1. Collagen Fibers The most numerous fibers of CT Composed of fibrils usually arranged in bundles of indefinite length. 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. 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 synthetized? E.g. : Deficiency of Collagen Type III can result in fragile skin syndromes 2. Elastic Fibers Individual, branching and anastomosing fibers; Might stain purple in HE (a) but hard to detect; more evident with special stains (resorcin-fuchsin - b, orcein - c) 0.2-5.0 μm diameter in loose CT 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. 3. Reticular Fibers Form a fine network (reticulum) that can be stained by silver → aka argentaffin fibers Are type III collagen, 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’ -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/ 3. Connective Tissues Classification Embryonic : – Mesenchyme Adult – Proper Connective Tissue: Loose CT Dense CT Reticular CT Adipose CT Special (will be studied in the following lectures) – Cartilage – Bone – Blood Adult (Proper) Connective Tissue Loose (CT Ubiqitinous tissue Loosely arranged fibers, always irregular Cellular constituents vary with location Dense CT Densely packed fibers Irregular and regularly arranged fibers Strong tissue Reticular CT Adipose CT Loose and Dense Irregular CT Loose* CT (more cells, few fibers, clear space) Dense* Irregular CT (fewer cells, many thick collagen fibers, irregularly packed) *Note the positioning of loose and dense irregular CT relative to an epithelium varies! Skin, tail of mouse section, 200x HE Loose and Dense Irregular CT Stratified keratinized squamous epithelium Loose* CT (more cells, few fibers, clear space) Dense* Irregular CT (fewer cells, many thick collagen fibers, irregularly packed) *Note the positioning of loose and dense irregular CT relative to an epithelium varies! Skin, tail of mouse section, 200x HE Loose and Dense Irregular CT Stratified keratinized squamous epithelium Loose* CT (Lots of cells, few fibers, clear space) Dense* Irregular CT (few cells, many thick collagen fibers, irregularly packed) *Note the positioning of loose and dense irregular CT relative to an epithelium varies! Lip section, 200x HE Dense Regular Connective Tissue Fibrocyte nuclei visible (very thin and elongated) Parallel arranged collagenous fibers Very strong, resists tensile forces Found in tendons, ligaments, cornea Tendon, 400x HE Reticular Connective Tissue Network of fine collagen fibrils =“reticular”, offering support for cells Usually synthesized by reticular cells Reticular CT is observable in lymph nodes and spleen Lymph node 250x, Silver stain It forms the stroma in lymph nodes (dividers for the mass of functional tissue – parenchyma). 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 Adipose Tissue 400x, HE ADD PHOTO FYI: Unilocular adipocytes can generate very common benign tumors called LIPOMAS