Histology of Specialized Connective Tissue - Bone PDF

B3 Histology of Specialized Connective Tissues Describe the basic components of bone. Bone tissue consists of: Cells (Osteoblast, Osteocytes and Osteoclast). Mineralized ECM that consists of inorganic and organic components. – Inorganic component:...

B3 Histology of Specialized Connective Tissues Describe the basic components of bone. Bone tissue consists of: Cells (Osteoblast, Osteocytes and Osteoclast). Mineralized ECM that consists of inorganic and organic components. – Inorganic component: Consists of calcium phosphate in the form of hydroxyapatite crystals. Both calcium and phosphate can be – Organic component: mobilized from the Consists primarily of: bone matrix and taken – Type I collagen fibers ( Tensile strength up in the blood. (1% equal to cast iron, 1/3 of the weight) calcium is in the blood, 99% stored in – Proteoglycans with glycosaminoglycan's bone). – Non-collagen proteins Gives rigidity and Gives elasticity and resilience to the bone. hardness to the bone.  Histology of Specialized Connective Tissues Describe the basic components of bone. The Functions of Bone include:  Histology of Specialized Connective Tissues Describe the different types of bone. Bones have several classifications based on: 1. Shape Long bones Tubular, a shaft and two heads Short bones Cuboidal Flat bones Plate-like Irregular Sesamoid Develop within tendons 2. Structure Macroscopic Compact bone Spongy bone Microscopic Lamellar bone Woven bone 3. Development Intramembranous bone formation Endochondral bone formation  Histology of Specialized Connective Tissues Describe the different types of bone on the basis of structure. Macroscopic (gross) structure of bone: – Compact (cortical) bone – Spongy (cancellous, medullary bone or trabecular bone). In long bones: – The shaft (diaphysis) consist of compact bone forming a hollow cylinder with a medullary cavity. The medullary cavity is filled with a sparse amount spongy bone and bone marrow. – The proximal and distal ends of the bone (epiphysis) consist of spongy bone covered by a thin outer layer of compact bone. The ends are also covered by articular (hyaline) cartilage. Marieb, E. N. Human Anatomy and Physiology © Benjamin Cummings Histology of Specialized Connective Tissues Describe the different types of bone on the basis of structure. Macroscopic (gross) structure of mature bone composed of: – compact (cortical) bone – spongy (cancellous, trabecular or medullary bone). Tortora, G. Principles of Human Anatomy © Wiley Publishers B1 Histology of Specialized Connective Tissues Describe the different types of bone on the basis of structure Two different types of bone on the basis of microscopic structure: Lamellar bone (mature) Regular alignment of collagen fibers. (Consist of lamellae which are thin layers of bone ). Found in a healthy adult skeleton. Found in both compact and spongy (cancellous) bone. Woven bone (immature) Irregular alignment of collagen fibers. Found in developing bone and under pathologic conditions (Healing fractures, osteogenic tumors and metastatic formation). Found in both compact and spongy (cancellous) bone.  B1 Histology of Specialized Connective Tissues Describe the following components of compact (cortical) bone: osteons, interstitial lamellae, periosteal lamellae, endosteal lamellae. Compact bone is composed of layers (lamellar) of bone in cylindrical units called osteons or Haversian systems. Osteons consist of: – Longitudinal Haversian canals at the center that contains blood vessels and nerves. – Concentric lamellae or Haversian lamellae (4-15 layers) surrounding the canal. In each lamella, Collagen fibers are arranged parallel to one another. In adjacent lamellae the collagen fibers run perpendicular. Each Lamella also consist of mineralized ECM & osteocytes in their lacunae with their cytoplasmic processes radiating through canaliculi (tunnel through ECM). – Volkmann’s canal interconnects Haversian canals (course transversely). B1 Histology of Specialized Connective Tissues Describe the following components of compact (cortical) bone: osteons, interstitial lamellae, periosteal lamellae, endosteal lamellae. Compact bone also consists of: – Periosteum The Outer layer (Fibrous layer with blood vessels and nerves): – Some vessels will enter Volkmann’s canals. – Thick anchoring collagen fibers called Sharpey’s fibers or perforating fibers will that attach the periosteum to the bone. The Inner layer (osteogenic / osteoprogenitor cells): – Potential to differentiate into osteoblast. – Endosteum Consist of osteogenic cells and reticular connective tissue Covers the walls of the spongy bone and lines the Haversian and Volkmann’s canals. B1 Histology of Specialized Connective Tissues Describe the following components of compact (cortical) bone: osteons, interstitial lamellae, periosteal lamellae, endosteal lamellae. Compact bone also consists of: – Interstitial lamellae lamellae located between osteons. – Circumferential lamellae Located beneath the periosteum (periosteal lamellae), Located beneath the endosteum of the marrow cavity (endosteal lamellae).  Histology of Specialized Connective Tissues Describe the following components of compact (cortical) bone: osteons, interstitial lamellae, periosteal lamellae, endosteal lamellae. B1 Histology of Specialized Connective Tissues Describe spongy (cancellous) bone. Spongy (cancellous or trabecular) bone: – Bone is arranged in spicules or trabeculae, with numerous interconnecting marrow spaces – The bone matrix is lameller and only has osteons if it is sufficiently thick. – Nourished mainly by diffusion from Marrow cavity. Tortora, G. Principles of Human Anatomy © Wiley Publishers B2 Histology of Specialized Connective Tissues Describe the following bone cells: osteoprogenitor. Osteogenic (Osteoprogenitor) cells: – Found in the innermost layer of the periosteum, and in the endosteum. – Derived from mesenchymal cells. – When stimulated these cells differentiate into osteoblasts. They can also differentiate into chondroblast and fibroblast. – Undergo Mitosis. Gartner, L.P., Color Textbook of Histology © Elsevier B2 Histology of Specialized Connective Tissues Describe the following bone cells: osteoblasts. Osteoblast: – Cuboid-shaped cell. – Basophilic cytoplasm. Cells have abundant RER, Golgi apparatus, free ribosomes, and numerous secretory vesicles. – Found as a single layer on a surface of developing bony. – Functions to secrete osteoid and to initiate & control mineralization. Osteoid: – Procollagen (type I collagen) – Proteoglycans/ Glycosaminoglycans – Non-collagen proteins » Osteocalcin (binds hydroxyapatite) » Osteonectin (binds type I collagen to hydroxyapatite) » Bone Sialoprotein (binds osteoblast to ECM through integrins). » Osteopontin (binds osteoclast to ECM through integrins) B2 Histology of Specialized Connective Tissues Describe the following bone cells: osteoblasts. Osteoblast: – Mineralization: Once the osteoid is formed the osteoblasts secrete calcium into the ECM via matrix vesicles. Alkaline phosphatase - hydrolyzes monophosphate esters to allow for free phosphate to bind to calcium and form hydroxyapatite crystals. The hydroxyapatite crystals will be distributed along the collagen fibers in a highly organized arrangement. – Osteoblasts are stimulated by: Vitamin D, Estrogen, and Growth Factors (IGF-1). B2 Histology of Specialized Connective Tissues Describe microscopic structure of osteoprogenitor and osteoblasts cells Osteoprogenitor Cell – Spindle Shaped – Scant Pale staining cytoplasm Sparse RER Poorly developed Golgi apparatus Osteoblast Cell – Arranged single layer of Cuboidal to Columnar Cells Abundant RER and Golgi apparatus (polarized) Gartner, L.P., Color Textbook of Histology © Elsevier B2 Histology of Specialized Connective Tissues Describe the following bone cells: osteocytes. Osteocytes: – Osteoblasts that become enclosed by ECM transform into osteocytes. – Smaller cell with reduced organelles and production of matrix proteins. – The osteocytes body resides in a lacuna. – Osteocytes also have cytoplasmic processes that extend into canaliculi to communicate with neighbor osteocytes via gap junctions (forming a complex cellular network). – Responsible for maintaining the bone matrix. Kierszenbaum A. L. Histology and Cell Biology © Elsevier  Histology of Specialized Connective Tissues Describe the following bone cells: osteoclasts. Osteoclast: Responsible for Bone resorption. Characteristics: large Multinucleated cells (6-12). Acidophilic cytoplasm. Derived from bone marrow. Monocytes. B2&4 Histology of Specialized Connective Tissues Describe the following bone cells: osteoclasts. Active Osteoclasts: – Osteoclast binds to bone surface via integrins – Becomes active after the sealing zone (prevents leakage of catabolic enzymes) and ruffled border (increases surface area) appears. – Located in a shallow depression called a subosteoclastic compartment or Howship’s lacuna. – Cytoplasm has Acidified Vesicles that: Insert into the ruffled border with their H-ATPase pumps. Creates an acidic environment in the lacuna for solubilizing mineralized bone. Demineralization occurs first. – Cathepsin K (enzyme) Released from the ruffled border into the lacuna to break down exposed organic matrix (collagen and noncollagenous Protein). – Degradation products are endocytosed and further broken down into amino acids, monosaccharides, disaccharides, and calcium which are released into nearby capillaries. Kierszenbaum, A. L. Histology and Cell Biology © Elsevier Mescher, A.L. Junqueira’s Basic Histology© McGraw Hill B2&4 Histology of Specialized Connective Tissues Describe osteoblast regulation of osteoclastogenesis Osteoclasts: – Regulation of osteoclast formation: Osteoblast secrete Macrophage Colony-Stimulating Factor(M-CSF) – Binds to monocyte – Induces the expression of RANK receptor on the monocyte (now macrophage) Osteoblast expresses a Transmembrane Ligand Nuclear Factor Kappa B Ligand (RANKL) – RANKL binds to RANK receptor on macrophage and commits the cell to osteoclastogenesis which includes rapid mitosis and fuse. Osteoprotegerin – Blocks RANKL binding to RANK – The osteoblast is directly activated by parathyroid hormone (PTH). Stimulates M-CSF and RANKL expression. – Osteoclast are directly inhibited by calcitonin. Kierszenbaum, A. L. Histology and Cell Biology © Elsevier Mescher, A.L. Junqueira’s Basic Histology© McGraw Hill  Histology of Specialized Connective Tissues Congenital Diseases in Bone Osteogenesis Imperfecta X-Ray Images Osteogenesis Imperfecta (Brittle Bone Disease) – Deficiencies in the synthesis of Type I Collagen. – Most common inherited disorder of connective tissue (mainly affecting bone). Leading to a decrease quality and density of bone. – Characterized by fragile bones and fractures. – Heterogenous group of genetic disorders (800 autosomal dominant mutations). – Two major types: Type I- normal life expectancy, childhood fractures, blue sclera and potential hearing loss. Type II is fatal in utero. Clinical Findings: – Dwarfism – Kyphoscoliosis – Bowing deformity – Hearing loss – Blue Sclera  PBBS 503 Structure & Function Dr. Derek Talbot Scholl College of Podiatric Medicine Rosalind Franklin University of Medicine & Science Lecture 23 -Histology of Specialized Connective Tissue – Bone II  Learning Objectives: B5. Describe bone formation: recognize the differences between intramembranous ossification and endochondral bone formation and regions of the body where each of these processes contribute to bone formation and growth. B6. Identify regions of the epiphyseal growth plate and recognize how the epiphyseal growth plate contributes to growth of long bones. B5 Histology of Specialized Connective Tissues Describe Bone Formation. Two types of bone formation: – Intramembranous Bone develops from mesenchyme. Occurs in flat bones. – Endochondral Bone develops from hyaline cartilage. Occurs in long bones, short bones and irregular bones. Marieb, E. N. Human Anatomy and Physiology © Benjamin Cummings B5 Histology of Specialized Connective Tissues Describe intramembranous bone formation. Bone develops directly from mesenchyme. Begins in fetal life and continues into childhood. Steps: Mesenchymal cells condense into a highly-vascularized membrane-like structure (CM). Mesenchymal cells differentiate into osteoprogenitor cells. Osteoprogenitor cells differentiate into osteoblasts. Osteoblasts secrete osteoid. Osteoblasts mineralize the matrix and become osteocytes as they are enclosed by bone. Mescher, A.L. Junqueira’s Basic Histology© McGraw Hill B5 Histology of Specialized Connective Tissues Describe intramembranous bone formation. Intramembranous bone formation occurs in the flat bones of the skull. Numerous ossification centers fuse forming a network of anastomosing trabeculae. The bone at this point is woven or immature bone. Final step is the remodeling of woven bone into lamellar bone by osteoclast resorption and osteoblast deposition. The surrounding mesenchyme forms the periosteum. B5 Histology of Specialized Connective Tissues Describe endochondral bone formation. Endochondral bone formation occurs in long bones, short bones and irregular bones. Involves mesenchyme differentiating into chondroblast and forming a hyaline cartilage model which is then resorbed and replaced by bone. Begins in fetal development and continues until adulthood. During fetal development the formation and growth of a hyaline cartilage model occurs. Marieb, E. N. Human Anatomy and Physiology © Benjamin Cummings B5 Histology of Specialized Connective Tissues Describe endochondral bone formation. Long bones: – 1) Ossification begins in the middle of the shaft with hypertrophy of the chondrocytes (3rd month fetal life) – 2) Hypertrophic Chondrocytes Secrete Vascular Endothelial Cell Growth Factor (VEGF). – VEGF induces: The perichondrium to become vascularized which leads to a bone collar. – Under high oxygen tension, Chondrogenic Cells become Osteogenic cells which differentiate into Osteoblast and a periosteal Bone collar is formed. The invasion of blood vessels from the perichondrium into the marrow cavity (periosteal sprouts or buds). – 3) Blood vessels continue to grow through the bony collar and bring in osteoprogenitor cells and precursor hemopoietic cells into the large cavities formerly occupied by The hypertrophic chondrocytes produce alkaline phosphatase (initiates hypertrophic chondrocytes. calcification). -Undergo apoptosis as calcification of the surrounding matrix takes place -> Forming empty large Cavities. B5 Histology of Specialized Connective Tissues Describe endochondral bone formation. Osteoprogenitor cells and hematopoietic cells reach the core of the calcified cartilage through the perivascular connective tissue surrounding the invading blood vessel. –Osteoprogenitor cells differentiate into osteoblasts which lay down osteoid around the calcified cartilage remnants. –Osteoclast begin to resorb the cartilage/calcified bone complex and is replaced by new bone. –Ossification moves towards both epiphyses. Bailey, F.R. Bailey’s Textbook of Microscopic Anatomy © Williams & Wilkins B5 Histology of Specialized Connective Tissues Describe endochondral bone formation. Long bones: Secondary ossification generally occurs in both epiphyses of long bones starting in late fetal development and continuing into the early teens. The process of secondary ossification is the same as in the shaft except that the hyaline cartilage remains at the articular surfaces and there is no bone collar. – Note: Some long bones only have a secondary ossification center in one epiphysis (metatarsals, metacarpals, and phalanges); and some have multiple secondary ossification centers in a single epiphysis (femur). Long bones sometimes have secondary centers of ossification in large tuberosities (tibia). Kierszenbaum, A. L. Histology and Cell Biology © Elsevier B5 Histology of Specialized Connective Tissues Describe endochondral bone formation. Short bones: – Examples are the carpal and tarsal bones. – Commonly have one primary center of ossification in the center of the cartilage model (however the calcaneus has a secondary center of ossification). Irregular bones: – Examples are vertebrae, os coxae, and scapula. – May have single or multiple primary and secondary centers of ossification (os coxae has three primary and five secondary centers of ossification).  Histology of Specialized Connective Tissues Describe epiphyseal plate. Long bone growth in length: Occurs at the Epiphyseal plate which is commonly located in the metaphysis (between the epiphysis and diaphysis). As the secondary and primary ossification centers expand, the growth plate will continue to grow and be replaced by bone until early adulthood. The growth of a long bone ceases with closure of the epiphyseal plates (bone replaces all the cartilage at the plate). – Epiphyseal line.  B6 Histology of Specialized Connective Tissues Describe epiphyseal plate. Long bone growth in length: Zones of the epiphyseal plate: – Zone of resting cartilage (resting or reserve zone): Chondrocytes are randomly distributed (are mitotically active). – Zone of proliferating cartilage (proliferation): Zone of Resting Cartilage Chondrocytes are undergoing rapid mitosis and organizing into columns. – Zone of maturing cartilage (maturation Zone of or hypertrophy): Proliferating Cartilage Chondrocytes enlarge. – Zone of calcifying cartilage Zone of Maturing (calcification): Cartilage Chondrocytes calcify the matrix (basophilic) and die (apoptosis) Zone of Calcifying leaving spaces for the ingrowth of Cartilage osteoblasts and vessels. – Zone of Ossification (Vascular Zone of Invasion): Ossification Osteoblasts lay down pink staining Osteoid (acidophilic) on the cartilage matrix. Osteoclasts resorb calcified cartilage and enlarge the marrow cavity. Trabecular bone is formed. Bailey, F.R. Bailey’s Textbook of Microscopic Anatomy © Williams & Wilkins Histology of Specialized Connective Tissues XRAY of epiphyseal plate in the knee 1 month 2 year old 5 year old 8 year old 12 year old Tortora, G. Principles of Human Anatomy © Wiley Publishers Histology of Specialized Connective Tissues Long bone growth in width: Appositional growth from the periosteum is responsible for growth in diameter (width).  PBBS 503 Structure & Function Dr. Derek Talbot Scholl College of Podiatric Medicine Rosalind Franklin University of Medicine & Science Lecture 24 -Histology of Specialized Connective Tissue – Bone III  Learning Objectives: B7. Describe how bone health is maintained by Vitamins C and D and describe bone defects resulting from deficiencies in each. B8. Describe the processes involved in fracture repair.  Histology of Specialized Connective Tissues Describe the vascular supply to bones. Long Bones (eg. humerus, radius, ulna, metacarpals, femur, tibia, fibula, metatarsals and phalanges): – Nutrient arteries, epiphyseal arteries, metaphyseal arteries and periosteal arteries. Short Bones (eg. carpals and tarsals): – Nutrient arteries. Flat Bones (eg. flat bones of the skull and sternum): – Nutrient arteries and periosteal arteries. Irregular bones (eg. vertebrae, scapula and os coxae): – Nutrient arteries and periosteal arteries. Note: – Nutrient, epiphyseal, and metaphyseal arteries pass through the compact bone into the marrow cavity and then the blood vessel enters into the Volkmann’s and Haversian canals. – Periosteal arteries vascularize the periosteum and the outer portion of compact bone. – The venous drainage parallels the arteries. – Nerves are found primarily in the periosteum but also in the Haversian and Volkmann canals. Marieb, E. N. Human Anatomy and Physiology © Benjamin Cummings Histology of Specialized Connective Tissues Describe the vascular supply to bones. X-Ray of: Nutrient Foramen through compact bone in the femur. _______________________ Periosteal arteries enter volkmann’s canals.  Histology of Specialized Connective Tissues Bone Remodeling Remodeling is the continuous replacement of old bone with newly formed bone. – Functions to: – Replace microscopic damage (microcracking). – Maintain calcium homeostasis – Bone is dynamic (Mechanical Adaptation) : Density can increase or decrease depending on the external load (Wolff’s law) – Capacity to adapt to changes in load and nutrient needs. Remodeling process – Osteoclast excavate a cylinder tunnel – Osteoblast fill in the space created Deposition of successive concentric lamellae Gartner, L.P., Color Textbook of Histology © Elsevier Histology of Specialized Connective Tissues Estrogen deficiency and Bone Remodeling Estrogen – Osteoblast under Estrogen influence: Decrease apoptosis and Decrease RANKL activity. – Osteoclast under Estrogen influence: Increase apoptosis and Decrease RANK induced activity. Estrogen Deficiency – Decreased Osteoblast activity and Increased Osteoclast activity. – Is associated with a gap between bone resorption and bone formation. Osteoporosis (Osteon, bone; poros, pore) – During the remodeling process, the osteoblast are unable to fully repair the resorptive defect during normal osteoclastic resorption leading to loss of bone mass. Bone fragility and susceptibility to fracture. – Possible reversal of bone loss with Estrogen therapy, Vitamin D, calcium and weight bearing exercise.  Histology of Specialized Connective Tissues Generalized Osteoporosis X-Ray Images Normal Anatomy Osteoporosis: – Image findings Wide spread osteopenia. Thin corticies. A decrease in bone mineral density of approximately 30% to 50% before it is demonstrated on the plain films. Resorption occurs in the horizontal trabeculae. Tortora, G. Principles of Human Anatomy © Wiley Publishers B7 Histology of Specialized Connective Tissues Nutritional Deficiencies and Bone Remodeling Vitamin D Important for calcium and phosphorous absorption by the small intestine. Stimulates Osteoblast to initiate mineralization. Vitamin D Deficiency In Adults, defect in mineralization of Osteoid (Osteomalacia). Decrease in the amount of calcium per unit of bone matrix. In Children, defect in mineralization of cartilage in the growth plate (Rickets). Vitamin C Important for the production of collagen in bone matrix and connective tissue matrix. Vitamin C Deficiency Deficient collagen production, causing a reduction in formation of bone matrix and bone development. Delayed wound healing (Scurvy). B8 Histology of Specialized Connective Tissues Describe fractures and repair of bone. A fracture of a bone results in the following steps: – Hemorrhage in the immediate area. – A. Procallus (provisional callus) formation: Clotting and the formation of granulation tissue (capillaries and fibroblast) – B. Soft callus formation: Phagocytic cells remove dead tissue. Osteoprogenitor cells differentiate into chondroblasts (under low oxygen tension) which transform the granulation tissue into hyaline cartilage which binds the fractured bone together. – C. Bony callus formation: Chondrocytes within the hyaline cartilage model will hypertrophy and release VEGF. Ultimately all the cartilage is replaced with primary bone (woven bone) by endochondral bone formation – D. Compact bone replaces the spongy bone (remodeling). Gartner, L.P., Color Textbook of Histology © Elsevier  B8 Histology of Specialized Connective Tissues Describe fractures and repair of bone. Fracture repair – Formation of a clot (hematoma) Within 48 hours after injury and last up to 5 days. – Soft Callus Hyaline cartilage usually, maybe fibrocartilage 1-2 weeks – Hard Callus 2 weeks 4 weeks 9 weeks Woven bone formation 2-3 weeks – Hard Callus Remodeling Trabeculae replaced by compact bone Lamellar bone is formed From 3 weeks on. Tortora, G. Principles of Human Anatomy © Wiley Publishers