The ductus arteriosus is a hole that allows the blood to skip the circulation to the lungs. However, when the baby is born, the blood must receive oxygen in the lungs and this hole is supposed to close. If the ductus arteriosus is still open (or patent) the blood may skip this necessary step of circulation. The open hole is called the patent ductus arteriosus.
Caring for a Bleeding Tooth. Some people mistakenly think that while brushing, a bleeding tooth is perfectly normal. It is not. Anytime there is any bleeding in the mouth, it is almost always a sign of periodontal disease. Even if you brush fairly hard, it should not cause healthy teeth and gums to bleed.
A dead tooth is a tooth that does not have a nerve inside it. The nerve has died. Normally teeth DO have a nerve inside them. It's what tells you if your coffee is hot or your ice cream is cold! I usually tell my patients that a tooth is a bit like a pencil. The nerve inside the tooth is like the pencil lead, running down the inside of the tooth.