Bone Formation and Joints A560 – Fall 2015

Lab 7 –Bone Formation and Joints A560 – Fall 2015

I. Introduction II. Learning Objectives III. Slides and Micrographs A. Bone (cont.) 1. General structure 2. Cells Bone Formation and Joints a. Osteoblasts b. Osteoclasts B. Bone Formation 1. Intramembranous ossification 2. Endochondral ossification C. Joints 1. Synovial 2. Intervertebral IV. Summary Lab 7 –Bone Formation and Joints A560 – Fall 2015

I. Introduction Bone Formation and Joints II. Learning Objectives III. Slides and Micrographs 1. Bone is a specialized type of connective tissue with A. Bone (cont.) a calcified (mineralized) extracellular matrix (ECM); 1. General structure it serves to support the body, protect internal 2. Cells organs, and acts as the body’s calcium reservoir. a. Osteoblasts 2. Major cells of bone include: osteoblasts (form b. Osteoclasts osteoid which allows matrix mineralization to B. Bone Formation occur), osteocytes (from osteoblasts; enclosed in 1. Intramembranous ossification lacunae and maintain the matrix), and osteoclasts 2. Endochondral ossification (locally erode bone matrix during bone formation C. Joints and remodeling). 1. Synovial 3. Bone growth occurs via two basic mechanisms: 2. Intervertebral intramembranous ossification (bone forms within IV. Summary mesenchymal membrane) and endochondral ossification (bone replaces hyaline cartilage)

4. Joints are places where bones meet (articulate), allowing at least the potential of bending or movement; examples include, synovial joints (diarthrosis) and intervertebral joints Lab 7 –Bone Formation and Joints A560 – Fall 2015

I. Introduction Learning Objectives II. Learning Objectives III. Slides and Micrographs 1. Understand the differences and similarities between intramembranous and A. Bone (cont.) 1. General structure endochondral bone formation and the key function of the periosteum in 2. Cells bone growth. a. Osteoblasts b. Osteoclasts 2. Understand the organization of the epiphyseal growth plate and its role in B. Bone Formation endochondral bone formation and growth of long bones. 1. Intramembranous ossification 2. Endochondral ossification C. Joints 3. Understand the structure of a typical synovial joint, including the nature 1. Synovial and functions of the synovium. 2. Intervertebral IV. Summary Lab 7 –Bone Formation and Joints A560 – Fall 2015 I. Introduction Slide 129: Tooth, H&E II. Learning Objectives III. Slides and Micrographs A. Bone (cont.) 1. General structure 2. Cells 104: Bone, H&E a. Osteoblasts Bone b. Osteoclasts B. Bone Formation 1. Intramembranous ossification 2. Endochondral ossification C. Joints 1. Synovial 2. Intervertebral IV. Summary Lab 7 –Bone Formation and Joints A560 – Fall 2015 I. Introduction Slide 129: Tooth, H&E II. Learning Objectives III. Slides and Micrographs A. Bone (cont.) 1. General structure 2. Cells a. Osteoblasts b. Osteoclasts perforating B. Bone Formation 1. Intramembranous ossification (Volkmann’s) canals 2. Endochondral ossification osteon C. Joints 1. Synovial 2. Intervertebral IV. Summary central canal osteocyte in lacuna Lab 7 –Bone Formation and Joints A560 – Fall 2015 Slide 104: Bone, H&E I. Introduction II. Learning Objectives III. Slides and Micrographs A. Bone (cont.) 1. General structure 2. Cells a. Osteoblasts b. Osteoclasts B. Bone Formation resorption 1. Intramembranous ossification canals 2. Endochondral ossification C. Joints osteon 1. Synovial 2. Intervertebral central IV. Summary canal

Osteon formation: resorption canals (with dimension of new osteon) are carved out of bone by osteoclasts; blood vessels and connective tissue invade and occupy the tunnel; osteoblasts begin to deposit new bone along the walls, forming lamellae; synthesis continuesfromperipheryto center until only central canal with neurovascular bundle remains in center Lab 7 –Bone Formation and Joints A560 – Fall 2015 Slide 34: Healing Bone Fracture, H&E

I. Introduction II. Learning Objectives Callus III. Slides and Micrographs A. Bone (cont.) 1. General structure 2. Cells a. Osteoblasts b. Osteoclasts B. Bone Formation 1 Cortical 1. Intramembranous ossification bone 2. Endochondral ossification C. Joints 1. Synovial Fracture 2. Intervertebral IV. Summary EC Hyaline 2 Oss Cartilage

Sections (1) and (2) are two rib segments from a fetal/newborn rabbit; (1) gives an example of a bone fracture and repair processes (the callus is a temporary formation of highly proliferative fibroblasts and chondroblasts extending from the periosteum down into the fracture to formnewbone);(2) gives an example of endochondral ossification (EC Oss)bonegrowth Lab 7 –Bone Formation and Joints A560 – Fall 2015 Slide 34: Healing Bone Fracture, H&E

I. Introduction II. Learning Objectives III. Slides and Micrographs A. Bone (cont.) 1. General structure 2. Cells CT a. Osteoblasts P b. Osteoclasts B. Bone Formation Act P 1. Intramembranous ossification 2. Endochondral ossification C. Joints M HC 1. Synovial 2. Intervertebral Wb IV. Summary

From the outside: (CT) is connective tissue proper surrounding the bone, note the abundant vasculature present; (P) is periosteum with clearly visible collagen bundles and (Act P) is an area of more active periosteum with lots of cellular differentiation occurring; (M) is marrow with abundant blood cells; (HC) are areas of hyaline cartilage; (Wb) is woven or primary bone being deposited upon hyaline cartilage (basophilic); there is an irregular arrangement of collagen fibers (acidophilic), large cell number, and reduced mineral content; (Tb) is mature (mineralized), trabecular bone; close examination shows endosteum on the edge of the bone bordering the marrow Lab 7 –Bone Formation and Joints Slide 34: Healing Bone Fracture, H&E A560 – Fall 2015 I. Introduction CT P II. Learning Objectives Cb III. Slides and Micrographs A. Bone (cont.) 1. General structure M 2. Cells a. Osteoblasts Tb b. Osteoclasts B. Bone Formation 1. Intramembranous ossification Wb 2. Endochondral ossification C. Joints 1. Synovial P 2. Intervertebral IV. Summary CT

From the outside (top): (CT) is connective tissue proper surrounding the bone; (P) is periosteum with clearly visible collagen bundles; (Cb) is cortical bone with lamellar arrangement, note the adjacent central canal with surrounding rings of cartilage; (M) is marrow with abundant blood cells; (Tb) is trabecular bone, distinguished from cortical bone by the lack of osteons; close examination shows endosteum on the edge of the bone bordering the marrow; (Wb) iswovenorprimarybonewithanirregulararrangementof collagen fibers, large cell number, and reduced mineral content; osteoid (unmineralized bone) is the pale, acellular layer just below osteoblasts which line the edges of the nearby marrow cavities Lab 7 –Bone Formation and Joints A560 – Fall 2015 Slide 34: Healing Bone Fracture, H&E

I. Introduction II. Learning Objectives III. Slides and Micrographs A. Bone (cont.) 1. General structure 2. Cells a. Osteoblasts marrow b. Osteoclasts B. Bone Formation 1. Intramembranous ossification 2. Endochondral ossification C. Joints 1. Synovial 2. Intervertebral endosteum IV. Summary lining trabecula

Endosteum lines all internal surfaces of bone (both cortical and trabecular); it is generally only a single cell‐layer thick, and consists of inactive and active osteoblasts Lab 7 –Bone Formation and Joints A560 – Fall 2015 I. Introduction Slide 34: Healing Bone Fracture, H&E II. Learning Objectives III. Slides and Micrographs A. Bone (cont.) 1. General structure 2. Cells a. Osteoblasts b. Osteoclasts B. Bone Formation 1. Intramembranous ossification 2. Endochondral ossification endosteum C. Joints 1. Synovial osteoid 2. Intervertebral IV. Summary lighter stained area between endosteum and mature bone

mature bone Osteoid is collagen‐rich, non‐mineralized precursor to true bone matrix; it is secreted by osteoblasts during bone growth, repair, and remodeling; osteoblast subsequently calcify the osteoid into bony hard bony matrix; in the process, they become trapped in the matrix (in lacunae) and become osteocytes Lab 7 –Bone Formation and Joints A560 – Fall 2015 Slide 34: Healing Bone Fracture, H&E I. Introduction II. Learning Objectives III. Slides and Micrographs A. Bone (cont.) 1. General structure 2. Cells a. Osteoblasts b. Osteoclasts B. Bone Formation 1. Intramembranous ossification 2. Endochondral ossification C. Joints inactive 1. Synovial periosteum: 2. Intervertebral w/ flattened IV. Summary osteoprogenitor cells

maturing bone with osteocytes Lab 7 –Bone Formation and Joints A560 – Fall 2015 Slide 34: Healing Bone Fracture, H&E I. Introduction II. Learning Objectives III. Slides and Micrographs A. Bone (cont.) 1. General structure 2. Cells a. Osteoblasts b. Osteoclasts active B. Bone Formation periosteum: 1. Intramembranous ossification w/ rounded 2. Endochondral ossification or cuboidal C. Joints osteoblasts 1. Synovial 2. Intervertebral IV. Summary

osteocyte

Osteoblasts develop from osteoprogenitor cells (from mesenchymal cells) and are found lining the external and internal bone surfaces; they make osteoid (collagen‐rich matrix) which they then calcify into true hard, bony matrix; they become trapped in the matrix and become osteocytes Lab 7 –Bone Formation and Joints A560 – Fall 2015

I. Introduction II. Learning Objectives Slide 130: Membranous Bone, Fetal Skull III. Slides and Micrographs A. Bone (cont.) 1. General structure 2. Cells a. Osteoblasts b. Osteoclasts B. Bone Formation 1. Intramembranous ossification 2. Endochondral ossification C. Joints 1. Synovial 2. Intervertebral osteoblasts IV. Summary

periosteum Lab 7 –Bone Formation and Joints A560 – Fall 2015

I. Introduction Slide 34: Healing Bone Fracture, H&E II. Learning Objectives III. Slides and Micrographs A. Bone (cont.) How many 1. General structure nuclei does this 2. Cells osteoclast have? a. Osteoblasts up to 200 is b. Osteoclasts possible, 5‐20 is B. Bone Formation usual 1. Intramembranous ossification 2. Endochondral ossification Osteoclast C. Joints 1. Synovial Howship’s lacuna 2. Intervertebral (space) IV. Summary

Osteoclasts are large, multinucleated cells; they resorb bone by secreting organic acids, which dissolve hydroxyapatite, and lysosomal enzymes, which break down the osteoid matrix; at the bone surface, osteoclasts lie in Howship's lacunae, surface depressions caused by the resorption of bone Lab 7 –Bone Formation and Joints A560 – Fall 2015

I. Introduction Slide 34: Healing Bone Fracture, H&E II. Learning Objectives III. Slides and Micrographs A. Bone (cont.) 1. General structure 2. Cells a. Osteoblasts b. Osteoclasts B. Bone Formation 1. Intramembranous ossification 2. Endochondral ossification Osteoclast with C. Joints ruffled border 1. Synovial (visible in EM) in 2. Intervertebral IV. Summary Howship’s lacuna Lab 7 –Bone Formation and Joints A560 – Fall 2015 Slide 130: Membranous Bone, Fetal Skull I. Introduction II. Learning Objectives III. Slides and Micrographs A. Bone (cont.) 1. General structure 2. Cells a. Osteoblasts b. Osteoclasts B. Bone Formation 1. Intramembranous ossification 2. Endochondral ossification C. Joints 1. Synovial 2. Intervertebral osteoclasts IV. Summary Lab 7 –Bone Formation and Joints A560 – Fall 2015

I. Introduction II. Learning Objectives III. Slides and Micrographs Intramembranous Ossification A. Bone (cont.) 1. General structure 2. Cells 1. Primary center of ossification: mesenchyme cells  osteoblasts a. Osteoblasts b. Osteoclasts 2. Osteoblast begin depositing bony matrix to form trabeculae, B. Bone Formation extending radially from the ossification center 1. Intramembranous ossification 2. Endochondral ossification 3. Marrow develops in spaces between trabeculae C. Joints 1. Synovial 4. Periosteum and endosteum develop from mesenchyme 2. Intervertebral membrane IV. Summary 5. Surfaces are remodeled to form compact bone Lab 7 –Bone Formation and Joints A560 – Fall 2015 Slide 130: Membranous Bone, Fetal Skull I. Introduction II. Learning Objectives III. Slides and Micrographs A. Bone (cont.) 1. General structure nasal cavity with 2. Cells cartilaginous nasal a. Osteoblasts septum in the b. Osteoclasts middle; surrounded by intramembranous B. Bone Formation bone development of 1. Intramembranous ossification the skull 2. Endochondral ossification C. Joints 1. Synovial 2. Intervertebral tongue in the oral cavity IV. Summary

developing teeth Side View Frontal View with surrounding intramembranous bone development of the jaw

Slide 130 – Fetal Skull Lab 7 –Bone Formation and Joints A560 – Fall 2015

I. Introduction Slide 130: Membranous Bone, Fetal Skull II. Learning Objectives III. Slides and Micrographs A. Bone (cont.) 1. General structure 2. Cells a. Osteoblasts b. Osteoclasts B. Bone Formation 1. Intramembranous ossification woven bone 2. Endochondral ossification C. Joints 1. Synovial 2. Intervertebral IV. Summary Lab 7 –Bone Formation and Joints A560 – Fall 2015 Slide 130: Membranous Bone, Fetal Skull I. Introduction II. Learning Objectives III. Slides and Micrographs A. Bone (cont.) 1. General structure 2. Cells a. Osteoblasts b. Osteoclasts B. Bone Formation woven bone 1. Intramembranous ossification 2. Endochondral ossification C. Joints hyaline 1. Synovial cartilage 2. Intervertebral IV. Summary

periosteum Lab 7 –Bone Formation and Joints A560 – Fall 2015

I. Introduction Endochondral Ossification II. Learning Objectives III. Slides and Micrographs A. Bone (cont.) 1. Zone of Reserve Cartilage: hyaline cartilage acts as source of 1. General structure cartilage to undergo ossification 2. Cells a. Osteoblasts 2. Zone of Proliferation: normal chondrocytes multiply b. Osteoclasts B. Bone Formation 3. Zone of Hypertrophy: chondrocytes enlarge and align 1. Intramembranous ossification 2. Endochondral ossification 4. Zone of Calcification: cartilage matrix calcifies; scaffold for new C. Joints bone 1. Synovial 2. Intervertebral 5. Zone of Ossification and Resorption: chondrocytes deteriorate IV. Summary and die; osteoblast invade and bone is deposited on the calcified matrix; osteoclasts begin remodeling process

Because the rates of proliferation and destruction are approximately equal, the epiphyseal plate does not change thickness; instead, it is displaced away from the middle of the diaphysis, resulting in growth in length of the bone Lab 7 –Bone Formation and Joints A560 – Fall 2015 Slide 34: Healing Bone Fracture, H&E I. Introduction II. Learning Objectives III. Slides and Micrographs A. Bone (cont.) 1. General structure 2. Cells a. Osteoblasts b. Osteoclasts B. Bone Formation 1. Intramembranous ossification 2. Endochondral ossification endochondral C. Joints ossification 1. Synovial 2. Intervertebral IV. Summary

Epiphysis Diaphysis (End) (Middle) Growth plate Lab 7 –Bone Formation and Joints A560 – Fall 2015 Slide 34: Healing Bone Fracture, H&E I. Introduction II. Learning Objectives III. Slides and Micrographs A. Bone (cont.) 1. General structure 2. Cells a. Osteoblasts b. Osteoclasts B. Bone Formation 1. Intramembranous ossification 2. Endochondral ossification C. Joints 1. Synovial 2. Intervertebral IV. Summary

zone of zone of zone of zone of reserve chondroblast chondrocyte calcification, cartilage proliferation hypertrophy ossification, and resorption Lab 7 –Bone Formation and Joints A560 – Fall 2015 Slide 34: Healing Bone Fracture, H&E I. Introduction II. Learning Objectives III. Slides and Micrographs A. Bone (cont.) 1. General structure 2. Cells a. Osteoblasts b. Osteoclasts B. Bone Formation 1. Intramembranous ossification 2. Endochondral ossification C. Joints 1. Synovial 2. Intervertebral IV. Summary

zone of reserve cartilage typical hyaline cartilage with chondrocytes arranged in small clusters, usually only one cell per lacuna (not grouped) Lab 7 –Bone Formation and Joints A560 – Fall 2015 Slide 34: Healing Bone Fracture, H&E I. Introduction II. Learning Objectives III. Slides and Micrographs A. Bone (cont.) 1. General structure 2. Cells a. Osteoblasts b. Osteoclasts B. Bone Formation 1. Intramembranous ossification 2. Endochondral ossification C. Joints 1. Synovial 2. Intervertebral IV. Summary

zone of chondroblast proliferation chondrocytes are dividing and increasing in number; chondrocytes are slightly larger in size, are closer to neighboring cells, and are beginning to form rows or stacks Lab 7 –Bone Formation and Joints A560 – Fall 2015 Slide 34: Healing Bone Fracture, H&E

I. Introduction II. Learning Objectives III. Slides and Micrographs A. Bone (cont.) 1. General structure 2. Cells a. Osteoblasts b. Osteoclasts B. Bone Formation 1. Intramembranous ossification 2. Endochondral ossification C. Joints 1. Synovial 2. Intervertebral IV. Summary

zone of chondrocyte hypertrophy chondrocytes are aligned in rows (along axis of growth) and are significantly larger than in preceding zones Lab 7 –Bone Formation and Joints Slide 34: Healing Bone Fracture, H&E A560 – Fall 2015

zone of calcification, ossification, and resorption chondrocytes undergo apoptosis (so nuclei are more condensed); small blood vessel and osteoprogenitor cells begin to invade, giving rise to osteoblasts which begin to lay down bone and become osteocytes Lab 7 –Bone Formation and Joints A560 – Fall 2015 Fig 8‐19 Synovial Joint

See: Fig 8‐19, 8‐20, 8‐21 Lab 7 –Bone Formation and Joints A560 – Fall 2015 Fig 8‐22 Intervertebral Disc

I. Introduction II. Learning Objectives III. Slides and Micrographs A. Bone (cont.) Vertebra with bone 1. General structure marrow cavity (BM) 2. Cells a. Osteoblasts b. Osteoclasts B. Bone Formation Concentric layers of fibrocartilage form the 1. Intramembranous ossification annulus fibrosus (AF) (Lt. “fibrous ring”) 2. Endochondral ossification C. Joints 1. Synovial Nucleus pulposus (NP) is the inner core of 2. Intervertebral the vertebral disc; it is composed of a gel‐like IV. Summary matrix consisting of water and a loose network of collagen fibers

Vertebra with bone marrow cavity Lab 7 –Bone Formation and Joints Common Confusion: A560 – Fall 2015 Cartilage vs. Bone I. Introduction II. Learning Objectives Cartilage: a specialized type of solid connective tissue III. Slides and Micrographs which, along with bone, is distinguished by its relative A. Bone (cont.) rigidity of the extracellular matrix (ECM); it is 1. General structure distinguishable from bone by its avascularity in addition to its lack of lymphatics and nerves; hyaline, the most 2. Cells common type, is pictured here a. Osteoblasts b. Osteoclasts Look for: (1) lack of vasculature, lymphatics, and nerves; B. Bone Formation (2) large proportion of cells to ECM; (3) chondrocytes may occur as pairs within a lacuna and tend to be clustered 1. Intramembranous ossification together (isogenous groups); (4) chondrocytes are usually 2. Endochondral ossification larger and rounder than osteocytes; (5) matrix is often not C. Joints Hyaline cartilage uniform and tends to heterogeneously stain 1. Synovial 2. Intervertebral Bone: a specialized type of solid connective tissue IV. Summary characterized by a mineralized ECM that stores calcium and phosphate

Look for: (1) vasculature; note the central canal (osteon) containing visible erythrocytes; (2) more ECM and fewer cells; (3) osteocytes are singular and spaced apart; (4) osteocytes are smaller and more condensed than chondrocytes; (5) canals and lamellar organization may be visible; (6) canaliculi may be visible linking osteocytes

Decalcified bone Lab 7 –Bone Formation and Joints A560 – Fall 2015 Summary

I. Introduction 1. During bone formation, woven bone (haphazard arrangement of collagen II. Learning Objectives fibers) gets remodeled into lamellar bone (parallel bundles of collagen in III. Slides and Micrographs layers known as lamellae). A. Bone (cont.) 1. General structure 2. Periosteum is a layer of dense connective tissue on the outer surface of 2. Cells bone; endosteum is a thin layer (generally only one cell layer) which lines a. Osteoblasts all the internal surfaces of bone. b. Osteoclasts B. Bone Formation 1. Intramembranous ossification 3. Major cells of bone include: osteoblasts (from osteoprogenitor cells; form 2. Endochondral ossification osteoid which allows matrix mineralization to occur), osteocytes (from C. Joints osteoblasts; enclosed in lacunae and maintain the matrix), and osteoclasts 1. Synovial (from hematopoietic lineage; locally erode bone matrix during bone 2. Intervertebral formation and remodeling). IV. Summary 4. Bone growth occurs via two basic mechanisms: • intramembranous ossification occurs when bone forms within mesenchymal membrane; forms bones of skull and jaw; primarily occurs only during development or fracture repair • endochondral ossification occurs when bone replaces hyaline cartilage; forms and grows all other bones except as noted for IM; occurs during development and throughout life Lab 7 –Bone Formation and Joints A560 – Fall 2015 Summary (cont.)

I. Introduction 5. During epiphyseal growth (elongation of bone), the growth plate, with its II. Learning Objectives zonal organization of endochondral ossification, allows bone to lengthen III. Slides and Micrographs without the epiphyseal growth plate enlarging; zones include: A. Bone (cont.) • Zone of reserve cartilage 1. General structure • Zone of proliferation 2. Cells • Zone of hypertrophy a. Osteoblasts • Zone of calcification b. Osteoclasts • Zone of ossification and resorption B. Bone Formation 1. Intramembranous ossification 2. Endochondral ossification 6. Joints are places where bones meet (articulate), allowing at least the C. Joints potential of bending or movement; examples include, synovial joints 1. Synovial (diarthrosis) and intervertebral joints (with tough outer layer of 2. Intervertebral fibrocartilage known as annulus fibrosus, and gel‐like core known as IV. Summary nucleus pulposus). Lab 7: Summary Features of Major Cells of Bone Tissue

Osteoblasts Osteocytes Osteoclasts

Precursor cell

Location

Percentage of all cells in bone

Function

Appearance

Sketch Lab 7: Comparison of Mechanisms of Bone Formation

Intramembranous Ossification Endochondral Ossification

Bones produced

Cartilage present

Type of bone produced

When occurs

Steps Involved