Look Out Below: A Case Study on Bone Tissue Structure and Repair
Mrs. Debbie Morgan is a 45-year-old female who works as a stocking clerk for a local home improvement store. While she was at work today a large box of metal rivets fell from a 20-ft.- high overhead shelf, striking her outstretched arm and knocking her to the ground. The ambulance personnel reported that she had lost quite a bit of blood at the accident scene and was “knocked out” when they arrived. To minimize further hemorrhage, the paramedics applied a pressure bandage to her arm.
You meet the paramedics as they bring Mrs. Morgan into the emergency room and begin to assess her for injuries. She is awake and alert, but complaining of severe left arm and back pain, plus she has a “killer headache.” To fully examine her injuries you remove four blood-soaked bandages from her arm. You notice a large open wound on her arm with what appears to be bone tissue sticking out of the skin. She also has bruises covering her left shoulder, left wrist, and lower back. To determine the extent of her injuries Mrs. Morgan undergoes several x-rays, which reveal the following:
1) fracture of the left humerus at the proximal diaphysis,
2) depressed fracture of the occipital bone,
3) fracture of the 3rd lumbar vertebral body.
Short Answer Questions
1. Define the following terms, used in the case and also in associated questions: a. hemorrhage
b. fracture c. proximal d. diaphysis
2. One way bones are classified is by their shape. How would you classify the bones fractured by Mrs. Morgan?
3. The body of Mrs. Morgan’s vertebra is fractured. What type of bone tissue makes up the majority of the vertebral body? Describe the structure and function of this type of bone.
4. The diaphysis of Mrs. Morgan’s humerus is fractured. What type of bone makes up the majority of the diaphysis of long bones like the humerus? Describe the layers of bone tissue found here.
5. Most connective tissue, including bone, is highly vascular. Which anatomical structures in Mrs. Morgan’s compact bone house blood vessels? What sign or symptom in Mrs. Morgan’s case is directly related to disruption of these structures by her bone fractures? How is the sign or symptom related to these anatomical structures?
6. Within days after a fracture, a “soft callus” of fibrocartilage forms. What fibers are found in this type of cartilage? Identify the cells required for fibrocartilaginous callus formation and list their functions.
7. As a fracture is repaired, new bone is added to the injury site. What term is used to describe the addition of new bone tissue? Identify which bone cell is responsible for this process and explain how it occurs.
8. In the final stage of bone repair, some of the osseous tissue must be broken down and removed. What term is used to define the breaking down of osseous tissue? Which bone cell would be best suited for this task?
9. The extracellular matrix (ECM) of bone is considered to be a composite material made up of organic and inorganic matter. What makes up the organic and inorganic portions of the matrix? Describe the cellular mechanism involved in breaking down this matrix; include the bone cell required for the process.
10.
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hemorrhage: bleeding, the escape of blood from a ruptured blood vessel
fracture: a break or crack in a bone
proximal: nearer to the center of the body or point of attachment
diaphysis: the shaft or main part of a long bone
2. The bones fractured by Mrs. Morgan can be classified as long bones.
3. The majority of the vertebral body is made up of cancellous or spongy bone tissue. This type of bone has a porous structure with trabeculae that provide support and strength. It is also involved in the production of red blood cells through hematopoiesis.
4. The majority of the diaphysis of long bones like the humerus is made up of compact bone tissue. Compact bone has a dense and solid structure that provides strength and support. It consists of layers called lamellae, which are composed of osteons or Haversian systems. Each osteon contains concentric rings of calcified matrix and osteocytes housed in lacunae.
5. Blood vessels in compact bone are housed within the Haversian canals and Volkmann's canals. Disruption of these structures by Mrs. Morgan's bone fractures may lead to a decrease in blood supply to the affected areas, causing ischemia or tissue damage. This can result in symptoms such as severe pain and tissue necrosis.
6. Fibrocartilage contains collagen fibers. The cells involved in fibrocartilaginous callus formation are fibroblasts, which produce the collagen fibers, and chondroblasts, which produce the ground substance of the cartilage. The fibrocartilaginous callus serves as a temporary structure that stabilizes the fracture site and provides a framework for new bone formation.
7. The addition of new bone tissue is called bone deposition or ossification. The bone cell responsible for this process is the osteoblast. Osteoblasts secrete organic matrix, which is then mineralized with calcium salts to form new bone tissue.
8. The breaking down of osseous tissue is called bone resorption. The bone cell best suited for this task is the osteoclast. Osteoclasts are large, multinucleated cells that secrete acid and enzymes to dissolve the mineralized matrix of bone, allowing for its breakdown and removal.
9. The organic portion of the extracellular matrix (ECM) of bone is composed mainly of collagen fibers produced by osteoblasts. The inorganic portion is made up of hydroxyapatite crystals, which consist of calcium and phosphate ions. The cellular mechanism involved in breaking down the matrix is referred to as bone remodeling. Osteoclasts are responsible for breaking down the matrix through bone resorption, releasing calcium and phosphate ions into the bloodstream.
10. The remodeling of bone tissue involves a balance between bone deposition and bone resorption. This process is controlled by specialized cells called osteoblasts and osteoclasts. Osteoblasts synthesize and deposit new bone matrix, while osteoclasts break down and remove old or damaged bone tissue. This continuous cycle allows for the adaptation and repair of bone tissue.
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