The Skeletal System PDF

The Skeletal System Bone Tissue 1 Functions of Bone & Skeletal System Support & protection Assistance in movement Body needs muscles to move Muscles need bone to have somewhere to attach Mineral homeostasis Blood cell production Hemopoiesis – pro...

The Skeletal System Bone Tissue 1 Functions of Bone & Skeletal System Support & protection Assistance in movement Body needs muscles to move Muscles need bone to have somewhere to attach Mineral homeostasis Blood cell production Hemopoiesis – production of RBC, WBC, and platelets Triglyceride storage Potential chemical energy Yellow bone marrow 2 Gross Anatomy 3 Gross Anatomy of Cartilage 4 Cartilage A type of connective tissue Collagen or elastic fibers and the associated matrix materials Provides provide strength and resilience Cartilage extracellular matrix is deposited by chondroblasts Mature into chondrocytes and sit in spaces within the extracellular matrix called lacunae A sheet of connective tissue known as the perichondrium covers the surface of most cartilage throughout the body 5 Hyaline Cartilage Composed of fine collagen fibers bound together by a resilient, gel-like matrix material Usually covered with perichondrium Chondrocytes within lacunae are found throughout Hyaline cartilage is the weakest but the most abundant cartilage in the body Function Provides flexibility and support, reducing friction, and absorbing shock 6 Hyaline Cartilage Forms a temporary skeleton in the fetus, which is then gradually ossified during childhood Also forms the epiphyseal plates of growing long bones Covers the articular surfaces of joints and provides support to respiratory passages. 7 Fibrocartilage Made up of thick bundles of: Collagen fibers Interspersed with chondrocytes in their lacunae. Strongest cartilage Providing strength and rigidity 8 Elastic Cartilage Made up of thread-like network of elastic and collagen fibers, interspersed with chondrocytes in their lacunae. Covered by perichondrium Function Provides and maintaining the shape of various structures Elastic cartilage is strong and elastic 9 Gross Anatomy of Bones 10 Gross Anatomy Each bone = classified as a discrete organ, due to the fact that it is constructed of several different types of tissue Tissues: Osseous tissue, cartilage, dense connective tissue, nervous tissue, hemopoietic tissue, and adipose tissue Complex and dynamic tissue Continually being remodeled to provide new bone, while the old bone is removed 11 Long Bones Composition A dense layer of cortical bone, which lies around the periphery of the bone, and spongy bone, which is found in the epiphyses Trabeculae within the epiphyses contain both red and yellow bone marrow. Red bone marrow responsible for blood cell production Fatty yellow bone marrow is present within the medullary cavity of the diaphysis. 12 Long Bones Diaphysis = shaft Epiphysis = one end of a long bone Metaphysis = growth plate region (btw diaphysis and epiphysis) Articular cartilage over joint surfaces acts as friction & shock absorber 13 Anatomy of Long Bones 14 Diaphysis Long, cylindrical structure which forms the main shaft of a long bone. Thick layer of compact bone that overlies a thin layer of spongy bone. The central part of the diaphysis is hollowed to form the medullary or marrow cavity Two main types of bone marrow: Red marrow = which comprises red blood cells, white blood cells, and platelets Yellow marrow = which mainly comprises fatty, adipose cells. At birth, all marrow present within the long and flat bones is red, but as we age, bone marrow changes from red to yellow and fills the inside of the medullary cavity 15 Epiphyses The rounded parts located at the proximal and distal ends of a long bone Interior Filled with spongy trabecular bone containing red bone marrow. Exterior surface Covered in compact bone in order to protect the fragile, spongy tissue below it 16 Metaphysis Btw the diaphysis and epiphyses of long bones. Epiphyseal plate Epiphyseal line 17 Anatomy of Long Bones 18 Periosteum Fibrous membrane that covers the exterior of each bone, except where bones are covered by articular cartilage Two layers: Outer fibrous layer of dense, irregular connective tissue, and an Inner, osteogenic layer that sits on the surface of bones and consists primarily of bone-producing osteoblasts and bone-destroying osteoclasts. 19 Periosteum Function Help with fracture repair, to nourish and protect the bone, and to act as an attachment point for tendons and ligaments Attached To underlying bone by thick bundles of collagen fibers called perforating fibers, also known as Sharpey's fibers Extends from the periosteum to the extracellular bone matrix Rich supply of nerve fibers as well as blood and lymph vessels Enter the diaphysis from the surrounding areas, via various nutrient foramina 20 Endosteum Internal bone surfaces facing the medullary cavity are covered by a thin layer of cells and connective tissue called the endosteum Covers the trabeculae of spongy bone and also lines the canals that pass through the cortical bone Has a rich neurovascular supply and contains both osteoblasts and osteoclasts 21 Periosteum and Endosteum 22 Anatomy of a Long Bone Medullary cavity = marrow cavity (contains yellow bone marrow, BV) Endosteum = lining of marrow cavity (single layer of bone forming cells and some connective tissue) Periosteum = tough membrane covering bone but not the cartilage Fibrous layer = dense irregular CT Osteogenic layer = bone cells & blood vessels that nourish or help with repairs 23 Blood & Nerve Supply of Bone Arteries Periosteal Arteries Nutrient Artery Metaphyseal Arteries Epiphyseal Arteries Veins Nutrient Veins Epiphyseal veins Metaphyseal Veins Periosteal Veins 24 Periosteal Arteries Accompanied by nerves Enter the diaphysis thru Volkmann’s canals Beneath the periosteum they divide into branches and thereby entering the Volkmann’s canals to supply the outer one third (1/3) portion of the cortex. The inner 2/3 of the cortex was supplied by the nutrient artery (to come) Supply the periosteum & outer part of compact bone Numerous beneath the muscular and ligamentous attachment. 25 Nutrient Artery Enters the shaft through the nutrient foramen Runs through the cortex. In the medullary cavity this artery divides Ascending and descending branches Each one of these two branches divides into parallel channels that head towards the respective end of the bone. At the place of metaphysis in case of adult bones these branches anastomose with epiphyseal, metaphyseal and periosteal arteries. The nutrient artery in this way nourishes the whole medullary cavity and inner 2/3 of the cortex as well as metaphysis. 26 Epiphyseal Arteries The arteries of epiphyses Supply the red bone marrow and bone tissue of the epiphyses 27 Metaphyseal Arteries These arteries directly go into the metaphysis and reinforce the metaphyseal branches of the primary nutrient artery. 28 Veins Nutrient Veins Accompany the nutrient vein Exit through the diaphysis Epiphyseal & metaphyseal veins Many Exit through the epiphysis Periosteal veins Exit through periosteum 29 30 Histology of Bone Tissue 31 Histology of Bone Tissue Extracellular matrix surrounding widely separated cells 15% water 30% collagen fibers 55% crystallized mineral salts The most abundant mineral salt is calcium phosphate Ca3(PO4)2 Combines with Ca(OH)2 = hydroxyapatite Combine with other mineral salts; calcium carbonate (CaCO3) and ions such as Mg, fluoride, potassium, and sulfate. A process called calcification is initiated by bone-building cells called osteoblasts 32 Histology of Bone Tissue Mineral salts are deposited and crystalize in the framework formed by the collagen fibers of the extracellular matrix Hard but also flexible Hardness = depends on crystallized inorganic mineral salts Flexibility = depends on collagen fibers 33 Bone Cells 34  Types of Bone Cells Osteogenic cells Osteoblasts Osteocytes Osteoclasts 35 Osteogenic Cells Unspecialized bone stem cells derived from mesenchyme Cell division Found Inner part of periosteum Endosteum Canals within bone Develop into osteoblasts 36 Osteoblasts Bone building cells Surround themselves Surface of growing with extracellular bones or active bone matrix and get trapped remodeling. in their secretions = Basophilic, osteocytes mononuclear, “cuboidal” shape Synthesize and secrete collagen fibers and other organic components to build extracellular matrix 37 Osteocytes Mature bone cells Derived from osteoblasts (within matrix) Ellipsoid cell, few organelles, mononuclear, dendritic process (gap junctions = communication btw osteocytes) Main cells in bone tissue and maintain its daily metabolism Exchange of nutrients and waste w/ the blood -cyte Means cell maintains and monitors tissue – but does not divide. 38 Osteoclasts Huge cells 15-20 nuclei Fusion of monocytes present w/I bone marrow or other blood producing tissue Ruffled border, powerful lysosomal enzymes & acids digest the protein and mineral components of the matrix Close contact w/ the bone surface in resorption bays (Howship’s lacunae) 39 Histology of Bone Tissue 40 41 Bone Matrix 42 Bone Matrix Organic Osteoid = secreted by osteoblasts and maintained by osteocytes Type 1 collagen & a little ground substance Flexibility and structure Inorganic Hydroxyapatite mineral Calcification facilitated by osteoblasts, deposits these mineral salts into the microscopic spaces in collagen Spaces Function = store red bone marrow & pathway of blood vessels Determines if the bone is compact or spongy bone 43 Compact vs. Spongy Bone 44 Compact vs. Spongy Bone Most bones have both But, their distribution and concentration vary based on the bone’s overall function. Compact (cortical) bone is dense so that it can withstand compressive force Spongy (cancellous) bone has open spaces and supports shifts in weight distribution. 45 46 Compact/Cortical Bone 47 Compact (Cortical) The denser, stronger of the two types of bone tissue. Found under the periosteum and in the diaphysis of long bones, Provides support and protection. 48 Compact (Cortical) – microscopic Microscopic structural unit of compact bone is called an osteon AKA Haversian system. Each osteon is composed of concentric rings of calcified matrix called lamellae (singular = lamella). Running down the center of each osteon is the central canal, (Haversian canal) Which contains blood vessels, nerves, and lymphatic vessels. The vessels and nerves branch off at right angles through a perforating canal, AKA Volkmann’s canals, 49 50 Compact (Cortical) – microscopic Volkmann's canals to extend to the periosteum and endosteum. Osteocytes are located inside spaces called lacunae (singular = lacuna) Found at the borders of adjacent lamellae. Canaliculi connect with the canaliculi of other lacunae and eventually with the central canal. This system allows nutrients to be transported to the osteocytes and wastes to be removed from them. 51 Circumferential Lamellae Are rings of calcified extracellular bone matrix that line the inner and outer surfaces of compact bone. 52 Osteon (Haversian System) The structural unit of compact bone is called an osteon or Haversian system Each osteon is an elongated, cylindrical structure consisting of a number of concentric rings of lamellae surrounding a central canal Osteons usually lie parallel to each other along the long axis of the bone 53 Central Canal (Haversian Canal) Channels that run through the core of each osteon Run longitudinally through the bone Facilitate the passage of neurovascular structures, such as small blood vessels and nerve fibers. 54 Interstitial Lamellae Areas of incomplete lamellae present in the areas between osteons This type of lamellae is formed from old fragments of osteons That have been partly destroyed during bone resorption or growth 55 Perforating Canals (Volkmann’s Canals) Transverse channels that lie at 90 degrees to the central canals and long axis of the bone Connect the blood and nerve supply of the periosteum with the neurovascular supply of the central canals and medullary cavity 56 Histology of Compact Bone 57  58 https://www.slideshare.net/robswatski/biol-1-tissue-lecture-presentation21-chp-6-bone  59 http://www.auburn.edu/academic/classes/zy/hist0509/html/Lec05Bnotes- General Features Lamellae Lacunae Canaliculi 60 Lamellae Concentric rings of calcified extracellular matrix. Collagen fibers in one lamella run in a single direction But in the adjacent lamella, they run in an opposite direction. Why = allows the functional unit of the bone to withstand torsion pressures. 61 Lacunae Tiny cavities located between the lamellae that contain the spider- like osteocytes. 62 Canaliculi Hair-like canals Filled with extracellular fluid, radiate from the lacunae Purpose To connect lacunae to each other Providing many routes for nutrients to reach the osteocytes and to remove their waste 63 64 Spongy/Cancellous Bone 65 Spongy Bone (Trabecular/ Cancellous) Much lighter than compact bone It consists of branching and anastomosing bars and plates of osseous tissue Where is spongy bone found? Majority of epiphyses in long bones Interior bone tissue of short, flat, and irregularly shaped bones Spongy bone can generally be found in bones that undergo a small amount of stress 66 Spongy Bone (Trabecular/ Cancellous) Contains osteocytes housed in lacunae Not arranged in concentric circles. Lacunae and osteocytes are found in a lattice-like network of matrix spikes called trabeculae (singular = trabecula). Trabeculae may appear to be a random network But each trabecula forms along lines of stress to provide strength to the bone. 67 Spongy Bone (Trabecular/ Cancellous) Provides balance to the dense and heavy compact bone by making bones lighter so that Muscles can move them more easily. The spaces in some spongy bones contain red marrow (provides protection) Where hematopoiesis occurs 68 69 Histology of Spongy Bone 70 Structure of Spongy Bone Trabecular or cancellous bone tissue 71 Comparing Compact & Spongy Bone Compact (Cortical) Spongy Bone Tissue Bone Tissue (AKA: Trabecular or Regular pattern Cancellous Bone) Few spaces Irregular pattern Strong (trabeculae) Under the periosteum Spaces filled with red of all bones bone marrow (blood cells) and yellow Bulk of diaphysis marrow Protection and support Interior of bone Resists stress Core of epiphyses and medullary cavity Protected by compact Most of interior of short, flat, sesamoid, and irregular bones 72 Bone Formation 73 Bone Formation (Ossification/Osteogenesis) When? Initial formation of bones in an embryo and fetus The growth of bones during infancy, childhood, and adolescence Remodeling of bone The repair of fractures 74 Embryo Bone Formation All embryonic connective tissue begins as mesenchyme. Intramembranous bone formation Endochondral ossification Formation of bone within hyaline cartilage, that develops from mesenchyme 75  Formation of bone directly from mesenchymal cells The flat bones of the face, most of the cranial bones, mandible and the clavicles (collarbones) 76 Embryo Bone Formation: Intramembranous Ossification Development of ossification center Chemical messages cause the cells of the mesenchyme to cluster together and differentiate (osteoprogenitor – osteoblasts) Ossification center - Osteoblasts secrete extracellular matrix of bone until surrounded Calcification of matrix Secretion of extracellular matrix stops (now osteocytes) Lie in lacunae and extend their narrow cytoplasmic processes into canaliculi that radiate in all directions Extracellular matrix ossifies Formation of trabeculae Development of periosteum Formation of trabeculae causes mesenchyme to condense 77 and form periosteum 78 Embryo Bone Formation: Endochondral Ossification Development of cartilage model Ends up replacing the cartilage model with bone Growth of the cartilage model Development of the primary ossification center Development of the medullary (marrow) cavity Development of the secondary ossification centers Formation of articular cartilage & the epiphyseal plate 79 Embryo Bone Formation: Endochondral Ossification Development of cartilage model Chemical messages cause the cells in mesenchyme to crowd together in the general shape of the future bone Develop chondroblasts – secrete cartilage extracellular matrix = cartilage model consisting of hyaline cartilage Perichondrium covering develops around the cartilage model 80 Embryo Bone Formation: Endochondral Ossification Growth of the cartilage model Chondroblasts get buried = chondrocytes Interstitial (endogenous) – growth from within (growth in length) Cell division of chondrocytes & secretion of the cartilage extracellular matrix Appositional (exogenous) – growth in width Deposition of the extracellular matrix material on the cartilage surface Chondrocytes within the calcifying cartilage die = spaces = merge into lacunae 81 Embryo Bone Formation: Endochondral Ossification Development of primary ossification center Proceeds inward Nutrient artery penetrates the perichondrium, stimulating osteoprogenitor cells to differentiate into osteoblasts Periosteal capillaries grow into the disintegrating calcified cartilage = primary ossification center Region where bone tissue will replace most of the cartilage 82 Embryo Bone Formation: Endochondral Ossification Development of medullary cavity Osteoclasts break down newly formed spongy bone – leaves a cavity Development of secondary ossification centers Epiphyseal artery enters = secondary ossification center Secondary ossification goes outward Formation of articular cartilage and epiphyseal plate 83 84 Bone Growth During Infancy, Childhood, & Adolescence The growth in length of long bones involves two major events: 1. Growth of cartilage on the epiphyseal plate 2. Replacement of cartilage by bone tissue in the epiphyseal plate (this is the way MOST growth occurs in childhood) Osteoclasts _________ the calcified cartilage, and osteoblasts invade the area ________bone matrix The activity of the epiphyseal plate is the way bone can increase in length At adulthood, the epiphyseal plates close and bone replaces all the cartilage leaving a bony structure called the epiphyseal line 85 Growth in Length: Interstitial Growth Long bones grow in length as a result of activity that occurs at the epiphyseal growth plate. Two major events control the growth in length of long bones: 1. Cartilage grows by a process of interstitial growth on the side of the epiphyseal plate closest to the epiphysis 2. Cartilage on the diaphyseal side of the bone is replaced with bone through endochondral ossification 86 Zones of Growth in Epiphyseal Plate Zone of resting/reserve cartilage Zone of proliferating cartilage Zone of hypertrophic cartilage Zone of calcified cartilage 87 Zones of Growth in Epiphyseal Plate: Zone of Resting/Reserve Cartilage Nearest the epiphysis Small scattered chondrocytes Not part of bone growth (at that time) Anchors growth plate to bone 88 Zones of Growth in Epiphyseal Plate: Zone of Proliferating Cartilage Proliferating = Rapid cell division Larger chondrocytes Arranged in stacked coins Divide to replace those on the diaphyseal side of the plate 89 Zones of Growth in Epiphyseal Plate: Zone of Hypertrophic Cartilage Cells enlarged & maturing chondrocytes Still in columns 90 Zones of Growth in Epiphyseal Plate: Zone of Calcified Cartilage Thin zone, cells mostly dead chondrocytes, b/c matrix calcified Osteoclasts removing matrix Osteoblasts & capillaries move in to create bone over calcified cartilage 91 Zones of Growth in Epiphyseal Plate "Real People Have Career Options," Resting/Reserve zone Proliferative zone Hypertrophic cartilage zone Calcified cartilage zon e Ossification zone https://courses.lumenlearning.com/boundless 92 -biology/chapter/bone/ 93 Growth in Epiphyseal Plate 94 Growth in Thickness: Appositional Growth Bones grow in thickness at the outer surface 95 Growth in Thickness: Appositional Growth http://accessmedicine.mhmedical.com/content.aspx?bookid=1687&sectionid=109632699 96 Bone Growth During Infancy, Childhood and Adolescence Remodeling of Bone Bone forms before birth and continually renews itself The ongoing replacement of old bone tissue by new bone tissue Old bone is continually destroyed and new bone is formed in its place throughout an individual’s life A balance must exist between the actions of osteoclasts and osteoblasts 97 Factors Affecting Bone Growth Nutrition Adequate levels of minerals and vitamins Calcium and phosphorus for bone growth Vitamin C for collagen formation Vitamins K and B12 for protein synthesis Sufficient levels of specific hormones During childhood need insulin like growth factor Promotes cell division at epiphyseal plate Need hGH (growth), thyroid (T3 &T4) and insulin Sex steroids at puberty Growth spurt and closure of the epiphyseal growth plate 98 Velocity Curves Rate of growth, not the total size (length or weight) Decline from the moment of birth Increase during puberty Decrease till adult height is reached Peak Height Velocity Maximum rate of growth in height 99 Hormonal Abnormalities Over secretion of hGH during childhood produces gigantism Under secretion of hGH or thyroid hormone during childhood produces short stature Both men or women that lack estrogen receptors on cells grow taller than normal Estrogen responsible for closure of growth plate 103 Control of Blood Calcium 104 Calcium Homeostasis & Bone Tissue Skeleton is reservoir of Calcium & Phosphate Calcium ions involved with many body systems Nerve & muscle cell function Blood clotting Enzyme function in many biochemical reactions Small changes in blood levels of Ca+2 can be deadly (plasma level maintained 9-11mg/100mL) Cardiac arrest if too high Respiratory arrest if too low Too much or too little Hypercalcemia = blood calcium levels rise above the normal level Hypocalcemia = when blood calcium levels drop below normal If either of these states occur, the body is able to activate the homeostatic mechanism (Feedback) Hormones Parathyroid hormone which is secreted by the parathyroid gland Calcitonin, which is secreted by the thyroid gland 105 Hypercalcemia Stimulus Increased blood Ca2 levels Receptor Parafollicular cells of the thyroid Control Center Parafollicular cells stimulate the thyroid gland to release increased levels of calcitonin into the blood Effectors 1. Calcitonin stimulates an increase in the number and the activity of osteoblast cells in bone, preventing calcium release into the blood 2. The level of Ca2 reabsorption in the kidney decreases Response Causes a decrease in Ca2 levels in the blood 106 Hypercalcemia 107 Hypocalcemia Stimulus Decreased blood Ca2 levels Receptor Chief cells of the parathyroid gland detect Control Center Chief cells stimulate the parathyroid gland to release parathyroid hormone (PTH) into the blood. Effectors 1. PTH stimulates an increase in osteoclastic activity in bone, releasing calcium into the blood 2. The level of Ca2 reabsorption in the kidney increases 3. PTH stimulates the formation of calcitriol, the active form of vitamin D, to promote the absorption of calcium from foods in the gastrointestinal tract Response Causes an increase in Ca2 levels in the blood 108 Hypocalcemia 109 110 Exercise and Bone Tissue Pull on bone by skeletal muscle and gravity is mechanical stress Stress increases deposition of mineral salts & production of collagen (calcitonin prevents bone loss) Lack of mechanical stress results in bone loss Reduced activity while in a cast Astronauts in weightlessness Bedridden person Weight-bearing exercises build bone mass (walking or weight-lifting) 111 Nutrition & Bone Tissue Importance of Ca in bones Cannot be absorbed from the small intestine without vitamin D. Vitamin D is also critical to bone health. Not as clearly understood, in bone remodeling. Milk and other dairy foods are not the only sources of calcium. This important nutrient is also found in green leafy vegetables, broccoli, and intact salmon and canned sardines with their soft bones. Nuts, beans, seeds, and shellfish provide calcium in smaller quantities. Sunlight on the skin triggers the body to produce its own vitamin D but many people it is not enough Vitamin D supplement. 112 113 Aging and Bone Tissue Bone is being built through adolescence, holds its own in young adults, but is gradually lost in aged. Demineralization = loss of minerals Very rapid in women 40-45 as estrogens levels decrease In males, begins after age 60 Decrease in protein synthesis Decrease in growth hormone Decrease in collagen production which gives bone its tensile strength Bone becomes brittle & susceptible to fracture 114 Osteoporosis Decreased bone mass resulting in porous bones Those at risk White, thin menopausal, smoking, drinking female with family history Athletes who are not menstruating due to decreased body fat & decreased estrogen levels People allergic to milk or with eating disorders whose intake of calcium is too low Prevention or decrease in severity Adequate diet, weight-bearing exercise, & estrogen replacement therapy (for menopausal women) Behavior when young may be most important factor 115 Osteoporosis There are two principal effects of aging on bone tissue: 1) Loss of bone mass Results from the loss of calcium from bone matrix The loss of calcium from bones is one of the symptoms in osteoporosis 2) Brittleness Results from a decreased rate of protein synthesis Collagen fibers gives bone its tensile strength The loss of tensile strength causes the bones to become very brittle and susceptible to fracture 116 Disorders of Bone Ossification Osteomalacia New adult bone produced during remodeling fails to ossify Hip fractures are common Rickets Calcium salts are not deposited properly Bones of growing children are soft Bowed legs, skull, rib cage, and pelvic deformities result 117