On March 1, 2023, Jamie Oh submitted an assignment on bones to Dr. Kelley in physiology. The final copy of the assignment is as below:

Assignment: Bones

1. What is considered a normal range of blood calcium levels, and can a blood draw detect the amount of calcium in bones? The acceptable range of blood calcium levels lies between 8.5 and 10.5 mg/dL. However, analyzing the calcium levels from a blood draw cannot determine the calcium levels in bones. This is because most of the calcium present in the body is located in bone tissues that are isolated from the circulatory system.

2. Can you name a couple of methods that can enhance calcium levels in our bloodstream? Contrarily, two known techniques used to heighten calcium levels in the blood stream are the absorption of calcium through the small intestine using Vitamin D and PTH (parathyroid hormone), which causes the depletion of calcium from the bone tissue and releasing said calcium to the bloodstream.

3. What is the origin of parathyroid hormone? How does this hormone influence blood calcium levels? The parathyroid hormone originates from the four small glands situated in the neck: the parathyroid glands. Parathyroid hormone (PTH) heightens the levels of calcium in the bloodstream by stimulating cells that break down bone tissues, known as osteoclasts. As such, calcium is released from the bones to the circulatory system.

4. What is the origin of Calcitonin? How does Calcitonin affect blood calcium levels? Calcitonin is produced by the body's C cells, also known as parafollicular cells, that are located in the thyroid gland. Calcitonin has the opposite effect of PTH; it inhibits osteoclast activity and encourages calcium deposition in the bone tissues, reducing calcium levels in the bloodstream.

5. What are the common types of fractures experienced by individuals, and how do they occur? There are three types of bone fractures: traumatic fracture is caused by an external impact to the bones; stress fracture is more commonly through overuse or repetitive stress, while pathological fracture occurs due to underlying medical conditions like bone cancer that lead to weakened bones and fractures.

6. What differentiates endochondral and intramembranous ossification? Endochondral ossification is the process by which most bones in the body are formed from cartilage gradually getting replaced by bone tissue. Endochondral ossification is most common in the formation of the long bones in the body. Intramembranous ossification is similar to endochondral but occurs in flat bones in the body by the formation of mesenchymal cells into bone tissue without any cartilage.

7. How different are osteoblasts, osteoclasts, and osteocytes? In the event that a patient has excessive calcium in their bloodstream, which hormone and bone cells are triggered, and why? Osteoblasts are responsible for bone generation, osteoclasts cause bone tissue breakdown, and osteocytes sustain bone tissues by regulating bone activities. If an individual has too much calcium in their bloodstream, parathyroid hormone (PTH) is activated, and osteoclasts are stimulated, releasing calcium from bone tissues into the bloodstream.

8. Could you enumerate three essential functions of bones? Bones have three critical functions: to support the framework of the human body; to provide protection for vital organs; and lastly, to store crucial minerals essential for body functioning.