Some nebulae create their own light, which sometimes has a fluorescent appearance, while others only reflect the light from nearby stars. Nebulae are often seen around dying stars, and it's thought they may be a natural process that occurs when a star is nearing the end of its life. Nebulae resemble thin clouds that have less atoms per cubic inch than a cloud of smoke.
When there is not enough thyroid hormone, neither the heart nor the blood vessels can function normally. In hypothyroidism, the reduced level of thyroid hormone causes the heart muscle to pump less vigorously, and eventually to become weakened. In addition, the heart muscle cannot fully relax after each heart beat.
During a heart attack, heart muscle cells die due to lack of oxygen. Cardiac enzymes from the dying cells leak into the bloodstream. In addition to a heart attack, other cardiac diseases that can cause elevated cardiac enzymes include: -- heart failure, or weakness of the heart muscle. -- inflammation of the sac surrounding the heart, or pericarditis. -- inflammation of the heart muscle, or myocarditis.