The relationship of fascia layers to hernias is that a hernia is any breach of a fascia layer. The fascia layers are connective tissues that lie between the abdominal cavity and sheets of muscle and abdominal fat. They extend from just below the chest to below the groin area.
The abdominal wall consists of seven layers: skin, superficial fascia, external and internal obliques, transversus, transversalis fascia, and the peritoneum. About halfway between the navel and the pubic region, the tissue comprising the abdominal walls changes in an area known as the semicircular line of Douglas. The tissue of the abdominal walls thins out below this line to the extent that only the peritoneum and the transversalis fascia separate the rectal muscles from the abdominal cavity. Any weakness, pressure or unusual strain can lead to a hernia in this area.
Hernias occur whenever an organ, blood vessel or fatty tissue pushes through an opening in the fascia. The most common causes are obesity, pregnancy, heavy lifting and strain from forced bowel movements and coughing. Men are anatomically prone to inguinal hernias in which a piece of the bladder or intestine pushes through the inguinal canal leading to the groin. Women are more prone to femoral hernias, in which a piece of intestine pushes through the cavity that contains the femoral artery leading to the upper thigh, and umbilical hernias, which occur just below the navel and are especially common in newborns and women who are pregnant.