A hollow medullary cavity filled with yellow marrow runs the length of the diaphysis of a long bone. The walls of the diaphysis are compact bone. The epiphyses, which are wider sections at each end of a long bone, are filled with spongy bone and red marrow. The epiphyseal plate, a layer of hyaline cartilage, is replaced by osseous tissue as the organ grows in length. The medullary cavity has a delicate membranous lining called the endosteum. The outer surface of bone, except in regions covered with articular cartilage, is covered with a fibrous membrane called the periosteum. Flat bones consist of two layers of compact bone surrounding a layer of spongy bone. Bone markings depend on the function and location of bones. Articulations are places where two bones meet. Projections stick out from the surface of the bone and provide attachment points for tendons and ligaments. Holes are openings or depressions in the bones.
Bone matrix consists of collagen fibers and organic ground substance, primarily hydroxyapatite formed from calcium salts. Osteogenic cells develop into osteoblasts. Osteoblasts are cells that make new bone. They become osteocytes, the cells of mature bone, when they get trapped in the matrix. Osteoclasts engage in bone resorption. Compact bone is dense and composed of osteons, while spongy bone is less dense and made up of trabeculae. Blood vessels and nerves enter the bone through the nutrient foramina to nourish and innervate bones.
articular cartilage
thin layer of cartilage covering an epiphysis; reduces friction and acts as a shock absorber
articulation
where two bone surfaces meet
canaliculi
(singular = canaliculus) channels within the bone matrix that house one of an osteocyte’s many cytoplasmic extensions that it uses to communicate and receive nutrients
central canal
longitudinal channel in the center of each osteon; contains blood vessels, nerves, and lymphatic vessels; also known as the Haversian canal
compact bone
dense osseous tissue that can withstand compressive forces
diaphysis
tubular shaft that runs between the proximal and distal ends of a long bone
diploë
layer of spongy bone, that is sandwiched between two the layers of compact bone found in flat bones
endosteum
delicate membranous lining of a bone’s medullary cavity
epiphyseal plate
(also, growth plate) sheet of hyaline cartilage in the metaphysis of an immature bone; replaced by bone tissue as the organ grows in length
epiphysis
wide section at each end of a long bone; filled with spongy bone and red marrow
hole
opening or depression in a bone
lacunae
(singular = lacuna) spaces in a bone that house an osteocyte
medullary cavity
hollow region of the diaphysis; filled with yellow marrow
nutrient foramen
small opening in the middle of the external surface of the diaphysis, through which an artery enters the bone to provide nourishment
osteoblast
cell responsible for forming new bone
osteoclast
cell responsible for resorbing bone
osteocyte
primary cell in mature bone; responsible for maintaining the matrix
osteogenic cell
undifferentiated cell with high mitotic activity; the only bone cells that divide; they differentiate and develop into osteoblasts
osteon
(also, Haversian system) basic structural unit of compact bone; made of concentric layers of calcified matrix
perforating canal
(also, Volkmann’s canal) channel that branches off from the central canal and houses vessels and nerves that extend to the periosteum and endosteum
periosteum
fibrous membrane covering the outer surface of bone and continuous with ligaments
projection
bone markings where part of the surface sticks out above the rest of the surface, where tendons and ligaments attach
spongy bone
(also, cancellous bone) trabeculated osseous tissue that supports shifts in weight distribution
trabeculae
(singular = trabecula) spikes or sections of the lattice-like matrix in spongy bone
1. Which of the following occurs in the spongy bone of the epiphysis?
A) bone growth
B) bone remodeling
C) hematopoiesis
D) shock absorption
C
2. The diaphysis contains ________.
A) the metaphysis
B) fat stores
C) spongy bone
D) compact bone
B
3. The fibrous membrane covering the outer surface of the bone is the ________.
A) periosteum
B) epiphysis
C) endosteum
D) diaphysis
A
4. Which of the following are incapable of undergoing mitosis?
A) osteoblasts and osteoclasts
B) osteocytes and osteoclasts
C) osteoblasts and osteocytes
D) osteogenic cells and osteoclasts
C
5. Which cells do not originate from osteogenic cells?
A) osteoblasts
B) osteoclasts
C) osteocytes
B
6. Which of the following are found in both compact bone and cancellous bone?
A) Haversian systems or osteons
B) Haversian canals
C) Volkmann’s canals
D) lacunae
D
7. Which of the following are only found in cancellous bone?
A) canaliculi
B) Volkmann’s canals
C) trabeculae
D) calcium salts
C
8. The area of a bone where the nutrient foramen passes forms what kind of bone marking?
A) a hole
B) a facet
C) a canal
D) a fissure
A
1. If the articular cartilage at the end of one of your long bones were to degenerate, what symptoms do you think you would experience? Why?
If the articular cartilage at the end of one of your long bones were to deteriorate, which is actually what happens in osteoarthritis, you would experience joint pain at the end of that bone and limitation of motion at that joint because there would be no cartilage to reduce friction between adjacent bones and there would be no cartilage to act as a shock absorber.
2. In what ways is the structural makeup of compact and spongy bone well suited to their respective functions?
The densely packed concentric rings of matrix in compact bone are ideal for resisting compressive forces, which is the function of compact bone. The open spaces of the trabeculated network of spongy bone allow spongy bone to support shifts in weight distribution, which is the function of spongy bone.