Lecture 09B: Abdominal Viscera

Learning Objectives

  • Describe the courses of vessels, lymphatics, and nerves supplying the esophagus & stomach.

  • Describe gastric cell types and their contribution to digestive function.

  • Describe the components and attachments of abdominal viscera: intra-abdominal esophagus, stomach, small intestine, large intestine, appendix.

  • Describe the courses of vessels, lymphatics, and nerves supplying the small intestine, large intestine, appendix, rectum, & anus.

  • Identify pertinent enteric histological components that contribute to the digestive process.

  • Describe the anatomic pathology and consequences of gastric and duodenal ulcers, pyloric stenosis, atresia, malrotation, volvulus, Meckel’s diverticulum, intussusception, appendicitis, diverticula, and polyps.

Stomach Anatomy

  • Cardia

    • Surrounds the opening of the esophagus distal to the gastroesophageal junction.

    • Secretes mucus and bicarbonate to protect the distal esophagus.

    • This region acts as a transition zone between squamous and gastric mucosa.

  • Fundus

    • The anterior portion of the stomach that forms a dome superior to the gastroesophageal junction.

    • Serves as a reservoir for ingested food and secretes hydrochloric acid, intrinsic factor, and pepsinogen.

  • Cardiac notch (angle of His)

    • The angle created where the esophagus enters the stomach.

    • Serves as a mechanical antireflux flap valve, closing with gastric distention to prevent reflux.

  • Body

    • The largest region central to the stomach.

    • Main site of acid and enzyme secretion, with strong muscular churning to form chyme.

    • Major site for protein digestion.

  • Antrum

    • Distal stomach that secretes mucus and gastrin, mechanically grinding food before emptying.

  • Incisura angularis

    • A sharp notch on the lesser curvature, marking the division between the body and antrum of the stomach.

    • Cells below this level start to change in the stomach (division of acid-secreting and gastrin-secreting regions).

  • Pylorus

    • The distal part of the stomach/pylorus (contains the pyloric sphincter).

    • Regulates gastric emptying and prevents duodenal reflux.

    • Also secretes mucus.

  • Rugae

    • Longitudinal mucosal folds lining the internal stomach to allow for stomach expansion and increase surface area.

  • Oblique Muscle

    • The innermost of three smooth muscle layers in the stomach.

    • In addition to circular and longitudinal muscle layers, it provides a unique churning motion, enhancing mechanical digestion.

  • Greater Curvature

    • The long, convex outer border of the stomach.

    • Attachment of the gastrosplenic ligament and greater omentum.

  • Lesser Curvature

    • The concave medial inner border of the stomach.

    • Attachment of the lesser omentum (composed of hepatogastric and hepatoduodenal ligaments).

Stomach Mucosal Structure

  • Mucosa

    • The innermost layers of the stomach wall composed of epithelium, lamina propria, and muscularis mucosae.

    • Protects underlying tissues from acidic gastric contents and digestive enzymes.

    • Must resist $HCl$ and pepsin via alkaline mucus regulated by prostaglandins.

  • Pit

    • Invaginations of mucosal epithelium that open into the lumen of the stomach.

    • Act as channels through which glandular secretions can be transported to the lumen.

    • Lined by mucous cells that secrete mucus and bicarbonate.

  • Neck

    • Transitional area between the pit and gland.

    • Contains mucous cells and stem cells that replenish all epithelial cell types every 3-5 days.

  • Gland

    • Gastric glands extend from the neck to the base of the mucosa, acting as primary secretors of mucus.

Gastric Cell Types and Functions

  • Parietal Cell

    • Located in upper/mid region of gland, primarily in fundus and body of the stomach.

    • Secretes hydrochloric acid ($HCl$) to denature proteins and activate pepsinogen.

    • Secretes intrinsic factor, which binds to vitamin $B_{12}$ and is essential for its absorption in the ileum.

    • Stimulated by vagal nerve, gastrin, and histamine.

  • ECL Cell

    • Located in fundic glands near parietal cells.

    • Enterochromaffin-like Cells secrete histamine to bind to $H_2$ receptors on parietal cells, stimulating H$^+$ secretion in the cAMP pathway.

    • Stimulated by gastrin and vagal activity; inhibited by somatostatin.

  • G-Cell

    • Located in pyloric glands (fewer in fundus).

    • Releases gastrin into the bloodstream in response to alkaline chyme and gastric distention.

    • Gastrin stimulates parietal cells to increase $HCl$ secretion, stimulates ECL cells to increase histamine production, and promotes mucosal growth and gastric motility.

  • Alkaline Tide

    • Temporary rise in blood pH due to bicarbonate secretion in the bloodstream as a byproduct of $HCl$ formation from parietal cells.

    • Maintains ionic balance to carry away bicarbonate from split carbonic acid.

  • Chief Cell

    • Located in the base of gastric glands.

    • Secretes pepsinogen in an inactive state to avoid self-digestion.

    • Pepsinogen is converted to pepsin by $HCl$, breaking down proteins into shorter peptides.

    • Also secretes gastric lipase that breaks down short-chain triglycerides.

  • D-Cell

    • Located throughout the stomach and concentrated in the antrum.

    • Secretes somatostatin that inhibits G-Cells, ECL cells, and parietal cells to decrease acid secretion.

    • Serves as a negative feedback regulator of acid secretion.

  • Other Neuroendocrine Cells

    • Modulate motility, blood flow, and secretion.

    • Enterochromaffin cells release serotonin to increase peristalsis.

    • $X/A$-like Cells secrete ghrelin (hunger hormone) mainly in fundus.

    • Others secrete vasoactive intestinal peptide, substance P, or other peptides.

Gastric Function and Regulation

  • Mucous Cells

    • Secrete mucus and bicarbonate to protect the epithelium from acids and enzymes.

  • Vagal Reflexes

    • Distention of the stomach from food activates mechanoreceptors, stimulating vagovagal reflexes, enhancing peristaltic waves (ECL cells secrete serotonin to enhance motility).

  • G-Cells and Gastrin Secretion

    • Presence of protein buffers increases gastric acidity, causing pH to rise, which removes inhibition from G-cells and parietal cells.

    • G-Cells, stimulated by peptides and vagal input, increase gastrin secretion.

  • Role of ECL and Parietal Cells

    • ECL cells stimulated by gastrin secretion and the vagus nerve increase histamine secretion.

    • Parietal cells are stimulated by gastrin and histamine, increasing $HCl$ secretion, generating alkaline tide in blood and additionally secreting intrinsic factor to bind vitamin $B_{12}$.

  • Chief Cells

    • Stimulated by gastrin and acid; secrete pepsinogen converted to pepsin in the acidic environment, and additionally secrete gastric lipase.

  • Somatostatin Release by D-Cells

    • D-Cells start releasing somatostatin when pH decreases to suppress parietal, G, and ECL cell activities.

  • X/A-like Cells Function

    • Release ghrelin during fasting to stimulate hunger.

Stomach Blood Supply

Arterial Supply

  • Celiac Trunk

    • Left Gastric Artery

    • Branches: esophageal branches.

    • Supplies the superior part of the stomach near the lesser curvature.

    • Anastomoses with right gastric artery on lesser curvature of the stomach.

    • Splenic Artery

    • Dorsal pancreatic artery; pancreatic branches; pancreatica magna artery; caudal pancreatic artery.

    • Short gastric arteries supply fundus and upper parts of stomach near the greater curvature.

    • The left gastroepiploic (gastro-omental) artery supplies the mid-part of stomach near the greater curvature and greater omentum.

    • Anastomoses with the right gastroepiploic artery.

    • Common Hepatic Artery

    • Gastroduodenal Artery

      • Supraduodenal artery; retroduodenal artery (upper duodenum); posterior superior pancreaticoduodenal artery; anterior superior pancreaticoduodenal artery (upper part of head of pancreas).

    • Right Gastroepiploic (gastro-omental) Artery: supplies lower part of pyloric region of stomach, right part of the greater curvature of the stomach and greater omentum.

    • Anastomoses with left gastroepiploic artery.

    • Proper Hepatic Artery

    • Right gastric artery branches into the right and left hepatic arteries which supply the liver.

Venous Drainage

  • Venous Supply

    • Left and right gastric veins.

    • Short gastric veins and left gastroepiploic vein (from splenic vein).

    • Right gastroepiploic vein (from superior mesenteric vein) draining into the portal vein.

Lymphatics

  • Visceral lymphatics follow arterial supply.

  • Gastric Lymph Nodes Grouped into 4 Major Zones

    • Zone I: Left gastric: drain cardia and superior lesser curvature.

    • Zone II: Right gastric nodes → hepatic nodes: drain body, inferior lesser curvature, and antrum.

    • Zone III: Short gastric & left gastroepiploic nodes → pancreaticosplenic nodes: drain fundus and superior greater curvature.

    • Zone IV: Right gastroepiploic nodes → subpyloric nodes → hepatic nodes: drain inferior greater curvature and pylorus.

  • All lymph from the stomach eventually passes to the celiac nodes located around the root of the celiac artery.

  • Celiac nodes → cisterna chyli → thoracic duct.

Innervation

Sympathetic Innervation

  • Preganglionic fibers from T6-T9 branch into the greater splanchnic nerve.

  • Synapse at the celiac ganglion.

  • Postganglionic fibers follow branches of the celiac trunk to the stomach.

  • Function: inhibits motility and secretion, constricts blood vessels, and contracts sphincters.

Vagus Nerve

  • Parasympathetic: Motor and sensory functions.

  • Anterior trunk: supplies anterior stomach wall and lesser curvature.

  • Posterior trunk: supplies posterior wall, fundus, greater curvature.

  • Function: stimulation of motility, secretion (stimulates parietal and chief cells), relaxation of sphincters.

Mixed Plexus

  • Contributions from sympathetic trunk and vagal trunks.

Enteric Nervous System

  • Composed of intrinsic neurons and glia within the walls of the entire GI tract, modulated by extrinsic parasympathetic and sympathetic nerve fibers.

  • Myenteric (Auerbach) Plexus: Located between circular and longitudinal muscle layers to control peristalsis and muscle tone.

  • Submucosal (Meissner) Plexus: Situated within submucosa to control glandular secretion, local blood flow, and mucosal activity, modulated by parasympathetic and sympathetic inputs.

Gastric Pathology

Peptic Ulcers

  • Defined as mucosal defects penetrating through muscularis mucosa due to exposure to acid and pepsin.

  • Result from an imbalance in mucosal defense mechanisms and damaging acidity.

  • Ulcers are named by location:

    • Gastric: most often along the lesser curvature of the stomach (incisura angularis).

    • Duodenal: most commonly in the first part of the duodenum.

    • ‘Peptic’ refers to benign occurrences.

Etiology

  • More than 90% of peptic ulcers are associated with Helicobacter pylori infection.

    • H. pylori produces urease, which is converted to ammonia, buffering local acid but damaging epithelium.

    • Induces inflammation, impairing the mucus barrier and increasing gastrin levels.

  • Duodenal ulcers are associated with hyperchlorhydria; gastric ulcers can show hypochlorhydria and malignant transformation.

  • Chronic NSAID use can contribute to ulcer formation; NSAIDs inhibit COX-1, decrease prostaglandins leading to decreased mucus production, blood flow, and impaired epithelial repair.

Complications of Peptic Ulcers

  • Bleeding: “coffee-ground” hematemesis or melena (stool containing partly digested blood).

  • Perforation: leads to peritonitis characterized by ‘board-like’ rigidity of the abdomen.

  • Patients experience epigastric pain.

  • Potential malignancy with gastric ulcers.

Treatment of Peptic Ulcers

  • Proton Pump Inhibitors (PPIs) or H2 blockers to suppress acid production and promote healing.

  • Antibiotic therapy to treat H. pylori infection.

  • Surgery if severe.

Surgical Augmentation Techniques

Fundoplication

  • Procedure where the gastric fundus is wrapped around the distal esophagus and sutured in place to reinforce the lower esophageal sphincter.

Antrectomy

  • Removal of gastric antrum where G-cells are primarily located to decrease acid secretion.

Pyloroplasty

  • Surgical enlargement of the pyloric canal to facilitate gastric emptying and decrease duodenogastric reflux.

Small Intestine Anatomy

  • Length: The longest part of the GI tract, extending from the pyloric orifice to the ileocecal fold.

  • Three Parts:

    • Duodenum

    • Jejunum

    • Ileum

  • Function: Chemical digestion, nutrient absorption, and disposal of unnecessary components.

Duodenum

  • Description: First and shortest part of the small intestine, about 10 inches long, with the widest lumen.

  • Location: Extends from pylorus to the duodenojejunal flexure, mostly retroperitoneal except for the beginning which is connected to the liver by the hepatoduodenal ligament.

Pyloric Sphincter

  • Circular thickening of the inner smooth muscle layer at the distal end of the pyloric canal of the stomach.

  • Encircles the pyloric orifice that opens into the first part of the duodenum.

  • Functions as a physiological valve, maintaining tonic contraction to prevent premature emptying of gastric contents.

  • Relaxes intermittently to allow small, regulated amounts of chyme into the duodenum for optimal digestion and buffering.

Functions of the Duodenum

  • Neutralization of gastric acid, chemical digestion, and some absorption.

Ligament of Treitz

  • Located at the beginning of the jejunum; holds jejunum up and pulls distal duodenum posteriorly.

Brunner’s Glands

  • Submucosal glands that produce alkaline mucus to help neutralize gastric acid.

Four Parts of the Duodenum

  1. Superior Part

    • Extends from the pyloric orifice to the neck of the gallbladder.

    • Most duodenal ulcers occur here.

    • Held superiorly by the hepatoduodenal ligament.

  2. Descending Part

    • Longest section, where the duodenum surrounds the head of the pancreas.

  3. Inferior Part

    • Crosses horizontally anterior to the inferior vena cava (IVC) and aorta.

    • Terminates at the duodenojejunal flexure.

  4. Ascending Part

    • Held superiorly by the Ligament of Treitz.

Duodenal Arterial Supply

  • Supply from:

    • Supraduodenal artery

    • Anterior superior pancreaticoduodenal branches

    • Posterior superior pancreaticoduodenal branches

    • Gastroduodenal artery (proximal to papilla)

    • Anterior inferior pancreaticoduodenal branches

    • Posterior inferior pancreaticoduodenal branches

    • First jejunal branch from the superior mesenteric artery (distal to papilla).

Duodenal Pathology

Pyloric Stenosis

  • Refers to the narrowing of the valve between the stomach and small intestine, preventing normal passage of food.

  • Symptoms include projectile vomiting, dehydration, weight loss/failure to thrive, and hunger/colic.

  • Repair usually done via pyloromyotomy.

Jejunum

Anatomy

  • Description: Proximal 2/5 of the small intestine extending from duodenojejunal flexure to transition with the ileum.

  • Location: Mostly in left upper quadrant, approximately 8 feet long.

Structure

  • Thicker wall and larger diameter than ileum.

  • Inner mucosa has prominent folds (plicae circulares) that increase surface area (3x) and slow chyme flow.

  • Contains long, densely packed villi (velvety) to increase surface area.

  • Each villus has a central lacteal (lymphatic capillary) and a capillary network for nutrient absorption.

  • Has less mesenteric fat, which may contribute to enhanced mobility for increased peristaltic efficacy in the jejunum, as vigorous mixing is required for maximum absorption.

Function

  • Completes most nutrient absorption, including carbohydrates, amino acids, water-soluble vitamins, and the majority of electrolytes.

Arterial Supply of Jejunum

  • Supply: Jejunal arteries branch off the superior mesenteric artery.

  • Characteristics: Less prominent anterior arcades and longer vasa recta (straight arteries) than the ileum.

Ileum

Anatomy

  • Description: Most distal portion of the small intestine, approximately 11 feet long, extending from the end of the jejunum to the ileocecal junction.

  • Location: Mainly positioned in the lower right quadrant.

Structure

  • Thinner walls and smaller lumen than jejunum; fewer, less prominent plicae circularis; smooth circular folds.

  • Villi are shorter and in fewer numbers than jejunum, resulting in reduced surface area for absorption.

  • Contains Peyer’s patches, clusters of lymphoid follicles that prevent bacterial entry into portal blood.

  • Increased mesenteric fat relative to the jejunum, contributing to its reduced need for mobility.

Function

  • Absorbs vitamin $B_{12}$ and iron, bile salts, and enhances immune function via Peyer’s patches due to increased bacteria.

Arterial Supply of Ileum

  • Supply: Ileal arteries branch off the superior mesenteric artery and the ileocolic artery branches off the superior mesenteric artery that supplies distal ileum at ileocecal junction.

  • More prominent anterior arcades and shorter vasa recta (straight arteries) than jejunum.

Mesenteric Arteries

Superior Mesenteric Artery

  • Branches supplying various regions include:

    • Inferior pancreaticoduodenal artery

    • Middle colic artery

    • Jejunal arteries

    • Ileal arteries

    • Right colic artery

    • Ileocolic artery

  • Areas supplied: lower duodenum & head of pancreas, transverse colon, jejunum, ileum, ascending colon, cecum, appendix (appendiceal branch) & terminal ileum.

Small Intestine: Venous Drainage

  • All venous drainage from the small intestine ultimately enters the hepatic portal system, which carries nutrient-rich blood to the liver for processing.

  • Veins: Largely parallel to the corresponding arteries.

    • Intestinal veins branch off the ileocolic vein, right colic vein, middle colic vein, pancreaticoduodenal veins, and right gastroepiploic vein draining into the superior mesenteric vein.

    • Branch off sigmoid vein, left colic vein, and superior rectal vein that drain into the inferior mesenteric vein, subsequently draining into the splenic vein.

Small Intestine: Lymphatics

  • Visceral Lymphatics: Follow arterial supply.

  • Drain into superior and inferior mesenteric nodes from the small intestine.

Enteric Histology

  • The small intestine (duodenum → jejunum → ileum) is the main site for chemical breakdown and absorption of nutrients, involving a coordinated process of:

    • Mechanical mixing (segmentation, peristalsis).

    • Pancreatic and brush-border enzymes.

    • Bile salts (for lipids).

    • Highly specialized mucosal surface (plicae circulares, villi, microvilli) maximizing surface area.

    • Most absorption occurs in the jejunum, with the ileum specializing in bile salts, vitamin $B_{12}$, and immune surveillance.

Mechanical Processing

  • Segmentation Contractions: Mix chyme with digestive secretions, exposing nutrients to absorptive surfaces.

  • Peristalsis: Propels chyme distally at a regulated pace to allow adequate digestion time.

Nutritional Absorption Processes

Carbohydrates

  • Luminal Phase (duodenum):

    • Pancreatic amylase breaks down starch into maltose, maltotriose, and $ ext{α}$-limit dextrins.

    • Salivary amylase plays a minor role (inactivated by gastric acid).

  • Membranous Phase (brush border of enterocytes):

    • Disaccharidases (maltase, sucrase, lactase, isomaltase) convert:

    • Maltose → glucose

    • Sucrose → glucose + fructose

    • Lactose → glucose + galactose

Proteins

  • Luminal Phase (stomach & duodenum):

    • Pepsin initiates protein digestion in stomach to polypeptides.

    • Pancreatic proteases (trypsin, chymotrypsin, elastase, carboxypeptidases) further break polypeptides into oligopeptides and amino acids.

    • Activation:

    • Trypsinogen activated by brush-border enteropeptidase → trypsin → activates other pancreatic zymogens.

  • Membranous Phase:

    • Brush-border peptidases break oligopeptides into dipeptides, tripeptides, and amino acids.

Lipids

  • Emulsification (stomach & duodenum):

    • Mechanical mixing + bile salts break large fat globules into emulsified droplets.

  • Enzymatic Digestion (duodenum):

    • Pancreatic lipase, aided by colipase, breaks triglycerides into monoglycerides + free fatty acids.

    • Phospholipase A₂ acts on phospholipids; cholesterol esterase acts on cholesterol esters.

  • Micelle Formation:

    • Products combine with bile salts to form micelles, allowing transport through the unstirred water layer to the enterocyte brush border.

  • Absorption:

    • Lipid components diffuse across the membrane (simple diffusion + some facilitated transport).

    • Inside enterocytes:

    • Long-chain fatty acids & monoglycerides are re-esterified to triglycerides.

    • Packaged into chylomicrons → enter lacteals (lymphatic vessels in villi) → thoracic duct → systemic circulation.

    • Short- and medium-chain fatty acids enter portal blood directly.

Surface Area and Absorption

  • Plicae Circulares, Villi, and Microvilli:

    • Expand surface area for absorption and slow transit time.

    • Total small bowel surface area is approximately 18 feet x 18 feet.

Brush Border Enzymes

  • Enteropeptidase:

    • Attached to duodenal brush border.

    • Activates trypsin which activates chymotrypsin & carboxypeptidase (pancreatic enzymes) to initiate the protein digestion process in the duodenum.

Crypts of Lieberkuhn

  • Contain structures:

    • Neuroendocrine cells, Paneth cells, stem cells, and enterocytes.

    • Enterocytes create an alkaline fluid to dilute chyme and aid absorption.

    • Paneth cells synthesize lysozyme, defensins, and TNF-$ ext{α}$ to protect the luminal surface.

    • Stem cells regenerate enterocytes from the top of the crypt, migrating towards the tip, with apoptosis occurring in 4-5 days.

    • Neuroendocrine cells produce several hormones including gastrin, cholecystokinin, and secretin.

Small Intestine Pathology

Atresia

  • Congenital absence or closure of a normal body opening or tubular structure.

  • Topical issues include obstruction with bowel distension, vomiting, potential aspiration, starvation, and jaundice if below bile duct.

  • Surgical repair can be achieved via duodenoduodenostomy or gastrojejunostomy.

Fetal Intestinal Rotation

  • Week 5: Midgut elongation and rotation begin, creating a physiologic herniation.

  • A 90° counterclockwise rotation (viewed from the front) occurs around the axial vitelline artery (which becomes the superior mesenteric artery, SMA).

  • Closure of Umbilical Ring: The gut subsequently undergoes an additional 180° counterclockwise rotation upon returning to the abdominal cavity (total rotation of 270°).

  • Morphogenesis leads components to fuse with mesodermal coverings and shape the final positioning of structures in the abdominal cavity.

Mesenteric Occlusion

  • Results in gangrene occurring within 1 hour.

Malrotation

  • A congenital condition where intestines do not form correctly during pregnancy and settle incorrectly in the abdomen.

  • Symptoms include bowel blockage or twisting (volvulus).

Meckel's Diverticulum

  • A remnant of the vitelline duct (omphalomesenteric duct) that arises from the ileum.

  • Represents a common defect found in the context of the rule of 2’s:

    • 2% of the population have one.

    • 50% of symptomatic lesions typically present by age 2, while others present in the first 2 decades of life.

    • Diverticuli in adults only become symptomatic about 2% of the time.

    • This condition is typically located within 2 feet of the ileocecal valve and is commonly about 2 inches in length.

    • 50% of cases contain heterotopic mucosa (usually gastric, occasionally pancreatic).

Intussusception

  • Defined as the “telescoping” of bowel.

  • Typically features a triad of symptoms:

    • Vomiting

    • Abdominal pain

    • Passage of blood via rectum

  • Complications can include obstruction, ischemia/necrosis, sepsis, and internal bleeding due to affected blood supply.

  • Potential lead points include lymphoid hyperplasia, Meckel's diverticulum, lymphoma of the bowel, and other entities involving the bowel.

  • Treatments may include barium enema or surgery to address the telescoping.

Large Intestine

Description

  • Extends from the distal ileum to the anus.

  • Larger in diameter than the small bowel.

  • Functions include:

    • Absorption of water & electrolytes (salts).

    • Formation and storage of feces.

    • Houses microbiota to aid in fermentation of undigested materials.

Regional Functions

  • Cecum

    • First part of the large intestine located in the right lower quadrant.

    • Receives chyme from ileum via ileocecal valve.

    • The vermiform appendix is attached, consisting of lymphoid tissue.

  • Ascending Colon

    • Runs along the right abdominal wall to the liver.

    • Absorbs most of the remaining water and other key nutrients from indigestible material, solidifying it into stool.

  • Transverse Colon

    • Runs horizontally across the abdomen.

  • Descending Colon

    • Runs down the left side of the abdominal wall, storing feces before it is emptied into the rectum.

  • Sigmoid Colon

    • S-shaped portion leading to the rectum.

    • Highly muscular, involved in storage of feces before defecation, contracts to increase pressure inside the colon, causing stool to move into the rectum.

  • Rectum

    • Straight muscular tube that stores feces.

    • Contains stretch receptors that initiate defecation reflex when full.

  • Anal Canal

    • Terminal segment containing an internal sphincter (involuntary, smooth muscle) and external anal sphincter (voluntary, skeletal muscle).

    • Ends at the anus where feces are expelled.

Structures of the Large Intestine

Among key structures are the taeniae coli (three longitudinal smooth muscle bands), haustra (sacculations formed by contraction of the taeniae), and epiploic appendages (small fat-filled pouches serving as reserves and providing lubrication).

  • Mucosa of colon: Lacks villi (in contrast to small intestine) but houses numerous goblet cells for mucus secretion and lubrication.

Arterial Supply of Large Intestine

Superior Mesenteric Artery

  • Branches include:

    • Inferior pancreaticoduodenal artery.

    • Middle colic artery.

    • Jejunal arteries.

    • Ileal arteries.

    • Right colic artery.

    • Ileocolic artery.

  • Areas supplied involve: head of pancreas, lower duodenum, transverse colon, jejunum, ileum, ascending colon, cecum, appendix (the appendiceal branch) & terminal ileum.

Inferior Mesenteric Artery

  • Branches include:

    • Left colic artery.

    • Sigmoid arteries (2-3).

    • Superior rectal artery.

  • Areas supplied encompass: descending colon, sigmoid colon, and superior part of rectum.

Rectum & Anal Arterial Supply

  • Superior Rectal Artery: Provided by the inferior mesenteric artery.

  • Middle Rectal Artery: Given by the internal iliac artery.

  • Inferior Rectal Artery: Given by the internal pudendal (from the internal iliac artery).

Venous Drainage of the Large Intestine

  • Middle Colic Vein: Drains regions such as the cecum, appendix, ascending colon, and transverse colon.

  • Superior Mesenteric Vein: Receives drainage from the left colic vein, sigmoid veins, and superior rectal vein draining regions of the descending colon, sigmoid colon, rectum, and transverse colon.

  • Inferior Mesenteric Vein: Directly connects to the splenic vein.

Lymphatics of the Large Intestine

  • The lymphatic drainage patterns follow the arterial blood supply, encompassing structures such as epicolic, paracolic, intermediate colic (ileocolic) and draining via superior/inferior mesenteric and pre-aortic (lateral aortic/celiac) structures.