Abdomen Anatomy Comprehensive Study Notes

Peritoneal Cavity

• Definition: the potential space between the parietal and visceral layers of the peritoneum.

• In life, surfaces of organs (visceral peritoneum) contact the parietal peritoneum of the body wall, reducing the peritoneal cavity to a potential space containing some serous fluid.

• The peritoneal cavity consists of two portions: the Greater Sac and the Lesser Sac (also known as the Omental Bursa).

Greater and Lesser Omentum

• Greater omentum: prominent, four-layered peritoneal fold that hangs from the stomach and the proximal part of the duodenum; after descending, it folds back and attaches to the anterior surface of the transverse colon and its mesentery.

• Greater omentum is divided into three portions:

  • Gastrocolic Ligament

  • Gastrophrenic Ligament

  • Gastrosplenic Ligament

• Lesser omentum: a much smaller, double-layered peritoneal fold that connects the lesser curvature of the stomach and the proximal part of the duodenum to the liver.

• The lesser omentum also connects the stomach to the triad of vessels that run between the duodenum and liver in the free edge of the lesser omentum.

• The greater omentum is divided into two portions:

  • Hepatogastric Ligament

  • Hepatoduodenal Ligament

Ligaments of the Greater Omentum

• Gastrocolic ligament: part attached to the greater curvature of the stomach; covers anteriorly the transverse colon and extends inferiorly to cover portions of the small intestine.

• Gastrophrenic ligament: connects the superior part of the greater curvature of the stomach to the inferior aspect of the diaphragm.

• Gastrosplenic ligament: passes from the greater curvature of the stomach to the spleen.

Lesser Omentum

• Connects the lesser curvature of the stomach and the proximal part of the duodenum to the liver.

• It also connects the stomach to the triad of structures in the free edge of the lesser omentum.

• Hepatogastric Ligament and Hepatoduodenal Ligament are the two portions of the lesser omentum.

Stomach and Omenta

Curvatures of the Stomach

• Greater Curvature

• Lesser Curvature

External Features of the Stomach

• The stomach is divided into four parts:

  • Cardia

  • Body

  • Fundus

  • Pyloric Region → Pyloric Antrum → Pyloric Canal

• The angular notch (incisura angularis) marks the junction of the body with the pyloric region along the lesser curvature.

Internal Features of the Stomach

• Gastric folds are called rugae.

• Rugae allow the stomach to stretch to accommodate large meals and help grip/move food during digestion.

Small Intestine

Small Intestine Overview

• Three portions: Duodenum, Jejunum, Ileum.

Duodenum

• C-shaped and molded around the head of the pancreas.

• Four parts: Superior, Descending, Horizontal, Ascending.

• First part has a mesentery and is very mobile; the rest of the duodenum is retroperitoneal (immobile).

Internal Features of the Duodenum

• On the inner surface of the medial wall of the second part are two mucosal elevations called papillae:

  • Minor duodenal papilla

  • Major duodenal papilla

Hepatopancreatic Ampulla of the Duodenum (of Vater)

• The common bile duct joins the main pancreatic duct to form the hepatopancreatic ampulla (of Vater).

• This ampulla has a sphincter: hepatopancreatic sphincter (of Oddi).

• After joining, the hepatopancreatic ampulla opens on the major duodenal papilla.

• The opening of the major duodenal papilla is the narrowest part of the biliary passages and a common site for gallstone impaction.

Accessory Pancreatic Duct in the Duodenum

• If present, opens on the minor duodenal papilla.

• Drains the uncinate process and the inferior part of the head of the pancreas.

• Usually joins the main pancreatic duct; in some individuals, it is a separate duct opening into the minor duodenal papilla.

Duodenojejunal Flexure

• The duodenojejunal flexure (duodenojejunal junction) is where the duodenum ends and the jejunum begins.

• Occurs at approximately $L2$ vertebral level.

Suspensory Ligament of the Duodenum (Ligament of Treitz)

• Ascending part of the duodenum is suspended by the suspensory muscle of the duodenum (ligament of Treitz).

• Band of retroperitoneal fibrous and muscular tissue that arises from the right crus of the diaphragm, descends, crosses to the opposite side, and anchors the intestine at the duodenal junction.

Jejunum and Ileum

• Jejunum begins at the duodenojejunal junction.

• Ileum ends at the ileocecal junction (junction of terminal ileum and cecum).

• The mesentery is a fan-shaped fold of peritoneum that attaches the jejunum and ileum to the posterior abdominal wall.

• The root of the mesentery extends from the duodenojejunal junction (on the left side of vertebra $L2$) to the ileocolic junction and the right sacroiliac joint.

Mesentery (General)

• The mesentery contains arteries, veins, nerves; the omental apron portion of the greater omentum is often seen turned up near the mesentery and viscera (as in the diagram).

• Key vessels within the mesentery include: Jejunal and Ileal arteries; Arteriae rectae; Superior mesenteric vessels.

Large Intestine

Large Intestine Overview

• The large intestine frames the small intestine on three sides:

  • Cecum and ascending colon frame on the right.

  • Transverse colon frames from above.

  • Descending and sigmoid colon frame on the left.

Ileocecal Junction

• The ileocecal junction is the union of the ileum (small intestine) with the cecum (large intestine).

• The ileocecal orifice (bounded by the ileocecal valve) allows material to cross from ileum to cecum.

Vermiform Appendix (Appendix)

• Blind intestinal diverticulum containing masses of lymphoid tissue.

• Has a short triangular mesentery (mesoappendix) attaching to the cecum and proximal part of the appendix.

• The mesoappendix contains the appendicular artery.

Ascending Colon

• Second part of the large intestine.

• Ascends on the right side of the abdomen from the cecum to the right lobe of the liver, then turns left at the right colic (hepatic) flexure.

Transverse Colon

• Third, longest, and most mobile part of the large intestine.

• Crosses the abdomen from the right colic flexure to the left colic (splenic) flexure; then turns inferiorly to become the descending colon.

• The left colic flexure is attached to the diaphragm by the phrenicocolic ligament.

• Between the two flexures, the transverse colon is freely movable.

• Its mesentery is the transverse mesocolon and it adheres to the inferior border of the pancreas.

Descending Colon

• Descends from the left colic flexure to the pelvis.

• Posterior surface is retroperitoneal (peritoneum on its anterior side only).

• Retroperitoneal definition: organs with peritoneum on the anterior side only and not suspended by a mesentery.

Sigmoid Colon

• S-shaped loop of variable length connecting the descending colon to the rectum.

• Usually has a long mesentery (sigmoid mesocolon) and substantial freedom of movement, especially in the middle portion.

• Rectosigmoid junction located at the level of vertebra $S3$.

Large Intestine: General Features

• Taeniae coli: three narrow longitudinal bands of smooth muscle that run from the base of the appendix to the wall of the rectum.

• Haustra: sacculations of the colon wall between the taeniae.

• Appendices Epiploicae: small fat-filled pouches hanging from the colon.

Cross-Sectional View (Key Relationships)

• Right colic flexure near the liver; transverse colon; left colic flexure near the spleen; diaphragmatic attachments; ceacal region with appendiceal artery and mesentery;

• Cecum, Vascular architecture: appendiceal artery, ileocolic artery, ileum, colon segments, and the taeniae coli.

Liver

Surface Features

• The liver has a convex diaphragmatic surface and a relatively flat visceral surface.

Structures on the Visceral Surface

• Inferior Vena Cava (IVC)

• Gallbladder

• Ligamentum Venosum

• Ligamentum Teres

• Porta Hepatis

Porta Hepatis (Gate for Hepatic Vessels)

• A transverse fissure where vessels, the hepatic nerve plexus, and hepatic ducts enter/leave the liver.

• Structures identifiable in the porta hepatis: Portal Vein, Hepatic Arteries, Hepatic Ducts.

• Study note: The common hepatic duct is formed by the union of the right and left hepatic ducts; they drain into the common hepatic duct.

Liver Lobes

• Right Lobe

• Left Lobe

• Quadrate Lobe

• Caudate Lobe

Relationship with Lesser Omentum

• The lesser omentum stretches from the lesser curvature of the stomach and the initial portion of the duodenum to the visceral surface of the liver.

• Hepatoduodenal ligament at the right margin of the lesser omentum contains the portal triad:

  • Portal Vein

  • Hepatic Artery Proper

  • Common Bile Duct

• Epiploic foramen (Winslow) is located at the hepatoduodenal ligament and provides access to the omental (lesser) sac; passing fingers inferiorly accesses the inferior recess of the lesser sac; passing superiorly accesses the superior recess.

Peritoneal Attachments and Recesses

• Falciform ligament attaches the liver to the anterior body wall and divides the liver into left medial and right lateral lobes; it also divides the subphrenic recess into right and left portions.

• Diaphragmatic surface is covered by visceral peritoneum except at the bare area of the liver.

• Bare area delineated by reflection of peritoneum from the diaphragm to the liver via the anterior and posterior layers of the coronary ligament.

• Anterior and posterior portions of the coronary ligament fuse to form the left and right triangular ligaments.

• Inferior part of the coronary ligament reflects onto the diaphragm and right kidney (hepatorenal ligament).

• Potential peritoneal space inferior to the hepatorenal ligament is the hepatorenal recess (of Morrison).

Biliary Ducts and Gallbladder

Biliary Ducts

• Right and left hepatic ducts drain into the common hepatic duct.

• Common hepatic duct joins with the cystic duct to form the bile duct (conveys bile to the duodenum).

• Callout: Hepatocystic triangle (of Callot) formed by cystic duct, common hepatic duct, and liver.

• Cystic artery is located within the hepatocystic triangle.

Gallbladder

• Stores bile produced by the liver.

• Connects to the bile duct via the cystic duct.

• Gallbladder regions: Fundus, Body, Neck.

• Contact relations: liver, duodenum, transverse colon, anterior abdominal wall.

Clinical Correlation: Cholecystoenteric Fistula

• Inflamed gallbladder can adhere to adjacent intestinal tract (duodenum or transverse colon).

• Fistula can form (cholecystoenteric fistula) allowing bile or gallstones to enter GI tract.

• Example: large gallstone can perforate into the duodenum and pass through jejunum and ileum to ileocecal valve; if impaction occurs at valve, bowel obstruction can result.

Spleen

• Located in the upper left quadrant, posterior to the stomach, just inferior to the diaphragm, opposite ribs $R9$-$R11$.

• Key features: Hilus, Visceral Surface, Diaphragmatic Surface.

• Peritoneal attachments: Splenorenal Ligament (to left kidney) and Gastrosplenic Ligament (to greater curvature of stomach).

Pancreas

Anatomy

• Head, Uncinate Process (Lingula), Neck, Body, Tail.

• The inferior vena cava (IVC) and the common bile duct lie posterior to the head of the pancreas.

• The uncinate process lies posterior to the superior mesenteric vessels.

Vessels and Ducts

• Anterior and posterior pancreaticoduodenal arteries arise from the superior pancreaticoduodenal artery.

• Inferior pancreaticoduodenal artery arises from the superior mesenteric artery.

• Main pancreatic duct begins at the tail and runs through the gland to the head, joins the common bile duct to form the hepatopancreatic ampulla (of Vater).

• The hepatopancreatic ampulla opens into the second part of the duodenum at the summit of the major duodenal papilla.

• The hepatopancreatic sphincter (of Oddi) surrounds the ampulla.

• The accessory pancreatic duct drains the uncinate process and inferior head; drains into the minor duodenal papilla; usually joins the main pancreatic duct, but may be separate.

Peritoneal Gutters (Peritoneal Recesses)

• Peritoneal gutters are spaces formed by peritoneum draping over viscera.

• Major spaces include:

  • Right Lateral (Paracolic) Gutter

  • Left Lateral (Paracolic) Gutter

  • Gutter to the Right of the Mesentery

  • Gutter to the Left of the Mesentery

Blood Vessels of the Abdomen

General Abdominal Blood Vessels

• Posterior abdominal wall vessels include: Abdominal Aorta and Right/Left Common Iliac Arteries.

• The abdominal aorta terminates at the level of vertebra $T4$ where it bifurcates into the right and left common iliac arteries.

Celiac Trunk and Branched Arteries

• Celiac trunk arises from the abdominal aorta just inferior to the diaphragm and has three main branches:

  • Common Hepatic Artery

  • Left Gastric Artery

  • Splenic Artery

Common Hepatic Artery and Branches

• Common Hepatic Artery branches:

  • Hepatic Artery Proper

  • Gastroduodenal Artery

• Hepatic Artery Proper branches:

  • Right Gastric Artery

  • Left Hepatic Artery

  • Right Hepatic Artery

• Gastroduodenal Artery branches:

  • Supraduodenal Artery

  • Superior Pancreaticoduodenal Artery

  • Right Gastroepiploic Artery

Splenic Artery Branches

• Short Gastric Arteries

• Left Gastroepiploic Artery (Left Gastro-Omental Artery)

Superior Mesenteric Artery (SMA)

• Arises from the abdominal aorta about $1 ext{ cm}$ caudal to the celiac trunk.

• Lies posterior to the neck of the pancreas and passes anterior to the third part of the duodenum and the left renal vein.

• SMA branches:

  • Inferior Pancreaticoduodenal Artery

  • Intestinal Branches and Vasa Recta

  • Ileocolic Artery

  • Appendicular Artery

  • Right Colic Artery

  • Middle Colic Artery

Inferior Mesenteric Artery (IMA)

• Arises from the abdominal aorta about $3 ext{ cm}$ superior to the aortic bifurcation.

• Branches:

  • Left Colic Artery

  • Sigmoid Arteries

  • Superior Rectal Artery

• The marginal artery (of Drummond) runs along the inner border of the large intestine and is formed by anastomoses between SMA and IMA branches.

Portal Vein and Venous Drainage to Portal System

• Tributaries to the portal vein include: Superior Mesenteric Vein (SMV), Splenic Vein, and Inferior Mesenteric Vein (IMV).

• SMV and Splenic Vein join posterior to the neck of the pancreas to form the Portal Vein.

• IMV may join SMV, Splenic Vein, or the junction of SMV and Splenic Veins (in some diagrams: IMV joins Splenic Vein).

• Tributaries to the portal vein also include: Right and Left Gastric Veins, Superior Pancreaticoduodenal Vein, and Paraumbilical Veins.

• The left gastric vein drains the lower esophagus; esophageal branches connect with azygos system.

• Paraumbilical veins accompany the ligamentum teres in the free lower border of the falciform ligament and connect with the periumbilical plexus; these are subcutaneous veins radiating from the umbilicus and are branches of the superior and inferior epigastric veins.

Portal Hypertension (Clinical Correlation)

• Portal hypertension arises from increased portal system pressure (often due to cirrhosis).

• Blood from the lower esophagus may flow into the azygos system, causing esophageal varices and potential bleeding.

• Enlargement/varices of veins in the rectum and around the umbilicus can occur, causing hemorrhoids and caput medusae.

Superior Mesenteric Syndrome (Nutcracker Syndrome) (Clinical Correlation)

• The left renal vein and the third part of the duodenum pass between the aorta posteriorly and SMA anteriorly.

• These structures can be compressed like nuts in a nutcracker, causing symptoms.

Kidneys and Suprarenal Glands

Kidneys

• Retroperitoneal bean-shaped organs on the posterior abdominal wall, one on each side of the vertebral column.

• The right kidney is lower than the left due to liver position.

• The renal hilus is the entrance to the renal sinus; located at the medial border of the kidney; through it pass renal veins, arteries, and ureters (

  • Renal vein is anterior,

  • Ureter is posterior,

  • Renal artery is between them).

Renal Fascia and Fat

• Renal fascia (false capsule) surrounds the kidneys; it is thicker on the lateral and posterior surfaces.

• It divides perirenal fat into two regions:

  • Perirenal Fat (fat inside renal fascia)

  • Pararenal Fat (fat outside renal fascia)

Venous Drainage (Renal Veins)

• Renal veins drain into the inferior vena cava (IVC).

• Left renal vein is longer and is compressed between the abdominal aorta (posterior) and the superior mesenteric artery (anterior).

• Left renal vein tributaries: Left Testicular (Ovarian) Vein.

• Right testicular (Ovarian) vein drains directly into the IVC; right ovarian vein drains into IVC.

Renal Arteries

• Renal arteries lie posterior to the renal veins and typically divide into two branches before entering the kidneys.

• Accessory renal arteries are common.

• In males, right and left testicular arteries originate directly from the aorta inferior to the renal arteries.

• In females, ovarian vessels cross the external iliac vessels to enter the pelvis.

• Right renal artery is typically longer than the left.

Kidney Anatomy

• Renal pelvis is the most posterior part of the renal hilus.

• Ureter is the inferior continuation of the renal pelvis and runs posterior to the testicular/ovarian vessels.

• Key internal structures: Renal Cortex, Renal Medulla, Renal Pyramids, Renal Papillae, Calyces Minora, Calyces Majora, Renal Columns (between pyramids).

• The renal cortex extends between pyramids as renal columns; the medulla contains the pyramids.

• Papillae project into Calyces Minores, which unite to form Calyces Majores; Majores unite to form the Renal Pelvis.

Suprarenal Glands (Adrenal Glands)

• Endocrine glands that produce hormones (adrenaline, aldosterone, cortisol).

• Separated from the superior pole of the kidneys by a thin layer of fat.

• Right suprarenal gland: roughly triangular, lies posterior to the IVC.

• Left suprarenal gland: semilunar, lies near the superior and medial borders of the left kidney.

Arterial Supply

• Superior Suprarenal Arteries (from inferior phrenic arteries)

• Middle Suprarenal Artery (from the abdominal aorta)

• Inferior Suprarenal Artery (from renal arteries)

Venous Drainage

• Each gland typically drained by a single vein.

• Left suprarenal vein drains to the left renal vein; right suprarenal vein drains to the IVC.

Abdominal Nerves

Major Nerves

• Subcostal Nerve (T12)

• Iliohypogastric Nerve (L1): courses between transversus and internal oblique; provides motor to those muscles and sensory above the pubis after perforating the external oblique aponeurosis.

• Ilioinguinal Nerve (L1): arises from a common trunk with the iliohypogastric; sometimes absent.

• Genitofemoral Nerve (L1, L2): pierces the anterior surface of the psoas major; divides into genital and femoral branches; the genital branch travels in the deep inguinal ring; involved in cremasteric reflex.

Sympathetic and Splanchnic Nerves

• Greater, Lesser, and Least Splanchnic Nerves

• Sympathetic trunks

• Intermesenteric (para-aortic) plexus

• Gray and white rami communicantes

Plexuses and Relationships

• The nerves interact with celiac, superior mesenteric, and aorticorenal ganglia.

• Lateral femoral cutaneous nerve (L2-L3), Femoral nerve (L2-L4), Obturator nerve (L2-L4), Genitofemoral (L1-L2), and other branches from the lumbar plexus.

• The pudendal nerve (S2-S4) exists and related to inferior aspects of the pelvis.

Muscles of the Posterior Abdominal Wall

• Psoas Major

• Psoas Minor

• Iliacus

• Quadratus Lumborum

• Transversus Abdominis

Diaphragm

Parts and Attachments

• Four portions:

  • Sternal Part (to the xiphoid process)

  • Costal Part (to the lower six ribs and costal cartilages)

  • Lumbar Part (to the superior three lumbar vertebral bodies)

  • Central Part (aponeurotic insertion of the muscle)

Crura and Openings

• Right Crus and Left Crus form the esophageal hiatus (through which the esophagus passes).

• A slip from the right crus (muscle) descends as the suspensory muscle of the duodenum (ligament of Treitz), supporting the duodenojejunal flexure.

• Arcuate ligaments (lumbocostal arches) are thickened transversalis fascia that provide attachments for diaphragmatic fibers:

  • Medial Arcuate Ligament (over psoas major)

  • Lateral Arcuate Ligament (over quadratus lumborum)

  • Median Arcuate Ligament (over the aorta)

Openings

• Caval Foramen

• Esophageal Hiatus

• Aortic Hiatus

• Notes: The higher the vertebral level, the more anterior (ventral) the opening/hiatus.

Spermatic Cord, Scrotum, and Testis

Spermatic Cord Contents

• Vas Deferens

• Testicular Artery

• Pampiniform Plexus of Veins

• Cremasteric Artery

• Artery to the Ductus Deferens

• Genital Branch of the Genitofemoral Nerve

• Autonomic Fibers

• Lymphatic Vessels

Cord Coverings

• External Spermatic Fascia (from external oblique aponeurosis)

• Cremasteric Muscle and Fascia (from internal oblique muscle)

• Internal Spermatic Fascia (from transversalis fascia)

Processus Vaginalis and Tunica Vaginalis

• Normally, the processus vaginalis fuses after testicular descent; the cord contains only a small remnant of peritoneum.

• Processus Vaginalis: embryologic outpouching of peritoneum; Tunica Vaginalis: derived from peritoneum surrounding the testis.

Scrotum Anatomy

• Outpouching of the anterior abdominal wall; contains most layers of the abdominal wall and spermatic cord.

• Dartos Fascia: superficial fascia of the scrotum; Dartos Muscle within it; gives a creased appearance to the scrotal skin; continuous with Scarpa’s fascia of the anterior abdominal wall and Colles’ fascia of the perineum.

• Deep to the dartos fascia are three fascial layers:

  • External Spermatic Fascia

  • Cremasteric Fascia

  • Internal Spermatic Fascia

• Coverings of the spermatic cord reflect the layers of the anterior abdominal wall.

Scrotum and Testis Details

• The scrotum contains the dartos muscle and fascia; skin becomes rugose due to the dartos.

• The posterior aspect includes the tunica vaginalis (visceral and parietal layers) surrounding the testis and epididymis; the tunica albuginea lies beneath.

• Vestige of the processus vaginalis may persist.

Key Clinical and Relationship Notes (Integrated)

• Portal Triad in the hepatoduodenal ligament: Portal Vein, Hepatic Artery Proper, Common Bile Duct.

• Epiploic (Winslow) Foramen as access to lesser sac; orientation matters for superior vs inferior recess awareness.

• Esophageal varices development in portal hypertension; caput medusae and hemorrhoids as possible sequelae.

• Nutcracker syndrome due to SMA crossing left renal vein and third part of the duodenum; clinical implications include hematuria, flank pain, or varices.

Study Questions (Review Points)

1) The right and left hepatic ducts join to form the common hepatic duct.
2) The right and left hepatic arteries are branches of the hepatic artery proper.

Notes on Terminology and Landmarks

• Peritoneal reflections define recesses (subphrenic, hepatorenal, subhepatic spaces).

• The coronary ligaments (anterior and posterior) fuse to form the left and right triangular ligaments; the inferior edge of the coronary ligament creates the hepatorenal ligament with the hepatorenal recess nearby (Morison's pouch).

• The falciform ligament divides the subphrenic recess and anchors liver to anterior abdominal wall.

• The lesser omentum connects stomach/duodenum to liver; the greater omentum hangs from the stomach and covers anterior abdominal organs as needed during inflammation or infection.

// End of notes (condensed, comprehensive coverage of provided transcript).