Small Large Intestion 2

Large Intestine: Relevant Features

  • General Characteristics

    • Wider in calibre than the small intestine.

    • Greater part is fixed in position.

  • Muscle Structure

    • Longitudinal muscle forms three ribbon-like bands called taeniae coli:

      • Taenia libera: located along the free border.

      • Taenia mesocolica: found on the posteromedial surface of the caecum.

      • Taenia omentalis: located on the superior surface of the colon.

  • Morphology

    • The colon is puckered and sacculated due to the arrangement of taeniae.

    • Appendices epiploicae: small bags filled with fat scattered over the surface of the large intestine.

  • Vascularization

    • Blood supply comes from the marginal artery of Drummond, formed by colic branches of the superior and inferior mesenteric arteries.

  • Lymphatic Drainage

    • Lymph drainage passes through four sets of lymph nodes:

      • Epicolic lymph nodes

      • Paracolic nodes

      • Intermediate nodes

      • Terminal nodes

Innervation

  • Sympathetic Supply: Midgut territory is supplied by coeliac and superior mesenteric ganglia (T11 to L1).

  • Parasympathetic Supply: Midgut supplied by the vagus nerve.

  • Hindgut Territory:

    • Sympathetic supply from lumbar sympathetic chain (L1, L2).

    • Parasympathetic supply from pelvic splanchnic nerve (nervi erigentes).

Caecum

  • Anatomy:

    • A large blind sac that is the commencement of the large intestine, located in the right iliac fossa above the lateral half of the inguinal ligament.

  • Dimensions:

    • Length: 6 cm

    • Width: 7.5 cm

Appendices and Arterial Supply

  • Caecal Anatomy:

    • The arterial supply is from caecal branches of the ileocolic artery.

    • Venous drainage into the superior mesenteric vein.

    • Sympathetic nerves derived from T11 to L1 and parasympathetic from vagus.

Ileocaecal Valve Structure

  • Anatomy:

    • Consists of two lips and two frenula:

      • Upper Lip: Horizontal, at the ileocolic junction.

      • Lower Lip: Longer, concave, at the ileocaecal junction.

Vermiform Appendix

  • General Characteristics:

    • Length varies from 2 to 20 cm, average of 9 cm; longer in children.

    • Diameter is about 5 mm with a narrow lumen.

  • Positions:

    1. Paracolic or 11 o’clock position: appendix passes upwards and to the right.

    2. Retrocaecal (12 o’clock position): lies behind the caecum or colon, most common at 65%.

    3. Upwards and to the left.

    4. Horizontally to the left (towards the sacral promontory).

    5. Pelvic or 4 o’clock position: descends into the pelvis (30%).

    6. Midinguinal or 6 o’clock position: lies below the caecum.

  • Appendicular Orifice:

    • McBurney’s point is the site of maximum tenderness in appendicitis, located at the junction of the lateral 1/3 and medial 2/3 of the line joining the right anterior superior iliac spine to the umbilicus.

Blood Supply and Nerve Supply

  • Appendicular Artery: Branch of the lower division of the ileocolic artery.

  • Venous Drainage: Through appendicular, ileocolic, and superior mesenteric veins to the portal vein.

  • Nerve Supply:

    • Sympathetic nerves from thoracic segments 9 and 10 via the coeliac plexus.

    • Parasympathetic from the vagus nerve.

  • Referred Pain: Felt at the umbilicus, similar to pain from the small intestine and testis.

Clinical Anatomy

  • Appendicitis: Inflammation of the appendix, commonly seen in adolescents.

    • McBurney’s point corresponds to the position of the appendix base.

Ascending Colon

  • Characteristics:

    • Length: 12.5 cm, extends from the caecum to the inferior surface of the right lobe of the liver.

Transverse Colon

  • Characteristics:

    • Length: 50 cm, extends from the right colic flexure to the left colic flexure.

    • Suspended by the transverse mesocolon, attached to the anterior border of the pancreas.

Descending Colon

  • Characteristics:

    • Length: 25 cm, extends from the left colic flexure to the sigmoid colon.

Sigmoid Colon

  • Characteristics:

    • Length: 37.5 cm, extends from the pelvic brim to the third piece of the sacrum.

Tables: Comparisons

  • Differences between Small and Large Intestine:

    • Appendix epiploicae: Present in large intestine, absent in small intestine.

    • Taeniae coli: Present in large intestine, absent in small intestine.

    • Sacculations: Present in large intestine, absent in small intestine.

    • Villi: Absent in large intestine.

  • Transverse Colon:

    • Right two-thirds supplied by the middle colic branch of superior mesenteric artery; left one-third supplied by ascending branch of left colic artery.

  • Hepatic vs. Splenic Flexure:

    • Hepatic flexure: anterior on the right side, right angle, supplied by right colic artery.

    • Splenic flexure: posterior on the left side, acute angle, supplied by left colic artery.

Key Facts

  • The small intestine features villi; most of the duodenum is fixed and retroperitoneal.

  • Pain from appendicitis may initially be referred to the umbilical region, eventually localizing to the right iliac fossa.

Meckel’s Diverticulum

  • Occurrence: 2% of the population.

  • Length: Typically 2 inches (5 cm).

  • Location: About 2 feet (60 cm) proximal to the ileocaecal valve, attached to the antimesenteric border of the ileum.

  • Caliber: Equal to that of the ileum.

  • Clinical Relevance: Can cause intestinal obstruction.