Question 3 (20 pts) This question is in part based on your Reading \"Bone Biolog

ID: 282477 • Letter: Q

Question

Question 3 (20 pts) This question is in part based on your Reading "Bone Biology" As an anatomist and histologist, I get annoyed by the use of skull-and- crossbones to indicate death or great danger. Bones are not dead quite the contrary, they are alive and constantly changing. Please (I) name the main cell types found in bony tissue and briefly explain the function of each. (II) Why do we have cells that break down bones even while we are building new bone? (III) What are the key differences between bone produced by endochondral ossification and that produced by intramembranous ossification? (IV) Summarize in a few sentences the key findings of the article on Bone Biology you just read. You are welcome to use outside resources while answering this question -just avoid any suspicion of plagiarism!

Explanation / Answer

The statement provided in the question that the bones are not dead as bony tissue is a living tissue, it is innervated by blood vessels and the cells in that are living and are constantly being replaced.

Ques I: Cell types in bone tissue and their function

Answer: There are four types of cells present in bone tissue:

1. Osteogenic cells:

These are the undifferentiated cells and are only ones, of the four cells found in bony tissue, which are capable of mitosis. They are located in the deepest part of the outer layer of bones (periosteum) and their function is to develop into osteoblasts.

2. Osteoblasts

The cells are aimed at bone formation. These are present in the growing region of the bone. They produce and release the proteinaceous collagen, which forms the bone matrix and the calcium salts, which are responsible for bone mineralization. Some of these cells get engulfed inside the bone and function as osteocytes while others remain on the surface. Those on the surface of the newly formed bone are slightly flattened and are responsible for bone maintenance. These surface lining cells are also known as Bone lining cells. So, they are involved in bone formation and repair.

3. Oseteocytes:

These are the most abundant of cells found in bone. These are present in bone matrix and have cytoplasmic extensions through which they are in reachable limits with osteoblasts and other osteocytes. These cytoplasmic extensions form channels known as canaliculi. Their function is to maintain the calcium and phosphate concentration in the matrix.

Osteoclasts:

These are large cells containing multiple nucleus are responsible for breakdown of bone. These are not derived from osteogenic cells but from white blood cells. These are present on the surface of bone in specialized spaces called Howship's lacunae. These cells are capable of phagocytosis and release enzymes which can dissolve the mineralized part of the bone and hence provide calcium in blood stream. These are involved in maintaining blood calcium levels and reshaping of bones along with osteoblasts.

Ques 2 Why do we have cells that breakdown bone even while we are building new bone?

Answer: The two cells involved in bone breakdown and bone formation are Osteoclasts and Osteoblasts respectively. Both these processes are going on in the bones even when no actual damage to the bone is there. This is because there are always small damages during normal functioning of the organism. This process of bone reshaping is known as Bone Remodeling.

The process is under control of various enzymes and hormones. The rate of remodeling is higher in growing children than in adults.

Ques 3: What are key differences in bones produced by endochondral ossification and that produced by intramembranous ossification?

Answer: Endochondral ossification: It is a process in which the bones are formed from the formed cartilage tissue. The already formed cartilaginous tissue gets calcified by the action of enzymes.

Intramembranous ossification: This process involves the formation of bones directly from the mesenchyme stem cells. This process does not involve the formation of cartilage.

Differences:

Bones formed by Endochondral ossification

Bones formed by Intramembranous ossification

1. These bones are formed indirectly from stem cells i.e. firstly cartilage is formed and then from preformed cartilage, the bones are formed.

1. These bones are formed directly from the stem cells

2. Chondrocytes are formed first and then they start the process of Ossification by causing mineral deposition

2. Chondrocytes are not involved.

3. Bones formed by this process are mostly after birth of the organism

3. Bones are formed before birth in embryonic stages.

4. The process is involved in natural healing of fracture and formation of long bones like femur

4. The process is involved in formation of skull bones, jaws and bones of face.

Ques 4 Summarize the findings of article on Bone Biology

Answer: The answer to this question depends on what article you was provided with but as per the questions asked the key points could be: