Connective Tissue PDF

Connective Tissue Connective Tissue Lecture Objectives • Describe the major components of connective tissue: • Protein fibers and ground substance of the extracellular matrix (ECM) • Cell types found in connective tissue • Describe the histologic appearances of connective tissue proper. • Describe...

Connective Tissue Connective Tissue Lecture Objectives • Describe the major components of connective tissue: • Protein fibers and ground substance of the extracellular matrix (ECM) • Cell types found in connective tissue • Describe the histologic appearances of connective tissue proper. • Describe some of the functions of connective tissue proper and specialized connective tissue. Connective Tissue Lecture Outline • Introduction • Extracellular matrix of connective tissue • Cells of connective tissue • Classification and examples of connective tissue Connective Tissue Lecture Outline • Introduction Tissue Basic Concepts There are ONLY FOUR basic tissues! • Epithelium • Connective tissue • Muscle • Nerve All tissues are composed of: • Cells • Extracellular matrix (stuff between cells) What Makes Connective Tissue Unique? • Extracellular matrix (ECM) is the major component of most types of connective tissue. • Cells are a minor component. • The other basic tissues (epithelium, muscle, nerve) are fundamentally different in that they are composed mainly of cells. Types of connective tissue Connective Tissue Specialized Connective Tissue Supporting Connective Tissue Adipose tissue Hematopoietic tissue Lymphoid tissue Cartilage Bone Connective Tissue Proper Surrounds delicate things like vessels Scaffolds mushy things like lymph nodes Connects bones Supports skin Connective Tissue Development • Connective tissue develops from a precursor tissue called mesenchyme (which arises from mesoderm). • Mesenchyme is an undifferentiated tissue present only in early embryonic life. • Develops into all connective tissues. • Also gives rise to vessels and smooth muscle. Mesenchyme: bland cells in lots of ground substance WOW. Connective Tissue Lecture Outline • Introduction • Extracellular matrix of connective tissue Composition of Extracellular Matrix (ECM) Protein fibers • Collagen fibers • Elastic fibers Ground substance • Glycosaminoglycans • Proteoglycans • Glycoproteins Tissue fluid (interstitial fluid) A thin watery fluid that brings nutrients, electrolytes, hormones, and oxygen from blood and dumps waste products into lymph. Two Main Protein Fibers in ECM Collagen fibers • Flexible, non-extensible • Over 20 types! • Made of polypeptide chains Elastic fibers • Thinner than collagen, and stretchier • Made of elastin and fibrillin Some (!) Types of Collagen Type Structure Light microscope Common locations Main function I 280-nm banded fibrils Thick! Can form fibers and bundles Skin, tendon, bone, dentin, cementum Resistance to tension II 280-nm banded fibrils Loose fibrils Cartilage Resistance to pressure III 280-nm banded fibrils Also called reticulin. Need silver stain to see. Skin, muscle, blood vessels, hematopoietic organs Maintains structure in expansible organs IV Cross-linked network Not visible All basal lamina Support, filtration VII Anchoring fibrils Not visible Epithelium and Anchors epithelium to basement connective tissue membrane Collagen Types I, II, III = “Fibrillar” Type Locations Microscopic Main function I Dermis, tendons, organ capsules Thick bundles. Resistance to tension Cartilage Thin fibers. Resistance to pressure Lymph nodes, spleen Thin fibers in a net-like arrangement. Flexible support for expansible organs II III Collagen Types I, II, III = “Fibrillar” Type Locations Microscopic Main function I Dermis, tendons, organ capsules Thick bundles. Resistance to tension Cartilage Thin fibers. Resistance to pressure Lymph nodes, spleen Thin fibers in a net-like arrangement. Flexible support for expansible organs II III “Reticular fibers”: from Latin reticulum (network) and rete (net) Collagen is assembled into bundles collagen molecules Bundle of collagen fibers collagen fiber collagen fibril Collagen fibrils, longitudinal and in cross-section, by EM Fibers and bundles of type I collagen Fibers and bundles of type I collagen. Fibroblasts at arrows. Reticular fibers (type III collagen) forming a network. These fibers are argyrophilic (stainable with silver stains). Elastic fibers are very thin and stretchy. Here they are in the wall of an artery. Elastic fibers are composed of elastin (stretchy!) surrounded by microfibrils (composed of fibrillin) Elastin core can expand and contract. Great for tissues that stretch (like large arteries and skin). Elastic fibers and collagen fibers in skin Ground substance • A viscous gel that fills spaces between cells and fibers in connective tissue. • Functions: binds water, fills space, acts as a barrier to infection, binds fibers and anchors cells to ECM. • Not well seen in histologic sections. • Main constituents: glycosaminoglycans, proteoglycans, glycoproteins Glycosaminoglycans (GAGs) are unbranched polysaccharide chains. There are two kinds: 1. Hyaluronic acid: simple, really long, and doesn’t need a core protein. Hyaluronic acid 2. All the other GAGs: more complex structurally, shorter, and always bound to a core protein. Heparan sulfate Chondroitin sulfate Dermatan sulfate Proteoglycans consist of a protein core with a bunch of attached GAGs. They contain more carbohydrate than protein. . Glycoproteins are globular proteins with attached carbohydrates. They contain more protein than carbohydrate. A Couple Important Glycoproteins Fibronectin • Present throughout connective tissue • Mediates normal cell adhesion and migration Laminin • Present in basal lamina • Helps epithelial cells stick to basal lamina • Also important in cell differentiation and migration Tissue (interstitial) fluid • Watery fluid similar to blood plasma • Continuously moves from capillaries into connective tissue due to hydrostatic pressure of blood. • Carries nutrients to connective tissue and picks up metabolic waste products. • Re-enters circulation by moving into venules and lymphatic vessels. What if there’s too much tissue fluid in CT? Sometimes, excess tissue fluid accumulates in connective tissue. This is called edema. Some causes include: Injury and inflammation This can cause increased permeability of capillaries, and leakage of fluid into connective tissue. Too few plasma proteins in blood This decreases the osmotic pressure within vessels, and fluid leaks out of vessels into connective tissue. Connective Tissue Lecture Outline • Introduction • Extracellular matrix of connective tissue • Cells of connective tissue A nice connective tissue cell: the fibroblast • Fibroblasts are the most common and functionally active cells in connective tissue. • Spindle-shaped nuclei and tapering cytoplasmic processes. • Make collagen, elastin, GAGs, proteoglycans and glycoproteins. Fibroblasts Connective Tissue Lecture Outline • Introduction • Extracellular matrix of connective tissue • Cells of connective tissue • Classification and examples of connective tissue Classification of connective tissue Connective Tissue Specialized Connective Tissue Supporting Connective Tissue Adipose tissue Hematopoietic tissue Lymphoid tissue Cartilage Bone Connective Tissue Proper Loose Dense Areolar Reticular Regular Irregular Delicate support around blood vessels Framework for lymph nodes Tendons Dermis Classification of connective tissue Connective Tissue Specialized Connective Tissue Supporting Connective Tissue Adipose tissue Hematopoietic tissue Lymphoid tissue Cartilage Bone Connective Tissue Proper Loose Dense Areolar Reticular Regular Irregular Delicate support around blood vessels Framework for lymph nodes Tendons Dermis Epithelium Loose connective tissue delicately supports epithelium Dense connective tissue provides deeper strength Loose and dense connective tissue proper Summary of connective tissue proper Type Loose areolar Microscopic Features Functions Lots of cells, lots of ground substance. Under epithelium, Provides delicate around glands and support and cushioning. blood vessels A few thin collagen fibers. Lots of cells, lots of ground Loose substance. reticular Vast network of reticular fibers. Forms a framework for cells. Lymph nodes, spleen, bone marrow Few cells, little ground substance. Provides strength and resists stretching forces in all different directions. Dermis, capsules surrounding organs Few cells, little ground substance. Provides strength and resists stretching forces in one direction. Tendons, ligaments Dense irregular Thick bundles of collagen fibers running in different directions. Dense regular Locations Thick bundles of parallel collagen fibers. Loose connective tissue: lots of cells, lots of ground substance, a few thin collagen fibers Dense connective tissue: fewer cells, less ground substance, thick bundles of collagen fibers Lymphocyte Elastic fibers Macrophage Fibroblast Macrophage Collagen fibers Loose areolar connective tissue Fibroblast Type III collagen Loose reticular connective tissue Loose reticular connective tissue (lymph node) Dense regular connective tissue (tendon) Dense irregular connective tissue (organ capsule) Connective Tissue with Special Properties • Adipose tissue • Elastic tissue • Hematopoietic tissue Adipose tissue Elastic connective tissue Elastic connective tissue (special elastic stain) Hematopoietic tissue