Chapter 6 Bones and Bone Tissue

BONE FUNCTIONS

• Shape: Bones give the body its structure.

• Support: The bones of the legs, pelvis, and spinal column support the body and hold it upright.

• Protection: Bones protect delicate internal organs.

• Movement: Movement of the arms and legs, as well as the ability to breathe, results from the interaction between muscles and bones.

• Electrolyte balance: Bones store and release minerals such as calcium and phosphorus.

• Blood production: Bones encase bone marrow, a major site of blood cell formation.

• Acid-base balance: Bone absorbs and releases alkaline salts to help maintain a stable pH.

• ​Long bones are longer than they are wide; they work like levers to move limbs. Examples include the femur of the thigh and the humerus of the arm.

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• Short bones are about as broad as they are long; they tend to be shaped like cubes. Examples include the carpal bones of the wrist and the tarsal bones of the ankle.

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• Flat bones are thin, flat, often curved bones; they protect organs (such as the bones of the skull, the ribs, and the sternum). Other flat bones (such as the scapulae) provide a large surface area for the attachment of muscles.

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• Irregular bones are often clustered in groups; they come in various sizes and shapes. Examples include the vertebrae and facial bones.

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• Sesamoid bones are small bones imbedded in tendons. The kneecap is an example of a sesamoid bone

• ​Diaphysis: Hollow cylinder made of compact bone; gives the bone strength

• Articular cartilage: Covers the epiphysis; eases the movement of the bone within a joint

• Medullary cavity: Central, hollow portion

• Endosteum: Epithelial membrane lining the medullary cavity

• Red bone marrow: Fills the medullary cavity in children; in adults, most marrow has turned to yellow marrow

• Periosteum: A dense, fibrous membrane covering the diaphysis; some of the fibers of the periosteum penetrate the bone, whereas other fibers weave together with the fibers of tendons to ensure a strong connection between muscle and bone; the periosteum contains bone-forming cells and blood vessels, making it crucial for bone survival

• Epiphyseal plate: The layer of cartilage separating the epiphysis from the diaphysis at the ends of a long bone in growing children (When growth stops, it is replaced with an epiphyseal line.)

Multiple Choice

Which of the following is not a function of bone

• Blood production

• Protection of internal organs

• Blood-glucose regulation

• Movement

Multiple Choice

A bone that is longer than it is wide such as the femur is classified as a....

• short bone

• long bone

• spongy bone

• flat bone

Multiple Choice

Which part of the long bone is made up of a hollow cavity surrounded by compact bone

• epiphysis

• diaphysis

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• Bone is called osseous tissue.

• Bone cells are osteoblasts, osteoclasts, and osteocytes. Osteocytes have a dual role: Some dissolve bone, whereas others deposit bone. This contributes to the maintenance of bone density whereas helping regulate blood levels of calcium and phosphorus.

• 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).

​Spongy, or cancellous, bone consists of a latticework of bone called trabeculae. 

• Trabeculae are arranged in a way that offers maximum strength. If the stress a bone is exposed to changes, the trabeculae will realign to compensate. The cavities between the trabeculae are filled with bone marrow.

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• Layers of matrix are arranged in concentric rings (called lamellae) around a central canal (called a haversian or osteonic canal). 

• This basic structural unit (consisting of the lamellae and haversian canal) is called an osteon. 

• Blood vessels and nerves run the length of the bone, through the center of the canal.

• Tiny gaps between rings of the lamellae, called lacunae, contain osteocytes. 

• Microscopic passageways, called canaliculi, connect the lamellae to each other.

Transverse passageways, called Volkmann’s canals, connect the haversian canals. These canals transport blood and nutrients from the bone’s exterior to the osteocytes locked inside.

Multiple Choice

What is the basic structural unit of bone

• osteon

• lacunae

• canaliculi

• ​Red bone marrow is charged with producing red blood cells. Nearly all of a child’s bones contain red bone marrow. In an adult, red bone marrow can only be found in the ribs, sternum, vertebrae, skull, pelvis, and the upper parts of the humerus (arm) and femur (thigh). All other bones contain yellow marrow. 

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• Yellow bone marrow replaces red marrow over time. The cells of yellow marrow are saturated with fat and no longer produce blood cells. In cases of severe, chronic blood loss or anemia, yellow marrow can change back into red marrow. 

Multiple Choice

Which person's body would have a higher percentage of red bone marrow?

• Child

• Adult

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• 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.

• 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. 

​Early in the life of a fetus, long bones are composed of cartilage; these cartilaginous bones serve as “models” for bone development.

1. 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.

2. Blood vessels penetrate the cartilage, and a primary ossification center develops in the middle of the diaphysis. 

3. 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. 

​link: http://resources.fadavis.com/thompson/animations/Bone%20Formation%20and%20Bone%20Growth.mp4

​Link:

http://resources.fadavis.com/thompson/animations/Fracture%20Healing.mp4

Multiple Choice

a fetus' first skeleton is composed primarily of

• epithelial tissue

• osseous tissue

• cartilage

• fibrous connective tissue