Hereditary Hemorrhagic Telangiectasia (HHT) is a genetic disorder that causes abnormalities of blood vessels, usually resulting in excessive bleeding (known as hemorrhaging). In order to understand HHT, you must first understand the way blood is pumped to and from the heart. Blood vessels are hollow structures that transport blood throughout the body.
There are two types of blood vessels: arteries and veins. Arteries
carry blood under high pressure away from the heart to all other areas
of the body. Blood then passes through capillaries, where oxygen,
nutrients and waste products can be exchanged. Veins carry blood that
should be under low pressure back to the heart. An artery does not
usually connect directly to a vein.
A person with HHT has a tendency to form blood vessels that lack
capillaries between the arteries and veins, meaning that arterial blood
under high pressure flows directly into a vein without first going
through the very small capillaries. The site of this abnormal connection
tends to be fragile and can rupture and result in bleeding.
This type of abnormal blood vessel is called a telangiectasia if it
involves small blood vessels. It is called an arteriovenous malformation
(AVM) if it involves large blood vessels. Telangiectases usually occur
on the surface of the body, such as the skin and the mucous membranes
that line the nose and the gastrointestinal tract. AVMs are found in the
lungs, liver and central nervous system. Read more...