Gross anatomy Week 5

Regions of the Anterolateral Abdominal Wall

• The anterolateral abdominal wall is divided into 4 quadrants: upper right, upper left, lower right, and lower left quadrants, by a vertical plane and a horizontal plane that intersect at the umbilicus.
• The 4 quadrants are further divided into 9 regions by 2 midclavicular planes and 2 horizontal planes (subcostal and transtubercular planes).

Regions of the Anterolateral Abdominal Wall (continued)

• The upper part (above subcostal plane) consists of: epigastric region (center), right and left hypochondriac regions.
• The middle part (between subcostal and transtubercular planes) consists of: umbilical region (center), right and left lateral regions (lumbar regions or flanks).
• The lower part (below transtubercular plane) consists of: pubic region, hypogastric region (center), and right and left inguinal (iliac) regions.

Layers of the Anterolateral Abdominal Wall

• From superficial to deep: skin, superficial fascia, muscles with their deep (investing) fasciae, transversalis fascia, extraperitoneal fascia, and parietal peritoneum.

Superficial Fascia

• Divided into 2 layers in the lower part of the anterior abdominal wall: superficial, fatty layer (Camper's fascia), and deep, membranous layer (Scarpa's fascia).

Abdominal Muscles

• 3 flat muscles on each side: external oblique, internal oblique, and transversus abdominis.
• On each side of the anterior midline, there is a long, vertical muscle (rectus abdominis) and a small muscle (pyramidalis) anterior to the lower part of rectus abdominis (absent in about 20% of people).

Muscles of the Anterolateral Abdominal Wall (continued)

• The 3 flat muscles are muscular (fleshy) posterolaterally and aponeurotic (fibrous) anteromedially.
• Their aponeuroses pass medially and enclose rectus abdominis (and pyramidalis, if present) to form the rectus sheath.
• In the midline of the anterior abdominal wall, the aponeuroses of the 3 right flat muscles join the aponeuroses of the 3 left flat muscles to form the linea alba.

External Oblique

• Origin: outer surface of the lower 8 ribs.
• Insertion: into the xiphoid process, linea alba, and pubic bone.
• Inguinal (Poupart's) ligament: lower border of the external oblique aponeurosis that extends from the anterior superior iliac spine (ASIS) to the pubic tubercle.

Transversus Abdominis

• Lies deep to the internal oblique.
• Origin: deep surface of the lower 6 costal cartilages, thoracolumbar fascia, iliac crest, and lateral ⅓ of the inguinal ligament.
• Insertion: into the xiphoid process, linea alba, and pubic bone.

Rectus Abdominis

• Long strap muscle that extends along the whole length of the anterior abdominal wall.
• Divided into segments by 3 transverse fibrous bands (tendinous intersections or inscriptions).

Actions of the Anterolateral Abdominal Muscles

• Their tone plays an important role in supporting and protecting abdominal organs.
• Oblique muscles are involved in flexion, lateral flexion, and rotation of the trunk.
• Rectus abdominis flexes the trunk.
• Transversus abdominis contributes little to trunk movements.
• By contracting simultaneously with the diaphragm, with the glottis of the larynx closed, anterolateral abdominal muscles increase intra-abdominal pressure, helping with evacuation of the contents of abdominal and pelvic hollow organs.

Rectus Sheath

• Formed by the aponeurosis of the 3 flat abdominal muscles.
• Contents: rectus abdominis, pyramidalis (if present), terminal parts of the lower 5 intercostal nerves and subcostal nerve, and superior and inferior epigastric vessels.

Nerves of the Anterolateral Abdominal Wall

• Ventral rami of T7 to T11 spinal nerves (7th to 11th intercostal nerves) and ventral ramus of T12 spinal nerve (subcostal nerve).
• Ventral ramus of L1 spinal nerve (iliohypogastric and ilioinguinal nerves).

Dermatomes of the Anterolateral Abdominal Wall

• T7: just inferior to the tip of the xiphoid process.
• T10: level of the umbilicus.
• L1: pubic symphysis and area immediately superior to it.

Arteries of the Anterolateral Abdominal Wall

• Superior epigastric artery: terminal branch of the internal thoracic artery.
• Inferior epigastric artery: originates from the distal part of the external iliac artery.
• Deep circumflex iliac artery: originates from the distal part of the external iliac artery.
• 10th and 11th posterior intercostal arteries, subcostal artery, and lumbar arteries.

Veins of the Anterolateral Abdominal Wall

• Superficial veins: form a network that radiates out from the umbilicus.
• Deep veins: accompany corresponding arteries and drain into internal thoracic, external iliac, posterior mediastinal, and lumbar (para-aortic) veins.

Lymphatic Drainage of the Anterior Abdominal Wall

• Superficial lymph vessels: above the level of the umbilicus, lymph drains upward toward the anterior axillary lymph nodes; below the level of the umbilicus, lymph drains downward toward the superficial inguinal lymph nodes.
• Deep lymph vessels: follow arteries and deep veins and drain into internal thoracic (parasternal), external iliac, posterior mediastinal, and lumbar (para-aortic) lymph nodes.

Inguinal Canal

• Oblique passage, approximately 4 cm in length, through the lower part of the anterior abdominal wall
• Lies parallel and immediately above the medial part of the inguinal ligament
• Contents:
  • In males: spermatic cord (formed by structures running between the testis and abdominopelvic cavity) and ilioinguinal nerve
  • In females: round ligament of uterus (fibrous cord that extends from the uterus to the labium majus), genital branch of genitofemoral nerve, and ilioinguinal nerve
• Openings:
  • Deep inguinal ring (opening in transversalis fascia) located approximately halfway between the ASIS and pubic tubercle
  • Superficial inguinal ring (opening in aponeurosis of external oblique) located immediately superior to the pubic tubercle
• Walls:
  • Anterior: aponeurosis of external oblique
  • Posterior: transversalis fascia
  • Inferior: inguinal ligament
  • Superior: lower borders of internal oblique and transversus abdominis

Abdominal Hernia

• Protrusion of abdominal contents beyond the normal confines of the abdominal wall
• Has three parts: hernial sac, contents of the sac, and coverings of the sac
• Sac: pouch (diverticulum) of parietal peritoneum
• Contents: may consist of any structure found within the abdominal cavity (e.g., piece of omentum, loop of small intestine, etc.)
• Coverings: formed by layers of the abdominal wall through which the hernial sac passes
• Approximately 75% of abdominal hernias occur in the inguinal region (most common type of abdominal hernia)

Types of Inguinal Hernias

• Indirect inguinal hernia:
  • Most common type of inguinal hernia (2/3 to 3/4 of inguinal hernias)
  • Hernial sac leaves the abdominal cavity lateral to the inferior epigastric vessels, through the deep inguinal ring
  • Results from a persistent processus vaginalis (outpouching of peritoneum that in the fetus is responsible for the formation of the inguinal canal)
  • More common in children and young adults
• Direct inguinal hernia:
  • Hernial sac leaves the abdominal cavity medial to the inferior epigastric vessels
  • Hernial sac protrudes through an area of relative weakness in the posterior wall of the inguinal canal
  • Inguinal (Hesselbach's) triangle is bounded by the inferior epigastric vessels (laterally), rectus abdominis (medially), and inguinal ligament (inferiorly)

Intraperitoneal and Retroperitoneal Relationships

• Intraperitoneal organ: organ that is almost totally covered with peritoneum
• Retroperitoneal organ: organ that is located posterior to the peritoneal sac and is only covered with peritoneum anteriorly

Peritoneal Folds

• Ligament: two-layered peritoneal fold that connects an organ to the abdominal wall or another organ
• Examples:
  • Falciform ligament: connects the liver to the anterior abdominal wall
  • Coronary ligament: connects the liver to the diaphragm
  • Splenorenal ligament: connects the spleen to the left kidney
  • Gastrosplenic ligament: connects the spleen to the stomach
• Omentum: peritoneal fold that passes from the stomach and proximal part of the duodenum to another organ
  • Lesser omentum: two-layered peritoneal fold that connects the lesser curvature of the stomach and the 1st part of the duodenum to the visceral surface of the liver
  • Greater omentum: hangs down from the greater curvature of the stomach, like an "apron", in front of the loops of the jejunum and ileum
• Mesentery: two-layered peritoneal fold that connects the intestines to the posterior abdominal wall
  • Allows blood vessels, lymph vessels, and nerves to reach the intestines from the posterior abdominal wall
  • Examples:
    • Mesentery of small intestine (or just simply "the mesentery"): connects the loops of the jejunum and ileum to the posterior abdominal wall
    • Transverse mesocolon (mesentery of transverse colon): connects the transverse colon to the posterior abdominal wall
    • Sigmoid mesocolon (mesentery of sigmoid colon): connects the sigmoid colon to the posterior abdominal and pelvic walls

Secondary Retroperitoneal Organs

• Early in development, all parts of the digestive tract are intraperitoneal and have a mesentery
• With further development, some parts of the digestive tract adhere to the posterior abdominal wall, lose their mesentery, and become retroperitoneal (more fixed in position)

Lesser Sac (Omental Bursa)

• Part of the peritoneal cavity located posterior to the lesser omentum and stomach
• Superior recess: upward extension of the lesser sac, located between the liver and diaphragm
• Inferior recess: downward extension of the lesser sac between the 2 anterior and 2 posterior layers of the greater omentum
• On the left, it is closed by the spleen, gastrosplenic ligament, and splenorenal ligament
• On the right, it communicates with the greater sac via the omental (epiploic) foramen

Epiploic (Omental) Foramen (Opening of Lesser Sac, Foramen of Winslow)

• Boundaries:
  • Anteriorly: right, free border of the lesser omentum (hepatoduodenal ligament)
  • Posteriorly: inferior vena cava
  • Superiorly: caudate lobe of the liver
  • Inferiorly: 1st part of the duodenum

Peritoneal Folds in the Lower Part of the Anterior Abdominal Wall

• 1 median umbilical fold: formed by the peritoneum that covers the median umbilical ligament
• 2 medial umbilical folds (1 on each side): formed by the peritoneum that covers the medial umbilical ligaments
• 2 lateral umbilical folds (1 on each side): formed by the peritoneum that covers the inferior epigastric vessels

Other Subdivisions of the Abdominal Cavity

• The transverse colon and its mesentery (transverse mesocolon) divide the abdominal cavity into supracolic and infracolic compartments
• Supracolic compartment: located above the transverse colon and its mesentery, contains the stomach, liver, gallbladder, and spleen
• Infracolic compartment: located below the transverse colon and its mesentery, contains most of the small and large intestines
• Free communication between the supracolic and infracolic compartments via the paracolic gutters