Posterior Abdominal Wall and Abdominal Viscera

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  • This presentationPosterior Abdominal Wall and Abdominal Viscera

    Learning Objectives

    • Describe the attachments, innervations, and actions of the major muscles of the posterior abdominal wall.

    • Discuss the structures that cross the diaphragm, through the diaphragmatic ligaments, hiatuses, and crura.

    • Explain the anatomy of the kidneys and ureters, including the pathway of urine filtrate out to the bladder.

    • Draw the arterial and venous distributions to the retroperitoneal organs.

    Presentation O incorporates multiple resources, including:

    • Snell’s Clinical Anatomy

    • Moore’s Clinical Anatomy

    • Gray’s Anatomy

    • Complete Anatomy

    • Netter’s Anatomy

  • Visuals in this presentation are referenced appropriately.

  • All information and images are for educational purposes.

Posterior Abdominal Wall

  • The posterior abdominal wall is formed by:

    • 5 lumbar vertebrae and their intervertebral discs

    • Ribs 11 and 12

    • Upper part of the bony pelvis

    • Psoas muscles

    • Quadratus lumborum muscles

    • Iliacus muscle

    • Diaphragm

    • Origin of transversus abdominis muscle

  • Major vessels, nerves, and organs are located on the inner surface of the posterior abdominal wall.

Muscles of the Posterior Abdominal Wall

Psoas Major Muscle

  • Covers the anterolateral surfaces of the vertebral bodies.

  • Origin:

    • Body of T12

    • Bodies and transverse processes of lumbar vertebrae

    • Intervertebral discs between them

  • Insertion:

    • Passes inferior to the inguinal ligament

    • Inserts into the lesser trochanter of the femur

  • Action:

    • Flexes the thigh at the hip when the trunk is stabilized

    • Flexes the trunk against gravity when the body is supine.

Psoas Minor Muscle

  • Associated with the psoas major muscle.

  • Prevalence: Absent in up to 40% of the population.

  • Origin:

    • Bodies of T12 and L1

    • Intervertebral disk between them

  • Insertion: Pectineal line.

  • Action: Weak flexor of the lumbar vertebral column.

  • Innervation: Both psoas muscles are innervated by the lumbar plexus.

Quadratus Lumborum Muscle

  • Origin:

    • Iliolumbar ligament

    • Tips of transverse processes of L5

    • Adjoining part of the iliac crest

  • Insertion:

    • Rib 12

    • Transverse processes of upper four lumbar vertebrae.

  • Actions:

    • Fixes or depresses rib 12

    • Contributes to lateral flexion of the trunk.

  • Innervation: Lumbar plexus.

Iliacus Muscle

  • Origin: Fills the iliac fossa.

  • Combines: With the psoas to form the iliopsoas muscle.

  • Insertion: Lesser trochanter of the femur.

  • Action:

    • Flexes the thigh when the trunk is stable

    • Flexes the trunk against gravity when the body is supine.

  • Innervation: Femoral nerve (branch of the lumbar plexus).

Review of Muscles

  • Muscle Names: Quadratus lumborum, Psoas minor, Iliacus, Psoas major.

  • Key Questions to Review:

    • Origin?

    • Insertion?

    • Action?

    • Innervation?

Abdominal Viscera

Kidneys

  • Location: Retroperitoneal, situated in the posterior abdominal region, lateral to the vertebral column. Extend from the superior part of T12 to the inferior part of L3.

  • Anterior Relations:

    • Layers surrounding the kidneys:

    • Perinephric fat: Accumulation of extraperitoneal fat.

    • Renal fascia: Membranous condensation of extraperitoneal fascia.

    • Paranephric fat: Posterior/posterolateral fat accumulation.

  • Structure:

    • Smooth surface covered by a fibrous capsule.

    • Consists of an outer cortex and inner medulla.

    • Hilum: Medially located slit allowing passage for renal vessels, lymphatics, and nerves; continuous with the renal sinus.

  • Cortex Extensions:

    • Renal columns divide the medulla into discontinuous aggregations of triangular tissue (renal pyramids).

Kidneys Structure Continued

  • Renal Papilla: The apex of the renal triangles.

  • Papillary Ducts: Surrounded by a minor calyx.

  • Minor Calyx: Proximal part of the ureter.

  • Major Calyx Formation:

    • Multiple minor calices unite in the sinus to form a major calyx.

    • 2-3 major calices unit to form the renal pelvis.

Kidneys: Vasculature

  • Arterial Supply: A single artery supplies each kidney.

    • The left kidney is situated higher than the right.

    • The right renal artery is longer and located posterior to the inferior vena cava (IVC).

  • Venous Supply: Multiple veins contribute to form the right and left renal veins.

    • The left renal vein is longer and crosses the midline between the abdominal aorta and superior mesenteric artery (SMA).

Ureters

  • Function: Muscular tubes that transport urine from the kidneys to the bladder.

  • Connection: Continuous superiorly with the renal pelvis at the ureteropelvic junction.

  • Pathway: The renal pelvis narrows as it descends through the renal hilum, then the ureters descend retroperitoneally, hugging the medial aspect of the psoas major.

  • Crossing Points:

    • Ureters cross either the end of the common iliac artery or the beginning of the external iliac artery before entering the pelvic cavity.

  • Clinical Note: Constrictions in the ureters are common sites for kidney stones to become lodged.

Ureters Blood Supply

  • Supplied by adjacent arterial branches as they descend towards the bladder:

    • Upper End: Supplied by renal arteries.

    • Middle Part: Supplied by abdominal aorta, gonadal arteries, or common iliac arteries.

    • Pelvic End: Supplied by internal iliac arteries.

Liver

  • Function: The largest gland in the body, located in the upper part of the abdominal cavity.

  • Lobes: Divided into a large right lobe and a small left lobe by the attachment of the peritoneal falciform ligament.

  • Bile Production: Produced at a rate of 40 mL/hour.

  • Biliary Pathway:

    • Interlobular ducts → right/left hepatic ducts → common hepatic duct → cystic duct → gallbladder.

Gallbladder

  • Shape: Pear-shaped sac lying on the undersurface of the liver with a capacity of 30-50 mL.

  • Function: Selectively absorbs bile salts; keeps bile acid, excretes cholesterol, and secretes mucus.

  • Parts: Includes fundus, body, and neck; neck becomes continuous with the cystic duct.

  • Common Bile Duct Formation: Cystic duct + common hepatic duct = common bile duct.

Pancreas

  • Location: Lies in the epigastrium and left upper quadrant, retroperitoneally.

  • Functions: Contains both endocrine and exocrine functions.

  • Duct System: Contains ducts that allow the passage of pancreatic juices to the duodenum. The main duct begins in the tail, runs the length of the gland, and opens into the 2nd part of the duodenum with the bile duct at the major duodenal papilla.

  • Structure: Consists of head, neck, body, and tail.

Spleen

  • Location: Upper left quadrant, posterior to the stomach.

  • Size: Fist-sized (approximately 5 inches).

  • Structure: Covered by a fibrous capsule; internally composed of red and white pulp:

    • Red pulp: Comprises 80% of tissue, contains blood vessels forming splenic sinusoids and cords.

    • White pulp: Lymphoid tissue aggregates within the red pulp.