Question

(9/22/25) summative assessmen assignr
7 of 7
why do astronauts often lose bone density during space travel?
the lack of mechanical stress reduces bone formation
osteoclasts are more active in space
they lack vitamin d
bones do not grow in zero gravity

Explanation:

Bones respond to mechanical stress. In space, the lack of normal mechanical stress (like that from gravity - related activities on Earth) reduces the signals that stimulate bone - forming cells. Osteoblasts are less active in bone formation, leading to bone density loss. Osteoclasts aren't necessarily more active in space; lack of vitamin D isn't the main reason for bone density loss in space; and bones can still grow in zero - gravity to some extent but the balance between bone formation and resorption is disrupted mainly due to lack of mechanical stress.

Answer:

The lack of mechanical stress reduces bone formation