The appendix (or vermiform appendix) is a winding tube that attaches to the cecum. Although the 7.6-cm (3-in) long appendix contains lymphoid tissue, suggesting an immunologic function, this organ is generally considered vestigial. However, at least one recent report postulates a survival advantage conferred by the appendix: In diarrheal illness, the appendix may serve as a bacterial reservoir to repopulate the enteric bacteria for those surviving the initial phases of the illness. Moreover, its twisted anatomy provides a haven for the accumulation and multiplication of enteric bacteria. The mesoappendix, the mesentery of the appendix, tethers it to the mesentery of the ileum.

Figure 16.7 The stomach has an extremely acidic environment where most of the protein gets digested. (credit: modification of work by Mariana Ruiz Villareal)

The first part of the large intestine is the cecum, a sac-like structure that is suspended inferior to the ileocecal valve. It is about 6 cm (2.4 in) long, receives the contents of the ileum, and continues the absorption of water and salts. The appendix (or vermiform appendix) is a winding tube that attaches to the cecum. Although the 7.6-cm (3-in) long appendix contains lymphoid tissue, suggesting an immunologic function, this organ is generally considered vestigial. However, at least one recent report postulates a survival advantage conferred by the appendix: In diarrheal illness, the appendix may serve as a bacterial reservoir to repopulate the enteric bacteria for those surviving the initial phases of the illness. Moreover, its twisted anatomy provides a haven for the accumulation and multiplication of enteric bacteria. The mesoappendix, the mesentery of the appendix, tethers it to the mesentery of the ileum.

Large Intestine

The large intestine includes the cecum, colon, and rectum.

A pouch that forms the first part of the large intestine. It connects the small intestine to the colon, which is part of the large intestine.

The entire colon is about 5 feet (150 cm) long, and is divided into five major segments. The rectum is the last anatomic segment before the anus.

The ascending and descending colon are supported by peritoneal folds called mesentery.

The right colon consists of the cecum, ascending colon, hepatic flexure and the right half of the transverse colon. The left colon consists of the left half of the transverse colon, splenic flexure, descending colon, and sigmoid.

Parts of Colon and Rectum

• Cecum (proximal right colon)
  6 x 9 cm pouch covered with peritoneum
• Appendix
  A vermiform (wormlike) diverticulum located in the lower cecum
• Ascending colon
  20-25 cm long, located behind the peritoneum
• Hepatic flexure
  Lies under right lobe of liver
• Transverse colon
  Lies anterior in abdomen, attached to gastrocolic ligament
• Splenic flexure
  Near tail of pancreas and spleen
• Descending colon
  10-15 cm long, located behind the peritoneum
• Sigmoid colon
  Loop extending distally from border of left posterior major psoas muscle
• Rectosigmoid segment
  Between 10 and 15 cm from anal verge
• Rectum
  12 cm long; upper third covered by peritoneum; no peritoneum on lower third which is also called the rectal ampulla. About 10 cm of the rectum lies below the lower edge of the peritoneum (below the peritoneal reflection), outside the peritoneal cavity
• Anal canal
  Most distal 4-5 cm to anal verge

What is the lower GI tract?

The lower gastrointestinal (GI) tract is the last part of the digestive tract. The lower GI tract consists of the large intestine and the anus.

The large intestine absorbs water and changes the waste products of the digestive process from liquid into formed stool. The large intestine includes

• the appendix, a finger-shaped pouch attached to the cecum
• the cecum, the first part of the large intestine, which is connected to the end of the small intestine
• the colon, which has four sections: the ascending colon, the transverse colon, the descending colon, and the sigmoid colon
• the rectum, the lower end of the large intestine leading to the anus

The anus is a 1-inch opening at the end of your digestive tract through which stool leaves your body. The anus includes the sphincter muscles—muscles that open and close and allow you to control bowel movements.

What are anatomic problems of the lower GI tract?

Anatomic problems of the lower GI tract are problems related to the structure of the lower GI tract. The parts of the lower GI tract may be in the wrong place, may not be shaped normally, or may not connect normally to other parts of the body.

Some anatomic problems of the lower GI tract arise when the lower GI tract does not develop normally before birth. These are called birth defects and include

• anorectal malformations
• colonic atresia and stenosis
• malrotation

Other anatomic problems, which might be present at birth or develop later, include

• intussusception
• colonic and anorectal fistulas
• rectal prolapse
• colonic volvulus

Parkinson’s disease is a brain disorder that leads to shaking, stiffness, and difficulty with walking, balance, and coordination. Symptoms usually begin gradually and get worse over time. Parkinson’s disease results from the loss of the dopamine-producing brain cells that control movement.

Many brain cells of people with Parkinson’s contain Lewy bodies, which are unusual clumps of the protein alpha-synuclein. Clumps of this protein are thought to be toxic to the cells and lead to their death. This protein has also been shown to accumulate in the gut of Parkinson’s patients. There is evidence that the protein may be able to travel from the gut to the brain via the connecting vagal nerve. Gastrointestinal symptoms are often associated with Parkinson’s disease and can start up to 20 years before the symptoms of brain cell degradation.

A team led by Dr. Viviane Labrie at the Van Andel Research Institute sought to explore whether the gut could be involved in triggering Parkinson’s disease. They focused on the appendix. Despite its reputation as a useless organ, the appendix is an immune tissue involved in the body’s defense against microbes and helps regulate bacteria in the intestine.

The team analyzed the records of nearly 1.7 million people whose health information was tracked for up to 52 years. They compared the chances of developing Parkinson’s disease among those who’d had their appendix removed with those who hadn’t. The work was supported in part by NIH’s National Institute of Neurological Disorders and Stroke (NINDS). Results appeared on October 31, 2018, in Science Translational Medicine.

People who'd had their appendix removed (an appendectomy) had a 19.3% lower chance of Parkinson’s disease. Those who lived in rural areas and had an appendectomy had an even lower chance, 25.4%. People who'd had an appendectomy and developed Parkinson’s showed a delayed onset of the disease relative to those who still had their appendix—an average delay of 3.6 years for those who’d had an appendectomy at least 30 years prior.

The team also found a build-up of the toxic form of alpha-synuclein in the appendixes of healthy volunteers. This suggests that the appendix may be a reservoir for the disease-forming protein and may be involved in the development of Parkinson’s disease.

“We were surprised that pathogenic forms of alpha-synuclein were so pervasive in the appendixes of people both with and without Parkinson’s. It appears that these aggregates—although toxic when in the brain—are quite normal when in the appendix. This clearly suggests that their presence alone in the gut cannot be the cause of the disease,” Labrie said.

“Parkinson’s is relatively rare—less than 1% of the population—so there has to be some other mechanism or confluence of events that allows the appendix to affect Parkinson’s risk,” she explains. “That’s what we plan to look at next; which factor or factors tip the scale in favor of Parkinson's?”

—by Tianna Hicklin, Ph.D.