Chapter 6: Osseous Tissue And Bone Structure

Chapter 6 Osseous Tissue and Bone Structure
1. classifications of bones by shape
(1) long bone
- long and thin
- arm and forearm, thigh (femur) and legs, palms, soles, fingers, toes

(2) flat bone
- thin with parallel surfaces
- skull, sternum, rib, scapulae

(3) sutural bone (Wormian bones)
- small, irregular bones
- between flat bones of the skull

(4) irregular bone
- complex shapes with short, flat, notched, or ridged surfaces
- spinal vertebrae, the bones of the pelvis, and several skull bones

(5) short bone
- small , thick and boxy
- tarsal (ankle), carpal (wrist)

(6) sesamoid bone
- small, flat, and shaped somewhat like a sesame seed
- develop inside the tendons; most commonly located near joints at the knees,
i. chondrocytes near the center of the shaft increase in size ii. matrix reduced to a series of struts that soon begin to calcify iii. enlarged chondrocytes die and disintegrate, leaving the cavities within the cartilage

II.i. blood vessels grow around the edges of the cartilage ii. cells of the perichondrium convert to osteoblasts iii. the shaft of the cartilage then becomes unsheathed in a superficial layer of bone

III. i. blood vessels penetrate the cartilage and invade the central region ii. fibroblasts migrating with the blood vessels differentiate into
i. remodeling; create a medullary cavity ii. osseous tissue of the shaft becomes thicker iii. the cartilage near each epiphysis is replaced by shafts of bone iv. further growth involves increases in length and diameter

V. capillaries and osteoblasts migrate into epiphysis, creating the secondary ossification centers

- intramembranous ossification (dermal ossification)
* produce dermal bones, e.g. mandible, clavicle
* 3 main steps
I. i.mesenchymal cells aggregate, differentiate into osteoblasts ii. begin ossification iii. bone expands as a series of spicules that spread into surrounding tissues

II. as the spicules interconnect, they trap blood vessels within the bone

III. i. bone assumes the structure of spongy bone ii. areas of spongy bone may later be removed, creating medullary cavity iii. through remodeling, spongy bone formed can be converted to compact bone.

5. lengthening of long bones
- occurs at specialized regions: epiphyseal plates
- contain epiphyseal cartilage that actively osteogenesis that increases the length of the region
- occurs from birth will early 20s at puberty, the combination of rising levels of sex hormones, growth hormone and thyroid hormone stimulates bone growth