Connective Tissue & Adipose Tissue - Chapter 5 & 6 PDF

Chapter 5 Connective tissue Connective tissue provides a matrix that supports and physically connects other tissues and cells together to form the organs of the body MOST abundant tissue in the human body Interstitial fluid - metabolic support to cells Made up of three structural elements Cel...

Chapter 5 Connective tissue Connective tissue provides a matrix that supports and physically connects other tissues and cells together to form the organs of the body MOST abundant tissue in the human body Interstitial fluid - metabolic support to cells Made up of three structural elements Cells (cytes, blast, clast) Fibers - ECM Ground substance - ECM Connective tissue All connective tissues originate from embryonic mesenchyme from the mesoderm Mesenchymal cells (MULTIPOTENT STEM CELLS) Undifferentiated Spindle-shaped Connective tissue General Function: Do not form an organ attachment transport of blood immune function storage of materials CELLS OF CONNECTIVE TISSUE According to mobility: Fixed Cells - Fibroblast, Fibrocyte - Adipocyte - Wandering Cells: Macrophages & the Mononuclear Phagocyte System Mast Cells Plasma Cells Leukocytes Fibroblasts the most common cells in connective tissue proper produce and maintain most of the tissue’s extracellular components Synthesize and secrete collagen and elastin fibroblast activity Active (“fibroblasts”) Quiescent (“fibrocyte”) Fibroblasts are targets of many families of proteins called growth factors that influence cell growth and differentiation. Adipocytes Aka Fat cells for cytoplasmic storage of lipid as neutral fats for the production of heat Adipose CT - serves to cushion and insulate the skin and other organs Macrophages highly developed phagocytic ability specialize in turnover of protein fibers and removal of dead cells, tissue debris, or other particulate material abundant at sites of inflammation eccentrically located, oval or kidney-shaped nucleus “histiocytes” Antigen presenting cells (APC) Activated Macrophages – when stimulated May fuse to form multinuclear giant cells Macrophages Macrophages derive from bone marrow precursor cells called monocytes early stages of repair and inflammation after tissue damage Mononuclear phagocyte system Mast cells oval or irregularly shaped cells response to allergen filled with basophilic secretory granules which often obscure the central nucleus metachromasia localized release of many bioactive substances Heparin Histamine Serine proteases Eosinophil & neutrophil chemotactic factors Cytokines Phospholipid Mast cells perivascular mast cells – skin, mesenteries mucosal mast cells – digestive and respiratory tracts function as sentinels detecting invasion by microorganisms Immediate hypersensitivity reactions anaphylaxis LYMPHOCYTE Type of white blood cell that consists of three cell populations: Th Cells: CD8 cytotoxic cells and CD4 helper cells B cells: humoral immunity via antibody secretion Natural killer cells: cytotoxic cells ○ Appearance of histology: Dark, round nucleus with a thin rim of cytoplasm Plasma Cells lymphocyte–derived, antibody-producing cells ACTIVATED B CELLS LYMPHOCYTE relatively large, ovoid cells have basophilic cytoplasm rich in RER and a large Golgi apparatus near the nucleus round nuclei frequently show peripheral clumps of heterochromatin, giving the structure a “clock-face” appearance Their average lifespan is only 10-20 days LEUKOCYTES AKA WBCs they leave blood by migrating between the endothelial cells of venules Involved in inflammation EOSINOPHILS, BASOPHIL, NEUTROPHILS, MONOCYTE Most leukocytes function in connective tissue only for a few hours or days and then undergo apoptosis Inflammation Cardinal / Major signs Redness - rubor Swelling - tumor Heat – calor / calore Pain – dolor / dolore Loss of function - Functio laesa Chemotaxis Three structural elements Cells Fibers Ground substance Fibers Elongated structures formed from proteins that polymerize after secretion from fibroblasts 3 main types: Collagen Reticular- reticulin Elastic - elastin Collagen their ability to form various extracellular fibers, sheets, and networks extremely strong and resistant to normal shearing and tearing forces most abundant protein (30%) in the human body provides significant TENSILE strength with limited flexibility FOUR MAJOR TYPES (I,II,III,IV) They can be categorized according to the structures formed by their interacting α-chains subunits: COLLAGEN STRUCTURE Pro-a-chain composed of the following sequence: Gly-X-Y Collagen is about 1/3 glycine X and Y are Proline or Lysine Modified in the cell to form a triple helix composed of 3 pro a-chains Procollagen triple helix is exported outside of the cell where it is modified to enable cross-linking between triple helices Final collagen fiber structure is multiple cross-linked collagen triple helices (1) Preprocollagen is translated from collagen mRNA in the RER to produce pro-a-chain (2) Proline and lysine within the a chain undergo hydroxylation in the RER Process requires vitamin C (ascorbic acid) (3) Hydroxylation enables the helical a chains to spontaneously form a triple helix in the RER (procollagen) via hydrogen and disulfide bonds -(4) Procollagen is exported via exocytosis to the extracellular space  Cross-linking between tropocollagen chains within collagen fibers continues to occur throughout life leading to increased stiffness of structures with age: skin, joints and arteries Elastic Fibers form sparse networks interspersed with collagen bundles in many organs, particularly those subject to regular stretching or bending have rubberlike properties Found in wall of large BVs Elastic lamellae Elastic fibers > fibrillin > microfibrils embedded in elastin Elastin PROTEIN ○ Highly elastic protein that allows tissues to be stretched and resume their native shape ○ Elastic nature often contributes to function of a tissue: lung and aorta Also found in large blood vessels, elastic ligaments, vocal cords, ligamentum flavum and bladder SYNTHESIS OF ELASTIC FIBERS ○ Synthesized by fibroblasts ○ Tropoelastin proteins are synthesized within the cell and then undergo exocytosis ○ Outside the cell, lysyl oxidase oxidizes lysine residues to generate reactive aldehydes and allysine, which enable tropoelastin proteins to cross-link and form elastin ○ Elastin is broken down by elastase Elastase is inhibited by a1-antitrypsin Reticular Fibers Found in delicate connective tissue Collagen type III characteristically stained black after impregnation with silver salts Argyrophilic Also PAS+ - high content of sugar chains Reticular fibers produced by fibroblasts Liver, endocrine glands, BM, spleen, LNs Three structural elements Cells Fibers Ground substance GROUND SUBSTANCE Highly hydrated, transparent, complex mixture of: GAGs, proteoglycans, multiadhesive glycoCHONs Filling the space between cells and fibers in connective tissue Functions to enable diffusion of nutrients and gases (e.g., O2) between cells and blood vessels Glycosaminoglycans (GAGs) AKA mucopolysaccharides long polymers of repeating disaccharide units (hexosamine and uronic acid) Hexosamine - glucosamine or galactosamine Uronic acid - glucuronate or iduronate Hyaluronan – largest and most ubiquitous GAG AKA hyaluronate, hyaluronic acid Synthesized by hyaluronan synthase Molecular diffusion; lubricating organs and joints Glycosaminoglycans (GAGs) 4 major GAGs: dermatan sulfate chondroitin sulfates keratan sulfate heparan sulfate All GAGs except hyaluronic acid bind to core proteins to form proteoglycans to form large, negatively-charged molecules that attract water High negative charge – sequester cations and water Space-filling, cushioning, and lubricant functions Proteoglycans core protein to which are covalently attached various numbers and combinations of the sulfated GAGs synthesized on RER, mature in the Golgi apparatus proteoglycans have attached GAGs Perlecan is the key proteoglycan in all basal laminae Aggrecan - heavily bound with chondroitin and keratan sulfate chains aggrecan-hyaluronan complexes - cartilage Multiadhesive Glycoproteins Large molecules with branched oligosaccharide chains Allow adhesion of cells to their substrate Laminin - adhesion for epithelial and other cells Fibronectin - specific binding sites for integrins; important both for cell adhesion and cellular migration Interstitial Fluid Water in the ground substance also contains plasma proteins of low molecular weight 2 main forces act on the water in capillaries: Hydrostatic pressure Colloid osmotic pressure Classification of connective or Supporting tissues Connective Tissue Proper Loose (Areolar) Dense irregular CT Dense regular CT Embryonic CT Mesenchyme Mucoid (mucous) Specialized CT Reticular Adipose Cartilage Bone Blood Connective Tissue Proper broadly classified as “loose” or “dense,” terms which refer to the amount of collagen present Loose (Areolar) Dense irregular CT Dense regular CT Loose (areolar) CT Forming a layer beneath the epithelial lining of many organs and filling the spaces between fibers of muscle and nerve typically contains cells, fibers, and ground substance in roughly equal parts Fibroblasts Collagen fibers, elastic, reticular Delicate consistency Flexible and not very resistant to stress Dense connective tissue has similar components as loose connective tissue, but with fewer cells Fibroblasts, type I collagen abundance of collagen here protects organs and strengthens them structurally. Dense connective tissue Dense irregular connective tissue LARGER RATIO OF FIBERS TO CELL Bundles of collagen fibers appear randomly interwoven, with no definite orientation provides resistance to stress from all directions Deep dermis layer of skin and capsules surrounding most organs Dense connective tissue Dense regular connective tissue consists mostly of type I collagen bundles and fibroblasts aligned in parallel For great resistance to prolonged or repeated stresses from the same direction Structures enable support for significant forces and stress Tendons, aponeuroses, ligaments Classification of connective or Supporting tissues Connective Tissue Proper Loose (Areolar) Dense irregular CT Dense regular CT Embryonic CT Mesenchyme Mucoid (mucous) Specialized CT Reticular Adipose Cartilage Bone Blood Classification of connective or Supporting tissues Connective Tissue Proper Loose (Areolar) Dense irregular CT Dense regular CT Embryonic CT Mesenchyme Mucoid (mucous) Specialized CT Reticular Adipose Cartilage Bone Blood EMBRYONIC CT Mesenchyme: gelatinous connective tissue consisting mostly of ground substance with sparse amounts of reticular fibers (type III) and mesenchymal cells Derived from the mesoderm and neuroectoderm-neural crest origin Differentiates into adult connective tissues, both proper and specialized (cartilage, bone, etc.) ○ Wharton's jelly: mucoid connective tissue found in the umbilical cord and subdermal connective tissue of the embryo that contains mostly ground substance with small amounts of reticular fibers (type III) and fibroblasts. Mucoid (mucous) CT Principal component of the fetal umbilical cord, where it is referred to as Wharton’s jelly Hyaluronan Gelatinous sparse collagen fibers and scattered fibroblasts similar to the tissue found in the vitreous chambers of eyes and pulp cavities of young teeth Chapter 6 Adipose Tissue Classification of connective or Supporting tissues Connective Tissue Proper Loose (Areolar) Dense irregular CT Dense regular CT Embryonic CT Mesenchyme Mucoid (mucous) Specialized CT Reticular Adipose Cartilage Bone Blood Adipose tissue fat-storing cells or adipocytes are typically found isolated or in small groups within loose or dense irregular connective tissue 15%-20% of the body weight in men, somewhat more in women storage depots for neutral fats, chiefly triglycerides key regulators of the body’s overall energy metabolism Adipocytes specialize in concentrating triglycerides as lipid droplet(s) Adipose tissue Adipocytes are active cells metabolically release hormones and various other important substances Conducts heat poorly and provides thermal insulation also fills spaces between other tissues help shape the body surface, and cushion regions subject to repeated mechanical stress DO NOT UNDERGO CELL DIVISION Adipose tissue 2 major types White adipose tissue Brown adipose tissue WHITE ADIPOSE TISSUE Specialized for relatively long-term energy storage undergo HYPERTROPHY Adipocytes: spherical when isolated but are polyhedral when closely packed in situ Completely developed: very large; contains a single huge droplet of lipid filling almost the entire cell Unilocular Signet-ring appearance Histological appearance: Unilocular pattern Large lipid inclusion (white appearance) Peripherally located round nucleus Peripherally located cytoplasm White adipose tissue White adipocytes can store triglycerides derived from three sources: Chylomicrons Very-low-density lipoproteins (VLDLs) Free fatty acids and glycerol LEPTIN “satiety factor” helps regulate the appetite regulating the formation of new adipose tissue BROWN ADIPOSE TISSUE constitutes 2%-5% of the newborn body weight, located mainly in the back, neck, and shoulders it is greatly reduced during childhood and adolescence Adults kidneys, adrenal glands, aorta, and mediastinum Color d/t very abundant mitochondria and large number of capillaries Multilocular heat production and warming the blood Brown adipose tissue Cells are polygonal and smaller Nucleus: more centrally located often closely packed around large capillaries subdivided by connective tissue partitions into lobules Main function: thermogenesis uncoupling protein-1 (UCP1) or thermogenin – heat production is greater END Thank you for listening!