Histology of Connective Tissue Midterm PDF

Med-1 HISTOLOGY OF CONNECTIVE TISSUE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy exchange, aid in the defense and protection...

Med-1 HISTOLOGY OF CONNECTIVE TISSUE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy exchange, aid in the defense and protection of the body, and form a site for storage of fat. TOPIC OUTLINE Gives metabolic support to cells as the I. Connective Tissue medium for diffusion of nutrients and waste II. Connective Tissue Cells products - Fibroblasts Its major constituent is the extracellular - Macrophages matrix (ECM) which consist of different - Mononuclear Phagocyte System combinations of protein fibers and ground - Mast Cells substance. - Mast Cell Secretion Originate from embryonic mesenchyme - Plasma Cells (mesoderm); mesenchyme cells are III. Fibers undifferentiated and have large nuclei, - Collagen spindle-shaped, with prominent nucleoli and a. Type 1 Collagen fine chromatin b. Collagen Subunit c. Collagen Synthesis d. Disorders of Collagen Synthesis e. Assembly of Type 1 Collagen IV. Reticular FIbers - Formation of Elastic Fibers - Elastic FIber Elasticity V. Ground Substance VI. Glycosaminoglycans - Proteoglycans - Multiadhesive glycoproteins VI. Movement of fluid in Connective Tissue VII. Types of Connective Tissue VIII. Connective Tissue Proper IX. Reticular Tissue X. Mucoid Tissue CELLS OF CONNECTIVE TISSUE XI. Checkpoint CONNECTIVE TISSUE Forms a continuum with epithelial tissue, muscle, and nervous tissue as well as other components of connective tisses Provides a matrix that supports and physically connects other tissues and cells together to form the organs of the body. Its primary functions are to: provide Fibroblasts structural support, serve as a medium for Most common cells in connective tissue; synthesize and secrete collagen and elastin, COURSE CODE: Histology CONNECTIVE TISSUE Transcribed by: Olermo, S.R., Peña A.J. 1  Med-1 HISTOLOGY OF CONNECTIVE TISSUE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy which form large fibers, as well as the GAGs, proteoglycans, and multiadhesive glycoproteins. Key cells in connective tissue proper Have large active nuclei and eosinophilic cytoplasm; spindle-shaped Eosinophilic cytoplasmic processes resemble collagen bundles Active fibroblasts have large, euchromatic nuclei and basophilic cytoplasm, while inactive fibroblasts (or fibrocytes) are smaller with more heterochromatic nuclei. Adipocytes Fat cells found in connective tissue of many organs. They are specialized for cytoplasmic storage of lipids as neutral fats, or less commonly for the production of heat. Macrophages They have well-developed phagocytic ability and specialize in turnover of protein fibers and removal of dead cells, tissue debris, or other particulate material. They are present in connective tissue of most organs and are often referred to by pathologists as “histiocytes”. Also generally, they have well-developed Golgi apparatus and many lysosomes. Derived from monocytes in which they have increased in cell size and in protein synthesis COURSE CODE: Histology CONNECTIVE TISSUE Transcribed by: Olermo, S.R., Peña A.J. 2  Med-1 HISTOLOGY OF CONNECTIVE TISSUE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy Mast Cells Oval or irregularly shaped cells whose cytoplasm is filled with basophilic secretory granules. Mast cell granules display metachromasia, which means that they can change the color of some basic dyes from blue to purple to red. They function in the local inflammatory response, innate immunity, and tissue repair. They also promote the allergic reactions, aka immediate hypersensitivity reactions - Heparin, a sulfated GAG that acts - Characteristic features of macrophages seen locally as an anticoagulant in this TEM are the prominent nucleus (N) - Histamine, which promotes and the nucleolus (Nu) and the numerous increased vascular permeability and secondary lysosomes (L). The arrows smooth muscle contraction indicate phagocytic vacuoles near the - Serine proteases, which activate protrusions and indentations of the cell various mediators of inflammation surface. - Eosinophil and neutrophil Mononuclear phagocyte system chemotactic factors, which attract Comprises macrophages and those leukocytes monocyte-derived cells like Kupffer cells in - Cytokines, polypeptides directing the liver, microglial cells in the CNS, activities of leukocytes and other Langer-hans cells in the skin, and cells of the immune system osteoclasts in bone tissue. - Phospholipid precursors for They are important for the uptake, conversion to prostaglandins, processing, and presentation of antigens for leukotrienes, and other important lipid lymphocyte activation. mediators of the inflammatory Monocytes formed in yolk sac and become response. residents in developing organs Originate from progenitor cells in bone Long-living cells with relative inactivity marrow COURSE CODE: Histology CONNECTIVE TISSUE Transcribed by: Olermo, S.R., Peña A.J. 3  Med-1 HISTOLOGY OF CONNECTIVE TISSUE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy - Mast cells are components of loose connective tissues, often located near small blood vessels (a) Plasma cells are large, ovoid cells, with - Mast cell secretion is triggered by basophilic cytoplasm. The round nuclei frequently reexposure to certain antigens and allergens show peripheral clumps of heterochromatin, giving 1. IgE antibodies bind to antigens and the structure a “clock-face” appearance. crosslink 2. Adenylate cyclase is activated 3. Ca++ enters 4. Rapid exocytosis of some granules 5. Phospholipases act on membrane phospholipids to produce and release leukotrienes Plasma Cells B-lymphocyte-derived, antibody-producing cells Ovoid cells that have basophilic cytoplasm (b) Plasma are often more abundant in infected due to their richness in RER; the Golgi tissues, as in the inflamed lamina propria shown apparatus and centrioles occupy a region here. a large pale golgi apparatus (arrows) at a that may appear pale in routine histologic juxtanuclear site in each cell is actively involved in preparations; their nucleus are generally the terminal glycosylation of the antibodies spherical but eccentrically placed (glycoproteins). Plasma cells leave their sites of They are often more abundant in infected origin in lymphoid tissues, move to connective tissues, as in the inflamed lamina propria tissue, and produce antibodies that mediate Average life span is only 10-20 days immunity. COURSE CODE: Histology CONNECTIVE TISSUE Transcribed by: Olermo, S.R., Peña A.J. 4  Med-1 HISTOLOGY OF CONNECTIVE TISSUE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy Leukocytes Leave blood by migrating between COLLAGEN endothelial cells of venules Function in connective tissue only for a few hours or days and then undergo apoptosis Most abundant protein in the body (30% of A process called diapedesis increases dry weight) greatly during inflammation, which is a Key element of all connective tissues, vascular and cellular defensive response to epithelial basement membranes, and injury or foreign substances, including external laminae of muscle and nerve cells pathogenic bacteria or irritating chemical Can be categorized according to structures substances. formed by their interacting a-chains subunits: - Fibrillar collagens, notably collagen types I, II, and III have subunits that aggregate to form large fibrils clearly visible in the electron or light microscope. - Network- or sheet-forming collagens such as type IV collagen have subunits produced by epithelial cells and are the major structural proteins of external laminae and the basal lamina in all epithelia. - Linking/anchoring collagens are short collagens that link fibrillar collagen to one another (Type VII collagen) FIBER Collagen fibers, reticular fibers and elastic fibers Elongated in structures formed from proteins that polymerize after secretion from fibroblasts Collagen and reticular fibers are both formed by proteins of the collagen family. Elastic fibers are composed mainly of the protein elastin COURSE CODE: Histology CONNECTIVE TISSUE Transcribed by: Olermo, S.R., Peña A.J. 5  Med-1 HISTOLOGY OF CONNECTIVE TISSUE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy Type I Collagen 3 polypeptide chains are selected, aligned, and stabilized by disulfide bonds at their Most abundant collagen carboxyl terminals Forms large eosinophilic bundles usually May be homotrimeric (identical) or called collagen fibers heterotrimeric (different sequence) Often densely fill the connective tissue, Has two α1- and one α2-peptide chains forming structures such as tendon, organ Triple helix is formed at ER capsules, and dermis Right handed held together by hydrogen bonds and hydrophobic interactions Undergoes exocytosis and is cleaved COLLAGEN SUBUNIT Tropocollagen (former name of collagen molecule) May be homotrimeric or heterotrimeric Length 300 nm; width 1.5 nm and has a head to tail COLLAGEN SYNTHESIS Each collagen molecule is a triple helix composed of three intertwined polypeptide chains Procollagen a-chains precursor of the collagen molecule COURSE CODE: Histology CONNECTIVE TISSUE Transcribed by: Olermo, S.R., Peña A.J. 6  Med-1 HISTOLOGY OF CONNECTIVE TISSUE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy Hydroxylation and glycosylation of procollagen α chains and their assembly into triple helices occur in the RER, and further assembly into fibrils occurs in the ECM after secretion of procollagen. Rough Endoplasmic Reticulum Synthesis of procollagen ⍺ chains Hydroxylation Glycosylation Assembly of procollagen triple helix Extracellular Matrix Conversion of procollagen to tropocollagen molecules Aggregation of tropocollagen to form collagen fibrils Formation of covalent cross-links ASSEMBLY OF TYPE I COLLAGEN Because there are many slightly different genes for procollagen α chains and collagen production Characteristic feature of type I collagen: depends on several posttranslational events Transverse striations with regular periodicity involving several other enzymes, many diseases involving defective collagen synthesis have been described. DISORDERS OF COLLAGEN SYNTHESIS Collagen biosynthesis can be interrupted or changed by defective enzymes or by disease processes in any of its several steps. Collagenopathies - Collagen disease - caused by a deficit or abnormality in the production of specific collagens - Most common to mutations in alpha chains The photo shows an SEM view of type I collagen fibrils closely aggregated as part of a collagen fiber. Striations are visible on the surface of the fibrils. COURSE CODE: Histology CONNECTIVE TISSUE Transcribed by: Olermo, S.R., Peña A.J. 7  Med-1 HISTOLOGY OF CONNECTIVE TISSUE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy 1. Rodlike triple-helix collagen molecules, each - Due to high content of sugar chains 300 nm long, self-assemble in a highly bound to type III collagen organized, lengthwise arrangement of - Contain up to 10% CHO (other overlapping regions. collagen has only 1%) 2. The regular, overlapping arrangement of subunits continues as large collagen fibrils FORMATION OF ELASTIC FIBERS are assembled. 3. This structure causes fibrils to have characteristic cross striations with alternating Stages seen in TEM dark and light bands when observed in the a. A developing fiber consists of microfibrils EM. composed of fibrillin subunits 4. Fibrils assemble further and are linked - 10 nm diameter (fibrillin microfibrils) s together in larger collagen fibers visible by composed of molecular subunits secreted by light microscopy. fibroblasts and smooth muscle cells 5. Type I fibers often form into still larger b. Elastin is deposited on the scaffold of microfibrils, aggregates bundled and linked together by forming growing, amorphous composite structures. other collagens. - also secreted by the fibroblasts and quickly become cross-linked into larger assemblies c. Elastin accumulates and ultimately occupies most RETICULAR FIBERS of the center ELASTIC FIBER ELASTICITY Elastic fibers a. Adrenal cortex b. Lymph node stretch reversibly Serve as supportive stroma in most lymphoid when force is and hematopoietic organs and many applied due endocrine glands to the many Consist mainly of collagen type III - heavily covalent, glycosylated lysine-rich Argyrophilic desmosine - Characteristically stained black after rings impregnation with silver salts Also PAS-positive COURSE CODE: Histology CONNECTIVE TISSUE Transcribed by: Olermo, S.R., Peña A.J. 8  Med-1 HISTOLOGY OF CONNECTIVE TISSUE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy Elastin polypeptide Viscous - Acts as both a lubricant and a major components of elastic fibers barrier to penetration of invaders multiple random-coil domains that straighten or stretch under force, and then relax Glycosaminoglycans (GAGs) also called mucopolysaccharides Desmosine long polysaccharides consisting of repeating Cross-links between elastin subunits disaccharide units, usually a uronic acid Covalent and cyclic structure and a hexosamine involves four converted lysines in two elastin a. Hexosamine - can be glucosamine molecules or galactosamine holds the aggregate together with little steric b. Uronic acid - can be glucuronic or hindrance to elastin movements iduronic acid give the entire network its elastic quality - Maintain the rubberlike properties Hyaluronic acid (Hyaluronan) - largest, almost unique, and most ubiquitous GAG - Directly synthesized into ECM GROUND SUBSTANCE - dense, viscous network of polymers, which binds water, allowing diffusion of molecules in connective tissue and in lubricating various organs and joints - Synthesized by hyaluronate synthase 4 major GAGs found in proteoglycans - dermatan sulfate - chondroitin sulfates - keratan sulfate - heparan sulfate All other GAGs are much smaller, sulfated, and are synthesized in Golgi complexes. Highly hydrated, transparent, complex mixture of three major kinds of macromolecules - Glycosaminoglycans (GAGs) - Proteoglycans - Multiadhesive glycoproteins Fill the space between cells and fibers in connective tissue COURSE CODE: Histology CONNECTIVE TISSUE Transcribed by: Olermo, S.R., Peña A.J. 9  Med-1 HISTOLOGY OF CONNECTIVE TISSUE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy Proteoglycans Multiadhesive Glycoproteins composed of a core protein to which are covalently attached various numbers and combinations of the sulfated GAGs Synthesized on RER, mature in Golgi apparatus and secreted by exocytosis Diverse - distinguished by their diversity contain a greater mass of polysaccharide chains than polypeptide - aggrecan - Perlacan - Key proteoglycan in basal - laminae of epithelia - Decorin - small proteoglycan, has a few GAG side chains and binds fibrils of type I collagen - Syndecan - have transmembrane core proteins and serve as additional attachments of the cell to the ECM - Versican - large chondroitin sulfate/dermatan sulfate proteoglycan All have multiple binding sites for cell surface belonging to the aggrecan/lectican integrins and for other matrix family macromolecules - integrins Aggrecan - very large (250 kDA) Large molecules with branched - core protein bearing many chondroitin oligosaccharide chains - has a role for sulfate and keratan sulfate chains adhesion - bound via a link protein to polymer of Laminin hyaluronic acid - Abundant in all basal and external - Most abundant and important in articular laminae cartilage of joints - Binds integrin, type IV collagen Fibronectin - Has binding sites for ECM components and for integrins at cell surfaces - Has important roles in cell migration and maintenance of tissue structure - forms insoluble fibrillar networks throughout connective tissue Integrin - act as matrix receptors for specific sequences on laminin, fibronectin, some collagens, and certain other ECM proteins COURSE CODE: Histology CONNECTIVE TISSUE Transcribed by: Olermo, S.R., Peña A.J. 10  Med-1 HISTOLOGY OF CONNECTIVE TISSUE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy MOVEMENT OF FLUID IN CONNECTIVE TISSUE Interstitial fluid - Water in the ground substance of (a) Laminin is concentrated in the basal lamina of connective tissue the stratified epithelium (top) and in the external - Has ion composition similar to that of laminae surrounding cross sectioned nerves and blood plasma muscle fibers. - Also contains plasma proteins of low molecular weight Capillaries in connective tissue bring various nutrients required by cells and carry away their metabolic waste products. - Smallest blood vessels - One third (⅓) is stored in the matrix of connective tissue - The hydrostatic pressure of the blood caused by the pumping action of the heart, which forces water out across the capillary wall - The colloid osmotic pressure produced by plasma proteins such as albumin, which draws water back into the capillaries (b) a fine network of fibronectin is localized more diffusely throughout the eCM COURSE CODE: Histology CONNECTIVE TISSUE Transcribed by: Olermo, S.R., Peña A.J. 11  Med-1 HISTOLOGY OF CONNECTIVE TISSUE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy Scattered leukocytes can be seen in both connective TYPES OF CONNECTIVE TISSUE tissues, along with the large irregular spaces of lymphatic vessels Based on the different combinations and densities of - Forms a layer beneath epithelial the cells, fibers, and other ECM components lining - Fills spaces between fibers of muscle and nerve - Typically contains cells, fibers, and ground substance in roughly equal parts - Also called areolar tissue - Most numerous cells are fibroblasts - Collagen, reticular, and elastic fibers are present Lamina propria - Thick layer - beneath the epithelial lining of the digestive system CONNECTIVE TISSUE PROPER Loose connective tissue (a) loose connective tissue (L) of a gland contains faintly stained ground substance with fine fibers of collagen and (b) Trichrome staining of a section from skin frequently forms a thin layer near epithelia, while dense irregular connective tissue (d) forms a thicker layer and is demonstrates the blue staining of collagen with this invariably much richer in larger bundles of collagen. method and its relative density in loose (L) and COURSE CODE: Histology CONNECTIVE TISSUE Transcribed by: Olermo, S.R., Peña A.J. 12  Med-1 HISTOLOGY OF CONNECTIVE TISSUE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy dense irregular (d) connective tissue. Mallory as the testis shown here. Here the capsule is Staining covered by a simple epithelium of serous mesothelial cells (S), which produce a hyaluronate-rich lubricant around such organs Dense regular connective tissue - Consists mostly of type I collagen bundles and fibroblasts aligned in parallel - for resistance to prolonged or repeated stresses exerted in the same direction - Very little ground substance with very few blood vessels - Great resistance to prolonged or repeated stress from the same direction - Examples: tendons, aponeuroses, ligaments - hold together (c) another example of dense irregular connective components of the musculoskeletal tissue, showing the randomly arranged large system. collagen bundles. The arrangement of collagen strengthens the tissues and resists tearing from all directions.u (a) Micrograph shows a longitudinal section of dense regular connective tissue in a tendon. Long, parallel bundles of collagen fibers fill the spaces (D) Dense irregular connective tissue (d) forms a between the elongated nuclei of fibrocytes. thick, protective capsule around many organs such COURSE CODE: Histology CONNECTIVE TISSUE Transcribed by: Olermo, S.R., Peña A.J. 13  Med-1 HISTOLOGY OF CONNECTIVE TISSUE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy (a) The diagram shows only the fibers and attached reticular cells (free, transient cells are not (b) The electron micrograph shows one fibrocyte in represented). reticular fibers of type iii collagen are a cross section of tendon, revealing that the sparse produced and enveloped by the reticular cells, cytoplasm of the fibrocytes is divided into numerous forming an elaborate network through which thin cytoplasmic processes extending among interstitial fluid or lymph and wandering cells from adjacent collagen fibers blood pass continuously. RETICULAR TISSUE Characterized by abundant fibers of type III collagen (reticulin) forming a delicate network that supports various types of cells - Reticulin is produced by modified fibroblasts (reticular cells). Forms an elaborate network through which interstitial fluid or lymph and wandering cells from blood pass continuously Macrophages and other cells of the mononuclear phagocyte system are also dispersed within these reticular tissues to monitor cells formed there or passing through and to remove debris. COURSE CODE: Histology CONNECTIVE TISSUE Transcribed by: Olermo, S.R., Peña A.J. 14  Med-1 HISTOLOGY OF CONNECTIVE TISSUE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy (b) The micrograph shows a silver-stained section CHECKPOINT of lymph node in which reticular fibers are seen as irregular black lines. reticular cells are also heavily stained and dark. Most of the smaller, more lightly 1. Identify what type of connective tissue stained cells are lymphocytes passing through the lymph node. A. MUCOID TISSUE Mucous connective tissue Principal component of fetal umbilical cord (Wharton’s jelly) Gelatinous, with sparse collagen fibers and scattered fibroblasts Has abundant ground substance composed mostly of hyaluronan Resembles embryonic mesenchyme B. Similar to tissue found in vitreous chambers of eyes and pulp 2. What do you call the wavy lines in the picture? A section of umbilical cord shows large fibroblasts surrounded by a large amount of very loose eCM containing mainly ground substances very rich in hyaluronan, with wisps of collagen. Histologically mucoid (or mucous) connective tissue resembles embryonic mesenchyme in many respects and is rarely found in adult organs. COURSE CODE: Histology CONNECTIVE TISSUE Transcribed by: Olermo, S.R., Peña A.J. 15  Med-1 HISTOLOGY OF CONNECTIVE TISSUE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy 3. Identify 4. Identify 5. Identify COURSE CODE: Histology CONNECTIVE TISSUE Transcribed by: Olermo, S.R., Peña A.J. 16  Med-1 HISTOLOGY OF ADIPOSE TISSUE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy Provides thermal insulation because adipose tissue conducts heat poorly TOPIC OUTLINE Fills spaces between other tissues and helps I. Adipose Tissue Shape body surfaces where pad-like II. White Adipose Tissue deposits act as shock absorbers, chiefly in III. Lipid Storage and Mobilization the soles and palms a. Chylomicrons Cushion regions subject to repeated b. Very low-density lipoproteins mechanical stress (VLDLs) IV. Histogenesis V. Brown Adipose Tissue VI. Obesity VII. Checkpoint ADIPOSE TISSUE Specialized connective tissue in which WHITE ADIPOSE TISSUE fat-storing cells (adipocytes) predominate Normally represents 15-20% or body weight in men; more in women Plays an important role in energy homeostasis Efficiently stores excess energy Storage for neutral fats, chiefly triglycerides, long-chain fatty acyl esters of glycerol Key regulator of body’s overall energy metabolism Now recognized as an endocrine organ for nutritional homeostasis and for releasing hormones and various other important substances The more common type of adipose tissue that is composed of cells that, when COURSE CODE: Histology ADIPOSE TISSUE Transcribed by: Olermo, S.R., Peña A.J. 1  Med-1 HISTOLOGY OF ADIPOSE TISSUE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy developed, contain one very large droplet of whitish-yellow fat in their cytoplasm Spherical when isolated but are polyhedral (b) Large (empty) when closely packed in situ; each cell is very adipocytes large, between 50 to 150 µm in diameter predominate in this Unilocular adipose tissue - because the typical white adipose triglycerides are stored in this single large tissue, which shows droplet only a small portion Specialized for long-term energy storage of micro vasculature. Often empty in standard microscopy because lipid is removed from cells by xylene or other solvents used in routine (c) Tissue was fixed histological techniques here with osmium Distribution changes significantly through life tetroxide, which and is partly regulated by sex hormones - preserves lipid (L) control adipose deposition in the breasts and and stains it black. thighs Most cytoplasmic organelles are near the (d) The specimen peripheral nucleus; most of the cytoplasm here was from a surrounds the nucleus and contains young mammal, and mitochondria, a small Golgi apparatus, a few the adipocytes cisternae of RER, and free polyribosomes marked with asterisks The lipid droplet-cytoplasm interface is are not yet unilocular, reinforced by intermediate filaments of having many small vimentin lipid droplets in their cytoplasm, which indicates that Great abundance of caveolae important for their differentiation is not yet complete. The lipid trafficking and formation of large eccentric nuclei of unilocular cells are indicated by triglyceride storage droplet arrowheads. Can store triglycerides derived from three sources ○ Chylomicrons ○ VLDLs (very-low-density lipoproteins) ○ FFA and glycerol (a) Large white adipocytes (A) are seen in the connective tissue associated with small blood vessels. The fat cells are empty because lipid was dissolved away in slide preparation COURSE CODE: Histology ADIPOSE TISSUE Transcribed by: Olermo, S.R., Peña A.J. 2  Med-1 HISTOLOGY OF ADIPOSE TISSUE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy Secretes a variety of adipokines, which LIPID STORAGE MOBILIZATION include hormones, growth factors, and cytokines Leptin – exclusive secreted by adipose tissue; involved in regulation of energy homeostasis; inhibits food intake and stimulates metabolic rate and loss of body weight – “satiety factor” Circulating satiety factor controls food intake when the body’s store of energy is sufficient. Triglycerides stored by cells of white adipose tissue can be derived from dietary fats brought to adipocytes as circulating: - CHYLOMICRONS - VLDL - FA and Glycerols Sources of Triglycerides Triglycerides stored in white adipose tissue originate from three main sources: 1. Dietary Fats: These are transported to adipocytes via circulating chylomicrons. 2. Liver-Synthesized Triglycerides: These are synthesized in the liver and transported through the bloodstream as very-low-density lipoproteins (VLDLs). 3. Local Synthesis: White adipocytes can also synthesize free fatty acids and glycerol from glucose, contributing to triglyceride formation COURSE CODE: Histology ADIPOSE TISSUE Transcribed by: Olermo, S.R., Peña A.J. 3  Med-1 HISTOLOGY OF ADIPOSE TISSUE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy 2. FFA enters adipocytes and combines with CHYLOMICRON AND VLDL glycerol and is deposited in lipid droplets. Formed from ingested lipids in epithelial cells 3. When adipocytes are stimulated, stored lipids are lining the small intestine and transported in mobilized and cells release FFA and glycerol. blood and lymph Consist of a core containing mainly of 4. FFA bind albumin in blood for transport triglycerides, surrounded by a stabilizing throughout the body. monolayer of phospholipids, cholesterol, and apolipoproteins Norepinephrine (& GH) activates hormone-sensitive lipase Role of Insulin in Triglyceride Storage Insulin plays a key role in enhancing lipid storage within white adipose tissue. It accelerates fatty acid synthesis from glucose, stimulates glucose uptake by adipocytes, and increases the production of lipoprotein lipase, which facilitates the storage of triglycerides. Lipid Mobilization When stimulated by nerves or hormones, such as Lipid Uptake and Storage in Adipocytes norepinephrine from sympathetic nerves, stored Triglycerides carried by chylomicrons and VLDL are lipids are mobilized within adipocytes. hydrolyzed at the luminal surfaces of blood Norepinephrine activates hormone-sensitive lipase, capillaries within the adipose tissue by lipoprotein which breaks down triglycerides at the surface of lipase, an enzyme synthesized by adipocytes. This lipid droplets. Free fatty acids are released into the process releases free fatty acids, which are taken bloodstream, where they bind to albumin for up by adipocytes through both active transport and transport throughout the body. The more diffusion. water-soluble glycerol is taken up by the liver for Within the adipocytes, free fatty acids recombine further processing. with glycerol phosphate, derived from glucose Insulin inhibits this lipid mobilization process by metabolism, to form triglycerides. These reducing the activity of hormone-sensitive lipase. triglycerides are stored as lipid droplets in the Other hormones, such as glucagon and growth adipocytes. Mitochondria and smooth endoplasmic hormone, promote the breakdown of triglycerides reticulum (SER) are involved in this lipid uptake and and the release of fatty acids from adipose tissue. storage process. Endocrine Function of White Adipose Tissue 1. Chylomicrons and VLDLs are hydrolyzed in In addition to its role in lipid storage, white adipose capillaries by lipoprotein lipase. tissue functions as an endocrine organ. It is the sole producer of the hormone leptin, a 16-kDa polypeptide that plays a vital role in regulating COURSE CODE: Histology ADIPOSE TISSUE Transcribed by: Olermo, S.R., Peña A.J. 4  Med-1 HISTOLOGY OF ADIPOSE TISSUE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy appetite and fat formation. Leptin acts on target cells Peroxisome in the hypothalamus and other organs, serving as a proliferator-activated “satiety factor” that helps regulate energy balance receptor gamma (PPAR𝛾) and fat deposition under normal physiological in complex with retinoid X conditions. receptor (RXR) - Master HISTOGENESIS switch for white adipocyte differentiation - target genes in adipose tissue influence lipogenic pathways and initiate the storage of triglycerides PR domain containing 16 (PRDM16) with PPAR𝛾 coactivator-1 (PGC-1) - Master switch for brown adipocyte differentiation Adipocytes are able to undergo transdifferentiation in response to thermogenic needs of an organism Transdifferentiation Brown adipocytes are able to transform into white adipocytes when the energy balance is positive and Mesenchymal stem cells differentiate as the body requires an increase of triglyceride storage progenitor cells for all types of connective capacity. Mature white adipocytes can transform tissue. into brown adipocytes to generate body heat. Preadipocytes developing within the lateral mesoderm produce white (and beige) White-to-brown transdifferentiation of adipose adipocytes - differentiation is first seen with tissue the appearance of preadipocytes Cold temperatures are sensed by the central Preadipocytes located in the paraxial nervous system, causing increased stimulation of mesoderm remain multilocular and the noradrenergic sympathetic nerve system. differentiate into brown adipocytes. Physical exercise stimulation is more complicated and involves the secretion of atrial and ventricular natriuretic peptides in the heart that act on the kidney, which in turn activate transcription factors essential for brown adipocyte differentiation BROWN ADIPOSE TISSUE COURSE CODE: Histology ADIPOSE TISSUE Transcribed by: Olermo, S.R., Peña A.J. 5  Med-1 HISTOLOGY OF ADIPOSE TISSUE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy Metabolic activity is largely regulated by norepinephrine released from the sympathetic nerve terminals - which stimulates lipolysis and hydrolysis of triglycerides as well as increases mitochondrial expression and activity of UCP-1 molecules. In experimental animals, UCP-1 activity has been shown to increase during cold stress. Constitutes 2%-5% of newborn body weight; greatly reduced during childhood and adolescence Has central spherical nucleus Contain many small lipid inclusions (multilocular) Color is due to abundant mitochondria containing cytochrome pigment - BROWN FAT Upregulated levels of uncoupling protein (UCP1) or thermogenin Function: heat production Subdivided into lobules by partitions of connective tissue Has rich supply of capillaries that enhance its color Thermogenesis is facilitated by UCP-1 found at the inner mitochondrial membrane. This type of heat production is known as nonshivering thermogenesis. OBESITY Thermogenin (uncoupling protein (UCP-1) permits the backflow of protons previously Excessive adipose tissue accumulation transported to the intramembranous space without Nutritional intake exceeds energy passing through the ATP–synthetase complexes. expenditure Adult obesity Hibernation - Hypertrophy of adipocytes In animals ending their hibernation period, or in Childhood obesity newborn humans exposed to an environment colder - Hyperplasia & hypertrophy of than the uterus, nerve impulses liberate adipocytes norepinephrine into brown adipose tissue. COURSE CODE: Histology ADIPOSE TISSUE Transcribed by: Olermo, S.R., Peña A.J. 6  Med-1 HISTOLOGY OF ADIPOSE TISSUE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy 2. What is primarily produced by adipose tissue and functions as “satiety factor”? 3. How is brown adipose tissue different in newborns compared to adults? 4. What changes occur in adipose tissue during obesity? Changes in adipocyte metabolism in obesity Adipocytes from obese individuals are hypertrophic and produce more leptin. Increased leptin secretion causes non adipose tissue to become resistant to leptin. Hypertrophic adipocytes also secrete high amounts of fatty acids and adipokines that promote insulin resistance. This leads to pathological accumulation of lipids in organs, such as the kidney (renal lipotoxicity), liver (nonalcoholic fatty liver disease), pancreas, and heart. CHECKPOINT 1. Identify A. B. COURSE CODE: Histology ADIPOSE TISSUE Transcribed by: Olermo, S.R., Peña A.J. 7  Med-1 HISTOLOGY OF CARTILAGE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy proteoglycans, interacting with collagen and elastic fibers. TOPIC OUTLINE The firm consistency of the cartilage ECM I. Cartilage allows tissue to bear mechanical stress II. Hyaline Cartilage without permanent damage - Matrix Because of its smooth, lubricated surface - Chondrocytes and resiliency, cartilage provides cushioning - Perichondrium and sliding regions within skeletal joints and III. Elastic Cartilage facilitates bone movements IV. Fibrocartilage Also guides development and growth of long V. Chondrogenesis bones, both before and after birth. VI. Checkpoint Consist of: Chondrocytes CARTILAGE embedded in an extensive ECM. It synthesize and maintain ECM components and are located in matrix cavities called lacunae. Perichondrium - Sheath of dense connective tissue that surrounds cartilage in most places; Harbors blood supply and nerve supply to the cartilage Territorial matrix are the matrix immediately around the lacuna. Interterritorial matrix are those (a) There are three types of adult cartilage that are more distant from lacunae distributed in many areas of the skeleton, particularly in joints and where pliable support is shows the interaction between type useful, as in the ribs, ears, and nose. Cartilage ii collagen fibrils and proteoglycans linked to hyaluronic acid. Link support of other tissues throughout the respiratory proteins non covalently bind the tract is also prominent. The photomicrographs show protein core of proteoglycans to the linear hyaluronic acid molecules. the main features of (b) hyaline cartilage, (c) The chondroitin sulfate side chains fibrocartilage, and (d) elastic cartilage. Dense of the proteoglycan electrostatically connective tissue or perichondrium is shown here bind to the collagen fibrils, forming a cross-linked matrix. The circled area with hyaline and elastic cartilage. is shown larger in the lower part of the figure. Physical properties of Tough, durable form of supporting these matrix components produce a highly hydrated, pliable material with connective tissue characterized by ECM with great strength. Approximately 75% of the wet weight of hyaline cartilage high concentrations of GAGs and is water. COURSE CODE: Histology CARTILAGE Transcribed by: Olermo, S.R., Peña A.J. 1  Med-1 HISTOLOGY OF CARTILAGE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy Physical properties depend on electrostatic Homogenous, semitransparent, amorphous bonds between type II collagen fibrils, Provides a low-friction surface hyaluronan, and the sulfated GAGs on Participates in lubricating synovial joints proteoglycans. Distributes applied forces to the underlying Semirigid consistency due to water bound to bone hyaluronan and GAGs - The high content of Forms the template for endochondral bone bound water allows cartilage to serve as a shock absorber, a role of major functional In adults, found in: articular surfaces of movable importance. joints, in the walls of larger respiratory passages Lacks vascular supplies and nerves - (nose, larynx, trachea, bronchi), in the ventral ends receives nutrients by diffusion from of ribs, where they articulate with the sternum and capillaries in adjacent connective tissue in the epiphyseal plates of long bones, where it (perichondrium) makes possible longitudinal bone growth. Chondrocytes receive nutrients by diffusion and exhibit low metabolic activity In embryo, forms the temporary skeleton that is gradually replaced by bone. Produced by chondrocytes and contains three major classes of molecules: Collagen Proteoglycans Multiadhesive glycoproteins HYALINE CARTILAGE 1. Collagen Molecules Collagen is the major matrix protein forming a three-dimensional meshwork. Types of collagen in hyaline cartilage: ○ Type II collagen: Main component, forming the bulk of the fibrils. ○ Type IX collagen: Facilitates interaction with matrix proteoglycan molecules. ○ Type XI collagen: Regulates fibril size. Most common type Glassy appearance COURSE CODE: Histology CARTILAGE Transcribed by: Olermo, S.R., Peña A.J. 2  Med-1 HISTOLOGY OF CARTILAGE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy ○ Type X collagen: Organizes fibrils MATRIX into a 3D hexagonal lattice for mechanical function. ○ Type VI collagen: Found at the periphery of chondrocytes, helps attach cells to the matrix. Types II, VI, IX, X, and XI are cartilage-specific collagens. 2. Proteoglycans The ground substance of hyaline cartilage contains three glycosaminoglycans: hyaluronan, chondroitin sulfate, and keratan sulfate. Aggrecan is the most important proteoglycan monomer in hyaline cartilage (250 kDa), with high affinity for water due to Dry weight is ~40% collagen (mostly type II) sulfate groups. Firm, hydrated gel of proteoglycans and Aggrecan forms large aggregates with structural glycoproteins hyaluronan via link proteins, contributing to Aggrecan – most abundant the biomechanical properties of hyaline Water bound to GAGs constitutes 60%-80% cartilage. of weight - Much of this water is bound Other proteoglycans, such as decorin, tightly to the aggrecan– hyaluronan biglycan, and fibromodulin, stabilize the aggregates, which create high osmotic matrix but do not form aggregates. swelling pressure. Chondronectin mediates adherence of 3. Multiadhesive Glycoproteins chondrocytes to ECM. These non-collagenous, CHONDROCYTES non-proteoglycan-linked glycoproteins influence interactions between chondrocytes and matrix molecules. Important examples include: May appear as isogenous aggregates - ○ Anchorin CII (Cartilage Annexin V): round and may appear in groups of up to Functions as a collagen receptor on eight cells that originate from mitotic chondrocytes. divisions of a single chondrocyte ○ Tenascin and Fibronectin: Involved Metabolize glucose by anaerobic glycolysis - in matrix stability. to produce lactic acid as the end product These glycoproteins serve as markers of Somatotropin – growth regulator, acts cartilage turnover and degeneration. indirectly, promoting the endocrine release COURSE CODE: Histology CARTILAGE Transcribed by: Olermo, S.R., Peña A.J. 3  Med-1 HISTOLOGY OF CARTILAGE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy from the liver of insulin-like growth factors, or cells will separate into individual lacunae as they somatomedins, which directly stimulates begin to secrete matrix. proliferation of chondrocytes There is a gradual ELASTIC CARTILAGE transition and differentiation of cells from the perichondrium to the cartilage, with elongated fibroblastic cells becoming larger and more rounded chondroblasts and chondrocytes (C) located within spaces or lacunae surrounded by the matrix (M) secreted by the cells Essentially similar to hyaline cartilage, but contains an abundant network of elastic PERICHONDRIUM fibers (elastin) in ECM Collagen type II- gives yellowish color Covers hyaline cartilage, except in articular More flexible - found in the auricle of the ear, cartilage the walls of the external auditory canals, the essential for the growth and maintenance of auditory (eustachian) tubes, the epiglottis, cartilage and the cuneiform cartilage in the larynx. Outer layer has type I collagen fibers and surrounded by perichondrium and it fibroblasts; inner layer also has increases in size by both appositional and mesenchymal stem cells - progenitor cells interstitial growth for chondroblasts that divide and differentiate Does not calcify during the aging process into chondrocytes. unlike hyaline cartilage The thin region of hyaline cartilage shown here has perichondrium (P) on both sides and shows larger lacunae containing isogenous groups of chondrocytes (C) within the matrix (M). Such groups of two, four, or more cells are produced by mitosis; the COURSE CODE: Histology CARTILAGE Transcribed by: Olermo, S.R., Peña A.J. 4  Med-1 HISTOLOGY OF CARTILAGE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy The chondrocytes (C) and overall organization of The axially arranged elastic cartilage are similar to those of hyaline aggregates of cartilage. Stains for elastin, however, reveal many chondrocytes (C) are dark-staining elastic fibers in the matrix (M), in seen to be surrounded by addition to the major components found in the small amounts of matrix hyaline matrix. elastic fibers provide greater and sepa rated by larger flexibility to this form of cartilage. regions with dense collagen (D) and a small FIBROCARTILAGE number of fibroblasts with elongated nuclei (arrows). CHONDROGENESIS Chondrogenesis The process of cartilage development begins with the aggregation of chondroprogenitor mesenchymal cells to form a mass of rounded, closely opposed cells. Essentially a mingling of hyaline cartilage Chondroblasts and dense connective tissue - Young chondrocytes undergoing Serves as very tough yet cushioning support rapid proliferation tissue - found in intervertebral discs, in Takes place primarily from center outward - attachments of certain ligaments, and in the therefore the more central cells have the pubic symphysis characteristics of chondrocytes, whereas the Chondrocytes appear singly and often in peripheral cells are typical chondroblasts. aligned isogenous aggregates- produce Superficial mesenchyme develops as matrix containing type II collagen. perichondrium. Sparse hyaline matrix with scarce Cartilage grows by interstitial growth or proteoglycans - makes the matrix of appositional growth fibrocartilage more acidophilic than that of - appositional growth, the process hyaline or elastic cartilage that forms new cartilage at the Versican > aggrecan surface of an existing cartilage Regions of fibroblasts and dense type I - interstitial growth, the process that collagen confer extra tensile strength forms new cartilage within an existing No perichondrium cartilage mass. Repair is very slow due to avascularity and low metabolic rate - Some repair can occur but only if the defect involves the perichondrium. COURSE CODE: Histology CARTILAGE Transcribed by: Olermo, S.R., Peña A.J. 5  Med-1 HISTOLOGY OF CARTILAGE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy (a) Mesenchyme is the precursor for all types of cartilage. (b) Mitosis and early differentiation produces a tissue with condensations of rounded cells called chondroblasts. (c) Chondroblasts are then separated from one another again by their production of various matrix components, which collectively swell with water and form the very extensive eCM. (d) Multiplication of chondroblasts within the matrix gives rise to isogenous cell aggregates surrounded by a condensation of the territorial matrix. In mature cartilage, this interstitial mitotic activity ceases and all chondrocytes typically become more widely separated by their production of matrix. COURSE CODE: Histology CARTILAGE Transcribed by: Olermo, S.R., Peña A.J. 6  Med-1 HISTOLOGY OF CARTILAGE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy 4. Identify CHECKPOINT 1. Label 5. Identify 2. Identify what type of cartilage 6. Identify 3. Identify and label the arrow COURSE CODE: Histology CARTILAGE Transcribed by: Olermo, S.R., Peña A.J. 7  Med-1 HISTOLOGY OF CARTILAGE SEMESTER 1 | ACADEMIC YEAR- 2024 | PROF: Dr. Ian Val Uy COURSE CODE: Histology CARTILAGE Transcribed by: Olermo, S.R., Peña A.J. 8