Abdomen
Nine Regions of the Abdomen
The abdomen is divided into nine regions by two horizontal planes (subcostal and
transtubercular) and two vertical planes (midclavicular):
1. Right hypochondriac (right upper region beneath the ribs)
2. Epigastric (upper central region between the ribs)
3. Left hypochondriac (left upper region beneath the ribs)
4. Right lumbar (right middle region near the waist)
5. Umbilical (center region around the navel)
6. Left lumbar (left middle region near the waist)
7. Right iliac (right lower region near the groin)
8. Hypogastric (lower central region below the navel)
9. Left iliac (left lower region near the groin)
These regions are important for describing the locations of pain, lesions, or other anatomical
findings.
Locations and Innervations of the Lateral and Medial Group Muscles
● Lateral group muscles: These include the external oblique, internal oblique, and
transversus abdominis. They are located on the sides of the abdomen and help with
trunk movements and maintaining abdominal pressure.
○ Innervation: These muscles are innervated by the lower intercostal nerves
(T7-T11), subcostal nerve (T12), and L1 nerve (iliohypogastric and ilioinguinal
nerves).
● Medial group muscles: This includes the rectus abdominis and pyramidalis muscles.
They are located in the midline of the abdomen and play a role in flexing the vertebral
column and stabilizing the pelvis.
○ Innervation: The rectus abdominis is innervated by the lower six
thoracoabdominal nerves (T7-T11).
Origin of the Inguinal Ligament
The inguinal ligament originates from the anterior superior iliac spine (ASIS) and extends to
the pubic tubercle. It is formed by the lower border of the aponeurosis of the external oblique
muscle and plays a critical role in forming the boundary of the inguinal canal.
Origin and Innervation of the Cremaster Muscle
● Origin: The cremaster muscle is derived from the internal oblique muscle, and it
surrounds the spermatic cord in males.
, ● Innervation: The muscle is innervated by the genitofemoral nerve (L1-L2).
● Clinical significance: The cremasteric reflex involves stroking the inner thigh, which
causes the cremaster muscle to contract and elevate the testis. This reflex is absent in
cases of testicular torsion, providing a diagnostic clue.
Location, Importance, and Contents of the Rectus Sheath
● Location: The rectus sheath is located on the anterior abdominal wall and encloses the
rectus abdominis muscle.
● Importance: It provides structural support and protection to the abdominal muscles,
vessels, and nerves.
● Contents: It contains the rectus abdominis, the superior and inferior epigastric arteries
and veins, and the terminal parts of the lower six thoracoabdominal nerves.
Location and Contents of the Inguinal Canal
● Male: In males, the inguinal canal contains the spermatic cord, which includes the vas
deferens, testicular vessels, nerves, and lymphatics.
● Female: In females, the inguinal canal contains the round ligament of the uterus.
Clinical Significance of Cryptorchidism and Hydrocele of the Cord
● Cryptorchidism: This refers to the failure of one or both testes to descend into the
scrotum. It increases the risk of infertility and testicular cancer.
● Hydrocele: This is the accumulation of fluid within the tunica vaginalis surrounding the
testis or along the spermatic cord. It may result from infection or trauma.
Contents of the Spermatic Cord
The spermatic cord contains the vas deferens, testicular artery, pampiniform plexus of veins,
lymphatics, cremasteric artery, genital branch of the genitofemoral nerve, and sympathetic nerve
fibers.
Direct vs. Indirect Inguinal Hernias
● Direct hernia: Occurs through a weakened area of the abdominal wall (Hesselbach’s
triangle) and typically affects older men. It is medial to the inferior epigastric vessels.
● Indirect hernia: Follows the pathway of the inguinal canal and usually results from a
congenital defect. It is lateral to the inferior epigastric vessels.
Intraperitoneal vs. Retroperitoneal Organs
● Intraperitoneal organs: Stomach, spleen, liver, parts of the small and large intestines
(jejunum, ileum, transverse colon, sigmoid colon).
● Retroperitoneal organs: Kidneys, pancreas, duodenum (except the first part),
ascending and descending colon, rectum.
, Clinical Significance of the Lesser Sac and Epiploic Foramen
The lesser sac (omental bursa) is an isolated part of the peritoneal cavity located behind the
stomach. The epiploic foramen (of Winslow) connects the greater and lesser sacs. Herniation
or infection can occur here, which may complicate surgical interventions.
Importance of the Greater Omentum
The greater omentum is a large fold of peritoneum that hangs from the greater curvature of the
stomach. It plays a significant role in immune response, fat storage, and infection control by
walling off inflamed areas.
Clinical Significance of Peritoneal Spaces and Compartments
Peritoneal spaces (e.g., subphrenic, subhepatic) can become sites of fluid accumulation during
infection (e.g., peritonitis), trauma, or cancer metastasis.
Structures of the Foregut, Midgut, and Hindgut
● Foregut: Esophagus, stomach, liver, pancreas, first part of the duodenum. Blood supply
is from the celiac trunk.
● Midgut: Distal duodenum, jejunum, ileum, ascending colon, and proximal transverse
colon. Blood supply is from the superior mesenteric artery.
● Hindgut: Distal transverse colon, descending colon, sigmoid colon, rectum. Blood
supply is from the inferior mesenteric artery.
Blood Supply and Venous Drainage of the Esophagus
The esophagus receives blood from the inferior thyroid artery, esophageal branches of the
aorta, and left gastric artery. Venous drainage occurs via the esophageal veins into the azygos
vein and left gastric vein. Esophageal varices occur due to portal hypertension, leading to
swollen veins and potential rupture, a serious condition seen in liver cirrhosis.
Histology of the Esophagus
The esophagus consists of four layers: mucosa, submucosa, muscularis externa, and
adventitia. It is lined with stratified squamous epithelium, which provides protection against
abrasion from swallowed food.
Epithelium of the Gastrointestinal Tract
The gastrointestinal tract (GI tract) is lined by different types of epithelium, depending on the
function of each section:
