14-10-21 - Pancreas and Liver

Question 1

What are the 5 parts of the pancreas?

Where is the pancreas located?

What is it close to?

Answer 1

• The 5 parts of the pancreas are the uncinate process, head, neck, body, and tail
• The pancreas is in the retroperitoneal space (except tail) in the C shapes section of the duodenum, and is tucked under the liver
• It is also close to major blood vessels, such as the aorta and inferior vena cava.

Question 2

What are the blood vessels that supply the pancreas?

Answer 2

• Pancreatic blood supply is mainly via the splenic artery (from the coeliac trunk)
• The pancreatico-duodenal arteries (from superior mesenteric artery or coeliac trunk) also supply the pancreas

Question 3

What are the ducts that come out of the pancreas?

What do they combine with?

How does the pancreas and liver connect to the small intestine?

What is the sphincter of Oddi?

What is its role?

Answer 3

• There is the main pancreatic ducts and the accessory pancreatic duct
• The main pancreatic duct combines with the common bile duct and the 3 components of the sphincter of Oddi.
• The common bile duct from the liver and main pancreatic duct connect to the small intestine at the ampulla of vater
• The sphincter of Oddi is a valve that regulates the flow of bile into the duodenum of the small intestine
• When it constricts/contracts, the bile refluxes back into the gallbladder
• When it relaxes, the bile can move into the duodenum

Question 4

What is the structure of the pancreas like?

Answer 4

• The pancreas consists of acinar cells attached to intercalated ducts inside lobules
• The intercalated ducts feed into intralobular ducts, which feeds into interlobular ducts
These then feed into the main pancreatic duct

Question 5

What are the exocrine secretions from the pancreas?

What are they secreted by?

What are the functions of these exocrine secretions?

Where are some of these secretions stored?

What pushes the secretion through the duct?

How much liquid is secreted?

What is its pH?

Answer 5

• Acinar cells in the pancreas secrete enzymes, proenzymes and some fluid into the intercalated duct.
• Proenzymes, also known as zymogens, are inactive enzyme precursors
• Duct cells of the pancreas secrete bicarbonate (HCO3-) into the lumen of the duct.
• The enzymes are needed for macronutrient digestion in the duodenum
• The bicarbonate is needed for neutralising acid content from the stomach to allow for a better pH for the pancreatic enzymes to work in.
• Enzymes are stored in vesicles of acinar cells until there is appropriate stimulation, which causes them to be released into the lumen
• There are no muscles involved in this secretion. The production of more secretion pushes secretion through the duct
• The pancreas secretes 1.5l of clear alkaline fluid a day (alkaline due to bicarbonate)

Question 6

What are examples of different types of enzymes secreted by the pancreas for digestion?

What is an enzyme responsible for activating some zymogens?

Answer 6

• Trypsinogen – zymogen that is activated by endokinase to digest protein
• Lipase – digests lipids (fats)
• α-amylase – digests starch

Question 7

How are endocrine secretions secreted by the pancreas?

What are examples?

Answer 7

• Hormones release from islets of Langerhans e.g insulin and glucagon (stimulates conversion of glycogen to glucose in liver)

Question 8

What stimulates duct cell secretion of Bicarbonate?

What are the channels responsible for moving bicarbonate into the duct?

What inhibits bicarbonate secretion?

Answer 8

• Secretin (increases cAMP levels) and Ach (increases Carbonic Anhydrase (CA) levels) stimulates duct cell secretion of bicarbonate
• cAMP is a messenger used for intracellular signal induction
• Ach (acetylcholine) is a neurotransmitter
• There are Cl- and HCO3- exchangers from the SLC26 family for the apical secretion of bicarbonate
• Camp-regulated CFTR chloride channel allows Cl- to move chloride back into the cell for more bicarbonate exchange
• Substance P inhibits bicarbonate secretion

Question 9

What is Cystic fibrosis?

What is it caused by?

What does it cause to happen?

Answer 9

• Cystic fibrosis
• Autosomal (non-sex chromosome) recessive disease
• Caused by a mutation in the CFTR gene, which codes for Camp-regulated chloride channel
• Leads to decrease in bicarbonate secretion, blockage of ducts, and eventual destruction of pancreas
• Lack of digestive enzyme leads to maldigestion of nutrients
• Produces thick, sticky mucus, which causes respiratory problems

Question 10

What is acute pancreatitis?

How is it caused?

What does it cause to happen?

Where is pathogenesis thought to be?

Answer 10

• Acute pancreatitis
• Inflammatory condition that may cause local damage to pancreas
• Most commonly caused by alcohol and gall stones
• Gall stones block ducts, which prevents enzymes reaching the duodenum, resulting in them refluxing back into the pancreas and causing inflammatory responses.
• Pathogenesis (development of disease) is thought to originate in the pancreatic acinar cells.

Question 11

Where is the liver situated in the body?

How heavy is the liver?

What are the 4 different lobes of the liver?

What are they separated by?

What are they next to?

Answer 11

• The liver lies under the abdomen, under the diaphragm and is surrounded by peritoneum
• The liver is the largest organ in the body (1200-1500g – 2% of bodyweight)
• The liver has a right, left, quadrate, and caudate lobe
• The left and right lobes are separated by the falciform ligament
• From a posterior view, the caudate lobe is the next to the IVC
• The gallbladder sits behind the quadrate lobe

Question 12

What is the anatomic unit of the liver?

What shape are lobules?

What do lobules contain at each corner and in the centre?

Describe the process of blood coming from the gut to the liver and what occurs.

How does bile flow relate to blood flow?

What is the main artery that feeds the liver?

Answer 12

• The anatomic unit of the liver are called lobules
• Lobules are hexagonal in shape
• The corner of Each hexagon contains a portal triad of hepatic artery, portal vein and bile duct, with a central vein at the centre of each hexagon.
• The portal vein brings blood full of nutrients back from the gut, and runs the blood through the portal veins in the portal triads
• The blood percolates (gradually filters through) through all the liver cells, which metabolise nutrients, break down waste, breaks down drugs or convert nutrients (e.g glucose into glycogen)
• All these things form bile and drain via canaliculi, which lie between hepatocytes (liver cells), which eventually form biliary ducts
• The blood then drains in the central vein in each hexagon, all of which feeds into the hepatic vein, which feeds into the IVC
• The bile flow is in the opposite direction to blood flow
• The hepatic artery is the main supply of oxygenated blood to the liver.

Question 13

What are the 5 main functions of the liver?

Answer 13

• Synthesis and secretion of bile
• Bile pigments (mainly bilirubin from breakdown of haemoglobin)
• Bile acids (responsible for the emulsifying (increasing surface area) effect of biles on fats and they increase the absorption of fatty acids by the small intestine)
• Bile is made from cholesterol, phospholipids, fatty acids, water, and electrolytes (all dumped into bile duct and stored in gallbladder)
• Metabolism and storage of carbohydrates, lipids, proteins and vitamins
• Gluconeogenesis (production of new glucose)
• Glycogenolysis (breakdown of glycogen)
• Lipogenesis (storage of fatty acids as triglycerides)
• Lipolysis (production of fatty acids from triglycerides)
• Detoxification of metabolic waste
• Removal of ammonia and ethanol +drug transformations
• Synthesis of blood clotting and anti-coagulant factor
• Fibrinogen and prothrombin
• Immune system function (Kupffer cells)
• Removal of intestinal bacteria from portal blood so systemic circulation is kept clear.

Question 14

What route does bile from the liver take to the common bile duct?

Answer 14

• Bile secreted into canaliculi in liver
• Bile enters small terminal ducts
• Interlobular ducts then form the right and left hepatic duct, which merge to form the common hepatic duct
• The common bile duct and the cystic duct from the gallbladder then merge to from the common bile duct

Question 15

What is the function of the gallbladder?

How is the gallbladder connected to the common hepatic duct?

What is the valve associated with the gallbladder?

What is it made from?

What occurs to sphincters, ducts, and bile in between meals?

What happens in the anticipation of meals?

Answer 15

• The gallbladder is a concentrating and storage reservoir for bile
• The gallbladder is connected to the common hepatic duct via the cystic duct
• The gallbladder has a spiral valve (valve of heister) formed from a mucous membrane that aids in the passage of bile into and out of the gall bladder
• In between meals, the sphincters, and ducts constrict/contract, which causes reflux of bile into the gallbladder
• In the anticipation of a meal, vagal reflexes cause CCK hormone to be released from the small intestine, which stimulates the contraction of the muscular component of the gallbladder, causing it to push bile into the common bile duct via the cystic duct.
• The ducts and sphincter of Oddi relaxes, allowing bile and digestive juices to move into the duodenum of the small intestine

Question 16

What are the 3 main functions of the gallbladder?

Answer 16

• Storage of bile for the emulsification of fats

• Concentration of hepatic bile
• Gallbladder bile is more concentrated, due to slow absorption of water through the walls of the gallbladder
• This makes it different from hepatic vile
• Production of bicarbonate (bile duct cells)
• Contributes to neutralisation of acid content from stomach.

Question 17

What are 2 biliary clinical conditions? What are they caused by?

What do they cause?

Answer 17

• Cholestasis
• Suppression of bile secretion
• Regurgitation of bile components leads to jaundice and pruritus (itching)
Damage to hepatocytes
• May be caused by mechanical obstruction

• Gallstones (cholelithiasis)
• Disturbance of bile secretion and cholesterol elimination leading to bile supersaturated with cholesterol
• About 80% consist of cholesterol

Question 18

Is the cephalic phase of digestion conscious or unconscious?

What are receptors stimulated by?

What nerve is responsible for this?

What does this cause to happen in the stomach?

Answer 18

• This is the only phase of digestion under conscious control
• Chemoreceptors and mechanoreceptors located in the oral and nasal cavities are stimulated by tasting, chewing, swallowing, smelling, and even thinking of food.
• This is done by the vagus nerve causing vagal reflexes (cranial nerve 10)
• This results in salivatory secretions and parasympathetic excitation in the stomach
• This causes pepsinogen digests (pepsin precursor - a zymogen) to be secreted by gastric chief cells in the stomach, and gastrin to be produced from G-cells in the stomach, which stimulates the secretion of HCl from parietal cells in the stomach, and the secretion of enzymes from pancreatic acinar cells

Question 19

When does the gastric phase of digestion begin?

What does this phase involve?

What are these reflexes responding to in the stomach?

What is produced in this phase?

Answer 19

• This phase begins when the bolus (food) enters the stomach
• The gastric phase involves a lot of reflex responses, most of these are local reflexes in nature, which are called vagovagal responses (vagal cholinergic responses for pancreas and gall bladder)
• These local reflexes enact or cause a lot of the responses in the stomach, whether it is from distension of the stomach, acid, or another substance
• Gastrin and histamine secretion are stimulated at this time too, both of which will increase acid production.

Question 20

How does the intestinal phase begin?

What happens in this phase?

What hormones are secreted?

What are they secreted by?

What do these hormones do?

What can these hormones work together to do?

Answer 20

• This phase begins with chyme (food) entering the duodenum of the small intestine
• There is further breakdown of material during this phase, but also absorption of nutrients.
• The release of CCK hormone from the duodenum is stimulated by amino acids and fatty acids
• The release of Secretin hormone from the small intestine is also stimulated by H+
• CCKs main function is to allow for the contraction of the gallbladder to increase bile secretion (which breaks down fat into fatty acids), and stimulation of the acinar cells in the pancreas to secrete digestive enzymes.
• Secretin aids in amplification of bile production by the liver, but also stimulates the pancreas to secret its exocrine components, like enzymes and bicarbonate, which can neutralise the acidic chyme, allowing for a better environment for the digestive enzymes to work in.
• CCK and secretin can also act together to inhibit peristaltic movements to allow for proper absorption.