Stages & regulation of pancreatic secretion

1Prof .Dr. Rashid Mahmood

A 25-year-old woman has persistent diarrhea, steatorrhea (fatty stools), and abdominal pain. An upper gastro-intestinal radiological series suggests a growth/ tumor beneath the stomach.Serum Amylase is raised.What is the probable cause of her symptoms? What dietary restrictions are required ?

Pancreatic Secretions:Regulation & Phases


Objectives• Goal/ Aim• By the end of this session students should be able to

understand the Phases and Regulation of Pancreatic Secretion

• Specific objectives• Student should be able to

Describe the Phases of Pancreatic secretionDescribe the Regulation of Pancreatic Secretion List the Factors affecting Pancreatic Secretion Identify the major hormones, and key neurotransmitters/

nervous pathways of gastrointestinal system


Lesson contents• Pancreatic Digestive Enzymes• Secretion of Bicarbonate Ions• Phases of Pancreatic secretions• Regulation of Pancreatic Secretion• Basic Stimuli that Cause Pancreatic Secretion• Multiplicative Effects of Different Stimuli • Hormones & neurotransmitters of

gastrointestinal system that control Pancreatic Secretions


Review: Components of Pancreatic

Secretion1. Exocrine

i. Digestive enzymes• Secreted by acinar cells

ii. HCO3- -• Secreted by duct cells

2. Endocrinei. Insulinii. Glucagon

Contd……


Pancreatic SecretionExocrine

+EndocrinePapilla of Vater &

Sphincter of Oddi


Pancreatic Digestive Enzymes• For digestion of Proteins

TrypsinChymotrypsinCarboxypeptidase Elastase

• For digestion of CarbohydratesPancreatic Amylase

• For digestion of FatsLipaseCholesterol EsterasePhospholipase Colipase (Activated by Trypsin)Bile salt activated Lipase

About 1 liter per day


For digestion of Proteins(Trypsin, Chymotrypsin, Elastase,

Carboxypeptidase) • Inactive (Proenzymes)

Trypsinogen, chymotrypsinogen, procarboxypolypeptidase

• Trypsin, Chymotrypsin, Elastase → Endopeptidases• Carboxypolypeptidase → Exopeptidases

Chyme Intestinal mucosa Enterokinase

Activation of Proenzymes inside lumen of intestine

Mechanism of stimulation of proenzymes

Contd…..


Trypsinogen Trypsin

Chymotrypsinogen Chymotrypsin

Procarboxypeptidase Carboxypeptidase

Enterokinase (Intestinal Mucosa)

Mechanism of stimulation of proenzymes


HCO3 - - Secretion by Pancreas

• Functions of HCO3 - - in duodenum1.To neutralize acidic pH of Stomach as the

duodenum cannot resist acidic pH 2.To block the peptic digestive activity of the

gastric juices3.To provide a appropriate pH for pancreatic

digestive enzymes


Assessment Q. 1• List 3 sources of HCO3 - -ions in duodenum

that help neutralize Gastric Acid.


Phases and Regulation of Pancreatic Secretion


Phases of Pancreatic Secretion •Three phases:

Cephalic phaseGastric phaseIntestinal phase.


1. Cephalic Phase (20%)

1,

2

3

2. Gastric Phase (10%)

3. Intestinal Phase (70%)

Phases of Pancreatic juice (Enzymes) secretion


Cephalic Phase of Pancreatic Secretion

• The same nervous signals from the brain that cause secretion in the stomach also cause acetylcholine release by the vagal nerve endings in the pancreas.

• 20 per cent of the total secretion of pancreatic enzymes

• But little of the secretion flows immediately through the pancreatic ducts into the intestine because only small amounts of water and electrolytes are secreted along with the enzymes.


Gastric Phase of Pancreatic Secretion

• Nervous stimulation of enzyme secretion continues

• Another 5 to 10 per cent of pancreatic enzymes

• But, again, only small amounts reach the duodenum because of continued lack of significant fluid secretion.


Intestinal Phase of Pancreatic Secretion

• Chyme enters the small intestine, pancreatic secretion becomes copious, mainly in response to the hormones

1.Cholecystokinin: Digestive Enzyme Secretion 65 to 80 per cent

2.Secretin: Secretion of Copious Quantities of Bicarbonate Ions—Neutralization of Acidic Stomach


Assessment Q. 2• Name the 3 Phases of Pancreatic

secretion


Regulation of Pancreatic Secretion

1. Nervous regulation2. Hormonal regulation


Regulation of Pancreatic Secretion

1

43

2


Hormone Site of secretion

Stimulus Function

Secretin “S” cells of duodenum

Acidic gastric juice 1.Mild effect on GIT motility(↓)2.Pancreatic secretion of bicarbonate3.Bicarbonate secretion by Bile duct

Cholecys-tokinin

“I” cells of duodenum & jejunum

Digestive products of fats, fatty acids & monoglycerids

•Strong contraction of gall bladder•Inhibition of stomach contraction•Pancreatic secretion of enzymes

Hormonal control of pancreatic secretion

Contd…..


Hormonal control of pancreatic secretion


Stimuli/ factors that stimulate pancreatic secretion

• AcetylcholineParasympathetic stimulation

• CholecystokininFats

• Secretin Acid and proteins in duodenum→ HCO3 by

Ducts

} Acinar cells

Enzymes


Assessment Q. 3• Name 3 stimuli/ factors that stimulate

pancreatic secretion


Summary• Pancreatic juice contains enzymes, ions, and water.• Pancreatic secretions are regulated in an integrated fashion

by endocrine and nervous system in response to signals coincident with the intake of meals.

• Pancreatic secretions are produced in Three phases:• In Cephalic phase, Acetylcholine (Parasympathetic

stimulation) causes Acinar cells to secrete Enzymes• Gastric phase has same effects as Cephalic phase • Enzymes produced in Gastric and Cephalic Phases are

generally not released into intestine until Water and ions including Bicarbonate are released in Intestinal phase by Secretin

• In Intestinal phase hormones Secretin and Cholecystokinin are released in response mainly to Acidic Chyme and fats in upper duodenum respectively


Resources 1. Guyton and Hall (Text book of physiology), 13th Edition2. Ganong (Text book of physiology), 24th Edition3.Berne & Levy Principles of Physiology (Koeppen BM), 6th Edition4. Human Physiology Stuart Ira Fox, 13th Edition5. Human Physiology : from cells to system Lauralee Sherwood, 9th Edition 6. Internet


Assessment Q. 4What are the latest additions of following Physiology books?1.Guyton and Hall2.. Ganong3.Lauralee Sherwood,


The End, Questions ?

Stages & regulation of pancreatic secretion

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