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Gastrointestinal > 5 - pancreas and liver > Flashcards

5 - pancreas and liver Flashcards

1
Q

what are the key properties of chyme leaving the stomach?

A

low ph
hypertonic (very concentrated)
partially digested

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2
Q

what are Brunner’s glands?

A

glands found in the duodenum that secrete alkaline mucosa protecting cells lining the duodenum from the acid chyme

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3
Q

how is the hypertonicity of chyme leaving the stomach altered?

A

stomach is impermeable to water. duodenum is permeable to water and draws in water from the ECF so chyme becomes isotonic - the release of chyme must be controlled as a result

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4
Q

how is the low pH of chyme and partially digested chyme (many proteins, fats and CHOs) altered upon leaving the stomach?

A

pancreas –>
enzymes (CCK) + bicarbonate (secretin)

liver –>
bile + bicarbonate

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5
Q

what does the duodenum secrete in response to chyme?

A

secretin and CCK (cholecystokinin)

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6
Q

what does secretin do?

A

stimulates pancreas to release aqueous bicarbonate

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7
Q

what does CCK do?

A
  • acts on the pancreas to stimulate the enzyme component

- acts on the gallbladder (contracts) and relaxes the sphincter of oddi

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8
Q

what is the sphincter of oddi?

A

it allows secretions from the pancreas AND gall bladder to get into the duodenum. can get blocked by gall stones

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9
Q

are pancreatic functions mainly endocrine or exocrine?

A

EXOCRINE! - 90%

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10
Q

what stimulates exocrine functions of the pancreas?

A

gut hormones (secretin and CCK)
autonomics:
- sympathetics inhibit
-parasympathetics (vagus) stimulates

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11
Q

describe the pancreatic structure

A

ACINAR sacs make up the pancreas
a sac:

+ lined by ACINAR CELLS (enzyme secreting)
+ ducts that feed in lined by DUCT CELLS (bicarbonate secreting)

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12
Q

what enzymes do acini cells release?

A

stimulated by CCK and vagus stimuli:
amylases, lipases and proteases

  • amylase and lipases are active
  • proteases are inactive (trypsin, chymotrypsin, elastase, carboxypeptidase once activated) – inactive protease enzymes are stored in zymogen granules
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13
Q

what are zymogen granules?

A

store inactive protease enzymes. they contain zymogen (inactive proteases like trypsinogen) which are converted to activate proteases (like trypsin) in the intestinal lumen

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14
Q

why are pancreatic proteases released in inactive forms?

A

as you dont want the proteases to act on the tissues of the duodenum itself. only once in the duodenum do they become activated

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15
Q

how do pancreatic secretions reach the duodenum?

A

pancreatic duct then ampulla of vater

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16
Q

what does the liver secrete into the duodenum in response to chyme?

A

BILE - 250 - 1000ml/day

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17
Q

where is bile stored?

A

in the gall bladder

18
Q

what does bile consist of?

A
  • bile acids and bile pigments

- alkaline solution

19
Q

key role of bile?

A
  • emulsifying fat (lipids) in duodenum so they can be readily digested by lipases secreted by pancreas
20
Q

what are the chief functional cell of the liver?

A

hepatocytes (80% of liver mass)

21
Q

what does the liver produce for export?

A

proteins and lipids - lots of rough and smooth ER/ stacks of golgi apparatus
contains lots of glycogen

22
Q

what drains into the liver?

what drains out of the liver?

A
  • All the blood from the gut (in) via the portal vein

- bile (out)

23
Q

describe the MACRO ANATOMY (lobes) of the liver

A

left
right
caudate
quadrate

left lobe is bigger than the right

24
Q

Describe the MICRO ANATOMY of the liver

A

liver contains lobules
hexagonal arrangement of cells, bile ducts and blood vessels (artery, vein, bile duct triad at the corners)

sheets of hepatocytes arranged towards central hepatic venule

25
Q

describe the structure of a liver lobule

A
  • hexagonal
  • triads at each corner (portal vein, hepatic artery and bile duct branches)
  • central vein in the middle
26
Q

what flows into and out of a lobule?

A

IN: blood - flows in towards the central vein via sinusoids (portal vein and hepatic artery)

OUT: bile - along canaliculi, bile duct and into the duodenum

27
Q

what is the functional area of the lobule called?

A

acinus

28
Q

what zones are most likely to get ischaemic?

A

blood drains from the periphery of the lobule to the centre - this creates a series of zones (1,2,3) corresponding to distance from arterial blood supply
toxic (zone 1) - e.g. paracetamol
ischaemic (zone 3)

29
Q

where is bile created?

A

created by hepatocytes duct cells in the liver - made continuously, needed intermittently

30
Q

where is bile stored?

A

gallbladder
it concentrates the bile (removes water and ions) - can lead to gallstones. CCK released from the duodenum stimulates gallbladder contraction

31
Q

what does bile do?

A

emulsifies fats aiding their digestion

32
Q

what route does bile take?

A

CCK contracts the gallbladder

common bile duct–> bile —> ampulla of vater –> duodenum

33
Q

what are the components of bile?

A

secreted by the hepatocytes:

  • bile salts (from bile acid)
  • pigments

secreted by cells lining the bile ducts and stimulated by secretin:
- alkaline juices

34
Q

what is bile acid?

A

synthesised in the liver but then conjugated to amino acids in the liver (glycine, taurine) which creates a bile salt

35
Q

what are bile salts?

A

conjugated bile acids. they are more soluble at duodenal pH then bile acids

they have an amphipathic structure:
hydrophilic end
hydrophobic end
act as a oil/water interface

they allow emulsification of dietary lipids

36
Q

how do bile salts aid the digestion of large globules of lipids?

A
  • lipids are large globules by the time they have reached the duodenum - so a small surface area for enzymes (lipases) to act
  • bile salts EMULSIFY FAT INTO SMALLER UNITS - increasing SA allowing lipases to act
  • bile salts then create micelles with products of lipid breakdown (cholesterol, monoglycerides, free fatty acids)
  • micelles act as a vehicle for transporting hydrophobic molecules (products of lipid digestion) towards enterocyte - (cell that forms the wall of the duodenum)
37
Q

what do micelles do?

A

They transport hydrophobic products of lipid digestion towards cells lining gut wall

38
Q

how are bile salts recycled?

A

+ micelle transports digested lipids to luminal membrane of enterocyte

+ lipids diffuse into intestinal epithelial cell (cytosol of enterocyte) but bile salts do not

+ entero - hepatic circulation of bile salts:
bile salts remain in gut (not enter enterocyte)
reabsorbed in terminal ilium
returned to liver in portal blood

+ liver recycles the bile salts

39
Q

what happens to lipid molecules inside the enterocyte ?

A
  • they are built back up to triglycerides, phospholipids and cholesterol
  • packed with apoproteins within enterocyte to form CHLOMICRONS
  • chylomicrons are exocytosed from the basolateral membrane of enterocyte
    they are too large to enter capillaries
    enter lymphatic capillaries –> thoracic duct
40
Q

what is steatorrhoea?

A

undigested fat appears in faces

  • pale
  • floating
  • foul smelling

due to pathology that affects the production of bile or bile reaching the duodenum e.g. pancreatitis

more fat stays in duodenum then exits

Gastrointestinal (1 decks)

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