Difficulty: Hard

Average Score: 44%

What causes osteoporosis?

Rationale

A decline in osteoblast activity while osteoclast activity continues at expected levels causes osteoporosis.

Osteoporosis is a skeletal disorder characterized by compromised bone strength predisposing a person to an increased risk of fracture. It is a result of an imbalance between bone resorption (breakdown) and formation. When osteoblast activity (bone formation) declines and osteoclast activity (bone resorption) continues at normal levels, more bone is broken down than is rebuilt, leading to decreased bone mass or density, which is a defining feature of osteoporosis.

A (An increase in osteocyte activity while osteoclast activity continues at expected levels) YOUR ANSWER

Osteocytes are mature bone cells that originate from osteoblasts. While they do play a role in bone remodeling, an increase in their activity doesn’t necessarily lead to osteoporosis. Osteoporosis occurs due to a decrease in bone formation (osteoblast activity) or an increase in bone resorption (osteoclast activity), not due to an increase in osteocyte activity.

B (A decline in osteoblast activity while osteoclast activity continues at expected levels) CORRECT

This is the correct choice. Osteoporosis is caused when osteoblast activity (bone formation) declines and osteoclast activity (bone resorption) continues at normal levels. The imbalance in bone remodeling results in more bone being broken down than is formed, leading to decreased bone mass or density.

C (An increase in osteocyte activity while osteoblast activity continues at expected levels) YOUR ANSWER

While osteocytes do play a role in bone remodeling, an increase in their activity doesn’t necessarily lead to osteoporosis when the osteoblast activity remains normal. Osteoporosis occurs due to an imbalance between bone formation (osteoblast activity) and bone resorption (osteoclast activity).

D (A decline in osteoclast activity while osteoblast activity continues at expected levels) YOUR ANSWER

A decline in osteoclast activity while osteoblast activity continues at expected levels would result in increased bone mass, not osteoporosis. This is because osteoclasts break down bone, and when their activity decreases, less bone is broken down while new bone continues to be formed by the osteoblasts.

Conclusion

Osteoporosis is a disease caused by an imbalance in the activities of osteoblasts and osteoclasts, the cells responsible for bone formation and resorption, respectively. Specifically, a decline in osteoblast activity while osteoclast activity continues at expected levels results in a net loss of bone, leading to the decreased bone density characteristic of osteoporosis. The other choices involve changes in osteocyte activity or a decrease in osteoclast activity, neither of which would lead to osteoporosis.

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