Abdominal Study Guide

Abdominal Wall Overview

• Abdominal wall reflects to get to the inside.
• Overview of abdomen, then viscera individually.
• Posterior abdominal wall and retroperitoneal space covered by Dr. Baker.

Learning Objectives

• Blue - clinical application.
• Studying figure - slides for studying.
• Glare - mnemonics (not directly tested).
• Big picture - necessary to understand, but not directly tested (unless associated with a learning objective).

Abdomen General Concepts

• Fungible area.
• Closed at the top (diaphragm).
• Continuous with the pelvic cavity inferiorly.
• Boundaries of pelvic cavity to be discussed next week.
• Enclosed by abdominal wall (anterior, anterolateral - today; posterior - Monday).
• Single large peritoneal cavity lined by peritoneum.
• Retroperitoneal space posterior to peritoneal cavity (to be discussed Monday).

Functions of the Abdomen

• Houses and protects viscera.
• Assists with breathing:
  • Inhalation: abdominal wall muscles relax to accommodate expansion of thoracic cavity.
  • Exhalation: abdominal wall contracts to help diaphragm elevate, assisting with forced expiration.

Components of the Abdomen

• Abdominal wall.
• Abdominal cavity (houses organs, peritoneal cavity).
• Peritoneal cavity (lined by peritoneum).
• Mesenteries (folds of peritoneum, anchor viscera).
• Retroperitoneal cavity.

Surface Anatomy

• Nine region pattern.
• Four quadrant pattern (used in this class).
• Quadrants contain different viscera.
• Clinically used to describe organ location or abnormalities/pain.
• Organs in each quadrant:
  • Learn as you learn the organs, then correlate with the table.
• Defining the quadrants:
  • Median plane: vertical line down the middle.
  • Horizontal plane: transumbilical plane (through the umbilicus).
  • Right upper quadrant, left upper quadrant, right lower quadrant, left lower quadrant.

Abdominal Wall Layers

• Superficial to deep:
  • Superficial fascia:
    • Fatty layer (Camper's fascia). $Camping \Rightarrow cold \Rightarrow fat$.
    • Membranous layer (Scarpa's fascia). More tough and tan-white in color.
  • Muscles:
    • Anterolateral (3 layers):
      • External oblique. Fiber direction same as external intercostals (hands in pockets).
      • Internal oblique. Fiber direction opposite of external oblique.
      • Transversus abdominis. Fibers go transversely (horizontally).
    • Anterior (midline):
      • Rectus abdominis. "Six pack" muscle, surrounded by the rectus sheath.
  • Transversalis fascia. Deep to transversus abdominis.
  • Extraperitoneal fascia. Deepest layer, outside the peritoneum.

Abdominal Wall Muscles Details

• External Oblique
  • Fiber direction: hands in pockets
  • One side contracting bends trunk, pulls anterior abdomen to opposite side
  • Both contracting flex trunk, compress abdominal contents
    • Internal Oblique
  • Fibers: opposite direction Internal Oblique
    • Unilaterally bends trunk, turns anterior part of abdomen to same side
• Transversus Abdominis
  • Fibers: Transverse
  • Compresses abdominal contents
  • Tilts pelvis forward helps with posture
• Rectus Abdominis
  • Rectus = straight (vertical muscle).
  • Tendinous intersections that anchor fibers.
  • Linea alba: thick band of connective tissue in the midline, where anterolateral muscles attach.
  • Rectus sheath surrounds rectus abdominis.
    • Anterior: entirely covered by rectus sheath.
    • Posterior: only upper three-quarters covered by rectus sheath.

Anterior and Posterior Rectus Sheath

• Above arcuate line:
  • External oblique and part of internal oblique aponeurosis go anterior to rectus abdominis.
    • The rest of the internal oblique aponeurosis and transverse abdominis aponeurosis go posterior to rectus abdominis.
      t * Below arcuate line:
    • All aponeuroses go anterior to rectus abdominis; no posterior sheath.
• This absence weakens area, important for surgery.

Arcuate Line Transition

• Arcuate line is midpoint between umbilicus and pubic symphysis.
• Inferior to arcuate line, all aponeuroses of the three muscles go anterior to the rectus abdominis muscle and no posterior rectus sheath in the lower part
• Know order of layers for incisions above and below the arcuate line.

Transversalis Fascia

• Deep to muscles.
• Lines abdominal cavity, continuous with pelvic cavity.

Summary

• Layers from anterior:
  • Fascia
  • Muscles
    *Transversalis Fascia

Abdomen Innervation

• Thoracoabdominal nerves (T7-T11 intercostal nerves, ventral rami).
• Subcostal nerve (below rib).
• L1 nerve.
• Dermatome landmarks:
  • Xiphoid process: T6/T7.
  • Umbilicus: T10.
  • Pubic symphysis: L1.

Blood Supply

• Superior epigastric artery (from internal thoracic).
• Inferior epigastric artery (typically from external iliac).
• Anastomose posterior to rectus abdominis muscle within rectus sheath (between posterior rectus abdominis muscle and anterior posterior rectus sheath).
• Venous drainage matches arteries (superior and inferior epigastric veins).

Inguinal Region

• Groin.
• Junction between anterior abdominal wall and thigh.

Inguinal Canal

• Slit-like passage extending inferomedially, superior to the inguinal ligament.
• Begins at deep inguinal ring; ends at superficial inguinal ring.
  • Deep Ring
    • Also called internal ring, located halfway between ASIS and pubic tubercle.
      • Immediately lateral to the inferior epigastric vessels.
      • Opening in transversalis fascia.
  • Superficial Ring
    • Also called external ring, located just superior to the pubic tubercle.
    • Triangular opening in external oblique aponeurosis.

Inguinal Canal Walls

• Anterior wall: aponeurosis of external oblique.
• Posterior wall: transversalis fascia.
• Superior wall (roof): transverse abdominis and internal oblique muscles.
• Inferior wall (floor): inguinal ligament (medial half).

Inguinal Canal Contents

• Both sexes: genital branch of genitofemoral nerve
• Males: spermatic cord.
• Females: round ligament of the uterus.
• Additionally: ilioinguinal nerve (travels superficial to the canal).

Inguinal Hernias

• Protrusion of peritoneal sac (sometimes with abdominal organs) through weakened area.
• Indirect hernias:
  • Go through deep inguinal ring, continue through the inguinal canal.
  • More common (especially in males).
  • Lateral to inferior epigastric vessels.
• Direct hernias:
  • Go directly through the posterior wall of the canal.
  • Medial to inferior epigastric vessels.

Abdominal Viscera Overview

• Viscera either suspended in peritoneal cavity by mesenteries or positioned between peritoneal cavity and musculoskeletal wall (retroperitoneal).
• Retroperitoneal structures covered on Monday.

GI Tract Overview

• Oral cavity, pharynx, esophagus passes through posterior mediastinum and diaphragm, stomach leads to duodenum
• Small Intestine: Duodenum (c-shaped, around head of pancreas)
  • Jejunum
  • Ileum: Transistions to cecum, right lower quadrant with appendix
• Large Intestine (Colon):
  • Cecum (RLQ) -> Ascending colon -> Right (hepatic) flexure -> Transverse colon -> Left (splenic) flexure -> Descending colon -> Sigmoid colon -> Rectum -> Anal canal -> Outside

Picture Frame Analogy:

• Picture frame = colon (ascending, transverse, descending); ascending and descending are retroperitoneal (two nails on either side).
• Picture = small intestines (duodenum, ileum).

Associated GI Organs

• Liver (right side, under diaphragm).
• Gallbladder (associated with liver; may be missing in donors).
• Pancreas

Peritoneal Cavity

• Lined by peritoneum.
• Parietal peritoneum (lining the abdominal wall).
• Visceral peritoneum (lining the organs).
• Peritoneal cavity (space between layers).
• Viscera suspended by mesenteries or retroperitoneal/infraperitoneal.

Subdivisions and Folds

• Two sacs with Peritoneal Cavity: Greater Sac, Lesser Sac/Omental Bursa (posterior to stomach, pancreas, liver).
• Omentum, mesenteries, and ligaments (folds or connections of peritoneum). Ligaments connect organs to each other or to the wall.
• Greater omentum: apron of fat hanging from greater curvature of the stomach and transverse colon.
• Lesser omentum: connects lesser curvature of the stomach to the liver; contains vessels dissected in lab.
• Mesentery: anchors small intestine in the center of the peritoneal and contains fat; vessels travel through vessels
  • Transverse mesocolon (mesentery of the transverse colon)
  • Sigmoid mesocolon (mesentery of the sigmoid colon).
• Ligaments: attachments of peritoneum that anchor organs to each other or to the wall.
  • Example - Gastrosplenic Ligament: Little sheet of peritoneum that connects the stomach and spleen

General Concepts About Abdomen

• Central gut tube suspended from posterior abdominal wall by mesenteries.
• Major viscera are retroperitoneal.
• Abdominal cavity lined by peritoneum. Parietal is the lining of the walls, Visceral is organ lining. The space between them is the peritoneal cavity.
• Organs are either intraperitoneal inside the cavity or retroperitoneal if they are behind it or pelvic if it's below it from the peritoneum.

Embryologic Development

• Purpose:
  • Understand primary/secondary retroperitoneal organs, blood supply, drainage, innervation.
• Primary retroperitoneal: develop in retroperitoneal area (e.g., kidneys).
• Secondary retroperitoneal: develop inside peritoneal cavity, then pushed back and anchored (e.g., ascending/descending colon = nails on picture frame).

Early GI Tract

*Longitudinal tube anchored by mesenteries with specific blood vessels
*Three Areas:
* Foregut
* Midgut
* Hindgut. Have their own blood supply, venous drainage, innervation, lymphatic drainage.

• These areas develop their own specific organs, organs turning around each other. Includes vessels developing with it.
• Remember: foregut = esophagus/stomach/first duedenum, midgut = rest of duod, jejunum/ileum, hindgut = colon to rectum/anus.

Blood Supply Development

• Foregut: coming from the celiac trunk.
• Midgut: coming from the superior mesenteric artery
• Hindgut: coming from the inferior mesenteric artery.

Foregut Development

• Distal esophagus, stomach, proximal duodenum, pancreas, liver.
• Stomach and duodenum twist, right and left vagus nerves become anterior and posterior.
• Forms greater and lesser omentum.

Midgut Development

• Distal duodenum, jejunum, ileum, first 2/3 of colon.
  • First, it herniates out of belly button-> Herniates into umbilicial cord-> pulled back in. This allows the small intestine on the inside and large intestine (colon) on the outside.
  • At the end of the process, anchoring down occurs -> Ascending and descending colon connect to posterior abdominal walls becoming retroperitoneal.

Section Development

*The tissue posterior to the ascending and descending is the anchors that attach the wall
*These connections require posterior abdominals to be relased

Hindgut Development

• End of transverse colon to beginning of rectum.
• Descending colon anchors to the wall. Descending colon anchors to the wall, rest being inntraperitoneal.

Main Takeaways from Embryology

• Foregut, midgut, hindgut (knowing which organs for each makes life easier).
• Twisting and turning, anchoring down.

Arteries

• Main artery: abdominal aorta (continuation of thoracic aorta).
• Three anterior branches (supply foregut, midgut, hindgut):
  • Celiac trunk (underneath diaphragm, at L1; supplies foregut).
  • Superior mesenteric artery (1 cm lower than celiac trunk, at L1; supplies midgut).
  • Inferior mesenteric artery (at L3; supplies hindgut).
• Lateral and posterior branches of abdominal aorta supply retroperitoneal structures.

Celiac Trunk Location

• Right after it enters the abdomen typically lies right underneath the diaphragm. Typically at vertebral level T12. Will give of the celiac trunk vessel immediately.
  Those three branches are the superior Interior Mesentary Arteries. Those vessels run in the mesentary

Three Branches

• For gut= supplies celiac trunk structures will supply light yellow orange structures, by the suppier mesenteric-> Hindgut, supplied by the Inferiror mesenteric.

Venous Drainage

• Two main systems:
  • Cable system (inferior vena cava, systemic circulation).
  • Portal system (hepatic portal vein, liver).

Inferior Vena Cava

• Major systemic vein, next to abdominal aorta (on the right).
• Drains abdomen, pelvis, perineum, lower limbs.
• Enters abdomen at T8 (I 8 10 eggs at noon).

Hepatic Portal Vein

• Drains spleen, pancreas, gallbladder, and GI tract (except inferior rectum).
• Brings blood to liver for metabolizing and detoxifying.
• Final common pathway for venous blood from those organs.
• Formed by the joining of the superior mesenteric vein and the splenic vein.
  • Thejoining happens behind the pancreas
• Communicates with cable system directly through hepatic veins (liver to inferior vena cava) and through anastomoses:
  Transports all blood through Gi Tract (exceopt the rectum)

Abdominal Communication from Cable and Portal System

• Lower esophagus area with a connection to the cable and other veins in general
• inferior of the rectum area with cable veins and areas with a port and cable vein that join for communication
• Embyrologic Communication
  • Communicatiions from the umbailicus (degenerated)

Lympathic drainage

• Lymph node anterior to the abdominal aorta. These drain into the preoartic Lymph node area. -> Celiac trunk, superior mesenteric lymph, inferior mesenteric nodes. Eventualall drain into the Cisterna Chyli to be the main drainage with all these drains draining back in
  • Lymphatics in relation to arterial supply: If the artery supply is that structure then the area that drains it will also drains to structure