Final answer:
Cyanosis is the bluish coloration of skin and mucous membranes due to insufficient oxygen in the blood, often associated with heart defects such as tetralogy of Fallot and patent foramen ovale, and requires immediate medical attention.
Step-by-step explanation:
The bluish color of the skin and mucous membranes due to ischemia or hypoxemia is called cyanosis. This occurs when there is a deficiency in the supply of oxygenated blood, which can be a result of several conditions, including severe septal defects such as tetralogy of Fallot and patent foramen ovale. A common manifestation of this is in "blue baby" syndrome, where a child's skin appears blue, especially when active, due to the heart failing to develop properly and insufficient oxygenation of blood.
Other body system diseases can also lead to changes in skin coloration. For instance, liver disease or liver cancer can lead to jaundice, a yellowing of the skin from excess bilirubin. In contrast, Addison's disease causes a deep bronze color due to excessive adrenocorticotropic hormone (ACTH). Sudden drops in oxygenation can cause the skin to appear ashen, while prolonged oxygen reduction can lead to cyanosis, signifying a serious health risk and the need for immediate medical attention.