Liver Lobed Septas Relations Clinical aspects Refer- bd chaurasya Diagrams -15 marks

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THE LIVER - Anatomy (15 Marks)

Reference: Gray's Anatomy for Students | Color Atlas of Human Anatomy Vol. 2 (BD Chaurasia equivalent level)

1. INTRODUCTION & POSITION

The liver is the largest visceral organ in the body. It is primarily situated in the right hypochondrium and epigastric region, extending into the left hypochondrium. It lies below the right dome of the diaphragm; its inferior border is nearly flush with the right costal margin, running diagonally to the left through the epigastric region.

Fig. 4.102 - Position of the Liver in the Abdomen:

Position of the liver in the abdomen showing midclavicular planes, subcostal plane, and intertubercular plane

The liver is an intraperitoneal organ. Except for the triangular bare area, it is completely covered by visceral peritoneum, giving it a smooth, glistening appearance.

2. SURFACES

The liver has two main surfaces:

A. Diaphragmatic Surface

Smooth and domed; lies against the inferior surface of the diaphragm
Subphrenic recess: separates the diaphragmatic surface from the diaphragm, divided by the falciform ligament into right and left portions
Hepatorenal recess (Morison's pouch): on the right side, between the liver and the right kidney/suprarenal gland - the most dependent peritoneal recess in the supine patient; fluid collects here first
The anterior surface is divided by the falciform ligament into right lobe and left lobe

B. Visceral Surface

Slightly concave; covered by visceral peritoneum except at the gallbladder fossa and porta hepatis
Subdivided by H-shaped grooves (see lobes below)
The porta hepatis forms the horizontal crossbar of the H and is the gateway to the liver

Fig. 4.105 - Visceral Surface of the Liver (showing all 4 lobes, porta hepatis, ligaments, impressions):

Visceral surface of the liver showing right lobe, left lobe, quadrate lobe, caudate lobe, porta hepatis, fissures, bile duct, portal vein, hepatic artery proper

Fig. 4.106 - Posterior View (Bare Area, Ligaments, and Visceral Impressions):

Posterior view of the liver showing bare area, falciform ligament, triangular ligaments, coronary ligaments, caudate lobe, IVC, impressions (gastric, renal, suprarenal, esophageal, colic), and quadrate lobe with gallbladder

3. LOBES OF THE LIVER

The liver is divided into 4 anatomical lobes. The H-shaped grooves on the visceral surface are the key landmarks:

Lobe	Boundaries	Functional Relationship
Right lobe	Largest lobe; to the right of the falciform ligament (anterior) and fissure for ligamentum teres (visceral)	Right hepatic artery and right portal vein
Left lobe	Smaller; to the left of the falciform ligament	Left hepatic artery and left portal vein
Quadrate lobe	Bounded on the left by the fissure for ligamentum teres and on the right by the gallbladder fossa; anterior part of visceral surface	Functionally related to the left lobe
Caudate lobe	Bounded on the left by the fissure for ligamentum venosum and on the right by the groove for the IVC; posterior visceral surface	Functionally separate from both right and left lobes; has independent portal and hepatic venous drainage

Fissures forming the H-shape:

Left limb of H: Fissure for the round ligament (ligamentum teres, a remnant of the umbilical vein) anteriorly + Fissure for the ligamentum venosum (remnant of ductus venosus / duct of Arantius) posteriorly
Right limb of H: Fossa for the gallbladder anteriorly + Groove for the IVC posteriorly
Horizontal crossbar: Porta hepatis

Diaphragmatic surface - Right and Left Lobes with Falciform Ligament:

Diaphragmatic surface of the liver showing right lobe, left lobe, falciform ligament, diaphragm, and gallbladder

4. PORTA HEPATIS

The porta hepatis (gateway of the liver) is the transverse fissure on the visceral surface where:

Entering: Portal vein (posterior), hepatic artery proper branches (anterior-left), nerves
Leaving: Right and left hepatic ducts, lymphatic vessels

The bile duct, hepatic artery proper, and portal vein travel in the hepatoduodenal ligament (free margin of the lesser omentum) to reach the porta hepatis.

5. ASSOCIATED LIGAMENTS

Ligament	Connection	Notes
Falciform ligament	Liver to anterior abdominal wall	Contains the round ligament of the liver (ligamentum teres); derived from the ventral mesentery
Hepatogastric ligament	Liver to lesser curvature of stomach	Part of lesser omentum
Hepatoduodenal ligament	Liver to duodenum	Contains portal triad: bile duct (right), hepatic artery (left), portal vein (posterior)
Right triangular ligament	Joins coronary ligaments on right
Left triangular ligament	Joins coronary ligaments on left	Terminates in fibrous appendix of liver
Anterior coronary ligament	Anterior boundary of bare area
Posterior coronary ligament	Posterior boundary of bare area

Bare area: Region on the diaphragmatic surface with no intervening peritoneum between liver and diaphragm. Bounded anteriorly by the anterior coronary ligament and posteriorly by the posterior coronary ligament.

6. SEGMENTS (COUINAUD'S SEGMENTAL ANATOMY)

The traditional anatomical lobes differ from functional (surgical) segments. The principal plane (Cantlie's line) divides the liver into right and left halves of approximately equal size - this imaginary line passes from the gallbladder fossa to the IVC and contains the middle hepatic vein.

Couinaud's 8 Segments (numbered clockwise from caudate lobe):

Segment	Name
I	Caudate lobe (posterior)
II	Lateral superior area (left lateral)
III	Left anterior lateral (lateral inferior area)
IV (IVa/IVb)	Medial segment (corresponds to quadrate lobe inferiorly)
V	Anterior medial - inferior area
VI	Right anterior lateral - posterior inferior area
VII	Posterior lateral - posterior superior area
VIII	Posterior medial - anterior superior area

Fig. 4.17 - Couinaud's Segments (anterior and posterior views):

Couinaud's segments of the liver showing all 8 color-coded segments with their names - anterior superior view (top) and visceral/posterior view (bottom) showing caudate lobe (segment I) with its right and left caudate lobes and caudate process

Right hepatectomy = removes segments V, VI, VII, VIII. Left hepatectomy = removes segments II, III, IV.

7. MICROSCOPIC ANATOMY / LOBULES (SEPTA)

The liver is enclosed in the visceral peritoneum and the Glisson's capsule (perivascular fibrous capsule), which sends septa into the liver substance forming a supporting connective tissue framework.

Three Lobule Models:

A. Classical (Hepatic) Lobule:

Functional unit centered on a central vein (terminal hepatic venule)
Polygonal shape; surrounded by connective tissue septa at the corners = portal areas / portal triads
Each portal triad contains:
- Interlobular vein (branch of portal vein)
- Interlobular artery (branch of hepatic artery)
- Interlobular bile duct
- All enclosed in the connective tissue of the Glisson capsule
Hepatocytes radiate from center toward periphery in cell plates separated by sinusoidal capillaries
Blood flows: Portal triad → sinusoids → central vein → hepatic vein → IVC
Space of Disse (perisinusoidal space): Between sinusoid wall and hepatocyte surface; contains microvilli, Ito cells (fat-storing), and filtered plasma
Sinusoidal endothelium is discontinuous (fenestrated, no basement membrane)
Kupffer cells: Hepatic macrophages on the luminal surface of the sinusoidal endothelium

B. Portal Lobule:

Places the portal area at the center; emphasizes bile flow direction
Triangular shape with central veins at the corners
Bile flows from central vein region → interlobular ducts

C. Hepatic Acinus (of Rappaport):

Rhombic shape; best correlates with metabolic zonation
Zone 1 (periportal): closest to blood supply; first affected by toxins, first to regenerate
Zone 2 (midzonal)
Zone 3 (centrilobular / perivenular): most susceptible to ischemia and hypoxic damage

Fig. 4.37 - Liver Lobule Diagrams (Classical, Portal, and Acinus models + electron micrograph):

Liver lobule diagrams showing: A - 3D classical lobule with central vein, sinusoids, portal triads; B - cross-section comparison of classical lobule (blue), portal lobule (green), and acinus (orange); C - hepatocytes and sinusoidal capillaries light micrograph; D - electron micrograph showing Disse space, Kupffer cells, and bile canaliculi

8. RELATIONS

Diaphragmatic Surface Relations:

Above: Diaphragm (separates it from pleura and base of right lung; on the left, separates it from pericardium/heart)
Anterior: Anterior abdominal wall

Visceral Surface Relations (impressions):

Structure	Lobe/Region
Esophagus	Left lobe (esophageal impression)
Anterior surface of stomach	Left lobe (gastric impression)
Superior part of duodenum	Right lobe/quadrate lobe
Lesser omentum	Between left lobe and stomach/duodenum
Gallbladder	Right and quadrate lobes (gallbladder fossa)
Right colic flexure	Right lobe (colic impression)
Right transverse colon	Right lobe
Right kidney	Right lobe (renal impression)
Right suprarenal gland	Right lobe (suprarenal impression)
IVC	Groove on posterior diaphragmatic surface

CT Axial Section - Liver Relations (labeled):

Axial CT with contrast showing liver relations: quadrate lobe, gallbladder, portal vein, IVC, right lobe, right crus, left lobe, neck of pancreas, stomach, aorta, spleen, left kidney, left crus

9. BLOOD SUPPLY, VENOUS DRAINAGE & NERVE SUPPLY

Arterial Supply:

Right hepatic artery and Left hepatic artery - both from the hepatic artery proper (branch of common hepatic artery from the celiac trunk)
The cystic artery to the gallbladder typically arises from the right hepatic artery

Portal Venous Supply:

Portal vein (5-8 cm long): formed behind the head of the pancreas by the union of the superior mesenteric vein and splenic vein
Carries nutrient-rich blood from the GI tract
Divides into right and left branches at the porta hepatis
Tributaries of splenic vein: left gastro-omental, short gastric, inferior mesenteric vein
Tributaries of superior mesenteric vein: jejunal/ileal veins, right gastro-omental, ileocolic, right colic

Fig. 4.107 - Arterial Supply to the Liver and Gallbladder:

Hepatic arterial supply showing hepatic artery proper, right and left hepatic arteries, cystic artery, left gastric artery, gastroduodenal artery, right gastric artery, splenic artery, superior mesenteric artery, abdominal aorta; with laparoscopic intraoperative view on right

Venous Drainage:

Several short hepatic veins drain into the IVC
Three main hepatic veins (right, middle, left)

Nerve Supply:

Hepatic plexus - autonomic nerves; a continuation of the celiac plexus

Lymphatics:

Drain to hepatic nodes along the porta hepatis → superior diaphragmatic nodes → parasternal nodes

10. CLINICAL ASPECTS

A. Portal Hypertension

When portal vein flow through the liver to the heart is impeded (most commonly by cirrhosis), blood pressure in the portal vein rises - portal hypertension. Portal-caval anastomoses open up at sites where portal and systemic venous systems communicate:

Site	Portal	Systemic	Clinical result
Lower esophagus	Left gastric vein	Esophageal veins (azygos)	Esophageal varices - most dangerous; 60% mortality per bleed
Umbilicus	Paraumbilical veins	Superficial epigastric veins	Caput medusae
Lower rectum/anal canal	Superior rectal vein	Middle/inferior rectal veins	Rectal varices
Retroperitoneum (Retzius veins)	Colic/intestinal veins	Lumbar/renal veins	Internal varices

B. Hepatorenal Recess (Morison's Pouch) - Clinical Significance

This is the most dependent part of the peritoneal cavity in the supine patient. In haemoperitoneum or peritonitis, fluid collects here first - critical for FAST (Focused Assessment with Sonography in Trauma) examination.

C. Liver Biopsy

Percutaneous (standard): Patient lies over the biopsy site; weight of liver compresses the puncture to stem bleeding
Contraindicated when ascites is present (liver floats away from abdominal wall; bleeding pours freely into ascitic fluid)
Transjugular liver biopsy: Access through right internal jugular vein → right brachiocephalic vein → SVC → IVC → right hepatic vein; biopsy taken through the hepatic vein wall - bleeding re-enters the circulation directly, avoiding haemoperitoneum risk

D. Liver Resection (Hepatectomy) for Metastases

Couinaud's segmental anatomy is essential for surgical planning
The principal plane (through middle hepatic vein, gallbladder fossa to IVC) divides liver into equal right and left halves for resection
Right hepatectomy: removes segments V, VI, VII, VIII
Segments V and VI are commonly involved in right lobe metastases
Left lobe contains only segments II and III anatomically; the lobes do NOT correlate with hepatic volume

E. Subphrenic Abscess

Pus collects in subphrenic and hepatorenal recesses following peritonitis or abdominal surgery
Right subphrenic abscess (between liver and diaphragm) is more common given the position of the hepatorenal recess
Presents with fever, right shoulder pain (referred via phrenic nerve, C3-C5)

F. Bare Area and Retroperitoneal Spread

The bare area of the liver is in direct contact with the diaphragm
Infections (e.g., amoebic liver abscess) can spread through the bare area into the right pleural cavity or pericardium

G. Jaundice and Biliary Obstruction

Obstruction of the bile duct (by gallstones, pancreatic head carcinoma) causes obstructive (post-hepatic) jaundice with pale stools, dark urine, and pruritus
The bile duct lies in the free margin of the hepatoduodenal ligament: bile duct (right) + hepatic artery (left) + portal vein (posterior)

Sources: Gray's Anatomy for Students, pp. 391-402; Color Atlas of Human Anatomy Vol. 2: Internal Organs, pp. 355-366

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