The intestines. The small intestine (or small bowel) runs from the stomach to the wider large intestine (or large bowel), which starts with the cecum, in the region of the appendix on the right side of the lower abdomen, ascends (ascending colon), turns left (transverse colon), turns downward (descending colon), becomes the sigmoid colon (as it sweeps from side to side a bit), then the rectum, before emerging at the anus.

A distressing dysfunction of the intestines, in which there's both overactivity of the involuntary contractions of the intestines' muscular wall and increased pain signals coming from those contractions. Treatment is based on decreasing the contractions (with a diet high in fibre, sometimes with antispasmodic drugs) and attempting to reduce the action of the pain-carrying nerves, both by sedating them (this means general sedation too, so it's often not very acceptable) and by re-educating them to be less sensitive. Treatment is time consuming and, ultimately, not always satisfactory. The symptoms of the irritable bowel syndrome are often confused with those of endometriosis; they are sometimes made worse with, and at the time of, premenstrual tension, or, in my experience of patients with it, by performance of a laparoscopy. Typically (but not always), there is an alternating tendency towards diarrhea or constipation; sometimes there is nausea with the spasms.

The colon.

The small intestine, leading out of the stomach; narrower but longer than the large intestine (or colon), to which it connects.

A defect of intestinal absorption caused by abnormal sensitivity to gluten in the diet that can first manifest with recurrent miscarriage or unexplained infertility, despite an absence of diarrhea or other disturbances of bowel function. Diagnosis is suggested by serum antigliadin antibodies and serum tissue transglutaminase (or endomysial) antibodies, but requires biopsy of the lining of the small intestine via gastroscopy for confirmation. Responds to a gluten-free diet.

Connects the large bowel (the colon) to the anus; lies behind the vagina in women.