The knee is a meeting place for four bones the femur (thigh bone), tibia (shinbone), fibula (calf bone), and patella (kneecap). CANDIDATE: Osteoblasts are large cells responsible for the synthesis and mineralization of bone during both initial bone formation and later bone remodelling. However, it pervades many aspects of clinical practice and therefore must be understood. These substances were later identified as bone morphogenetic proteins (BMPs). The zone is the truegerminal layer of the growth plate and Type IIcollagen synthesis is increased. Chapter 20 – Structure and function of connective tissue. These fill the gaps between osteons and are remnants of bone remodelling. The third globular domain, G3, is near the C terminal of the core protein. Once secreted, procollagen peptidases remove the N-terminal and C-terminal propeptides. RANK, expressed on osteoclast precursors, is a key regulator of osteoclastogenesis. EXAMINER: Can you draw a picture of collagen and proteoglycans? COMMENT: Bone models and remodels in response to the mechanical stresses it experiences, resulting in a minimal-weight structure that is adapted to its applied stresses. Muscle is attached to the bones it moves by tendons, thick lengths of connective tissue that pull on the bones like rope. Be clear about the differences between gap and contact healing. It develops from the mesoderm. Collections of tissues joined in units to serve a common function compose organs. 3. EXAMINER: What are the management options for osteoarthritis? and then a focus midway through on the biomechanical properties of articular cartilage. EXAMINER: What controls the differentiation of osteoblasts? Animal tissues are grouped into four basic types: connective, muscle, nervous, and epithelial. Rubin’s classification of bone dysplasia is based on the type of abnormality (hypo-/hyperplasia) and the site involved in the bone: (1) epiphyseal, (2) physeal, (3) metaphyseal, (4) diaphyseal location. EXAMINER: What is the structure of collagen (Figure 20.18)? They help chondrocytes bind to the macromolecules of the matrix. This is in the score 8 zone for candidates. Zone VI is the junction of the growth plate with the metaphysis, the region where the transitionfrom cartilage to bone occurs. You ‘the candidate’ should explain this as you draw out articular cartilage and not allow the examiner to get in and ask you these questions.11,12. Transforming growth factors (TGFs) have an important role in skeletal tissue, particularly certain members of the TGF-b gene family which includes the bone morphogenetic proteins involved in morphogenesis and regulation of endochondral ossification and in bone remodelling. COMMENT: That is a very specific question, but a common theme. In this case the width of the femoral neck has increased to dissipate weight throughout the bony area by increasing surface area and strength through redistribution of bone. New blood vessels invade the haematoma, fibroblasts from the periosteum colonize the haematoma and produce collagen fibres. Flow in immature, developing bone is centripetal because the highly vascularized periosteal system is the predominant component. EXAMINER: What do you know about the collagen structure in osteogenesis imperfecta (OI)? CANDIDATE: A viscoelastic material will exhibit a time-dependent behaviour when subjected to a constant load or constant deformation. COMMENT: It’s easy to get confused with these facts. Woven bone can be either immature (fracture callus) or pathological. These small GTPases are signalling proteins that regulate a number of cell processes such as membrane ruffling, cytoskeletal organization and trafficking of vesicles, which are required for osteoclast function. COMMENT: This is an esoteric question that tests knowledge of the interaction between proteoglycan and water. The extracellular matrix is made up of fibres and ground substance. CANDIDATE: These interact with collagen fibrils and stabilize the matrix framework. Figure 20. Blood. EXAMINER: What about compression and tension of bone? It is made up both of specialized cells that affix to other tissues as well as what is known as the extracellular matrix. Glycosaminoglycan can link to a protein core by sugar bonds to form a proteoglycan aggrecan (see Figure 20.14). COMMENT: The biomechanical properties of articular cartilage can be complicated to understand and tests higher-order thinking relating to structure. It is regulated by receptor activator of nuclear factor κB (RANK), RANK ligand (RANKL) and osteoprotegerin (OPG). The pericellular matrix is a thin layer adjacent to the cell membrane, completely surrounding the chondrocyte. Because the proteoglycans are bound closely, the closeness of the negative charges creates a repulsion force that must be neutralized by positive ions in the surrounding fluid. Function of Areolar Connective Tissue December 15, 2020 / in Feeds / by Grace Wahito. These non-helical regions are denoted telopeptides and they play a role in the registering of collagen α chains and cross-linking. BMPs are the only molecules so far discovered capable of independently inducing endochondral ossification in vivo. The cutting filling cone has a head of osteoclasts that cut through the bone, and a tail of osteoblasts that form a new secondary osteon. Candidates may then be asked to explain why the layers appear like this, with reference to the three-dimensional ultrastructure.10. 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. High levels of alkaline phosphatase synthesis of type X and type II collagen cell death by hypoxia. EXAMINER: What are the properties of a viscoelastic material? Water accounts for between 65% and 80% of the extracellular matrix, proteoglycans and glycoaminoglycans 10–15% with small amounts of glycoproteins and degradative enzymes. The structure terminates as a closing zone in which osteoblasts close the newly excavated osteon by adding centripetal layers of lamellar bone inward from the cement line boundary. Osteoprogenitor cell: precursors to osteoblasts that line the Haversian system and can be stimulated to differentiate into osteoblasts and form new bone. The osteoprogenitor cells originate from mesenchymal stem cells and line the Haversian canals, endosteum and periosteum. While the triphasic nature of cartilage is a physically intuitive way to model cartilage, it is also very complex. Thinnest layer with the highest concentration of collagen and water and the lowest concentration of proteoglycan. Osteocytes occupy lacunae that are contained within the calcified matrix of bone between lamellae. It does so by forming sacs that contain the organs and attach to nearby structures so they do not simply float about freely. Osteoblasts form a closely packed sheet on the surface of the bone, from which cellular processes extend through the developing bone. EXAMINER: What’s the importance of water? These tissues vary in their structure, function, and origin. This paper mentioned Perren’s strain theory and introduced some exciting new ideas on fracture healing to challenge our traditional views on these complicated healing mechanisms. Besides, they are the wide-spaced cell in the small cavities … Type XI constrains the proteoglycan matrix. Water can be squeezed out of the layer to help create lubrication. For bone these include: EXAMINER: What are the functions of bone? CANDIDATE: Osteoblasts, osteoclasts, osteocytes, bone lining cells and osteoprogenitor cells. The most superficial part is called the lamina splendens,13 providing a very low-friction lubrication surface. Components of connective tissue. Venous flow in mature bone is centripetal. Fail to master this diagram at your peril. For strains greater than 2% and less than 100%, a fracture occurs and is considered to be the beginning of the ‘bone-healing organ’. 1. The histological structure can be divided into four zones. The topic is large with a number of subtopics within the main topic that the examiners can easily focus in on. EXAMINER: How do osteoclasts resorb bone? Tissue cannot be produced when strain conditions exceed the tissue strain tolerance. There are two causes for this nonlinear effect. So you may try to carefully prop up the lumber on the foundation. 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. COMMENT: Candidates may be asked more specific details about each option such as indications, complications, results, especially if in the adult pathology viva and aiming for score 8. This group is also involved in later stages of bone growth. Creep is time-dependent deformation of a material under constant load that is below its yield strength. This fluid support is not uniform between the different zones of the tissue, with the superficial zone demonstrating the highest support (95%) compared to the deep zone (70% of applied load). Collagen fibres are orientated more parallel to each other. Microfracture is suited for medium-size defects with little or no bone loss in lower-demand older patients. G1 and G2 are near the N terminus and separated by a short interglobular domain. CANDIDATE: Osteoblasts are derived from undifferentiated mesenchymal cells; they are bone-forming and lay down osteoid (type 1 collagen) as well as activating osteoclasts to resorb bone via the receptor activator of nuclear factor κβ (RANK) and its ligand (RANKL) system. Proteoglycans trap and hold water, providing the tissue with its turgid nature that resists compression. The mechanical behaviour differs according to the direction of applied force: the bone’s greatest strength is parallel to the longitudinal axis. EXAMINER: Draw a cross-section of articular cartilage (Figure 20.12). 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. Learn about a little known plugin that tells you if you're getting the best price on Amazon. As such the challenge for the Intercollegiate Board is to avoid asking the same questions each and every exam sitting. Tap card to see definition 👆. This is an A-list topic. EXAMINER: Can you draw the histological appearance of articular cartilage? Osteocytes are derived from osteoblasts, or bone-forming cells, and are essentially osteoblasts surrounded by the products they secreted. May function as a barrier to the passage of large molecules from the synovial fluid. EXAMINER: Describe the changes in articular cartilage with osteoarthritis. Esoteric or un-Googleable questions are also fairly common in this section. (c) Metaphyseal–epiphyseal system is the periarticular vascular complex that penetrates the cortex and supplies the metaphysis, physis and epiphysis with end arterioles. Connective tissue that provides support and framework for the body consists of fibrous proteins and nonfibrous ground substance in varying proportions depending on their functions.. 2. Compressive forces inhibit longitudinal growth; tension stimulates it. Whenever feasible, any internal or external fixation device should be applied to the tension side to provide maximum stability. There is a direct relationship between permeability and water content and an inverse relationship between permeability and proteoglycan content. 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. 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. EXAMINER: Can you draw out the graphs of creep and stress relaxation (Figures 20.19 and 20.20)? COMMENT: There are other minor functions, but again, keep it simple. Figure 20.16 Candidate drawing of proteoglycan aggregate. COMMENT: Primary and secondary bone healing comes up repeatedly in the viva exam and candidates need to be very clear about the distinction between them. Split the process into intracellular and extracellular events. Stronger and less flexible than woven bone. CANDIDATE: A viscoelastic material demonstrates creep and stress relaxation. EXAMINER: What are the properties of articular cartilage? This type of repair tissue is much weaker than hyaline cartilage and displays poor long-term performance due to poor compressive strength and durability. CANDIDATE: The main types of bones cells, and their function, are as follows: 2. 1. Animal Tissue. Type IX (an injury to the periosteum which could interfere with membranous growth). Click to share on Twitter (Opens in new window), Click to share on Facebook (Opens in new window), Click to share on Google+ (Opens in new window), on Chapter 20 – Structure and function of connective tissue, Chapter 20 – Structure and function of connective tissue, Chapter 31 – Drawings for the FRCS (Tr & Orth), Chapter 19 – Anatomy and surgical approaches, Immature (embryonic/neonatal skeleton, metaphyseal region fracture healing), Dense collagen fibres, varied mineral content, greater turnover, more cells per unit volume, Formed by intramembranous or endochondral ossification, contains collagen fibres, Randomly arranged collagen fibres, disorganized, Highly ordered, stress-orientated collagen fibres, Isotropic: independent of direction of applied forces, Anisotropic: mechanical behaviour differs according to direction of applied force, Bone’s greatest strength is parallel to its longitudinal axis, Weaker, more flexible, more easily deformed, Rods (thin trabeculae), plates (thick trabeculae), Subjected to bending, torsional and compressive forces, Predominantly subjected to compressive forces, Proteoglycans and glycosaminoglycans (10–15%), Degradative enzymes (matrix metalloproteinases). A given load produces less deformation over a shorter period of time than a longer period of time. This serves to regulate the response of cartilage to compression by preventing rapid and excessive fluid exudation from the tissue with compression loading and by promoting interstitial fluid pressurization for load support. 1. Connective tissue: A material made up of fibers forming a framework and support structure for body tissues and organs. Figure 20.21 Hysteresis. Figure 20.4 Several tropocollagen molecules are aggregated in an organized head-to-tail fashion into a structure called a collagen fibril. They have an important role in the homoeostasis of calcium and phosphate metabolism. With increasing age there is an age-related decline in the ability of chondrocytes to maintain the tissue. The proteoglycan aggregates are basically responsible for the turgid nature of the cartilage and in articular cartilage they provide the osmotic properties needed to resist compressive loads. The superficial zone contains a high density of flat cells with approximately three times as many cells in the region compared to the larger cells of the deeper zone. the opposite way around) (Figure 20.4). 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. Chondrocytes become less responsive to the proliferative and anabolic effects of growth factors. CANDIDATE: The blood supply to bone is derived from three sources. COMMENT: These are fairly straightforward questions but may catch the unprepared candidate out. With OI the majority of identified mutations are single nucleotide substitutions that result in alteration of glycine codons within the triple helical domain of either of the chains of type I procollagen (Figure 20.8). Cell-based, biological replacement options (autologous chondrocyte implantation [ACI], stem cell therapy, tissue engineering). EXAMINER: What is the function of matrix glycoproteins? Full-thickness defects arise from damage that penetrates deep into the subchondral bone. To make the subject less predictable the topic focus can be changed mid viva onto different more detailed areas within this large topic such as proteoglycan structure and function. The triple helical structure is not the same as the α helix that is formed by a single polypeptide chain and is the defining feature of all collagen. Callus mineralization (hard callus). They lie within a small space called a lacuna, which is contained in the calcified matrix of bone. CANDIDATE: Secondary bone healing involves the formation of fracture callus. The triphasic nature of cartilage explains how fluid is drawn back into the cartilage matrix after being excreted during compression. They are also called gristle. Some authors have suggested that because it is a very thin structure it has negligible shock-absorbing capacity compared to the surrounding muscle and bone. Both BMP2 and BMP7 are approved for use in acute tibial fractures and complex non-unions. There are four major categories of bodily tissue: nervous, epithelial, muscle, and connective tissue. Use the orthopaedic 20-second diagram. Connective tissue is found in between other tissues everywhere in the body, including the nervous system. However, it is sometimes a thin line between the two. As the name implies, connective tissues often bind other organs together, hold organs in place, cushion them, and fill space. (1) The water content or porosity is reduced. It has an architecture of 3D lattice rods and plates, high porosity with large spaces between trabeculae and predominantly subjected to compressive loads. Functions of Connective Tissues Connective tissues perform many functions in the body, but most importantly, they support and connect other tissues; from the connective tissue sheath that surrounds muscle cells, to the tendons that attach muscles to bones, and to the skeleton that supports the positions of the body. These collagen fibrils can be seen with an electron microscope and exhibit a 67-nm D-period banded appearance due to staggered gaps between the heads and tails of the molecules in each row. In BHN, the bone is in homeostasis when under tolerable strain (much less than 2%). Imagine constructing a house using typical building components. Quantitative defects are often heterozygous, with one copy not producing any collagen. EXAMINER: What are the functions of articular cartilage? Collagen fibres are arranged parallel to the joint surface, forming a dense mat. 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. Connective tissue; Muscular tissue; Nervous tissue. EXAMINER: What do we mean by tensegrity architecture? Connective Tissue Function Connective tissue function is structural, metabolic, and protective. Connective tissues can have various levels of vascularity. In the knee, these bones are the femur and tibia. The principal functions of the areolar connective tissues are: It holds the organs in place Provides water and salts for nearby tissues Cells of the body … Chondrocytes have no contact with neighbouring cells and are spheroidal. EXAMINER: Tell me about matrix metabolism. Triple helix steric hindrance. Increased water content leads to increased permeability, decreased strength and decreased elasticity. EXAMINER: What type of collagen is present in bone? Collagen fibres arranged obliquely at right angles to each other. Osteoblasts lay down collagen matrix in microscopic thin, layered sheets called lamellae. consider the whole fracture to be a ‘bone-healing organ’ that works as a functional unit and responds to biological and mechanical stimuli. This arrangement results in a constrained structure that imparts a tight kink in the polypeptide chain with the glycine chain preventing steric hindrance that would otherwise impair wrapping of the helical band. Osteocytes lie within the substance of fully formed bone. Permits load-dependent deformation of articular cartilage by its movement both in and out and within cartilage. Affixing to bone, muscle, or other nearby tissues, connective tissue is distributed throughout the body, forming tendons, ligaments, cartilage, fat, and even contributing to blood and lymph. EXAMINER: What is the gene coding for OI? Synthesis is increased adapt to the distance from the bone will remodel itself over time to become stronger to the. 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