Anatomy of the pancreas, Liver, Gall bladder and tree

What are the different zones in the liver? How are they split up?

The lobes of the liver are made up of microscopic units called lobules which are hexagonal in shape. − The acinus is the functional structural unit of the liver. It is an elliptical unit which has a portal triad at the centre, a central vein at each pole and also has 3 zones: 1. Zone 1 (Periportal) = contains most oxygenated blood and performs most of the hepatic metabolic activity. It receives most blood from the hepatic artery and portal vein so is therefore most susceptible to damage from toxins carried into the liver in the portal vein and those absorbed from the alimentary canal (eg paracetamol poisoning). 2. Zone 2 (midzone) 3. Zone 3 (centrilobular) = this is furthest from the portal triad and closest to the central vein and therefore most susceptible to ischaemic damage (eg in heart failure)

How many segments does the Liver have? When is this clinically important?

the liver has 8 segments 'of Couinaud'. Segment 1 corresponds to the caudate lobe; segment 2 to 4 represent the left lobe; segment 4 to 8 represent the right lobe. They have been divided according to their supply by the hepatic artery and portal vein which is important to consider when resecting part of the liver due to cancer

Pancreatic anatomy: What does it do?

• Abdominal glandular organ with a digestive (exocrine) and hormonal (endocrine) function • Exocrine: HCO3- and enzymes (Acinar cells) • Endocrine: Hormone released from islets of Langerhans - insulin and glucagon

What is the pancreases anatomical position?

• Apart from the tail, it is a reteroperitoneal structure located in the upper abdomen in the epigastum and left hypochondrium

What is the neurovascular supply to the gall bladder?

• Arterial supply: Cystic artery (from the hepatic artery proper) • Venous drainage: Cystic vein (to the portal vein) • Parasympathetic, sympathetic and sensory information. Celiac plexus carries sympathetic and sensory fibres - whereas the vagus nerve delivers parasympathetic innervation. • The vagus nerve is the one that stimulates the contraction of the gall bladder. • The main stimulator of bile secretion is cholecystokinin, which is secreted in the duodenum and travels in the blood

List the anatomical structure of the biliary tree, right from the liver to the small intestine

• Bile is secreted from the gallbladder into the GIT via the biliary tree. The tree is a series of ducts receiving stuff from the liver, gallbladder and pancreas • It begins with the left and right hepatic ducts, which drain bile from the liver. • The two ducts come together to form the common hepatic duct (Laying next to the hepatic vein). As this comes down it is joined by the cystic duct - a continuation of the neck of the gall bladder. • The hepatic duct and cystic duct combine to form the common bile duct • This common bile duct comes down and joins with the pancreatic duct, eventually via the ampulla of Vater into the duodenum (controlled by the sphincter of Oddi)

Where does the common bile duct lay in relation to the pancreas?

• Crosses the posterior surface of the head of the pancreas • The common bile duct and pancreatic duct combine to form the hepaticpancreatic ampulla

What are the different surfaces of the liver?

• Diaphragmatic surface: o Refers to the anterosuperior surface of the liver o Smooth and convex o Mostly, this is covered by the peritoneum, apart from a section known as the bare area • Visceral surface: o Covers the posteroinferior aspect of the liver o Moulded by surrounding organs o Lies in contact with the oesophagus, right kidney, right adrenal gland, right colic flexure, duodenum, gallbladder and the stomach

If the bile doesn't drain out of the ampulla of Vater, where does it drain from?

• Drains the uncinate process and the inferior part of the head of the pancreas into the minor duodenal papilla. Usually this flows into the main pancrwatic duct, but sometimes it's a separate duct.

List the different bits of the pancreas

• Head o Widest part o Connected to the C shaped duodenum by connective tissue • Uncinate process o Arises from lower part of head and extends medially to lie beneath the pancreas • Neck o Between head and body of pancreas • Body o Centrally located, crossing the midline of the human body • Tail o The left end of the pancreas, laying proximally to the hilum of the spleen

What is the nerve supply to the Liver? What is the lymphatic drainage of the Liver?

• Hepatic plexus supplies the parenchyma - innervated by the hepatic plexus which contains sympathetic (from coeliac plexus) and parasympathetic (vagus) nerve fibres • These fibres enter the liver at the porta hepatis, and follow the course of branches of the hepatic artery and portal vein. • Glisson's capsule, is innervated by branches of the lower intercostal nerves. Thus when the capsule becomes distended there's a sharp, well localised pain.

What is the liver? What are its brief functions?

• Largest internal organ and largest gland in the body • With the exception of lipids, every substance absorbed by the gut is taken through the liver • The liver also stores bile and glycogen • Intraperitoneal organ and positioned in the right upper quadrant Surfaces of the liver: • Convex diaphragmatic surface, anterior, superior and some posterior with a flat concave visceral surface, separated anteriorly by a sharp inferior border

What is the blood supply to the pancreas?

• Pancreatic arteries come from mostly the splenic arteries. • The head is also supplied by the (Anterior and posterior) superior and inferior Pancreaticoduodenal arteries which are branches of the gastroduodenal and superior mesenteric arteries respectively • Venous drainage is into the superior mesenteric branches of the hepatic portal vein

What is the anatomical structure of the gall bladder? And the names of the different regions?

• Pear-shaped sac • Fundus o Rounded into of the gall bladder • Body o Largest part • Neck o Continuous with the cystic duct, leading to the bilary tree o The neck contains a mucosal fold, Hartmann's pouch (where Gallstones become lodged)

What's the main sphincter in the biliary system? Are there any others?

• So there's loads of sphincters in this region • All smooth muscle • Sphincter of bile duct, controlling the flow of bile • Sphincter of the pancreatic duct, preventing the reflux of bile into the pancreatic duct • Hepatopancreatic sphincter, Sphincter of oddi. Which is around the hepatopancreatic ampulla (ampulla of Vater) prevents duodenal content from entering the ampulla

What are the three hepatic recesses?

• Subphrenic recesses o Superior extensions of the peritoneal cavity o Located between the anterior and superior aspects of the liver and diaphragm o Either side of the falciform ligament • Hepatorenal recess (Morrison pouch) o Subhepatic space on right side inferior to the liver and anterior to the kidney o This is the deepest part of the peritoneal cavity when supine, and is where fluid collects in a bed bound patient • Subhepatic space o Between the inferior surface of the liver and the transverse colon

What is the function of the gall bladder? What lobe of the liver is it associated with? what height does it sit at?

• Temporary storage of bile and concentration • It is concentrated and released from the gall bladder in response to eating • Peritoneal structure, laying in the right hypochondriac region • Concentrated bile is better at emulsification and the pH is better at neutralisation • Associated with quadrate lobe of liver • Tip of 9th costal cartilage on the right

Macroscopic structure of the liver: What are the different lobes of the liver? What is the Liver surrounded by?

• The entire liver is covered by a fibrous layer (Glisson's capsule) • The ligaments and surface depressions divide the liver into four lobes • It is divided into the right and left lobe by the faciform ligments • There are a further accessory lobes that arise from the right love and are located on the visceral surface of the liver o Caudate lobe ♣ Upper aspect of the visceral surface ♣ Lies between the IVC and a fossa (remnant of foetal ductus venosus) ♣ Bare area o Quadrate lobe ♣ Located on the lower aspect of the visceral surface ♣ Lies between the gall bladder and a fossa produced by ligamentum teres (Remnant of foetal umbilical vein) • Between the caudate and quadrate lobes is a deep fissure known as the porta hepatis. It transmits all the vessels, nerves and ducts entering or leaving the liver.

Describe the duct system of the pancreas

• The exocrine compartment is a serous gland • It is comprised of shit loads of berry-like clusters of cells called acini, connected by short intercalated ducts. • Intercalated duct cells beginning within acini are called centroacinar cells. • The intercalated ducts drain into a network of intralobular collecting ducts, which in turn drain into the main pancreatic duct • The pancreatic duct runs the length of the pancreas and unites with the common bile duct - forming the hepatopancreatic ampulla of Vater, which opens into the duodenum

Microscopic structure of the Liver

• Under the microscope, the hepatocytes are arranged into lobules - making up the structural units of the liver. • Each lobule is hexagonal shaped and is drained by a venule in its centre - the central vein • At the periphery of the hexagon, there are thee structures known as the portal triad. At each of the 6 corners there are: o Arteriole - A branch of the hepatic artery o Venule - A branch of the hepatic portal vein entering the liver o Duct - A branch of the bile duct leaving the liver (Lymphatics, bile duct and vagus nerve fibres as well

Arterial supply and venous drainage of the Liver?

• hepatic artery proper o Supplies the liver with arterial blood o Derived from the coeliac trunk (aorta) • Hepatic portal vein o Supplies the liver with deoxygenated blood, carrying nutrients absorbed from the small intestine o This is the dominant blood supply to the liver parenchyma and allows the liver to perform its gut related functions (such as detoxification) • Venous drainage of the liver is achieved through three hepatic veins, which drains into the inferior vena cava

Give the anatomical position and relations of the Liver

Anatomical position and relations: • Positioned in the right hypochondrium and epigastric areas, extending into the left hypochondrium • During embyolgical development the liver is formed within part of the ventral mesentery - which suspends the foregut organs from the anterior abdominal wall. Anterior: • Anterior to the liver is the anterior abdominal wall and ribcage Superior: • Superior to the liver is the diaphragm (separating the abdominal cavity from the thoracic cavity) Posterior: • Posterior to the liver are the oesophagus, stomach, gall bladder and the first part of the duodenum (Foregut derived organs)

What is the Liver capsule called?

Capsulated = ie surrounded by a strong connective tissue ('Glisson's capsule)

Give the anatomy (and movement) of bile ducts and flow in the Liver

Hepatic lobules: • Liver lobes are made up of lobules which are hexagonal in shape • They comprise of rows of hepatocytes which radiate from a central vein • At each of the 6 corners of these lobules lay a hepatic artery, portal vein & bile duct Bile flow • The space of Disse in the liver is where the components of bile come together, it is between a hepatocyte and sinusoid (small blood vessel) • It is then secreted into the biliary canaliculi where it flows into the biliary tree then to the duodenum The biliary tree is as follows: • Biliary cancaliculi -> bile ductules -> bile ducts (located at the edge of lobules) -> intra-hepatic ducts -> hepatic ducts (which leave each liver lobe) • The left and right hepatic ducts join -> common hepatic duct • Common hepatic duct joins the cystic duct from the gallbladder -> common bile duct which leads to the duodenum

What are the three different ligaments of the liver? What are these ligaments?

Ligaments are formed between the liver and surrounding organs - they're a double layer of peritoneum • Falciform ligament: o Extends between the liver and anterior abdominal wall o The free edge contains ligamentum teres • Lesser omentum o Carries the portal triad (Portal vein, hepatic artery and bile duct) o Passes from the liver to the lesser curvature of the stomach • Coronary ligaments, Triangular ligaments • Also, the posterior surface of the liver is secured to the inferior vena cava by hepatic veins and fibrous tissue

What is Riedel's Lobe?

Riedel's Lobe = an anatomical variation where there is a downward projection of the right lobe of the liver. It moves with respiration and can descend as far down as the right iliac fossa. It is more common in women but is usually asymptomatic