Chapter #6: Bones and Skeletal Tissues

Skeletal Cartilages  Found in adults where flexible skeletal tissue is needed  Contains no blood vessels or nerves  Surrounded by the perichondrium (dense irregular connective tissue) that resists outward expansion  Three types – hyaline, elastic, and fibrocartilage

Hyaline Cartilage  Provides support, flexibility, and resilience  Only contains fine collagen fibers  Is the most abundant skeletal cartilage  Includes these types:  Articular – covers the ends of long bones  Costal – connects the ribs to the sternum  Respiratory – makes up larynx, reinforces air passages  Nasal – supports the nose

Elastic Cartilage  Similar to hyaline cartilage, but contains elastic fibers  Found in the external ear and the epiglottis

Fibrocartilage  Highly compressed with great tensile strength  Found where there is heavy pressure and stretch  Found in menisci of the knee and in intervertebral discs

Growth of Cartilage  Appositional “growth from outside” - cells in the perichondrium secrete matrix against the external face of existing cartilage  Interstitial “growth from inside” – lacunae-bound chondrocytes inside the cartilage divide and secrete new matrix, expanding the cartilage from within  Calcification of cartilage occurs  During normal bone growth  During old age

Classification of Bones  206 bones of the body are divided into two groups: 1. Axial skeleton “long axis of the body” - bones of the skull, vertebral column, and rib cage - mostly involved in protecting, supporting or carrying other body parts

2. Appendicular skeleton – bones of the upper and lower limbs & girdles (shoulder and hip) - primarily for locomotion

Axial and Appendicular Skeleton

Classification of Bones: By Shape  Long bones – longer than they are wide (e.g., humerus)

 Short Bones -cube shaped bones of the ankle and wrist Sesamoid Bone - special type of short bone - bones that form within tendons (patella)

 Flat Bones - thin, flattened and a bit curved (sternum and most skull bones)

 Irregular Bones - bones with complicated shapes (vertebrae and hip bones)

Functions of Bones  Support – form the framework that supports the body and cradles soft organs  Protection – provide a protective case for the brain, spinal cord, and vital organs  Movement – provide levers for muscles

Functions of Bones cont….  Mineral storage – reservoir for minerals, especially calcium and phosphorus  Blood cell formation – hematopoiesis occurs within the marrow cavities of bones

Bone Structure  Bones are considered organs b/c they are made up of many types of tissues: * mostly osseous tissue * nervous tissue in their nerves * cartilage in their articular cartilages * fibrous connective tissues lining cavities * muscle and epithelial in their blood vessels

Bone Structure Gross Anatomy of a Bone A. Bone Markings - Bulges, depressions, and holes that serve as:  Sites of attachment for muscles, ligaments, and tendons  Joint surfaces  Conduits for blood vessels and nerves  Named in different ways:

1. projections (bulges) - grow outward from the surface - those that are sites of muscle and ligament attachment include:  Tuberosity – rounded projection  Crest – narrow, prominent ridge of bone  Trochanter – large, blunt, irregular surface  Line – narrow ridge of bonee – sharp, projection  Process – any bony prominence  Tubercle – small rounded projection or process  Epichondyle – raised area on or above a condyle  Spine – sharp, slender, often pointed projection

- Projections that help to form joints include:  Head – bony expansion carried on a narrow neck  Facet – smooth, nearly flat articular surface  Condyle – rounded articular projection  Ramus – armlike bar of bone

2. Depressions and openings - serve as a passage for nerves and blood vessels - include the following:  meatus – canal like passageway  Sinus – cavity within a bone, filled with air and lined with mucous membrane  Fossa – shallow, basinlike depression in a bone, often serving as an articluar surface  Groove – furrow  Fissure – narrow, slitlike opening  Foramen – round or oval opening through a bone

Gross Anatomy cont…. B. Bone Textures 1. Compact bone – dense outer layer/ looks smooth and homogeneous 2. Spongy bone – composed of small, needlelike pieces of bone called trabeculae and lots of open space

C. Structure of a Long Bone  Long bones consist of a: - diaphysis - epiphysis  Diaphysis - Tubular shaft that forms the axis of long bones - Composed of compact bone that surrounds the medullary cavity - Yellow bone marrow (fat) is contained in the medullary cavity

 Epiphyses - expanded ends of long bones - exterior is compact bone, and the interior is spong bone - joint surface is covered with articular (hyaline) cartilage - e piphyseal line separates the diaphysis from the epiphyses

Structure of a Long Bone

D. Bone Membranes 1. Periosteum - double-layered protective membrane covering the diaphysis - outer fibrous layer is dense regular connective tissue - inner osteogenic layer is composed of osteoblasts and osteoclasts

-Richly supplied with nerve fibers, blood, and lymphatic vessels, which enter the bone via nutrient foramina - Secured to underlying bone by hundreds of connective tissue fibers called Sharpey’s fibers 2. Endosteum – delicate membrane covering internal surfaces of bone

E. Structure of Short, Irregular, and Flat Bones  Thin plates of periosteum-covered compact bone on the outside with endosteum-covered spongy bone (diploë) on the inside  Have no diaphysis or epiphyses  Contain bone marrow between the trabeculae

Microscopic Anatomy of a Bone  Four major cell types found in bone tissue: 1. osteogenic “osteoprogenitor cells” 2. osteoblasts: bone forming cells 3. osteocytes: mature bone cells 4. osteoclasts: large cells that reabsorb or break down bone matrix (Organic components of Bone)

 Inorganic Components of Bone Include: Hydroxyapatites, or mineral salts  Sixty-five percent of bone by mass  Mainly calcium phosphates  Responsible for bone hardness and its resistance to compression

Compact Bone Anatomy A. Osteon (Haversian System): structural unit of compact bone

Osteon Structure includes:  Lamella – weight-bearing, column-like matrix tubes composed mainly of collagen  Haversian, or central canal – central channel containing blood vessels and nerves  Volkmann’s canals – channels lying at right angles to the central canal, connecting blood and nerve supply of the periosteum to that of the Haversian canal

B. Osteocytes – mature bone c ells C. Lacunae – small cavities in bone that contain osteocytes D. Canaliculi – hairlike canals that connect lacunae to each other and the central canal