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Secretary Functions- Pancreas Flashcards

1
Q

Pancreatic secretions: source and destination

A

The exocrine secretions of the pancreas that drain into the small bowel are derived from two distinct cells, ductal cells and acinar cells

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2
Q

Acinar secretions

A

are enzyme-rich secretions that provide the enzymes necessary for digestion for carbohydrates, proteins, nucleic acids, and lipids

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3
Q

ductal secretions

A

are HCO3 rich and neutralize acidic chyme to allow for proper function of pancreatic enzymes

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4
Q

Islets of Langerhans produce…

A

α (A) cells (20%) - Glucagon

β (B) cells (70%) - Insulin (amylin)

d (D) cells (5%) - Somastotatin

pp cells (5%) - Pancreatic polypeptide

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5
Q

pancreatic innervation (what do para and symp do?)

A

inhibited by sympathetic; stimulated by parasympathetic NS (Note from lecture: we don’t want insulin in the bloodstream during fight or flight; we need that glucose!)

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6
Q

anatomic aspects of the pancreas

A

Wirsung’s duct-major duct

Ampulla of Vater = hepatopancreatic ampulla or hepatopancreatic duct

Duct of Santorini-accessory collecting duct

Sphincter of Oddi

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7
Q

groups of acini

A

lobules

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8
Q

lumen drained by…

A

ductule–> intralobular ducts–> pancreatic duct

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9
Q

Cells of ductule & centroacinar cells produce

A

large volume of watery fluid containing Na+ HCO3-

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10
Q

Intercalated ducts-receive

A

secretions from acini

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11
Q

Intralobular ducts-receive

A

fluid from intercalated ducts

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12
Q

Pancreatic juice: divided into :

A

Aqueous bicarbonate component, enzymatic component

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13
Q

Aqueous (NaHCO3 - bicarbonate) component of pancreatic secretions

A

neutralizes HCl in chyme deactivates pepsin when H+ enters duodenum, S cells secrete Secretin, which acts on pancreatic ductal cells to increase HCO3- production prevents damage to duodenal mucosa buffers pH for maximal enzymatic activity

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14
Q

Enzymatic component of pancreatic juice

A

approx. 15 enzymes are produced

digests proteins, carbohydrates, lipids and nucleic acids when small peptides, amino acids and fatty acids enter duodenum

CCK is released by I cells, stimulating enzyme secretion

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15
Q

Composition of normal human pancreatic juice

A

Cations (Na, K, Ca, Mg, pH approx 8.0) Anions (HCO3, Cl-, SO4-2, HPO4-2) Digestive enzymes (95% of protein in juice), other proteins 80% by weight of proteins secreted are proteases 40% of proteases is trypsinogen (inactive precursor of trypsin)

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16
Q

What hormones stimulate protein secretion

A

ACh, CCK, Secretin, VIP stimulates protein secretion

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17
Q

hormones that stimulate protein secretion all increase

A

Ca 2+ (2nd messenger)

Activation of protein kinases increases acinar cell secretion

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18
Q

ACh & CCK stimulate

A

NaCl secretion, through phosphporylation of ion channels

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19
Q

Most powerful stimulas for HCO3- secretion?

A

secretin, which activates adenylyl cyclase

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20
Q

ACh stimulation of HCO3- secretion

A

ACh activates Gq, which in turn stimluates PLC to release DAG (which stimulates PKC) and IP3 (which releases Ca2+ from internal stores)

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21
Q

Secretin generates…

A

electrical gradient that favors NaHCO3 co-transport

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22
Q

Activator and Substrate: Amylase

A

a: Cl-, S: starch, glycogen

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23
Q

Activator and Substrate: Trypsinogen

A

activated to Trypsin by Enterokinase (brush border of duodenum) Enterokinase released from brush border membrane by bile salts Active trypsin once formed, acts auto-catalytically (like enterokinase) to activate trypsinogen, etc. Substrate: starch, glycogen

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24
Q

Activator and Substrate: Chymotrypsins

A

a: trypsin (Endo-peptidase), S: proteins, polypeptides, elastin, other proteins

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25
Activator and Substrate: Proelastase-Elastase
a: trypsin (endo-peptidase), S: proteins, polypeptides
26
Activator and Substrate: Procarboxypeptidase A (carboxypeptidase A)
a: trypsin (exo-peptidase), S: proteins, polypeptides
27
Activator and Substrate: Procarboxypeptidase B (Carboxypeptidase B)
a: trypsin (exo-peptidase), S: proteins, polypeptides
28
Lipase substrate
triglycerides
29
nonspecific esterase
cholesteryl esters
30
Activator and Substrate: pro-phospholipase A2- (PLA2)
a: trypsin S: phospholiids
31
Ribonuclease substrate
RNA
32
Deoxyribonuclease
DNA
33
Activator and Substrate: Procolipase (Colipase does NOT activate lipase)
a: trypsin, s: fat droplets
34
Activator and Substrate: monitor peptide
a: intestinal content, s: feedback- secretion
35
trypsin inhibitors
protects against trypsin in acinar, ductular cells
36
glycoproteins
protect against protease-mediated mucosal injury
37
Which pancreatic enzymes do not have proenzymes?
ribonucleases, amylases, lipase
38
enzyme inhibitors
Pancreas also produces enzyme inhibitors to inactivate trace amounts of active enzyme formed within.
39
Protection against enzymatic autodigestion
packaging of many digestive proteins as zymogens--\> precursor proteins lack enzymatic activity selective sorting of secretory proteins and storage in zymogen granules--\> restricts the interaction of secretory proteins with other cellular compartments protease inhibitors in the zymogen granule--\> block the action of prematurely activated enzymes condensation of secretory proteins at low pH--\> limits the activity of active enzymes nondigestive proteases --\> degrade active enzymes. Bottom line: pancreatic proteolytic enzymes are stored and secreted in an inactive form (also, a trypsin inhibitor is present in acini and duct cells). Enterokinase- located on intestinal mucosal cells.
40
Activation of pancreatic proteolytic enzymes
Proteolytic enzymes are secreted into duodenum as inactive precursors, which are activated in gut lumen. The process begins in the lumen, the duodenal brush border enzyme, enterokinase cleaves a hexapeptide from trypsinogen, converting it to active enzyme trypsin. Trypsin then catalyzes the formation of more trypsin and activates chymotrypsinogen, pro-carboxypetidases and pro-phospholipases.
41
Hormonal control of pancreatic exocrine secretion
acid in duodenal lumen --\> secretin release from duodenal mucosa (secretin carried by blood)--\> + pancreatic duct cells --\> secretion of aqueous NaHCO3 solution into duodenal lumen--\> neutralizes acid in duodenal lumen Fat and protein products --\> increase CCK release from duodenal mucosa (CCK carried by blood)--\> + pancreatic acinar cells--\> increased secreation of pancreatic digestive enzymes into duodenal lumen --\> digestion of fat and protein products in duodenal lumen
42
What is the primary stimulant of fluid and electrolyte secretion in the pancreas?
Secretin
43
What is the primary stimulant of enzyme secretion in the pancreas?
CCK
44
What is the primary factor in regulation of amount of fluid and HCO3- secretion by the pancreas?
Amount of acid entering the duodenum
45
What determines the amount of enzyme secretion by the pancreas?
quantity of fat and protein entering the duodenum
46
4 things that regulate overall pancreatic secretion
ACH, CCK, Secretin, vagovagal reflexes Intestinal stimuli promote most secretions, but stimuli during cephalc and gastric phases also promote secretion.
47
ACh stimulates
acinar secretion and potentiates the Action of CCK by vagovagal reflexes
48
why is it important to neutralize the acid in the duodenum?
stop duodenal ulcers pancreatic lipase is inactivated at low pH-- need to digest the fat others?
49
What receptors do acinar cells of the pancreas have? What about ductal cells?
Acinar cells: CCK (CCK-A) and Ach (M) Ductal cells: CCK, ACh, secretin
50
What potentiate the effects of secretin?
CCK and ACh
51
What's the most important stimulant for enzyme secretion during the intestinal phase?
CCK
52
What cells are stimulated to secrete CCK, and what stimulates them?
I cells stimulated by the presence of amino acids, small peptides an fatty acids in the duodenum
53
Role of CCK in pancreatic exocrine secretion
CCK- potent stimulus of acinar secretion acts on CCK-B receptors via stimulation of vagal afferents duodenum vago-vagal refelxes stimulate cholinergic (ACh) and noncholinergic (GRP, VIP) NTs HCO3- secretion from ductular cells potentiates secretin effect of HCO3- secretion
54
CCK effects on digestive system outside of pancreas
CCK has multiple effects in duodenal cluster - coordinates GI activity (secretion) to food - contracts gall bladder - relaxes the sphincter of Oddi - slows gastric motility - retards gastric emptying
55
CCK released in response to...
CCK-RP is released in response to fatty acids, aromatic amino acids, etc. into duodenum large quantities of proteins in duodenum, CCK are released by CCK-PR and MP
56
What controls release of CCK?
monitor peptide (MP) and CCK-RP controls release of CCK
57
CCK effects
Bottom Line: increases enzymatic secretion from pancreas More detail: ØCCK- potent stimulus of acinar secretion Ø acts on CCK-B receptors Ø via stimulation of vagal afferents duodenum Ø vago-vagal refelxes stimulate cholinergic (ACh) and noncholinergic (GRP, VIP) NTs Ø HCO3- secretion from ductular cells Ø potentiates secretin effect of HCO3- secretion ØCCK has multiple effects in duodenal cluster Ø coordinates GI activity (secretion) to food Ø contracts gall bladder Ø relaxes the sphincter of Oddi Ø slows gastric motility Ø retards gastric emptying
58
What happens to CCK when little or no protein in diet?
trypsin degrades the peptides (CCK-RP/MP) and terminates the release of CCK
59
When too much protein in the diet...
both protein and peptides (CCK-RP/MP) compete for trypsin and other proteolytic enzymes and both are are degraded slowly
60
Monitor peptide
There's a red box around it, so it must be important.
61
Role of secretin in pancreatic exocrine release
²Secretin released from S cells in duodenal mucosa, stimulates pancreatic ductular cells when acidic chyme enters duodenum to neutralize H+ ²pancreatic secretions volume increases from low volume protein rich fluid to high absolute volume ²as the secretory rate rises, the pH and bicarbonate concentration also rises concentrations of Cl- and HCO3- are inversely related to those of Na+ and H+ in stomach
62
Achlorhydric
= (unable to secrete gastric acid) ## Footnote secondary to disease - on drugs, proton pump inhibitors, bicarbonate fail to release secretin even in presence of a fatty meal
63
pancreatic secretions falling below 10%--\>
signs of malabsorption and indigestion
64
Factors causing secretin release
* S cells in duodenal mucosa acts as pH meters * S cells secretes secretin when pH falls due to entry of acidic chyme •Secretin binds to receptors on - pancreatic ductular cells - epithelial cells lining bile ducts - duodenum * Cells stimulate to secrete HCO3-in duodenum * Increase in pH will inhibit secretin release Fatty acid meals evoke secretin release Secretin release is sensitive to pH
65
Stages of pancreatic secretion
Cephalic phase: secretions from acinar cells & Gastric phase secretions are low in volume, high conc of digestive enzymes cholinergic vagal input during cephalic phase vago-vagal reflexes by gastric distention during gastric phase Intestinal phases: secretions from ductular cells and acinar cells secretions high volume with decreased conc of proteins secretin stimulates basolateral duct epithelial cells CCK, ACh, GRP stimulates acinar cells
66
Stimulants and regulatory pathways of the stages of pancreatic secretion
Cephalic: Sight, smell, Vagal pathways Taste, Mastication Gastric: Distention, Vagal-cholinergic Gastrin? Intestinal: Amino acids, Cholecystokinin Fatty acids Secretin H+ Enteropancreatic reflexes
67
most common causes of pancreatitis
alcohol abuse and gallstones
68
cystic fibrosis and the pancreas
genetic disease, disorder of pancreatic secretion that results from a defect in Cl- channel that is caused by a mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. This results in a thick secretions into the pancreatic duct that may obstruct the duct and cause pancreatic insufficiency
69
steatorrhea
feces may float, have an oily appearance, and be particularly foul-smelling. These patients are often treated with supplementary pancreatic enzymes. fat in the stool-early sign of pancreatic dysfunction 60% fat and 30-40% proteins and carbohydrates not absorbed reduced pancreatic enzyme (lipase) and bicarbonate secretion low pH inactivates lipase
70
pancreatitis (acute and chronic)
retention of secretion in pancreas leads to autodigestion of pacreatic tissue obstructive (gallstone occluding pancreatic duct, or a malignancy)-acute hereditary-expression of a mutated trypsin molecule that is resistant by trypsin inhibitors. Trypsin digests pancreatic tissue-chronic inflammation of the pancreatic tissue (alcohol abuse)-chronic
71
drugs and toxins causing pancreas pathophysiology
Immunosuppresants, anticonvulsants, thiazides
72
autoimmune diseases causing pancreas pathophysiology
celiac disease, IgG4,
73
genetic abnormalities causing pancreas pathophysiology
weak SPINK1, CFTR, CTRC genes and insult by alcohol, gallstones, etc may precipitate pancreatitis – both acute and chronic
74
cystic fibrosis and pancreas pathophysiology
autosomal recessive genetic mutation in the CFTR Cl channel Primarily affects caucasians Lack chloride transporter at apical membrane Leads to decreased water, HCO3, & Cl excretion, with concentration of protein in acinar ducts and blockage…. gland autodigestion/destruction Progressive pulmonary and pancreatic insufficiency - chronic
75
Kwashiorkor
--\> reduction in pancreatic secretion except amylase
76
diabetes and the pancreas
Reduced pancreatic enzyme secretion in the absence of pancreatic disease

GI part 2 (16 decks)

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