Part B Bone Structure

Bones Bones are organs!Bones are organs! –Contains various types of tissues Osseous tissue (dominates) Nervous tissue Cartilage Fibrous connective tissue (lining cavities) Muscle and epithelial tissues in blood vessels

Bones We will look at bone structure on three levels Gross Microscopic Chemical

Gross Anatomy Bone Markings, Bone Textures, Bone Structures

Bone Markings Surface features of bones –Sites for attachments for muscles, tendons and ligaments –Joint surfaces –Passages for nerves and blood vessels

Bone Markings Categories of bone markings –Projections Bulges that grow outward from the bone surface –Depressions and openings Indentations, holes, and cavities

Projections That Are Sites of Muscle and Ligament Attachment 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

Projections That help to Form Joints Head – bony expansion carried on a narrow neck Facet – smooth, nearly flat articular surface Condyle – rounded articular projection Ramus – armlike bar of bone

Depressions and Openings Allowing Blood Vessels & Nerves to Pass Meatus – canal-like passageway Sinus – cavity within a bone Fossa – shallow, basinlike depression Groove – furrow Fissure – narrow, slitlike opening Foramen – round or oval opening through a bone

Bone Textures Compact bone – dense outer layer –Looks solid to the eye Spongy bone – honeycomb or spongy appearance –Has small needle-like or flat pieces called trabeculae filled with red or yellow bone marrow

Structure of Long Bone General structure of Long Bones –Diaphysis –Epiphyses –Membranes

Structure of Long Bone Diaphysis –Shaft constructed of a thick collar of compact bone that surrounds the medullary cavity

Structure of Long Bone Medullary Cavity –Cavity of the shaft –Contains yellow marrow (mostly fat) in adults –Contains red marrow (for blood cell formation) in infants

Structure of Long Bone Epiphyses –Expanded ends of long bones –Exterior is compact bone, interior is spongy bone –Joint surface is covered with articular cartilage –Epiphyseal line separates the diaphysis from the epiphyses

Structure of Long Bone Articular cartilage –Covers the external surface of the epiphyses –Made of hyaline cartilage –Decreases friction at joint surfaces

Structure of Long Bone Epiphyseal Line –Remnant of epiphyseal plate Disc of hyaline cartilage that grows during childhood to lengthen the bone

Structure of Long Bone Membranes of long bones –Periosteum –Endosteum

Structure of Long Bone Periosteum –Outside covering of the bone Except joint surfaces –Glistening white, double- layered membrane

Structure of Long Bone Periosteum –Outer Fibrous layer is dense connective tissue –Inner osteogenic layer (next to bone surface) is mostly osteoblasts (bone germinators) and osteoclasts (bone breakers)

Structure of Long Bone Periosteum –Richly supplied with nerve fibers, lymphatic vessels, blood vessels which enter the diaphysis by a nutrient foramen (opening)

Structure of Long Bone Sharpey’s fibers –Secures periosteum to underlying bone –Made of collagen fibers –Extends into bone matrix

Structure of Long Bone Arteries –Supplies bone cells with nutrients

Structure of Long Bone Endosteum –Delicate connective tissue –Contains osteoblasts & osteoclasts

Structure of Long Bone Endosteum –Covers internal surfaces of bone Medullary cavity Trabeculae (spongy) Canals through compact bone

Structure of Long Bone Figure 6.3

Structure of Short, Irregular, and Flat Bones

Thin plates of periosteum-covered compact bone on the outside with endosteum-covered diploë on the inside Spongy bone in flat bone is called diploë

Structure of Short, Irregular, and Flat Bones Have no diaphysis or epiphyses Contain bone marrow between the trabeculae

Hematopoietic Tissue

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, and the head of the femur and humerus –Remember, the diploë is the spongy bone of flat bones

Yellow marrow is found in the medullary cavities Yellow marrow can revert back to red marrow if a person becomes very anemic and needs enhanced red blood cell production

Microscopic Anatomy

Microscopic Structure of Compact Bone Haversian system, or osteon –the structural unit of compact bone

Microscopic Structure of Compact Bone Each osteon is a group of hollow tubes of bone matrix, called lamella, each one placed outside the next

Microscopic Structure of Compact Bone Each osteon is oriented parallel to the long axis of the bone

Microscopic Structure of Compact Bone Osteons are like tiny weight- bearing pillars

Microscopic Structure of Compact Bone Lamella –The weight- bearing, column—like matrix tubes composed mainly of collagen

Microscopic Structure of Compact Bone Haversian, or central canal –channel in the center of the osteon –containing blood vessels and nerves

Microscopic Structure of Compact Bone Volkmann’s canals –channels lying at right angles to the central canal, connecting blood and nerve supply of the periosteum to that of the central canal

Microscopic Structure of Bone: Compact Bone Osteocytes –Mature bone cells –Spider-shaped Lacunae –small cavities in bone that contain osteocytes

Microscopic Structure of Bone: Compact Bone Canaliculi –Tiny, hair-like canals –connect lacunae to each other and the central canal –Forms a transport system

Microscopic Structure of Compact Bone Figure 6.6a, b

Organic components and inorganic components

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

Chemical Composition of Bone: Inorganic Hydroxyapatites, or mineral salts –Sixty-five percent of bone by mass –Mainly calcium phosphates –Responsible for bone hardness and its resistance to compression

Chemical Composition of Bone: Inorganic Hydroxyapatites, or mineral salts –Bone is half as strong as steel in resisting compression and fully as strong as steel in resisting tension –Bones last long after death, sometimes many centuries

Paris catacombs

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