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.