Human Anatomy Week 4 - Notes

Anterior Abdominal Region Overview

• Anterior abdominal region divided into various landmarks, cavities, regions, and dermatomes for anatomical reference.
• Landmarks include:
  • Linea alba: Vertical indentation dividing abdomen, visible with low subcutaneous tissue.
  • Linea semilunaris: Lateral boundary of the rectus abdominis.
  • Costal margin: Inferior border of the ribs.
  • Xiphoid process: Anatomical landmark at the lower end of the sternum.
  • Inguinal ligament: Separates lower abdomen from thigh.

Cavities

• Thoracic Cavity: Encloses heart and lungs.
• Abdominal Cavity: Contains digestive organs.
• Pelvic Cavity: Houses reproductive organs and lower part of the gastrointestinal tract.

Abdominal Regions and Quadrants

• Regions: Right hypochondrium, right flank, right inguinal, epigastric, umbilical, pubic, left hypochondriac, left flank, left inguinal.
• Quadrants: Divided by linea alba.
  • RUQ: Liver (right lobe), gallbladder, portions of stomach, duodenum, pancreas, right kidney.
  • LUQ: Liver (left lobe), spleen, stomach, proximal jejunum, pancreas.
  • RLQ: Cecum, appendix, ileum, right ovary, urinary bladder (if full).
  • LLQ: Sigmoid colon, left ovary, urinary bladder (if full).

Dermatomes

• Nipple line: Corresponds to T4 dermatome.
• Umbilicus: Marks T10 dermatome.

Layers of the Abdominal Wall

• Comprised of multiple layers from superficial to deep:
  • Skin
  • Superficial fascia (Camper's and Scarpa's)
  • Investing and deep fascia
  • Muscular layers: Rectus abdominis, external oblique, internal oblique, transversus abdominis.
  • Endoabdominal (transversalis) fascia
  • Parietal peritoneum

Muscles of the Anterior Abdominal Wall

• Functions include trunk support, movement, and rotation.
• Innervation: Thoracoabdominal nerves (T7-T12).
• Muscles:
  • External Oblique: Most superficial, fibers run in a downward direction.
  • Internal Oblique: Fibers oriented 90 degrees to external oblique.
  • Transversus Abdominis: Horizontal fibers acting as a tight corset.
  • Rectus Abdominis: Central muscle, effective trunk flexor.

Rectus Sheath

• Comprised of aponeurosis layers from external and internal obliques, aids in muscle containment.

Inguinal Canal

• Formed by external oblique fascia; potential site for herniation.
• Contains deep and superficial rings for structures to pass through.

Vascular Supply

• Arterial Supply:
  • Superior Epigastric Artery: From internal thoracic artery.
  • Inferior Epigastric Artery: Branches off from external iliac artery.
  • Musculophrenic Artery: Supplies lateral abdominal muscles.
• Venous Drainage: Gastrointestinal organs drain via the hepatic portal vein, entering the liver for filtration.

Peritoneal Cavity

• Potential space between abdominal organs and wall lined by parietal peritoneum.
• Intraperitoneal Organs: Stomach, liver, spleen are covered by peritoneum.
• Retroperitoneal Organs: Kidneys and pancreas lie posterior to the peritoneum.

Major Functions of GI Tract

• Digestion and absorption of nutrients.
• Endocrine functions managed by pancreas and liver.

Liver and Gallbladder

• Liver produces bile for fat digestion; gallbladder stores bile.
• Detoxifies substances, metabolizes nutrients, and produces plasma proteins.

Spleen

• Involved in red blood cell breakdown and storage.
• Vulnerable to rupture in abdominal trauma.

Innervation of Viscera

• Sympathetic and parasympathetic innervation governs digestive processes.
• Vagus nerve influences upper gastrointestinal tract function; pelvic splanchnic nerves impact lower sections.### Nervous System Input
• Parasympathetic input derives from cranial nerves and sacral nerve roots, primarily through the vagus nerve.
• Sympathetic innervation originates from thoracic and lumbar segments of the spinal cord, featuring its own ganglia outside the spinal cord.
• Parasympathetic stimulation enhances enzyme release, increases blood flow to the digestive tract, and boosts peristalsis, while sympathetic activity diminishes peristalsis and diverts blood flow from visceral organs.

Referred Pain Patterns

• Liver and gallbladder pain can radiate to the right shoulder, neck, and scapula due to upper thoracic cervical innervation.
• Musculoskeletal pain is typically localized and identifiable through palpation, movements, or specific tests, unlike visceral pain, which does not follow predictable patterns.
• Abdominal organs may cause referred pain both in the abdomen and the back.

Posterior Abdominal Wall and Pelvic Floor

• The diaphragm, a posterior abdominal wall muscle, is essential for respiration and trunk stability, innervated by the phrenic nerve (C3-C5).
• Psoas major, originating from T12-L5, is crucial for hip flexion, lateral lumbar flexion, and lumbar extension, innervated by the APRs of L2-L3.
• Iliacus, originating from the iliac fossa and ala of the sacrum, flexes the thigh and stabilizes the hip, innervated by the femoral nerve (L2-L3).
• Quadratus lumborum assists in trunk extension and lateral trunk flexion, its innervation comes from T12-L4 APRs.

Sacroiliac Joint (SIJ)

• The SIJ facilitates force transfer between the trunk and lower extremities, critical for mobility and childbirth.
• Contains c-shaped joints with no true synovial joint surfaces and an average lumbosacral angle of 140 degrees, typically maintaining lordosis.
• Ligaments such as the iliolumbar ligament stabilize the lumbar spine against rotation, while sacrotuberous and sacrospinous ligaments prevent ilium rotation.

Movements of the Sacroiliac Joint

• Nutation refers to the anterior tilting of the sacrum, while counter nutation involves a posterior movement, both contributing to load transmission and spine stabilization.

Pubic Symphysis

• A fibrocartilaginous joint at the anterior meeting point of pubic bones, reinforced by ligaments, with minimal movement but crucial for SIJ adaptation.

Pelvic Floor Muscles

• The pelvic floor consists mainly of levator ani muscles, which support pelvic viscera and help maintain urinary continence.
• Comprises the puborectalis, pubococcygeus, and iliococcygeus muscles, along with the coccygeus for additional support.

Kidney Function and Structure

• The kidneys regulate fluid volume, acid-base balance, electrolyte concentrations, blood pressure, and excrete waste products.
• Kidney pain often radiates to the lumbar region, indicating potential complications or secondary issues in patients with limited kidney function.
• Urine formation relies on filtration, reabsorption, secretion, concentration, and eventual excretion through the urinary tract.

Urinary and Reproductive Systems

• The bladder serves as a muscular reservoir for urine, controlled by the autonomic nervous system, leading to the urethra for expelling urine.
• In males, the reproductive system includes the testes and spermatic cord with the vas deferens, while in females, the vagina extends through the pelvic floor.

Test your knowledge on the anatomy of the abdominal region with this quiz. Explore questions about abdominal quadrants, key muscles, and important landmarks like the gallbladder and xiphoid process. Perfect for students of anatomy seeking to reinforce their understanding.