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Chapter #6: Bones and Skeletal Tissues

Skeletal CartilagesFound in adults where flexible skeletal tissue is neededContains no blood vessels or nervesSurrounded by the perichondrium (dense irregular connective tissue) that resists outward expansionThree types hyaline, elastic, and fibrocartilage

Hyaline CartilageProvides support, flexibility, and resilienceOnly contains fine collagen fibersIs the most abundant skeletal cartilageIncludes these types:Articular covers the ends of long bonesCostal connects the ribs to the sternumRespiratory makes up larynx, reinforces air passagesNasal supports the nose

Elastic CartilageSimilar to hyaline cartilage, but contains elastic fibersFound in the external ear and the epiglottis

FibrocartilageHighly compressed with great tensile strengthFound where there is heavy pressure and stretchFound in menisci of the knee and in intervertebral discs

Growth of CartilageAppositional growth from outside - cells in the perichondrium secrete matrix against the external face of existing cartilageInterstitial growth from inside lacunae-bound chondrocytes inside the cartilage divide and secrete new matrix, expanding the cartilage from withinCalcification of cartilage occursDuring normal bone growthDuring old ageClassification of Bones206 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 ShapeLong 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 BonesSupport 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 StructureBones 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 StructureGross Anatomy of a Bone

A. Bone Markings - Bulges, depressions, and holes that serve as:Sites of attachment for muscles, ligaments, and tendonsJoint surfacesConduits 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 projectionCrest narrow, prominent ridge of boneTrochanter large, blunt, irregular surfaceLine narrow ridge of bonee sharp, projectionProcess any bony prominenceTubercle small rounded projection or process Epichondyle raised area on or above a condyleSpine sharp, slender, often pointed projection

Projections that help to form joints include:Head bony expansion carried on a narrow neckFacet smooth, nearly flat articular surfaceCondyle rounded articular projectionRamus armlike bar of bone 2. Depressions and openings - serve as a passage for nerves and blood vessels - include the following:meatus canal like passagewaySinus cavity within a bone, filled with air and lined with mucous membraneFossa shallow, basinlike depression in a bone, often serving as an articluar surfaceGroove furrowFissure narrow, slitlike openingForamen round or oval opening through a boneGross 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 BoneLong 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 Sharpeys fibers

2. Endosteum delicate membrane covering internal surfaces of bone

E. Structure of Short, Irregular, and Flat BonesThin plates of periosteum-covered compact bone on the outside with endosteum-covered spongy bone (diplo) on the insideHave no diaphysis or epiphysesContain bone marrow between the trabeculae

Microscopic Anatomy of a BoneFour 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 saltsSixty-five percent of bone by massMainly calcium phosphatesResponsible 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

Volkmanns 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 cellsC. Lacunae small cavities in bone that contain osteocytes

D. Canaliculi hairlike canals that connect lacunae to each other and the central canal