6.1 Abdominal Anatomy

Abdominal Wall Overview

• Boundaries of the Abdominal Cavity:

  • Superior: Diaphragm

  • Anterior and Posterior: Lateral walls

  • Inferior: Pelvic floor

Functions of the Abdominal Wall

• Protection of Internal Organs: Provides a barrier against external forces.

• Muscle Attachment: Supports muscle attachment for torso movements.

• Movement: Facilitates movement in activities like bending and twisting.

• Intra-Abdominal Pressure: Plays a role in processes like coughing, vomiting, and childbirth.

Components of the Abdominal Cavity

• Contents:

  • Peritoneum (membrane)

  • Digestive Organs (stomach, duodenum(small intestine first section), pancreas)

  • Liver and Spleen

  • Intestines (small and large)

  • Kidneys and Adrenal Glands

  • Blood vessels, lymphatics, and nerves

• Functions:

  • Nutrient absorption

  • Excretion

  • Homeostasis (maintenance of stable internal conditions)

Associated Bones

• Lumbar Vertebrae (L1-L5)

• Sacrum (5 fused vertebrae)

• Coccyx (3–5 fused bones)

Muscles of the Abdominal Wall

• Anterolateral Muscles:

  • External Oblique

  • Internal Oblique

  • Transversus Abdominis

  • Rectus Abdominis

  • Pyramidalis*

Specific Muscle Functions

• External Oblique: leteral

  • Action: Flexes vertebral column, ipsilateral lateral flexion (same side), contralateral trunk rotation (opposite side).

  • Origin: Lower 8 ribs

  • Insertion: Iliac crest / pubis

• Internal Oblique: leteral

  • Action: Flexes vertebral column, ipsilateral lateral flexion, ipsilateral trunk rotation.

  • Origin: Anterior iliac crest and inguinal ligament

  • Insertion: Costal cartilages of lower 4 ribs, abdominal aponeurosis, linea alba.

• Transversus Abdominis: leteral

  • Action: Compress and support abdominal viscera.

  • Origin: Thoracolumbar fascia, iliac crest, internal surfaces of ribs 7–12

  • Insertion: Linea alba, pubic crest, pubic symphysis.

• Rectus Abdominis:

  • Action: Trunk flexion, tenses anterior abdominal wall.

  • Origin: Pubic symphysis, pubic crest

  • Insertion: Xiphoid process, costal cartilages 5–

    

    7.

Posterior Abdominal Wall Muscles

• Muscles:

  • Psoas Major (and Minor*)

  • Iliacus

  • Quadratus Lumborum

• Iliopsoas: Group formed by Psoas Major and Iliacus, important for hip flexion and trunk flexion.

Trunk Flexion and Extension

• Agonist in Trunk Flexion: Rectus Abdominis

• Synergists: External and Internal Obliques

• Agonists in Trunk Extension: Erector Spinae group; Abdominal muscles serve as antagonists.

• External Oblique Functions:

  • Pulls the chest downwards.

  • Compresses the abdominal cavity, increasing intra-abdominal pressure as seen in a Valsalva maneuver.

  • Performs ipsilateral (same side) side-bending and contralateral (opposite side) rotation. For example, the right external oblique causes side-bending to the right and rotation to the left.

• Internal Oblique Functions:

  • Functions similarly to the external oblique but rotates ipsilaterally.

  • For instance, the left internal oblique would side bend to the left and rotate to the left.

• contralateral rotation is motion created by a muscle that
  rotates the abdomin to the opposite side from where it is located (eg. left-sided external oblique muscle that rotates the trunk to the right side)

Nervous Supply

• Anterolateral Wall:

  • Intercostal nerves (T5-T11) and thoracic subcostal (T12) for anterior abdominal wall.

  • Iliohypogastric and ilioinguinal (L1) for inguinal region.

supply anterior abdominal wall as well as thoracic region

• Posterior Wall:

  • Subcostal nerve from T12

  • Lumbar plexus from anterior rami(L1-L4): (lower limb)

    *ilioinguinal/iliohypogastric: (abdominal muscles and skin of abdomen)

    *inguinal & pubic regions genitofemoral,

    *femoral nerves (supplies flexors of hip and extensors of leg &
    associated skin regions)

  • Lumbosacral trunk from anterior rami of L4 (inf branch) & L5 (joins sacral plexus in pelvis)

  • genitofemoral (L1-2), (supplies genital and upper thigh region)

  • obturator (L2-4), through obturator foramen, supplies

Inguinal Region

• Male Composition: Spermatic cord, nerves, vessels, vas deferens, coverings of spermatic cord, scrotum, cremaster muscle, testis

• Female Composition: Round ligament of the uterus.

  

Blood Supply to the Abdominal Wall

• Arteries:

  • Internal Thoracic Artery (epigastric)

  • Aorta (lumbar arteries)

  • External and Internal Iliac Arteries

  • Femoral Artery

• Veins:

  • Drainage to axillary and femoral regions.

Lymphatic Drainage

• Components:

  axillary, inguinal

  • Phrenic, Celiac, Superior, and Inferior Mesenteric lymph nodes.

  • Common Iliac and Internal Iliac lymph nodes for lower regions.