Look Out Below: A Case Study on Bone Tissue Structure and Repair

One way bones are classified is by their shape. How would you classify the bones fractured by Mrs. Morgan?

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 vertebrae is an irregular bone

Define the following terms, used in the case and also in associated questions: a. hemorrhage b. fracture c. proximal d. diaphysis

*hemorrhage* - bleeding or the abnormal flow of blood. can be external like in this case or internal *fracture*- breaks in the continuity of a bone's structure *proximal*- point of attachment of a limb clostest to the the trunk *diaphysis* - narrow elongated center portion of a long bone: the shaft

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.

Bone deposition, mineral deposition or ossification are terms used to describe the process of adding new bones tissue to an injured or weak area. the cells that function in this process is the osteoblast. This bone secretes both type I collagen fibers and osteoid ground substances via exocytosis. the osteoid ground substance will become hardened (ossified) with the addition of calcium and phosphorus

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?

Bone or mineral resorption is the term used to describe dissolving away osseous tissue. the osteoclast (bone breaker) secrets substances by exocytosis that dissolve the bone matrix

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.

Collagen fibers, glycosaminoglycans and glycoproteins are organic while hydroxyapatite (crystallized calcium and phosphate ) makes up the most of the inorganic portion - Acid phosphates secreted by *osteoclast* target collagen fibers for destruction. The osteoclasts 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 others uses.

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.

Most of the vertebral body is made up of spongy bone. Spongy bone is made up of trabeculae (small bean) and 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

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?

The perforating and central canals house arteries and veins plus nerves in compact bone. Mrs. Morgan is hemorrhaging 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

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.

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

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.

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