Detailed Anatomy of Abdominal Vasculature and Viscera

Abdominal Regions and Viscera Positioning

Quadrant and Nine-Region Systems

Understanding the positioning of abdominal viscera is crucial for physical examination and diagnosis.

• Four-Quadrant Pattern:

  • Right Upper Quadrant (RUQ)
  
  • Left Upper Quadrant (LUQ)
  • Right Lower Quadrant (RLQ)
  • Left Lower Quadrant (LLQ)

• Nine-Region Pattern:

  • Right hypochondriac
  
  • Epigastric
  • Left hypochondriac
  • Right lumbar
  • Umbilical
  • Left lumbar
  • Right inguinal
  • Hypogastric (pubic)
  • Left inguinal

Peritoneum

• Characteristics:
  • Thin serous membrane lining the abdominal cavity and covering most viscera
  
  • Forms a closed sac in males but has two openings in females (uterine tubes)

Intraperitoneal vs. Retroperitoneal Structures

• Intraperitoneal Organs:

  • Stomach
  
  • Liver
  • Spleen
  • Part of the duodenum
  • Jejunum
  • Ileum
  • Transverse and sigmoid colon

• Retroperitoneal Structures:

  • Suprarenal glands
  • Aorta and IVC
  • Duodenum (2nd-4th parts)
  • Pancreas (except tail)
  • Ureters
  • Ascending and descending colon
  • Kidneys
  • Esophagus
  • Rectum (partial)

Esophagus

• Constrictions:
  • Cervical constriction
  
  • Thoracic (aortobronchial) constriction
  • Diaphragmatic constriction
• Anatomical Features:
  • Transition from skeletal to smooth muscle in the middle third
  
  • Gastroesophageal junction transition of mucosal lining
  • Anterior and posterior vagal trunks accompany the esophagus

Stomach

Anatomical Features

• Regions:
  • Cardiac
  
  • Fundic
  • Body
  • Pyloric
• Curvatures:
  • Greater curvature
  
  • Lesser curvature
• Notable Structures:
  • Cardiac notch
  
  • Angular incisure
  • Pyloric sphincter
  • Gastric folds (rugae)
• Muscle Layers:
  • Inner circular layer
  
  • Outer longitudinal layer

Small Intestine

Sections

1. Duodenum:

   • Approximately 25 cm (10 inches)
   
   • Duodenojejunal junction
   • First few centimeters are smooth muscle
   • Major and minor duodenal papillae

2. Jejunum:

   • Occupies the upper left quadrant
   
   • Less fat in mesentery
   • Long, straight arteries and veins
   • Abundant circular folds

3. Ileum:

   • Occupies the lower right quadrant
   
   • More fat in mesentery
   • Shorter, straight arteries and veins
   • Fewer circular folds

Functional Aspects

• Absorption of nutrients and water

• Total length is approximately 6 to 7 meters (22 feet)

Large Intestine

Features

• Larger diameter compared to the small intestine

• Retroperitoneal and Intraperitoneal Parts:
  • Sacculation (haustra)
  • Omental appendices (fat accumulations)
  • Three longitudinal muscle bands (tenia coli)

Specific Regions

• Ileocecal Region:
  • Contains the ileocecal junction
  
  • Vermiform appendix with its own arterial supply (appendicular artery)
• Paracolic Gutters:
  • Lateral to ascending and descending colon
  
  • Blood-free mobilization possible by cutting peritoneum along these gutters

Blood Supply of Abdominal Viscera

Major Arteries

1. Celiac Trunk (Foregut):

   • Supplies abdominal esophagus, stomach, duodenum (up to major duodenal papilla), liver, pancreas, gallbladder, and spleen
   

2. Superior Mesenteric Artery (Midgut):

   • Supplies duodenum (part), jejunum, ileum, cecum, appendix, ascending colon, and transverse colon
   

3. Inferior Mesenteric Artery (Hindgut):

   • Supplies descending colon, sigmoid colon, rectum, and upper part of the anal canal
   

Anastomoses

• Marginal Artery:
  • Formed by anastomoses between right, middle, and left colic arteries
  
  • Provides collateral circulation in case of inferior mesenteric artery stenosis

Nerve Supply of Abdominal Viscera

• Autonomic Nerve Fibers:
  • Course with arteries
  
  • Include both sympathetic and parasympathetic fibers

Specific Plexuses

• Aortic Plexus

• Superior Hypogastric Plexus
• Hypogastric Nerve
• Pelvic Splanchnic Nerves
• Inferior Hypogastric Plexus

Clinical Considerations

• Duodenal Ulcers:
  • Often occur in the superior part (duodenal cap)
  
  • Posterior ulcers may erode onto major arteries, causing severe bleeding
  • Anterior ulcers can lead to peritonitis