GIT Physiology: pancrease & biliary secretions.

1. Gastrointestinal physiology
GIT Secretions (Cont).
Dr.M.A.M.Shaikhani.

2. Pancreatic secretions:
• Pancreas; complex gland ( similar to salivary glands)
Except of having an Endocrine part(secreting insulin&
glucagons)
• Digestive part which consist of acini secreting digestive
enzymes :
• 1.Pancreatic lipase: for digesting fats.
2.Pancreatic Amylase: for
digesting carbohydrates.
3.Pancreatic
Trypsin,chymotrypsin,carboxypolypeptidase,elastase &
neuclease: for digesting proteins.
• All Secreted in an inactive form in the acini inside
pancrease :
• (trypsinogen,chymptrypsinogen,procarboxypolypeptidas
e) to prevent autodigestion of pancreas & this
inactivation is facilitated by a substance called trypsin

3. Pancreatic secretions:
• When this trypsin inhibitor is overwhelmed by
pancreatic duct obstruction or pancreatic diseases or
damag,e the proteolytic inactive enzymes are activated
inside pancreatic acini leading to acute pancreatitis
causing death or pancreatic insufficiency.

4. Pancreas
• Endocrine
– Insulin,glucagon
• Exocrine
– Enzymes
(acini)
– Bicarbonate
(ducts)

5. Activation of Pancreatic Enzymes:
• Inactive panc enzymes are only activated when they reach the SI .
• by an enzyme released from SI cells; enterokinase stimulated by
the presence of chyme.
• 1st
enzyme activated is trypsinogen to active trypsin & trypsin in
turn activates the other enzymes: CTP&PCP.
• Pancreatic ductioles & ducts secreting HCO3 important for
neutralizing the acid of the chyme coming to the upper SI from
stomach & for preparing the optimal alkaline medium essential
for digestion in SI.

6. Regulation of pancrearic secretion:
• I by vagi(ACH), Cholycystokinin(CCK) & Secretin.
• ACH, Cholycystokinin(CCK) :cause secretion of mainly digestive
enzymes
• While Secretin causes mainly secretion of large amounts of
HCO3.
• Secretin released from upper SI cells ( S cells) in the presence of
acidic chyme causes secretion of large amounts of HCO3 from
pancreatic ducts( for neutralization of acidic chyme coming from
stomach resulting in formation of Nacl & water)
• Secretion of pancreatic enzymes mainly under the control of CCK
which is secreted by SI cells (I-cells) in response to the presence of
food in upper SI specially protein&fat digestion end
products(peptones, proteoses & long chain fatty acids. )
• Vagal stimulations helps both processes but the effects of Secretin
& CCK are more pronounced.

7. Phases of pancreatic secretion:
The same for of gastric acid secretion:
1.cephalic phase. 2.gastric phase. 3.intestinal phase.

9. Bile secretion:
•It helps :
• Fat digestion by saponification & emulsification of fats.
• Essential for excretion of several important waste products from
blood as billirubin & cholesterol.
•The amount is 1000ml./day.
•Composition of bile :about 50% are bile salts + billirubin,
cholesterol,lecithin & plasma electrolytes.
•In the gall bladder water & large amounts of electrolytes except
Ca++ are reabsorbed by gall bladder mucosa, but the other
constituents bile salts,cholesterol & lecithin are not reabsorbed so
become highly concentrated.

10. Figure 24.21a, b
The Gallbladder

11. Figure 24.21a, b
Bile Salts and Emulsification
fat
globule
Water (polar)
bile
salts
fat droplets
bile salt
phospholipids
triglycerides
Increases surface
area for attack
by lipases.
polar coating

12. Emptying of gall bladder:
• Needs:
• Contraction of gall bladder wall & relaxation of
sphincter of oddi(SOO)
• CCK plays an important role in contraction of gall
bladder wall & to less degree relaxation of (SOO)
• Relaxation of (SOO) mainly in response to movement of
the wall of upper SI.

14. Bile salts & their functions:
• 0.6gms. is secreted /day.
• Synthesized from cholesterol which is converted to cholic acid &
chenodeoxycholic acid & both combine with glycin or taurin to
form glyco or tauro conjugated bile acids.
• Functions:
• The main functions is :
• 1.Emulsificatin of fats to form micelles to facilitate Fat absorption
• 2.Secretion of some important waste products as billirubin &
cholesterol.
• The enterohepatic circulation of bile salts from the SI is through
the terminal ileum TI to the liver then to SI again ,so in TI disease
or removal, this enterohepatic circulation of bile salts is
interupted causing bile salts deficiency and so fat malabsorption.
• The hormone Secretin causes secretion of HCO3 & not bile acids
from the bile ductioles for neutralization of excess acid coming
from stomach in cooperation with the pancreatic HCO3.
• CCK causes secretion of bile& bile acids.

15. Gall
bladder
Cholesterol
Large
intestine
Ileum Duodenum
Liver
Bile
salts
StomachBile
salts
Bile
salts
Bile
salts
Bile
salts
Bile
salts
Sphincter
of
Oddi
Portal
circulation
These salts are reabsorbed in the ileum and returned to
the liver where they are once again secreted into bile
 only 3-4 g of bile salts in body, thus highly recycled
=
active transport

16. Gall stones formation:
• Is mainly due to imbalance between bile salts & cholesterol
content of bile ,either more cholesterol or less bile salts so excess
cholesterol will precipitate to form cholesterol gall stones.
• Causes of gall stones:
• 1.Too much absorption of water to form concentrated bile easy to
precipitate.
• 2.Too much absorption of bile acids.
• 3.Too much secretion of cholesterol into the bile mainly from diet.
• 4.Inflamation of gall bladder epithelium.
• Medical therapy of gall stones:
• Although the mainstay of gall stones therapy is surgery,sometimes
the patient is given bile salts in form of ursodeoxycholic acid or
chenodeoxycholic acid for at least 1 year, which help in
redissolution of cholesterol gall stones by increasing the ratio of
bile salts in relation of cholesterol.

17. Secretions of SI:
• Of 3 types:
• 1.Brunner glands for mucose secretion.
• 2.Crypts of Liberkhan for secretion of pure extracellular fluid to
aid absorption of intestinal contents by active secretion of HCO3
& Cl- into the crypts these cause osmotic movement of water.
• 3.SI enzymes present on villi brush border consisting of;
• A.Several different peptidases for splitting peptides into amino
acids.
• B.Several disaccharidases as sucrase,maltase,isomaltase and
lactase.
• C.Small amounts of intestinal lipase for splitting neutral fats into
glycerol & fatty acids.
• The regulation of SI secretions is by local enteric stimuli through
local enteric reflexes and hormonal secretions specially Secretin &
CCK.

18. Large intestinal secretions:
Are:
• 1.Mucose secreted by mucose cells in colonic wall .
• The mucose protects the colonic wall from excoriation & bacterial
activity and provides an adherent medium for holding feces
together.
• 2.HCO3 by crypts of Liberkhan ,stimulated by tactile stimuli &
pelvic PS nerves.
• The HCO3 protects the colonic wall from acids formed deep in
the feces by intestinal flora.
• No Enzymes in the colon & no digestion.

19. MCQs:
Pancrease:
A. Is the only gland that contain all the 3 major digestive enzymes.
B. The proteolytic enzymes are active inside the pancrease.
C. Is the same as salivary glands.
D. Its Enzyme secretions is under hormonal control only.
E. Is the main source of Lipase in GIT.

20. MCQs:
Lipase:
A. Is present only in the pancrease.
B. Small amounts is present in saliva.
C. Small amount is present in the stomach.
D. Is absent on the small intestinal brash boarders.
E. Bile is essential for its action.

21. MCQs:
Match the following:
A.Secreten. F. Contraction of gall bladder.
B. Enterokinase. G.Inhibits proteolytic enzymes.
C. Trypsin inhibitor. H. Activates proteolytic enzymes.
D. CCK. 1. Stimulates pancreatic bicarbonate.
E. Bile acids. J. Inhibt cholesterol precipitation.

22. MCQs:
CCK Actions include:
A. Pancreatic enzymes secretion.
B. Pancreatic enzymes activation.
C. Pancreatic bicarbonates secretion.
D. Bile secretion stimulation.
E. Gall bladder contraction.

23. MCQs:
Bile acids:
A. Help digestion of fat.
B. Consumed in fat digestion.
C. Is in continuous enterohepatic circulation.
D. Prevent gall stone formation.
E. Have many therapeutic uses .

24. MCQs:
Small intestinal villi brush boarders contain the following enzymes:
A. Peptidases.
B. Disacharidases.
C. Lipase.
D. Amylase.
E. Gelatiase.