Advanced Human Anatomy: The Abdomen

• Advanced Human Anatomy is taught by Cristina V. Dieni, PhD.
• Contact information is: Phone: 942-421, ext 2248 or Email: [email protected]

The Abdomen

• The abdomen is located inferiorly to the thorax and superiorly to the pelvis.
• The abdomen is composed of skeletal muscles, the abdominal cavity, and visceral structures.

Key Surface Landmarks:

• Rectus sheath
• Linea alba
• Semilunar line
• Tendinous intersections
• Umbilicus
• Iliac crest
• Inguinal ligament

Abdominal Topography

• The abdomen can be divided into four quadrants or nine regions for descriptive and diagnostic purposes.

Four Abdominal Quadrants:

• Right Upper Quadrant (RUQ): contains the right lobe of the liver, gallbladder, right kidney, and portions of the stomach, small, and large intestine.
• Left Upper Quadrant (LUQ): includes the left lobe of the liver, stomach, pancreas, left kidney, spleen, and portions of the large intestine.
• Right Lower Quadrant (RLQ): features the cecum, vermiform appendix, portions of the small intestine, reproductive organs (right ovary in females, right spermatic cord in males), and the right ureter.
• Left Lower Quadrant (LLQ): is composed of most of the small intestine, portions of the large intestine, the left ureter, and reproductive organs (left ovary in females, left spermatic cord in males).

Nine Abdominal Regions:

• Epigastric Region: contains the liver and stomach.
• Right Hypochondriac Region: includes the liver, gallbladder, and right colic (hepatic) flexure.
• Left Hypochondriac Region: features the stomach and the left colic (splenic) flexure.
• Umbilical Region: consists of the stomach, pancreas, and small intestine.
• Right Lumbar Region: contains the ascending colon.
• Left Lumbar Region: includes the descending colon.
• Right Iliac Region: contains the cecum and appendix.
• Left Iliac Region: is composed of the descending and sigmoid colon.
• Hypogastric Region: features the small intestine, sigmoid colon, and rectum.

Anterolateral Abdominal Wall Layers:

• Skin
• Superficial fascia
• Investing fascia
• Abdominal muscles
• Endoabdominal fascia
• Extraperitoneal fat
• Peritoneum These layers protect the abdominal organs and contribute to movement and stability.

Muscles of the Anterolateral Abdominal Wall:

• The anterolateral abdominal wall is composed of three flat layers (two abdominal obliques and the transversus abdominis muscle).
• The muscles include a vertically oriented pair of rectus abdominis muscles within the rectus sheath.
• The rectus abdominis extends from the pubic symphysis and crest to the xiphoid process and costal cartilages 5-7.

Principal Muscles of Anterolateral Abdominal Wall:

• External Oblique: Originates from the external surfaces of the 5th-12th ribs and inserts into the linea alba, pubic tubercle, and anterior half of the iliac crest, innervated by the inferior six thoracic nerves/subcostal nerve. It compresses/supports abdominal viscera and flexes/rotates the trunk.
• Internal Oblique: Originates from the thoracolumbar fascia, anterior two-thirds of the iliac crest, and lateral half of the inguinal ligament. It inserts into the inferior borders of the 10th-12th ribs, linea alba, and pubis via the conjoint tendon; innervated by the anterior rami of the inferior six thoracic nerves and the 1st lumbar nerve. It compresses/supports abdominal viscera and flexes/rotates the trunk.
• Transversus Abdominis: Originates from the internal surfaces of costal cartilages 7-12, thoracolumbar fascia, iliac crest, and lateral third of the inguinal ligament, inserts into the linea alba with the aponeurosis of the internal oblique, pubic crest, and pecten pubis via the conjoint tendon. It is innervated by the anterior rami of the inferior six thoracic nerves/1st lumbar nerve, and compresses and supports the abdominal viscera.
• Rectus Abdominis: Originates from the pubic symphysis and pubic crest, inserts into the xiphoid process and costal cartilages 5-7, is innervated by the anterior rami of the inferior six thoracic nerves and compresses abdominal viscera/flexes the trunk.

Innervation:

• The anterior rami of T7-L1 innervate the anterolateral abdominal skin and muscles.

Arterial Blood Supply:

• Musculophrenic: a terminal branch of the internal thoracic artery that courses along the costal margin.
• Superior Epigastric: arises from the terminal end of the internal thoracic artery, anastomosing with the inferior epigastric artery at the level of the umbilicus.
• Inferior Epigastric: arises from the external iliac artery and anastomoses with the superior epigastric artery.
• Superficial Circumflex Iliac: arises from the femoral artery and anastomoses with the deep circumflex iliac artery.
• Superficial Epigastric: arises from the femoral artery and courses toward the umbilicus.
• External Pudendal: arises from the femoral artery and courses toward the pubis.

Lymphatic Drainage:

• Lymphatic drainage parallels venous drainage.
• Lymph flows into the following lymph node collections:
  • Axillary Nodes: drain the area above the umbilicus
  • Superficial Inguinal Nodes: drain the area below the umbilicus
  • Parasternal Nodes: drain along the internal thoracic vessels
  • Lumbar Nodes: drain internally to the along the abdominal aorta
  • External Iliac Nodes: drain along the external iliac vessels

Abdominal Wall Hernias

• Are technically abdominal wall hernias.
• Often called ventral hernias to distinguish them from inguinal hernias

Types of abdominal hernias:

• Umbilical hernia: usually seen up to age 3 years and after 40
• Linea alba hernia: often seen in the epigastric region and more common in males; rarely contains visceral structures (e.g., bowel).
• Linea semilunaris (spigelian) hernia: usually occurs in midlife and develops slowly
• Incisional hernia: occurs at the site of a previous laparotomy scar

Inguinal Region

• The inguinal region/groin marks the transition between the lower abdomen and upper thigh.
• This region comprises a weakened area of the lower abdominal wall, making it vulnerable to inguinal hernias.
• Marks the inguinal ligament

Inguinal Canal

• The inguinal canal is a passage through the lower abdominal wall that allows structures to pass from the abdominal cavity to the external genitalia.