AS Lecture 6 - The Pancreas

Question 1

What is the shape of pancreas?

Answer 1

Subdivided into head, neck, body, tail, and uncinate process

Question 2

How does the pancreatic juice reach the duodenum?

Answer 2

Via main and accessory pancreatic ducts

Question 3

What are the main posterior relations of the pancreas?

Answer 3

IVC, abdominal aorta and left kidney

Question 4

How do you define endocrine and exocrine secretions?

Answer 4

Endo - to blood stream, carried by blood to distant target organs Exo - through duct, to nearby tissue

Question 5

What are the main secretions of the pancreas and their actions?

Answer 5

Insulin - reduces BGL Glucagon - Increases BGL Somatostatin - Regulates alpha/beta cells in IoL

Question 6

What is the endocrine functional part of the pancreas and what does it do?

Answer 6

Islets of Langherhans: secretes hormones into blood (insulin, glucagon, somatostatin and pancreatic polypeptide), regulation of blood glucose, metabolism and growth effects

Question 7

What is the exocrine functional part of the pancreas and what does it do?

Answer 7

98% of gland - secretes pancreatic juice into duodenum via pancreatic duct/common bile duct, digestive function

Question 8

How are the pancreatic cells differentiated?

Answer 8

Exo: ducts - acini (grape-like clusters of secretory units), acinar cells secrete proenzymes into ducts Endo: Derived from branching duct system, lose contact with ducts - becoming islets, differentiate into alpha and beta cells secreting into blood

Question 9

What is the composition of the Islets of Langherhans?

Answer 9

Alpha cells-secrete glucagon > 15-20% Beta cells secrete insulin > 60-70% Delta cells secrete somatostatin > 5-10%

Question 10

What are the 2 components of pancreatic juice?

Answer 10

Low vol, viscous, enzyme rich from acinar cells Duct and centroacinar cells release high vol, watery, HCO3 rich juice

Question 11

What is the bicarbonate secretion made from?

Answer 11

Rich in bicarbonate, alkaline pH

Question 12

Why does bicarbonate secretion stop when pH is still acid (pH 5)?

Answer 12

Bile also contains bicarbonate, and helps neutralise the acid chyme Brunner’s glands secrete alkaline fluid

Question 13

What is the first step in bicarbonate secretion?

Answer 13

Catalysed by carbonic anhydride, separation of H+ and HCO3-, Na+ moves down gradient via para cellular junctions, then H2O follows.

Question 14

What is the second step in bicarbonate secretion?

Answer 14

Cl/HCO3 exchange at lumen, Na/H exchange at basolateral membrane into bloodstream Exchange is driven by electrochemical gradient as high ec Na, high Cl in lumen compared to intracellular

Question 15

What is the third step in bicarbonate secretion?

Answer 15

Na gradient into cell from blood maintained by Na/K pump, uses ATP so 1ry active transport

Question 16

What is the fourth step in bicarbonate secretion?

Answer 16

K returns to blood via K channel and Cl returns to lumen via Cl channel

Question 17

How are enzymes stored and released in acinar cells?

Answer 17

Enzymes for digestion of fat, proteins and carbs are synthesised and stored in zymogen granules

Question 18

How is trypsin activated and what effect does that have on the other proteases released?

Answer 18

Enterokinase (duodenal brush border) breaks down trypsinogen into trypsin which then activates other proteins

Question 19

How can pancreatic enzyme secretion change and what effect does this have?

Answer 19

Pancreatic secretion adapts to diet, but pancreatic enzymes are essential for normal digestion of a meal and lack of these can lead to malnutrition

Question 20

What is steatorrhoea?

Answer 20

Increased faecal fat which occurs when pancreatic lipase secretion significantly reduced

Question 21

How is pancreatic secretion controlled?

Answer 21

Vagus nerve - cholinergic, and communicates info from gut to brain

Question 22

What are the phases of control of secretion and what happens in each phase?

Answer 22

Initial cephalic phase - reflex response to smell/thought of food, enzyme rich component only, low volumes so mobilises enzymes Gastric phase - Stimulation of pancreatic secretion originating from food arriving in the stomach (same as cephalic phase) Intestinal phase - hormonally mediated when gastric chyme enters duodenum, w/both components of pancreatic juice stimulated

Question 23

How are the bicarbonate and enzymatic secretions controlled?

Answer 23

Both components separately controlled Bicarbonate controlled by Secretin (cAMP) Enzyme secretion controlled by vagal reflex and by Cholecystokinin (Ca2+/PLC)

Question 24

What other functions does cholecystokinin have?

Answer 24

Also stimulates bile secretion

Question 25

How is bicarbonate secretion controlled?

Answer 25

S cells have chemosensors in duodenum lining, which detect the pH of duodenum, and secrete secretin in blood, which travel to pancreatic duct, form HCO3 -> has a negative feedback component

Question 26

How is enzyme secretion to the duodenum from the pancreas controlled?

Answer 26

C cells on duodenum wall, secrete CCK when they detect peptides and fats, which is carried to pancreas, attach to acinar cells and they secrete proenzymes and lipases Vagus nerve also sends signal to inhibit release of proenzymes

Question 27

How is cholecystokinin switched off?

Answer 27

Turns off when meal eaten, absorption of fats and peptides removes local luminal stimulus for CCK release from mucosa

Question 28

How do CCK, vagus nerve and secretin interact together to increase bicarbonate secretion?

Answer 28

CCK alone doesn’t affect bicarbonate secretion CCK can markedly increase bicarbonate secretion that has been stimulated by secretin Vagus nerve has the same effect as CCK Secretin has NO EFFECT on enzyme secretion

Question 29

How is the pancreas developed in the embryo?

Answer 29

A foregut derivative arising at foregut-midgut junction Duodenum forms a c shape, ventral bud swings round to lie adj to the dorsal bud and both fuse together Ventral bud duct becomes the main pancreatic duct

Question 30

Where is the islet tissue most abundant?

Answer 30

In the tail

Question 31

Fill in the blanks of the pancreas divisions

Answer 31

Question 32

Where does the pancreas lie in the body?

Answer 32

Mainly on posterior abdominal wall extending from C-shaped duodenum to hilum of spleen

Question 33

What are the close relations of the pancreas?

Answer 33

Coeliac and superior mesenteric artery

Question 34

What is an adapted feature of the islets of Langherhans for endocrine function?

Answer 34

Highly vascular ensuring that all endocrine cells have close access to a site for secretion

Question 35

What is the function of the bicarbonate secretion?

Answer 35

Neutralises acidic chyme from stomach: preventing damage to duodenal mucosa, raises pH to optimum range for pan enzymes to work Washes low vol enzyme secretion out of pancreas into duodenum

Question 36

Where is the bicarbonate secretion secreted from?

Answer 36

Duct and centroacinar cells

Question 37

What would happen if the CFTR was defective when dealing with pancreatic HCO3 secretion?

Answer 37

Without CFTR, the pancreatic juices become less liquid, and can cause big problems, especially the breakdown of the pancreas

Question 38

How are proteases and trypsin released from acinar cells?

Answer 38

Proteases released as inactive proenzymes, protects acini and ducts from auto digestion Trypsin inhibitor present to prevent trypsin activation Enzymes activated ONLY in duodenum

Question 39

What happens if the pancreatic duct is blocked?

Answer 39

May overload protection resulting in auto-digestion, a.k.a. acute pancreatitis