Bone and Cartilage

Cartilage Tensile Strength and durability is due to:

Collagen provides tensile strength and durability, however, proteoglycans are also important. For example, if you inject papain (an enzyme that digests the protein cores of proteoglycans) into the ears of a rabbit, after a few hours the ears will loose their stiffness and droop.

Periosteal lamellae of compact bone

(part of endochondral bones structure)- outer region of compact bone. layers secreted, as the bone grew, by osteoblasts associated with the inner side of the periosteum - appositional growth - circumferential lamellae -

3 Types of cartilage qualities depend on?

1)1. Differences in the type of collagen and concentration of collagen and elastin fibers in the extracellular matrix 2)2. The types of proteoglycan molecules that these fibers are associated with.

ENDOCHONDRAL BONE - what is it?

1. A template of hyaline cartilage is layed down prior to calcification and the establishment of true bone. During fetal development, this template is shaped like a miniature copy of the bone that will form from it. 2. Most of the bones in the mammalian body are initially formed by endochondral means.

HISTOGENESIS OF CARTILAGE

1. Interstitial growth during embryogenesis 2.2. Appositional growth of cartilage during embryogenesis and subsequent juvenile development.

Intramembranous

1. Mesenchymal cells aggregate and begin to secrete matrix that is characterized by bundles of collagen fibers. 2. The mesenchymal cells loose their characteristic appearance and round up becoming true osteoblasts. The osteoblasts become oriented in an epithelial-like layer along the forming bone matrix. 3. The secreted osteoid matrix has a high affinity for calcium salts, that are brought into the area of bone formation by circulatory system. These deposit within and on the matrix to form calcified bone. 4. As a strand of matrix is invested with inorganic salts it is called a spicule. Spicules fuse with one and other to form trabeculae. As the osteoblasts at the surface continue to secrete osteoid matrix, growth will continue in an appositional manner. This secretion by the osteoblasts is cyclic and results in layers of bone material called lamellae - lamellar bone. 4. As a strand of matrix is invested with inorganic salts it is called a spicule. Spicules fuse with one and other to form trabeculae. As the osteoblasts at the surface continue to secrete osteoid matrix, growth will continue in an appositional manner. This secretion by the osteoblasts is cyclic and results in layers of bone material called lamellae - lamellar bone. 5. The initial spicule formation and the deposition of lamellae traps some of the osteoblasts within lacunae in the calcifying osteoid matrix. Once trapped, these cells are considered mature osteocytes or bone cells. Osteocytes have cellular processes that extend through canaliculi and contact similar processes of adjacent osteocytes 6. Growing adjacent trabeculae will contact and fuse forming the structure of the mature bone.

endosteum

3. Important roles of the periosteum and endosteum are nutrition of bone cells and provision of osteoblasts for bone histogenesis and repair. •Lines the internal surfaces of bones - one cell thick •Does not exhibit two distinct layers

perichondrium-

A connective tissue capsule surrounding elastic and hyaline cartilage and is composed of fibroblasts and associated fibers and ground substance.

Osteocytes of Endochondral Bone

As discussed osteocytes of this tissue are embedded within a matrix that consists of organic (osteoid matrix) and inorganic (calcium phosphate salts) components.

Extracellular Matrix of Hyaline Cartilage?

Hyaline Cartilage-a. Dominant protein component of extracellular matrix is collagen (type 2). but also contains proteoglycans and hydroluronic acid.

Hyaline Cartilage important in formation of?

Important in embryonic formation and later growth of long bones - forms epiphyseal plates of long bones

HISTOGENESIS OF SKELETAL STRUCTURE

Intramembranous Endochondral Bone Formation

fibrocartilage of central disk and peripheral disk?

The fibrous cartilage forming the intervertebral discs varies in appearance from the center of the disc (the nucleus pulposus) the the periphery of the disc (the annulus fibrosus). Centrally, the fibrous matrix is very loose. The jelly-like consistency of the central part allows the intervertebral discs to function as a shock absorber. Towards the periphery, the fibrous matrix is organised into layers. It is often visible that the fibres of different layers are oriented at angles to each other - similar to the orientation of the thread in radial tires. Chondrocytes are very flattened in the periphery and may be difficult to find.

Perichondrium of Fibrocartilage

There is not one!

Fibrocartilage composition help it to function for?

c. Resists compression and shear forces. Has durability and high tensile strength.

Endochondral

formed from cartilage template that is subsequently replaced by bone (e.g. vertebral column, long bones of limbs).

Chondroblasts

immature cartilage cells. Secrete extracellular matrix, but are not yet imprisoned in a lacuna

Connective Tissue is important for ?

support of soft tissues •formation and growth of long bones •durability of articular joints

osteoblast

•Immature bone cells that synthesize and secrete the osteoid matrix that will calcify as the bones extracellular matrix. •Matrix is composed of glycoproteins and collagen. • Are located on the surfaces of forming bone and are not yet embedded in the calcified extracellular (osteoid) matrix. • Have cytoplasmic processes that bring them into contact with neighboring osteoblasts, as well as nearby osteocytes. •Ultrastructure shows organelle systems typical of protein secreting cells.

Osteocytes

•Mature bone cells - osteoblasts that have become embedded in calcified bone matrix. •They reside in lacunae within the matrix •Are in contact with neighboring osteocytes via cytoplasmic processes that extend through small tunnels called canaliculi. •Contacting cytoplasmic processes are characterized by gap junctions. This allows communication between osteocytes and is important in the tranfer of nutrients to these cells since they generally are far removed from blood capillaries. •The cells are flattened and their internal organelles exhibit the characteristics of cells that have reduced synthetic activity.

Chondrocytes location within tissue, shape, organelle characteristics?

•Mature cartilage cells that are embedded in the extracellular matrix. •Reside in small spaces within the matrix that are called LACUNAE. •Sometimes form groups of 2 or 3 - ISOGENIC GROUP •Chondrocytes have an Elliptic shape. •Organelle systems in cytoplasm are typical of cells that secrete.

Osteoclasts

•These are large multinucleate cells •Act to reabsorb bone during specific stages in bone formation and healing, and during the continual reworking of internal bone architecture that occurs throughout life. •Important in maintaining calcium balance in the body - respond to calcitonin (secreted by parafolllicular cells of thyroid/ultimobranchial bodies - lowers Ca++ concentration in blood), •and parathyroid hormone (secreted by parathyroid glands - raises Ca++ concentration in blood)

Cartilage extracellular matrix (ground substance) contains mainly?

•collagen and in some cases elastin fibers •glycosaminoglycans •proteoglycans*, proteoglycan agregates •water

Hyaline Cartilage is mainly found where as an adult? 3 places

•outer wall of respiratory passages (e.g. trachea) •ventral ends of ribs, and •on surfaces of bone joints where it is called articular cartilage.

Fibrocartilage arrangement/composition of chondrocytes, extracellular component?

a. An irregular, dense, fibrous tissue with thinly dispersed, encapsulated chondrocytes. (in a row) contains type 1 collagen, many large bundles of collagen fibers

Endochondral Bone Strucutre

a. An outer layer of connective tissue called the periosteum. b. A thick cortical layer of compact (dense) bone. c. A medullary or central volume of spongy (cancellous) bone where the bone marrow resides.

Elastic Cartilage- 5 main characteristics What does extracellular matrix contain? an example where to find elastic cartilage Chondrocyte arrangement? Ground substance? etc....2 more

a. High concentration of elastin fibers in extracellular matrix. (e.g. external ears-pinna) b. Ground substance - yellow in color (due to elastin content) c. Chondrocytes are more closely packed, no isogenic groups. d. Chondrocytes exhibit less accumulation of glycogen and lipids than in hyaline cartilage. e. Does not calcify

Hyaline cartilage undergoes calcification in____________ and also as a part of the _____________.

bone formation (forms template for bone) and aging process (arthritis)

outer region of compact bone

consisting of multiple osteons and interstitial bone a. osteon a. concentric sub-layers (lamellar bone) surrounding longitudinal tunnels for blood vessels and nerves that are called the haversian canals

Fibrous cartilage (fibrocartilage) is found?

d. Found at connection of tendons to bone and in intervertebral discs and some joints

Intramembranous

direct formation of bone structure with no cartilage template (e.g. flat bones of skull)

Nutrition of Cartilage Cells is dependent on?

the diffusion of nutrients from blood capillaries in perichondrium and/or adjacent tissues. Cartilage itself is devoid of blood vessels.

Hyaline Perichondrium

•vascularized connective tissue sheath surrounding cartilage (except in case of articular cartilage). •rich in collagen. •main cell type - fibroblasts •Inner layer contains cells that are thought by some to be fibroblasts and by others to be undifferentiated mesenchyme cells. In any event, the cells can differentiate to form chondroblasts.