Bones and Skeletal Tissues Part A

Skeletal Cartilages Consist primarily of water this is what allows it to spring back to its original shape after being compressed. Contain no blood vessels or nerves Surrounded by dense connective tissue, the perichondrium contains blood vessels for nutrient delivery to cartilage acts as a girdle to resist outward expansion

Skeletal Cartilages Hyaline cartilages Elastic cartilages Provide support, flexibility, and resilience Most abundant type Elastic cartilages Similar to hyaline cartilages, but contain more stretchy elastic fibers Better able to stand up to repeated bending Only found in the external ear and the epiglottis Fibrocartilages Collagen fibers—have great tensile strength Areas subjected to heavy pressure and stretch- menisci (knee)

Respiratory tube cartilages in neck and thorax Epiglottis Larynx Thyroid cartilage Cartilage in external ear Cartilages in nose Trachea Cricoid cartilage Lung Articular Cartilage of a joint Cartilage in Intervertebral disc Costal cartilage Respiratory tube cartilages in neck and thorax Pubic symphysis Bones of skeleton Axial skeleton Meniscus (padlike cartilage in knee joint) Appendicular skeleton Cartilages Articular cartilage of a joint Hyaline cartilages Elastic cartilages Fibrocartilages Figure 6.1

Growth of Cartilage Cartilage grows in two ways: Appositional “growth from the outside” Cells secrete matrix against the external face of existing cartilage Interstitial “growth from the inside” Chondrocytes divide and secrete new matrix, expanding cartilage from within Under certain conditions calcification of cartilage (calcium salts are deposited in the matrix) occurs during Normal bone growth Old age THIS IS NOT BONE 2 separate tissues!

Bones of the Skeleton Two main groups, by location Axial skeleton (brown) Skull, vertebral column, and rib cage Appendicular skeleton (yellow) Bones of the upper and lower limbs and the girdles.

Cartilage in Cartilages in external ear nose Articular Cartilage of a joint Cartilage in Intervertebral disc Costal cartilage Pubic symphysis Meniscus (padlike cartilage in knee joint) Articular cartilage of a joint Figure 6.1

Classification of Bones by Shape Long bones Longer than they are wide All limb bones except the patella, wrist, and ankle bone are long bones. Short bones Cube-shaped bones (in wrist and ankle) Sesamoid bones (within tendons  patella)

Classification of Bones by Shape Flat bones Thin, flat, slightly curved Sternum, scapulae, ribs, and most skull bones Irregular bones Complicated shapes that fit none of the other classes Vertebrae and hip bones

Functions of Bones Support Protection Movement For the body and soft organs (framework) Protection For brain, spinal cord, and vital organs Movement Levers for muscle action muscles use bones as levers to move the body.

Functions of Bones Storage Minerals (calcium and phosphorus) and growth factors Blood cell formation (hematopoiesis) in marrow cavities Triglyceride (energy) storage in bone cavities

Bone Markings Bulges, depressions, and holes serve as Sites of attachment for muscles, ligaments, and tendons Joint surfaces Channels for blood vessels and nerves

Bone Markings: Projections Table 6.1

Bone Markings: Projections Projections (grow outward from bone surface) that help to form joints

Bone Markings: Depressions and Openings

Bone Textures Compact bone Spongy bone Dense outer layer that looks smooth and solid Spongy bone Honeycomb of trabeculae internal layer filled with bone marrow

Structure of a Long Bone Diaphysis (shaft) Forms the long axis of the bone Constructed from a thick compact bone collar that surrounds a central medullary (marrow) cavity Medullary cavity in adults contains fat (yellow marrow)

Structure of a Long Bone Epiphyses Bone ends Compact bone exterior & spongy bone interior Epiphyseal line remnant of growth plate- a disc of hyaline cartilage that grows during childhood to lengthen the bone Articular (hyaline) cartilage on joint surfaces

Articular cartilage Compact bone Proximal epiphysis Spongy bone Epiphyseal line Periosteum Compact bone Medullary cavity (lined by endosteum) (b) Diaphysis Distal epiphysis (a) Figure 6.3a-b

Membranes of Bone Periosteum Covers the entire external surface of bones Outer fibrous layer dense irregular connective tissue Inner osteogenic layer mainly bone forming cells Nerve fibers, nutrient blood vessels, and lymphatic vessels enter the bone via nutrient foramina Secured to underlying bone by perforating “Sharpey’s” fibers Tufts if collagen fibers that extend from the fibrous layer into the bone matrix

Membranes of Bone Endosteum Delicate connective tissue membrane on internal surfaces of bone Covers the trabeculae of spongy bone and lines the canals that pass through compact bone Also contains osteoblasts and osteoclasts

Structure of Short, Irregular, and Flat Bones All consist of: Periosteum-covered compact bone on the outside Endosteum-covered spongy bone within Spongy bone called diploë in flat bones Bone marrow between the trabeculae

Location of Hematopoietic Tissue (Red Marrow) Red marrow cavities of adults Trabecular cavities of the heads of the femur and humerus Trabecular cavities of the diploë of flat bones In most adult long bones the fat containing medullary cavity extends well into the epiphysis and little red marrow is present  blood cell production occurs in the heads of the femur (thigh bone) and humerus (long bone of arm) The red marrow found in the diploë of flat bones (sternum) or some irregular bone (hip) is much more active in hematopoiesis and these sites are routinely used for obtaining bone marrow biopsies when problems with blood forming tissue are suspected. Red marrow of newborn infants Medullary cavities and all spaces in spongy bone

Microscopic Anatomy of Bone Cells of bones Osteogenic cells Stem cells in periosteum and endosteum that give rise to osteoblasts Osteoblasts Bone-forming cells Osteocytes Mature bone cells Osteoclasts Cells that break down bone matrix

Microscopic Anatomy of Bone: Compact Bone Although compact bone looks solid it is riddled with passageways for nerves, blood vessels, and lymphatic vessels Osteons—structural units “Tiny pillars” Lamellae Weight-bearing Column-like matrix tubes Haversian canal Contains blood vessels and nerves

Microscopic Anatomy of Bone: Compact Bone Perforating (Volkmann’s) canals At right angles to the central canal Connects blood vessels and nerves of the periosteum and central canal Lacunae—small cavities that contain osteocytes Canaliculi—hairlike canals that connect lacunae to each other and the central canal

Microscopic Anatomy of Bone: Spongy Bone Trabeculae Align along lines of stress No osteons Contain irregularly arranged lamellae, osteocytes, and canaliculi Capillaries in endosteum supply nutrients

Chemical Composition of Bone: Organic Osteogenic cells, osteoblasts, osteocytes, osteoclasts Osteoid—organic bone matrix secreted by osteoblasts Ground substance (proteoglycans, glycoproteins) Collagen fibers Provide strength and flexibility

Chemical Composition of Bone: Inorganic Hydroxyapatites (mineral salts) Tiny, tightly packed crystals in and around the collagen fibers in the extracellular matrix 65% of bone by mass Mainly calcium phosphate crystals Responsible for hardness and resistance to compression