Answer to Question 1
As mentioned, vitamin A also supports reproduction and regulates growth. In men, retinol participates in sperm development, and in women, vitamin A supports normal fetal development during pregnancy. Children lacking vitamin A fail to grow; given vitamin A supplements, these children gain weight and grow taller.
The growth of bones illustrates that growth is a complex phenomenon of remodeling. To convert a small bone into a large bone, some bone cells must undo parts of the bone before other cells can build new bone, and vitamin A participates in the dismantling. The cells that break down bone contain acid and enzymes that dissolve the minerals and digest the matrix. With the help of vitamin A, these bone-dismantling cells destroy selected sites in the bone, removing the parts that are not needed. After completing their work, the bone-dismantling cells die, leaving their excavation site to be rebuilt by the bone-building cells.
Answer to Question 2
phylloquinone (K1); menaquinone (K2)
Vitamin D Preparations
Three active forms of vitamin A: all-trans-retinol, -retinal, and –retinoic acid
Growth of World Trade, 1870–2010
Data for Calculating Productivity Growth in Erewhon
The development and maintenance of malignant growth
The generation, removal, and role of reactive oxygen species (ROS) in cell injury