Chapter 5 Bones

Functions of Endosteum

*Covers the trabeculae of spongy bones and inner surfaces of central canals. *Contains osteoprogentor cells. *Active during growth and whenever repair or remodeling is underway. *Usually one cell layer thick.

Functions of Periosteum

*Isolates and protects the bone from surrounding tissues. *It provides a route and a place for attachment for circulatory and nervous supply. *It actively participates in bone growth and repair. *It attaches the bone to the connective tissue network of the deep fascia.

Results of Intramembranous Ossification

*Lack Lamellae *External mesenchymal cells become periosteum *Periphery trabecular thicken into compact bone on both surfaces *Central trabecular remains distinct resulting in spongy bone.

Sinus or antrum

A chamber within a bone, normally filled with air.

Trochanter

A large, rough projection.

Line

A low ridge.

Sulcus

A narrow groove.

Neck

A narrower connection between the epiphysis and diaphysis.

Meatus or canal

A passageway through the substance of a bone.

Spine

A pointed process.

Crest

A prominent ridge.

Tuberosity

A rough projection.

Foramen

A rounded passageway for blood vessels and/or nerves.

Fossa

A shallow depression.

Facet

A small, flat articular surface.

Tubercle

A small, rounded projection.

Trochlea

A smooth, grooved articular process shaped like a pulley.

Condyle

A smooth, rounded articular process(bump).

Fibrous Cartilage

AKA: fibrocartilage. Contains little ground substance, may lack a perichondrium, and the matrix is dominated by collagen fibers. Fibrocartilaginous pads lie in areas of high stress, such as between the pubic bones of the pelvis and around or within a few joints and tendons. In these positions fibrous cartilage resists compression, absorbs shocks, and prevents damaging bone-to-bone contact.

Bone

AKA: osseous tissue. Roughly 1/3 of the matrix of bone consists of collagen fibers. The balance is a mixture of calcium salts, primarily calcium phosphate with lesser amounts of calcium carbonate. This combination gives bone truly remarkable properties. Collagen fibers are weaker, but relatively flexible. In bone, the minerals are organized around the collagen fibers. The result is a strong, somewhat flexible combination that is very resistant to shattering. Unlike cartilage, bone undergoes extensive remodeling on a regular basis and complete repairs can be made even after severe damage. Bones also respond to stress placed upon them, growing thicker & stronger with exercise and thin and brittle with inactivity.

Periosteum

Almost all bone surfaces are sheathed by a periosteum composed of a fibrous outer layer and a cellular inner layer. It is incomplete only at joints, where bones articulate. It assists in the attachment of a bone to surrounding tissues and to associated tendons and ligaments. The cellular layer functions in bone growth and participates in repairs after injury.

Fissure

An elongated cleft.

Ramus

An extension of a bone making an angle to the rest of the structure.

Process

Any projection or bump on bone.

Tendons

Are cords of dense regular connective tissue that attach skeletal muscles to bones and cartilage.

Epiphyseal closure

At maturity the rate of epiphyseal cartilage production slows and the rate of osteoblast activity accelerates. As a result, the epiphyseal cartilage gets narrower and narrower, until it ultimately disappears.

Intramembranous Ossification

Begins @ 8 wks. of embryonic development. 3 steps *Step 1: Mesenchymal tissue (cells that form conn. & muscular tissue) becomes highly vascularized, and the mesenchymal cells enlarge and differentiate into osteoblasts. Osteoblasts secrete osteoid and osteocytes appear. *Step 2: Bone grows outward from ossification center. It is an active process needing oxygen and nutrients supplied by blood vessels. As blood vessels branch within the matrix, bone growth accelerates. *Step 3: Multiple ossification centers form & the newly deposited bone assumes the structure of spongy bone. Continued deposition of bone by osteoblasts located close to blood vessels results in the formation of compact bone.

Ossification

Bone replacing existing tissue.

Heterotopic bones

Bones in abnormal locations.

Short bones

Bones that are boxlike in appearance. Their external surfaces are covered by compact bone, but the interior contains spongy bone. IE: carpal bones and tarsal bones.

Pneumatized bones

Bones that are hollow or contain numerous air pockets such as the ethmoid.

Long bones

Bones that are relatively long and slender. They have a diaphysis, two metaphyses, two epiphysis, and a medullary cavity. IE: humerus, radium, ulna, femur, tibia, and fibula.

Sesamoid bones

Bones that are usually small, round, and flat. They develop inside tendons and are most often encountered near joints at the knee, the hands, and feet. Few individuals have them at every possible location, but everyone has sesamoid patellae.

Irregular bones

Bones that have complex shapes with short, flat, notched, or ridged surfaces. Their internal structure is equally varied. IE: The vertebrae that form the spinal column and several bones in the skull.

Flat bones

Bones that have thin, roughly parallel surfaces of compact bone. Resembles a spongy sandwich. Such bones are strong but relatively light. They provide protection for underlying tissues and offer an extensive surface area for the attachment of skeletal muscles. IE: roof of the skull, the sternum, ribs, and scapulae.

Chondrocytes

Cartilage Cells

Perichondrium

Cartilage is usually set apart from surrounding tissues by a fibrous perichondrium. The perichondrium contains two distinct layers: an outer, fibrous layer of dense irregular connective tissue and an inner, cellular layer.

Osteoblasts

Cells that are cuboidal in shape and found on the inner or outer surfaces of the bone. These cells secrete the organic components of the bone matrix. This matter is called osteoid, it later becomes mineralized through an unknown mechanism. Osteoblasts are responsible for the the production of new bone, a process called osteogenesis.

Canaliculi

Channels that radiate through the matrix from lacuna to lacuna and toward free surfaces and adjacent blood vessels. They contain fine cytoplasmic processes and ground substance, and interconnect the osteocytes situated in adjacent lacunae. Tight junctions interconnect these processes and provide a route for the diffusion of nutrients and waste products form one osteocyte to another across gap junctions.

Aponeuroses

Collagenous sheets or ribbons that resemble flat, broad tendons.

What are the two types of osseous tissue

Compact bone and spongy bone

Elastic Tissue

Contains large # of elastic fibers which gives the tissue have a springy, resilient nature. This gives it the ability to stretch and rebound and allows it to tolerate cycles of expansion and contraction. They often underly transitional epithelia and is also found in the walls of blood vessels and surrounding the respiratory passageways.

Elastic Cartilage

Contains numerous elastic fibers that make it extremely resilient and flexible. Among other structures, elastic cartilage forms the: *external flap(auricle or pinna) of the external ear *epiglottis *the airway to the middle ear (auditory tube) *small cartilages of the larynx (cuneiform)

Canaliculi

Form a branching network for the exchange of materials between the blood vessels and the osteocytes. Long slender passages in the matrix.

Dense Irregular Connective Tissue

Form an interwoven meshwork & do not show and consistent pattern. Provides strength & support to areas subjected to stress form many directions. The Dermis is a layer of dense irregular tissue that gives skin its strength.

Lamellae

Matrix layers of calcium matrix in which the lacunae are sandwiched between.

Osteocytes

Mature bone cells. They maintain and monitor the protein and mineral content of the surrounding matrix. Each osteocyte directs both the release of calcium from bone to blood and the deposition of calcium salts in the surrounding matrix.

Hyaline Cartilage

Most common type of cartilage. It is tough but somewhat flexible, this is the weakest type of cartilage. Examples of this type in adult body: *connections between ribs and sternum *the supporting cartilages along the conducting passageways of the respiratory tract *the articular cartilages covering opposing bone surfaces within the synovial joints, such as elbow or knee

Ligaments

Resemble tendons, but they connect bone to bone. They contain significant #'s of elastic fibers as well as collagen fibers, and they can tolerate a modest amount of stretching.

Lacunae

Small chambers in which chondrocytes live.

Perforating fibers or Sharpey's fibers

The collagen fibers incorporated into bone tissue from tendons and from the superficial periosteum.

Head

The expanded articular end of an epiphysis, often separated from the shaft by a narrower neck.

Ossification Center

The location in a bone where the ossification begins.

Calcification

The process of depositing calcium salts into tissues.

Osteogenesis

The process that produces new bone.

Diaphysis

The shaft of the bone.

Lacunae

The small chambers that the osteocytes occupy. They are sandwiched between layers of calcified matrix.(lamellae)

Epiphysis

The two ends of the bone.

When does bone growth occur?

When osteoblasts are creating more bone matrix than osteoclasts are removing.

Lacunae

Within the matrix contain bone cells, or osteocytes. The lacunae are often organized around blood vessels that branch through the bony matrix.

Osseous tissue

contains specialized cells and an extracellular matrix consisting of protein fibers and a ground substance. The matrix of bone tissue is solid and sturdy due to the deposition of calcium salts around the protein fibers. It is usually separated from surrounding tissues by a fibrous periosteum. When they surround another tissue, the inner bony surfaces are lined by a cellular endosteum.