Large Intestine Anatomy

Large Intestine

Sarah Abutineh, MD
Medical Gross Anatomy
Fall 2025, LMU-CDM

Learning Objectives

  • Describe all regions of the large intestine

  • Identify blood supply and innervation to all parts of the lower gastrointestinal tract (GIT)

  • Define points of anastomoses between the Superior Mesenteric Artery (SMA) and Inferior Mesenteric Artery (IMA).

  • Draw out the blood supply involving major branches of SMA and IMA.

Presentation Resources

  • This presentation is prepared from multiple resources, including:

    • Snell’s Clinical Anatomy

    • Moore’s Clinical Anatomy

    • Gray’s Anatomy

    • Complete Anatomy

    • Netter’s Anatomy

  • Images in this presentation are referenced accordingly

  • All information and images in this presentation are intended for educational purposes

Overview of the Large Intestine

  • Extends from the distal end of the ileum to the anus

  • Approximately 1.5 meters in length in adults

  • Primary functions:

    • Absorbs fluids and salts from gut contents

  • Consists of the following regions:

    • Cecum

    • Appendix

    • Colon

    • Ascending colon

    • Transverse colon

    • Descending colon

    • Sigmoid colon

    • Rectum

    • Anal canal

  • Comparison of large intestine vs. small intestine:

    • Larger internal diameter in the large intestine

    • Contains omental appendices

    • Features of colonic structure:

    • Taeniae coli

    • Haustra of the colon

Cecum and Appendix

  • Cecum:

    • May cross the pelvic brim, located in the true pelvis

    • Appendix:

    • Attached to the cecum posteromedially

    • Structure: narrow, hollow, blunt tube containing aggregations of lymphoid tissue

    • Mesoappendix:

    • Contains appendicular vessels

    • McBurney’s point:

    • Anatomical landmark, located one-third of the distance from the anterior superior iliac spine to the umbilicus

Appendix Blood Supply

  • Supplied by branches of the ileocolic artery from the Superior Mesenteric Artery (SMA):

    • Anterior cecal artery

    • Posterior cecal artery

    • Appendicular artery

Appendicitis

  • Pathophysiology:

    • Due to obstruction of the appendix (causes may include fecalith or enlargement of lymphoid tissue)

    • Obstruction leads to bacterial proliferation and invasion into the appendix wall, which results in:

    • Increased pressure in the walls

    • Occlusion of blood vessels

    • Stasis of lymph and necrosis of the wall

    • Potential perforation leading to peritonitis

  • Symptom progression:

    • Initial pain: right groin pressure

    • Progresses to periumbilical and colicky pain

    • After 6-10 hours, pain localizes to the right iliac fossa and becomes constant

    • Associated symptoms: fever, nausea, vomiting

  • Treatment: appendectomy

Colon

  • Ascending colon:

    • Extends from the right groin to the right hypochondrium

    • Terminates at the right colic flexure (hepatic flexure)

  • Transverse colon:

    • Extends from the right hypochondrium to the left hypochondrium

    • Terminates at the left colic flexure (splenic flexure)

  • Descending colon:

    • Extends from the left hypochondrium to the left groin

  • Sigmoid colon:

    • Enters the upper part of the pelvic cavity

Colon Flexures and Gutters

  • Hepatic flexure:

    • Located inferior to the right lobe of the liver

  • Splenic flexure:

    • Located inferior to the spleen

    • Attached to the diaphragm by the phrenicocolic ligament

  • Structural note:

    • Splenic flexure is higher and more posterior than hepatic flexure

  • Paracolic gutters:

    • Right/left paracolic gutters located lateral to ascending/descending colon

Sigmoid Colon

  • Description:

    • Final segment of the colon

    • Begins above the pelvic inlet and extends to the level of S3

    • Characterized by mobility except at the beginning and end

    • The mobile part is suspended by the mesocolon

Colon Blood Supply

  • Ascending colon:

    • Supplied by:

    • Colic artery

    • Anterior cecal artery

    • Posterior cecal artery (all branches from the ileocolic artery from SMA)

    • Right colic artery (direct branch from SMA)

  • Transverse colon:

    • Supplied by:

    • Right colic artery (SMA)

    • Middle colic artery (SMA)

    • Left colic artery (IMA)

  • Descending colon:

    • Supplied by: left colic artery (IMA)

  • Sigmoid colon:

    • Supplied by: sigmoidal arteries from the IMA

  • Anastomotic connections form the marginal artery

Rectum and Anal Canal

  • Rectum:

    • Located retroperitoneally

  • Anal canal:

    • Positioned inferior to the rectum

    • Starts at the termination of the sigmoid mesocolon

Rectum and Anal Canal Blood Supply

  • Main vascular supply:

    • Superior rectal artery (branch of IMA)

    • Middle rectal artery (a branch of internal iliac artery)

    • Inferior rectal artery (a branch of internal pudendal artery from internal iliac)

  • Hemorrhoid classification based on blood supply:

    • Internal hemorrhoids receive blood from the superior rectal artery

    • External hemorrhoids are supplied by the middle and inferior rectal arteries