M104 T1 L6 Flashcards
(129 cards)
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
2
Q
What occurs in the jejunum?
A
this is where the bulk of chemical digestion and nutrient absorption occur
3
Q
What occurs in the ileum?
A
further digestion and absorption, particularly of vitamin B 12
4
Q
What are the three main types of primary secretions present in the SI? (PIB)
A
pancreatic juice
intestinal juice
bile
5
Q
What are the most common endocrine hormones secreted from the SI?
A
secretin
CCK
GIP
6
Q
What are the two types of secretory cells in SI villi?
A
enterocytes
goblet cells
7
Q
What are the three types of secretory cells in the intestinal glands of the SI?
A
enterocytes enteroendocrine cells paneth cells (phagocytosis)
8
Q
What cell secretes isotonic fluid?
A
enterocytes
9
Q
What substance do paneth cells secrete?
A
lysozymes
10
Q
Where are Brunner’s glands located?
A
in the sub mucosa of the duodenum only
11
Q
What substance do Brunner’s glands secrete?
A
secrete mucus and HCO3- rich fluid
neutralises acidic chyme
12
Q
What is the cell turnover of absorptive and secretary epithelial cells?
A
rapid - every three to six days
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
14
Q
How long does it take orally ingested food contents to exit the SI?
A
8 - 9 hours
15
Q
What substances is intestinal juice made up of? (AM.MEWL)
A
alkaline/mucus containing fluid
mucus, electrolytes, water, lysozymes
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
17
Q
What is the role of CCK?
A
stimulate pancreatic and gallbladder secretion
18
Q
What is the role of secretin?
A
stimulate pancreatic and biliary bicarbonate secretion
19
Q
What is the role of GIP?
A
stimulates insulin release
weakly inhibits acid secretion
20
Q
Where do secretions entering the pancreas go?
A
they drain into the main pancreatic duct
21
Q
What is the accessory pancreatic duct a branch of?
A
the major pancreatic duct / the duct of Wirsung
22
Q
What branches drain into the ampulla of Vater?
A
the main pancreatic duct and the common bile duct
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
24
Q
What are the two other names for hepatopancreatic sphincters?
A
the sphincter of Oddi
Glisson’s sphincter
25
What is the microstructure of the pancreas like?
it consists of clusters of glandular epithelial cells
26
What are the two types of glandular epithelial cells in the pancreas?
exocrine acinar clusters - 99%
| endocrine pancreatic islets - 1%
27
What substances does pancreatic juice contain?
water, electrolytes
sodium bicarbonate
pro-enzymes
28
What is the role of endocrine pancreatic islets?
to secrete hormones straight into the bloodstream
29
What are the four cell types in endocrine pancreatic islets?
alpha, beta, and delta cells - produce important hormones
| F cells - pancreatic ppts
30
What substances do alpha and beta pancreatic islets secrete?
[GI - gastrointestinal ab, ab]
alpha - glucagon
beta - insulin
31
What substances do delta pancreatic islets and F cells secrete?
delta - somatostatin
| F cells - PP
32
What substances do acinar cells secrete?
enzymes, NaCl, fluid
33
What substances do the duct cells secrete?
NaHCO3 and fluid
34
What is the effect of NaHCO3?
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
35
How is acinar enzyme production upregulated?
ACh - released by P/S NS (para: vagal)
| CCK – triggered by the presence of chyme, containing fat and protein products in the duodenum
36
What are the features of pancreatic juice secreted from acinar cells?
low volume and enzyme rich
37
How is ductal bicarbonate and water production upregulated?
Secretin - released in the presence of H+ ions (acidic chyme)
38
What are the features of pancreatic juice secreted from ductal cells?
high volume
low enzyme
HCO3- rich
39
What are the 13main pancreatic enzymes?
```
Proteolytic (5)
a-amylase (1)
Lipases (3)
Nucleases (2)
Trypsin inhibitor (and Procolipase) (2)
```
40
Which pancreatic enzyme type is secreted in inactive form and why?
proteases, to avoid autodigestion within the pancreas
41
What is the role of nucleases?
to digest RNA and DNA to nucleic acids
42
What is the role of trypsin inhibitors?
they neutralise any trypsin that is accidentally activated within the pancreas itself to prevent autopancreatic digestion
43
Where are pancreatic proteases activated?
in the brush border of the SI
44
What enzymes are secreted by acinar cells? (CAT)
chymotrypsin, amylase, trypsin
45
How are pancreatic proteases produced?
as zymogens - inactive precursors
46
When are zymogens activated?
when they reach the SI or the brush border
47
What happens when zymogens reach the SI or the brush border?
enterokinase cleaves hexapeptide to form active trypsin from trypsinogen
48
What is the role of active trypsin in the SI?
it cleaves and activates other proteases
| this prevents pancreatic autodigestion
49
What type of cell does secretin act on?
pancreatic duct cells
50
How does secretin work to produce a HCO3− rich pancreatic juice?
it stimulates bicarbonate secretion out of the cell into the duct lumen
in exchange for chloride ion moving into the cell
51
How are chloride and bicarbonate ions swapped when under the effects of secretin?
the Cl−/HCO3− exchange at the apical cell membrane
52
Which channel recycles chloride ions out of the cell when the cell is under secretin influence?
the CFTR chloride channel
53
What happens when sodium is secreted transcellularly when under secretin influence?
it is secreted into the duct lumen
| it follows down an electrochemical gradient created by negative bicarbonate ions moving into the lumen
54
How is the movement of sodium ions associated with other substances when under secretin influence?
sodium ions are secreted transcellularly into the duct lumen
they follow HCO3 secretion down its electrochemical gradient
water follows by osmosis
55
What is the CFTR chloride channel influenced by?
secretin stimulation via cyclic upregulation of cAMP
56
What does the ionic composition of pancreatic juice depend on?
secretory rate
| whether it is stimulated or unstimulated
57
What is the unstimulated secretory rate for pancreatic juice like?
low secretion rates
| the electrolyte content remains similar to that found in blood plasma
58
What is the stimulated secretory rate for pancreatic juice like?
a high concentration of bicarbonate ions and Na+ in the pancreatic juice
a low concentration of Cl-
59
What channel will be affected in patients with cystic fibrosis?
they lack a functional Cl− CFTR channel in the luminal membrane
60
What are the effects of a defunctional Cl− CFTR channel?
defective ductal fluid secretion
| causes the ducts to become blocked with precipitated enzymes and mucus
61
What are the effects of blocked ducts caused by a defunctional Cl− CFTR channel?
the pancreas undergoes fibrosis
| impaired secretion of needed pancreatic enzymes for digestion of nutrients - malabsorption
62
How is a defunctional Cl− CFTR channel caused by cystic fibrosis treated?
oral pancreatic enzyme supplements are taken with each meal
63
What conditions will lead to dysfunction in enzyme activation process?
cystic fibrosis
| pancreatitis
64
What are the most common causes of pancreatitis?
gallstones
| alcohol abuse
65
What is pancreatitis pathologically caused by?
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
How much bile is secreted per day?
up to 1 L
67
What waste products are eliminated by bile salts?
bilirubin
cholesterol
drugs
68
How is bilirubin produced?
a waste product from haem in RBC degradation
69
What gives faeces its brown colour?
the breakdown product stercobilin
70
What is bile synthesised by?
by hepatocytes lining sinusoids in the liver acinus
71
Where does the portal venule receive blood from?
the portal vein coming directly from the GI tract
72
What happens to the blood coming from the portal vein coming from the GI tract to the liver?
it mixes with the oxygenated blood of the portal arteriole
| the blood then runs down the sinusoids and drains into the central vein
73
What structures are on either side of the sinusoid carrying blood from the portal arteriole?
sheets of hepatocytes
| they are exposed to the blood in the sinusoids for high functioning metabolic activity
74
Where does bile drain into?
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
Where is bile stored under resting conditions?
```
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
Through what ducts is bile released when secreted?
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
What is bilirubin from originally?
haem groups that have had their iron removed from them
| from old or faulty RBCs
78
How is haem converted into bilirubin?
oxidised by haem oxygenase into green biliverdin
| reduced by biliverdin reductase into bilirubin
79
Where does bilirubin conversion and production occur?
in the spleen and kupffer cells
80
Where is bilirubin transported?
to the liver
| bc it is hydrophobic, in its unconjugated form it is tightly bound to albumin
81
What happens to bilirubin once it reaches the liver?
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
What happens once bilirubin diglucuronide is excreted in bile into the gut?
the gut bacteria are then able to hydrolyse the bilirubin and deconjugate it to then form urobilinogen
83
What is the process by which gut bacteria hydrolyse bilirubin?
Gut bacterial hydrolysis (b glucuronidase)
84
What is urobilinogen reduced to?
stercobilin
| this is excreted in faeces
85
What can happen to urobilinogen once deconjugated from bilirubin?
enterohepatic reabsorption can occur
excreted in faeces
re-secreted in bile - most of it
excreted in urine - a small amount (gives yellow colour)
86
What event can lead to jaundice?
when the processes by which bilirubin is either produced or excreted are disrupted
this may be disrupted by an underlying disease process
87
What level of bilirubin in the blood indicates jaundice?
serum bilirubin >30-60 uM/L
88
What is jaundice physiologically caused by?
the build-up of bilirubin in the blood
89
What is the sign of severe jaundice?
yellow discoloration of skin
90
What are the three types of jaundice?
Pre-hepatic
Hepatocellular/congenital
Post-hepatic
91
What is pre-hepatic jaundice caused by?
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
What is a condition that can cause pre-hepatic jaundice?
haemolytic anaemia
93
What is hepatocellular jaundice caused by?
reduced hepatocyte function
94
What is an example of hepatocellular jaundice?
Crigler-Najjar syndrome
95
What causes Crigler-Najjar syndrome?
absence of glucuronyl transferase which leads to increased unconjugated bilirubin
96
What is post-hepatic jaundice caused by?
obstruction to normal bile drainage
| build up of conjugated bilirubin
97
What is an example of post-hepatic jaundice?
gallstone obstruction of bile flow
98
What primarily triggers bile secretion?
CCK
secretin
vagal and enteric ACh stimulation
99
What are the effects of CCK in terms of bile secretion?
causes the gall bladder to contract
causes the sphincter of Sphincter of Oddi to relax
allows bile to flow into the duodenum
100
What is CCK released in response to the presence of?
fat content in the duodenum
101
What is secretin released in response to the presence of?
acidic chyme
102
What is the effect of secretin release?
causes the liver ductal cells to secrete a more watery bicarbonate-containing fluid into the bile
103
What happens to bile salts during enterohepatic circulation?
active reabsorption of the bath salts in the ilium of the SI and then re-secretion into bile from hepatocytes
104
What is the process by which bile salts are continuously recycled?
enterohepatic circulation
105
What percentage of bile salts are recycled?
94%
| this proportion of bile salts return via portal vein to drive bile synthesis in the liver
106
What happens to hydrophobic drugs in the liver? (paracetamol)
they are deactivated by the liver and excreted into bile
| these drugs can also undergo enterohepatic recycling
107
What is the effect of enterohepatic recycling?
it slows the rate of drug elimination
108
What are two examples of gallbladder disease?
asymptomatic cholelithiasis
| biliary colic
109
What are gallstones commonly caused by?
Excessive water and bile salt reabsorption from bile
Excessive cholesterol in bile causing precipitation (associated with a high fat diet)
epithelial Inflammation
110
What is biliary colic caused by?
a blockage of the cystic duct that can affect different areas of the biliary tract
111
What can epithelial inflammation be caused by?
low grade chronic infection
112
What is contained in the dense granules of paneth cells?
lots of antimicrobial peptides
| lots of immunomodulating proteins
113
Where are paneth cells located?
in the SI crypts of Lieberkühn
114
What is the role of the immunomodulating proteins contained in the dense granules of paneth cells?
regulate the composition of the intestinal flora
115
What is the role of immunomodulators?
to support immune function by modifying the immune system's response to a threat in a beneficial way
116
What cell types are electrolytes and water from intestinal juice secreted by?
secretory enterocytes
117
What is the significance of the Ligament of Treitz?
despite being a relatively small structure, it has clinical implications in surgical procedures and in rare cases of small bowel obstruction
118
Where is procolipase activated and by what?
in the intestinal lumen by trypsin
119
What is the co-factor of pancreatic lipase?
colipase
120
What is the difference between co-enzymes and cofactors?
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
What are the ten subtypes of pancreatic proteases?
trypsinogen 1-3
proelactase 1&2
chymotrypsinogen
procarboxypeptidase A1&2, B1&2
122
What is the difference between trypsin and chymotrypsin?
they're both pancreatic proteases, they just hydrolyse different parts of amacs
trypsin activates chymotrypsin from chymotrypsinogen
123
What are the two different nucleases?
DNase & RNase
124
What are the three different types of pancreatic lipolytic enzymes?
(gastric) lipase
phospholipase A2
pancreatic lipase
125
What is the polarity of bile salts like?
amphipathic
126
What are the different actions of bile in the body?
emulsification
elimination
digestion
127
What type of vitamins do bile salts help to absorb?
fat-soluble vitamins like A, D, E, and K
128
What is the quantity of SI secretions?
3.2-3.7 L (bile produced is varied)
129
What are the quantities of the different constituent secretions in the SI?
intestinal juice - 1.2L
exocrine pancreatic juice - 1.5L
bile - 0.5-1 L
