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 => bv ?

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? = arteries

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?

what happens when it constricts/ relaxes?

Answer 3

Here’s a simplified version with less focus on functions:

1. Main Pancreatic Duct & Accessory Pancreatic Duct:
   
   • The main pancreatic duct carries digestive enzymes from the pancreas.
   • The accessory pancreatic duct is a smaller duct that also carries some enzymes from the pancreas.
2. Common Bile Duct:
   
   • The common bile duct carries bile from the liver and gallbladder.
3. Ampulla of Vater:
   
   • The main pancreatic duct and the common bile duct both empty into the small intestine at the ampulla of Vater.
4. Sphincter of Oddi:
   -The sphincter of Oddi is a muscular valve that surrounds the ampulla of Vater.
   
   • The sphincter of Oddi is a valve that controls the flow of bile and pancreatic juices into the small intestine (duodenum).

• 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

Here’s a clearer breakdown of the pancreas structure and duct system:

1. Acinar Cells:
   
   • The pancreas contains acinar cells that are responsible for producing digestive enzymes. These cells are located in clusters called lobules.
2. Duct System:
   
   • The enzymes produced by the acinar cells are drained through a series of ducts:
     
     • The intercalated ducts are the smallest ducts that receive the enzyme secretion from the acinar cells.
     • These intercalated ducts drain into intralobular ducts, which are slightly larger ducts within the lobules.
     • The intralobular ducts then feed into interlobular ducts, which are larger ducts that connect different lobules.
     • Finally, all the ducts converge into the main pancreatic duct, which carries the digestive enzymes to the small intestine.

In short, the pancreas has a network of ducts that start from the acinar cells and become progressively larger, eventually leading to 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?

Answer 5

1. Pancreatic Secretions:
   Acinar Cells:

These specialized cells in the pancreas produce:
Enzymes: Digest food in the small intestine.
Proteins: Broken down by enzymes like trypsin and chymotrypsin.
Fats: Broken down by lipase.
Carbohydrates: Broken down by amylase.
Proenzymes (zymogens): These are inactive forms of enzymes, stored in the pancreas to prevent self-digestion. They activate only when they reach the small intestine.
Fluid: Helps carry enzymes into the ducts.
Duct Cells:

Duct cells secrete bicarbonate (HCO₃⁻).
Why Bicarbonate?
Neutralizes the acidic chyme that comes from the stomach.
Creates the perfect pH environment (slightly alkaline) for the pancreatic enzymes to work properly.
2. How Enzymes Are Stored and Released:
Storage: Enzymes and zymogens are kept in small storage units called vesicles within acinar cells.
Release: When digestion is triggered (e.g., by the hormone CCK), the enzymes are released into the ducts and carried to the duodenum.
3. Movement of Secretions:
There are no muscles pushing pancreatic secretions.
Instead, the production of fluid and enzymes creates pressure in the ducts, naturally moving the secretions into the small intestine.
4. Daily Pancreatic Output:
The pancreas produces about 1.5 liters of clear, alkaline fluid every day.
The fluid’s alkalinity comes from bicarbonate, which is essential for neutralizing stomach acid and protecting the small intestine.

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

Here’s a clearer explanation of how bicarbonate secretion works in pancreatic duct cells:

Stimulators of Bicarbonate Secretion:
1. Secretin:
- A hormone that increases levels of cAMP in duct cells.
- cAMP acts as a signaling messenger inside the cell, telling it to secrete bicarbonate (HCO₃⁻).

2. Acetylcholine (Ach):
   
   • A neurotransmitter that increases the activity of an enzyme called Carbonic Anhydrase (CA).
   • CA helps produce bicarbonate inside the duct cells.

Mechanism of Bicarbonate Secretion:
- Exchangers:
- The duct cells have special proteins on their surface, called Cl⁻/HCO₃⁻ exchangers (from the SLC26 family).
- These exchangers swap chloride ions (Cl⁻) coming out of the cell with bicarbonate ions (HCO₃⁻) going into the ducts.

• CFTR Chloride Channel:
  
  • The CFTR channel (regulated by cAMP) allows chloride ions (Cl⁻) to move back into the duct cells.
  • This recycling of chloride helps the exchangers work continuously, keeping bicarbonate secretion going.

Inhibition of Bicarbonate Secretion:
- Substance P:
- This molecule blocks bicarbonate secretion, reducing its release into the ducts.

Summary:
- Secretin and Ach stimulate bicarbonate secretion through different mechanisms:
- Secretin uses cAMP to activate secretion.
- Ach increases carbonic anhydrase, boosting bicarbonate production.
- Bicarbonate is secreted into the ducts via Cl⁻/HCO₃⁻ exchangers, with the help of the CFTR channel to recycle chloride.
- Substance P inhibits this process, reducing bicarbonate release.

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

Here’s a clearer explanation of liver structure and function:

Liver Structure (Hexagon Model):
- The liver is made up of hexagon-shaped units called lobules.
- Portal Triads:
- Each corner of a hexagon contains a portal triad, which includes:
1. A branch of the hepatic artery (carries oxygen-rich blood).
2. A branch of the portal vein (carries nutrient-rich blood from the gut).
3. A bile duct (collects bile from liver cells).
- Central Vein:
- At the center of each hexagon is the central vein, where filtered blood drains after passing through the liver.

Blood Flow in the Liver:
1. Portal Vein:
- Brings nutrient-rich blood from the gut to the liver via the portal triads.
2. Hepatic Artery:
- Brings oxygen-rich blood to supply the liver cells with oxygen.
3. Blood Percolation:
- Blood flows from the portal vein and hepatic artery through small spaces in the lobule called sinusoids.
- As blood flows, liver cells (hepatocytes) process nutrients, break down waste, metabolize drugs, and store nutrients (e.g., glucose as glycogen).
4. Drainage:
- After filtering through the hepatocytes, blood flows into the central vein at the center of the lobule.
- The central veins merge into the hepatic vein, which drains into the inferior vena cava (IVC).

Bile Flow (Opposite to Blood Flow):
- Hepatocytes also produce bile as they process nutrients and break down waste.
- Bile Pathway:
1. Bile drains into tiny channels called canaliculi, located between hepatocytes.
2. Canaliculi transport bile toward the bile ducts in the portal triads (at the edges of the hexagons).
3. From there, bile moves out of the liver and into the gallbladder or intestine.

Key Point:
- Blood Flow: From the portal triads (at the corners) toward the central vein (at the center).
- Bile Flow: From the center (canaliculi) toward the portal triads (opposite to blood flow).

In summary, the liver processes blood for nutrients and waste and sends bile in the opposite direction of the blood flow.

Question 13

What are the 5 main functions of the liver?

smdsi

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

*
* Hepatocytes → Canaliculi → Terminal Ducts → Interlobular Ducts → Right and Left Hepatic Ducts → Common Hepatic Duct → Common Bile Duct.
This pathway efficiently transports bile from the liver to the gallbladder and the intestine for digestion

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? => + what does small intestine do

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?

why is gallbladder bile diff from hepatic

Answer 16

Functions of the Gallbladder and Bile Pathway:

Gallbladder Functions:
1. Storage of Bile:
- The gallbladder stores bile, which is used for the emulsification (breakdown) of fats in the small intestine.

2. Concentration of Bile:
   
   • Hepatic bile (produced by the liver) becomes more concentrated in the gallbladder.
   • This happens because water is slowly absorbed through the walls of the gallbladder.
3. Difference Between Gallbladder Bile and Hepatic Bile:
   
   • Gallbladder bile is more concentrated than hepatic bile due to this water absorption process.

Bile Duct Contribution:
1. Production of Bicarbonate:
- Bile duct cells produce bicarbonate (HCO₃⁻).
2. Function of Bicarbonate:
- Helps neutralize the acidic content of chyme coming from the stomach into the small intestine.

Summary:
- The gallbladder stores and concentrates bile, making it more potent for fat digestion.
- Bile duct cells contribute by adding bicarbonate to neutralize stomach acid, creating a suitable environment for enzymes to work in the small intestine.* 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 and Liver Damage

Cholestasis:
- Definition: A condition where bile secretion is suppressed or blocked.
- Effects:
- Regurgitation of bile components: Bile components flow back into the bloodstream.
- Symptoms:
- Jaundice: Yellowing of the skin and eyes due to bilirubin buildup.
- Pruritus (itching): Caused by the buildup of bile salts in the skin.
- damage to hepatocytes:
- Can occur due to mechanical obstruction (e.g., bile ducts blocked by stones or other factors).

Gallstones (Cholelithiasis):
- Cause: Disturbance in bile secretion and cholesterol elimination, leading to:
- Bile becoming supersaturated with cholesterol.
- Composition:
- About 80% of gallstones are made of cholesterol.

Summary:
- Cholestasis leads to the suppression of bile flow, causing jaundice and itching.
- Gallstones form when bile is supersaturated with cholesterol, often leading to obstruction and liver cell damage.

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?
=> what is released and by what cells

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

Here’s a clearer explanation of this phase of digestion:

Phase Overview:
- This phase starts when chyme (partially digested food) enters the duodenum (first part of the small intestine).
- In this phase, the food is further broken down, and nutrients are absorbed.

Hormones Involved:
1. CCK (Cholecystokinin):
- Released from the duodenum when amino acids and fatty acids are detected in the chyme.
- Main functions of CCK:
1. Stimulates the gallbladder to contract and release bile (which helps break down fats into fatty acids).
2. Stimulates the pancreas to release digestive enzymes from acinar cells (to help break down proteins, fats, and carbohydrates).

2. Secretin:
   
   • Released from the small intestine when the chyme is acidic (contains high levels of H+).
   • Main functions of Secretin:
     
     1. Increases bile production by the liver to help with digestion.
     2. Stimulates the pancreas to release bicarbonate (which neutralizes the stomach acid in the chyme, creating a better environment for digestive enzymes).

CCK and Secretin Together:
- Both hormones can reduce peristalsis (intestinal movement) to allow more time for proper absorption of nutrients.

Summary:
- When food enters the small intestine, CCK and Secretin are released to help with digestion and absorption.
- CCK helps release bile and digestive enzymes, while Secretin helps neutralize stomach acid and promotes bile production.
- Together, they help regulate the digestive process and ensure proper absorption of nutrients.