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The posterior vagus nerve gives rise to the criminal nerve of Grassi.

This nerve supplies the cardia and fundus of the stomach. It is called a criminal nerve because it is often missed during a vagotomy procedure and can result in recurrent peptic ulcer disease.

Nerve supply of the stomach:

The sympathetic supply arises from T5-T12 spinal segments and is distributed to the stomach via the greater and lesser splanchnic nerves and the celiac plexus. They perform the following functions:

• Vasoconstriction
• Constriction of the pyloric sphincter and inhibition of gastric motility
• Carry visceral pain sensations

The parasympathetic supply arises from the right and left vagus nerves. The anterior vagal trunk is formed from the left vagus nerve, whereas the posterior vagal trunk is formed from the right vagus nerve. They perform the following functions:

• Secretomotor to the gastric glands
• Motor to the gastric musculature
• Relaxation of pyloric sphincter and promoting gastric emptying
• Carry sensations such as fullness, nausea, and probably pain.

The right gastric vein receives the prepyloric vein of Mayo.

The prepyloric vein serves as the guidepost for the surgeons to identify the pylorus of the stomach. The common pattern of venous drainage of the stomach is as follows:

Veins of the stomach Right gastric vein Left gastric vein

Right gastroepiploic vein

Left gastroepiploic vein Short gastric veins

Drains into Portal vein Portal vein

Superior mesenteric vei n

Splenic vein Splenic vein

Among the given options, the intestinal lymph trunk is the last structure to drain lymphatics from the stomach.

The intestinal lymph trunk is a major lymphatic channel in the abdomen. It receives lymphatics from the pre-aortic group of lymph nodes such as coeliac nodes, superior mesenteric nodes, and inferior mesenteric nodes. The intestinal lymph trunk finally drains into the cisterna chyli.

The lymphatic drainage of the stomach can be divided into four zones as shown in the image below.

The clinical scenario is suggestive of superior mesenteric artery syndrome or Wilkie syndrome. In this condition, the third part of the duodenum is compressed by the superior mesenteric artery causing bowel obstruction.

The mid-portion of the third part of the duodenum lies in the angle between the superior mesenteric artery anteriorly and the abdominal aorta posteriorly.

Parts of the duodenum and their characteristics:

Parts of the duode num

First(5 cm) Second(8 cm)

Third(10 cm)

Fourth(2.5 cm)

Extent

Duodenal end of pylorus to superior duodenal flexure

Superior duodenal flexure t o inferior duodenal flexure

Inferior duodenal flexure t o ascending portion of the f ourth part of duodenum

From the left of aorta to du odenojejunal flexure

Anterior relations Quadrate lobe of liver

Right end of greater oment umOrigin of transverse me socolonMesentery of upper ascending colon and hepat ic flexure

Transverse mesocolonOrigi n of the root of mesenteryS uperior mesenteric vessels

Transverse colonTransvers e mesocolon

Posterior relations

Gastroduodenal arteryCom mon bile ductPortal vein

Right psoas majorLateral e dge of inferior vena cavaHil um of right kidneyRight re nal vessels

Right ureterRight gonadal vesselsInferior vena cavaAb dominal aortaRight Psoas major

Left renal vesselsLeft gona dal vesselsAbdominal aorta Left psoas majorLeft symp athetic trunk

The splenic artery does not supply the duodenum. The major vessels supplying the duodenum are:

• Gastroduodenal artery - branch of the common hepatic artery
• Superior mesenteric artery - anterior branch of the abdominal aorta.

Branches of the gastroduodenal artery supplying the first and second parts of the duodenum and head of the pancreas are:

• Posterior superior pancreaticoduodenal artery
• Anterior superior pancreaticoduodenal artery
• Supraduodenal artery
• Retroduodenal arteries
• Pancreatic branches

Note: The first and second parts of the duodenum also receive minor blood supply from the right gastric artery and the right gastroepiploic artery.

Branches of the superior mesenteric artery supplying the second, third, and fourth parts of the duodenum, and the head and uncinate process of the pancreas are:

• Inferior pancreaticoduodenal artery - anterior and posterior branches supply the second and third parts of the duodenum
• First jejunal artery - supply the fourth part of the duodenum

The image shows plicae circulares which are also known as valvulae conniventes. They are more prominent in the jejunum.

Plicae circulares are the circular mucosal folds. They frequently branch and stack upon each other, giving the jejunum a characteristic feathery appearance in single contrast radiography.

Meckel's diverticulum projects from the antimesenteric border of the terminal ileum. It is commonly located 2 feet proximal to the ileocaecal valve.

Peyer's patches are lymphoid aggregates present in the submucosa and are arranged longitudinally along the antimesenteric border of ileum.

The transverse colon is the longest part of the large intestine, measuring 50 cm in length on an average. It is intraperitoneal in location and suspended by the transverse mesocolon.

Lengths of various parts of the large intestine are as follows:

Intestinal segme nt

Caecum Ascending colon Transverse colon

Approximate len gth

6 cm

15 to 20 cm

50 cm

Intestinal segme nt

Descending colo n

Approximate len gth

25 to 30 cm

Sigmoid colon Rectum

Anal canal

37.5 cm

15 cm

2 to 5 cm

The structures marked in the image are appendices epiploicae and they are usually absent in the caecum.

Appendices epiploicae are small fat-filled peritoneal pouches scattered over the surface of the large intestine. They are very abundant on the surface of the sigmoid colon and tend to be absent from caecum, rectum, and appendix.

The below image shows the appendices epiploicae.

The middle and left colic arteries contribute to the formation of the marginal artery of Drummond at the splenic flexure. The splenic flexure (Griffith's point) is a watershed area of the colon which is more prone to ischemia.

The anastomotic vessel that runs in the mesentery along the inner margin of the colon is called the marginal artery of Drummond. From this artery, numerous small branches are given to the large bowel. It is formed by:

• Branches of superior mesenteric artery - middle colic, right colic, and ileocolic arteries
• Branches of inferior mesenteric artery - left colic, sigmoid, and superior rectal arteries

When ischemia occurs at Griffith's point, the blood supply in this region is augmented by another arterial loop called the inner arterial arc (of Riolan). This arc connects the main trunk of the middle colic artery with the ascending branch of the left colic artery.

Note: Sudeck's point is another watershed area present at the rectosigmoid junction. The sigmoid artery anastomoses with the superior rectal artery at this site.

The middle rectal artery is a content of the lateral rectal ligament.

The condensation of the endopelvic fascia that surrounds the middle rectal vessels is referred to as the lateral rectal ligament. Branches of the inferior hypogastric plexus also enter the rectum through this ligament.

Blood supply of the rectum:

Artery

Superior rectal artery Middle rectal artery

Inferior rectal artery

Branch of

Inferior mesenteric artery

Anterior division of the inter nal iliac artery or inferior ve sical artery

Internal pudendal artery

Location Mesorectum

Lateral rectal ligament

Ischio-rectal fossa

Parts supplied

Upper two-thirds of the rect um

Middle third of the rectum

Distal third of the rectumAn al canal with internal and ex ternal anal sphinctersPerian al skin

The external anal sphincter is made up of striated muscle fibres. It is not a continuation of the outer longitudinal muscle of the rectum

The external anal sphincter is made up of two parts - upper(deep) and lower (subcutaneous or superficial). The pudendal nerve innervates the external anal sphincter and it is under voluntary control.

Muscles of the anal canal:

• External anal sphincter
• Internal anal sphincter: It is the terminal thickened part of the inner circular muscle of the
• large intestine. It extends from the anorectal junction to the anal verge. It is innervated by the autonomic nervous system: parasympathetic - relaxation; sympathetic - contraction.
• Conjoint longitudinal muscle: It lies between the internal anal sphincter and the external anal sphincter. It is the continuation of the outer longitudinal muscle of the rectum. The muscle fibres distally fan out and traverse the internal and external anal sphincter. It has a protective effect
• on haemorrhoids. This muscle degenerates as age advances.
• Treitz's muscle: It is the submucosal muscle of the anal canal. It is attached to the conjoint longitudinal muscle by the Park's ligament. It maintains the integrity of the anal cushions and plays an important role in preventing haemorrhoids.

The nerve mediating pain in external haemorrhoids is pudendal nerve S2, 3, and 4. Differences between external and internal haemorrhoids:

External haemorrhoids

Located distal to the dentate line

Innervated by the inferior rec tal branch of pudendal nerve S2, 3, and 4 (somatic nerve)

Pain sensitive

Internal haemorrhoids

Located proximalto the denta te line

Innervated by parasympathet ic fibres S2, 3, and 4, and sy mpathetic fibres L1 and 2

Pain insensitive

The area marked 'A' on the posterior surface of the liver is related to the esophagus. The image given below shows the relations of the posterior surface of the liver.

Couinaud's segments are divided based on the distribution of the portal vein. Veins of the liver:

• Portal vein- collects the blood from the gall bladder, pancreas, and spleen, and abdominal part of the alimentary tract. It transfers the blood collected from these organs to the liver.
• Hepatic vein- collects the de-oxygenated blood from the liver. It directly drains into the
• inferior vena cava and ultimately into the heart.

Note: Left hemihepatectomy involves the resection of segments II, III, and IV. Right hemihepatectomy involves the resection of segments V, VI, VII, and VIII.

Cholecysto-vena caval line (Cantlie line) separates right and left lobe of the liver.

Cantlie line is an imaginary line that that divides the liver into 2 planes. It extends from the midpoint of the gallbladder fossa at the inferior margin of the liver back to the midpoint of the inferior vena cava (IVC) and contains the middle hepatic vein.

The right part of the liver includes Couinaud's segments V, VI, VII, and VIII.

The given CT abdomen shows a large cystic lesion in the right lobe, presumed to occur due to appendicitis.

Segment IV (left medial sector) corresponds to the quadrate lobe and not the caudate lobe (segment I). It is a part of the physiological left lobe of liver (segments II, III, and IV) and is drained by the left hepatic duct.

The physiological left lobe is supplied by the left hepatic artery and left branch of the portal vein. The physiological right lobe of the liver (segments V, VI, VII, and VIII) is drained by the right hepatic duct, and supplied by the right hepatic artery and right branch of the portal vein.

80 of blood supply to the liver is through the portal vein whereas 20 is through the hepatic artery.

Pringle's maneuver is compressing the hepatic pedicle at the free edge of the lesser omentum. It is used for rapid control of hemorrhage from the vessels entering the porta hepatis (hepatic pedicle). This is conveniently done by dividing the lesser omentum immediately to the left of these structures and passing a tape around them through the epiploic foramen.

The below image shows the Pringle maneuver.

The area marked in the image is the caudate lobe of the liver. Caudate lobe hypertrophy is seen in Budd-Chiari syndrome.

This segment is unique in that it receives blood supply from both the right and left portal veins and hepatic arteries. It directly drains into the inferior vena cava.

It also forms the superior boundary of the epiploic foramen. The image given below shows the posterior surface of the liver.

Hepatic veins do not enter/exit the liver at the porta hepatis and are least likely to be involved by a tumor in that location.

Porta hepatis is a deep, transverse fissure that is situated on the inferior surface of the right lobe of the liver.

Structures entering at porta hepatis:

• Portal vein
• Hepatic artery
• Hepatic nervous plexus

Structures exiting the porta hepatis:

• Right and left hepatic bile ducts
• Lymphatics

The classical feature of portal hypertension are ascites, splenomegaly, esophageal varices and distended veins around the umblicus.

Clinical note:

Pringle maneuver- rapid control of hemorrhage from the vessels entering the porta hepatis can be obtained by compressing them in the free edge of the lesser omentum.

The below image shows Pringle maneuver.

The fibrous sheath surrounding the hepatic artery, bile duct, and portal vein in each liver segment is referred to as Valoean sheath.

This is an extension of the Glisson’s capsule, which becomes condensed as a sheath around the branches of the portal triad structures as they enter the liver parenchyma. This arrangement of sheaths facilitates surgical control of the right and left vasculo-biliary pedicles of the liver.

Hartmann’s pouch is seen in the gallbladder.

Hartmann's pouch (infundibulum) is an outpouching at the junction of the neck of the gallbladder and the cystic duct. Although it is frequently seen, it is not a constant feature of the gallbladder. It serves as a potential space for the gallstones to get lodged.

Option A: Pouch of Douglas or recto-uterine pouch is the most dependent part of the abdomen in the erect position in females.

Option B: Rathke's pouch is an ectodermal outpouching from the developing pharynx that gives rise to the anterior pituitary.

Option C: Morison's pouch or hepatorenal pouch is the most dependent part of the abdomen in the supine position and pathological fluid may collect here.

The marked structure in the image is the cystic artery. It is a branch of the right hepatic artery.

The cystic artery is the main source of blood supply to the biliary system. After originating from the right hepatic artery, it passes posterior to the common hepatic duct and superior to the cystic duct at the hepatobiliary triangle. On reaching the superior aspect of the neck of the gallbladder, it divides into a superficial branch and a deep branch.

The images given below show the cystic artery.

Spiral valves of Heister are the mucosal folds present in the cystic duct. In most cases, they are responsible for causing difficulty in the passage of catheter through the cystic duct.

The mucosa of the cystic duct forms 2–10 crescentic folds which are spirally arranged to form the spiral valve of Heister, also called spiral folds. These are continuous with those in the neck of the gallbladder. The function of these spiral folds is unknown but they may help to preserve the patency of this narrow, tortuous duct.

The cystic duct drains the gallbladder into the common hepatic duct. It unites with the common hepatic duct to form the common bile duct.

Note: Tortuous course of the right hepatic artery, also known as Moynihan's hump or caterpillar hump, is a rare but important anomaly to be recognized to prevent intraoperative vascular

and biliary injuries during surgical procedures involving the liver and biliary apparatus.

The given clinical scenario is suggestive of injury to the spleen.

The spleen is a wedge-shaped organ and extends from the 10th rib to the 12th rib in the left hypochondrium. It lies along the long axis of the 11th rib and is likely to be injured in blunt trauma to the abdomen. Laceration of the spleen leads to profuse intra-abdominal bleeding and hypovolemic shock.

It is not palpable in a normal adult. For the spleen to be palpable, it has to become 3 times its normal size.

Note: Anatomical variations exist among human beings. Some sources mention that spleen is related to the ›th to 11th ribs; however, Gray’s textbook of Anatomy, mentions it as the 10th to 12th ribs.