L15 - GI Accessory organs physiology

Question 1

What are the components of the pancreas and their functions?

Answer 1

• Within pancreatic duct - interlobular ducts (stem-like structures)
• Interlobular ducts - lobules attached
• Lobules - made of acinar cells + duct cells
• Acinar cells:
• stimulated by CCK + ACh
• secretes inactive enzyme-rich fluid - zymogens (activated in duodenum)
• enzymes - proteolytic + amylase + lipolytic
• Duct cells:
• stimulated by secretin
• secretes aqueous fluid rich in HCO3- (pH~8) – neutralise acidic chyme entering duodenum
• Nervous reflex — medulla oblongata + vagal innervation

Pancreatic juice:
- enzymes + HCO3- rich fluid
- travel to duodenum with bile via sphincter of Oddi

Question 2

What is pancreatitis, its causes, and its treatment?

Answer 2

What?
- When pancreatic enzymes are activated within the pancreas, causing them to attack the organ itself

2 forms:
- Acute - becomes chronic when pancreatic tissue is destroyed + scarring develops
- Chronic

Causes:
- Gallstones
- Alcohol abuse
- Unknown causes (idiopathic)

Treatment:
- Pain+infection management
- Electrolyte therapy
- Surgery (extreme case)

Question 3

What are the components of the liver and their functions?

Answer 3

Liver has double blood supply:
- oxygenated blood from hepatic artery (25%)
- de-oxygenated blood + nutrients from portal vein (75%)

• Bile duct attached to liver
• Lymphatic vessel - immune system + lipid metabolism
• Portal triad (tract) - makes up hepatic artery, portal vein, bile duct + lymphatic vessel
• Portal vein - transport substances absorbed from small intestine to liver
• Some nutrients end up in sinusoids to reach vena cava via central vein
• some nutrients taken up by hepatocytes - metabolised
• Hepatocytes - arranged in radial pattern around central vein into functional units -> lobules
• Lobules - form lobes of liver - 2 main lobes of liver
• Hepatocytes - main function is metabolic activity and then secreted into bile via bile canaliculi
• rest of by-products into hepatic vein
• Bile canaliculi - takes bile to bile duct
• Kupffer cells in lobules - bactericidal activity
• Space of Disse - lipocytes involved in vitamin A metabolism

Question 4

What does bile consist of?

Answer 4

• Bile salts:
• emulsify fat into smaller droplets
• secreted by hepatocytes
• Bile cholesterol
• made soluble by bile salts
• secreted by hepatocytes
• Bile pigments (bilirubin)
• give colour to faces/urine
• secreted by hepatocytes
• HCO3- ions
• neutralises acidic chyme
• secreted by epithelial cells lining bile duct
• Stimulation of bile secretion increased by vagal innervation + secretin hormone

Question 5

What is the enterohepatic circulation?

Answer 5

• Recycling pathway from liver to intestine, then back to liver
• Bile salts:
• absorbed in ilium during digestion of fatty meal
• returned back to liver via portal vein
• secreted back out into bile duct
• only 5% lost in faeces
• Liver synthesises new bile salts from cholesterol to replace it
• Enterohepatic circulation occurs several times during digestion of large meal.

Question 6

What is the function of gallbladder?

Answer 6

• Storage of concentrated bile
• Concentrated = water + ions extracted and absorbed into blood
• also has increased insoluble cholesterol levels
• When not eating - bile enters gallbladder by cystic duct - hence sphincter of Oddi closed

During meal:
- protein+fat rich chyme enters duodenum
- CCK stimulated
- CCK stimulates gallbladder to contract + sphincter of Oddi to relax (open)
- bile then enters duodenum

Question 7

What are gallstones?

Answer 7

• Crystalline deposits that accumulate when there is too much cholesterol and not enough bile salts
• Cholesterol crystallises out of solution

Treatment:
- can be dissolved using drugs
- cholecystectomy - removal of gallbladder (extreme case)

Question 8

Why is jaundice a symptom of gallstones?

Answer 8

Jaundice -> yellowish colourisation of the skin + eyes

Why?
- Gallstones can block the common bile duct — prevents bile + pancreatic secretions from entering intestine, hence failure to neutralise + digest nutrients

• ↑bilirubin levels in blood plasma (due to blockage of bile) — diffuses into tissues => gives rise to yellowish colour of skin + eyes