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M104 T1 > M104 T1 L6 > Flashcards

M104 T1 L6 Flashcards

1
Q

What is the role of the duodenum?

A

receives acidic chyme from the stomach via the pyloric sphincter and then mixing its and neutralising the acid contents

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2
Q

What occurs in the jejunum?

A

this is where the bulk of chemical digestion and nutrient absorption occur

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3
Q

What occurs in the ileum?

A

further digestion and absorption, particularly of vitamin B 12

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4
Q

What are the three main types of primary secretions present in the SI? (PIB)

A

pancreatic juice
intestinal juice
bile

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5
Q

What are the most common endocrine hormones secreted from the SI?

A

secretin
CCK
GIP

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6
Q

What are the two types of secretory cells in SI villi?

A

enterocytes

goblet cells

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7
Q

What are the three types of secretory cells in the intestinal glands of the SI?

A 
enterocytes 
enteroendocrine cells
paneth cells (phagocytosis)
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8
Q

What cell secretes isotonic fluid?

A

enterocytes

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9
Q

What substance do paneth cells secrete?

A

lysozymes

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10
Q

Where are Brunner’s glands located?

A

in the sub mucosa of the duodenum only

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11
Q

What substance do Brunner’s glands secrete?

A

secrete mucus and HCO3- rich fluid

neutralises acidic chyme

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12
Q

What is the cell turnover of absorptive and secretary epithelial cells?

A

rapid - every three to six days

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13
Q

What is a negative consequence of rapid cell turnover in absorptive and secretary epithelial cells?

A

the cells are particularly vulnerable to radiation and chemotherapy

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14
Q

How long does it take orally ingested food contents to exit the SI?

A

8 - 9 hours

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15
Q

What substances is intestinal juice made up of? (AM.MEWL)

A

alkaline/mucus containing fluid

mucus, electrolytes, water, lysozymes

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16
Q

What are the three key endocrine hormones that are secreted into vasculature secreted by? (SIK)

A

Secretin - S cells
CCK - I cells
GIP - K cells

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17
Q

What is the role of CCK?

A

stimulate pancreatic and gallbladder secretion

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18
Q

What is the role of secretin?

A

stimulate pancreatic and biliary bicarbonate secretion

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19
Q

What is the role of GIP?

A

stimulates insulin release

weakly inhibits acid secretion

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20
Q

Where do secretions entering the pancreas go?

A

they drain into the main pancreatic duct

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21
Q

What is the accessory pancreatic duct a branch of?

A

the major pancreatic duct / the duct of Wirsung

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22
Q

What branches drain into the ampulla of Vater?

A

the main pancreatic duct and the common bile duct

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23
Q

What is the role of the hepatopancreatic sphincter?

A

controls the flow of digestive juices through the ampulla of Vater into the second part of the duodenum

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24
Q

What are the two other names for hepatopancreatic sphincters?

A

the sphincter of Oddi

Glisson’s sphincter

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25
Q

What is the microstructure of the pancreas like?

A

it consists of clusters of glandular epithelial cells

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26
Q

What are the two types of glandular epithelial cells in the pancreas?

A

exocrine acinar clusters - 99%

endocrine pancreatic islets - 1%

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27
Q

What substances does pancreatic juice contain?

A

water, electrolytes
sodium bicarbonate
pro-enzymes

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28
Q

What is the role of endocrine pancreatic islets?

A

to secrete hormones straight into the bloodstream

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29
Q

What are the four cell types in endocrine pancreatic islets?

A

alpha, beta, and delta cells - produce important hormones

F cells - pancreatic ppts

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30
Q

What substances do alpha and beta pancreatic islets secrete?

A

[GI - gastrointestinal ab, ab]
alpha - glucagon
beta - insulin

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31
Q

What substances do delta pancreatic islets and F cells secrete?

A

delta - somatostatin

F cells - PP

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32
Q

What substances do acinar cells secrete?

A

enzymes, NaCl, fluid

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33
Q

What substances do the duct cells secrete?

A

NaHCO3 and fluid

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34
Q

What is the effect of NaHCO3?

A

responsible for the slightly alkaline pH which provides an environment at which these enzymes best function
inactivates the acidic chyme and any enzymes that work at the pH of the gastric juice

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35
Q

How is acinar enzyme production upregulated?

A

ACh - released by P/S NS (para: vagal)

CCK – triggered by the presence of chyme, containing fat and protein products in the duodenum

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36
Q

What are the features of pancreatic juice secreted from acinar cells?

A

low volume and enzyme rich

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37
Q

How is ductal bicarbonate and water production upregulated?

A

Secretin - released in the presence of H+ ions (acidic chyme)

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38
Q

What are the features of pancreatic juice secreted from ductal cells?

A

high volume
low enzyme
HCO3- rich

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39
Q

What are the 13main pancreatic enzymes?

A 
Proteolytic (5)
a-amylase (1)
Lipases (3)
Nucleases (2)
Trypsin inhibitor (and Procolipase) (2)
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40
Q

Which pancreatic enzyme type is secreted in inactive form and why?

A

proteases, to avoid autodigestion within the pancreas

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41
Q

What is the role of nucleases?

A

to digest RNA and DNA to nucleic acids

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42
Q

What is the role of trypsin inhibitors?

A

they neutralise any trypsin that is accidentally activated within the pancreas itself to prevent autopancreatic digestion

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43
Q

Where are pancreatic proteases activated?

A

in the brush border of the SI

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44
Q

What enzymes are secreted by acinar cells? (CAT)

A

chymotrypsin, amylase, trypsin

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45
Q

How are pancreatic proteases produced?

A

as zymogens - inactive precursors

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46
Q

When are zymogens activated?

A

when they reach the SI or the brush border

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47
Q

What happens when zymogens reach the SI or the brush border?

A

enterokinase cleaves hexapeptide to form active trypsin from trypsinogen

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48
Q

What is the role of active trypsin in the SI?

A

it cleaves and activates other proteases

this prevents pancreatic autodigestion

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49
Q

What type of cell does secretin act on?

A

pancreatic duct cells

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50
Q

How does secretin work to produce a HCO3− rich pancreatic juice?

A

it stimulates bicarbonate secretion out of the cell into the duct lumen
in exchange for chloride ion moving into the cell

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51
Q

How are chloride and bicarbonate ions swapped when under the effects of secretin?

A

the Cl−/HCO3− exchange at the apical cell membrane

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52
Q

Which channel recycles chloride ions out of the cell when the cell is under secretin influence?

A

the CFTR chloride channel

53
Q

What happens when sodium is secreted transcellularly when under secretin influence?

A

it is secreted into the duct lumen

it follows down an electrochemical gradient created by negative bicarbonate ions moving into the lumen

54
Q

How is the movement of sodium ions associated with other substances when under secretin influence?

A

sodium ions are secreted transcellularly into the duct lumen
they follow HCO3 secretion down its electrochemical gradient
water follows by osmosis

55
Q

What is the CFTR chloride channel influenced by?

A

secretin stimulation via cyclic upregulation of cAMP

56
Q

What does the ionic composition of pancreatic juice depend on?

A

secretory rate

whether it is stimulated or unstimulated

57
Q

What is the unstimulated secretory rate for pancreatic juice like?

A

low secretion rates

the electrolyte content remains similar to that found in blood plasma

58
Q

What is the stimulated secretory rate for pancreatic juice like?

A

a high concentration of bicarbonate ions and Na+ in the pancreatic juice
a low concentration of Cl-

59
Q

What channel will be affected in patients with cystic fibrosis?

A

they lack a functional Cl− CFTR channel in the luminal membrane

60
Q

What are the effects of a defunctional Cl− CFTR channel?

A

defective ductal fluid secretion

causes the ducts to become blocked with precipitated enzymes and mucus

61
Q

What are the effects of blocked ducts caused by a defunctional Cl− CFTR channel?

A

the pancreas undergoes fibrosis

impaired secretion of needed pancreatic enzymes for digestion of nutrients - malabsorption

62
Q

How is a defunctional Cl− CFTR channel caused by cystic fibrosis treated?

A

oral pancreatic enzyme supplements are taken with each meal

63
Q

What conditions will lead to dysfunction in enzyme activation process?

A

cystic fibrosis

pancreatitis

64
Q

What are the most common causes of pancreatitis?

A

gallstones

alcohol abuse

65
Q

What is pancreatitis pathologically caused by?

A

pancreatic enzymes being activated within the pancreas (and surrounding tissues) rather than on the brush border in the SI
results in the autodigestion of the tissues

66
Q

How much bile is secreted per day?

A

up to 1 L

67
Q

What waste products are eliminated by bile salts?

A

bilirubin
cholesterol
drugs

68
Q

How is bilirubin produced?

A

a waste product from haem in RBC degradation

69
Q

What gives faeces its brown colour?

A

the breakdown product stercobilin

70
Q

What is bile synthesised by?

A

by hepatocytes lining sinusoids in the liver acinus

71
Q

Where does the portal venule receive blood from?

A

the portal vein coming directly from the GI tract

72
Q

What happens to the blood coming from the portal vein coming from the GI tract to the liver?

A

it mixes with the oxygenated blood of the portal arteriole

the blood then runs down the sinusoids and drains into the central vein

73
Q

What structures are on either side of the sinusoid carrying blood from the portal arteriole?

A

sheets of hepatocytes

they are exposed to the blood in the sinusoids for high functioning metabolic activity

74
Q

Where does bile drain into?

A

the blind ended canaliculi - drains on into the bile duct
the bile duct for storage in the gall bladder
the duodenum via direct drainage

75
Q

Where is bile stored under resting conditions?

A 
in the gall bladder
bile will pass down into the right and left hepatic ducts of the liver
join to form the common hepatic duct
travels along the cystic duct 
into the gall bladder
76
Q

Through what ducts is bile released when secreted?

A

it moves down into the common bile duct
joins with the main pancreatic duct
the hepatic pancreatic sphincter is stimulated open
bile is secreted into the duodenum

77
Q

What is bilirubin from originally?

A

haem groups that have had their iron removed from them

from old or faulty RBCs

78
Q

How is haem converted into bilirubin?

A

oxidised by haem oxygenase into green biliverdin

reduced by biliverdin reductase into bilirubin

79
Q

Where does bilirubin conversion and production occur?

A

in the spleen and kupffer cells

80
Q

Where is bilirubin transported?

A

to the liver

bc it is hydrophobic, in its unconjugated form it is tightly bound to albumin

81
Q

What happens to bilirubin once it reaches the liver?

A

it is taken up by the hepatocytes in the liver
it is conjugated by hepatocytes with glucuronic acid to form bilirubin diglucuronide
then this is the form that is excreted in bile into the gut

82
Q

What happens once bilirubin diglucuronide is excreted in bile into the gut?

A

the gut bacteria are then able to hydrolyse the bilirubin and deconjugate it to then form urobilinogen

83
Q

What is the process by which gut bacteria hydrolyse bilirubin?

A

Gut bacterial hydrolysis (b glucuronidase)

84
Q

What is urobilinogen reduced to?

A

stercobilin

this is excreted in faeces

85
Q

What can happen to urobilinogen once deconjugated from bilirubin?

A

enterohepatic reabsorption can occur
excreted in faeces
re-secreted in bile - most of it
excreted in urine - a small amount (gives yellow colour)

86
Q

What event can lead to jaundice?

A

when the processes by which bilirubin is either produced or excreted are disrupted
this may be disrupted by an underlying disease process

87
Q

What level of bilirubin in the blood indicates jaundice?

A

serum bilirubin >30-60 uM/L

88
Q

What is jaundice physiologically caused by?

A

the build-up of bilirubin in the blood

89
Q

What is the sign of severe jaundice?

A

yellow discoloration of skin

90
Q

What are the three types of jaundice?

A

Pre-hepatic
Hepatocellular/congenital
Post-hepatic

91
Q

What is pre-hepatic jaundice caused by?

A

excessive RBC breakdown
build up of unconjugated bilirubin
bc the processes which bilirubin is dealt with are overloaded due to the excessive production of bilirubin

92
Q

What is a condition that can cause pre-hepatic jaundice?

A

haemolytic anaemia

93
Q

What is hepatocellular jaundice caused by?

A

reduced hepatocyte function

94
Q

What is an example of hepatocellular jaundice?

A

Crigler-Najjar syndrome

95
Q

What causes Crigler-Najjar syndrome?

A

absence of glucuronyl transferase which leads to increased unconjugated bilirubin

96
Q

What is post-hepatic jaundice caused by?

A

obstruction to normal bile drainage

build up of conjugated bilirubin

97
Q

What is an example of post-hepatic jaundice?

A

gallstone obstruction of bile flow

98
Q

What primarily triggers bile secretion?

A

CCK
secretin
vagal and enteric ACh stimulation

99
Q

What are the effects of CCK in terms of bile secretion?

A

causes the gall bladder to contract
causes the sphincter of Sphincter of Oddi to relax
allows bile to flow into the duodenum

100
Q

What is CCK released in response to the presence of?

A

fat content in the duodenum

101
Q

What is secretin released in response to the presence of?

A

acidic chyme

102
Q

What is the effect of secretin release?

A

causes the liver ductal cells to secrete a more watery bicarbonate-containing fluid into the bile

103
Q

What happens to bile salts during enterohepatic circulation?

A

active reabsorption of the bath salts in the ilium of the SI and then re-secretion into bile from hepatocytes

104
Q

What is the process by which bile salts are continuously recycled?

A

enterohepatic circulation

105
Q

What percentage of bile salts are recycled?

A

94%

this proportion of bile salts return via portal vein to drive bile synthesis in the liver

106
Q

What happens to hydrophobic drugs in the liver? (paracetamol)

A

they are deactivated by the liver and excreted into bile

these drugs can also undergo enterohepatic recycling

107
Q

What is the effect of enterohepatic recycling?

A

it slows the rate of drug elimination

108
Q

What are two examples of gallbladder disease?

A

asymptomatic cholelithiasis

biliary colic

109
Q

What are gallstones commonly caused by?

A

Excessive water and bile salt reabsorption from bile
Excessive cholesterol in bile causing precipitation (associated with a high fat diet)
epithelial Inflammation

110
Q

What is biliary colic caused by?

A

a blockage of the cystic duct that can affect different areas of the biliary tract

111
Q

What can epithelial inflammation be caused by?

A

low grade chronic infection

112
Q

What is contained in the dense granules of paneth cells?

A

lots of antimicrobial peptides

lots of immunomodulating proteins

113
Q

Where are paneth cells located?

A

in the SI crypts of Lieberkühn

114
Q

What is the role of the immunomodulating proteins contained in the dense granules of paneth cells?

A

regulate the composition of the intestinal flora

115
Q

What is the role of immunomodulators?

A

to support immune function by modifying the immune system’s response to a threat in a beneficial way

116
Q

What cell types are electrolytes and water from intestinal juice secreted by?

A

secretory enterocytes

117
Q

What is the significance of the Ligament of Treitz?

A

despite being a relatively small structure, it has clinical implications in surgical procedures and in rare cases of small bowel obstruction

118
Q

Where is procolipase activated and by what?

A

in the intestinal lumen by trypsin

119
Q

What is the co-factor of pancreatic lipase?

A

colipase

120
Q

What is the difference between co-enzymes and cofactors?

A

enz - organic, bind loosely to the substrate active site, help with substrate recruitment
cof - inorganic or organic, don’t bind the substrate, are helper mlcs

121
Q

What are the ten subtypes of pancreatic proteases?

A

trypsinogen 1-3
proelactase 1&2
chymotrypsinogen
procarboxypeptidase A1&2, B1&2

122
Q

What is the difference between trypsin and chymotrypsin?

A

they’re both pancreatic proteases, they just hydrolyse different parts of amacs
trypsin activates chymotrypsin from chymotrypsinogen

123
Q

What are the two different nucleases?

A

DNase & RNase

124
Q

What are the three different types of pancreatic lipolytic enzymes?

A

(gastric) lipase
phospholipase A2
pancreatic lipase

125
Q

What is the polarity of bile salts like?

A

amphipathic

126
Q

What are the different actions of bile in the body?

A

emulsification
elimination
digestion

127
Q

What type of vitamins do bile salts help to absorb?

A

fat-soluble vitamins like A, D, E, and K

128
Q

What is the quantity of SI secretions?

A

3.2-3.7 L (bile produced is varied)

129
Q

What are the quantities of the different constituent secretions in the SI?

A

intestinal juice - 1.2L
exocrine pancreatic juice - 1.5L
bile - 0.5-1 L

M104 T1 (15 decks)

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