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BMSC2225 Absorption and Excretion - GI Tract Physiology > GIT secretions > Flashcards

GIT secretions Flashcards

1
Q

How much saliva is secreted daily?

A

Approximately 1.5 L

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2
Q

What are the functions of saliva?

A 
Lubrication
Dilution of foul tastes
Maintaining oral hygiene
Maintaining dental mineralisation
First stage of digestion
Solvation allowing taste of food
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3
Q

Describe how saliva maintains oral hygiene

A

Lysozymes and peptidases break down bacteria in the mouth
Cleans food particles from between teeth
Contains lactoferrin to remove iron so bacteria cannot grow

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4
Q

Describe how saliva maintains dental mineralisation

A

Increases oral pH to protect against acid

Contains calcium and fluorine

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5
Q

Which enzymes are present in saliva?

A

Amylase and lingual lipase

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6
Q

When is lingual lipase activated?

A

When the pH is < 4

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7
Q

What are the three salivary glands?

A

Submandibular
Parotid
Sub-lingual

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8
Q

What type of saliva is secreted from the submandibular gland?

A

Seromucin

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9
Q

What type of saliva is secreted from the parotid gland?

A

Serous

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10
Q

What type of saliva is secreted from the sublingual gland?

A

Mucin

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11
Q

Which cells secrete the primary secretion of saliva?

A

Salivary acinar cells

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12
Q

How is the primary secretion of saliva modified?

A

Epithelial cells in the striated duct add or remove water or ions

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13
Q

How is flow rate from the salivary duct controlled?

A

Myoepithelial cells contract and relax

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14
Q

Describe the ionic composition of saliva relative to plasma

A

High potassium and bicarbonate

Low sodium and chloride

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15
Q

Describe the two stage hypothesis of saliva secretion

A

The ductal epithelium is impermeable to water, making the saliva hypotonic and only modified by ion movement once it leaves the acinus

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16
Q

How does flow rate alter the composition?

A

When flow rate is high, there is less time for modification making the saliva more watery

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17
Q

What influences the bicarbonate levels in saliva

A

The nature of the stimuli causing saliva secretion

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18
Q

What stimuli on the higher centres may increase saliva secretion?

A

Conditioned reflexes

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19
Q

What stimuli on the higher centres may decrease saliva secretion?

A

Fear
Mental effort
Dehydration

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20
Q

What stimuli on the salivary centres may increase saliva secretion?

A

Taste
Chewing
Smelling food
Feeling food

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21
Q

Describe how parasympathetic innervation increases saliva secretion

A

Activation of muscarinic receptors by acetylcholine causes contraction of the myoepithelium which increases the flow rate
Vasoactive intestinal peptide increases vasodilation and increases secretion

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22
Q

Which ions are absorbed by the ductal epithelium?

A

Sodium and chloride

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23
Q

Which ions are secreted by the ductal epithelium?

A

Potassium and biocarbonate

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24
Q

Describe how sympathetic innervation increases saliva secretion

A

Noradrenaline release causes myoepithelial contraction

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25
Q

Where does the pancreas secrete into?

A

Duodenum

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26
Q

What are the exocrine effects of the pancreatic secretions?

A

Nutrient digestion

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27
Q

What are the endocrine effects of the pancreatic secretions

A

Controlling glucose homeostasis

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28
Q

Describe the two stage hypothesis of pancreatic secretion

A

Sodium hydrogencarbonate is released in the primary secretion
Bicarbonate is exchanged for chloride in the duct

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29
Q

What stimulates release of pancreatic enzymes?

A

Increases intracellular calcium stimulates release of cholecystokinin or increases the vasovagal response

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30
Q

Where are pancreatic enzymes released from?

A

Pancreatic acinar cells

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31
Q

What hormone increases secretion of bicarbonate rich secretions?

A

Secretin

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32
Q

Describe cephalic regulation of pancreatic secretions

A

Vagal innervation increases gastrin releasing peptide and enzyme secretion
Gastrin releasing peptide increases gastrin release
Gastrin increases enzyme secretion

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33
Q

Describe gastric regulation of pancreatic secretions

A

Release of gastrin increases release of enzymes

Distension of the stomach intitiates the vasovagal response which causes enzyme release

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34
Q

Describe the intestinal regulation of pancreatic secretions

A

Protons and lipids in the intestine increase secretin release
Amino acids and lipids in the intestine increase CCK release
The vasovagal response

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35
Q

How much is secreted daily from the pancreas?

A

1.5 L

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36
Q

How much is secreted daily from the stomach?

A

2L

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37
Q

What are the functions of gastric secretions?

A

Protein digestion
Protection of stomach lining
Vitamin B12 absorption
Preventing infections

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38
Q

Are are the majority of gastric pits located?

A

Fundus

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39
Q

What are the cell types in the gastric pits

A 
Mucous neck cell
Parietal cell
Enterochromaffin like cell
Chief cell
D-cell
G-cell
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40
Q

What do mucous neck cells secrete?

A

Mucus and bicarbonate

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41
Q

What is the role of mucus?

A

To protect the stomach lining from the acidic contents

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42
Q

What is the role of bicarbonate?

A

To buffer the contents of the stomach

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43
Q

What is secreted by parietal cells?

A

Gastric acid and intrinsic factor

44
Q

What is the role of gastric acid?

A

To aid digestion

45
Q

What is the role of intrinsic factor?

A

To facilitate vitamin B12 absorption

46
Q

What is secreted by enterochromaffin like cells?

A

Histamine

47
Q

What is the role of histamine?

A

Stimulate parietal cells

48
Q

What is secreted by chief cells?

A

Pepsinogen and gastric lipase

49
Q

What is the role of pepsinogen?

A

To be converted into pepsin which digests proteins

50
Q

What is secreted by D cells?

A

Somatostatin

51
Q

What is the role of somatostatin

A

A negative feedback effect on gastric acid release from G cells

52
Q

What is secreted from G cells?

A

Gastrin

53
Q

What is the role of gastrin?

A

To stimulate enterochromaffin like cells

54
Q

Which cell are pyloric pits rich in?

A

G cells

55
Q

Describe the process of acid secretion

A

Water breaks down in the parietal cell releasing a proton and hydroxide ion.
The Na/K/ATPase sets up a potassium gradient
The proton is actively pumped into the lumen via a H/K transporter
Bicarbonate is produced by carbonic anhydrase
Biarbonate is exchanged for chloride on the basolateral membrane, setting up a chloride gradient
Chloride passes through a transporter into the lumen

56
Q

What is the alkaline tide?

A

The bicarbonate pumped into the blood over the basolateral membrane causes the it to be more alkaline

57
Q

What drug can inhibit acid secretion?

A

Omeprazol

58
Q

What is the distribution of pH in the gastric lumen?

A

The closer to the lining, the higher the pH

59
Q

What stimulates gastric mucus secretion?

A

Prostaglandins

60
Q

What inhibits gastric mucus secretion?

A

Aspirin or ethanol

61
Q

What does acetylcholine increase in the stomach?

A

Parietal cell secretion
Histamine release
Gastrin releasing peptide release

62
Q

What drug inhibits the action of histamine?

A

Cimetidine

63
Q

What cephalic factors stimulate acid secretion?

A

Food in mouth

Anger or tension

64
Q

What cephalic factors inhibits acid secretion?

A

Fear

Depression

65
Q

What gastric factors stimulate acid secretion?

A

Gastric distension

Hypertonicity

66
Q

What gastric factors inhibit acid secretion?

A

Protons

67
Q

What intestinal factors stimulate acid secretion?

A

Products of digestion

68
Q

What structure in the chief cell secretes pepsinogen?

A

Zymogen granules

69
Q

What stimuli cause pepsinogen release?

A

Acetylcholine
Secretin
Gastrin
Cholecystokinin

70
Q

At what pH can pepsinogen be cleaved?

A

pH <5

71
Q

Which gastric secretion is the only essential one?

A

Intrinsic factor

72
Q

What does absence of intrinsic factor cause?

A

Pernicious anaemia

73
Q

How is pernicious anaemic treated?

A

Injection of cyanocobalamin

74
Q

Which enzyme converts trypsinogen to trypsin?

A

Enterokinase

75
Q

Which enzyme converts chymotrypsinogen to chymotrypsin?

A

Trypsin

76
Q

Which enzyme converts procarboxypeptidase to carboxypeptidase?

A

Trypsin

77
Q

What are the main secretions of the small intestine?

A

Sodium hydrogencarbonate

Sodium chloride

78
Q

What is secreted from the crypts and Brunner’s glands?

A

Sodium hydrogencarbonate

79
Q

What is the role of sodium hydrogencarbonate in the small intestine?

A

Protection from gastric hydrogen ions

80
Q

What are the thought functions of NaCl in the small intestine?

A

Osmotic equilibration

Flushing of pathogens

81
Q

Where do secretions come from in the small intestine?

A

Enterocytes in the crypts of Lieberkuhn

82
Q

What are the role of Paneth cells?

A

Secretion of lysozymes for antibacterial action

83
Q

What stimulates sodium chloride secretion?

A

Vasoactive intestinal peptide and noradrenaline

Acetylcholine

84
Q

Describe the process of sodium chloride secretion

A

M3 muscarinic receptors stimulate calcium ion release
VIP and calcium ions increase cAMP levels within the cell
cAMP activates CFTR chloride channel
Chloride is brought in via Na/Cl/K transporter and exported via CFTR
Na/Cl/K transporter creates a Na gradient between the interstitium and the cell
Na passively moves transcellularly into the lumen

85
Q

How does the cholera toxin cause secretory diarrhoea?

A

The cholera toxin chronically activates the GPCRs via GTPase inhibition, which causes increased cAMP in the cell
This causes overactivation of the CFTR channel, and therefore excess chloride secretion
Results in excess water drawn into the lumen by osmosis

86
Q

What occurs in the large intestine?

A

Sodium and chloride is reabsorbed

Potassium and bicarbonate is secreted

87
Q

What stimulates sodium reabsorption in the large intestine?

A

Aldosterone

88
Q

What are the eight main roles of the liver?

A 
Regulation of metabolism
Glycogen storage
Production of ketone bodies
Conversion of ammonia to urea
Synthesis of plasma proteins
Storage of iron and vitamins A, D and B12
Detoxification
Bile formation
89
Q

What are the functions of bile?

A

Aiding fat digestion
Acting as a route for metabolite excretion
Neutralisation of duodenal acidity

90
Q

What are the three stages in bile secretion?

A

Formation
Storage and concentration
Expulsion and transport

91
Q

Describe the pathway that bile travels through into the duodenum

A 
Hepatocytes
Canniculi
Intrahepatic small bile ducts
Left and right hepatic ducts
Common hepatic duct
Gallbladder
Duodenum
92
Q

Describe the composition of bile

A

50% bile acids
40% phospholipids
4% cholesterol
2% bile pigments

93
Q

Describe the production of bile salts

A

Cholesterol is converted into primary bile acids

Bile acids are conjugated to taurine or glycine

94
Q

What causes conversion of cholic acid to deoxycholic acid?

A

Bacterial changes in the colon

95
Q

What properties of bile salts make it good to aiding with fat digestion

A

They are amphipathic so will surround fat droplets to make them more accessible to enzymes

96
Q

What is enterohepatic cycling?

A

The cycling of bile acids and salts from the ileum back to the liver

97
Q

Describe the process of enterohepatic cycling in terms of bile salts

A

The bile salt is drawn into the enterocyte via a sodium transporter
The bile salt then moves into the portal blood along with a bile acid via an anion exchanger
The bile salt is then drawn into the hepatocyte via another sodium transporter
A bile salt and a bile acid are then transported into the canniculi via an ATP dependent transporter

98
Q

Describe the process of enterohepatic cycling in terms of bile acids

A

The bile acid is passively drawn into the enterocyte
The bile salt then moves into the portal blood along with a bile acid via an anion exchanger
The bile salt is then drawn into the hepatocyte via an organic anion exchanger
A bile salt and a bile acid are then transported into the canniculi via an ATP dependent transporter

99
Q

Why do bile acids move passively into the enterocytes while bile salts require a transporter?

A

Bile acids are hydrophobic so can pass through the cell membrane

100
Q

Describe bile acid dependent fluid secretion

A

The bile acid is actively secreted from the hepatocytes and pull cations with them
This creates an osmotic gradient, so water follows the cations

101
Q

Describe bile acid independent fluid secretion

A

This occurs within the bile duct and gallbladder
Sodium and chloride are reabsorbed and carbonate is secreted in exchange
Water follows the sodium and chloride to concentrate the bile

102
Q

Describe how bile is modified to better neutralise acidity

A

Secretin levels increase in response to duodenal acidity

Secretin increases bile secretion resulting in secretion of dilute bile

103
Q

Describe how bile is modified to emulsify fats

A

Protein and fat digestion in duodenum stimulates release of cholecystokinin
CCK stimulates gallbladder contraction and relaxation of the sphincter of Oddi resulting in secretion of concentrated bile

104
Q

What happens to bile during fasting?

A

The sphincter of Oddi is closed, so bile moves into the gallbladder

105
Q

What happens to bile during eating?

A

CCK release causes gallbladder contraction and opening of the sphincter of Oddi to release bile

BMSC2225 Absorption and Excretion - GI Tract Physiology (8 decks)

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