Integument, Bone & Joint Lectures 2024 PDF

Integument, bone & joint Foundational Veterinary Sciences, SVF 120 Edward Snelling Anatomy building, office 2-15 Physiology building, lab ground floor Experimental physiology, biomechanics & biochemistry www.edwardsnelling.com ...

Integument, bone & joint Foundational Veterinary Sciences, SVF 120 Edward Snelling Anatomy building, office 2-15 Physiology building, lab ground floor Experimental physiology, biomechanics & biochemistry www.edwardsnelling.com  Outcomes Demonstrate knowledge and understanding of the: 1. Structure & function of the integument 2. Structure & function of bone 3. Growth & remodeling of bone 4. Structure & function of joints and of cartilage L1 General integument function The integument (skin): 1. Prevents desiccation barrier to water loss 2. Prevents infection barrier to foreign bodies 3. Assists in thermoregulation blood flow and hair coat dynamics 4. Acts as a sensory organ mechano-, thermo-, chemoreceptors 5. Excretes water and salts 6. Synthesizes vitamin D L1  General integument structure Colville & Bassert, 2015 L1  General integument structure The integument (skin) is categorised into three (3) layers: 1. Epidermal layer 2. Dermal layer (corium) 3. Hypodermal layer (subcutaneous layer) L1  General integument structure Epidermal layer: avascular, Hair shaft primarily cellular squamous epithelial cells: (1) keratinocytes multiply at basement membrane pushing older cells toward surface Epidermal layer and undergo keratinization (cells Sebaceous fill with keratohyalin granules, Dermal gland layer organelles degenerate, and Hair follicle become lifeless sheets of keratin), Hypodermal (2) melanocytes produce melanin layer stored in melanosome granules L1  General integument structure Dermal layer: vascular, primarily Hair shaft fibro-elastic connective tissue, this layer also contains hair follicles, nerve endings, glands, smooth muscle, blood vessels, Epidermal layer lymph vessels, and various types Sebaceous of receptors (mechano-, thermo-, Dermal gland layer and chemoreceptors) Hair follicle Hypodermal layer L1  General integument structure Hypodermal layer: primarily Hair shaft adipose tissue (fat) and loose connective tissue Epidermal layer Sebaceous Dermal gland layer Hair follicle Hypodermal layer L1  Hair structure and function Hair function: traps insulating layer of air important for thermoregulation piloerection and pilorelaxation, under the action of the ‘arrector pili muscle’, allows for control of the thickness of the insulating layer of air, and thus provides some control over heat loss colour important in absorbing solar radiation in the visible spectrum colour important for camouflage in some species L1  Hair structure and function Hair structure: each strand is comprised of three layers: (1) a central ‘medulla’ containing flexible soft keratin, (2) a ‘cortex’ containing rigid hard keratin, and (3) a ‘cuticle’ containing rigid hard keratin (a single layer of cells, normally arranged like roof tiles to prevent clumping) the ‘shaft’ is the part of the hair located above the skin surface, the ‘root’ is the part embedded below the skin surface each hair is anchored by the ‘hair follicle’, which is an invagination of the epidermal layer that extends down into the dermal layer L1  Hair structure and function Hair structure (continued): the deepest part of the hair follicle expands to form the ‘hair bulb’, where a mound of dermal cells called the ‘papilla’ is covered with rapidly dividing epithelial cells called the ‘matrix’ as the epithelial cells divide and grow, older cells are pushed upward, they become ‘keratinized’ and die. Sound familiar? L1  Hair structure and function Colville & Bassert, 2015 L1  Hair growth cycle Hair growth cycle: hair undergoes a routine cycle of growing and shedding hair can also undergo once-off shedding (blowing the coat), influenced by genetics and environment (e.g. shedding is often heaviest in the spring) hair cycle is differentiated into three phases: the (1) ‘anagen phase’ is the period of growth as epithelial cells are added at the ‘matrix’, the (2) ‘catagen phase’ represents the transition between anagen and telogen phases, and the (3) ‘telogen phase’ is the quiescent state induced by shortening of the hair follicle L1  Hair growth cycle Colville & Bassert, 2015  Glands of the skin Sebaceous glands: generally found all regions of the skin, embedded in the dermal layer a sac-like structure (alveolus) with a single duct that empties into a hair follicle (although some empty directly onto skin surface) the sac is lined with epithelial cells that synthesize and store an oily substance composed primarily of free fatty acids, and when the cells rupture they release this ‘sebum’ into the sac contraction of ‘arrector pili muscle’ forces sebum through the duct and into the hair follicle, where it coats the base of the hair and the surrounding skin helps retain moisture, anti-bacterial and anti-fungal properties L1  Glands of the skin Sweat glands (sudoriferous glands): generally found all regions of the skin, embedded in the dermal and/or hypodermal layer occur in most domestic mammals, but more prevalent in larger species (especially humans and horses) there are two types of sweat gland: (1) ‘eccrine sweat glands’ secrete directly onto the skin surface (common in humans, but sparse among domestic animals), and (2) ‘apocrine sweat glands’ secrete into hair follicles (common among cats, dogs, sheep, cattle, horses) function in evaporative cooling, heat is drawn from the skin as water molecules change from the liquid phase to the gaseous phase L1  Glands of the skin Colville & Bassert, 2015 L1  Test your knowledge Which of the following are functions of the integument? A. Provide barrier to water loss B. Provide barrier to infection C. Assist in thermoregulation D. Act as a sensory organ E. All of the above L1  Test your knowledge Which phase of the hair cycle is characterized by a period of growth as epithelial cells are added at the ‘matrix’? A. Anagen phase B. Catagen phase C. Telogen phase D. Shedding phase E. Growing phase L1  Test your knowledge Which of the following statements regarding the thermoregulatory function of the hair coat is incorrect? A. The hair coat traps an insulating layer of air B. Piloerection and pilorelaxation allow for some control over heat loss from the body C. Hair coat colour affects the absorption of radiation from the sun D. Hair coat colour affects the emission of radiation from the body E. Hair coat colour is important for camouflage in some species L1 General skeletal function Exoskeleton Endoskeleton: 1. Support & locomotion long bones of the forelimbs and hindlimbs 2. Protect internal organs flat bones of the cranium, ribs, sternum 3. Homeostasis and synthesis Ca2+ & PO43 – store (fetus, lactation, eggshell) hematopoiesis (RBC, WBC, platelets) L2  Bone structure Hyaline (articular) cartilage Spongy (cancellous/trabecular) bone Epiphysis Epiphyseal (growth) plate Spongy (cancellous/trabecular) bone Metaphysis Periosteum, osteoprogenitors & osteoblasts line the outer surface Compact (cortical) bone Diaphysis Endosteum, osteoprogenitors & osteoblasts line the inner surfaces Medullary (marrow) cavity Reece, 2015 L2  Bone structure Vessels & nerves Inner lamellae Interstitial lamellae Endosteum, contiguous with spongy bone Lacuna, containing osteocyte Volkmann canal Lamellae of bone (bone matrix) Osteonal endosteum Central (Haversian) canal, containing vessels & nerves Outer Lacuna, containing osteocyte lamellae Periosteum Reece, 2015 L2  Bone structure An osteon (Haversian system) – a repeating functional unit of bone Canaliculi Osteoblast, bone Lacuna ossification Osteocyte Osteoclast, bone resorption Nerve Central (Haversian) canal Cytoplasmic extensions, connect via gap junctions Lymphatic Lamellae of bone Artery vessel Vein (bone matrix) L2  Flat bones vs long bones 1. Flat bones (e.g. plates of the skull, ribs, sternum, pelvis) outer compact bone (cortical bone) and inner spongy bone (cancellous or trabecular bone) protect internal organs, Ca2+ & PO43 – store, hematopoiesis 2. Long bones (e.g. humerus, femur) as above, outer compact bone (cortical bone) and inner spongy bone (cancellous or trabecular bone) support & locomotion, Ca2+ & PO43 – store, hematopoiesis L2  Compact bone vs spongy bone 1. Outer compact bone (cortical bone) dense organization providing strength and rigidity nutrients & gases exchanged along vessels within central (Haversian) canals, around which are lamellae, which form an osteon (Haversian system) – a repeating functional unit of bone 2. Inner spongy bone (cancellous or trabecular bone) sparse arrangement providing strength and some flexibility while reducing weight nutrients & gases exchanged with extracellular fluid no osteon units, rather lamellae arranged to form spicules of bone L2 Compact bone vs spongy bone Compact bone Spongy bone L2  Bone cells 1. Osteoblasts synthesize the organic portion of the matrix, i.e. the osteoid containing collagen and proteins produce the inorganic portion of the matrix, i.e. hydroxyapatite 2. Osteocytes mature bone cells ‘trapped’ within the lacunae might be able to revert back to osteoblast during remodeling cytoplasmic extensions within the canaliculi, communicate with other osteocytes or osteoblasts L2  Bone cells 3. Osteoclasts large, mobile, multi-nucleated cells responsible for bone resorption release acids and acid-tolerant proteolytic enzymes (specific proteases) that ‘breakdown’ the organic portion and ‘dissolve into solution’ the inorganic portion of the bone matrix L2  Bone matrix Osteoblasts synthesize the ‘bone matrix’, before becoming trapped, and turning into osteocytes. Bone matrix is composed of: 1. Organic portion osteoid (non-mineralized component), composed of collagen and proteins provides tensile (resilient) strength 2. Inorganic (mineral) portion hydroxyapatite, composed of calcium phosphate crystals provides rigid strength L2  Test your knowledge Which of the following are functions of the skeletal system? A. Provide support & facilitate locomotion B. Protect internal organs C. Hematopoiesis D. Ca2+ & PO43 – homeostasis E. All of the above L2  Test your knowledge Which of the following statements regarding spongy bone (cancellous or trabecular bone) is incorrect? A. Lamellae are arranged to form spicules of bone B. Nutrients & gases exchange with extracellular fluid C. Covered by endosteum, which is contiguous with the inner surface of the compact bone D. Comprised mostly of osteon (Haversian system) L2  Test your knowledge The inorganic portion of the bone matrix is composed of calcium phosphate crystals, generally in the form of hydroxyapatite, which provides the bone with: A. Strength and rigidity B. Substantial torsional flexibility C. Substantial lateral and compressive flexibility D. None of the above L2  Growth in length of bone Growth in length of long bones occurs at the epiphyseal (growth) plate/s, under control of growth hormone (somatotropin) secreted by the pituitary gland Epiphyseal plate has three (3) distinct layers: 1. Zone of proliferation: columns of chondrocytes multiplying, secrete cartilaginous matrix 2. Zone of maturation: chondrocytes stopped multiplying and have become enlarged 3. Zone of hypertrophy (zone of provisional calcification): further enlargement and vacuolization of chondrocytes, cartilaginous matrix begins to calcify L3  Growth in length of bone Next, chondrocytes undergo cell death, osteoblasts deposit thin layer of loosely organized collagen matrix onto the calcified cartilage, calcification of the new matrix follows, forming new spongy woven bone Lastly, osteoclasts resorb this spongy woven bone and the calcified cartilage, and then osteoblasts build sheets of true lamellar bone L3  Growth in length of bone epiphyseal bone quiescent cartilage cells proliferating cartilage cells epiphyseal (growth) maturing cartilage cells plates hypertrophic cartilage cells zone of calcified cartilage vascular invasion and spongy woven bone formation Reece, 2015 L3  Growth in diameter of bone Growth in diameter of long bones occurs by deposition of new bone by osteoblasts within the outer periosteum and accompanied resorption of older bone by osteoclasts at the interior of the shaft This allows the increase in bone diameter to keep pace with the increase in bone length (important for biomechanics), and it also allows for marrow cavity expansion (important for haematopoiesis) Growth in diameter of long bones is also responsive to chronic localised stress loads, e.g. tennis players have thicker (and denser) bones of the dominant arm L3 Growth in diameter of bone L3  Cost of bone growth ‘Using blood flow index to Post-pouch estimate the metabolic cost adult kangaroos of bone growth’ (bipedal) In-pouch joey kangaroos Other adult mammals (quadrupedal) Hu et al, 2018 L3  Cost of bone growth ‘Using blood flow index to Post-pouch estimate the metabolic cost adult kangaroos of bone growth’ (bipedal) In-pouch joey kangaroos Other adult mammals (quadrupedal) Hu et al, 2018 L3  Bone remodeling Remodeling is undertaken by bone remodeling units, and the process can be described by four (4) distinct steps: 1. Activation: identification of the site to be remodeled. Quiescent osteoblasts lining the bone surface retract, expose bone matrix, and osteoclasts then bind to exposed site 2. Resorption: osteoclasts release acids and proteolytic (protein degrading) enzymes dissolving the bone matrix, breakdown products enter the osteoclasts, then extruded into the extracellular fluid, leaving a depression in the bone matrix, then osteoclasts leave L3  Bone remodeling Remodeling can be described by four (4) distinct steps (cont.): 3. Reversal: osteoblasts move back along the surface and into the vacated depression 4. Formation: osteoblasts deposit new osteoid (non-mineralized component, composed of collagen and proteins) in discrete layers of lamellae, and then mineralisation occurs some time later L3  Bone remodeling Four small Close-up of a micro-fractures micro-fracture in in a spicule of the trabeculae trabeculae bone with osteoblasts to be resorbed and osteoclasts and replaced in the quiescent state Activation: Resorption: Osteoblasts Osteoclasts bond retract and with exposed osteoclasts bone matrix, activate and secrete acids move in to site and enzymes of exposed bone causing the matrix dissolution of matrix material Reece, 2015 L3  Bone remodeling Resorption: Reversal: Breakdown Osteoclasts products enter leave and the osteoclasts inactivate, while and then exit the surrounding other side into osteoblasts the extracellular move into the fluid, leaving a depression depression Formation: Formation: Osteoblasts Mineralisation produce new occurs some bone matrix to time later fill depression, some become ‘trapped’ and give rise to osteocytes Reece, 2015 L3  Cost of bone remodeling ‘Using blood flow index to estimate the metabolic cost of bone remodeling’ Allan et al, 2014 L3  Cost of bone remodeling ‘Using blood flow index to estimate the metabolic cost of bone remodeling’ Reptiles Allan et al, 2014 L3  Cost of bone remodeling ‘Using blood flow index to estimate the metabolic cost of bone remodeling’ Mammals Birds Reptiles Allan et al, 2014 L3  Cost of bone remodeling ‘Using blood flow index to estimate the metabolic cost Dinosaurs! of bone remodeling’ Mammals Birds Reptiles Allan et al, 2014 L3  Test your knowledge Growth in length of long bones occurs at the epiphyseal (growth) plate/s and is under the control of which hormone secreted by the pituitary gland? A. Growth hormone (somatotropin) B. Parathyroid hormone (PTH) C. Calcitriol (1,25-dihydroxyvitamin D) D. Calcitonin E. Erythropoietin (EPO) L3  Test your knowledge Growth in diameter of long bones generally occurs by: A. Chondrocyte proliferation within the outer periosteum, secretion of cartilaginous matrix that then ossifies, and resorption of older bone by osteoblasts at the interior of the shaft B. Chondrocyte proliferation within the outer periosteum, secretion of cartilaginous matrix that then ossifies, and resorption of older bone by osteoclasts at the interior of the shaft C. Deposition of new bone by osteoclasts within the outer periosteum and resorption of older bone by osteoblasts at the interior of the shaft D. Deposition of new bone by osteoblasts within the outer periosteum and resorption of older bone by osteoclasts at the interior of the shaft L3  Joint types Three (3) joint types can be classified by degree of movability: 1. Synarthrosis (fibrous joints, cartilaginous joints) fixed, immovable, e.g. cranium 2. Amphiarthrosis (fibrous joints, cartilaginous joints) semi-moveable, e.g. vertebral joints 3. Diarthrosis (synovial joints) moveable two types: (1) ball & socket joint [e.g. shoulder and hip], and (2) hinge joint [e.g. knee and elbow] synovial membrane (synovium) surrounds the whole joint and contains the synovial fluid lubricant within the synovial capsule L4  Diarthrosis – synovial joint Periosteum Synovial membrane (synovium) Fibrous capsule Joint cavity Synovial membrane (synovium) Patella Hyaline (articular) cartilage Femur Synovial fluid Meniscus Synovial membrane Fat pad Hyaline (articular) cartilage Bursae Tibia Ligament Reece, 2015 L4  Cartilage Cartilage contains chondrocytes (cartilage cells) that produce, and are surrounded by, a ‘matrix’ of collagen and elastin, often enclosed within the perichondrium Cartilage is non-innervated & avascular Intermittent pumping action of weight-bearing & joint motion provides bulk flow of fluid that facilitates diffusion L4  Cartilage chondrocytes matrix perichondrium Reece, 2015  Cartilage Three (3) cartilage types can be defined by the relative composition of this ‘matrix’: 1. Hyaline (articular) cartilage larynx, tracheal rings, joint surfaces (articular) epiphyseal (growth) plates of long bones in growing animals at joints it reduces friction, weight-bearing, absorbs shock in young it has capacity for repair, but loses much of that capacity with cessation of bone growth L4  Cartilage Three (3) cartilage types (cont.): 2. Elastic cartilage external ear, epiglottis functions to provide shape & support 3. Fibrous cartilage (fibrocartilage) intervertebral disks, symphysis functions to provide rigidity, absorb shock L4  Test your knowledge Which of the following joint types is fixed and immovable? A: Synarthrosis B: Amphiarthrosis C: Diarthrosis D: Synovial joints E: All of the above L4  Test your knowledge Cartilage contains which of the following cell types embedded within the matrix of collagen and elastin? A: Keratinocytes B: Chondrocytes C: Osteocytes D: Osteoblasts E: Osteoclasts L4  Further reading Recommended: 1. Clinical Anatomy and Physiology for Veterinary Technicians, Third edition, Chapters 6 and 7, pp 147 – 209 Auxiliary: 2. Hu et al (2018) Femoral bone perfusion through the nutrient foramen during growth and locomotor development of western grey kangaroos Macropus fuliginosus. JEB 221, jeb168625 3. Allan et al (2014) Blood flow for bone remodelling correlates with locomotion in living and extinct birds. JEB 217, 2956 – 2962 Supplement: anatomical orientation