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Gastrointestinal System > Lecture 5.1: Gastrointestinal Physiology > Flashcards

Lecture 5.1: Gastrointestinal Physiology Flashcards

1
Q

What are zymogen granules?

A

Specialised storage organelles in the exocrine pancreas that allow the sorting, packaging and regulated apical secretion of digestive enzymes

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2
Q

What pancreatic enzymes are produced in their inactive form? (2)

A
  • Trypsin
  • Chymotrypsin
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3
Q

Why are some pancreatic enzymes produced in their inactive form?

A

If these proteases were released in their active form, they would end up digesting the pancreas causing massive destruction of the pancreas

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4
Q

What enzyme cleaves trypsinogen into trypsin?

A

Enteropeptidase

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5
Q

What is the role of Cholecystokinin (CCK)? (4)

A
  • Stimulates the gallbladder to contract and release
    stored bile into the intestine
  • Stimulates the secretion of pancreatic juice
  • Relaxation of sphincter of Oddi to allow bile into
    duodenum
  • May induce satiety
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6
Q

What hormone stimulates release of enzyme rich secretions from the pancreas?

A

Gastrin

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7
Q

What hormone stimulates release of hydrogen-carbonate rich secretions from the pancreas?

A

Secretin

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8
Q

What are the 5 main roles of the Liver?

A
  • Bile production
  • Carbohydrate, protein and lipid metabolism
  • Protein synthesis
  • Vitamin D synthesis
  • Detoxification
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9
Q

What is bile comprised of? (6)

A
  • Bile Salts
  • Phospholipids
  • Cholesterol
  • Conjugated Bilirubin
  • Electrolytes
  • Water
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10
Q

Name 2 bile acids

A
  • Cholic Acid
  • Chenodeoxycholic Acid
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11
Q

What cells produce Secretin? Why is secretin produced?

A
  • Released from S cells of duodenal mucosa in response
    to acidic chyme
  • Resulting in release of HCO3- rich solution
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12
Q

What do I-Cells of the duodenal and upper jejunal mucosa produce?

A

Cholecystokinin (CCK, pancreozymin)

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13
Q

What is the consequence of reduce bile/pancreatic lipase secretion?

A

Reduced fat emulsification and digestion and uptake and thus there is fat in the stool causing diarrhoea

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14
Q

What are the 4 anatomical lobes of the liver?

A
  • Right
  • Left
  • Caudate
  • Quadrate
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15
Q

What are the functional lobes of the liver? (2)

A
  • True Right
  • True Left
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16
Q

What 2 ligaments help suspend the liver in the abdomen?

A
  • Falciform ligament
  • Coronary ligament
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17
Q

What is a Hepatic Lobule?

A

The anatomic unit of the liver

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18
Q

What is a Hepatic Acinus?

A

A unit that contains a small portal tract at the center and terminal hepatic venules at the periphery

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19
Q

How is bilirubin conjugated in the liver?

A

Bilirubin is conjugated within the hepatocyte to glucuronic acid by uridine-diphosphoglucuronic glucuronosyltransferase (UDPGT)

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20
Q

What is conjugated bilirubin?

A

The form of bilirubin which has been conjugated with glucoronic acid and is excreted in the bile

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21
Q

What is unconjugated bilirubin?

A

Bilirubin that is bound to a certain protein (albumin) in the blood

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22
Q

Where is bile made?

A

Liver

23
Q

Where is bile stored?

A

Gallbladder

24
Q

What are the functions of bile? (4)

A
  • Aid in the digestion of fat via fat emulsification
  • Absorption of fat and fat-soluble vitamins
  • Excretion of bilirubin and excess cholesterol
  • Provides an alkaline fluid in the duodenum to
    neutralise the acidic pH of the chyme that comes from
    the stomach
25
Q

How much of pancreatic tissue is exocrine?

A

95-98%

26
Q

Pancreatic juice flows via the………. and enters the…..

A

Pancreatic juice flows via the main pancreatic duct and enters the duodenum

27
Q

Bile and main pancreatic duct converge near to the duodenum at the…..?

A

Hepatopancreatic ampulla

28
Q

What controls the entry of contents into the duodenum?

A

Sphincter of Oddi

29
Q

Functional anatomy of the exocrine pancreas

A
  • It consists of lobules of acinar cells that secrete
    enzymes/fluid into microscopic ducts
  • Intercalated ducts
  • The intercalated ducts are lined with epithelial cells
    (duct cells) that secrete a HCO3- rich solution
  • Intercalated ducts drain into intralobular ducts and in
    turn into interlobular ducts
  • Interlobular ducts empty into the main pancreatic duct
    (this runs along the length of the pancreas)
  • The main pancreatic generally fuses with the bile duct
    before draining into the duodenum
30
Q

What is the smaller pancreatic duct that empties directly into the duodenum called?

A

Duct of Santorini

31
Q

How ml of Pancreatic Juice produced everyday?

A

~1500ml

32
Q

What are the 2 components of Pancreatic Juice?

A
  • Aqueous
  • Enzyme
33
Q

What does the aqueous component of pancreatic juice contain?

A
  • HCO3- rich
  • pH ~ 8
  • Neutralizes acidic chyme (along with intestinal
    secretions)
34
Q

What does the enzyme component of pancreatic juice contain?

A

Proteases, carbohydrase’s, lipases – all contained within the aqueous component

35
Q

What cells are primarily involved in the formation of alkaline pancreatic fluid?

A
  • The source is primarily the columnar epithelial cells
    that line the ducts
  • At rest from the intercalated and intralobular ducts
  • When stimulated interlobular ducts as well
36
Q

How is alkaline pancreatic fluid formed?

A
  • HCO3- ions (from CO2) exchanged for Clions in the
    lumen and H+ ions exchanged for Na+in the interstitial
    fluid
  • Cl- ions cross the apical membrane via Cl- channels
    including the cystic fibrosis transmembrane
    conductance regulator (CFTR)
  • Na+ ions diffuse from the interstitial fluid via a
    paracellular pathway (maintains electroneutrality) and
    water follows by osmosis (can be either transcellular
    or paracellular)
37
Q

What enzyme is responsible for the majority of the digestion of polysaccharides? How does it work?

A
  • Pancreatic amylase
  • It breaks 1,4 glycosidic bonds (not 1,6 bonds that link
    the chains of glucose molecules)
38
Q

Main products of pancreatic amylase activity (3)

A
  • Disaccharides
  • Trisaccharide’s
  • α-limit dextrins
39
Q

Fat within chyme undergoes…?

A

Emulsification (essentially large aggregations of lipids are dispersed to become more numerous smaller aggregations)

40
Q

Why is emulsification important?

A

Increase the surface area for pancreatic lipases to act

41
Q

Pancreatic lipase can be inhibited by bile salts, how it its activity restored?

A

By combining with colipase

42
Q

How is Pancreatic Secretion regulated?

A

Neuroendocrine Control

43
Q

Regulation of Pancreatic Secretion: Parasympathetic

A
  • Acinar and ductal cells express M3 receptors
  • PANS activation results in increased secretions of both
    cells
  • SANS inhibits secretion – probably via decreasing
    blood flow
44
Q

Regulation of Pancreatic Secretion: Endocrine

A
  • Secretin and CCK stimulate the production of the
    HCO3- rich fraction of pancreatic juice (maintains
    duodenal pH)
45
Q

Control of pancreatic secretion can be divided into 3 phases, name them

A
  • Cephalic
  • Gastric
  • Intestinal
46
Q

What cells produce bile?

A

Hepatocytes

47
Q

What is Cholagogue?

A

A substance which promotes gallbladder contraction

48
Q

Bile salts are amphipathic, what does this mean?

A

They have both hydrophobic (orange) and hydrophilic (blue) regions

49
Q

How do bile salts emulsify fats?

A

The bile salts insert themselves into fat globules in chyme – this disrupts the globule forcing regions of it to bud off as lipid droplets

50
Q

What are two important aspects to the formation of bile acids?

A
  • Bile acid dependent component
  • Bile acid independent component
51
Q

What are two important aspects to the formation of bile acids?: Bile Acid Dependent Component

A
  • The first depends upon how quickly bile salts (BS) are
    returned back to the hepatocytes via the
    enterohepatic circulation
  • Active removal from blood with active secretion into
    bile
52
Q

What are two important aspects to the formation of bile acids?: Bile Acid Independent Component

A
  • Secretion of water and electrolytes –active transport of
    Na+and passive movement of Cl- and water
  • Similarly, active transport of HCO3- and passive
    movement of water and Na+ B
53
Q

What percentage of of bile slats that enter the intestine are recycled?

A

c.95%

54
Q

How are bile salts that enter the intestine recycled?

A
  • Via an active transport mechanism (ASBT apical
    sodium bile transporter
  • OAT basolateral organic anion transporter) in the distal
    ileum
  • Many return to the liver unaltered
  • Some deconjugated in the intestinal lumen
  • Some are converted to secondary bile acids
  • Some secondary bile acids are insoluble and are
    excreted in faeces

Gastrointestinal System (22 decks)

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