Skeletal Tissue PDF

Chapter 7 Osseous Tissue 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Bone Structure and Function The skeleton is more than a supporting fram...

Chapter 7 Osseous Tissue 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.  Bone Structure and Function The skeleton is more than a supporting framework – The skeletal system is composed of dynamic living tissues – It interacts with all other organ systems – It continually rebuilds and remodels itself Components of the skeletal system – Bones, Cartilage, Ligaments, etc. Bones perform several basic functions – Support and protection – Movement – Hemopoiesis – Storage of mineral and energy reserves 2  Periosteum Flat bone of skull Bone Tissue Types of bone – Compact bone also called dense or cortical bone relatively dense connective bone tissue appears white, smooth, and solid Periosteum Compact bone 80% of bone mass – Spongy bone also called cancellous or trabecular bone 20% of bone mass lighter in weight than compact bone well adapted for distributing stress – the beams and rods distribute the stress to resist breaking What’s found here? 3 Skeletal System: Bone Marrow Red bone marrow – Also known as myeloid tissue – Hemopoietic (blood cell forming) – Contains reticular connective tissue, immature blood cells, and fat – Children vs. adults Red bone marrow Yellow bone marrow – Product of red bone marrow degeneration – May convert back to red bone marrow – Marrow transplant (a) Red bone marrow in the adult Yellow bone marrow (b) Head of femur, sectioned 1 1  Articular cartilage Anatomy of Long Bone Spongy bone Proximal epiphysis Epiphyseal line Metaphysis Compact bone Spongy bone Medullary cavity (contains yellow bone Spongy bone marrow in adult) Osteocyte Parallel lamellae Endosteum Osteoclast Nuclei Osteoblasts Endosteum Osteoprogenitor Periosteum Medullary cavity cell Perforating fibers Diaphysis (b) Endosteum Nutrient artery through nutrient foramen Nerves pass through here Compact bone Innervate bone, periosteum, endosteum, Osteocyte and marrow cavity Fibrous layer Concentric lamellae Mainly sensory nerves that detect any pain Nociceptors Cellular layer Periosteum Perforating fibers Metaphysis (c) Periosteum Distal 4 epiphysis Articular cartilage  Bone connective tissue – Also called osseous connective tissue Composition of the Bone – Composed of cells and extracellular matrix Extracellular matrix  Organic components – 35% Collagen is like flexible Osteoid produced by osteoblasts steel – for tensile strength Collagen, proteoglycans, glycoproteins, Chondroitin sulfate Strong but flexible  Inorganic components – 65% Ca3(PO4)2, Ca(OH)2, hydroxyapatite, Ca10(PO4)6(OH)2 Other minerals also incorporated into crystals Rigid, inflexible and brittle Hydroxyapatite is like concrete – for weight bearing – compressional Proportion of organic and inorganic substances strength – Correct proportion allows optimal functioning – Loss of protein????? – Insufficient calcium results????? Bone is like steel enforced concrete and far superior because it can repair and remodel itself. 5  Bone Matrix OsteoCHONDROprogenitor Four type of bone cells Bone formation – Begins with secretion of osteoid – Process requires vitamin C, vitamin D, calcium, and phosphate. Osteoblast – Proceeds with calcification, when hydroxyapatite crystals deposited Budding matrix (forms bone matrix) – Calcium and phosphate ions precipitate out forming crystals vesicles and perform – Scurvy & Rickets exocytosis Osteocyte (maintains bone matrix) Some osteoblasts differentiate into transcytosis osteocytes. Integrin & podosomes Cells connected via gap Fusing bone (a) Bone cells junctions marrow cell Nuclei Endosteum Osteoclast Bone resorption Lysosomes – Bone matrix destroyed by osteoclasts: Proteases and H + – Chemically digest organic matrix components Ruffled border – May occur when blood calcium levels low Resorption lacuna – Transcytosis is a type of transcellular transport in which (b) Osteoclast various macromolecules are transported across the interior of a cell. 6  Perichondrium Cartilage Growth Matrix Hyalinecartilage Chondrocyte in lacuna (a) Interstitial Growth (b) Appositional Growth 1 A chondrocyte within a lacuna begins to exhibit mitotic activity. 1 Mitotic activity occurs in stem cells within the perichondrium. Strength of cartilage comes from collagen and Lacuna Perichondrium Mesenchymal Chondrocyte cells resilience from the proteoglycans. Matrix New cartilage Osteochon Both bones and cartilage have chondroitin sulfate matrix droprogeni tor cells Older cartilage Stages of cartilage growth 2 Two cells (now called chondroblasts) are produced by mitosis from one chondrocyte and occupy one lacuna. matrix During early embryonic development 2 New undifferentiated stem cells and committed cells that differentiate Into chondroblasts are formed. Chondroblasts produce new matrixat – interstitial and appositional growth occur Chondroblast the periphery. Undifferentiated simultaneously Lacuna stem cells Committed cells As cartilage matures  semi-rigid 3 Each cell produces new matrix and begins to separate differentiating into chondroblasts New cartilage – interstitial growth declines rapidly from its neighbor. Each cell is now called a chondrocyte. matrix Chondroblast secreting new matrix – further growth primarily appositional New matrix Older cartilage Lacuna matrix After cartilage is fully mature Chondrocyte 3 As a result of matrix formation, the chondroblasts push apart and become chondrocytes. Chondrocytes continue to produce more matrix at the – new cartilage growth stops periphery. – growth occurs only after injury Perichondrium Undifferentiated stem cells 4 Cartilage continues to grow internally. – limited due to lack of blood vessels New matrix Chondrocyte New cartilage secreting new matrix matrix Chondrocyte Older cartilage Mature matrix chondrocyte © The McGraw-Hill Companies, Inc./Al Telser, photographer  Bone Formation Ossification – Also known as osteogenesis – The formation and development of bone connective tissue – Begins in the embryo and continues through childhood and adolescence Ossification centers form by the 8th through 12th weeks of embryonic development – Occurs through intramembranous ossification or endochondral ossification 1. Intramembranous ossification – Also known as dermal ossification – Produces: flat bones of the skull and some of the facial bones, mandible, maxilla, central part of the clavicle Begins when mesenchyme becomes thickened with capillaries Fontanels close by age 2 : Posterior, sphenoid, mastoid, and anterior. 2. Endochondral ossification – Begins with a hyaline cartilage model – Produces most bones of the skeleton, including: bones of the upper and lower limbs, pelvis, vertebrae, ends of the clavicle 10  Flat bone of skull Intramembranous Ossification 5th week – thickening of the mesenchymal membrane surrounding the brain with randomly oriented collagen fibers Ossification centers form by 8th week of 1 Ossification centers form 2 Osteoid undergoes 3 Woven bone and 4 Lamellar bone replaces development. within thickened regions calcification. surrounding woven bone, as compact of mesenchyme. periosteum form. and spongy bone form. Ossification proceeds radially from the center Osteocyte and forms more bone appositionally. Osteoid Bone formation and growth is an active process which required oxygen and nutrients. Thus blood vessels grow towards developing bone. Osteoid Some blood vessels become trapped in Osteoblast developing bone and become interwoven. Ossification Osteoblast Newly center alcified bone calcified bone Compact Spongy Blood vessel matrix bone bone Woven bone has collagen fibers randomly Collagen Mesenchymal Trabeculaof Trabecula of fiber cell wovenbone woven bone Lamellar bone present whereas in lamellar bone, the collagen Mesenchyme Periosteum fibers have been arranged in lamellae Mesenchyme condensing to form condensing to form Exocytosis of collagen Matrix vesicles thethe periosteum periosteum Intramembranous ossification completed by 2 For hydroxyapatite Mesenchymal cells in more strength. yrs of age when fontanels close the spaces develop to form endosteum and bone marrow (heomopoetic cells) 11  Child Late teens to adult Articular cartilage Articular cartilage Epiphyseal line Spongy bone (remnant of epiphyseal plate) Epiphyseal plate Spongy bone Endochondral Periosteum Compact bone Ossification Medullary cavity Compact bone Medullary cavity Periosteum Medullary Epiphyseal cavity has plate grown Articular cartilage Spongy 5 Bone replaces cartilage, bone except the articular cartilage Articular Epiphyseal and epiphyseal plates. cartilage line 6 Epiphyseal plates ossify and form epiphyseal lines. The articular cartilage Humerus from a 5-year-old is the remnant of child. Note the unfused embryonic cartilage 1 epiphyses and diaphyses. X-ray of an adult humerus.  Bone Growth in Length Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Growth at the epiphyseal plate Zone 1: Zone of 1. Interstitial cartilage growth dependent resting cartilage upon cartilage growth here Bone growth in length – Flexible hyaline cartilage permits growth Zone 2: Zone of – Pushes zone of resting cartilage toward the proliferating cartilage epiphysis – New hyaline cartilage replaced by bone – Similar to endochondral ossification during development Zone 3: Zone of hypertrophic cartilage Neither epiphyses nor short bones have an epiphyseal plate. Zone 4: Zone of – How do they grow? calcified cartilage – Articular cartilage LM 70x Zone 5: Zone of ossification (a) Epiphyseal plate 14  Achondroplastic Dwarfism – Characterized by abnormal conversion of hyaline cartilage to bone – Long bones of limbs will stop growing in childhood – Other bones with continued normal growth – Short in stature but with a large head – Failure of chondrocytes in epiphyseal plate to grow and enlarge – Inadequate endochondral ossification 1  Bone Growth Epiphyseal plate Epiphyseal – Maintains thickness during childhood Epiphyses plates – At puberty: Increased rate of cartilage production Diaphysis Also increased rate of ossification – At maturity: Slowed rate of cartilage production Also shows increased osteoblast Epiphyses activity Narrows until it disappears Remnant is an internal thin line of compact bone termed epiphyseal line Diaphyses (b) X-ray of a hand 15  Bone Growth in Width Compact bone Periosteum Bone deposited by osteoblasts Medullary Periosteum Bone resorbed cavity by osteoclasts Medullary cavity Compact bone Infant Child Young adult Adult Appositional Growth  Circumferential lamellae 16  Factors influencing Bone Remodeling Continual process of bone deposition and resorption – Dependent on the coordinated activities of osteoblasts, osteocytes, and osteoclasts – Occurs at periosteal and endosteal surfaces of a bone – Occurs at different rates – 20% of skeleton replaced yearly Mechanical stress – Results from skeletal muscle contraction and gravitational forces – Occurs in weight-bearing movement and exercise – Required for normal bone remodeling – Osteocytes detect the stress – Causes increase in bone strength Increase OR Decrease bone mass – Astronauts, Bed ridden, Casts, etc. – From removal of mechanical stress – Reduced osteoid and demineralization 17 Osteoblasts & Osteoclasts 1  Hormones Influence Bone Growth and Remodeling Hormones 3. Sex hormones – Bind to cellular receptors of specific cells and initiate – Estrogen and testosterone secreted in large amounts at specific cellular changes puberty – Some altering rates of chondrocyte, osteoblast, and – Increase rate of cartilage growth and bone formation in osteoclast activity epiphyseal plate – Affect bone composition and growth patterns – Ossification rate greater than cartilage growth – Growth plate closing more quickly in response to estrogen 1. Growth hormone – Produced by anterior pituitary gland 4. Glucocorticoids – Stimulates liver to produced another hormone, – Group of steroid hormones – cortisol, cortisone, etc. somatomedin (Insulin like Growth factor - IGF) – Released from adrenal cortex – both directly stimulate growth of cartilage at epiphyseal – Increases bone loss and impairs growth at epiphyseal plate plate 5. Serotonin 2. Thyroid hormone – Most bones with serotonin receptors – Secreted by thyroid gland – If levels too high - osteochondroprogenitor cells are – Helps regulate normal cartilage growth activity at the prevented from becoming osteoblasts epiphyseal plates – Plays a role in rate and regulation of normal bone – Influences basal metabolic rate of Osteocytes remodeling – Hypothyroidism 18  Pituitary Gigantism and Pituitary Dwarfism Sultan Kosen from Turkey hypersecretion of GH during childhood when epiphyseal plates are still open 8-9 feet is common Rare Acromegaly He Pingping from China Hyposecretion of GH during childhood 4 ft is maximum 1/30,000 Middle-aged adults are most commonly affected. Symptoms include enlargement of the face, 1 hands, and feet.  Activation of Vitamin D to Calcitriol – Rickets - deficient calcification of osteoid tissue Due to lack of vitamin D Darker individuals Covered individuals Staying indoor Osteomalacia Ultraviolet or Dietary intake light (e.g., milk) PTH —OH Calcidiol OH CH2 HO CH2 HO OH Precursor molecule HO CH2 OH (7-dehydrocholesterol) HO —OH Calcitriol Vitamin D3 (cholecalciferol) 2 Vitamin D3 is converted to 3 Calcidiol is converted to calcidiol in the liver (when 1 The precursor molecule calcitriol in the kidney (when an —OH group is added). is converted to Vitamin D3 another —OH group is added). 20 (cholecalciferol).  Regulating Blood Calcium Levels Ca2+ STIMULUS Regulating calcium concentration in 1 Low calcium blood is essential Calcium is required for: RECEPTOR Calcitriol 2 Parathyroid glands Parathyroid – muscle contraction, neurotransmitter detect low calcium. hormone release Vitamin D converted to calcitriol, and then released from kidneys exocytosis, stimulation of heart Parathyroid pacemaker cells, blood clotting, etc. glands CONTROL CENTER – Serum levels 8.9 – 10.1mg/dL PTH 3 Parathyroid glands release PTH Two primary hormones regulate blood calcium: PTH + Calcitriol – Calcitriol – Parathyroid hormone Ca2+ EFFECTORS – additional hormones important in bone remodeling Kidneys Small Bone intestine HOMEOSTASIS RESTORED Blood calcium levels rise and return to PTH and calcitriol act PTH and calcitriol act 5 normal. This is regulated by a negative 4a synergistically to 4b synergistically to 4c Calcitriol increases feedback mechanism. absorption of calcium increase activity of decrease calcium from small intestine. osteoclasts. excreted in urine.  Regulating Blood Calcium Levels: Calcitonin Released from the thyroid gland in response to high blood calcium levels Less significant role than PTH or calcitriol Inhibits osteoclast activity in bone connective tissue Increased calcium deposition Stimulates kidneys to increase loss of calcium in the urine Greatest effect during greatest bone turnover Entire function still unclear – absence of calcitonin or high levels of calcitonin do not impact the calcium regulation – Therapeutic injections do not help 22  Osteoporosis Effects of Aging – Reduced bone mass sufficient to compromise normal function Two ways aging affects bone – Weakened bones may fracture 1. Decreased tensile strength of bone – Linked to age, race, menopause, and smoking 2. Bone loss of calcium and other minerals history Osteopenia Reduced hormones with age – Occurs slightly in all people with age - begins – Include growth hormone, estrogen, and testosterone as early as age 35-40 – Contributes to reduction in bone mass – Osteoblast activity declines; osteoclast activity at previous levels – Vertebrae, jaw bones, epiphyses lose large amount of mass – Women lose more of their skeletal mass every decade than men 25  Bone Fracture and Repair Breaks in bone – Termed fractures – Occur as result of unusual stress or impact – Increased incidence with age due to normal thinning and weakening of bone Types of fractures – Stress fracture thin break caused by increased physical activity bone experiences repetitive loads (e.g., runners) – Pathologic fracture – Simple fracture – Compound fracture 23  Bone repair https://www.youtube.com/watch?v=USbjj0wWvYA 1  Bone Repair Fracture healing – Simple fracture about 2 to 3 months to heal – Compound fracture longer to heal – Generally becomes slower with age – Some require surgical intervention to heal correctly Fibro- cartilaginous Macrophages Osteoblasts (soft) callus Fibroblasts Apposition Osteoclast Chondroblasts al growth Compact bone s and Medullary Primary at fracture site osteoblast cavity bone s Hematoma Hard callus Periosteum Regenerating Compact bone blood vessels 1 A fracture hematoma forms. 2 A fibrocartilaginous 3 A hard (bony) callus forms. 4 The bone is remodeled. (soft) procallus forms. a solid swelling of clotted blood within the tissues. 24