Lecture 5 : Secretions of the Pancreas

Question 1

What is the pancreas

Answer 1

Gland located behind stomach

Endocrine and exocrine function, exocrine directly involved in GI function, secreting digestive enzymes and fluid rich in bicarbonate ions, up to 1.5L a day.

bicarbonate ions in pancreatic fluid neutralise acidity of chyme coming from stomach before entry into small intestine

Question 2

Exocrine structure and function of pancreas

Answer 2

Each lobule drains to ductular network.

Pancreas mainly secretes digestive enzymes to digest food types, and alkaline juices to neutralise acids and prevent ulcers.

Intralobular duct
Interlobular ducts
Main duct (connects entire gland to lumen of GI tract, and merges with common bile duct to form ampulla of Vater)

Question 3

Sphincter of Oddi function

Answer 3

Prevents reflux of bile and pancreatic juices into duodenum, and prevents backflow of intestinal content into bile / pancreatic ducts.

Question 4

Pancreatic Acinus

Answer 4

Secretory unit of pancreas. Cluster of acinar cells.

Secrete :
- zymogens, which are inactive enzyme precursors
- Digestive enzymes
- Isotonic plasma-like fluid accompanying secretory proteins

Stimulation is mediated through CCK receptors and ACh receptors loacrted on basolateral cell membrane

Question 5

Functions of 3 pacnreatic CELL TYPES, acinar, duct, ceontroacinar and goblet

Answer 5

Acinar - Specialised for production / export of large quantities of protein

Duct - Transport of electrolytes

Goblet - mucus secretion for lubrication, hydration and protection

Question 6

What is inside pancreatic juices

Answer 6

Question 7

Fed vs Fasted state in secretion of pancreatic juices

Answer 7

Fed State / absorptive state :
- Pacreatic secretion increases 4-20 fold above normal levels

Fasted State :
- Low level of release of enzymes from pancreas

Question 8

What is CCK

Answer 8

Released from duodenal I cells

CCK stimulates pancreatic acinar cells to increase secretion of enzymes or enzyme precursors.

CCK levels increase due to CCK receptor activation or parasympathetic nervous system, or releasing factors (eg. LCRF)

In fasting state LCRFs degraded by digestive enzymes so no CCK stimulation.

Question 9

Duct cell secretions

Answer 9

Secretes HCO3- rich fluid alkalinising and hydrating protein (enzyme) rich secretions of acinar cell.

Optimises pH for enzyme activity, whilst also neutralising acid and preventing ulcers.

Secretin and ACh activation stimulates production of HCO3-

Question 10

Secretin

Answer 10

From S cells, when duodenum is acidic.

Question 11

Cystic Fibrosis

Answer 11

Question 12

Phases of pancreatic secretion diagram, cephalic, gastric and intestinal

Answer 12

Question 13

What can inhibit pancreatic secretion

Answer 13

Somatostatin

From D cells in islets of langerhans of pancreas

Inhibiting release of CCK and secretin

Question 14

How is autodigestion prevented in pancreas

Answer 14

Storing proteases in precursor form, as zymogens. Become active after coming into contact with bowel border enzyme enterokinase.

Synthesising protease inhibitors. Trypsin inhibitors copackaged into secretory granule.

Only when zymogens come into contact with bowel border enzyme enterokinase, is trypsinogen converted to trypsin, which initiatives conversion of zymogens to active form.

Question 15

Acute Pancreatitis

Answer 15

Question 16

Chronic Pancreatitis and its Treatments

Answer 16