Explanation:
The respiratory and circulatory systems work together to get oxygen into the body. Blood vessels allow oxygen from the respiratory system to enter, and the blood subsequently carries oxygen-rich blood to tissues and cells. This oxygen is essential to the health of tissues and cells.
Explanation:
Endogenous stains are those that a tooth picked up while it was still developing. Tetracycline stains fall under this heading. Tetracycline, an antibiotic, attaches to the dentin of teeth when it is consumed between the time of birth and the development of permanent teeth (between the ages of one and twelve), causing a stain to become deeply ingrained.
