Study Guide #18 - Chapter 4: The Abdomen

BIO475 Lecture Study Guide #18: Chapter 4 – The Abdomen (Part 4 – Pages 201-222)

Posterior Abdominal Wall

  1. Location of the Posterior Abdominal Wall

    • The posterior abdominal wall is located at the back of the abdomen, supporting the abdomen and providing attachment for various structures.

  2. Major Components of the Posterior Abdominal Wall (Refer to Fig. 4.97)

    • a) Blood Vessels and Lymphatics

      • The posterior abdominal wall contains major arteries and veins including the abdominal aorta and inferior vena cava.

    • b) Nervous System

      • This includes major nerve plexuses such as the lumbar plexus, consisting of lumbar nerves and autonomic nerves.

    • c) Organs

      • Important organs include the kidneys and suprarenal (adrenal) glands.

  3. Skeletal Components of the Posterior Abdominal Wall (Refer to Fig. 4.98)

    • The most posterior part of the posterior abdominal wall is formed by the vertebral column (lumbar vertebrae) and the pelvis (particularly the ilium).

  4. Muscle Components (Refer to Fig. 4.99)

    • a) Psoas Major and Minor

      • The psoas major is involved in hip flexion and stabilization of the lumbar spine, while the minor assists in the flexion of the lumbar spine.

    • b) Quadratus Lumborum

      • This muscle helps in lateral flexion of the spine and stabilizes the pelvis.

    • c) Iliacus

      • The iliacus muscle also participates in hip flexion and works in concert with the psoas major to form the iliopsoas muscle group.

    • d) Diaphragm

      • The diaphragm separates the thoracic cavity from the abdominal cavity and is the primary muscle of respiration.

  5. Structures Passing Through or Around the Diaphragm (Refer to Fig. 4.100)

    • Several vital structures traverse the diaphragm including the aorta, inferior vena cava, esophagus, and various nerves such as the phrenic nerve.

Kidneys

  1. Function and Location of the Kidneys (Refer to OpenStax Chapter 25, Fig. 4.103)

    • a) Function

      • The kidneys filter blood, remove waste through urine, regulate electrolyte balance, and maintain pH levels.

    • b) Location

      • The kidneys are located retroperitoneally, between the T12 and L3 vertebrae, posterior to the abdominal cavity.

  2. Key Points of Contact with Other Structures (Refer to Figs. 4.103, 4.104, and 4.105)

    • The kidneys are in close contact with the diaphragm, the liver (right kidney), spleen (left kidney), and various blood vessels and lymphatics.

  3. Fat and Fascia Coverings of the Kidneys (Refer to Fig. 4.106)

    • Each kidney is surrounded by a layer of perirenal fat, which provides cushioning and insulation, as well as a renal fascia that anchors the kidneys to surrounding structures.

  4. External Features of the Kidneys (Refer to Fig. 4.104)

    • Kidneys are bean-shaped, with a convex lateral border and a concave medial border that features the renalis hilum where blood vessels enter and exit.

  5. Internal Features of the Kidneys (Refer to Fig. 4.107)

    • a) Renal Cortex

      • The outer region of the kidney containing nephrons, responsible for filtering blood.

    • b) Renal Medulla

      • The inner region organized into pyramids that contain the loops of Henle and collecting ducts.

    • c) Renal Pyramids

      • Triangular-shaped regions in the medulla that contain the nephron structures.

    • d) Renal Papilla

      • The tips of the renal pyramids empty urine into minor calyces.

    • e) Renal Sinus

      • A cavity within the kidney that houses the renal pelvis, calyces, and blood vessels.

    • f) Minor and Major Calyx; Renal Pelvis

      • The minor calyces surround the renal papillae and converge to form major calyxes, which drain into the renal pelvis before exiting the kidney through the ureter.

  6. Blood Vessels Entering and Leaving the Kidneys (Refer to Figs. 4.107 and 4.108)

    • The renal artery enters at the hilum, branching off from the abdominal aorta, while the renal vein exits at the hilum, draining into the inferior vena cava.

Ureters

  1. Structure and Function of the Ureters (Refer to Fig. 4.109)

    • The ureters are muscular tubes that transport urine from the kidneys to the bladder through peristalsis. They are retroperitoneal structures with a lumen that constricts at certain points.

  2. Kidney-Related Medical Situations

    • a) Urinary Tract Stones

      • Hard mineral and salt deposits that form within the kidneys and can obstruct urine flow, causing pain and infection.

    • b) Urinary Tract Cancers

      • Malignancies that can develop in any part of the urinary system including the bladder and kidneys, often requiring surgical or chemotherapy intervention.

    • c) Kidney Transplant

      • A surgical procedure to replace a failing or diseased kidney with a healthy kidney from a donor, necessitating immunosuppressive therapy post-transplant.

  3. Structure and Function of the Suprarenal Glands (Adrenal Glands) (Refer to Fig. 4.112)

    • The suprarenal glands are small, triangular-shaped glands located on top of each kidney, involved in producing hormones such as cortisol, adrenaline, and aldosterone, which regulate metabolism, immune response, and blood pressure.

  4. Blood Vessels Supplying the Suprarenal Glands (Refer to Fig. 4.112)

    • Blood supply comes from the inferior phrenic artery, aorta, and renal arteries, ensuring a rich vascular supply.

  5. Sympathetic Innervation of the Suprarenal Glands (Refer to Fig. 4.112)

    • The glands receive strong sympathetic innervation via the splanchnic nerves, which stimulate the adrenal medulla to release adrenaline and noradrenaline in response to stress.

  6. Pathway of the Abdominal Aorta (Refer to Fig. 4.113)

    • The abdominal aorta runs down the length of the abdomen, starting from the diaphragm (T12) and bifurcating into the left and right common iliac arteries at the L4 vertebra.

  7. Branches of the Abdominal Aorta (Superior to Inferior Order)

    • A detailed list of branches includes:

      • Inferior phrenic arteries: supply the diaphragm.

      • Celiac trunk: supplies blood to the liver, stomach, and spleen.

      • Superior mesenteric artery: supplies the small intestine and part of the colon.

      • Renal arteries: supply the kidneys.

      • Gonadal arteries: supply the reproductive organs (testes/ovaries).

      • Inferior mesenteric artery: supplies the distal colon.

      • Lumbar arteries: supply the muscles and skin of the lower back.

      • Common iliac arteries: lead to the lower limbs.

  8. Pathway of the Inferior Vena Cava (Refer to Fig. 4.115)

    • The inferior vena cava begins at the union of the common iliac veins in the pelvis and ascends along the right side of the vertebral column to drain into the right atrium of the heart.

  9. Tributaries of the Inferior Vena Cava (Inferior to Superior Order)

    • Includes tributaries from the lumbar veins, renal veins, gonadal veins, hepatic veins, and common iliac veins, contributing to venous return from the lower body, kidneys, and abdominal organs.

  10. Absence of Veins from Gastrointestinal Tract Emptying into Inferior Vena Cava (Refer to Fig. 4.116)

    • Veins from the gastrointestinal tract drain into the hepatic portal system, which supplies blood to the liver before it returns to the general circulation via the inferior vena cava, avoiding direct entry from these organs.

  11. Deep Vein Thrombosis (DVT)

    • DVT is a condition where blood clots form in deep veins, commonly in the legs, presenting risk of complications like pulmonary embolism.

    • Treatment: Anticoagulants may be used, and in severe cases, placement of an inferior vena cava filter may be required to prevent clots from reaching the lungs (retrieving before systemic circulation).

  12. Major Collections of Lymph Nodes in the Posterior Abdominal Wall (Refer to Fig. 4.118)

    • Collections include the lumbar (aortic) lymph nodes which drain lymph from the lower extremities, the pelvis, and abdominal viscera.

  13. Cysterna Chyli (Refer to Fig. 4.118)

    • A dilated sac that serves as a major lymphatic collecting channel situated at the level of L1-L2, receiving lymph from the lower limbs and intestinal tract, giving rise to the thoracic duct.

  14. Major Components of the Nervous System in the Posterior Abdomen (Refer to Figs. 4.93, 4.94, 4.95, 4.96, 4.119)

    • a) Lumbar Plexus: a network of nerves that supplies the lower abdomen and lower limbs.

    • b) Autonomic Nerves: innervate organs and vessels in the abdomen, regulating involuntary functions.

    • c) Sympathetic Trunk: provides sympathetic fibers that align with the thoracic splanchnic nerves.

    • d) Splanchnic Nerves: convey visceral sensory information and sympathetic supply to the abdominal organs.

    • e) Phrenic Nerve: controls the diaphragm.

  15. Postganglionic Neurons of the Sympathetic Nervous System (Refer to Fig. 4.120)

    • Some postganglionic neurons that supply the gastrointestinal tract do not travel through the sympathetic trunk; instead, they synapse in ganglia located near or within the target organs (prevertebral ganglia).

  16. Postganglionic Neurons of the Parasympathetic Nervous System (Refer to Fig. 4.120)

    • These postganglionic neurons are located in ganglia that are close to or within the target organs of the gastrointestinal system, providing localized control over organ function.

  17. Pain in the Anterior Thigh and Medical Issues with the Large Intestine (Refer to Table 4.5)

    • Pain in the anterior thigh may be referred pain resulting from irritation of the large intestine due to shared nerve pathways in the lumbar plexus area, demonstrating the complex interconnection between bodily regions and their innervation.

  18. Lumbar Plexus

    • The lumbar plexus is a network of spinal nerves situated in the posterior abdominal wall that contributes to the motor and sensory nerve supply of the lower limbs, aiding in leg movement and sensation. (Isolated view in Fig. 4.121 and in the abdomen in Fig. 4.122)

  19. Targets of the Main Branches of the Lumbar Plexus

    • a) Iliohypogastric: innervates the abdominal muscles and skin above the pubis.

    • b) Ilioinguinal: provides sensation to the skin of the groin and parts of the thigh.

    • c) Genitofemoral: sensory innervation to the skin of the groin and motor to the cremaster muscle.

    • d) Lateral Cutaneous Nerve of Thigh: supplies sensation to the lateral thigh.

    • e) Femoral: innervates the anterior thigh muscles.

    • f) Obturator: innervates the medial thigh muscles.