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Clinical Case Study
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:
fracture of the left humerus at the proximal diaphysis,
depressed fracture of the occipital bone,
fracture of the 3rd lumbar vertebral body.
Short Answer Questions
1.) Define the following terms, used in the case and also in associated questions:
hemorrhage
fracture
proximal
diaphysis
2.) One way bones are classified is by their shape. How would you classify the bones fractured by Mrs. Morgan?
The body of
3). 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
Explanation / Answer
1.
1 a..Haemorrhage: Bleeding or the abnormal flow of blood. Can be external like in this case or internal
b. Fracture: break in the continuity of a bone’s structure
c. Proximal: a point of attachment of a limb closets to the trunk
d. Diaphysis: narrow elongated centre portion of a long bone; the shaft
2.
Flat, long, short, and irregular are the classifications of bones based on their shape. Mrs. Morgan’s humerus is a long bone, the occipital bone is flat, and vertebra is an irregular bone.
3.
Most of the vertebral body is made up of spongy bone. The spongy bone is made up of trabeculae (small beam) that have an open arrangement of osseous tissue, which helps decrease the weight of bone. Additionally, spongy bone trabeculae align along stress lines to prevent breakage.
4.
The diaphysis of a long bone is made up almost entirely by compact bone. Compact bone is made up of lamella (layers) that are named according to their shape or position within compact bone.
• Concentric lamellae = circular shape; form the osteon
• Interstitial lamellae = located in between the osteons
• Circumferential lamellae = located at the outer/inner surfaces of compact bone
5.
The perforating and central canals house arteries and veins plus nerves in compact bone. Mrs. Morgan is haemorrhaging as a result of her bones breaking. When bones break the jagged ends of the bones can pierce the blood vessels within the bone causing uncontrolled bleeding. Additionally the soft tissue (muscle, skin) surrounding the bone can be damaged resulting in further blood loss.
6.
Collagen fibers are found in high abundance in the fibrocartilage tissue matrix.
Fibroblasts = produce collagen fibers that bridge the gaps between fracture ends
Chondroblasts = secrete cartilage matrix
7.
Bone deposition, mineral deposition, or ossification are terms used to describe the process of adding new bone tissue to an injured or weak area. The cell that functions in this process is the osteoblast. This bone cell secretes both type I collagen fibers and osteoid ground substance via exocytosis. The osteoid ground substance will become hardened (ossified) with the addition of calcium and phosphorous.
8. Bone or mineral resorbtion is the term used to describe dissolving away osseous tissue. The osteoclast (bone breaker) secretes substances by exocytosis that dissolve the bone matrix.
9.
Collagen fibers, glycosaminoglycan, and glycoproteins are organic while hydroxyapatite (crystallized calcium and phosphate) makes up most of the inorganic portion.
Acid phosphates secreted by the osteoclast target the collagen fibers for destruction. The osteoclast has hydrogen pumps present in high numbers on the ruffled border. As hydrogen ions are pumped out they combine with chloride ions forming hydrochloric acid (HCl). The acid acts directly on hydroxyapatite to liberate calcium. Additionally HCL increases the solubility of calcium so it can be transferred back into the blood for other uses.
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