Histology & Genetics Connective Tissues (HG201A) PDF

HISTOLOGY & GENETICS T02 HG201A | Dr. Ronnie Mayo | PSU School of Medicine Year 1 | Batch 2028 08/19/2024...

HISTOLOGY & GENETICS T02 HG201A | Dr. Ronnie Mayo | PSU School of Medicine Year 1 | Batch 2028 08/19/2024 CONNECTIVE TISSUES ○ Mesenchyme– primarily found in the embryo and OUTLINE contains: cells: spindle shaped, relatively uniform gap junctions I. Connective Tissue IV. Classification of CT viscous ground substance in A. Origin A. Soft extracellular space B. Function 1. Loose collagen and reticular fibers: few, very II. Extracellular Matrix a) Areolar A. Ground substance b) Adipose fine and relatively sparse B. Extracellular fibers c) Reticular the small amounts of collagen fibers is 1. Collagen 2. Dense consistent with the limited physical 2. Reticular a) Dense stress on the growing fetus 3. Elastic Regular ○ Mucous CT– present in the umbilical cord and III. CT Cell Types b) Dense consists of A. Resident Irregular 1. Fibroblast B. Skeletal ECM: almost gelatin like, composed 2. Macrophage 1. Cartilage mainly of hyaluronan 3. Adipocyte a) Hyaline ground substance: Wharton’s jelly 4. Mast cells b) Elastic occupies large intercellular spaces 5. Adult stem c) Fibrocartila cells: spindle shaped, widely separated, cells -ge B. Wandering 2. Bone appear much like fibroblasts 1. Lymphocytes a) Woven collagen fibers: thin and wispy 2. Plasma cells b) Haversian 3. Neutrophils 3. Dental WHARTON’S JELLY MESENCHYMAL STEM CELL MARKERS 4. Eosinophils a) Dentine Some cells from Wharton’s jelly express mesenchymal stem 5. Basophils b) Enamel 6. Monocyte C. Specialized CT cell markers and differentiate into osteocytes, chondrocytes, (Macrophages) 1. Blood adipocytes, and neural-like cells. 2. Lymphoid V. References FUNCTION Can act as a protective layer of the body CONNECTIVE TISSUE Structural support Arises from the mesoderm in the embryo ○ Ex: skeletal bones Consists of Connect one structure to another cells positioned far apart, and ○ Ex: Tendon (muscle to bone) surrounding extracellular matrix (ECM) ○ Ex: Ligaments (bone to bone) Fibroblasts– major cell type in connective tissues Components are dependent on location and function Important in the formation of the different types of ○ Ex: Skeletal bones extracellular fibers function: structural support Produce and maintain the ground substance components: calcified ECM, calcium, Cell type and ECM components depend on type of phosphorus, etc. connective tissue ○ Ex: Lymph, Adipose cells, Blood (Specialized ECM can appear like a gel or like a hard CT), Cartilage (soft bone), Bone (calcified/hard) substance (ex: bones) ORIGIN The mesoderm gives rise to almost all of the CT ○ Except head region (derived from ectoderm hu way of the neural crest cells) Mesenchyme– primitive connective tissue ○ In the head region, it is sometimes called ectomesenchyme ○ Established through proliferation and migration of mesodermal and specific neural crest cells ○ Maturation and proliferation gives rise to: various CT of the adult muscle, vascular, urogenital systems serous membranes of the body cavities EMBRYONIC CONNECTIVE TISSUE Fig 2.1. Functions of Connective Tissues Embryonic CT is classified into two subtypes: - HG201A TRANSCRIBERS: Plete, Cait, Escote, Gamba, Manila, Padasas, Rodriguez M, Sarmiento, Taha, Toledo, Villas 1  EPITHELIAL TISSUES AND HISTOLOGY BASICS TRANS #2 CT EXTRACELLULAR MATRIX Occur in the reticular lamina of basement The extracellular matrix (ECM) consists of ground membranes substance (nonfibrous area) and large protein Typically surround adipocytes, smooth fibers (collagen, retricular and elastic) produced by muscles and nerve fibers, and small blood the fibroblasts. vessels Exceptions in fibroblast production: ○ Schwann cells secrete reticular fibers GROUND SUBSTANCE ○ Endoneurium of peripheral nerves Watery, largely unstained ECM that is more abundant ○ Tunica media of blood vessels than fibers in some types of connective tissue ○ Muscularis of alimentary canal highly hydrated (with much bound water), gel-like Support rapidly changing populations of mixture composed mainly of glycosaminoglycans proliferating cells and phagocytic cells of the (GAGs), proteoglycans, and multiadhesive stroma of hemopoeitic tissue (bone marrow), spleen glycoproteins. & lymph nodes Function: fills spaces between cells and fibers, allowing molecule diffusion, acting as a lubricant, and serving as a barrier to invaders. GAGs: Long, negatively charged polysaccharides that attract water, contributing to the ECM's cushioning and lubricating functions. Proteoglycans: Core proteins with attached GAGs, playing roles in ECM structure and function. Glycoproteins: Proteins that help cells adhere to and communicate within the ECM. EXTRACELLULAR FIBER COLLAGEN FIBER Fig 2.4. Reticular Fibers in the lymph node most abundant protein in ECM and in human body Produced by fibroblasts ELASTIC FIBER Collagen fibrils Thinner than collagen fibers Bundles of fine, thread-like subunits of the fiber Arranged in branching pattern to form a 3D network Properties: High tensile strength Allows body tissue to spring back into shape Function: help tissue withstand stretching and Found in organs subject to regular stretching or deformation bending Location: Commonly found in tendons. lungs, skin, urinary bladder Structure: Composed of a triple helix called Composite of fibrillin, which forms a network of tropocollagen (collagen molecule) microfibrils, embedded in a larger mass of cross- linked elastin Fine structure: Elastin Fig 2.2. Triple helix structure of Collagen (tropocollagen) ○ Central core ○ Loosely cross-linked ○ Extensible protein rich in proline and glycine ○ Also contains desmosine and isodesmosine, unique to elastin Responsible for covalent bonding of elastin molecules to one another ○ Elastic Lamellae Fenestrated sheets of elastic found in walls of arteris & other large blood vessels ○ Resists digestion by most protease, but is hydrolyzes by pancreatic elastase Glycoprotein Outer Coat Fig 2.3. Bundle of Collagen Fibers under electron microscope ○ Microfibrils (fibrillin) organise elastic core ○ For elastogenesis RETICULAR FIBER For the formation (genesis) of elastin Provide the supporting framework for cellular (elasto) constituents of various tissues and organs Produced by fibroblasts and smooth muscle cells Consists of collagen fibrils like collagen type I but is composed of type III collagen Reticular Cell Produces collagen for reticular fibers In most other locations, fibroblasts produce reticular fibers: HG201A TRANSCRIBERS: Plete, Cait, Escote, Gamba, Manila, Padasas, Rodriguez M, Sarmiento, Taha, Toledo, Villas 2  EPITHELIAL TISSUES AND HISTOLOGY BASICS TRANS #2 Fig 2.7. Photomicrograph of a connective tissue specimen Fig 2.5. Electron micrograph of an elastic fiber in a routine H&E-stained, paraffinembedded preparation shows nuclei of fibroblasts (F) RESIDENT CELLS Activated fibroblasts (wound repair or when ECM Relatively stable material is produced) → cytoplasm is more extensive, Exhibit little movement may display basophilia Regarded as permanent residents of the tissue FIBROBLASTS Principal cell of connective tissue Located close to collagen fibers Responsible for synthesis of collagen, elastic and reticular fibers, complex carbohydrates of ground substance → research suggests a single fibroblast can produce all ECM components Examine with TEM → cytoplasm exhibits profiles of rER and Golgi apparatus Fig 2.8. During wound repair, activated fibroblasts (F) exhibit more basophilic cytoplasm MYOFIBROBLAST Elongated, spindly connective tissue cell → characterized by bundles of actin filament with associated actin motor proteins (e.g. nonmuscle myosin) Displays properties of fibroblasts and smooth muscle cells BUT lacks a surrounding basal lamina Often exists as an isolated cell Not readily identifiable in H&E preparations Fibronexus ○ Site of actin fibers attachment to the plasma membrane ○ Serves as cell-to-ECM anchoring junction ○ Basis of mechanotransduction system → force generated by the contraction of intracellular actin bundles is transmitted to the ECM Fig 2.6. Electron micrograph of fibroblasts. Shows distended cisternae of the ER, indicating active synthesis. Membranes of the Golgi apparatus (G) are in proximity to the rER. Collagen fibrils (CF) surround the cells, almost all of which have been cut in cross-section and thus appear as small dots at this magnification. H&E PREPARATION Often only nucleus is visible Elongated or disc-like structure HG201A TRANSCRIBERS: Plete, Cait, Escote, Gamba, Manila, Padasas, Rodriguez M, Sarmiento, Taha, Toledo, Villas 3  EPITHELIAL TISSUES AND HISTOLOGY BASICS TRANS #2 Fig 2.9. Electron micrograph of myofibroblasts. Shows ADIPOCYTES areas with moderate amount of rER. Contain aggregates of thin filaments and cytoplasmic densities (arrows) that are Connective tissue cell specialized to store neutral characteristic of smooth muscle cells. fat and produce a variety of hormones Differentiate from mesenchymal stem cells and MACROPHAGES gradually accumulate fat in their cytoplasm a.k.a. Tissue Histiocytes Located throughout loose connective tissue as Phagocytic cells derived from monocytes that contain individual cells and groups of cells an abundant number of lysosomes Involved in the synthesis of a variety of hormones, Release secretory products related to immune inflammatory mediators, and growth factors. response, anaphylaxis, and inflammation Difficult to identify unless they display obvious phagocytic activity MAST CELLS Indented or kidney-shaped nucleus Large, ovoid cells with a spherical nucleus and cytoplasm filled with large, basophilic granules Arise from a pluripotential hemopoietic stem cell (HSC) in bone marrow Differentiate in connective tissue Numerous in skin and mucous membranes but NOT in the brain and spinal cord 2 typesof human mast cells: ○ Connective tissue mast cells found in skin, intestinal submucosa, breast and axillary lymph nodes → contain granule-associated tryptase and chymase; lattice-like internal structure ○ Mucosal mast cells found in lungs and intestinal mucosa → produce only tryptase; scroll-like internal structure MAST CELL SECRETORY PRODUCTS Fig 2.10. Photomicrograph of macrophages (M) in the Mast cells’ basophilic granules store chemical connective tissue from the area of wound healing. substances known as mediators of inflammation Presence of an indented or kidney-shaped nucleus (N). ○ Preformed mediators: Stored in granules and Several mature neutrophils with segmented nuclei located released at time of mast cell activation in the connective tissue that surround blood vessel {BV) Histamine: increases permeability of small filled with red and white blood cells. blood vessels, causing edema in surrounding tissue and an itching sensation in the skin Examine with TEM → surface exhibits numerous folds Heparin: anticoagulant; useful for treatment and finger-like projections of thrombosis Serine proteases (tryptase and chymase): Tryptase released together with histamine; Chymase plays role in generating angiotensin II in response to vascular tissue injury Eosinophil chemotactic factor (ECF): Counteract effects of histamine Neutrophil chemotactic factor (NCF) ○ Newly synthesized mediators: Mostly lipids and cytokines, often absent in resting cells Leukotriene C (LTC4): similar to histamine; trigger prolonged constriction of smooth muscle in the pulmonary airways, causing bronchospasm Tumor necrosis factor α (TNF-α): antitumor effects Interleukins, Growth Factors, and Prostaglandin D2 Fig 2.11. Electron micrograph of a macrophage. Distinct ADULT STEM CELLS AND PERICYTES population of endocytotic vesicles, early and late Found in many tissues and organs, reside in specific endosomes, lysosomes, and phagolysosomes. The surface sites called niches of the cell reveals a number of finger-like projections, some of which may be sections of surface folds. Cannot differentiate into multiple lineages Bone marrow has a unique reservoir of stem cells MESENCHYMAL STEM CELLS Found in loose connective tissue of an adult HG201A TRANSCRIBERS: Plete, Cait, Escote, Gamba, Manila, Padasas, Rodriguez M, Sarmiento, Taha, Toledo, Villas 4  EPITHELIAL TISSUES AND HISTOLOGY BASICS TRANS #2 Give rise to differentiated cells CD56 ○ Function in repair and formation of new tissue, CD94 such as in wound healing ○ Note: these proteins are not found in other ○ Development of new blood vessels lymphocytes (neovascularization) ○ Not antigen specific Vascular pericytes are mesenchymal stem cells REASON: because they neither produce ○ a.k.a. Adventitial cells or perivascular cells immunoglobulins nor express TCR on ○ Found around capillaries and venules their surface ○ Can differentiate into: ○ Similarity with T lymphocyte: Osteoblasts They destroy virus-infected cells and Adipocytes some tumor cells by CYTOTOXIC Chondrocytes MECHANISM Fibroblasts ○ Note the importance of antigens: In response to the presence of antigens, lymphocytes become LYMPHOCYTES, PLASMA CELLS, AND OTHER activated, divides, and have clones CELLS OF IMMUNE SYSTEM LYMPHOCYTE: Involved in Immune Responses PLASMA CELLS smallest wandering cells in the connective tissue PLASMA CELLS: Has thin rim of cytoplasm surrounding a deeply Antibody-producing cells from B Lymphocytes staining, heterochromatic nucleus Normal components of salivary gland, lymph nodes, Cytoplasm: sometimes not visible hematopoietic tissue Most numerous in: lamina propria of the respiratory Derived from B lymphocyte and GIT ○ Remember: once derived, they have only REASON: because they are involved in LIMITED migratory ability and short life span (10- immunosurveillance against pathogens and 30 days) foreign substances that enter the body by Relatively large, ovoid crossing the EPITHELIAL lining has considerable amount of cytoplasm ○ Displays strong basophilia LYMPHOCYTE: Heterogeneous population of at least ○ REASON: due extensive rER 3 Major Functional Cell Types ○ Note the difference with Golgi Apparatus: GA: lack staining, appear as clear area CLUSTER OF DIFFERENTIATION OF under light microscope DIFFERENTIATION (CD) PROTEINS PC: has clumps of peripheral Its expression on the plasma membrane heterochromatin alternating with clear characterizes the lymphocyte areas of euchromatin in the nucleus Important role: Recognize specific ligands in target (check pic, page 202) cells TYPICAL FEATURES OF PLASMA CELLS ○ Considered as special marker protein because it 1. Nucleus: spherical and eccentrically positioned is present only on specific types of lymphocytes (offset) 2. Small (not larger than the lymphocytes’s nucleus) 3 FUNCTIONAL CELL TYPES– Classification is based on 3. Has large clumps of peripheral heterochromatic CD proteins alternating with clear areas of euchromatin T Lymphocytes ○ Characterized by presence of: Take note of this analogy for this arrangement: CD2 Heterochromatin is like the numbers of a CD3 clock or the spoke of the wheel (versus CD5 euchromatic: more relaxed) CD7 T-cell receptors (TCRs) How can they have heterochromatic nuclei despite ○ Have long lifespan synthesizing large amounts of protein? ○ effectors in cell-mediated immunity. REASON: Because despite producing large amounts B lymphocytes of protein, they produce ONLY ONE TYPE OF ○ Characterized by the presence of: PROTEIN. CD9 ○ ∴ only a small segment of the genome is exposed CD19 for transcription CD20 Added context: Why is a heterochromatic nucleus not Attached immunoglobulins IgM and lgD suitable for protein synthesis? ○ Recognize antigen ○ A heterochromatic nucleus is tightly packed and ○ Variable life span less accessible, making it difficult for the cell to ○ Effectors of antibody-mediated (humoral read and use the DNA. immunity) ○ Their clones mature into plasma cells EOSINOPHILES, MONOCYTES, NEUTROPHILS B lymphocyte NEUTROPHILS AND MONOCYTES ○ Characterized by the presence of: CD16 HG201A TRANSCRIBERS: Plete, Cait, Escote, Gamba, Manila, Padasas, Rodriguez M, Sarmiento, Taha, Toledo, Villas 5  EPITHELIAL TISSUES AND HISTOLOGY BASICS TRANS #2 ○ rapidly migrate from the blood to enter the Associated with the epithelium of glands and connective tissue due immune response and surrounds the smallest blood vessels. tissue injury Initial site where pathogenic agents that have ○ Sequence: breached an epithelial surface are challenged Neutrophils migrate > and destroyed by cells of the immune system. monocyte follows > Thus, it is the site of inflammatory and immune monocyte differentiate into macrophage reactions. EOSINOPHIL Most cell types are transient wandering cells ○ Functions in allergic reactions and parasitic that migrate from local blood vessels in response infections to specific stimuli. ○ Can be found in normal connective tissue as well Example: Lamina propria Lamina propria of the intestine (due to chronic immunologic response here) SPECIALIZED CONNECTIVE TISSUE BLOOD Is a specialized connected tissue consisting of cells and fluid extracellular material called plasma. Propelled mainly by rhythmic contractions of the heart, about 5L of blood in an average adult moves unidirectionally within the closed circulatory system. Blood cells and their derivatives include the following: Fig 2.12. Loose Areolar Connective Tissue ○ Erthrocytes (RBCs) Deliver the oxygen to the tissues and, in ADIPOSE exchange, bind carbon dioxide for White adipose (unilocular) removal from the tissue. ○ Contains Connective Tissue fibres (e.g. ○ Leukocytes (WBCs) reticulin) Leave the blood and migrate to the ○ Subcutaneous tissues where they become functional ○ Each cell contains one fat droplet and perform various activities related to ○ Specialized for relatively long-term immunity. energy storage. 2 Major Groups ○ Adipocytes of white adipose tissue are Granulocytes spherical when isolated but are Agranulocytes polyhedral when closely packed in ○ Platelets situ. Promote blood clotting and help repair ○ The distribution of white adipose tissue minor tears or leaks in the walls of small changes significantly through childhood blood vessels, preventing loss of blood and adult life and is partly regulated by from the microvasculature. sex hormones controlling adipose Lymphoid deposition in the breasts and thighs. Reticular connective tissue filled with large number of lymphocytes. Brown adipose (multilocular) It can be either diffuse within areas of loose ○ Multiple fat droplets connective tissue or surrounded by capsules, ○ Contains many mitochondria forming discrete (Secondary) lymphoid organs. ○ Energy release (heat) ○ High levels in neonates/infants SOFT ○ In adults it is found only in scattered areas (e.g. around the kidneys, adrenal LOOSE glands, aorta, and mediastinum). AREOLAR ○ The small lipid droplets, abundant Areolar means “small open space”. mitochondria, and rich vasculature all Can be described as packing material. contribute to its principal function (heat Characterized by thin and relatively sparse production and warming the blood). collagen fibers. Its ground substance ○ Cells of this tissue receive direct occupies more volume than the fibers. sympathetic innervation, which Has a viscous to gel-like consistency and regulates their metabolic activity. plays an important role in the diffusion of oxygen and nutrients from the small vessels that course through this connective tissue as well as in the diffusion of carbon dioxide and metabolic wastes back to the vessels. Located beneath the epithelia that cover the body surfaces and line the internal surfaces of the body. HG201A TRANSCRIBERS: Plete, Cait, Escote, Gamba, Manila, Padasas, Rodriguez M, Sarmiento, Taha, Toledo, Villas 6 EPITHELIAL TISSUES AND HISTOLOGY BASICS TRANS #2 Can be found in liver endocrine glands, lymph nodes and spleen. Fig 2.13. Locules of Adipose Connective Tissue (locule=small compartment) Fig 2.16. Reticular fibers in a lymph node DENSE Similar components as loose connective tissue but with fewer cells. Abundance of collagen provides organ protection and strengthens them structurally Further subcategorized into two basic types based on organization of its collagen fibers Dense irregular connective tissue Dense regular connective tissue DENSE IRREGULAR Bundles of collagen fibers appear randomly interwoven, with no definite orientation Contains relatively little ground substance Fig 2.14. Adipose Connective Tissue Examples include the deep dermis layer of skin and the capsules surrounding most organs. SYNOVIAL MEMBRANE It lines the joint cavity. It extends folds and villi into the joint cavity and produces the lubricant synovial fluid (blood plasma, hyaloronan and glycoproteins). In different diarthrotic joints the synovial membrane may have prominent regions with dense connective tissue or fat. The superficial regions of this tissue are usually well-vascularized, with many porous (fenestrated) capillaries. Fig 2.17. Collagen fibrils in dense irregular connective tissue. Thin outer layer (intima) - macrophages or This atomic force microscope image of type I collagen fibrils in fibroblasts the connective tissue shows the banding pattern on the Vascularised inner layer (subintima) - can be surface of collagen fibrils loose areolar, loose fibrous or adipose. DENSE REGULAR Characterized by ordered and densely packed arrays of fibers and cells. Consists mostly of type I collagen bundles and fibroblasts aligned in parallel for great resistance. Requires vitamin C for formation. Examples include Tendons Ligaments Aponeuroses Fig 2.15. Synovial membrane. RETICULAR Characterized by abundant fibers of type III collagen forming a delicate network supporting various cell types. Reticular fibers of type III collagen, aka reticulin, are produced and enveloped by the reticular cells. HG201A TRANSCRIBERS: Plete, Cait, Escote, Gamba, Manila, Padasas, Rodriguez M, Sarmiento, Taha, Toledo, Villas 7  EPITHELIAL TISSUES AND HISTOLOGY BASICS TRANS #2 Fig 2.18. Micrograph shows a longitudinal section of dense regular connective tissue in a tendon. Long, parallel bundles of collagen fibrils fill the spaces between the elongated nuclei of fibrocytes. SKELETAL Cartilage- tough, durable form of supporting connective tissue chondrocytes and highly specialized matrix ( extracellular matrix ). (Photos from: https://digitalhistology.org/) Chondrocytes- essential participant in producing and Fig 2.19. Hyaline Cartilage (Trachea 400x) maintaining matrix, cartilage consist of cells (chondros- cartilage + kytos-cell) Extracellular matrix- solid and firm but pliable, 95% of cartilage volume Lacunae- spaces throughout cartilage matrix, where chondrocytes are located Type II collagen fibers- permits diffusion of substances between blood cells Physical properties of collagen depends on electrostatic bonds between type II collagen fibrils, hyaluronan, and the sulfated GAGs on densely packed proteoglycans Perichondrium- sheath of dense connective tissue that Fig 2.20. Diagram of transitional area between the surrounds cartilage in most places and harbors the blood perichondrium and the cartilage matrix supply serving the cartilage and small neural component. Matrix TYPES OF CARTILAGE Avascular and respire under low oxygen tension A) HYALINE CARTILAGE- characterized by matrix dry weight of hyaline cartilage nearly 40- collagen containing type II collagen fibers, CAGs, proteoglycans, embedded in a firm, hydrated gel of and multi adhesive glycoproteins. proteoglycans and structural glycoproteins. produced by chondrocytes Aggrecan- approximately 150 GAG side participates in lubricating synovial joints chains of chondroitin sulfate and keratin and distributes applied forces to the sulfate is the most abundant underlying bones proteoglycan of hyaline cartilage. distinguished by homogenous, Chondronectin- binds specifically to amorphous matrix GAGs, collagen and integrins, mediating appears glassy in living state, hyaline the adherence of chondrocytes to the comes from the word hyalos means ECM. glassy Chondrocytes most common of the three types Cells occupy relatively little of the hyaline homogenous, semi transparent in the cartilage mass. fresh state ○ Chondroblasts- has elliptic shape with calcifies with aging long axis parallel to the surface Location ○ Isogenous aggregates- round and may Articular surface of movable joints appear in groups of up to eight cells that Fetal skeletal tissue, epiphyseal plates, costal originate from mitotic divisions of a single cartilage of rib cage, nasal cavity, thyroid, rings of chondroblasts trachea, plates in bronchi ○ Somatotropin- major regulator of hyaline cartilage and pituitary derived protein 3 Major Classes of Molecules in the Hyaline Matrix 1. Collagen Molecules Type II, VI, IX, X, and XI *Type X- crucial for mechanical function *Type VI- help chondrocytes attach to the matrix framework 2. Proteoglycans- 3 kinds of glycosaminoglycans (GAGs): Hyaluronan Chondroitin sulfate Keratan sulfate *Aggrecan- the most important monomer in hyaline cartilage; responsible for the unique biochemical property of hyaline cartilage HG201A TRANSCRIBERS: Plete, Cait, Escote, Gamba, Manila, Padasas, Rodriguez M, Sarmiento, Taha, Toledo, Villas 8  EPITHELIAL TISSUES AND HISTOLOGY BASICS TRANS #2 3. Multiadhesive glycoproteins- noncollagenous Composition: and nonproteoglycan-linked glycoproteins Chondrocytes Have clinical value as markers of ○ occur singly and often in ligned cartilage turnover and degeneration isogenous aggregates Anchorin CII ○ produce type II collagen and other ECM Tenascin components Fibronectin Matrix with dense irregular connective tissues B) ELASTIC CARTILAGE essentially similar to hyaline cartilage except that it contains an abundant network of elastic fibers in addition to a meshwork of collagen type II fibrils, which give fresh elastic cartilage a yellowish color. Does not calcify during the aging process Location Epiglottis Pinna of external ear, external acoustic meatus, auditory tube, Cartilages of larynx Composition Chondrocytes Collagen fibers (perichondrium) Bundles of elastic fibers (elastin) in matrix Fig 2.22. Fibrocartilage (Pubic Symphysis 400x) Table 2.1. Features of the different types of cartilage Features Hyaline Elastic Fibrocartilage Presence of Yes Yes No perichondrium (except articular cartilage and epiphyseal plates) Undergoes Yes No Yes (during calcification bone repair) Cell types Chondroblast Chondroblast Chondrocyte and and and fibroblast chondrocyte chondrocyte Fig 2.21. Elastic Cartilage (Pinna of external ear 10x) DENTAL C) FIBROCARTILAGE Mineralized Connective Tissue a combination of dense regular connective tissue Teeth - major component of oral cavity and are and hyaline cartilage essential for beginning the digestive process. takes various forms in different structures but There are normally 32 permanent teeth, arranged in essentially a mingling of hyaline cartilage and two bilaterally symmetric arches in maxillary and dense connective tissue. mandibular bones. Location Consist of several layers of specialized tissue Interval disc, pubic symphysis, sternoclavicular ○ Dentin joints ○ Enamel ○ Cementum HG201A TRANSCRIBERS: Plete, Cait, Escote, Gamba, Manila, Padasas, Rodriguez M, Sarmiento, Taha, Toledo, Villas 9 EPITHELIAL TISSUES AND HISTOLOGY BASICS TRANS #2 DENTIN ○ Like bone, cementum is 65% mineral and ○ Most abundant dental tissue. contains the highest concentration of fluoride of ○ It is a calcified tissue harder than bone. any mineralized tissue. ○ Consisting of 70% hydroxyapatite. ○ Secreted by odontoblast Columnar cells that contain well- developed rER, a large Golgi apparatus, and other organelles associated with synthesis and secretion of large amounts of proteins. ○ Organic matrix contains: Type I collagen Proteoglycans ○ Its unique tubular structure and biochemical composition support the more rigid enamel and cementum overlying the surface of the tooth. ENAMEL ○ Hardest component of the human body. ○ Protects the tooth against abrasion and acids. ○ Consist of 96% calcium hydroxyapatite and only 2%-3% organic materials including very few proteins and no collagen. ○ Hard, thin, translucent layer of acellular mineralized tissue that covers the crown of the Fig 2.23. Diagram of a molar’s internal structure, with: [a] tooth. enamel-covered crown, [b] cementum-covered roots anchoring the tooth to alveolar bone of the jaw, and [c] Slightly ○ Other ions, such as fluoride, can be incorporated constricted neck where enamel and cementum covering meets or adsorbed by hydroxyapatite crystals. at the gingiva. Enamel containing fluorapatite is more THE PERIODONTIUM resistant to acidic dissolution caused by Comprises the structures responsible for microorganisms maintaining the teeth in the maxillary and Hence, the addition of fluoride to mandibular bones. toothpaste and water supplies. The periodontium is a connective tissue ○ Produced by tall polarized cells known as consisting of four components: ameloblasts of the enamel organ. Cementum ○ Amelogenin Periodontal ligament (PDL) Main structural protein of developing Alveolar bone, and enamel. Associated gingival tissue ○ Enamel consists of a uniform, interlocking REFERENCES columns called enamel rod (prisms) Each about 5 um in diameter Ross, M. H., & Pawlina, W. (2010). Histology: A text CEMENTUM and atlas: With correlated cell and molecular biology ○ Thin,pale-yellowish layer of bone-like calcified (9th ed.). Philadelphia: Lip pincott Williams & Wilkins. tissue covering the dentin root of the teeth. Mescher, A.L. (2021) Junqueira’s Basic Histology ○ Cementum is softer and more permeable than Text & Atlas. 16th Edition, McGraw Hill. dentin. Department of Anatomy and Neurobiology and the ○ Easily removed by abrasion when the root Office of Faculty Affair (2024) Digital Histology. Virginia surface is exposed to the oral environment. Commonwealth University School of Medicine and ALT ○ Produced by cementoblasts. Lab - VCU. https://digitalhistology.org Large cuboidal cells that resembles the Young, B. et. al. (2014) Wheater’s Functional Histology: osteoblast of the surface growing bone. A Text and Color Atlas. 6th edition. Elsevier. HG201A TRANSCRIBERS: Plete, Cait, Escote, Gamba, Manila, Padasas, Rodriguez M, Sarmiento, Taha, Toledo, Villas 10 EPITHELIAL TISSUES AND HISTOLOGY BASICS TRANS #2 APPENDIX HG201A TRANSCRIBERS: Plete, Cait, Escote, Gamba, Manila, Padasas, Rodriguez M, Sarmiento, Taha, Toledo, Villas 11