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Physiology 1 Semester 2 > Pancreatic Exocrine Secretions and Control > Flashcards

Pancreatic Exocrine Secretions and Control Flashcards

1
Q

State the secretions produced by the pancreas

A
  • Duct cells secrete NaHCO3
  • Pancreatic islet cells secrete hormones - insulin from beta cells, glucagon from alpha cells and somatostatin from delta cells
  • Acinar cells secrete digestive enzymes
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2
Q

What cells form the exocrine portion of the pancreas?

A

Acinar cells

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3
Q

Where do the secretions travels through once secreted?

A

Secretions go from intercalated ducts -> intralobular ducts -> extralobular ducts -> interlobular ducts -> main duct

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4
Q

State briefly the effect of secretin and CCK on the pancreas

A

CCK effects acinar cells and causes them to secrete digestive enzymes - done when there is lipid heavy chyme in the duodenum

Secretin acts on duct cells and causes them to secrete aqueous NaHCO3 solution - done when there is acidic chyme in the duodenum

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5
Q

Describe the structure of the pancreas including the cells of the ducts

A
  • Acinar - berry like secretory portion similar to a grape- duct resembles the stalk - is primarily pyramidal epithelial cells
  • Microvilli extend from the apical surface of the epithelium into the lumen of the acini
  • Acini form sacs - connect to the ductal tree - empties into the duodenum
  • Intercalated ducts - squamous/cuboidal epithelial cells
  • Intralobular ducts - cuboidal or low columnar epithelial cells
  • Extralobular ducts - columnar epithelial cells
  • Interlobular ducts - columnar epithelial/goblet cells
  • Pancreatic duct which enters the duodenum at the common bile duct
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6
Q

How much solution does the pancreas secrete a day?

A

1.5L of fluid a day

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7
Q

In what form are enzymes secreted in and why?

A

Inactive form (zymogens) to prevent auto digestion

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8
Q

Where are pancreatic enzymes activated?

A

Duodenum

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9
Q

State the anions and cations present in the pancreatic juice

A

Anions that are secreted in the pancreatic juice - HCO3-, Cl-, SO4 2-, HPO4 2-

Cations that are secreted in the pancreatic juice - Na+, K+, Ca2+, Mg2+

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10
Q

State the alkaline secretions of the pancreas

A

HCO3- rich juice from the pancreas and gallbladder help to neutralise gastric acid so pH increases from 6 to 7

Secretion from pancreas is similar to that in salivary glands but it is a HCO3- rich juice

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11
Q

Describe how composition of pancreatic juice changes through the duct

A
  • Epithelial cells actively exchange Cl-/HCO3- - Cl- comes into the duct cell and -HCO3- goes out of the duct cell
  • H+ is actively eliminated by Na+/H+ exchanger - H+ exits the duct cell and Na+ enters the duct cell via the exchanger
  • H+ is exchanged for K+ driven by Na+/K+ ATPase- Na+ exists the duct cell and K+ enters the duct cell
  • H+ neutralises HCO3- (H2CO3 forms)
  • CO2 and HCO3- are produced in the blood
  • CO2 diffuses in and forms H2CO3 with H2O
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12
Q

What is concentration of HCO3- in the pancreatic juice proportional to?

A

The concentration of HCO3- in the blood

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13
Q

Describe a study in which secretin was given to an experimental animal and state what effects it had on HCO3-, Cl-, amylase and K+

A
  • The concentration of HCO3- increases significantly
  • The concentration of Cl- decreases
  • The concentration of amylase decreases slightly
  • The concentration of K+ decreases slightly
  • Hence there is a reciprocal change in concentrations of Cl- and HCO3- upon secretin infusion
  • Reduced amylase and Cl- concentrations upon secretin infusion may be a dilution effect due to the increase in volume of the secreted pancreatic juice
  • This is because the stimulated pancreas causes an increase of [HCO3-] rich secretions
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14
Q

State the enzymes that are secreted from the pancreas

A
  • Proteolytic enzymes (trypsin, chymotrypsin and carboxypeptidases)
  • Amylase
  • Lipase
  • Ribonuclease
  • Deoxyribonuclease
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15
Q

What is the activator and substrate for trypsin?

A

Activator - Secreted as trypsinogen activated by enterokinase/enteropeptidase and by trypsin

Substrate - Proteins and polypeptides

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16
Q

State the substrate of lipases

A

Triglycerides

17
Q

State the activator and substrate of pancreatic alpha amylase

A

Activator - Activated by Cl-

Substrate - Starch

18
Q

State the substrate of ribonuclease and deoxyribonuclease

A

Ribonuclease - RNA
Deoxyribonuclease - DNA

19
Q

State the activators and substrates of elastase and phospholipase A2

A
  • Elastase -
    Activated by trypsin
    Elastin
  • Phospholipase A2 -
    Activated by trypsin
    Phospholipids
20
Q

State the activator and substrates of chymotrypsins

A

Activator - Secreted by chymotrypsinogen, activated by trypsin

Substrate - Proteins and polypeptides

21
Q

State the activators and substrates of carboxypeptidase A/B and colipase

A

Carboxypeptidase A/B -
Activated by trypsin
Proteins and polypeptides

Colipase -
Activated by trypsin
Fat droplets in concert with pancreatic lipase

22
Q

What are proteolytic enzymes secreted as and why?

A
  • Enzymes secreted as proenzymes
  • Digestion of proteins so the pancreas is at risk of autodigestion
23
Q

Describe where enterokinase is secreted, why it is secreted and what it does

A
  • In the brush border of duodenum
  • Secreted in response to CCK
  • Converts trypsinogen to trypsin
  • Trypsin causes an auto acatalytic chain reaction (auto activation and activation of other proenzymes)
24
Q

What are inhibitors of autodigestion?

A

Kazal inhibitor, enzyme Y

Intracellular pH of zymogen granule - acidic to keep zymogens inactive

25
Q

What happens during acute pancreatitis?

A
  • Trypsin activates phospholipase A2 in the pancreatic duct
  • This causes the conversion of lecithin to isolecithin
  • Isolecithin causes disruption of pancreatic tissue, membrane damage and necrosis
26
Q

Describe what amylase does

A
  • Active
  • CHO digestion
  • Polysaccharides -> disaccharides
27
Q

Describe what lipases do

A
  • Fat digestion - triglycerides -> fatty acids and glycerol
  • Pancreatic insufficiency - poor digestion of lipids and their malabsorption which causes steatorrhoea (fatty stool)
28
Q

State the % of amylase, trypsin and lipase that reach the small intestine

A
  • Amylase- 75%
  • Trypsin 20%
  • Lipase 1%
29
Q

Describe how pancreatic secretions and controlled including in the 3 phases

A
  • Neuroendocrine signals - neural and hormonal factors
  • Vagal (parasympathetic) stimulation - enhances the rate of secretion of enzymes and aqueous components of pancreatic juice
  • Sympathetic stimulation inhibits secretion
  • Secretin and CCK stimulate secretion of pancreatic fluid (bicarbonate and enzyme rich secretions respectively)
  1. Cephalic phase - vagal (acetylcholine and VIP) stimulation of gastrin release from the antrum - some enzyme rich pancreatic juice
  2. Gastric phase - distension (vago vagal reflex on fundus or antrum) , amino acids and peptides in the antrum stimulate gastrin secretion causing the release of enzyme rich pancreatic juice (shown by the fact that a vagotomy causes a 50% reduction in response to acidic chyme)
  3. Intestinal phase - secretin and CCK; enterohepatic reflexes - acidic chyme in duodenum and jejunum induce secretion of pancreatic juice (HCO3- and enzymes) - H+ stimulates S cells in duodenum to secrete secretin which acts on duct cell receptors to cause HCO3- secretion - protein+lipid breakdown stimulates I cells to secrete CCK which acts on acinar cells to cause secretions
30
Q

Summarise the actions of secretin and CCK

A

Secretin - from mucosa of duodenum and jejunum
- Induces pancreatic duct cells to secrete HCO3- rich pancreatic juice but decreases enzyme content
- Secretin also stimulates production of bile by the liver

CCK from duodenum and jejunum in response to fatty acids (amino acids and peptides)
- Stimulates pancreatic acinar cells to synthesise and release enzyme rich pancreatic juice (and stimulates the secretion of concentrated bile from gallbladder for fat absorption)
- CCK contracts the gallbladder and relaxes the sphincter of Oddi - bile is released into duodenum
- CCK potentiates the effects of secretin which is a weak agonist of acinar cells

31
Q

Describe why those with cystic fibrosis have GI issues

A
  • Causes the pancreatic ducts to become blocked due to thick mucus build up
  • The bicarbonate rich pancreatic secretions therefore cannot enter the duodenum
  • Hence food is not digested and broken down properly as there are less enzymes in the duodenum
  • This has a knock on effect in the intestines as they are unable to fully absorb all the nutrients

Physiology 1 Semester 2 (50 decks)

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