Long Bone:  A long bone is one that is cylindrical in shape, being longer than it is wide.  Shape of a bone, not its size.  Long bones are found in: Arms (humerus, ulna, radius) & fingers (metacarpals, phalanges) and also Legs (femur, tibia, fibula), and toes (metatarsals, phalanges).  Long bones function as levers; they move when muscles contracts.  Structure of a Long Bone: • Diaphysis: Shaft & Composed of compact bone • Epiphysis: Ends of the bone & Composed mostly of spongy bone • Periosteum: Outside covering of the diaphysis & Fibrous connective tissue membrane • Endosteum: inner layer of bone • Arteries: Supply bone cells with nutrients • Articular cartilage: Covers the external surface of the epiphyses • Made of hyaline cartilage • Medullary cavity: Cavity of the shaft • Contains yellow marrow (mostly fat) • Contains red marrow (for blood cell formation)  Growth and Ossification of long bones:  Endochondral ossification: • It is the process of bone development from hyaline cartilage. • All of the bones of the body including long bones (except for the flat bones) are formed through endochondral ossification • Endochondral ossification begins with points in the cartilage called “primary ossification centers.” • They mostly appear during fetal development • These cartilage points are responsible for the formation of the diaphyses of long bones. • Secondary ossification occurs after birth and forms the epiphyses of long bones • The diaphysis and both epiphyses of a long bone are separated by a growing zone of cartilage (the epiphyseal plate). • When the child reaches skeletal maturity (18 to 25 years of age), all cartilage is replaced by bone, fusing the diaphysis and both epiphyses together (epiphyseal closure).  Bone Cells: Bones are made of four main kinds of cells: 1. Osteoblasts 2. Osteocytes 3. Osteoclasts 4. Lining cells. • Osteoblasts: are responsible for making new bone • Osteocytes: Mature bone cells are called osteocytes • Osteoclasts: Bone-destroying cells • Lining cells: These cover the outside surface of all bones and are also formed from Osteoblasts.

1. Long Bone:
 A long bone is one that is cylindrical in shape, being longer than it is
wide.
 Shape of a bone, not its size.
 Long bones are found in: Arms (humerus, ulna, radius) & fingers
(metacarpals, phalanges) and also Legs (femur, tibia, fibula), and
toes (metatarsals, phalanges).
 Long bones function as levers; they move when muscles contracts.
 Structure of a Long Bone:
• Diaphysis: Shaft & Composed of compact bone
• Epiphysis: Ends of the bone & Composed mostly of spongy bone
• Periosteum: Outside covering of the diaphysis & Fibrous connective
tissue membrane
• Endosteum: inner layer of bone
• Arteries: Supply bone cells with nutrients
• Articular cartilage: Covers the external surface of the epiphyses
• Made of hyaline cartilage
• Medullary cavity: Cavity of the shaft
• Contains yellow marrow (mostly fat)
• Contains red marrow (for blood cell formation)

2.  Growth and Ossification of long bones:
 Endochondral ossification:
• It is the process of bone development from hyaline cartilage.
• All of the bones of the body including long bones (except for the flat
bones) are formed through endochondral ossification
• Endochondral ossification begins with points in the cartilage called
“primary ossification centers.”
• They mostly appear during fetal development

3. • These cartilage points are responsible for the formation of the
diaphyses of long bones.
• Secondary ossification occurs after birth and forms the epiphyses
of long bones
• The diaphysis and both epiphyses of a long bone are separated by a
growing zone of cartilage (the epiphyseal plate).
• When the child reaches skeletal maturity (18 to 25 years of age), all
cartilage is replaced by bone, fusing the diaphysis and both
epiphyses together (epiphyseal closure).
 Bone Cells: Bones are made of four main kinds of cells:
1. Osteoblasts
2. Osteocytes
3. Osteoclasts
4. Lining cells.
• Osteoblasts: are responsible for making new bone
• Osteocytes: Mature bone cells are called osteocytes
• Osteoclasts: Bone-destroying cells
• Lining cells: These cover the outside surface of all bones and are
also formed from Osteoblasts.