okay, to recap:
The appendix is an extension of bowel that creates an eddy , or sump, off the first portion of the colon. Stool is mixed in the distensable well of the cecum before being pushed on. Some of the stool may pass into the appendix, but appendiceal peristalsis pushes it back into the colon. The appendix also makes mucous and antibodies which are also pushed into the cecum by peristalsis.
So, now lets hypothesize a small hard ball of stool gets pushed down into the opening of the appendix and gets stuck.
The bowel, including the appendix, as wells as other muscular tubes such as the ureter, don't like having something stuck in them. Remember, they are designed to move stuff on down the road. When the ball of stool gets stuck in the opening of the appendix, the appendix will sense that stretch and will squeeze extra hard and in waves to try to push the obstruction out. This will cause some vague cramping, usually centered in the mid abdomen around the navel.
The appendix will also make mucous in the Crypts of Lieberkuhn in an attempt to both lubricate the stool ball and to develop a pressure force behind the ball of stool.
If the ball remains stuck, the pressure will build up in the appendix behind the obstruction and the appendix will distend.
The stretching and distension of the appendix will make the vague cramping of the abdomen around the navel worse. The cramping in the appendix will cause a hormone release, and will trigger colicy peristaltic contractions in nearby sections of the bowel, enhancing the vague colicy pain.
A natural phenomenon described by Starling's law is that as you stretch a hollow structure, the stretching increases the tension or pressure in the wall of the structure. As the appendix stretches, then, the pressure in the wall of the appendix increases, and gradually this pressure becomes higher than the blood pressure in the capillaries and small veins. Blood flow is impeded and the appendix becomes starved for blood and oxygen; it becomes ischemic and starts to die.
As the appendix becomes oxygen deprived, the ischemic tissues will set up an release chemicals that will also cause pain and inflammation of both the appendix and of the lining, or peritoneum, of the abdomen around the appendix, in the right lower quadrant of the abdomen. At this point, as the appendix is becoming inflamed and ischemic, the person's pain will change from a vague, colicy pain around the navel, to a sharp, burning or stabbing pain in the right lower quadrant of the abdomen. This is now appendicitis.
The distension ill continue to increase as will the pressure inside the appendix. Eventually, a section or the ischemic appendix will have died sufficiently to become weak. At this point, just like a balloon, the appendix will rupture, and the mucous and stool in the appendix will leak in to the abdomen.
Curiously, at this point, with the distension relieved, many people will feel better - the pressure/stretch pain is gone instantly as the appendix ruptures, and the leaked fluid and stool from the rupture needs a few hours to develop significant infection and inflammation. The surgeon always needs to be very wary of the patient with right lower quadrant pain who suddenly feels better. It can mean either that the appendix has ruptured, or that the appendix succeeded in pushing the stool ball and has decompressed.
Left untended, the leaked mucous and stool will act in one of three ways -
The rupture will be contained by the other contents of the abdomen, the omentum and bowel, and the body's healing methods will gradually, over a few days, clean up the area and seal off the appendix. That inflammatory process may actually also cause the resorption of the appendix itself.
The second possibility is that the leaked material is walled off, but the body can't cleanse the infection, and an abscess forms in the right lower quadrant of the abdomen. This is what happened to King Edward VII of England.
The third possibility is that the body will not effectively contain the infection and that it will rapidly spread throughout the abdomen, leading to a generalized peritonitis. This is the sequela of a ruptured appendicitis that used to lead to a rapid death.