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WEEK 24:
Bone 1:
| Question | Answer |
|---|---|
| cartilage | avascular, specialised connective smooth tissue |
| function of cartilage with bone and joints | cartilage can act as a smooth surface for bone articulation within joints playing a role in bone formation and providing structural support |
| typical function of cartilage | often functioning as shock absorbers of the body |
| cartilage can be tough or flexible depending on | composition of matrix |
| cells in cartilage | chondrocytes |
| bone organisation | dense outer shell (compact bone) and inner spongy/ cancellous bone (arranged in interconnecting trabeculae with spaces for bone marrow) |
| periosteum | fibrous connective tissue layer limiting bone (not present at joint ends of long bones) |
| endosteum | lines interior of bones |
| matrix of cartilage composes of (3) | type II collagen, proteoglycans, and other proteins |
| chondrocytes | specialised cartilage cells that produce a matrix of collagen and other proteins (ECM) |
| collagen | protein that helps give cartilage its shape and specific properties |
| type II collagen | fibrillar collagen that is restricted to cartilages |
| proteoglycans | special type of protein that provides biomechanical properties crucial for cartilages proper functioning and are key players in chondral diseases |
| non collagenous proteins | help cartilage attract water and give it its shape and specific properties |
| perichondrium | dense layer of fibrous connective tissue covering the surface of most of the cartilage in the body |
| layers in the perichondrium (2) | outer fibrous layer and inner chondrogenic layer |
| outer layer of perichondrium | fibrous |
| inner layer of perichondrium | chondrogenic |
| inner chondrogenic layer of perichondrium contains | chondroblasts |
| outer fibrous layer of perichondrium contains | fibroblasts |
| cartilage ECM main components (2) | fibres (collagen II) and ground substance (protein aggregates made of proteoglycans and GAGs) |
| proteoglycan aggregates | proteoglycan monomers attached to a molecule of hyaluronin making it hydrophilic and provides compressive strength making it a flexible cushioned surface (proteoglycans + GAGs) |
| proteoglycans | contain numbers glycosaminoglycans (GAGs) attached to a core protein (bottle brush structure with negatively charged chains) |
| the ground substance of cartilage ECM is woven with | collagen to form an elastic and compressible structure |
| GAGs (3) | chondroitin-4-sulphate, chondroitin-6- sulphate, and keratan sulphate. |
| cartilage cells are derived from | embryonic mesenchyme |
| structure of cartilage cells | clusters of chondroblasts (rounded) surrounded by a layer of perichondrium |
| growth of cartilage is via (2) | interstitial and appositional growth |
| what happens to cells after matrix deposition | they become less and active and become maintaining cells |
| interstitial growth of cartilage | mainly happens during childhood and adolescence where chondroblasts in the cartilage divide and grow making the cartilage matrix expand from within |
| appositional growth of cartilage | new chondroblasts from the perichondrium add new surface layers of matrix to the existing matrix, thus expanding the girth of the cartilage |
| how are chondrocytes arranged in hyaline cartilage | in groups in a matrix containing type II collagen |
| perichondrium in hyaline cartilage | usually present except at articular surfaces |
| where is hyaline cartilage found | end of long bones, ventral rib cartilage, templates for endochondral bone formation, and tracheal rings |
| how are chondrocytes arranged in elastic cartilage | compacted in matrix containing type II collagen and elastic fibres |
| perichondrium in elastic cartilage | present |
| where is elastic cartilage found | pinna of ear, auditory canal, laryngeal cartilages, and epiglottis |
| how are chondrocytes arranged in fibrocartilage | in rows in a matrix with type I collagen bundles in rows |
| perichondrium in fibrocartilage | absent |
| where is fibrocartilage found | intervertebral discs, pubic symphysis, joint capsules, ligaments and tendons |
| hyaline cartilage | type II collagen only - smooth glistening (glassy) articular surfaces |
| elastic cartilage | type II collagen and elastin |
| fibrocartilage | type II and type collagen - strong |
| what type of tissue is bone | specialised connective tissue |
| what minerals does bone provide | reservoir for calcium and phosphate |
| bone marrow in bone supports what process | haematopoiesis (making new RBCs) |
| bone is composed of | cells and ECM |
| requirements for bone ECM | strong enough to support body yet light enough to be moved (max strength and low weight) |
| role of cells in the bone | produce, mediate and maintain remodel matrix |
| bone structure and organisation | dense outer shell (compact bone), inner spongy/ cancellous bone (arranged in interconnecting trabeculae with spaces for bone marrow) |
| dense outer shell of bone | compact bone |
| inner spongy/ cancellous bone | arranged in interconnecting trabeculae with spaces for bone marrow |
| periosteum | fibrous connective tissue layer limiting bone and is not present at the joint ends of long bones |
| periosteum is not present where | at the joint ends of long bones |
| endosteum | lines the interior of bones |
| organic bone matrix | produced by osteoblasts, containing type I collagen and non collagenous proteins (which mediate mineral deposition), providing tensile and compressive strength |
| inorganic bone matrix | made of calcium phosphate (hydroxyapatite) and is deposited in the organic matrix making up 66% of the dry weight of bone (hardness) |
| bone cells are from | mesenchymal stem cells |
| mesenchymal stem cells differentiate into | osteoprogenitor cells |
| osteoprogenitor cells differentiate into | osteoblasts |
| order of differentiation of bone cells | mesenchymal stem cells -> osteoprogenitor cells -> osteoblasts |
| osteoblasts | layer down organic bone matrix and mediates mineralisation of osteoid |
| when do osteoblasts become osteocytes | when surrounded by mineralised bone |
| osteocyte | maintains matrix |
| osteoclasts | bone resorbing/eating cells |
| osteoblasts secrete | collagen and matrix vesicles |
| matrix vesicles contain | enzymes and proteins |
| why do matrix vesicles contain enzymes and proteins | to control availability of calcium and phosphate so that mineral is precipitated |
| immature/ new bone | woven bone which has haphazard fibre arrangement and is mechanically weak needing fracture repair |
| mature bone | lamellar bone with regular parallel collagen, strong and found in all adult bone and is arranged as osteons (aligned with the direction of force) |
| osteogenesis imperfecta (OI)/ brittle bone disease | congenital disease where defective collagen chain disrupts structure of triple helix leading to a fragile skeleton |
| type II OI | fatal in utero or perinatal |
| type I OI | increased childhood fractures |
| trabecular bone | has lamellae with osteocytes in lacunae which is connected to one another via canaliculi |
| difference between trabecular bone and compact bone | compact bone has central canals and perforating canals which contain blood and lymph vessels and nerves but trabecular bone does not have central canals or perforating canals and their vessels and nerves travel between spaces in the trabeculae |
| where do blood vessels, lymph vessels and nerves travel in compact bone | in perforating and central canals |
| where do blood vessels, lymph vessels and nerves travel in trabecular bone | between spaces in trabeculae |
| trabecular bone function | reduces weight and provides space for marrow |
| struts/ trabeculae are arranged in trabecular bone to | provide maximum resistance to stresses |
| where is trabecular bone found | wrists, vertebrae and femoral neck |
| osteoporosis | thinning of both cortical and trabecular bone but thinned trabecular are prone to fracture eg hip fractue and |
| compact bone is made of | osteons which are functional units that act as weight bearing pillars |
| osteons are made up of | concentric rings of lamellar bone around a central nutrient canal |
| central canal contains | blood vessels, lymph vessels, and nerves |
| position of perforating canals to central canals | perforating canals run at right angles to the central canals |
| what is normal bone maintenance and turnover | continuous process where old bone tissue is broken down by cells (osteoclasts) and replaced with new bone formed by osteoblasts to allow bone to constantly remodel and repair to maintain its strength and structure (remodelling) |
| cortical bone (dense outer layer) turnover compared to trabecular bone (spongy inner bone) | cortical bone has a slower turnover rate to trabecular bone |
| factors affecting turnover (2) | hormones (oestrogen, parathyroid hormone PTH) and vitamin D |
| phases of bone remodelling (4) | resting, resorption, reversal, and formation (RRRF) |
| osteoclasts | bone resorbing cell which is a phagocytic cell from monocyte macrophage cell line. It is multinucleate and mobile which helps it attach to bone surface and resorb bone leaving a pit behind (Howships lacuna) |
| (Howships lacuna) | pit left behind after osteoclast eats bone |
| resting phase | prolonged resting period before new bone remodelling |
| when does resorption phase occur | when osteoclasts are activated |
| resorption phase | osteoclasts on the bone surface become activated and resorb bone matrix |
| reversal phase | resorbed bone surface is prepared by mononuclear cells to allow maximum osteoblast adherence |
| formation phase | osteoblast progenitors form osteoid matrix to complete the mineralisation of the bone |
| compare and explain bone remodelling in children and adults | bone turnover and remodelling is slower in adults than children |
| how can bone remodelling increase (3) | change in function (running, tennis, jumping), repair of fractures, and disease (eg Paget's disease) |
| how much compact bone is replaced annually | 5% |
| how much cancellous bone is replaced annually | 25% |
| PTH stimulates what | bone resorption by osteoclasts |
| receptors for PTH are located where | on osteoblasts |
| osteoclast precursors have | RANK (receptor activator of nuclear factor Kappa B) receptors on their cell membranes |
| osteoblasts have | ligand for RANK receptor on their cell membranes (RANKL) |
| PTH upregulates what | RANKL |
| when PTH upregulate RANKL what happens | RANKL bind to RANK and stimulates the differentiation of osteoclasts |
| osteoblasts also produce what by binding to RANKL | osteoprotegrin- which prevents resorption |
| osteoprotegrin | produced by osteoblasts and prevent resorption |
| what determines bone resorption | ratio of RANKL: osteoprotegrin |
| relationship between osteoblasts and osteoclasts are via (3) | PTH RANKL and osteoprotegrin process, direct cell to cell contact, and cytokine signalling |
| explain direct cell-cell contact | osteoblasts and osteoclasts can directly interact through cell adhesion molecules eg E-cadherin, which facilitates signalling between them |
| explain cytokine signaling | osteoblasts secrete various cytokines eg M-CSF (macrophage colony stimulating factor) that stimulate osteoclast proliferation and differentiation |
| factors which disrupt osteoblast and osteoclast balance (3) | hormonal imbalance, mechanical stress, and aging |
| explain how hormonal imbalances disrupt osteoblast and osteoclast balance | hormones like oestrogen and PTH imabalance/ dysregulation can lead to bone diseases like osteoporosis |
| explain how mechanical stress disrupt osteoblast and osteoclast balance | changes in mechanical loading on bones can influence osteoblast and osteoclast activity impacting bone remodeling |
| explain how ageing disrupt osteoblast and osteoclast balance | with age, balance between bone formation and resorption can shift towards increased resorption leading to bone loss |
| explain cause of osteoporosis | loss of bone mass where mineralisation of bone is normal (increase porosity) but due to disuse (wheelchair, mobility problems), hormones (eg oestrogen levels decreased), and low peak bone mass |
| when is bone gradually lost | after approximately 30 years old |
| why does menopause lead to osteoporosis | oestrogen is osteoprotective but in menopause the levels are decreased |
| why does disuse like wheelchair or mobility problems lead to osteoporosis | need mechanical stress (movement) for remodelling but wont occur if no move |
Created by:
kablooey
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