Bones and Bone Tissue

Bone Functions Shape Support Protection Movement Electrolyte balance Blood production Acid-base balance

Classification of Bones Flat bones Irregular bones Long bones Short bones

Classification of Bones Long bones Short bones Flat bones Irregular bones Sesamoid bones

Parts of a Long Bone Diaphysis Epiphysis Articular cartilage Medullary cavity Endosteum Bone marrow Periosteum Diaphysis Articular cartilage Medullary cavity Endosteum Red bone marrow Yellow marrow Periosteum Epiphyseal plate

Question Which of the following are functions of bone? Choose all that apply. A. Electrolyte balance B. Blood production C. Acid-base balance D. Regulation of blood glucose

Bone Tissue Osteoblasts: Osteoblasts: Help form bone Osteoclasts: Osteoclasts: Dissolve unwanted bone Osteocytes: Osteocytes: Are mature osteoblasts embedded in hardened bone matrix

Bone Tissue Bone is called osseous tissue. Bone cells are osteoblasts, osteoclasts, and osteocytes. Bone matrix consists of collagen fibers and crystalline salts (primarily calcium and phosphate); the matrix of bone is hard and calcified. Bone has a strength rivaling that of steel and reinforced concrete. Collagen fibers in the matrix make bone highly resistant to stretching forces (tensile strength); calcium salts allow bones to resist strong squeezing forces (compressional strength); bone cannot endure much twisting (torsional strength).

Types of Bone Tissue Compact bone Compact bone Forms shafts of long bones and surfaces of other bones Compact bone is dense and solid. Spongy (cancellous) bone Spongy (cancellous) bone Found in ends of long bones and middle of other bones Spongy bone is always surrounded by compact bone.

Spongy Bone Trabeculae Spongy, or cancellous, bone consists of a latticework of bone called trabeculae. Trabeculae are arranged in a way that offers maximum strength.

Compact Bone Osteon Haversian canal Lamellae Volkmann’s canal Canaliculi Lacunae

Compact Bone Lamellae Haversian or osteonic canal Osteon Lacunae Canaliculi Volkmann’s canals

Question What is the basic structural unit of bone? A. Osteon B. Lacunae C. Canaliculi D. Osteocyte

Bone Marrow Bone marrow is a type of soft tissue that fills the medullary cavity of long bones and the spaces of spongy bone. Red marrow: Red marrow: Produces red blood cells Yellow marrow: Yellow marrow: Saturated with fat

Bone Development Intramembranous ossification Endochondral ossification

Bone Development The bones of skull and face start out as connective tissue. Then groups of stem cells in the tissue differentiate into osteoblasts. Clusters of osteoblasts (called centers for ossification) deposit matrix material and collagen. Eventually, calcium salts are deposited and the bones are calcified. This is called intramembranous ossification.

Bone Development Most bones evolve from cartilage: After about 3 months’ gestation, the fetus has a skeleton composed mostly of cartilage. At that time, the cartilage begins to turn into bone. This process, which begins in long bones, is called endochondral ossification.

Endochondral Ossification

1.Early in the life of a fetus, long bones are composed of cartilage; these cartilaginous bones serve as “models” for bone development. 2.Osteoblasts start to replace the chondrocytes (cartilage cells), coating the diaphysis in a thin layer of bone. They then produce a ring of bone that encircles the diaphysis. Soon, the cartilage begins to calcify. 3.Blood vessels penetrate the cartilage, and a primary ossification center develops in the middle of the diaphysis. 4.The bone marrow cavity fills with blood and stem cells. Ossification continues—proceeding from the diaphysis toward each epiphysis—and the bone grows in length. Eventually, secondary ossification centers appear in the epiphyses.

Bone Growth Bone lengthening occurs at the epiphyseal plate for a fixed period. Bone widening continues throughout the life span. View animation on “Bone formation and bone growth”

Fracture Repair 1. Initial hematoma transforms into granulation tissue. 2. Granulation tissue transforms into a soft callus. 3. A hard callus forms around the fracture. 4. Remodeling replaces the callus tissue with bone. View animation on “Fracture healing”

Question A fetus’ first skeleton is composed primarily of: A. epithelial tissue. B. osseous tissue. C. cartilage. D. fibrous connective tissue.