Histology: Connective Tissue & Bones (PDF)

COURSE : HISTOLOGY : TOPIC 4 ,5 PART4 :CONNECTIVE TISSUE PART 5 :CARTILAGE AND BONES BY Prof.Maibouge Salissou, (PhD), Endowed Chair Pathologist CONTACTS: January 2025...

COURSE : HISTOLOGY : TOPIC 4 ,5 PART4 :CONNECTIVE TISSUE PART 5 :CARTILAGE AND BONES BY Prof.Maibouge Salissou, (PhD), Endowed Chair Pathologist CONTACTS: January 2025 Email [email protected] Watsap: 0780079459 Research gate: https://www.researchgate.net/profile/Maibouge-Mahamane-Salissou PART4 : CONNECTIVE TISSUE  Learning objectives: 1. Know that cells, fibers and ground substance constitute connective tissue. 2. Be able to describe the relationship of these constituents, their structures and functions. 3. Learn the distribution of collagen types (Types I, II, III and IV) in the connective tissue types. Connective tissue is comprised of cells, formed fibers, and amorphous extracellular matrix (ground substance). Both the fibers and ground substance are secreted by the connective tissue cells that are interspersed and embedded in the matrix.  INTRODUCTION  Connective tissue : Basic tissues which gives structural and metabolic support to other tissues and organs of the body.  It connects other tissues aiding in defense and protection, serving as a medium of exchange of nutrients between tissues, storage of fat, and thermoregulation.  GENERAL FEATURES : Made of (a) cells, (b) fibres, and (c) ground substance.  Its major constituent is extracellular matrix which gives connective tissue its strength.  All types of connective tissue have the same basic structure, their physical properties depend on the composition of the extracellular  CLASSIFICATION OF CONNECTIVE TISSUE  1. Loose areolar connective tissue : is a vascular, delicate, flexible, fibers are loosely arranged.  It serves as a packing material by filling spaces between various tissue eg :lamina propria.  (i) few loosely arranged collagen and elastic fibres; (ii) large number of connective tissue cells (iii) large amount of ground substance  2. Dense collagenous connective tissue : tough tensile ,the collagen fibers are densely packed giving strength and resistance to traction forces. two types: Regular and Irregular.  3. Connective tissue with special properties : 1. Reticular connective tissue - forms a supporting framework for spleen, lymph nodes, bone marrow, liver, glands, and striated muscle fibers.  LOOSE CONNECTIVE TISSUE  Loose (areolar) connective tissue is distributed widely, since it constitutes much of the superficial fascia and invests neurovascular bundles,Subcutaneous tissue  The cells and intercellular elements described above help form this more or less amorphous, watery tissue.  it has Presence of (i) few loosely arranged collagen and elastic fibres; (ii) large number of connective tissue cells (fibroblasts, fibrocytes, mast cells, etc.); (iii) large amount of ground substance. LOOSE CONNECTIVE TISSUE 1. Pericyte 2. Collagen fibers 3. Erythrocyte in capillary 4. Monocyte 5. Lymphocyte 6. Adipocyte 7. Mast cell 8. Eosinophil 9. Plasma cell 10. Fibroblast  DENSE CONNECTIVE TISSUE  C. Dense, Irregular Connective Tissue  1. Predominantly collagenous - dermis, capsule of spleen and other organs, such as the prostate gland.  2. Predominantly elastic - for example, the elastic membrane of large arteries.  D. Dense, Regular Connective Tissue  1. Collagenous - tendons, most ligaments, cornea  2. Elastic - elastic ligaments (ligamentum nuchae flavate and interspinous ligaments), true vocal cords  The main function of the collagen fi bers is to impart tensile strength to the tissue  In tendon the Presence of (i) bundles of parallel collagen fibres; (ii) rows of tendon cells (fibrocytes) between the fibre bundles; (iii) less amount of ground substance.  DENSE CONNECTIVE TISSUE /TENDON 1. Collagen bundle 2. Nucleus of fibroblast 3. Capillary 4. Tendon (dense regular connective tissue)  DENSE IREGULAR CONNECTIVE TISSUE Dense Irregular Collagenous Connective Tissue (Dermis of Skin). Presence of (i) irregular bundles of collagen fibres cut at different planes; (ii) less cells and ground substanc  ELASTIC CONNECTIVE TISSUE  Elastic fibers contain bundles of micro fibrils and consist of the glycoprotein, fibrillin.  Elastin, an amorphous component, is added to the micro fibrils and forms the major part of the elastic fiber.  Organs containing elastic fibers ( urinary bladder) can undergo considerable expansion and return passively to their original shape.  Elastic fibers cannot be distinguished with conventional methods and require special stains. Elastic tissue is yellow in color.  Some ligaments are made up of elastic tissue( ligamentum nuchae,ligamenta flava, vocal ligaments)  ELASTIC TISSUE BV blood vessel C cytoplasm CF collagen fibril CF bundle of collagen fibers D duct F fibroblast Dense Elastic ConnectiveTissue.Presence of (i) branching refractile bundles of elastic fibres;ii) less cells and ground substance between fibre bundles. 1. Internal elastic lamina (of arteriole) 2. Microfibrils and elastin  SOMES DISEASES OF ELASTIC TISSUE  Keloid Formation :an overabundance of collagen in the healing process, thus developing elevated scars called keloids.  Marfan syndrome is an inherited connective tissue disorder resulting from molecular defects in the FBN-1 gene that encodes the glycoprotein, fibrillin-1.  This disease is marked by impairment of elastic tissues throughout the body including the aorta, where aneurysms can occur and potentially cause sudden death if they tear or rupture  RETICULAR CONNECTIVE TISSUE  It consists of reticular fibers that form the supportive stroma of many tissues and organs.  They are long, thin, extracellular fibers.  They do not form bundles like collagen fibers but appear as a felt-like aggregation of branching fibers (thin type III collagen fibers.)  Reticular connective tissue constitute the structural framework of bone marrow ,liver and many lymphoid structures.  Their selective staining with metallic silver visualized by light microscopy is most likely due to precipitation of reducible silver salts on an external coating of bound proteoglycans.  Reticular fibers are synthesized by fibroblasts during wound healing in  RETICULAR TISSUE SILVER STAIN These form the structural framework of a cortical lymphatic 1. Reticular fibers nodule (LN). The small round cells are probably lymphoid cells (LC), whereas the larger cells, closely associated with 2. Macrophage the reticular fibers, may be reticular cells (RC  ADIPOSE TISSUE  It is a specialized loose connective tissue that contains large numbers of adipocytes.  Adipocytes are specialized for the synthesis, storage, and mobilization of neutral fats known as triglycerides.  Lipoprotein lipase, an enzyme produced by the adipocyte, releases fatty acids and monoglycerides  Re-esterification into triglycerides occurs in the smooth endoplasmic reticulum of the adipocyte, followed by their storage in the lipid droplet.  There are two types of adipose tissue, white (unilocular) and brown (multilocular)  MORPHOLOGY OF ADIPOSE TISSUE  Unlike other connective tissues, adipose tissue is composed of adipose cells so closely packed together that the normal spherical morphology of these cells becomes distorted.  Groups of fat cells are subdivided into lobules by thin sheaths of loose connective tissue septa housing mast cells, endothelial cells of blood vessels, and other components of neurovascular elements.  Each fat cell is invested by reticular fibers, which, in turn, are anchored to the collagen fibers of the connective tissue septa.  ADIPOSE TISSUE A adipocyte 1. Adipocyte BV blood vessel C cytoplasm 2. Arteriole F fibroblast 3. Connective FD fat droplet N nucleus tissue NF nerve fiber 4. Venule S septum 5. Nucleus of  PART5 :CARTILAGE AND BONES Learning objectives: 1. Describe the components and organization of cartilage and bone. 2. Relate the structure of bone and cartilage to their function. 3. Understand the differences between the development and growth of cartilage and bone. 4. Describe the processes of intramembranous bone development and endochondral ossification  TOPIC OUTLINES o GENERAL FEATURES o CARTILAGE CELLS o CHONDROBLAST VERSUS CHONDROCYTES o SPECEFIC CHARACTERISTIC o HYALINE CARTILAGE o FIBROCARTILAGE o ELASTIC CARTILAGE o SOME DISEASE OF CARTILAGE o CHONDROSARCOMA o SECTION B: BONES  GENERAL FEATURES  Cartilage forms the supporting framework of certain organs, the articulating surfaces of bones and many parts of the body  Cartilage is a nonvascular, strong, pliable structure composed of a firm matrix of proteoglycans  Fibers are either collagenous or a combination of elastic and collagenous, depending on the cartilage type.  Cellular components are Chondrocytes, which are found in small spaces known as lacunae.  Chondroblasts and chondrogenic cells, both are located in the perichondrium.  Most cartilage is surrounded by a dense irregular collagenous connective  GENERAL FEATURES Cartilage is a modified connective tissue. It resembles ordinary connective tissue in that the cells in it are widely separated by a considerable amount of intercellular material or matrix. Cartilage differs from connective tissue by nature of the ground substance Three main types of cartilage can be recognised depending on the number and variety of fibres in the matrix. The outer fibrous layer is composed mostly of fibroblasts and collagen fibers.  The inner chondrogenic layer is composed of chondroblasts and chondrogenic cells which give rise to chondroblasts  CARTILLAGE CELLS  The cells of cartilage are called chondrocytes.  They lie in lacunae present in the matrix  Their nucleus is euchromatic and mitochondria, endoplasmic reticulum and Golgi complex are prominent while also termed chondroblasts  Chondrocytes synthesize and secrete proteins and ground FIG 1 CHONDROBLAST VERSUS CHONDROCYTES  SPECEFIC CHARACTERISTIC  Cartilage supports regions of the body that require varying degrees of flexibility.  It is an avascular structure nourished by diffusion.No nerves are present in cartilage.  Regeneration of cartilage is poor. Its damage results in a connective tissue scar.  It is covered externally by a dense connective tissue sheath known as perichondrium, except over articular surface of cartilage in the joint cavities.  Perichondrium is made up of two layers: 1. Outer fibrous layer 2. Inner chondrogenic layer. FIGURE 2 CARTILLAGE  HYALINE CARTILAGE  It has matrix homogeneous its collagen fibrils present in the matrix have the same refractive index as that of the ground substance giving him glassy appearance.  Hyaline cartilage is present at the articulating surfaces of most bones,laryngeal, costal, and nasal part  It help Supports soft tissues. Provides gliding area for the joint, facilitating movements.  Osteoarthritis It is marked by degradation of the cartilage matrix and altered chondrocyte metabolism due to a decreased glycosaminoglycan content in the matrix accompanied by increased water content.  Enhanced matrix metalloproteinase enzyme activity make degradation of  HYALINE CARTILAGE 1. Articular surface 2. Chondrocyte 3. Spongy bone The perichondrium: fibrous (F) and 4. Subchondral bone chondrogenic (CG) layers chondrocytes (C). 5. Calcified cartilage HYALINE CARTILLAGE  FIBRO CARTILLAGE  Fibrocartilage : has dense bundles of collagen fibres oriented in the direction of functional stress with rows of chondrocytes between the bundles. It does not have a perichondrium  Chondrocytes are smaller oriented in parallel longitudinal rows..  Is present in only a few places Functionally, it combines the tensile strength, firmness, and durability of tendon and the resistance to compression of cartilage.  A herniated disc affects the intervertebral disc and can cause severe pain or numbness if the protruding disc impinges on a nerve or the spinal cord.  It results from loss of elasticity of the disc and subsequent rupture of the annulus fibrosis, which allows the protrusion of the nucleus pulposis into  FIBRO CARTILAGE The chondrocytes (C) are aligned in parallel rows The 1. Spongy bone of vertebra matrix contains thick bundles of collagen fibers (CF), which 2. Nucleus pulposis are arranged in a regular fashion between the rows of 3. Annulus fibrosis cartilage cells. No perichondrium. 4. Compact bone of  FIBROCARTILAGE Absence of perichondrium.  ELASTIC CARTILAGE  It is characterised by elastic fibres in the matrix.e.g. ear pinna , epiglottis.  It has a perichondrium. The matrix, in addition to the type II collagen fibers, contains a wealth of coarse elastic fibers that impart to it a characteristic appearance.  Has more flexibility and elasticity than the other 2 types of cartilage. Its Chondrocytes are spherical in shape and are contained in lacunae.  They are similar to chondrocytes of hyaline cartilage, except that are closely packed found singly in lacunae. Only a few isogenous nests of chondrocytes are present.  Cystic chondromalacia affect elastic cartilage in the auricle of the ear or the epiglottis. ELASTIC CARTILAGE 1. Chondrocyte 2. Matrix 3. Perichondrium  ELASTIC CARTILAGE (i) elastic fibres in the matrix nonhomogeneous);(ii) closely packed chondrocytes with eccentric nuclei; (iii) perichondrium covering the cartilage. CARTILAGE TYPE CHARACTERISTIC AND LOCATION  SOME DISEASES OF CARTILAGE : CHONDROSARCOMA  Chondrosarcoma, a malignant tumor that develops in existing cartilage or bone, is one of the most common cancers of bone.  Three types of chondrosarcoma, depending on their location. central chondrosarcoma it develops in the marrow cavity  Peripheral chondrosarcoma makes it initial appearance outside and then invades the bone  Juxtacortical chondrosarcoma, begins in the region of the metaphysis and invades the bone  Symptom is pain localized to the site of the lesion, presence of malignant chondrocytes in a matrix that resembles that of hyaline cartilage  Chondromas are benign neoplasms of cartilage.  CHONDROSARCOMA Observe the dense population of atypical chondrocytes dispersed within the hyaline cartilage–like matrix in this section from a patient PART B BONES  INTRODUCTION  Bone is a vascular connective tissue consisting of cells and calcified extracellular materials, known as the matrix.  The calcified matrix is composed of calcium crystals; type I collagen, glycoproteins  Cancellous bone Has large, open spaces surrounded by thin, anastomosing plates of bone. The large spaces are marrow spaces, and the plates of bones are trabeculae composed of lamellae.  Compact bone is much denser than cancellous bone. Its spaces are much reduced in size, and its lamellar organization is much more precise and thicker.It is covered and lined by soft connective tissues.  Marrow cavity is lined by endosteum having osteoprogenitor  BONES GENERAL FEATURES  Bone is rigid and hard because the matrix is infiltrated with inorganic salts.  Bone gives attachment to muscles and serves as a lever for muscular action. It bears body weight. It protects vital organs like brain, heart and lungs.  Bone stores calcium, phosphate and other ions. It contains bone marrow, which is a haemopoietic tissue.  Morphologically bone consists of externally, a solid shell of cortical bone called compact bone.  Internally,of trabeculae separated by marrow spaces called spongy bone.  Microscopically, compact bone consists of:1. Primary/formed bone during LAMELLAE TYPE OF BONE  BONE COMPOSITION  Bone is made of cells, fibres and ground substance. In addition, its extracellular matrix is infiltrated with inorganic salts like calcium phosphate for hardness and rigidity.  The needles are arranged parallel to collagen fibres and partly within them.  The organic components like collagen give plasticity to bone, allowing it to remodel according to the functional demands placed upon it.  1. Cells: (a) Osteoprogenitor cells:(b) Osteoblasts (c) Osteocytes Osteoclasts  2. Fibres (95%)type I collagen.  3. Ground substance (5%) which give elasticity and resilience.  CELLS OF BONE  Osteoblasts elaborate bone matrix, become surrounded by the matrix they synthesized, and calcify the matrix via matrix vesicles that they release..  Osteoblasts possess parathyroid receptors on their cell membrane, and in the presence of parathormone, they release macrophage colony– stimulating factor that induces the formation of osteoclast precursors.  Osteoblasts have expressed on their cell surface RANKL (receptor for activation of nuclear factor kappa B ligand), for differentiate into osteoclasts.  Osteoblasts release osteoclast-stimulating factor which activates osteoclasts to begin resorbing bone. OSTEOBLAST VERSUS OSTEOCYTES BONE CELLS  SPONGE BONE The bony plates of cancellous bone are called trabeculae which are slender and anastomosing. Each trabeculus is made up of lamellae between which there are lacunae containing osteocytes.  Spongy bone is present in fetuses and young children and is characterized by coarse collagen fibers that are oriented randomly.  Osteomalacia is caused by vitamin D deficiency; similarly rickets in children it show high amounts of unmineralized osteoid  where bone mineral fails to be deposited in normally formed bone matrix. Osteoids account for 40% to 50% of bone Trabeculae exhibit parallel lamellae of bony matrix and osteocytes in  SPONGE BONE (i) presence of bony trabeculae 1. Osteoclast separated by marrow space containing 1. Trabeculae of spongy 2. Osteocyte bone marrow; bone 3. Osteoblasts (ii) absence of Haversian systems and 2. Osteoclast lamellar arrangement; 3. Bony matrix 4. Blood vessel (iii) presence of osteoblasts and 4. Osteoid (newly 5. Woven bone osteoclasts on the surface of bony synthesized bone) (trabecula) trabeculae; 5. Osteoblasts 6. Lamellar bone (iv) osteocytes are seen embedded in the (trabecula) OSTEOMALECIA OSTEOPETROSIS Osteopetrosis is a constellation of heritable disorders that result in denser bones with possible skeletal malformations.  The disease may be the early onset type or the delayed onset type  Early onset type may begin in infancy can result in early death due to anemia, uncontrollable bleeding, and rampant infection. The thickening of the bones and slight facial deformities may be evident.  Bones become thicker the diameters of the foramina become smaller and nerves passing through those constricted openings may become compressed and cause considerable pain. OSTEOPOROSIS Osteoporosis is a decrease in bone mass arising from lack of bone formation or from increased bone resorption.  It occurs commonly in old age because of decreased growth hormone and in postmenopausal women because of decreased estrogen secretion. In the latter, estrogen binding to receptors on osteoblasts stimulate the secretion of bone matrix.  Without sufficient estrogen, osteoclastic activity reduces bone mass without the concomitant formation of bone, therefore making the bones more liable to fracture. OSTEOPORESIS  COMPACT BONE  Compact bone is surrounded by dense irregular collagenous connective tissue, the periosteum, which is attached to the outer circumferential lamellae by Sharpey’s fibers.  Blood vessels of the periosteum enter the bone via larger nutrient canals or small Volksmann’s canals, which convey blood vessels to the Haversian canals also interconnect adjacent Haversian canals.  Each osteon is composed of concentric lamellae of bone whose collagen fibers are arranged so that they are perpendicular to those of contiguous lamellae.  The inner circumferential lamellae are lined by endosteal lined cancellous  STRUCTURE OF COMPACT BONE  Compact bone consists of three systems of bony lamellae arranged in an orderly manner:  1. Circumferential system – Outer periosteal – Inner endosteal 2. Haversian system or osteon 3. Interstitial system 1.Circumferential System :Outer circumferential system consists of circular lamellae of bony matrix that lie immediately beneath the periosteum.  Inner circumferential system also consists of circular lamellae of bony matrix that lie adjacent to the endosteum.  Osteocytes are found between the lamellae in the lacunae. Both circumferential systems have the marrow cavity as the centre; the outer CROSS SECTION OF COMPACT BONE  COMPACT BONE 1. Periosteum 2. Capillary in Haversian canal 3. Concentric lamella 4. Osteocyte 5. Trabecula COMPACT BONE  HAVERSIAN SYSTEM OR OSTEON  Are found between the outer and inner circumferential systems of compact bone.  Cylindrical, branching principal structural units of compact bone;they lie parallel to the long axis of the shaft.  Each system consists of a central canal, Haversian canal, surrounded by 4–20 concentric lamellae of bony matrix.  The Haversian canals communicate with each other, with the periosteum and with the internal medullary cavity via Volkmann’s canals which penetrate via lamellae of Haversian system.  Each Haversian system is formed by successive deposition of bony lamellae around the neurovascular structures in the canal from the OSTEON  COMPACT BONE Cross section of decalcifi ed bone, skeletal This is a cross section of decalcified muscle compact bone osteons or haversian (SM) The outer fibrous periosteum (FP) canal systems (Os) as well as and the inner osteogenic periosteum (OP) interstitial lamellae (IL). central inner circumferential (IC) lamellae, haversian canal (HC) lamellae (L).  BONE FORMATION/OSSIFICATION  Ossification is the process by which bone is formed from a soft tissue model eg hyaline cartilage model.  It starts at the centre , from which it spreads until the whole model is converted into bone.  Bones are formed by two methods, namely, 1. Intramembranous ossification: bone formation from condensed mesenchyme e.g. Flat bone  2. Endochondral ossification:bone formation from cartilage—cartilage model. e.g. Long bones  INTRAMEMBRANOUS OSSIFICATION  Stage I: Condensation of mesenchyme occurs in the area where bone formation is to take place;stellate mesenchymal cells become spindle- shaped cells.  Stage II: Formation of membrane  The spindle-shaped mesenchymal cells differentiate into fibroblasts and begin to lay down collagen fibres  Stage III: Differentiation of osteoblasts and formation of osteoid  Stage IV: Formation of calcified matrix and establishment of centre of ossification  Osteoblasts secreting alkaline phosphatase resulting in deposition of calcium salts as crystals OSSIFICATION  ENDOCHONDRAL OSSIFICATION  long and short bones of the body, except clavicle, are formed by endochondral ossification. Stage I: Formation of mesenchymal model ;The stellate mesenchymal cells become rounded and condensed in the area where long bone is to be formed Stage II: Formation of cartilage model The rounded mesenchymal cells become differentiated into chondroblasts and start laying down cartilage matrix.  Perichondrium is also formed around the cartilage. Stage III: Appearance of primary centre of ossification and formation of ENDOCHONDRIAL OSSIFICATION STAGE IV: APPEARANCE OF SECONDARY CENTRES OF OSSIFICATION AND FORMATION OF EPIPHYSIS  ENDOCHONDRIAL BONE FORMATION A.hyaline cartilage C. periosteal bud (4), and osteoclastic D/epiphyseal (10) and Vascular periostum (11). activity (5). 7 second ossification center B Vascularization of perichondrium (2) : (1) (via intramembranous bone formation).Chondrocytes in the center of the cartilage E/epiphyseal plate (8) and the covering of the epiphyses (9) END OF TOPIC