Abdominal Wall Anatomy: Structure and Function

Abdominal Wall Anatomy - Introduction

• Anterior and lateral abdominal wall muscles are the focus.
• Abdominal wall muscles create a tube for movement and core stabilization.
• Muscles support the viscera, enabling trunk flexion, lateral flexion, and rotation.

Functions of Abdominal Wall Muscles

• Muscles form a protective wall for abdominal viscera.
• They regulate opposing abdominal pressures, affecting thoracic pressure.
• They elevate intra-abdominal pressure for actions like coughing, sneezing, defecation, urination, and vomiting.
• Muscles stabilize the trunk during lifting by increasing abdominal pressure, adding rigidity and support.

Abdominal Wall Structure and Layers

• Muscle and connective tissues form a strong, mobile, protective trunk.
• Abdominal muscles work with back and lower limb muscles for movement and balance.
• Layers include skin, superficial fascia, Camper's fascia (fatty), and Scarpa's fascia.
• Above the umbilicus, superficial fascia acts normally; below it, Camper’s fascia stores fat.
• Scarpa's fascia is denser, continuing into lower limb fascia and connecting to the perineum via Colles fascia.

Linea Alba

• The linea alba is a key central line for abdominal muscle function.
• It is a white line of abdominal muscle attachment.

Muscle Layers

• The external oblique is the most superficial muscle layer.

External Oblique

• Fibers run from ribs 5-12 to the linea alba, pubic tubercle, and anterior iliac crest.
• Fibers run anteriorly and inferiorly.

Internal Oblique

• Located under the external oblique, fibers run anteriorly and superiorly, almost perpendicular to the external oblique.
• Originates from the anterior iliac crest and thoracolumbar fascia and attaches to ribs 10-12.
• Fibres insert into the pubis bone via the conjoint tendon.

Transversus Abdominis

• This is the deepest muscle layer, featuring transverse fibers.
• It wraps around from the thoracolumbar fascia, connects to costal cartilages of ribs 7-12, and attaches to the anterior iliac crest and linea alba.

Muscle Layer Function

• The external oblique, internal oblique, and transversus abdominis create a strong, multi-directional wall.
• The layered structure is similar to intercostal muscles, making a robust body wall.
• Muscles are innervated by intercostal nerves (T7-T11).
• T12 is the subcostal nerve, and the ilioinguinal and iliohypogastric nerves originate from L1.

Rectus Abdominis

• These muscles run vertically on either side of the linea alba.
• Tendinous intersections divide the muscles, creating a "six-pack" appearance.
• Defined muscles need low body fat because of Camper's fascia storing fat.
• Straight muscles run from the xiphoid process and costal cartilages to the pubic crest and symphysis.

Pyramidalis

• This muscle is anterior to the rectus abdominis.
• It runs from the pubic crest to the linea alba.
• The pyramidalis is present in about 80% of the population.

Muscle Attachments and Functionality

• Lateral muscles become aponeuroses to attach to the linea alba.
• The external oblique's aponeurosis passes anterior to the rectus abdominis.
• The internal oblique's aponeurosis splits, surrounding the rectus abdominis on both sides.
• The transverse abdominis aponeurosis passes posterior to the rectus abdominis.
• All muscles work together, necessitating comprehensive training.

Arcuate Line

• Layers change at the arcuate line.

Conjoint Tendon

• The conjoint tendon is formed by the aponeuroses of the transversus abdominis and internal oblique muscles.
• It attaches to the pubic crest and superior pubic ramus, anchoring muscles.
• The conjoint tendon is an Important part of the posterior wall of the inguinal canal.

Semilunar Line

• The semilunar line is the lateral border of the rectus abdominis muscle.
• The semilunar line marks where lateral muscles become aponeuroses, forming the rectus sheath.