(23.7) Liver, Gallbladder & Pancreas

Describe Function of the Liver

1. Production of bile 

Role of Bile

1. Fat emulsifier

Describe Function of the Gallbladder

1. Stores and concentrates bile that is not needed immediately for digestion

   • Concentrates it by absorption water and ions

Describe Function of the Pancreas

1. Supplies most enzymes needed to digest chyme,

2. Supples bicarbonate to neutralize stomach acid 

Describe the histologic anatomy of the Liver

1. Liver lobules

   • Hexagonal structural and functional units 

   • Composed of plates of hepatocytes (liver cells) that filter and process nutrient-rich blood 

   • Central vein located in longitudinal axis

2. Portal triad in each corner of lobule contains: 

   • Branch of hepatic artery → which supplies oxygen 

   • Branch of hepatic portal vein → which brings nutrient-rich blood from intestine 

   • Bile duct → which receives bile from bile canaliculi 

What constitute a portal triad?

A bile duct along with a portal venule and arteriole → the blood vessels provide blood flow to the lobule and the bile duct drains bile.

Structure and Function of Hepatocytes 

STRUCTURE 

• Hepatocytes have increased rough and smooth ER, Golgi apparatus, peroxisomes, and mitochondria 

FUNCTION

1. Produce ~900 mL bile per day

2. Process bloodborne nutrients

   • EX: Store glucose as glycogen and make plasma proteins

3. Store fat-soluble vitamins

4. Perform detoxification

   • EX: Converting ammonia to urea

Composition and Enterohepatic circulation of Bile  

Yellow-green, alkaline solution containing: 

1. Bile salts 

   • Cholesterol derivates that function in fat emulsification and absorption 

2. Bilirubin 

   • Pigment formed from heme 

3. Cholesterol 

4. Triglycerides 

5. Phospholipids 

6. Electrolytes 

Effect and Cause of Hepatitis 

• EFFECT 

  • Inflammation of the liver

• CAUSE

  • Usually viral infection, drug toxicity, wild mushroom poisoning

Effect and Cause of Cirrhosis 

• EFFECT 

  • Progressive, chronic inflammation from chronic hepatitis or alcoholism 

• CAUSE

  • Liver → Fatty, fibrous → Portal hypertension

Structure and Function of Gallbladder 

STRUCTURE 

• Muscular contractions release bile via cystic duct, which flows into bile duct

FUNCTION 

1. Store and concentrate bile by absorbing water and ions

Effect and Cause of Gallstones 

Biliary calculi

• EFFECT 

  • Can obstruct flow of bile from gallbladder 

  • Painful while gallbladder contracts against sharp crystals

• CAUSE

  • Too much cholesterol or too few bile salts 

Effect and Cause of Obstructive Jaundice  

• EFFECT 

  • Blockage can cause bile salts and pigments to build up in blood → resulting in jaundiced (yellow) skin

• CAUSE

  • Gallstones 

  • Liver failure 

Location of the Pancreas 

• Mostly retroperitoneal, deep to greater curvature of stomach 

• Head is encircled by duodenum; tails abuts spleen

Structure and Function of Pancreas

STRUCTURE

• Acini

  • Clusters of secretory cells that produce zymogen granules containing proenzymes

• Ducts

  • Secrete to duodenum via main pancreatic duct

  • Smaller duct cells produce water and bicarbonate

FUNCTION

• Exocrine function → produce pancreatic juice containing enzymes and bicarbonate into the small intestine

Composition of Pancreatic Juice 

1200-1500 mL/day is produced containing:

1. Watery

2. Alkaline solution (pH 8) to neutralize acidic chyme coming from stomach

3. Electrolytes

4. Primarily HCO₃^-

5. Digestive enzymes

   • Proteases (for proteins) → secreted in inactive form to prevent self-digestion

   • Amylase (for carbohydrates)

   • Lipases (for lipids)

   • Nucleases (for nucleic acids)

T/F: Proteases are secreted in active form

→ FALSE

Proteases are secreted in an INACTIVE form → they are activated after they reach duodenum

State the roles of bile and pancreatic juice in digestion.

Bile duct from the liver & pancreatic duct join at he duodenal wall and deliver bile and pancreatic juice to the intestine

• Bile

  • Fat emulsifier

• Pancreatic juice

  • Supplies most enzymes needed to digest chyme

    • Proteases (for proteins) → secreted in inactive form to prevent self-digestion

    • Amylase (for carbohydrates)

    • Lipases (for lipids)

    • Nucleases (for nucleic acids)

  • Supples bicarbonate to neutralize stomach acid 

Describe how bile and pancreatic juice secretion into the small intestine are regulated.

• Bile and pancreatic juice secretions are BOTH stimulated by neural and hormonal controls 

• Hormonal controls include: 

  1. Cholecystokinin (CCK) → Increases output of enzymatic-rich pancreatic juice.

  2. Secretin → Increases output of pancreatic juice rich in bicarbonate ions

  3. Gastric Inhibitory Peptide → Stimulates insulin release and mildly inhibits HCl production

  4. Gastrin → Increases HCl secretion and stimulates contraction of intestinal muscle