function of connective tissue

Fibrocartilage develops at the bone ends and this is subsequently calcified and replaced by woven bone or osteoid. Although excellent short-term clinical outcomes have been reported, the clinical durability of marrow-stimulated repair tissue declines with longer follow-up. The junction between the deep and calcified zone is called the tidemark. They are also called gristle. COMMENT: [Figure 20.3] Remember to keep the diagram simple. These substitutions for glycine within the triple helix are severely destabilizing and interrupt the triple helix. It also gives reinforcement to joints, strengthening and supporting the articulations between bones. CANDIDATE: Articular cartilage undergoes significant structural, matrix composition and mechanical changes with age. EXAMINER: Correct answer! CANDIDATE: Primary bone healing is a direct attempt by the cortex to re-establish the Haversian structure after a fracture but without fracture callus formation. CANDIDATE: A viscoelastic material will exhibit a time-dependent behaviour when subjected to a constant load or constant deformation. Osteoblasts secrete receptor activator of nuclear factor κβ ligand (RANKL) and macrophage colony-stimulating factor (M-CSF) to activate osteoclasts. 1. COMMENT: These are the two main functions of articular cartilage, although some textbooks mention other minor roles.7 There is some controversy as to the relative importance of articular cartilage as a shock absorber. It does so by forming sacs that contain the organs and attach to nearby structures so they do not simply float about freely. However, it pervades many aspects of clinical practice and therefore must be understood. CANDIDATE: Cortical bone is compact with a high matrix mass per unit volume, low porosity and is subjected to bending, torsional and compressive forces. You may end up speaking to an orthopaedic paediatric professor! This molecule is then released into the extracellular space by transport through the Golgi apparatus and converted into collagen by procollagen peptidases that cleave the water-soluble, non-helical N- and C-terminal portions of the procollagen molecule to form tropocollagen. Rigid internal compression fixation, which minimizes strain, will lead to primary fracture healing. Different Types … The degradation products of collagen and other matrix components are endocytosed, transported through the cell and exocytosed through a functional secretory domain. Whenever feasible, any internal or external fixation device should be applied to the tension side to provide maximum stability. With children they can be used in fibrous dysplasia, osteogenesis imperfecta and Perthes’ disease. As it comprises about 20-25% of total body weight in healthy individuals, the main function of adipose tissue is to store energy in the form of lipids (fat). They have significant effects on the growth plate chondrocytes, and IGFs retained in bone matrix are important in the regulation of bone remodelling. This process is controlled via the RANKL system (inhibited by osteoprotegerin) of activated osteoblasts. RANK, expressed on osteoclast precursors, is a key regulator of osteoclastogenesis. The fibres account for 10–20% and are almost exclusively Type II collagen. According to Wolff’s and Heuter–Volkmann’s laws: remodelling occurs with motion at the fracture site. COMMENT: The viva may just begin by candidates being shown a diagram of the bone Haversian system and being asked to talk through the diagram. In BHN, the bone is in homeostasis when under tolerable strain (much less than 2%). Muscle is attached to the bones it moves by tendons, thick lengths of connective tissue that pull on the bones like rope. Figure 20.15 Proteoglycan aggrecan. EXAMINER: What about qualitative versus quantitative collagen deficiencies in osteogenesis imperfecta (OI)? Most significantly, connective tissue is the stage for inflammation. In the deeper zones, they are arranged in columns, reflecting the articular cartilage role in growth of the epiphysis. However, only 2% of Salter–Harris fractures result in a significant functional disturbance. You’ll also discover what unique functions this tissue serves within your body. Its most distinctive attribute, this matrix is made up of fluid; gound substance, a gel that contains nutrient molecules like hyaluronic acid that are composed of carbohydrates and protein; and protein-based fibers like collagen and elastin. Microscopic appearances include surface irregularities and erosions, deterioration of the tidemark, fissuring and damage to the cartilage structure. There is direct osteonal remodelling and healing without external callous formation. Lamellar bone can tolerate up to 10% strain, and when this relative stability is present, the fracture heals with callus or secondary fracture healing. EXAMINER: Can you give me an example of Wolff’s law? Fibroblasts are large flat spindle-shaped cells with processes that extend out from the ends of the cell body. EXAMINER: How do osteoclasts resorb bone? EXAMINER: What is an osteoclastic cutting cone? Figure 20.20 Stress relaxation. Type IX (an injury to the periosteum which could interfere with membranous growth). The matrix is divided into three distinct regions with respect to the distance from the chondrocyte cell membrane. CANDIDATE: Collagen is a triple helix of three polypeptide chains. CANDIDATE: The process can be divided into three overlapping stages: (1) cartilage matrix damage, (2) chondrocyte response to tissue damage (3) decline of the chondrocyte synthetic response with progressive loss of tissue. Zone V is the zone of the matrix calcification as this calcified matrix becomes the scaffolding forbone deposition in the metaphysis. However, most candidates are now more aware of A-list topics than ever before and have pre-learnt their answers. Click card to see definition 👆. Proteoglycans trap and hold water, providing the tissue with its turgid nature that resists compression. Collagen is secreted as an oversized molecule, procollagen, with specialized enzymes removing the N and C terminal propeptides leaving a triple helix with short non-triple helical stubs at the amino and carboxyl terminal chain ends. The normal direction is centrifugal; however, following endosteal damage this system is reversed to centripetal. This enzyme allows hydroxyl groups on lysines and hydroxyl lysines to be converted into aldehyde groups that covalently bond between tropocollagen molecules to form a collagen fibril. Osteoclasts are derived from a haemopoietic monocyte cell lineage. But there is a catch: you cannot use anything to attach these parts together. Fail to master this diagram at your peril. What pathological processes are involved in the development of osteoarthritis? It is usually found in the diaphysis of long bones. Figure 20. (b) More complex drawing of collagen assembly. Reversal refers to a 1- to 2-week interval between completion of resorption and initiation of bone matrix formation. CANDIDATE: [At the very end of the topic after discussing primary and secondary bone healing, Perren’s strain theory] There was a very well-written important paper published recently that discussed fracture healing. EXAMINER: Can you draw a cutting cone out? Enzymes include aggracanase and metalloproteinases degrade the matrix. The zone is the truegerminal layer of the growth plate and Type IIcollagen synthesis is increased. COMMENT: That is a very specific question, but a common theme. It is regulated by receptor activator of nuclear factor κB (RANK), RANK ligand (RANKL) and osteoprotegerin (OPG). The major functions of connective tissue include: Binding and supporting. 4. (1) The water content or porosity is reduced. EXAMINER: Can you draw out the graphs of creep and stress relaxation (Figures 20.19 and 20.20)? Cell-based, biological replacement options (autologous chondrocyte implantation [ACI], stem cell therapy, tissue engineering). Below this is a cellular layer with chondrocytes parallel to surface, flat-shaped, high density, many cells 1–3 thick. EXAMINER: What is the function of matrix glycoproteins? A group of cells similar in structure, function, and origin is called tissues. COMMENT: These are fairly straightforward questions but may catch the unprepared candidate out. Figure 20.19 Creep. and then a focus midway through on the biomechanical properties of articular cartilage. The amount of water present in cartilage depends on the concentration of proteoglycans and the stiffness and strength of the collagen network. Learn about a little known plugin that tells you if you're getting the best price on Amazon. The most superficial part is called the lamina splendens,13 providing a very low-friction lubrication surface. Middle (transitional) zone: 40–60% of thickness. The most common glycosaminoglycan in articular cartilage is chondroitin-sulphate (two subtypes, chondroitin-4-sulphate and chondroitin-6-sulphate), then keratin sulphate and dermatan sulphate. CANDIDATE: The main types of bones cells, and their function, are as follows: 2. OATS is recommended for smaller lesions, lesions in high-demand athletes, and lesions with associated bone loss. 2. CANDIDATE: The production of extracellular matrix, its organization, maintenance and breakdown are controlled by the chondrocyte. An inflammatory phase with local accumulation of macrophages, MSC, cytokines. The collagen fibres in the deep zone penetrate through the tidemark into the calcified cartilage to provide structural stability for articular cartilage on the subchondral bone. EXAMINER: So, which type of bone is isotropic? CANDIDATE: The Haversian system, or osteon, is the basic structural unit of cortical bone and lies parallel to the long axis of the bone. Like many other joints in the body, the knee has a dense, fibrous, connective tissue that seals the joint space between the bones. Cancellous bone is found in the metaphysis or epiphysis of long bones. It contains no cells, a clear film of collagen fibrils with little proteoglycan. CANDIDATE: MSCs are multipotent stem cells that can differentiate into a variety of cell types. Storing reserve fuel. Animal tissues are grouped into four basic types: connective, muscle, nervous, and epithelial. It reduces the coefficient of friction down to 0.0020, which is 30 times superior to the best performing artificial joint. CANDIDATE: Osteoclastogenesis refers to the process of osteoclast differentiation and function. CANDIDATE: An eccentrically loaded bone has a compression and tension side. I had no idea that connective tissue had so many jobs within the human body. The amino acids are glycine, proline and lysine. CANDIDATE: The wet weight proportions of articular cartilage are water (65–80%), collagen (10–20%), proteoglycans (10–15%), chondrocytes (5%) and other matrix components such as adhesives and lipids. The fibers give the tissue its denseness and strength and are what helps connective tissue function properly. If you have to talk about dry weight mention that collagen accounts for 40–70% of the dry weight and that approximately 90% of the dry mass of articular cartilage is made up of proteoglycan aggrecan, type II collagen and hyaluronan. CANDIDATE: This is an activated osteoclast. Elliott et al. In the past, there was a predictable line of questions the examiners would ask. CANDIDATE: Arterial flow in mature bone is centrifugal (inside to outside), which is the net effect of the high-pressure nutrient artery system and the low-pressure periosteal system. COMMENT: Candidates may be pressed in a bit more detail about the differences between woven and lamellar bone, especially at the beginning of a viva, because it is basic information candidates would be expected to know. EXAMINER: How does collagen synthesis take place? They help chondrocytes bind to the macromolecules of the matrix. Ligaments not only hold the bones together but prevent the joints from moving beyond their normal range of motion, and they also support the bones at the joint, as in keeping the arm from popping out of its socket at the shoulder joint. EXAMINER: What are the differences between articular cartilage and meniscus? Abstract. Practise the drawing and discussion of it at least 10 times. Another function of connective tissue is the transport of nutrients and metabolic byproducts between the bloodstream and the tissues to which it adheres. Venous flow in mature bone is centripetal. PG aggregation promotes immobilization of the PGs within the fine collagen meshwork. EXAMINER: What runs in a Haversian canal? The pat… CANDIDATE: Cartilage is a biphasic, viscoelastic and anisotropic material demonstrating both creep and stress relaxation. The proportions of these components vary from one … Figure 20.16 Candidate drawing of proteoglycan aggregate. Creep is time-dependent deformation of a material under constant load that is below its yield strength. Over 50 years ago, Urist made the key discovery that demineralized bone fragments implanted either subcutaneously or intramuscularly in animals induced bone formation. One function of connective tissue is to link the structures of locomotion. Articular cartilage changes with ageing versus osteoarthritis is more of a section 3 (pathology) topic but there will be a large overlap with section 2 material (structure and function of articular cartilage). CANDIDATE: Articular cartilage permeability decreases non-linearly with compression. Candidate drawing. Creating dense networks of fibers, connective tissue is made up of proteins like collagen, elastin, and intercellular fluid, and while its form can range from a thin sheet to a rope of fibers, its constitution is fairly similar throughout the body. CANDIDATE: Isotropic refers to uniform properties in all directions, independent of the direction of load application. The head of the cutting cone is made up of osteoclasts (which bore holes through hard cortical bone). COMMENT: Urist 1965 is the paper to quote.4 Be able to mention something about BMP2 and BMP7. Hydroxylation of selected proline and lysine residues. EXAMINER: What is the difference between cortical and cancellous bone (Table 20.2)? Once secreted, procollagen peptidases remove the N-terminal and C-terminal propeptides. Collagen monomers are then covalently cross-linked with each other after certain residues are oxidized by lysyl oxidase. These tissues are made of similar cells to have the same physiological function in the body. There is: 1. 2. Glycosylation of selected hydroxylysine residues. Osteoprogenitor cell: precursors to osteoblasts that line the Haversian system and can be stimulated to differentiate into osteoblasts and form new bone. Hyaline cartilage should be thought of as a fluid-filled wear-resistant surface. Osteocytes are osteoblasts that have become trapped in bone matrix (comprising up to 90% of the cells in bone). Water is attracted and retained in articular cartilage by the ionic pressure created by the high level of negative charges on glycosaminoglycan (GAG) chains on proteoglycan molecules. Articular cartilage is definitely on the top 10 list for ‘must-know’ how-to-draw diagrams. Derived from mesenchymal stem cells, chondrocytes produce and maintain ECM, and are the main cell type of articular cartilage. COMMENT: Candidates that do not understand this concept particularly well may become trapped quite easily by the examiners (just like water gets trapped by proteoglycans). What connective tissue is composed of cells in a solid matrix arranged around central canal? The fibrous connective tissue functions to provide strength to the inner layer of skin and … The primary elements of connective … Using BHN, the behaviour of a ‘bone-healing organ’ was determined with respect to the mechanical strain applied to the organ. CANDIDATE: An osteoclastic cutting cone is a mechanism to remodel cortical bone by osteoclastic tunnelling (cutting cones). The structural unit of type 1 collagen is called tropocollagen and is a trimer composed of three polypeptide chains. It is the boundary between the calcified and uncalcified cartilage. The outer fibrous layer is structural, less cellular and continuous with the joint capsule, while the inner cambial layer is vascular, osteogenic and contributes to bone growth and fracture healing. Extracellular events include terminal peptide cleavage and cross-linkage and self-assembly of collagen fibrils. Image Source: jotscroll.com. Coagulation and fibrin formation. COMMENT: Make sure you know the definition of an organ.1 Try to avoid giving an answer that will lead you up a blind alley. Inheritance can be autosomal dominant or recessive. Similarly, bones are joined to one another at joints by ligaments, which may resemble narrow bands or broad sheets. The triphasic nature of cartilage explains how fluid is drawn back into the cartilage matrix after being excreted during compression. Yet another function of connective tissue is to encapsulate structures like muscles and joints and thereby transport vital nutrients between these structures and the bloodstream. They are multinucleated giant cells that resorb bone and are characterized by a cytoplasm that has a homogeneous foamy appearance due to a high concentration of vesicles and vacuoles. May function as a barrier to the passage of large molecules from the synovial fluid. EXAMINER: Describe the structure of bone. There will be concrete for a foundation, lumber, insulation, windows and doors, roofing materials and all of the other necessary parts. Candidates may be asked very general questions or questions in more detail, so you need to cover both bases. In the early stages of disease, loss of proteoglycan is reversible, whereas at later stages there is irreversible loss. 3. EXAMINER: Draw a cross-section of articular cartilage (Figure 20.12). Section 2 of the basic science (Tr & Orth) syllabus is a large topic, difficult to grasp at face value as it appears quite removed from the average orthopaedic surgeon’s practice. The extracellular matrix of bone contains substances that can stimulate new bone formation when implanted into extraskeletal sites in a host. EXAMINER: Describe the structure of the periosteum. EXAMINER: What are the biomechanical properties of cartilage? Collagen fibres arranged obliquely at right angles to each other. At its tip, osteoclastic resorption takes place while in the latter parts of the cone osteoblasts deposit osteoid with subsequent mineralization. B, bone; OB, osteoblast; CC, calcified cartilage; C, cartilage matrix. Connective tissue is one of the four basic types of animal tissue, jollof epithelial tissue, muscle tissue, and nervous tissue. All forms of connective tissue are composed of (1) extracellular fibres, (2) an amorphous matrix called ground substance, and (3) stationary and migrating cells. For bone these include: EXAMINER: What are the functions of bone? Y… It contains mainly proteoglycans, as well as glycoproteins and other non-collagenous proteins. COMMENT: Draw and talk about the different layers. Type X is only found near the calcified zone. Types of animal tissue include epithelial tissue and connective tissue, and their structure and functions in animals are discussed below. CANDIDATE: The three main functions of bone are: 2. It also regulates the ability of cartilage to dissipate energy during cyclic loading. COMMENT: Draw the standard picture seen in many text books (Figure 20.13). COMMENT: A picture was shown of an osteoclast in Howship’s lacuna (Figure 20.1). All connective tissue is derived from mesoderm, the middle germ cell layer in the embryo. One of the important functions of the connective-tissue cells is to maintain conditions in the extracellular spaces that favour this exchange. There may be areas of full-thickness cartilage loss with the subchondral bone exposed and often sclerotic. Stress relaxation is the decrease in stress required to maintain constant strain over time. Intracellular events include post-translational hydroxylation of proline and lysine and subsequent glycosylation. Over time there is a decreased interstitial fluid support that causes an increased loading of the solid phase including chondrocytes. This can be rote-learned from various tables, but a more detailed understanding is a safer bet in case follow-up questions focus in on more comprehensive detail. Runx2 is a multifunctional transcription factor that induces differentiation of multipotent mesenchymal cells into immature osteoblasts. The nutrient arteries are branches of the systemic circulation and enter the bony mid-diaphysis through the nutrient foramen passing to the medullary canal before branching into ascending and descending vessels and arteriolar branches supplying the inner two-thirds of the diaphyseal cortex (endosteal circulation). Non-nitrogen-containing BPNs are metabolized into non-functioning ATP analogues, which cause eventual osteoclast apoptosis. A proteoglycan aggrecan has three globular domains, G1, G2 and G3. These canals branch into large transverse Volkmann canals that provide circulation to the cortical bone. PGs have an average lifespan of 3 months and have a great capacity for retaining water, which gives compressive strength and elasticity to the tissue. Zone II is the upper proliferative or columnarregion. EXAMINER: What do you know about the collagen structure in osteogenesis imperfecta (OI)? (Figure 20.17.). Matrix regions differ in their collagen content, collagen fibril diameter, collagen fibril orientation and proteoglycan and non-collagenous protein content and organization. CANDIDATE: Skeletal dysplasias are a large group of rare, complex, heterogeneous disorders that involve cartilage and bone. Gives the articular cartilage its tensile stiffness. Bone lining cells: inactive osteoblasts. These tissues together form the organs in the body. (b) The low-pressure periosteal system circulation. Rate of creep is governed by the rate at which fluid is forced out from the tissue, which, in turn, is governed by the permeability and stiffness of the porous-permeable, collagen–proteoglycan solid matrix. Despite chondrocyte proliferation and increased collagen and proteoglycan synthesis this response fails to halt disease progression. COMMENT: Elastic cartilage exists in the epiglottis and the eustachian tube. Adipose Tissue. EXAMINER: What types of cartilage do you know about? CANDIDATE: Functions of the periosteum include: Medium through which muscles, tendons and ligaments are attached. Comminuted fractures can tolerate more motion than simple fractures, because in a comminuted fracture the overall motion is shared among many fracture gaps. Aggregation of collagen fibrils to form a collagen fibre. Fibroblast growth factor stimulates proliferation of mesenchymal cells in the developing limb that leads to limb outgrowth. Low metabolic activity, hence low healing potential. Two chains are α1 chains and the third chain is α2. CANDIDATE: These interact with collagen fibrils and stabilize the matrix framework. 2. This law suggests mechanical factors influence longitudinal growth, bone remodelling and fracture repair. The femoral neck width of obese people changes to accommodate the added weight. One function of connective tissue is to link the structures of locomotion. EXAMINER: What do we mean by the term matrix region? Also explore over 6 similar quizzes in this category. CANDIDATE: There are two main macroscopic types of bone, either (1) lamellar or (2) woven. CANDIDATE: The racket-holding arms of tennis players are stronger than the other arm. While the triphasic nature of cartilage is a physically intuitive way to model cartilage, it is also very complex. EXAMINER: What about hysteresis and strain-dependent mechanical properties (Figures 20.21 and 20.22)? EXAMINER: Can you draw a picture of collagen and proteoglycans? Osteocytes occupy lacunae that are contained within the calcified matrix of bone between lamellae. The collagen triple helix forms because both the α1 and α2 chains contain repeat sequences of amino acids (-gly-X-Y), where gly is glycine, X is proline and Y is usually hydroxyproline. A mechanical role in supporting the body’s tissues, providing attachment for muscles and protecting internal organs. Bone healing, primary vs. secondary. Stronger and less flexible than woven bone. Osteoprotegerin inhibits bone resorption by binding and inactivating RANKL. Primary soft callus formation. This results in increased cross-linking of collagen molecules altering the biomechanical properties of cartilage resulting in increased stiffness and an increased susceptibility to fatigue failure. COMMENT: Contact healing – essentially no or minimal fracture gap. COMMENT: Candidates may be asked to directly compare the biomechanical changes of ageing with osteoarthritis in cartilage. Protecting. Glycosaminoglycan can link to a protein core by sugar bonds to form a proteoglycan aggrecan (see Figure 20.14). They increase the local signals needed to initiate the cascade of bone healing. Highly vascularized periosteal system is reversed to centripetal proteases then break down organic. Remodelling occurs in small packets of cells in bone homeostasis when under tolerable strain much... 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