A Short Course in Anatomy

To understand hemorrhoids, we need to review the anatomy of the digestive system. Since we're interested in hemorrhoids, let's start backward - from the anus.

The anus is the end-point of the digestive system. It contains sweat and oil glands, hair follicles, as well as many nerve endings, which make it very sensitive to pain and erotic stimulation.

The anal opening is an oval opening located about an inch in front of the spine. When closed, the anus is about an inch in circumference - however, the external sphincter muscle that circles it can stretch to about five times the size. Inside the anal opening is the anal canal. It is approximately two inches deep, with an encircling internal sphincter muscle that controls the passage of stool in the elimination process.

On top of the anal canal, there is a ring of tissue fold arranged in zigzag or sawtooth pattern called the dentate line. Underneath this line lies some vestigial glands - in our evolutionary ancestors, these glands secrete odors that attract mates. Now, however, these glands are empty and unused.

About an inch above the dentate line is the rectum, or the last holding place for feces in the elimination process. The rectum is approximately six inches long, with folds called the valves of Houston. These valves serve as shelves where the feces rest between bowel movements. When the stool becomes heavy, the valve presses against the rectal wall, which results in the "the call of nature" signal or the urge to defecate.

On top of the rectum lies the large intestine (also known as the colon or bowel). It is six foot in length, and is divided into four components: the sigmoid colon, the descending colon, the transverse colon, and the ascending colon. The ascending colon is connected to the small intestine by a structure called the ceccum.

The digestive process of food stops at the small intestine and the fecal waste water-removal process starts at the ascending colon. Fecal matter starts as liquid waste at the cecum and ends up as solid waste in the sigmoid colon.