Abdominal Cavity, Walls and Muscles

Abdominal Cavity Boundaries:

• Superior border is defined by the inferior thoracic aperture.
• Inferior border is defined by the pelvic inlet.
• The abdominal cavity is covered anteriorly and posteriorly by the peritoneum.

Abdominal Wall Layers:

• Skin is the outermost layer.
• The superficial fascia (Camper's fascia) is fatty.
• The superficial fascia (Scarpa's fascia) has:
  • Fascia lata
  • Linea alba (straight line)
  • Fundiform ligament and vulva.
• Fascia is a fibrous connective tissue layer surrounding muscles, blood vessels, and nerves.

Muscles of the Abdominal Wall:

• External Oblique forms:
  • Aponeurosis (rectus sheath).
  • Linea alba
  • Inguinal Ligament, the ASIS to pubic tubercle.
• Internal Oblique contributes to the rectus sheath and linea alba.
  • Fibers run superomedially, or perpendicular to the external oblique.
• Transversus Abdominis is the deepest muscle layer and contributes to the rectus sheath.

Transversalis Fascia

• Separates the muscular layer from the peritoneum.
• Extraperitoneal fascia/fat lies between the transversalis fascia and peritoneum.
• Parietal peritoneum is the lining of the abdominal cavity.

Arcuate Line

• Hernias, surgical incisions, and vascular considerations are important for regions below the arcuate line.
• The rectus sheath is absent posteriorly below the arcuate line.
• Umbilical hernias can occur because of an opening.
• Incisions below the arcuate line are preferred due to less tension.

Abdominal Wall Arteries:

• Superficial arteries (supply skin and superficial fascia):
  • Musculophrenic artery (branch of internal thoracic) - superior.
  • Superficial epigastric and circumflex iliac arteries (branches of femoral artery) - inferior.
• Deep arteries (supply muscles and deeper structures):
  • Superior epigastric artery (branch of internal thoracic) - superior.
  • Intercostal, lumbar, and subcostal arteries - lateral and posterior.
  • Inferior epigastric, deep circumflex, and external iliac arteries - inferior.
• Hernias typically occur lateral or medial to the inferior epigastric artery.

Lymphatic Drainage of Abdomen:

• Above the umbilicus drains mostly to the axillary lymph nodes, and some to the parasternal nodes.
• Below the umbilicus drains to the superficial inguinal nodes.

Peritoneum and Mesentery:

• The parietal peritoneum lines the abdominal cavity.
• The visceral peritoneum covers the abdominal organs.
• The mesentery is a double layer of peritoneum, and suspends the small intestine.

Peritoneal vs Retroperitoneal:

• Intraperitoneal organs include stomach, spleen, liver, first and fourth parts of the duodenum, jejunum, ileum, transverse and sigmoid colon.
• Retroperitoneal organs include aorta, esophagus, second and third parts of the duodenum, ascending and descending colon, pancreas, kidneys, ureters and adrenal glands.

Omentum:

• The greater omentum has left and right gastro-omental vessels.
• First step is to insufflate the abdomen using a trocar, revealing the greater omentum.
• The lesser omentum has:
  • The omental bursa.
  • Hepatogastric and heptoduodenal ligaments.

Peritoneal Cavity:

• The greater sac extends from the diaphragm to the pelvis.
• Connection between greater and lesser sacs through the omental foramen.
• The lesser sac (omental bursa) is located behind the stomach and lesser omentum.

Foregut Blood Supply

• Celiac trunk/arteries (common hepatic, left gastric, splenic) are the foregut.
• It supplies esophagus, stomach, liver, gallbladder and bile ducts, pancreas, proximal duodenum.

Midgut

• Superior mesenteric artery(SMA) supplies midgut.
• It supplies lower duodenum, jejunum, ileum, cecum, appendix , ascending colon, proximal 2/3 of transverse colon.

Hindgut

• Inferior mesenteric artery (IMA) is the arterial supply
• This supplies the distal 1/3 of the transverse colon, descending colon, sigmoid colon, rectum, upper anal canal.

Stomach Anatomy:

• Cardia is the region near the entrance of the esophagus
• Fundus is the upper, rounded portion
• Body is the main central region
• Pylorus (antrum and canal with sphincter and orifice) regulates emptying.

Stomach Arterial Supply:

• Arterial supply to the stomach comes from the celiac trunk.
• Lesser curvature:
  • Left gastric artery (direct branch of celiac trunk).
  • Right gastric artery (branch of hepatic artery proper of the common hepatic).
• Greater curvature:
  • Left gastro-omental artery (branch of splenic artery).
  • Right gastro-omental (branch of gastroduodenal of the common hepatic).
• Fundus/upper stomach:
  • Short gastric arteries (branches of splenic artery).
• Celiac trunk > Common hepatic > Hepatic artery proper > Right gastric.

Small Intestine:

• Duodenum consists of superior, descending, inferior, and ascending portions.
• Jejunum has plicae circulares and is the proximal 2/5 of the small intestine.
• Ileum is the distal 3/5 of the small intestine.
• Blood supply to the duodenum is via the common hepatic artery via:
  • Pancreaticoduodenal artery
  • Gastroduodenal artery
  • Jejunal artery (SMA)
• The superior part of the duodenum is most common for ulcers.
• More plica circulares are in the jejunum than in the ileum.

Large Intestine:

• Cecal artery (SMA) supplies the cecum and appendix.
• Appendix contains lymph tissue.
• McBurney’s point (1/3 between the ASIS and the belly button).
• Left and right paracolic gutters are peritoneal recesses (spaces) located between the ascending and descending colon and the abdominal wall.
• The blood supply to the large intestine (colon) is via the SMA, IMA and marginal artery.
• The rectum has arterial supply from IMA, internal iliac and pudendal arteries.
• Below the dentate line hemorrhoids have more pain than above.

Liver:

• The falciform ligament, which attaches to the anterior abdominal wall..
• Posterior surface of liver anatomy: left/right/caudate/quadrate lobes, renal, gastric, esophageal and colic impressions.
• The posterior surface has hepatic ducts where left + right hepatic = common hepatic.
• Bile is stored in the Gallbladder:

Gallbladder:

• Neck, body and fundus.
• Ducts: cystic which merges with common hepatic to become (common) bile duct.

Liver Arterial Supply:

• Liver: common hepatic artery.
• Gallbladder: cystic artery (branch of the common hepatic).

Pancreas:

• Features head, neck, body, tail.
• Contains main and accessory pancreatic ducts.
• Supplied by splenic, common hepatic, and SMA.

Spleen:

• Sits under diaphragm at rib 9 & 10
• The Hilum
• Contains red and white pulp
• It is supplied via the splenic artery

Veins:

• Left renal vein drains:
  • Kidney
  • Adrenal gland
  • Gonads
• Common iliac veins drain:
  • Lower limb
  • Pelvis
  • Peritoneum
• The hepatic portal system drains into:
  • Intestines
  • Spleen
  • Pancreas
  • Gallbladder
  • And becomes: Hepatic veins
• Poto-caval anastamoses occur through the:
  • Inferior esophagus
  • Superior rectum
  • Beds drained by systemic vessels
• Liver disease and thrombocytopenia and varices can be a recipe for disaster.

Nerves:

• Abdominal organs receive autonomic innervation via the paravertebral/prevertebral plexus.
  • Sympathetic nerves are splanchnic nerves (greater, lesser, least, lumbar).
  • Parasympathetic nerves are vagus and pelvic splanchnic.
• Celiac Plexus (Foregut) receives fibers from the greater and lesser splanchnic nerves and vagus nerve.
• Aortic plexus:
  • The Superior Mesenteric Plexus (Midgut) receives fibers from the lesser and least splanchnic nerves and vagus nerve.
  • The Inferior Mesenteric Plexus (Hindgut) receives fibers from the lumbar splanchnic nerves and pelvic splanchnic nerves.
• Hypogastric Plexus (Pelvic Organs) connects the abdominal autonomic system to the pelvic ANS.