text: Peyer's patches, located within the ileum of the small intestine, are an important part of the digestive tract's local immune system. They are part of the lymphatic system, and provide a site for antigens from potentially harmful bacteria or other microorganisms in the digestive tract to be sampled, and subsequently presented to the immune system.
  Clinical significance
  The small intestine is a complex organ, and as such, there are a very large number of possible conditions that may affect the function of the small bowel. A few of them are listed below, some of which are common, with up to 10% of people being affected at some time in their lives, while others are vanishingly rare.
  Small intestine obstruction or obstructive disorders
  Meconium ileus
  Paralytic ileus
  Volvulus
  Hernia
  Intussusception
  Adhesions
  Obstruction from external pressure
  Obstruction by masses in the lumen (foreign bodies, bezoar, gallstones)
  Infectious diseases
  Giardiasis
  Ascariasis
  Tropical sprue
  Tape worm (Diphyllobothrium latum, Taenia solium, Hymenolepis nana)
  Hookworm (e.g. Necator americanus, Ancylostoma duodenale)
  Nematodes (e.g. Ascaris lumbricoides)
  Other Protozoa (e.g. Cryptosporidium parvum, Cyclospora, Microsporidia, Entamoeba histolytica)
  Bacterial infections
  Enterotoxigenic Escherichia coli
  Salmonella enterica
  Campylobacter
  Shigella
  Yersinia
  Clostridium difficile (antibiotic-associated colitis, Pseudomembranous colitis)
  Mycobacterium (Mycobacterium avium paratuberculosis, disseminated Mycobacterium tuberculosis)
  Whipple's disease
  Vibrio (cholera)
  Enteric (typhoid) fever (Salmonella enterica var. typhii) and paratyphoid fever
  Bacillus cereus
  Clostridium perfringens (gas gangrene)
  Viral infections
  Rotavirus
  Norovirus
  Astrovirus
  Adenovirus
  Calicivirus
  Neoplasms (cancers)
  Adenocarcinoma
  Carcinoid
  Gastrointestinal stromal tumor (GIST)
  Lymphoma
  Sarcoma
  Leiomyoma
  Metastatic tumors, especially SCLC or melanoma