Q1 (Long Answer): The Liver — 15 Marks

1. Anatomical Position

2. External Features (Surfaces and Lobes)

Surfaces

• Smooth, convex, dome-shaped
• Faces anteriorly, superiorly, and posteriorly
• Related to the inferior surface of the diaphragm
• The falciform ligament divides the subphrenic recess into right and left areas on this surface
• Contains the bare area (not covered by peritoneum) posteriorly, where the liver directly contacts the diaphragm

• Faces inferiorly and posteriorly
• Covered with visceral peritoneum except at the gallbladder fossa and porta hepatis
• Bears impressions from related organs (see Relations)

Lobes

1. Right lobe — the largest
2. Left lobe — smaller, extends into the epigastrium
3. Caudate lobe — on the posterior visceral surface, between the IVC and ligamentum venosum
4. Quadrate lobe — on the inferior visceral surface, between the gallbladder fossa and ligamentum teres

• Left sagittal fissure: contains the ligamentum teres (anteriorly) and ligamentum venosum (posteriorly)
• Right sagittal fissure: contains the gallbladder fossa (anteriorly) and groove for IVC (posteriorly)
• Transverse fissure = porta hepatis

Ligaments

• Falciform ligament — connects liver to anterior abdominal wall; contains ligamentum teres in its free border
• Coronary ligaments (anterior and posterior) — attach liver to diaphragm
• Triangular ligaments (right and left) — where anterior and posterior coronary ligaments meet laterally
• Lesser omentum — connects porta hepatis to lesser curvature of stomach

3. Internal Features (Structure)

• The liver is divided into 8 functional segments (Couinaud's segments), based on distribution of portal vein, hepatic artery, and bile ducts
• Segment I = Caudate lobe; segments II–VIII numbered clockwise
• The principal plane (along the middle hepatic vein, from gallbladder fossa to IVC) divides the liver into roughly equal right and left halves
• The functional unit is the hepatic lobule: hexagonal, with a central vein and portal triads at the corners
• Each portal triad contains: portal vein branch, hepatic artery branch, bile ductule
• Hepatic sinusoids connect portal tracts to the central (terminal hepatic) vein
• Hepatic cells (hepatocytes) are arranged in plates (laminae) between sinusoids

4. Relations

Diaphragmatic surface relations:

• Anteriorly: diaphragm, right costal cartilages 7–11, xiphoid process, anterior abdominal wall (left lobe)
• Superiorly: diaphragm separates liver from right pleura, right lung, pericardium, and heart
• Posteriorly: diaphragm, right kidney and suprarenal gland (via hepatorenal recess), esophagus (left lobe), aorta, IVC

Visceral surface impressions (structures related to inferior surface):

• Right lobe: right kidney (renal impression), right colic flexure (colic impression), duodenum (duodenal impression), right suprarenal gland (suprarenal impression)
• Left lobe: stomach (gastric impression), esophagus
• Quadrate lobe: superior part of duodenum, pylorus, transverse colon
• Caudate lobe: abdominal aorta, IVC

Porta hepatis (transverse fissure) — structures entering/leaving:

• Entering: portal vein (posterior), hepatic artery proper (left), common hepatic duct (right/anterior)
• Leaving: lymphatic vessels
• The hepatoduodenal ligament (free edge of lesser omentum) encloses these structures

5. Vascular Supply

Arterial supply:

• Hepatic artery proper — branch of the common hepatic artery → from the celiac trunk (T12)
• Divides into right and left hepatic arteries at the porta hepatis
• Supplies ~25% of the liver's blood (but 50% of oxygen due to high O₂ content)

Venous supply (dual blood supply):

• Portal vein — formed by the union of the superior mesenteric vein and splenic vein behind the neck of the pancreas (at L1–L2)
• Supplies 75% of total hepatic blood flow (nutrient-rich, but less oxygenated)
• Drains into hepatic sinusoids

Venous drainage:

• Hepatic veins (right, middle, and left) drain the liver
• Empty into the inferior vena cava just below the diaphragm (T8)

6. Nerve Supply

• Sympathetic fibers: from T7–T10 via splanchnic nerves → celiac ganglion → hepatic plexus (vasoconstrictor effect)
• Parasympathetic fibers: from the vagus nerve [X] (both anterior and posterior vagal trunks) — involved in metabolic regulation
• Sensory (pain) fibers: travel via the right phrenic nerve (C3, C4, C5) — hence liver/diaphragm pain is referred to the right shoulder tip

7. Applied Anatomy

1. Hepatomegaly: Liver enlargement is palpated below the right costal margin. Causes include heart failure, cirrhosis, hepatitis, malignancy.
2. Liver biopsy: Performed percutaneously in the right 8th or 9th intercostal space in the mid-axillary line (during expiration to avoid pneumothorax). Guided by ultrasound.
3. Liver trauma: Most commonly injured abdominal organ. The right lobe is most vulnerable. Blunt trauma can cause hepatic lacerations → hemoperitoneum.
4. Couinaud's segmental anatomy: Essential for hepatic surgery. A right hepatectomy removes segments V, VI, VII, VIII; leaving I–IV.
5. Obstructive jaundice: Obstruction of the bile duct system (gallstones, carcinoma of head of pancreas) causes post-hepatic jaundice; the liver appears enlarged.
6. Portal hypertension: Leads to splenomegaly, ascites, and development of portosystemic collaterals (varices).
7. Riedel's lobe: A tongue-like projection of the right lobe — a normal variant that can be mistaken for a tumor or enlarged gallbladder.

8. Sites of PortoCaval (Portosystemic) Anastomosis

Clinical Significance:

• Esophageal varices (site 1) are the most dangerous — rupture causes massive upper GI bleeding requiring urgent intervention (banding, sclerotherapy, TIPSS)
• Caput medusae (site 3) is a clinical sign of portal hypertension
• Varices at the anorectal junction must be distinguished from true hemorrhoids (which are submucosal arteriovenous plexuses)