83-93 Abdomen

Abdomen. Antero-Lateral Abdominal Wall. Regions. Layered Topography – Fasciae, Muscles.

🗺 Abdominal Regions (based on surface anatomy)

• Divided by two vertical and two horizontal planes:

  • Vertical: Midclavicular lines (right and left)

  • Horizontal: Subcostal plane (L2) and transtubercular plane (L5)

• Nine regions:

  1. Right hypochondriac

  2. Epigastric

  3. Left hypochondriac

  4. Right lumbar (flank)

  5. Umbilical

  6. Left lumbar (flank)

  7. Right iliac (inguinal)

  8. Hypogastric (pubic)

  9. Left iliac (inguinal)

🧱 Layered Topography of the Antero-Lateral Abdominal Wall

1. Skin

2. Superficial Fascia (subcutaneous tissue)

• Above umbilicus: single layer

• Below umbilicus: two layers

  • Camper’s fascia: superficial, fatty layer

  • Scarpa’s fascia: deep, membranous layer (important surgically)

3. Muscular Layer

• Three flat muscles (lateral abdominal wall):

  • External oblique - Fibers run inferomedially ("hands in pockets")

  • Internal oblique - Fibers run superomedially (perpendicular to external oblique)

  • Transversus abdominis - Fibers run horizontally

• One vertical muscle (anterior abdominal wall):

  • Rectus abdominis

    • Lies in the rectus sheath, has tendinous intersections

    • Bordered by linea alba (midline) and linea semilunaris (lateral margin)

• Pyramidalis muscle (small, triangular; present in some individuals anterior to rectus abdominis)

4. Rectus Sheath

• Formed by the aponeuroses of the three flat muscles

• Encloses the rectus abdominis and pyramidalis

• Sheath composition differs above and below the arcuate line

5. Transversalis Fascia

• Thin, deep fascia lining the internal surface of the abdominal wall

6. Extraperitoneal Fat

• Variable in thickness; separates fascia from parietal peritoneum

7. Parietal Peritoneum

• Serous membrane lining the abdominal cavity

⚙ Function

• Protects abdominal viscera

• Assists in forced expiration, coughing, urination, defecation, childbirth

• Helps maintain posture and increase intra-abdominal pressure

⚠ Clinical Relevance

• Hernias (inguinal, umbilical) occur through weak points in the abdominal wall

• Surgical incisions must respect muscle/fascial layers and neurovascular planes

• Knowledge of fascia (Scarpa’s) important in drainage and suturing

Inguinal Canal.

Inguinal Canal

📍 Location & Structure

• Oblique passage (~4 cm long) in the lower anterior abdominal wall

• Runs above the medial half of the inguinal ligament, from deep inguinal ring (lateral) to superficial inguinal ring (medial)

🧠 Walls of the Inguinal Canal

• Anterior wall: aponeurosis of external oblique, reinforced laterally by internal oblique

• Posterior wall: transversalis fascia, reinforced medially by conjoint tendon

• Roof: arching fibers of internal oblique and transversus abdominis

• Floor: inguinal ligament and lacunar ligament

📦 Contents

• In males: Spermatic cord (ductus deferens, testicular artery, pampiniform plexus, etc.)

• In females: Round ligament of the uterus

• In both: Ilioinguinal nerve

⚠ Clinical Relevance

• Common site for inguinal hernias (direct and indirect)

• Deep inguinal ring = potential weak point in abdominal wall

Rectus Abdominis Sheath

📍 Definition

• Fibrous sheath enclosing the rectus abdominis and pyramidalis muscles

• Formed by aponeuroses of external oblique, internal oblique, and transversus abdominis

🧱 Structure

• Above arcuate line (≈1/3 of the way from umbilicus to pubic symphysis):

  • Anterior layer: external oblique + ½ internal oblique aponeurosis

  • Posterior layer: ½ internal oblique + transversus abdominis aponeurosis

• Below arcuate line:

  • All three aponeuroses pass anterior to rectus abdominis

  • Posterior wall absent → only transversalis fascia and peritoneum behind muscle

⚠ Clinical Relevance

• Important in abdominal incisions (e.g., C-section, hernia repair)

• Weak area below arcuate line more prone to herniation

Linea Alba.

📍 Definition

• Midline fibrous raphe formed by the interlacing aponeuroses of the abdominal wall muscles

• Extends from xiphoid process to pubic symphysis

🧱 Structure

• Lies between the two rectus abdominis muscles

• Relatively avascular (useful for midline surgical incisions)

⚙ Function

• Provides attachment and reinforcement for abdominal wall muscles

• Maintains structural integrity of anterior abdominal wall

⚠ Clinical Relevance

• Diastasis recti: separation of rectus muscles along linea alba (common post-pregnancy)

• Midline incisions preferred here to reduce bleeding and nerve damage

Abdominal Cavity. Walls, Regions.

🧱 Walls of the Abdominal Cavity

• Anterior wall: Formed by abdominal muscles — rectus abdominis, external and internal obliques, transversus abdominis

• Posterior wall: Lumbar vertebrae, psoas major, iliacus, quadratus lumborum, and transversus abdominis

• Lateral walls: Continuation of anterior and posterior muscles

• Superior boundary: Inferior surface of the diaphragm

• Inferior boundary: Continuous with the pelvic cavity (no physical separation)

🗺 Regions of the Abdomen

Divided into 9 regions using:

• 2 vertical planes: midclavicular lines

• 2 horizontal planes: subcostal (L2) and transtubercular (L5)

Regions:

1. Right hypochondriac

2. Epigastric

3. Left hypochondriac

4. Right lumbar

5. Umbilical

6. Left lumbar

7. Right iliac (inguinal)

8. Hypogastric (pubic)

9. Left iliac (inguinal)

Peritoneum - Structure, Blood and Nerve Supply.

Peritoneum

🧬 Structure

• Serous membrane lining the abdominal cavity

• Two continuous layers:

  • Parietal peritoneum – lines internal surface of abdominal wall

  • Visceral peritoneum – covers abdominal organs

• Peritoneal cavity: Thin potential space between the two layers containing peritoneal fluid

💉 Blood Supply

• Parietal peritoneum: Supplied by vessels of the abdominal wall (e.g., intercostal, lumbar arteries)

• Visceral peritoneum: Supplied by the same blood vessels that supply the organ it covers (e.g., celiac trunk, SMA, IMA)

🧠 Nerve Supply

• Parietal peritoneum:

  • Somatic innervation → sharp, localized pain

  • Supplied by intercostal nerves, lumbar plexus

• Visceral peritoneum:

  • Autonomic innervation → dull, poorly localized pain

  • From sympathetic and parasympathetic fibers (depending on organ)

Peritoneal Compartment of the Abdominal Cavity.

Peritoneal Compartments of the Abdominal Cavity

1. Intraperitoneal Space

• Organs suspended by mesenteries, completely surrounded by visceral peritoneum

• Examples: stomach, liver, jejunum, ileum, transverse colon, sigmoid colon

2. Retroperitoneal Space

• Organs lie behind the peritoneum, only anterior surface covered by it

• Examples: kidneys, pancreas (except tail), duodenum (parts 2–4), ascending/descending colon, abdominal aorta

3. Subperitoneal (Infraperitoneal) Space

• Organs located beneath the peritoneum, mostly in the pelvis

• Examples: urinary bladder, rectum, reproductive organs

🧠 Additional Compartments & Recesses

• Greater sac: Main peritoneal cavity

• Lesser sac (omental bursa): Posterior to stomach and lesser omentum

• Omental foramen (of Winslow): Connects greater and lesser sacs

• Subphrenic and subhepatic spaces: Important for fluid accumulation

• Paracolic gutters: Pathways for fluid spread along colon sides

⚠ Clinical Relevance

• Ascites: fluid accumulation in the peritoneal cavity

• Peritonitis: inflammation due to infection or perforation

• Intraperitoneal injections use the peritoneal cavity for drug absorption

• Surgical anatomy (e.g., laparotomy or laparoscopy) relies on peritoneal reflections and compartments

Upper Region of the Peritoneal Cavity. Organs, Peritoneal Structures

📍 Boundaries

• Located above the transverse colon and mesocolon

• Lies primarily in the epigastric and hypochondriac regions

• Includes the supracolic compartment of the peritoneal cavity

🧠 Main Organs in the Upper Peritoneal Cavity

• Liver

• Gallbladder

• Stomach

• Spleen

• Superior part of the duodenum

• Pancreas (only tail is intraperitoneal)

• Esophagus (abdominal part)

🧬 Peritoneal Structures - Ligaments and Omenta

• Lesser omentum: from liver to lesser curvature of stomach and duodenum

  • Contains: hepatic artery proper, portal vein, common bile duct

• Greater omentum: hangs from greater curvature of stomach over intestines

• Falciform ligament: connects liver to anterior abdominal wall

• Coronary and triangular ligaments: suspend liver from diaphragm

• Gastrosplenic ligament: connects stomach to spleen (contains short gastric vessels)

• Splenorenal ligament: spleen to left kidney (contains splenic vessels, tail of pancreas)

🔄 Peritoneal Recesses/Spaces

• Lesser sac (omental bursa): posterior to stomach and lesser omentum

• Greater sac: main part of peritoneal cavity

• Subphrenic spaces: between diaphragm and liver

• Subhepatic space (Morrison’s pouch): between liver and right kidney — site of fluid accumulation

Upper Region of the Peritoneal Cavity. Topographic Relations of the Organs, Vessels and Nerves

🔍 Topographic Relations of Organs

🏷 1. Liver

• Right hypochondrium, extending to epigastric region

• Anterior: diaphragm and anterior abdominal wall

• Posterior: inferior vena cava, esophagus, stomach, right kidney, and adrenal gland

• Related vessels: portal triad in hepatoduodenal ligament

• Innervation: celiac plexus, vagus nerves

🏷 2. Stomach

• Left hypochondrium and epigastric region

• Anterior: anterior abdominal wall, left lobe of liver, diaphragm

• Posterior (stomach bed): pancreas, spleen, left kidney, adrenal gland, transverse mesocolon

• Supplied by: left gastric, right gastric, right and left gastroepiploic arteries

• Innervation: vagus nerves, celiac plexus

🏷 3. Spleen

• Left hypochondrium, intraperitoneal

• Anterior: stomach

• Posterior: diaphragm, ribs 9–11

• Inferior: left colic flexure

• Vessels: splenic artery and vein (within splenorenal ligament)

• Innervation: celiac plexus

🏷 4. Gallbladder

• Lies on inferior surface of liver, in right hypochondrium

• Contacts anterior abdominal wall at tip of 9th costal cartilage (Murphy’s point)

• Drains into common bile duct

• Innervation: celiac plexus, right phrenic nerve (referred pain to shoulder)

🏷 5. Duodenum (superior part)

• First 2 cm is intraperitoneal, then retroperitoneal

• Located in epigastric region, just right of midline

• Close relations to liver, gallbladder, and pancreas

🏷 6. Pancreas (mostly retroperitoneal)

• Lies posterior to stomach, across epigastric region

• Tail enters splenorenal ligament (intraperitoneal)

• Related to splenic artery, superior mesenteric vessels, and portal vein

• Innervation: celiac and superior mesenteric plexuses

Omental Bursa.

🟨 Omental Bursa (Lesser Sac)

📍 Definition

• A peritoneal recess located posterior to the stomach and lesser omentum

• Part of the supracolic compartment of the peritoneal cavity

🧱 Boundaries

• Anterior:

  • Lesser omentum (hepatogastric ligament)

  • Posterior wall of stomach

  • Gastrocolic ligament (part of greater omentum)

• Posterior:

  • Pancreas

  • Left kidney and suprarenal gland

  • Peritoneum covering posterior abdominal wall

• Superior:

  • Caudate lobe of the liver

• Inferior:

  • Fused layers of greater omentum

• Left:

  • Gastrosplenic and splenorenal ligaments

• Right (entry point): Omental (epiploic) foramen of Winslow

  • Connects lesser sac to greater sac

  • Bounded by:

    • Anterior: hepatoduodenal ligament (with portal triad)

    • Posterior: inferior vena cava

    • Superior: caudate lobe of liver

    • Inferior: first part of duodenum

⚙ Function

• Allows free movement of stomach and pancreatic expansion

• Provides a space for surgical access to posterior stomach and pancreas

Greater Omentum – Formation, Parts.

🟧 Greater Omentum

📍 Definition

• A large peritoneal fold hanging like an apron from the greater curvature of the stomach

• Drape-like structure covering the anterior surface of the intestines

🏗 Formation

• Develops from the dorsal mesogastrium during embryogenesis

• Folds over itself to form four layers of peritoneum:

  • 2 layers descend from the stomach

  • Fold back and ascend to fuse with the transverse colon and its mesocolon

📦 Parts of the Greater Omentum

1. Gastrocolic ligament:

   • Largest part

   • Connects stomach to transverse colon

   • Covers intestines like an apron

2. Gastrosplenic ligament:

   • Connects stomach to spleen

   • Contains short gastric vessels

3. Gastrophrenic ligament:

   • Connects stomach to diaphragm

⚙ Functions

• Fat storage

• Immune defense – contains lymphoid aggregates (milky spots)

• Limits spread of infection (“policeman of the abdomen”)

• Mobility allows sealing of inflamed areas (e.g., in appendicitis)

⚠ Clinical Relevance

• Site of fluid accumulation in peritonitis

• Used in omentum flaps for surgical reconstruction

• May adhere to inflamed organs and isolate infections

Portal Vein. Formation, Position. Anastomoses with the Superior and Inferior Venae Cavae.

Portal Vein (Vena Portae Hepatis)

📍 Formation

• Formed by the union of the:

  • Superior mesenteric vein (SMV)

  • Splenic vein

• This union typically occurs behind the neck of the pancreas at the level of L2 vertebra

📍 Position

• Ascends posterior to the pancreas and duodenum, then runs within the hepatoduodenal ligament (part of lesser omentum)

• Lies posterior to the common bile duct and proper hepatic artery (in the portal triad)

• Enters the liver at the porta hepatis, dividing into right and left branches to supply respective lobes

• Not a true vein: does not drain into the heart directly; instead, it brings nutrient-rich blood from the gastrointestinal tract to the liver for processing

🧠 Function

• Carries 75% of liver's blood supply

• Transports nutrients, toxins, and metabolites from:

  • GI tract (stomach, intestines)

  • Pancreas

  • Spleen

  • Gallbladder

🔄 Porto-Caval Anastomoses

(Anastomoses between the portal and systemic (caval) venous systems)

🩸 Sites of Anastomoses

1. Esophageal veins

   • Portal: left gastric vein

   • Caval: esophageal veins → azygos → SVC

   • Clinical relevance: esophageal varices in portal hypertension

2. Rectal veins

   • Portal: superior rectal vein

   • Caval: middle and inferior rectal veins → internal iliac → IVC

   • Clinical relevance: internal hemorrhoids

3. Paraumbilical veins

   • Portal: paraumbilical veins (from left branch of portal vein)

   • Caval: superficial epigastric veins → femoral vein → IVC

   • Clinical relevance: caput medusae (dilated periumbilical veins)

4. Retroperitoneal veins

   • Portal: veins of colon, duodenum, pancreas

   • Caval: lumbar and renal veins → IVC

   • Clinical relevance: hidden site of bleeding in portal hypertension

⚠ Clinical Relevance

• Portal hypertension (e.g., in liver cirrhosis) → blood diverted through anastomoses → varices and bleeding

• Transjugular intrahepatic portosystemic shunt (TIPS): procedure to reduce portal pressure by connecting portal vein to hepatic vein

Lower Region of the Peritoneal Cavity. Organs. Peritoneal Structures,

Lower Region of the Peritoneal Cavity (Also called the infracolic compartment)

📍 Boundaries

• Located below the transverse colon and transverse mesocolon

• Divided by the mesentery of the small intestine into:

  • Right infracolic space

  • Left infracolic space

🧠 Organs in the Lower Peritoneal Cavity

• Jejunum and ileum (intraperitoneal)

• Ascending colon and descending colon (secondarily retroperitoneal)

• Sigmoid colon (intraperitoneal)

• Cecum and appendix (intraperitoneal)

• Upper part of rectum (partially peritonealized)

🧬 Peritoneal Structures

• Mesentery of the small intestine

  • Suspends jejunum and ileum

  • Contains superior mesenteric vessels, lymph nodes, fat, and nerves

• Transverse mesocolon

  • Suspends the transverse colon

  • Separates supracolic and infracolic compartments

• Sigmoid mesocolon

  • Suspends sigmoid colon

  • Contains inferior mesenteric vessels

• Paracolic gutters (right and left)

  • Allow communication between upper and lower peritoneal cavity

  • Important in spread of infection or fluid (e.g. in peritonitis)

⚠ Clinical Relevance

• Peritoneal recesses and gutters direct spread of fluid, infection, or metastasis

• Knowledge of mesenteric root and paracolic gutters is critical in surgery and imaging

• Important in procedures like peritoneal dialysis and laparoscopy

Lower Region of the Peritoneal Cavity. Topographic Relations of the Organs, Vessels and Nerves.

🔍 Topographic Relations

🏷 Small Intestine (Jejunum and Ileum)

• Occupy umbilical, lumbar, and hypogastric regions

• Jejunum: mostly upper left abdomen

• Ileum: mostly lower right abdomen and pelvis

• Suspended by mesentery from posterior abdominal wall, root runs obliquely from L2 to right sacroiliac joint

🏷 Cecum and Appendix

• Cecum: right iliac fossa, intraperitoneal

• Appendix: variable position (most commonly retrocecal)

• Supplied by ileocolic artery (branch of SMA)

• Innervation: sympathetic (T10-T12) and vagal parasympathetic

• Pain from appendicitis often starts periumbilically (T10), then localizes to McBurney's point

🏷 Ascending and Descending Colon

• Retroperitoneal

• Ascending: right lumbar region

• Descending: left lumbar region

• Blood supply:

  • Ascending colon: right colic artery (SMA)

  • Descending colon: left colic artery (IMA)

🏷 Sigmoid Colon

• Intraperitoneal, located in left iliac and hypogastric regions

• Suspended by sigmoid mesocolon

• Blood supply: sigmoid arteries from inferior mesenteric artery

🏷 Rectum (Upper Part)

• Lies partly within peritoneum (upper third only)

• Peritoneum covers anterior and lateral surfaces in upper part

• Supplied by:

  • Superior rectal artery (from IMA)

  • Venous drainage includes portal-systemic anastomosis

🔌 Vessels and Nerves

🩸 Arterial Supply

• Superior mesenteric artery (SMA): small intestine, cecum, ascending and proximal 2/3 of transverse colon

• Inferior mesenteric artery (IMA): distal 1/3 of transverse colon, descending colon, sigmoid colon, rectum

🔄 Venous Drainage

• Follows arteries → drains into portal vein via:

  • Superior mesenteric vein

  • Inferior mesenteric vein (may join splenic vein)

🧠 Innervation

• Sympathetic: from thoracic and lumbar splanchnic nerves via superior and inferior mesenteric plexuses

• Parasympathetic:

  • Vagus nerve: up to mid-transverse colon

  • Pelvic splanchnic nerves (S2–S4): for distal colon and rectum

The Unpaired Visceral Branches of the Abdominal Aorta - the Coeliac Trunk, the Superior and Inferior Mesenteric Arteries. Position and Branches.

🔴 Unpaired Visceral Branches of the Abdominal Aorta

These arteries supply the abdominal gastrointestinal tract and associated organs, and arise anteriorly from the aorta.

Celiac Trunk (Coeliac Artery)

📍 Position

• Arises at the level of T12, just below the aortic hiatus of the diaphragm

• Very short (~1–2 cm), trifurcates immediately

🌿 Branches

1. Left gastric artery

   • Smallest branch

   • Ascends to esophagus → follows lesser curvature of the stomach

2. Splenic artery

   • Tortuous; runs along superior border of the pancreas to spleen

   • Gives off:

     • Short gastric arteries (to fundus of stomach)

     • Left gastroepiploic artery (to greater curvature)

3. Common hepatic artery

   • Courses to the right toward liver

   • Divides into:

     • Proper hepatic artery → right and left hepatic arteries

     • Gastroduodenal artery → right gastroepiploic artery + superior pancreaticoduodenal artery

     • Right gastric artery

🧠 Supplies

• Liver, stomach, spleen, pancreas, esophagus, duodenum (proximal to major papilla)

Superior Mesenteric Artery (SMA)

📍 Position

• Arises at L1, ~1 cm below celiac trunk

• Passes behind pancreas and over the third part of the duodenum

• Enters mesentery of the small intestine

🌿 Branches

1. Inferior pancreaticoduodenal artery Anastomoses with superior pancreaticoduodenal (from celiac trunk)

2. Jejunal and ileal branches - 12–15 branches to small intestine; form arterial arcades and vasa recta

3. Ileocolic artery Supplies ileum, cecum, appendix

4. Right colic artery Supplies ascending colon

5. Middle colic artery Supplies transverse colon

🧠 Supplies

• Lower duodenum, jejunum, ileum, cecum, appendix, ascending colon, proximal 2/3 of transverse colon

Inferior Mesenteric Artery (IMA)

📍 Position

• Arises at L3, just above aortic bifurcation

• Descends to the left toward pelvic brim

🌿 Branches

1. Left colic artery Supplies descending colon

2. Sigmoid arteries - 2–4 branches to sigmoid colon

3. Superior rectal artery - Continuation of IMA; supplies upper part of rectum

🧠 Supplies

• Distal 1/3 of transverse colon, descending colon, sigmoid colon, and upper rectum

🩸 Clinical Note: Marginal Artery (of Drummond)

• Formed by anastomoses between branches of SMA and IMA (e.g., middle and left colic arteries)

• Provides collateral blood flow to colon

The Hepatic Portal System - Constituting Veins. Position of the Portal Vein. Anastomoses Between the Portal and Systematic Circulation

🟣 Hepatic Portal System

📍 Function

• Collects nutrient-rich, oxygen-poor blood from the digestive tract and associated organs

• Delivers it to the liver for metabolism, detoxification, and storage

• Does not drain directly into the heart — returns blood to the heart via hepatic veins → IVC

🧱 Constituting Veins of the Portal System

The portal vein is formed by the union of:

• Superior mesenteric vein (SMV)

• Splenic vein

The splenic vein often also receives:

• Inferior mesenteric vein (IMV) - May join splenic vein or drain directly into SMV

Additional tributaries of the portal vein:

• Left and right gastric veins (stomach)

• Cystic vein (gallbladder)

• Paraumbilical veins (from anterior abdominal wall)

🔵 Portal Vein – Position

• Begins posterior to the neck of the pancreas (L2 level), where SMV and splenic vein join

• Ascends posterior to the first part of the duodenum

• Enters the hepatoduodenal ligament (with common bile duct and hepatic artery proper)

• At the porta hepatis, it divides into right and left portal branches to supply liver lobes

🔄 Porto-Systemic (Porto-Caval) Anastomoses

Sites where portal circulation communicates with systemic venous circulation
→ Important in portal hypertension (e.g., cirrhosis), where blood is redirected through these alternate routes

1. Esophageal Anastomosis

• Portal: left gastric vein

• Systemic: esophageal veins → azygos → SVC

• ⚠ Esophageal varices — can rupture and cause fatal bleeding

2. Rectal Anastomosis

• Portal: superior rectal vein

• Systemic: middle and inferior rectal veins → internal iliac → IVC

• ⚠ Internal hemorrhoids

3. Paraumbilical Anastomosis

• Portal: paraumbilical veins (from left portal vein)

• Systemic: superficial epigastric veins → femoral vein → IVC

• ⚠ Caput medusae — dilated periumbilical veins

4. Retroperitoneal Anastomosis

• Portal: veins of colon, duodenum, pancreas

• Systemic: lumbar and renal veins

• ⚠ Usually clinically silent, but can contribute to hidden hemorrhage

⚠ Clinical Relevance

• Portal hypertension → blood backs up into systemic channels → varices, ascites, splenomegaly

• TIPS procedure: shunt created between portal and hepatic veins to reduce portal pressure

• Hepatic encephalopathy may result from toxins bypassing liver via anastomoses

The Abdominal Aorta. Parietal (Lateral) and Paired Visceral Branches.

🔴 Abdominal Aorta

• Continuation of the thoracic aorta beginning at the aortic hiatus of the diaphragm (T12)

• Descends anterior to the vertebral column

• Ends at the level of L4, where it bifurcates into the right and left common iliac arteries

🧱 Paired Visceral Branches

(Supply internal organs)

1. Middle Suprarenal Arteries

• Arise at level L1

• Supply adrenal (suprarenal) glands

2. Renal Arteries

• Arise at level L1–L2 (just below SMA)

• Pass laterally to each kidney

• Right renal artery is longer and passes behind the inferior vena cava (IVC)

3. Gonadal Arteries

• Testicular arteries (males) / Ovarian arteries (females)

• Arise at level L2, below renal arteries

• Descend along psoas major muscle into pelvis

• Testicular arteries enter inguinal canal, ovarian arteries go to ovary and uterine tube

🧱 Parietal (Lateral & Posterior) Branches

(Supply body wall, muscles, vertebrae)

1. Inferior Phrenic Arteries

• First paired branches, arise just below diaphragm at T12

• Supply the diaphragm and give superior suprarenal branches to adrenal glands

2. Lumbar Arteries (usually 4 pairs)

• Arise from posterolateral surface of aorta at L1–L4

• Supply posterior abdominal wall muscles, skin, vertebrae, and spinal cord

3. Median Sacral Artery (unpaired but related)

• Small artery arising near aortic bifurcation (L4)

• Descends in midline over sacrum

• Supplies sacrum, coccyx, and lower vertebral column

⚠ Clinical Note

• Abdominal aortic aneurysm (AAA) often occurs below renal arteries

• Renal artery stenosis may lead to secondary hypertension

• Paired arteries must be carefully identified in abdominal surgery (e.g. nephrectomy)

The Superior and Inferior Vena Cava. Position. Main Tributaries. Anastomoses Between the Two Caval Veins.

🟦 Superior Vena Cava (SVC)

📍 Position

• Formed by the union of the right and left brachiocephalic veins (at the level of the first costal cartilage, behind the right sternoclavicular joint)

• Descends vertically in the superior mediastinum, right to the ascending aorta and trachea

• Opens into the right atrium of the heart at the level of the third costal cartilage

🔄 Main Tributaries

• Brachiocephalic veins (right and left) — formed by subclavian and internal jugular veins

• Azygos vein (drains thoracic wall and mediastinal structures)

• Internal thoracic veins

• Thoracoepigastric vein (important in collateral circulation)

🟩 Inferior Vena Cava (IVC)

📍 Position

• Formed by the union of the right and left common iliac veins at the level of L5 vertebra

• Ascends on the right side of the vertebral column, posterior to the liver and diaphragm

• Passes through the caval opening of the diaphragm at T8 level

• Empties into the right atrium

🔄 Main Tributaries

• Common iliac veins

• Lumbar veins

• Renal veins (right and left)

• Hepatic veins

• Gonadal veins (right drains directly, left drains into left renal vein)

• Inferior phrenic veins

🔄 Anastomoses Between SVC and IVC

Collateral Pathways for venous return if either vena cava is obstructed:

1. Azygos–hemiazygos system - Connects IVC tributaries (lumbar veins) with SVC tributaries (azygos vein)

2. Thoracoepigastric vein - Connects superficial epigastric vein (tributary of femoral vein/IVC system) to lateral thoracic vein (tributary of axillary vein/SVC system)

3. Vertebral venous plexuses - Provide communication along the vertebral column between SVC and IVC systems

4. Internal thoracic and inferior epigastric veins

⚠ Clinical Relevance

• Obstruction of IVC or SVC leads to development of collateral venous pathways to maintain venous return

• These anastomoses become dilated and visible in cases of SVC syndrome or IVC obstruction