Anatomy and Histology of the Large Intestine

The Large Intestine (Intestinum crassum)

Overview and Main Divisions

The large intestine is the final section of the digestive tract, responsible for water absorption, fecal formation, and excretion. It is anatomically divided into three main parts, each with distinct features and functions.

• Cecum (Blinddarm): The initial pouch-like segment, which includes the vermiform appendix.

• Colon (Grimmdarm): The longest portion, subdivided into:

  • Ascending colon

  • Transverse colon

  • Descending colon

  • Sigmoid colon

• Rectum (Mastdarm): The terminal straight segment, ending at the anal canal.

Functions:

• Resorption of water and minerals: The large intestine absorbs water and electrolytes from indigestible food matter.

• Transport and excretion: It compacts waste into feces and moves it toward excretion via the rectum and anal canal.

Anatomical Features of the Large Intestine

The large intestine is characterized by several unique macroscopic structures that distinguish it from the small intestine.

• Teniae coli: Three distinct longitudinal bands of smooth muscle running along the colon. These bands contract to produce the haustra.

• Haustra coli: Sacculations or pouches of the colon wall, giving it a segmented appearance. These are formed by the contraction of the teniae coli.

• Omental appendices (Appendices epiploicae): Small, fat-filled pouches of visceral peritoneum attached along the colon.

Example: The presence of haustra and teniae coli can be observed during a colonoscopy, helping to distinguish the large intestine from the small intestine.

Summary Table: Main Parts and Features of the Large Intestine

Part	Main Features	Function
Cecum	Vermiform appendix	Receives chyme from ileum; immune function (appendix)
Colon	Teniae coli, haustra, omental appendices	Water/electrolyte absorption, fecal formation
Rectum	Anal canal, straight muscular tube	Fecal storage and excretion

Key Terms and Definitions

• Cecum: The first part of the large intestine, located in the lower right abdomen.

• Vermiform appendix: A narrow, worm-like extension of the cecum, rich in lymphoid tissue.

• Colon: The main, tubular portion of the large intestine, divided into four regions (ascending, transverse, descending, sigmoid).

• Rectum: The final straight segment of the large intestine, leading to the anal canal.

• Teniae coli: Three longitudinal muscle bands unique to the colon.

• Haustra coli: Pouch-like segments of the colon wall.

• Omental appendices: Fatty peritoneal pouches attached to the colon.

Additional info:

• The large intestine lacks villi, which are present in the small intestine, but contains numerous goblet cells for mucus secretion.

• The vermiform appendix is considered to have an immune function due to its lymphoid tissue.