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AEU > Regulation of the GI tract - secretion > Flashcards

Regulation of the GI tract - secretion Flashcards

1
Q

Digestion depends on extensive well regulated secretion of digestive juices. What aids this?

A
  • epithelial cells within the walls of the stomach/intestine
  • discrete large glands situated outside the tract - salivary gland, liver and pancreas
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2
Q

In order to aid enzymes present in the tract what do digestive juices have?

A
  • digestive juices have a composition and pH that is well adapted to the characteristic of the enzymes in that part of the tract
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3
Q

What makes up digestive secretions?

A
  • water (98%)
  • ions
  • mucus
  • enzymes

(Wallace must ingest edam)

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4
Q

What are the 4 functions of saliva?

A
  • lubrication
  • antibacterial effect
  • enzymic digestion
  • pH regulation
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5
Q

How does saliva lubrication aid digestion?

A
  • contains mucin which facilitates chewing and swallowing
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6
Q

What are the antibacterial substances in saliva?

A
  • lysozyme and antibodies present in saliva
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7
Q

How does saliva enzymic digestion aid in digestion?

A
  • amylase breaks down starch
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8
Q

How does saliva help pH regulation?
what is Ruminants pH?

A
  • bicarbonate neutralises acid produced by bacteria
  • pH = 8.2
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9
Q

Saliva secretion is under control by what?

A
  • saliva secretion is entirely under neural control (automimic - parasympathetic)
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10
Q

Epithelial cells in the stomach produce what?

A
  • Epithelial cells produce a mucus which is viscous and high in bicarbonate
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11
Q

What are the 4 types of cells found in the glandular part of the stomach?

A
  • mucin producing cells
  • parietal cells
  • chief producing cells
  • endocrine cells

(my people can eat)

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12
Q

What are the functions of mucin producing cells, parietal cells and chief cells?

A
  • mucin producing cells produce alkaline mucus
  • parietal cells produce hydrochloric acid
  • chief cells produce pepsinogen (inactive zymogen for pepsin)
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13
Q

What are the 3 types of endocrine cells found in the glandular region of the stomach? what layer are they found in?

A
  • G-cells which produce gastrin
  • ECL-cells which produce histamine
  • D-cells which produce somatostatin
  • all of these cells found within the epithelial layer
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14
Q

What is the purpose of intrinsic factors within the stomach?

A
  • Intrinsic factors help to ensure absorption of B12 in the stomach
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15
Q

How does somatostatin impact G cells?

A
  • somatostatin has a negative impact on G-cells
  • the more somatostatin produced, the fewer G cells there are
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16
Q

What are the 3 phases of gastric secretion?

A
  • cephalic phase
  • gastric phase
  • intestinal phase
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17
Q

Describe the cephalic phase

A
  • normally elicited by sight, smell, and taste of food.
  • entirely mediated by the vagus nerve
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18
Q

Describe the gastric phase

A
  • elicited by the presence of food in the stomach
  • mediated via neural reflexes and hormones
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19
Q

Describe the intestinal phase

A
  • initial stimulatory effect, followed by an inhibitory effect
  • mediated via neural reflexes and hormones
20
Q

During the intestinal phase of gastric secretions there is initially a stimulatory effect followed by an inhibitory effect why is this?

A
  • to ensure the secretions are not continuous
21
Q

The pancreas has both exocrine and endocrine functions what are these functions?

A
  • exocrine - products are pancreatic juices
  • endocrine - products are insulin, glucagon, somatostatin
22
Q

Pancreatic juices have an aqueous components and an enzymic component - what do these components do?

A
  • aqueous component - alkaline due to a high concentration of bicarbonate stimulated by secretin
  • enzymic component - digestion for all major classes of foodstuffs
23
Q

Proteases digest proteins what are the three proteases produced by the pancreas? give their inactive forms and active form

A
  • trypsinogen > trypsin
  • chymotrypsinogen > chymotripsin
  • procarboxypeptidase > carboxypeptidase
24
Q

What is the function of alpha amylase?

A
  • to digest starch
25
Q

Lipases digest fats, what are the 3 lipases produced by the pancreas?

A
  • triacylglycerol hydrolase
  • cholesterol ester hydrolase
  • phospholipidase A2
26
Q

What are the key points about the cephalic phase of pancreatic secretions?

A
  • cephalic phase increases in association with feeding
  • its mediated by the vagal nerves that run into the glands
  • affected by gastrin secretion in the stomach
27
Q

What are the key points about the gastric phase of the pancreatic secretions?

A
  • increases in association with feeding
  • mediated by the vagal nerves to the glands and gastrin secretion in the stomach
28
Q

when does the intestinal phase of pancreatic secretion begin?

A
  • when chyme enters the duodenum
29
Q

How is the intestinal phase of pancreatic secretion mediated?

A
  • mediated by secretin and CCK release
30
Q

What is the function of secretin?

A
  • inhibits gastrin release from G cells
  • inhibits response of parietal cells to secretagogues
  • stimulates pancreas to produce bicarbonate rich fluid
  • increase production of bile by the liver
31
Q

What is the function of CCK?

A
  • inhibits secretions from parietal cells
  • stimulates pancreas to increase enzyme secretion
32
Q

The liver receives what type of blood?

A
  • both arterial and venous blood
33
Q

What is the role of the liver in digestion?

A
  • it has hepatocytes that produce bile which are important in fat digestion
  • it handles nutrients absorbed from the intestine and regulates their release into the blood
  • ( other functions not directly associated with processing nutrients)
34
Q

Bile which is produced by hepatocytes is excreted into what?

A
  • bile canaliculi (common bile duct)
35
Q

where is bile stored when there is no digestion occurring?

A
  • the gall bladder
36
Q

When digestion starts the gall bladder slowly contracts, sphincter of Oddi relaxes - how does this control the release of bile?

A
  • when the sphincter is relaxed bile is released into the small intestine
  • when its contracted there is no bile released
37
Q

What does bile contain?

A
  • 95% water
  • bile acids
  • cholesterol
  • phospholipids
  • bile pigments (Bilirubin)
38
Q

How are primary bile acids made?

A
  • synthesised from cholesterol in the hepatocyte
39
Q

How are secondary bile acids formed?

A
  • when primary bile acids undergo dihydroxylation by bacteria in the small intestine
40
Q

How are bile salts formed?

A
  • primary + secondary bile acids conjugate with an amino acids (taurine/glycine)
41
Q

What is the function of bile salts?

A
  • bile salts are more water soluble than bile acids and act as detergents to emulsify lipids
  • they form spherical micelles which are important in digestion and absorption of fats
42
Q

How do bile acids recirculate back to the liver?

A
  • by enterohepatic circulation
43
Q

How is bile and bicarbonate production increased?

A
  • acidic duodenal contents stimulate secretin which in addition to increasing bicarbonate from the pancreas and production of bile
44
Q

What happens when fat is detected on CCK producing cells?

A
  • stimulates CCK
  • opens the sphincter of Oddi
  • more bile is released into the small intestine
45
Q

Is neural stimulation important in bile production?

A
  • NO

AEU (10 decks)

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