Adobe Systems Department of Histology and Embryology 1 . Bone, Cartilage Ossification [USEMAP] Adobe Systems Department of Histology and Embryology 2 Cartilage perichondrium The Histology Guide | Cartilage, Bone & Ossification http://udspace.udel.edu/handle/19716/1814 https://www.histology.leeds.ac.uk/bone/cartilage.php [USEMAP] Cartilage Cartilage is a type of supportive connective tissue. It is very imporatant in shock absorbance, reducing friction in joints, and in providing structure of internal organs. Cartilaginous tissue is very flexible and rich in ECM witch has abundant amorphous ground substance. The main structure of this substance is collagen type II, and there are also some elastic fibers (content of these vary from type to type). This type of tissue is avascular and without innervation, therefore this properties are provided by some supportive structures that will be described later on. Cells of cartilage are called chondroblasts and chondrocytes. These cells have high synthetic activity and therefore – euchromatic nucleus, well developed RER and Golgi apparatus. They produce type II collagen and elastin. Differentiation starts from the perichondrium as perichondral fibroblast and progressively change shape from flat cells (chondroblast) to more rounded shape (chondrocytes) as they move towards the core of the cartilage. The extracellular matrix is rich in hyaluronic acid. As chondroblast changed into chondrocytes are in the core of the cartilage, they divide and make an isogenous group in a common space – lacuna. Perichondrium is a supportive layer that surrounds the cartilage and has an important role in nutrition. The perichondrium is highly innervated and vascularized. It has two main layers – outer fibrous layer and inner chondrogenic layer. Another way cartilage can be nurtured is by synovium – it is a fluid produced by the cells of the synovial membrane of the joint capsule and secreted to the joint cavity. Adobe Systems Department of Histology and Embryology 3 Hyaline cartilage Isogenous group Results from mitosis of chondrocyte present in a lacuna. Chondron merged isogenous group [USEMAP] Hyaline cartilage Flexible and strong type of cartilage specialized in sustaining mechanical impact and providing structure. We can observe it on joint surfaces of bones, growth plates of long bones, larynx, trachea and parts of the bronchial tree, also in skeleton model of a fetus and in the rib cartilages. Special feature of hyaline cartilage is that it is supported by perichondrium (except for joints where it is supported by synovium). The chondroblasts are arranged in isogenous groups – those are groups of few cells in a common lacuna inside the matrix of the cartilage. This is darker appearing matrix that surrounds the isogenous groups is called territorial matrix (basophilic). Adobe Systems Department of Histology and Embryology 4 Elastic cartilage Isogenous groups are absent Chondrocytes are idolated [USEMAP] Elastic cartilage Consists of elastic fibers, and collagen II. It is highly flexible. It has no isogenous groups. Nutrition of this cartilage is realized by perichondrium. Can be found in - epiglottis, cuneiform and corniculate cartilages (of larynx), auricle and external acoustic meatus and in the eustachian tube. Adobe Systems Department of Histology and Embryology 5 Fibrous cartilage Kosti a chrupavka – kejmi – album na Rajčeti Chondrocytes arranged between thick collagen fibers and reduced amorphous ground substance. No perichondrium and no isogenous groups https://kejmi.rajce.idnes.cz/Kosti_a_chrupavka/ [USEMAP] Fibrous cartilage This type of cartilage is less flexible, it is stiffer, and it is positioned in places where mechanic resistance is needed. Special features are – high content of collagen type I, No isogenous groups, No perichondrium. Found in - intervertebral disc (anulus fibrosus), pubic symphysis and in menisci of the knee joint Adobe Systems Department of Histology and Embryology 6 Chondrogenesis Cartilage | Junqueira's Basic Histology, 14e | AccessMedicine ... https://accessmedicine.mhmedical.com/content.aspx?sectionid=109632650&bookid=1687 [USEMAP] From mesenchymal cells to chondrocytes in isogenous group, the scheme illustrates the basic steps and morphological changes in differentiation. So, mesenchymal cells work as precursor cells. They start to proliferate and also differentiate which leads to development of a dense tissue full of chondroblasts. These cells produce loads of matrix, as they do so, they are moving away from each other. Tissue between chondroblasts is likely to be hydrated, so at the end it forms bulky ECM. Chondroblasts are ready to proliferate and to form isogenous groups. They produce so called territorial matrix and by doing so they form the typical figures called chondrons. Adobe Systems Department of histology and embryology 7 Bone tissue Bone Tissue Flashcards | Quizlet Pressure effecting on morphology of hydroxyapatite crystals in ... Hydroxyapatite crystals https://quizlet.com/ca/225591476/bone-tissue-flash-cards/ https://pubs.rsc.org/en/content/articlelanding/2011/ce/c0ce00090f/unauth#!divAbstract [USEMAP] Cells of bone tissue Osteoblast – “bone building cell” – they are present on the surfaces (inner and outer) of the bones. Highly active cells that synthesize bone matrix, as they produce it, they become surrounded by their own product. This is the part of bone remodeling process. Those cells activity can be regulated according to body needs. Typical features of this cell are - highly developed RER & Golgi (collagen synthesis), euchromatic nucleus (transcription), typically arranged in one layer. The cell cytoplasm has roughly cuboidal shape and extensive cytoplasmic extensions. The bone matrix is called osteoid. Osteocytes – less active form of osteoblast, has less cytoplasmic extensions and the synthetic activity is reduced. Those cells are positioned in tiny spaces between lamellae called lacuna. They are surrounded by bone matrix. Osteoclast - “bone destroying cells” those cells are aimed to resorb the cell and therefore their description as “destroying”, the process of bone resorption is a highly regulated process. Typical morphological features of those cells: localized on the bone surface in specific places – resorption bays. Osteoclasts are multinucleated – formed by fusion of few cells. One side of those cells has a rough border. Together with the action of osteoblast, those cell continuously resorb and synthesize bone matrix – bone remodeling. Adobe Systems Department of histology and embryology 8 Bone tissue Primary (woven) Secondary (lamellar) Compact Spongy Adobe Systems Department of histology and embryology 9 Woven vs lamellar bone Pojivové tkáně (vazivo, chrupavka, kost) = buňky + extracelulární ... https://slideplayer.cz/slide/5980857/ [USEMAP] Another classification can be made based on the stage of bone maturity. Here we divide two types of bones into woven bone – primary bone. Lamellar bone – definite bone with typical arrangement of Haversian system or osteon. Woven bone – (AKA primary bone, AKA fibrillar bone) this is a form of bone which we can identified during bone development in a growing fetus or in newly formed bone at the growth plate in growing child. The woven bone that is newly formed is replaced eventually by a lamellar bone. Histological features of woven bone: Cells are randomly dispersed in the ECM. Collagen fibers are oriented randomly in all directions. Low content of inorganic compounds. Lamellar bone – (AKA secondary bone) typically arranged in a circular osteon structures (=Haversian system). Circularly arranged in regular manner, layers of calcified ground substance with collagen fibers (i.e. extracellular matrix) and cell – osteocytes in between these layers. This type of bone is the adult form of compact bone. For orientation purposes lets imagine a long bone as a tube. The surface of the diaphysis is the external surface of the compact, lamellar bone. And the cavity inside the tube is the medullary cavity that houses the bone marrow (where blood cells are formed). The outer surface of the bone is lined by periosteum and the inner surface is lined by endosteum. Adobe Systems Department of histology and embryology 10 Compact vs Spongy bone https://ostrava.educanet.cz/www/biologie/index84f784f7.html?option=com_content&view=article&id=38&I temid=38 https://docplayer.cz/11100179-Obecna-nauka-o-kostech-osteologie.html https://www.pinterest.com/pin/307230005811868086/ Soustava kosterní (opěrná) bone tissue anatomy - Google Search | Basic anatomy and physiology ... [USEMAP] Bone tissue can be thought of as spongy bone or compact bone. Quick remainder on anatomical structure of a long bone – at the end’s epiphysis, at the middle - diaphysis. Spongy – due to its appearance, trabecular network of cavities - allow housing of the bone marrow. Spongy bone usually found in the epiphysis of long bones, in the core of short bones and in the middle layer of flat bones (in the skull it is termed “diploe”). Compact usually at the surface of the bone – tightly arranged at lamellae (plates) with compressed osteocytes between layers (details of structure below). Outer surface of the bone – periosteum lines it – dens irregular connective tissue having the cells: 1) osteoblast, 2) osteoclast. The periosteum is attached firmly to the bone surface by strong fibers – Sharpey's fibers. The endosteum lining the inner surface of the bone is made of thin layer of loos collagen connective tissue housing osteoprogenitor cells and osteoblasts. One of the important function of the endosteum is bone repair, this is made to large extent by the osteoprogenitor cells. Adobe Systems Department of histology and embryology 11 Ossification 1.Zone of resting cartilage 2.Zone of proliferation 3.Zone of hypertrophia 4.Zone of calcification 5.Zone of ossification From right to left – cartilage is on the right, fibrillar bone on the left. [USEMAP] Ossification Formation of bone is called ossification, there are two main types of bone formation – endochondral (indirect) and intramembranous ossification (direct). Intramembranous: typical type of ossification for flat bones such as bones of the calvaria (skull vault). In this type of ossification there is formation of bone producing cells directly from mesenchymal cells (embryonic connective tissue cells) without a cartilage model. Basic steps: mesenchymal tissue condense mesenchymal cells differentiate into osteoprogenitor cells  differentiation into osteoblast – osteoid synthesis  ossification centers appear in the condensed mesenchyme  ossification centers fuse. Endochondral ossification: mostly seen in the formation of long bones. In this type of bone formation mesenchymal cells make a hyaline cartilage model and this in turn ossify into a bone tissue. During child’s growing phase of life, the long bone consists of growth plate (= growth cartilage = epiphysial plate) at the junction of diaphysis and epiphysis. At this place the cartilage grows and the ossify continuously and thus the bone is elongated. The epiphysial plate ossify completely at 18 – 25 years. When observing the growing cartilage under a microscope one may identify several zones: Resting cartilage zone - hyaline cartilage. Zone of intensive mitosis – proliferating zone of chondroblasts. Zone of hypertrophia – chondroblasts grow in size (not in number of cells). While growing they compress the matrix in between the cells. Zone of calcification – chondroblasts undergo apoptosis and the matrix is calcified. Zone of ossification – osteoblast differentiate from the periosteum, (previously perichondrium) and start osteoid production. Marrow cavities are formed in the places of former chondroblasts. Keep in mind that the formed bone is now woven bone – primary. It will be eventually replaced by definitive secondary bone. Adobe Systems Department of Histology and Embryology 12 Klára Dolinová Peter Staňo Yehonatan Solomonov Petr Vaňhara Department of Histology and Embryology (EN) - Barevné provedení 2020 [USEMAP]