Study Notes on Regional Anatomy of the Abdomen & Pelvis

Regional Anatomy of the Abdomen & Pelvis

Instructor Information

  • Course: Human Anatomy HSS2011
  • Instructor: Prof. Helen Law
  • Position: Associate Head & Associate Professor
  • Department: Radiography (Medical Imaging)
  • Faculty: Health & Social Sciences
  • Email: hthelen@polyu.edu.hk
  • Semester: 2025, Semester 1, Week 10

Week 10: Major Organs of the Abdomen & Pelvis

Digestive Organs
  • Major Organs:
    • Teeth
    • Tongue
    • Pharynx
    • Esophagus
    • Stomach
    • Small intestine
    • Large intestine
    • Liver
    • Gallbladder
    • Pancreas
  • Functions:
    • Processes and digests food.
    • Absorbs and conserves water.
    • Absorbs nutrients.
    • Stores energy reserves.
Genitourinary Organs
  • Major Organs:
    • Kidneys
    • Ureters
    • Urinary bladder
    • Urethra
  • Functions:
    • Excretes waste products from the blood.
Male Reproductive Organs
  • Major Organs:
    • Testes
    • Epididymides
    • Ductus deferentia
    • Seminal vesicles
    • Prostate gland
    • Penis
    • Scrotum
  • Functions:
    • Produces male sex cells (sperm), seminal fluids, and hormones.
    • Sexual intercourse.
    • Controls water balance by regulating urine volume.
    • Stores urine prior to voluntary elimination.
    • Regulates blood ion concentrations and pH.
Female Reproductive Organs
  • Major Organs:
    • Ovaries
    • Uterine tubes
    • Uterus
    • Vagina
    • Labia
    • Clitoris
    • Mammary glands
  • Functions:
    • Produces female sex cells (oocytes) and hormones.
    • Supports developing embryo from conception to delivery.
    • Provides milk to nourish newborn infant.
    • Sexual intercourse.

Learning Outcomes for Week 10

  1. Delineate the abdominal quadrants (4) and regions (9).
  2. Define the boundaries of the abdominal and pelvic cavities.
  3. Describe major structures piercing the diaphragm.
  4. Describe the peritoneum and its functions.
  5. Describe the arterial blood supply, venous drainage, and lymphatic drainage of the abdomen and pelvis.
  6. For nerve innervation, refer to Week 6 - Senses and Autonomic Nervous System (Slides 53 & 54).

Abdominopelvic Quadrants

  • Right Upper Quadrant (RUQ)
  • Right Lower Quadrant (RLQ)
  • Left Lower Quadrant (LLQ)
  • Left Upper Quadrant (LUQ)
  • The quadrants are formed by two perpendicular lines that intersect at the navel (umbilicus).

Abdominopelvic Regions

  • 9 Regions:
    • Left hypochondriac region
    • Right hypochondriac region
    • Left lumbar region
    • Right lumbar region
    • Left inguinal region
    • Right inguinal region
    • Epigastric region
    • Umbilical region
    • Hypogastric (pubic) region
  • Mid-clavicular lines help delineate these regions.

Anatomical Relationships

  • Important anatomical relationships of the abdominal cavity include:
    • Liver
    • Gallbladder
    • Large intestine
    • Small intestine
    • Appendix
    • Stomach
    • Spleen
    • Urinary bladder
    • Caecum

Landmarks for Reference

  • L1 (Transpyloric plane):
    • Pylorus of the stomach.
    • Approximately at L3: Inferior border of costal margin.
    • At L4: Iliac crest.
    • At L5: Intertubercular plane; origin of the inferior vena cava (IVC).
    • Interspinous plane: Anterior superior iliac spine (ASIS) at S1.
Landmarks for Physical Examination
  • Pubic Symphysis
  • Gall Bladder: Mid-clavicular line × costal margin.
  • Caecum (Appendicitis): 1/3 ASIS→Umbilicus (McBurney’s point).
  • Femoral artery: 1/2 ASIS→Pubic symphysis.

Body Cavities

  • Components:
    • Thoracic cavity
    • Anterior chest wall:
      • Sternum
      • Costal cartilages
    • Lateral chest wall:
      • Ribs and intercostal muscles
    • Posterior chest wall:
      • Thoracic vertebrae and ribs
    • Thoracic inlet and outlet:
      • Inlet = sternum (manubrium), 1st ribs, T1
      • Outlet = diaphragm

Defining the Boundaries of the Abdominal Cavity

  • Anterior abdominal wall: Muscles and fibrous layers.
  • Lateral abdominal wall: Muscles.
  • Posterior abdominal wall: Muscles, lumbar vertebrae.
  • Inlet: Diaphragm.
  • Outlet: Pelvic cavity.

The Anterolateral Abdominal Wall

  • Important structures:
    • Linea alba
    • External oblique
    • Internal oblique
    • Transversus abdominis
    • Rectus abdominis
    • Tendinous inscriptions

The Posterior Abdominal Wall

  • Muscles:
    • Iliopsoas muscle: Inserts to lesser trochanter of femur; powerful flexor of thigh at hip joint.
    • Psoas major muscle
    • Quadratus lumborum
    • Iliacus muscle
Transverse Section of Abdomen
  • Contains:
    • Rectus abdominis
    • External oblique
    • Internal oblique
    • Transversus abdominis
    • Psoas muscle
    • Quadratus lumborum
  • Thoracolumbar fascia: Surrounds the posterior abdominal wall.

Abdominal Inlet

  • Comprised of:
    • Sternal portion of diaphragm
    • Xiphoid process
    • Costal portion of diaphragm
  • Thoracic cavity, pleural cavity, pericardial cavity, and abdominal cavity transitions noticed.

The Diaphragm

  • Key openings and their positions:
    • Caval hiatus (T8): For inferior vena cava, phrenic nerve, and additional vessels.
    • Oesophageal hiatus (T10): For oesophagus, vagus nerve, and blood vessels.
    • Aortic hiatus (T12): Located between crura; transmits abdominal aorta, azygos vein, and thoracic duct.

Pelvic Cavity and Perineum

  • Define the pelvic inlet and pelvic outlet:
    • Pelvic Inlet: From sacral promontory to superior margin of pubic symphysis.
    • Pelvic Outlet: From tip of coccyx to inferior margin of pubic symphysis.
Pelvic Diaphragm (Pelvic Floor)
  • Composed of:
    • Coccygeus muscle
    • Levator ani muscle
  • Affects the function of pelvic organs and contributes to pelvic stability.

Perineal Body

  • Description: A fibromuscular node located deep to skin between the anus and vaginal opening (in females) or posterior to scrotal skin (in males).
  • Importance: Damage can lead to incontinence and prolapse of pelvic organs.

Urogenital & Anal Triangles

  • Urogenital Triangle:
    • Boundary includes pubic symphysis, ischial tuberosity, and perineal body.
    • Superficial transverse perineal muscle.
  • Anal Triangle:
    • Includes external anal sphincter muscle, anus, and coccyx.

Peritoneum

  • Structures:
    • Parietal peritoneum: Lines abdominal wall.
    • Visceral peritoneum: Covers organs.
  • Functions:
    • Supports organs and provides lubrication.
    • Contains folds such as omentum, mesentery, and ligaments.
  • Peritoneal cavity: Space between parietal and visceral layers.
    • Intraperitoneal organs: Fully surrounded by visceral peritoneum.
    • Retroperitoneal organs: Located behind parietal peritoneum; includes organs like the kidneys.

Omentum & Mesenteries

  • Omentum: Fold of peritoneum containing blood vessels, nerves, lymphatics, and adipose tissue.
    • Greater omentum: Extends from greater curvature of stomach to anterior of transverse colon, providing an apron-like cover over small intestinal organs.
    • Lesser omentum: Connects lesser curvature of the stomach to the liver.

Peritoneal Dialysis

  • Procedure using a dialysis solution bag in the peritoneal cavity.
  • Complications:
    • Peritonitis: Inflammation of the peritoneum due to infection.

Vascular Supply of the Abdomen

Abdominal Aorta
  • Location: Posterior abdominal wall retroperitoneal space from vertebra T12 to L4.
  • Branches Include:
    • Inferior phrenic a.
    • Adrenal a.
    • Renal a.
    • Gonadal a.
    • Lumbar a.
    • Common iliac a. (terminal segment bifurcates).
Arterial Supply in the Pelvis
  • Branches of Common Iliac Artery: Internal and external iliac arteries supplying pelvic muscles and viscera.
  • Gonadal artery arises directly from the aorta.
Major Arteries by Region
  1. Celiac trunk: Supplies foregut (liver, spleen, stomach).
  2. Superior Mesenteric Artery (SMA): Supplies midgut (small intestine, proximal 2/3 of transverse colon).
  3. Inferior Mesenteric Artery (IMA): Supplies hindgut (distal 1/3 of transverse colon to the rectum).

Venous Drainage

Inferior Vena Cava (IVC)
  • Function: Drains blood from lower limbs and pelvic organs via:
    • External iliac veins
    • Internal iliac veins
    • Right and left gonadal veins
    • Note on malignancies and venous plexus spread to vertebral column.
Hepatic Portal System
  • Collects blood from the GI tract:
    • Blood from liver sinusoids drains into hepatic veins, which empty into IVC.- Includes contributions from splenic vein, superior mesenteric vein, and inferior mesenteric vein.

Lymphatic Drainage in Abdomen & Pelvis

Key Components
  • Right lymphatic duct
  • Thoracic duct
  • Cisterna chyli: Dilated sac collecting lymph from lower body and intestines, serving as the origin of the thoracic duct.

Nerve Innervation in Abdomen & Pelvis

Sympathetic Division
  • Pathway: Arises from thoracic and lumbar spinal cord.
  • Features include relatively short preganglionic fibers and relatively long postganglionic fibers.
  • Innervates organs such as stomach, spleen, pancreas, kidneys, uterus, and urinary bladder.
Parasympathetic Division
  • Pathway: Arises from cranial/sacral spinal cord.
  • Features include long preganglionic fibers terminating in or near target organs and very short postganglionic fibers.

References

  • Martini, Nath & Bartholomew (2024). Fundamentals of Anatomy & Physiology, 12th edition. Boston: Pearson.
  • Saladin (2024 release). Human Anatomy. New York, N.Y: McGraw-Hill.