All our bones start out as cartilage soon to be replaced by bone

• High water content
• Contains no nerves or blood vessels
• Surrounded by the peri-chon-drium (dense irregular connective tissue) that resists outward expansion

• Perichondrium

• contains blood vessels = nutrient source = limits cartilage thickness

• Three types of skeletal cartilage – 

hyaline, elastic, and fibro-cartilage

• All have chondrocytes encased in lacunae in an extracellular matrix

Hyaline Cartilage

• Provides support, flexibility, and resilience
• Is the most abundant skeletal cartilage (oooh, good test question)
• Is present in these cartilages:

• Articular – covers the ends of long bones
• Costal – connects the ribs to the sternum
• Respiratory – makes up the larynx and reinforces air passages

• Nasal – supports the nose

Elastic Cartilage

• Similar to hyaline cartilage but contains elastic fibers
• Better able to withstand bending

• Found in the external ear and the epiglottis

Fibrocartilage

• Highly compressed with great tensile strength
• Contains collagen fibers
• Found in menisci of the knee and in intervertebral discs

• Axial skeleton 

• bones of the skull, vertebral column, and rib cage  (Axis, axel, axle)

• Appendicular skeleton

• bones of the upper and lower limbs, shoulder, and hip
• Locomotion and manipulation

• Femur, large (form follows function)

•  hollow tube = very strong for support

• Pisiform, wrist bone

• small, lots of joints = motion

• Long bones 

• longer than they are wide
  (e.g., humerus)
•  All limb bones (except the knee cap)
• And, not the little wrist bones like the pisiform
• Well, not the little ankle bones like the cuboid, either
• But, all the other limb bones are long bones.

• Short bones

• Cube-shaped bones of the wrist and ankle

• Bones that form within tendons (e.g., patella, knee cap, other sesamoid bones)

• Flat bones

• thin, flattened, and a bit curved (e.g., sternum, and most skull bones)

• Irregular bones

• bones with complicated shapes (e.g., vertebrae and hip bones)

Function of Bones

• Support – 
• Protection – 
• Movement – 
• Mineral storage – 
• Blood cell formation 

• 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

• Mineral storage

•  reservoir for minerals, especially calcium and phosphorus

• Blood cell formation

• hematopoiesis occurs within the marrow cavities of bones

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

Bone Markings: Projections –
Sites of Muscle and Ligament Attachment

• Tuberosity – 
• Crest – 
• Trochanter

• Line – 
• Tubercle – 
• Epicondyle
• Spine – 
• Process – 

• Tuberosity 

• rounded projection

• Crest

• narrow, prominent ridge of bone

• Trochanter 

• large, blunt, irregular surface

• Line

• narrow ridge of bone

• Tubercle

• small rounded projection

• Epicondyle

• raised area above a condyle

• Spine

• sharp, slender projection

• Process

• any bony prominence

• bony expansion carried on a narrow neck

• Facet (bone marking)

• mooth, nearly flat articular surface

• Condyle

• rounded articular projection

• Meatus 

• canal-like passageway

• Compact bone

• honeycomb of trabeculae filled with yellow bone marrow

Structure of Long Bones

•  consist of a diaphysis and an 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 spongy bone
• Joint surface is covered with articular (hyaline) cartilage
• Epiphyseal line separates the diaphysis from the epiphyses

• Periosteum (bone membrane)

• double-layered protective membrane

• Outer fibrous layer is dense irregular 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 Sharpey’s fibers

• Endosteum 

• – delicate membrane covering internal surfaces of bone

Structure of Short, Irregular, and Flat Bones

• Thin plates of periosteum-covered compact bone on the outside with endosteum-covered spongy bone on the inside -                                                     (endosteum-covered spongy bone = diploë)

• Have no diaphysis or epiphyses

• Contain bone marrow between the trabeculae
• -carpal, vertebra, sternum

Location of Hematopoietic Tissue (Red Marrow) in infants

• Found in the medullary cavity and all areas of spongy bone 

Location of Hematopoietic Tissue (Red Marrow) in adults

• Found in the diploë of flat bones, the head of the femur and humerus, in vertebra

Microscopic Structure of Bone: Compact Bone - 

• Haversian system, or osteon 

• the structural unit of compact bone

• weight-bearing, column-like matrix tubes composed mainly of collagen

• central channel containing blood vessels and nerves

• channels lying at right angles to the central canal, connecting blood and nerve supply of the periosteum to that of the Haversian canal

• Osteocytes

• hairlike canals that connect lacunae to each other and the central canal

Chemical Composition of Bone: Organic

• Osteoblasts – bone-forming cells
• Osteocytes – mature bone cells
• Osteoclasts – large cells that resorb or break down bone matrix

• Osteoid – unmineralized bone matrix composed of proteoglycans, glycoproteins, and collagen