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sem 2 Liver and GI > Pancreatic exocrine secretion and its control > Flashcards

Pancreatic exocrine secretion and its control Flashcards

1
Q

where does the pancreas lie?

A

close to the duodenum and under the liver

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2
Q

the secretions from the pancreatic duct join with what?

A

join with the secretions coming from the gall bladder and liver via the common bile duct

common bile duct joins with the pancreatic duct to form the ampulla of Vater

these secretions are emptied into the duodenum

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3
Q

what controls the secretions going into the duodenum?

A

sphincter of Oddi

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4
Q

when will the sphincter of Oddi relax?

A

if there is acidic chime or lipid containing chyme in the duodenum

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5
Q

what is special about the pancreas?

A

its an endocrine and exocrine gland

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6
Q

explain the endocrine and exocrine potions of the pancreas

A

endocrine portion - islets of langerhans

exocrine portion - composed of the acinar and duct cells

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7
Q

acinar cells

A

cells secrete pancreatic digestive enzymes which are used to breakdown carbohydrates, fats, proteins and nucleic acids

stimulated by CCK

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8
Q

duct cells

A

secrete aqueous NaHCO3 solution

stimulated by secretin

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9
Q

islets of langerhans

A

primary component of endocrine pancreas

clusters of endocrine cells located throughout the pancreas, but most abundant in the tail of the pancreas

secrete hormones into bloodstream

insulin, glucagon, somatostatin

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10
Q

ampulla of Vater

A

where secretions of the pancreas and secretion of the gall bladder (and liver) join before sphincter of Oddi

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11
Q

are the bicarbonate rich secretions that duct cells secrete similar to saliva?

A

identical

except there is far more bicarbonate in the duct cell secretions

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12
Q

bicarbonate secretions from duct cells are under the influence of what?

A

secretin

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13
Q

enzyme secretion from acing cells are under the influence of what?

A

CCK

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14
Q

structure of acinar cells

A

pyramidal in shape

arranged as acini (clusters of cells resembling a many-lobed berry)

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15
Q

the acini form what?

A

sacs which connect to the ductal tree and will eventually empty their contents into the duodenum

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16
Q

what ducts begin within the acini?

A

intercalated ducts, and the duct cells are called centroacinar cells

form the smallest members of the pancreatic duct system

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17
Q

what do the intercalated ducts drain into?

A

intralobular ducts (which are lined with cuboidal epithelium)

intralobular ducts then lead into larger interlobular ducts in surrounded by columnar epithelium

these lead onto the pancreatic duct

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18
Q

what might happen to the pancreatic juices as they flow through the ducts?

A

composition may be changed

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19
Q

how much fluid does the pancreas secrete every day? what does the fluid consist of?

A

1.5L

consists of sodium and HCO3- juice, albumin, globulin and digestive enzymes

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20
Q

in what form are the enzymes in the acing cells secreted and why?

A

secreted in an inactive form (zymogen, trypsinogen), to prevent auto digestion

this is because if they were active they would start digesting the pancreas and damaging other cells

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21
Q

where are the enzymes released by acinar cells activated?

A

duodenum

22
Q

name anions that are secreted in the pancreatic juice

A

HCO3-, Cl-, SO42-, HPO42-

23
Q

name cations that are secreted in the pancreatic juice

A

Na+, K+, Ca2+, Mg2+

24
Q

role of somatostatin

A
  • inhibits production of insulin and glucagon

- inhibits gut peptides, secretin, CCK, gastrin and motilin

25
Q

why is HCO3- rich hypertonic juice important?

A

really need to neutralize the acidic chyme

26
Q

how HCO3- is taken up by epithelial cells of the pancreas

look at notes

A

structure is:

lumen – duct cell – blood

  • epithelial cells actively exchange Cl- for HCO3- (HCO3- enters lumen from duct cells and Cl- leaves lumen into duct cell)
  • H+ is actively eliminated into blood from the duct cell, more CO2 and HCO3- are produced in the blood as a result
  • H+ is exchanged for K+ and Na+ (they enter the duct cell)
  • H+ neutralizes blood HCO3-, forming H2CO3
  • CO2 and HCO3- are produced in the blood
  • CO2 diffuses into lumen from blood, and forms H2CO3 with H2O
27
Q

[HCO3-] in the blood is proportional to what?

A

[HCO3-] in pancreatic juice and its rate of production

28
Q

if the rate of HCO3- secretion is low, what happens?

A

the fluid produced is mainly by the intralobular ducts

29
Q

If you give someone secretin IV what happens?

A

increase in HCO3- and decrease in Cl-, but both go back to base levels

there is a reciprocal relationship

30
Q

major types of enzymes released from pancreas

A

ϖ Proteolytic enzymes (trypsin released as trypsinogen, chymotrypsin, carboxypeptidase)

ϖ Amylase (activated by Cl-, hydrolyses starch into maltose)

ϖ Lipase

ϖ Ribonuclease

ϖ Deoxyribonuclease

31
Q

what happens in acute pancreatitis

A

level of pancreatic alpha amylase is increased

-this is a useful diagnostic test

32
Q

if the enzymes weren’t released as proenzymes why would this be bad?

A

the pancreas would be at risk of autodigestion

33
Q

how is trypsinogen converted to trypsin?

A

trypsin by the enterokinases within the brush border

34
Q

trypsin is autocatalytic, what does this mean?

A

autoactivation of other proenzymes

35
Q

Amylase

A

involved in carbohydrate digestion, converting polysaccharides to disaccharides

36
Q

Lipases

A

important in fat digestion, converting triglycerides to fatty acids and glycerol

37
Q

pancreatic insufficiency of lipase will lead to what?

A

malabsorption of fats = steatorrhea (fat in faeces)

38
Q

chymotrypsin C dual role

A

high [Ca2+] of duodenum, allows activation of trypsinogen

low [Ca2+] of duodenum, it facilitates trypsin degradation

39
Q

percentage of secreted enzymes that reach the small intestine

A

Amylase -> 75%
Trypsin -> 20%
Lipase -> 1%

Digestive enzymes have the capacity to survive different lengths of time in the small intestine

40
Q

what do some foods contain (example)?

A

inhibitors of digestive enzymes

e.g. soybeans contain Bowman-Birk inhibitor which stops trypsin and chymotrypsin activities

41
Q

what is controlling pancreatic secretions?

A
  • neuroendocrine signals play a role
  • vagal (parasympathetic) stimulation enhances the rate of secretion of enzymes and the aqueous components of pancreatic juice
  • this vagal reflex may be initiated by distension of the duodenum
  • sympathetic stimulation inhibits secretion! this is may be due to decreased blood flow
  • key mediators are secretin and CCK, stimulate secretion of pancreatic fluid
42
Q

different phases of secretion

A
  1. Cephalic phase
  2. Gastric phase
  3. Intestinal (duodenal) phase
43
Q

cephalic phase

A

when we see/smell food there is vagal (Ach and VIP) stimulation of gastric release from the antrum

this going on seems to promote some enzyme-rich pancreatic juice

44
Q

gastric phase

A

distension and amino acids/peptides in antrum stimulates gastrin release

this also seems to promote secretion of enzyme-rich pancreatic juice

45
Q

intestinal phase

A

under the influence of secretin and CCK

Acidic chyme in duodenum and jejunum induces secretion of pancreatic juice

46
Q

where is secretin released from and what does it do?

A
  • mucosa of duodenum and jejunum
  • induces pancreatic duct cells to secrete HCO3- rich pancreatic juice, but ↓ enzyme content
  • stimulates production of bile by the liver
  • secretin effects are amplified by CCK
47
Q

where is CCK released from and what does it do?

A

released by duodenum and jejunum in response to FATTY ACIDS(amino acids, and peptides)

  • stimulates pancreatic acinar cells to synthesise and release enzyme-rich pancreatic juice
  • stimulates the secretion of concentrated bile from gallbladder for fat absorption
  • contracts the gallbladder and relaxes the sphincter of Oddi, causing release of bile into duodenum

(NO and VIP also relax the sphincter of Oddi)

48
Q

what can abnormal mucus do?

A

blocks ducts in the pancreas, affecting pancreatic secretions and therefore affecting protein, lipid and carbohydrate digestion

49
Q

consequences of obstruction of the pancreatic duct by thick mucus

A

contributes to the gastrointestinal symptoms in patients with cystic fibrosis (CF)

50
Q

list some major symptoms of CF

A

due to dysfunction of exocrine glands, sweat glands secrete excessive sodium and chloride

lungs also produce thickened mucus

51
Q

consequences of the CF symptoms

A

Severe malabsorption
Steatorrhoea
Recurrent chest infections
Sterility in 98% of males

52
Q

why does CF cause sterility in 98% of males

A

due to congenital bilateral aplasia of the vas deferens (CBAVD) – vas deferens fails to develop properly

vas deferens carries the newly made sperm to the back of the prostate gland where it joins the outlets of the seminal vesicles. the sperm can then be released into the semen during intercourse

sem 2 Liver and GI (11 decks)

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