Abdominal Region Notes (DPT 17.1-17.8)
Functions of the Abdominal Wall
Protection and stabilization of abdominal contents
Trunk rotation and flexion (helps maintain posture)
Maintain and control intra-abdominal pressure for parturition and defecation
Respiration: opposes the diaphragm during exhalation
Surface Anatomy and Palpations
Quadrants (four-quadrant method): divide through the umbilicus
Left upper, Right upper, Left lower, Right lower
Nine-region scheme (lines: right & left midclavicular planes; subcostal and intertubercular planes)
Regions: R. Hypochondriac, Epigastric, L. Hypochondriac
R. Lumbar, Umbilical, L. Lumbar
R. Iliac, Hypogastric, L. Iliac
Palpable Surface Anatomy
Umbilicus: vertebral level L3-L4; innervation from T10
Linea alba and semilunaris: palpable vertical facial lines in abdominal region
Inguinal ligament: tight fusion of fascial layers; forms a shelf for the spermatic cord (round ligament) to rest
Xiphoid process and costal arch
Pelvic landmarks:
Iliac crest
Iliac tubercle
Anterior superior iliac spine (ASIS)
Pectin pubis (pectineal line)
Pubic tubercle
Fascial and Muscular Layers of the Anterior Abdominal Wall
1) Skin
2) Camper’s fascia (superficial fascia) – fatty layer
3) Scarpa’s fascia (deep fascia) – serous fascial layer
4) External oblique
Origin: External surfaces of ribs 5-12
Insertion: Linea alba, pubic tubercle, and anterior half of iliac crest
Action: compress and support abdominal viscera; flex and rotate trunk
Innervation: thoracoabdominal nerves (anterior rami of T7-T11) and subcostal nerve (T12)
5) Internal oblique
Origin: Thoracolumbar fascia, anterior 2/3 of iliac crest, and connective tissue deep to inguinal ligament
Insertion: Inferior borders of ribs 10-12, linea alba and pubis via conjoint tendon
Action: compress and support abdominal viscera; flex and rotate trunk
Innervation: thoracoabdominal nerves (anterior rami of T7-T11) and first lumbar nerve (L1)
6) Rectus abdominis
Origin: Pubic symphysis and pubic crest
Insertion: Xiphoid process and costal cartilages 5-7
Action: Flexes trunk (lumbar vertebrae) and compresses abdominal viscera; can act as antagonist to the diaphragm; stabilizes and controls pelvic tilt (antilordosis)
Innervation: Thoracoabdominal nerves (anterior rami of inferior six thoracic nerves)
Important distinctions: Above the arcuate line, the internal oblique tendons split and muscles wrap anteriorly (external oblique & half internal oblique) and posteriorly (transversus abdominis & half internal oblique) relatively around the rectus abdominis. Below the arcuate line, the tendons fuse and muscles wrap only anteriorly around the rectus abdominis, leaving only the transversalis fascia and parietal peritoneum to contain viscera. This makes the area weaker and more prone to hernias.
7) Transversus abdominis
Origin: Internal surfaces of ribs 7-12; costal cartilages, thoracolumbar fascia, iliac crest, and connective tissue deep to inguinal ligament
Insertion: Linea alba with aponeurosis of internal oblique, pubic crest and pectin pubis via conjoint tendon
Action: Compresses and supports abdominal viscera
Innervation: Thoracoabdominal nerves (anterior rami of T7-T11) and first lumbar nerve (L1)
8) Transversalis fascia
Layer of fascia lining the internal abdominal wall; forms the deep inguinal ring (learned in inguinal region lectures)
9) Parietal peritoneum
What it is: Serous lining of the peritoneum; produces serous fluid to lubricate abdominal organs
Where it is: Usually not tightly fused with transversalis fascia; can contain fat stores
Innervation: Somatic body wall nerves (e.g., intercostal nerves and subcostal nerves)
Note: Inferior epigastric arteries/veins lie between the transversalis fascia and parietal peritoneum
Posterior Abdominal Wall Musculature
1) Psoas major
Origin: Transverse processes of lumbar vertebrae; sides of vertebral bodies of T12-S1
Insertion: Lesser trochanter of femur
Innervation: Anterior rami of lumbar nerves L1-L3
Action: Acting inferiorly – flexes thigh; acting superiorly – flexes vertebral column laterally to balance trunk; when sitting acts inferiorly to flex trunk
2) Psoas minor
Origin: Sides of vertebral bodies of T12-L1
Insertion: Pectineal line and iliopubic eminence
Innervation: L1
Action: Weak trunk flexor
3) Iliacus
Origin: Superior two thirds of iliac fossa, ala of sacrum and anterior sacro-iliac ligaments
Insertion: Lesser trochanter of femur and shaft inferior to it
Innervation: Femoral nerve (L2-L4)
Action: Flexes thigh and stabilizes hip joint; acts with psoas major
4) Quadratus lumborum
Origin: Medial half of inferior border of 12th rib and tips of lumbar transverse processes
Insertion: Iliolumbar ligament and internal lip of iliac crest
Innervation: Anterior branches of T12 and $L1-L4 nerves
Action: Extends and laterally flexes vertebral column; fixes 12th rib during inspiration
Lumbar Plexus
The lumbar plexus is composed of spinal nerves L1-L4, sometimes L5 may be included. Nervus furcalis L4 is the forked nerve, contributing to both lumbar and sacral plexuses.
1) Subcostal nerve
Arises from: T12
Innervates: External oblique muscle and skin of the anterolateral abdominal wall
2) Iliohypogastric nerve
Arises from: L1
Innervates: Abdominal muscles and overlying skin
3) Ilioinguinal nerve
Arises from: L1
Innervates: Skin of inguinal and pubic regions; innervates skin of scrotum or labia majora
4) Genitofemoral nerve
Arises from: L1-L2 (divides into genital and femoral branches)
Innervates: Skin below the inguinal ligament, including cremaster muscle
5) Lateral femoral cutaneous nerve
Arises from: L2-L3
Innervates: Anterolateral skin of thigh
6) Femoral nerve
Arises from: L2-L4 (posterior division)
Innervates: Iliacus, hip flexors, knee extensors; skin of anterior thigh
7) Obturator nerve
Arises from: L2-L4 (anterior division)
Innervates: Medial thigh skin and adductors
8) Accessory obturator nerve (usually not present)
Arises from: L3-L4
Innervates: Pectineus, hip joint
9) Lumbosacral trunk
Arises from: L4-L5
Innervates: Joins sacral plexus
Abdominal Wall Vasculature
1) Superior epigastric artery
Origin: Internal thoracic artery
Course: Descends in rectus sheath deep to rectus abdominis
What it oxygenates: Rectus abdominis and superior part of the anterolateral wall
2) Subcostal artery
Origin: Aorta
Course: Descends in abdominal wall between internal oblique and transversus abdominis
What it oxygenates: Lateral region of abdominal wall
3) Inferior epigastric artery
Origin: External iliac artery
Course: Runs superiorly and enters rectus sheath, deep to rectus abdominis
What it oxygenates: Rectus abdominis and medial part of the anterolateral abdominal wall
4) Deep circumflex iliac artery
Origin: External iliac artery
Course: Runs on deep aspect of anterior abdominal wall, parallel to inguinal ligament
What it oxygenates: Iliacus muscle and inferior part of the anterolateral abdominal wall
5) Superficial circumflex iliac artery
Origin: Femoral artery
Course: Runs in superficial fascia along inguinal ligament
What it oxygenates: Superficial abdominal wall of inguinal region and adjacent anterior thigh
6) Superficial epigastric artery
Origin: Femoral artery
Course: Runs in superficial fascia towards umbilicus
What it oxygenates: Subcutaneous tissue and skin over pubic and inferior umbilical region
7) Lumbar arteries (4 pairs)
Origin: Abdominal aorta
Course: Posterior abdominal wall
What they oxygenate: Posterior abdominal wall
Anastomoses
1) Superior epigastric & inferior epigastric arteries
2) Musculophrenic artery & ascending branch of the deep circumflex iliac artery
3) Superficial circumflex iliac & deep circumflex iliac arteries
Formative Assessment & Practice Exam Questions
1) What is the action of the rectus abdominis muscle?
A. Rotates trunk
B. Flexes trunk \, & \, compresses abdominal viscera
C. Compresses diaphragm
D. Tenses the linea alba
E. Lateral trunk flexion
Answer: B
2) You have a patient with pain in their left side after a bicycle accident. After testing, you determine pain at the origin of the external oblique muscle. Where is this pain located, specifically?
A. anterior 2/3 of the iliac crest
B. Internal surfaces of ribs 7-12 costal cartilages
C. Pubic symphysis and pubic crest
D. Linea alba and pubic tubercle
E. External surfaces of ribs 5-12
Answer: E
3) A patient complains of pain when flexing the left thigh, but not when flexing the trunk or bending to the sides. They have pain in the left hip when walking/standing. This suggests injury to the __ muscle.
A. Quadratus lumborum
B. iliacus
C. psoas major
D. psoas minor
E. diaphragm
Answer: C
4) The obturator nerve innervates which structures?
A. Hip flexors
B. Knee extensors
C. Anterolateral skin of the thigh
D. Thigh adductors
E. Abdominal muscles
Answer: D
Connections to foundational principles and real-world relevance
The abdominal wall anatomy supports core functions such as maintaining posture, protecting viscera, and managing intra-abdominal pressure during activities like coughing, defecation, and parturition.
The rectus sheath and arcuate line concept illustrate how fasciae and aponeuroses shift around the rectus abdominis, affecting hernia risk in different regions.
The lumbar plexus integrates motor and sensory innervation to the abdominal wall, pelvis, and lower limb; clinical injury to these nerves can produce abdominal wall anesthesia or motor weakness.
The arterial network (epigastric, intercostal, and lumbar arteries) demonstrates key collateral pathways that can sustain blood supply if one route is compromised, and explains patterns seen in abdominal wall hernias and surgical dissections.
Ethical/philosophical/practical implications
Understanding detailed regional anatomy guides safe surgical approaches and reduces iatrogenic injury to motor nerves and vasculature during abdominal procedures.
Knowledge of innervation and vascular supply supports accurate diagnosis of pain patterns and avoids unnecessary interventions.
Key numerical references and LaTeX notation used in this section
Vertebral levels and innervation ranges cited:
Umbilicus level: L3-L4; innervation T10
External oblique innervation: T7-T11 (thoracoabdominal nerves) and T12 (subcostal nerve)
Internal oblique innervation: T7-T11 and L1
Rectus abdominis innervation: anterior rami of inferior six thoracic nerves (approx. T7-T12)
Psoas major innervation: L1-L3
Iliacus innervation: femoral nerve L2-L4
Quadratus lumborum innervation: T12-L4 (anterior branches)
Arterial origins and courses often noted with standard venous/arterial nomenclature (e.g., T12$$ for subcostal; internal thoracic for superior epigastric; external iliac for inferior epigastric and deep circumflex iliac).
If you want, I can reorganize these notes into a printable one-page quick reference or create a mini-outline that corresponds to each slide/section for exam review.