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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
Where does the pancreas secrete into?
Duodenum
26
What are the exocrine effects of the pancreatic secretions?
Nutrient digestion
27
What are the endocrine effects of the pancreatic secretions
Controlling glucose homeostasis
28
Describe the two stage hypothesis of pancreatic secretion
Sodium hydrogencarbonate is released in the primary secretion Bicarbonate is exchanged for chloride in the duct
29
What stimulates release of pancreatic enzymes?
Increases intracellular calcium stimulates release of cholecystokinin or increases the vasovagal response
30
Where are pancreatic enzymes released from?
Pancreatic acinar cells
31
What hormone increases secretion of bicarbonate rich secretions?
Secretin
32
Describe cephalic regulation of pancreatic secretions
Vagal innervation increases gastrin releasing peptide and enzyme secretion Gastrin releasing peptide increases gastrin release Gastrin increases enzyme secretion
33
Describe gastric regulation of pancreatic secretions
Release of gastrin increases release of enzymes | Distension of the stomach intitiates the vasovagal response which causes enzyme release
34
Describe the intestinal regulation of pancreatic secretions
Protons and lipids in the intestine increase secretin release Amino acids and lipids in the intestine increase CCK release The vasovagal response
35
How much is secreted daily from the pancreas?
1.5 L
36
How much is secreted daily from the stomach?
2L
37
What are the functions of gastric secretions?
Protein digestion Protection of stomach lining Vitamin B12 absorption Preventing infections
38
Are are the majority of gastric pits located?
Fundus
39
What are the cell types in the gastric pits
``` Mucous neck cell Parietal cell Enterochromaffin like cell Chief cell D-cell G-cell ```
40
What do mucous neck cells secrete?
Mucus and bicarbonate
41
What is the role of mucus?
To protect the stomach lining from the acidic contents
42
What is the role of bicarbonate?
To buffer the contents of the stomach
43
What is secreted by parietal cells?
Gastric acid and intrinsic factor
44
What is the role of gastric acid?
To aid digestion
45
What is the role of intrinsic factor?
To facilitate vitamin B12 absorption
46
What is secreted by enterochromaffin like cells?
Histamine
47
What is the role of histamine?
Stimulate parietal cells
48
What is secreted by chief cells?
Pepsinogen and gastric lipase
49
What is the role of pepsinogen?
To be converted into pepsin which digests proteins
50
What is secreted by D cells?
Somatostatin
51
What is the role of somatostatin
A negative feedback effect on gastric acid release from G cells
52
What is secreted from G cells?
Gastrin
53
What is the role of gastrin?
To stimulate enterochromaffin like cells
54
Which cell are pyloric pits rich in?
G cells
55
Describe the process of acid secretion
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
What is the alkaline tide?
The bicarbonate pumped into the blood over the basolateral membrane causes the it to be more alkaline
57
What drug can inhibit acid secretion?
Omeprazol
58
What is the distribution of pH in the gastric lumen?
The closer to the lining, the higher the pH
59
What stimulates gastric mucus secretion?
Prostaglandins
60
What inhibits gastric mucus secretion?
Aspirin or ethanol
61
What does acetylcholine increase in the stomach?
Parietal cell secretion Histamine release Gastrin releasing peptide release
62
What drug inhibits the action of histamine?
Cimetidine
63
What cephalic factors stimulate acid secretion?
Food in mouth | Anger or tension
64
What cephalic factors inhibits acid secretion?
Fear | Depression
65
What gastric factors stimulate acid secretion?
Gastric distension | Hypertonicity
66
What gastric factors inhibit acid secretion?
Protons
67
What intestinal factors stimulate acid secretion?
Products of digestion
68
What structure in the chief cell secretes pepsinogen?
Zymogen granules
69
What stimuli cause pepsinogen release?
Acetylcholine Secretin Gastrin Cholecystokinin
70
At what pH can pepsinogen be cleaved?
pH <5
71
Which gastric secretion is the only essential one?
Intrinsic factor
72
What does absence of intrinsic factor cause?
Pernicious anaemia
73
How is pernicious anaemic treated?
Injection of cyanocobalamin
74
Which enzyme converts trypsinogen to trypsin?
Enterokinase
75
Which enzyme converts chymotrypsinogen to chymotrypsin?
Trypsin
76
Which enzyme converts procarboxypeptidase to carboxypeptidase?
Trypsin
77
What are the main secretions of the small intestine?
Sodium hydrogencarbonate | Sodium chloride
78
What is secreted from the crypts and Brunner's glands?
Sodium hydrogencarbonate
79
What is the role of sodium hydrogencarbonate in the small intestine?
Protection from gastric hydrogen ions
80
What are the thought functions of NaCl in the small intestine?
Osmotic equilibration | Flushing of pathogens
81
Where do secretions come from in the small intestine?
Enterocytes in the crypts of Lieberkuhn
82
What are the role of Paneth cells?
Secretion of lysozymes for antibacterial action
83
What stimulates sodium chloride secretion?
Vasoactive intestinal peptide and noradrenaline | Acetylcholine
84
Describe the process of sodium chloride secretion
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
How does the cholera toxin cause secretory diarrhoea?
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
What occurs in the large intestine?
Sodium and chloride is reabsorbed | Potassium and bicarbonate is secreted
87
What stimulates sodium reabsorption in the large intestine?
Aldosterone
88
What are the eight main roles of the liver?
``` 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
What are the functions of bile?
Aiding fat digestion Acting as a route for metabolite excretion Neutralisation of duodenal acidity
90
What are the three stages in bile secretion?
Formation Storage and concentration Expulsion and transport
91
Describe the pathway that bile travels through into the duodenum
``` Hepatocytes Canniculi Intrahepatic small bile ducts Left and right hepatic ducts Common hepatic duct Gallbladder Duodenum ```
92
Describe the composition of bile
50% bile acids 40% phospholipids 4% cholesterol 2% bile pigments
93
Describe the production of bile salts
Cholesterol is converted into primary bile acids | Bile acids are conjugated to taurine or glycine
94
What causes conversion of cholic acid to deoxycholic acid?
Bacterial changes in the colon
95
What properties of bile salts make it good to aiding with fat digestion
They are amphipathic so will surround fat droplets to make them more accessible to enzymes
96
What is enterohepatic cycling?
The cycling of bile acids and salts from the ileum back to the liver
97
Describe the process of enterohepatic cycling in terms of bile salts
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
Describe the process of enterohepatic cycling in terms of bile acids
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
Why do bile acids move passively into the enterocytes while bile salts require a transporter?
Bile acids are hydrophobic so can pass through the cell membrane
100
Describe bile acid dependent fluid secretion
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
Describe bile acid independent fluid secretion
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
Describe how bile is modified to better neutralise acidity
Secretin levels increase in response to duodenal acidity | Secretin increases bile secretion resulting in secretion of dilute bile
103
Describe how bile is modified to emulsify fats
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
What happens to bile during fasting?
The sphincter of Oddi is closed, so bile moves into the gallbladder
105
What happens to bile during eating?
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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