1. No, a woman in labor does not voluntarily contract the uterus. The uterus is made of smooth muscle, over which she cannot voluntarily control. When she pushes, she contracts the voluntary abdominal muscles. This puts pressure on the internal organs and helps expel the baby from the uterus.

2. While it is true that the structural and functional properties of these tissues is due mainly to their extracellular matrix, one must remember that the matrix is produced by cells and its properties are therefore attributable to cellular function. Therefore, this presents no exception to the cell theory.

3. Periodic pressure on the cartilage causes an "ebb and flow" of water in and out of its matrix. As pressure is applied and water squeezed out, it carries metabolic wastes with it. As water flows back in when pressure is relieved, it carries nutrients and oxygen with it. Therefore when cartilage is not subject to the stresses of exercise, it is starved for nutrients and oxygen and smothered in its own metabolic waste. Hence the chondrocytes stop producing new matrix, they die, and the cartilage as a whole degenerates.

4. Remember that neurons are not the only cells in the brain. Glial cells outnumber them and are capable of mitosis. Brain tumors are composed of neuroglia, not neurons.

5. The answer to both questions is based on the necessity for a good blood supply to furnish the rapid nutrient and oxygen delivery and waste removal necessary for a high rate of tissue metabolism and cell division. Bone heals faster than cartilage because bone is quite vascular and cartilage is avascular. Simple columnar epithelium regenerates faster than stratified squamous epithelium because every cell of a simple columnar epithelium is close to a blood supply in the underlying areolar tissue, whereas most cells of a stratified squamous epithelium are not.

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