Anatomy of Posterior Abdominal Region

Posterior Abdominal Region

• The posterior abdominal region is behind the abdominal part of the gastrointestinal tract.
• It is enclosed by the bones and muscles of the posterior abdominal wall.
• Structures passing through this area include the abdominal aorta, inferior vena cava, sympathetic trunks, and lymphatics.
• Kidneys and suprarenal glands are also located in this region.

Psoas Major

• Origin: lateral surface of vertebral bodies, transverse processes, and intervertebral discs of T12 to L5.
• Insertion: lesser trochanter of femur.
• Innervation: anterior rami of L1 to L3 spinal nerves.
• Function: flexion of thigh at hip joint

Psoas Minor

• Origin: lateral surface of vertebral bodies of T12 and L1 and intervening intervertebral disc.
• Insertion: pectineal line and iliopubic eminence.
• Innervation: anterior rami of L1 spinal nerve.
• Function: weak flexion of lumbar region.
• Absent in 40% of the population.

Quadratus Lumborum

• Origin: transverse process of L5 vertebra, iliolumbar ligament, and iliac crest.
• Insertion: transverse processes of L1 to L4 vertebrae, lower border of the 12th rib.
• Innervation: anterior rami of T12 to L4 spinal nerves.
• Function: depresses and stabilizes the 12th rib; lateral bending of the trunk.

Iliacus

• Origin: iliac fossa, sacrum, iliolumbar and anterior sacroiliac ligaments.
• Insertion: lesser trochanter of femur.
• Innervation: femoral nerve.
• Function: flexion of thigh at hip joint.

Renal Tubule

• It is a long tubular passageway that begins in the renal corpuscle.
• Consists of the proximal convoluted tubule, loop of Henle, and distal convoluted tubule.

Collecting Ducts

• Receive fluid from many nephrons.
• Each duct carries fluid to a papillary duct which drains into a minor calyx.

Kidney Histology

• Nephrons
  • Renal corpuscle: consists of a central tuft of capillaries, the glomerulus, which is surrounded by a glomerular capsule called Bowman's capsule.
  • Glomerulus: network of capillaries supplied by an afferent arteriole and drained by an efferent arteriole
    • Mesangial cells: located between capillaries
  • Bowman's capsule: a cup-like sac at the beginning of the renal tubule, encloses the glomerulus and collects fluid filtered from blood, known as glomerular filtrate.
    • Parietal layer: outer layer, lined with simple squamous epithelium, also called capsular layer.
    • Visceral layer: inner layer, composed of branched cells called podocytes, which form a filtration membrane.
    • Capsular space: between parietal and visceral layers, also called urinary or Bowman’s space.

Filtration & Structures

• Filtration happens in the renal corpuscle.
• Blood pressure forces water and dissolved solutes out of the glomerular capillaries into the capsular space.
• This produces a protein-free solution (filtrate) similar to blood plasma.

Nephrons Continued

• The tubes into which fluid passes are called renal tubules.
• Each renal tubule consists of:
  • Proximal convoluted tubule
  • Nephron loop (loop of Henle)
  • Distal convoluted tubule
• Filtrate gradually changes composition along the renal tubule.
• Each nephron empties into collecting ducts.
• Functions:
  • Reabsorb useful organic nutrients that enter filtrate.
  • Reabsorb more than 90% of the water.
  • Secrete waste products that failed to enter the filtrate.

The Nephron

• Proximal Convoluted Tubule: reabsorption of water, ions, and all organic nutrients.
• Distal Convoluted Tubule: secretion of ions, acids, drugs, and toxins, variable reabsorption of water, sodium ions, and calcium ions (under hormonal control).
• The proximal and distal convoluted tubules are located in the cortex.
• They are separated by a U-shaped nephron loop, also called the loop of Henle.
• Nephron loop (loop of Henle):
  • Thin descending limb: further reabsorption of water.
  • Thick ascending limb: both sodium and chloride ions (under hormonal control).
  • The limbs of the loop of Henle extend partially into the medulla forming the descending and ascending thin segments.

Juxtaglomerular Complex (JGC)

• Consists of the macula densa - tall epithelial cells of the DCT near the renal corpuscle, and unusual smooth muscle fibers of the afferent arteriole closely associated with the macula densa called juxtaglomerular cells.
• Also called the juxtaglomerular apparatus.

Kidney Structure

• Renal cortex:
  • Contains the renal corpuscles, proximal and distal convoluted tubules.
• Renal medulla:
  • Contains the loops of Henle and collecting ducts.
• Renal pelvis:
  • Funnels urine from the collecting ducts into the ureter.
• Glomerular capsule:
  • Parietal layer: outer layer, lined with simple squamous epithelium.
  • Visceral layer: inner layer, composed of branched cells called podocytes which form a filtration membrane.
  • Glomerulus: a network of capillaries supplied by an afferent arteriole and drained by an efferent arteriole.
• Proximal convoluted tubule: cells have microvilli and mitochondria for reabsorption.
• Distal convoluted tubule: cells are smaller and less active, contribute to the reabsorption of water and ions.
• Loop of Henle: cells are thin and involved in water and salt reabsorption.
• Collecting duct: cells are involved in the final adjustment of urine concentration and reabsorption of water.
• Papillary duct: located in the renal medulla, delivers urine to the minor calyx.

Explore the anatomy of the posterior abdominal region, including vital structures such as the kidneys and major muscles like the psoas major and minor. This quiz covers origins, insertions, innervations, and functions of key muscles involved in hip flexion and lumbar support. Test your knowledge of this important anatomical area!