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 cellsC. Lacunae – small cavities in bone that

contain osteocytes

D. Canaliculi – hairlike canals that connect

lacunae to each other and the

central canal