Gastrointestinal secretions and their control Flashcards
1
Q
How much water is ingested daily through diet?
A
2000 mL
2
Q
How much water is added to the gut from saliva?
A
1500 mL
3
Q
How much water is added from gastric secretion?
A
2000 mL
4
Q
How much water is added from bile?
A
500 mL
5
Q
How much water is added from pancreatic secretion?
A
1500 mL
6
Q
How much water is added from intestinal secretion?
A
1500 mL
7
Q
How much water is absorbed in the small intestine?
A
8500 mL
8
Q
How much water is absorbed in the colon?
A
350 mL
9
Q
How much water is lost in feces?
A
150 mL
10
Q
What cells produce the primary secretion of saliva?
A
Acinar cells.
11
Q
What ultimately drives the secretion process in salivary glands?
A
The Na⁺ pump on the basolateral side of the cells.
12
Q
What types of transporters and channels are involved in saliva secretion?
A
Na⁺/K⁺ ATPase (Na⁺ pump)
Cl⁻ and HCO₃⁻ transporters
Na⁺ and K⁺ channels
Water (H₂O) channels
13
Q
What is the final composition of the primary secretion of saliva?
A
Watery and isotonic with plasma.
14
Q
What happens to the primary saliva secretion as it passes through the duct?
A
It gets modified.
15
Q
What ions are reabsorbed in the duct?
A
Na⁺ (sodium) and Cl⁻ (chloride).
16
Q
What ions are added to the saliva in the duct?
A
K⁺ (potassium) and HCO₃⁻ (bicarbonate).
17
Q
What is the final composition of saliva after modification?
A
HCO₃⁻ rich (bicarbonate-rich)
Hypotonic secretion
18
Q
How does flow rate affect saliva composition?
A
At high flow rates, modification is less effective.
Less Na⁺ & Cl⁻ reabsorption occurs, so saliva remains more isotonic.
More HCO₃⁻ remains in the final secretion.
19
Q
What ions are present in saliva?
A
Ca²⁺ (calcium) and phosphate.
20
Q
What large molecules are found in saliva
A
Mucins (glycoproteins)
Lysozyme
Amylase
Released from acinar cells by exocytosis
21
Q
What is the role of Immunoglobulin A (IgA) in saliva?
A
Made by nearby plasma cells (B lymphocytes).
Binds to a receptor on the basolateral side of acinar cells.
Transported into the lumen of the gland.
22
Q
How does saliva help with food processing?
A
It lubricates food for chewing and swallowing.
23
Q
What enzyme in saliva aids digestion?
A
Amylase, which initiates starch digestion.
24
Q
How does saliva protect against microbes?
A
Several saliva components have antimicrobial activities
25
How does saliva help protect teeth?
Maintains pH balance.
Ca²⁺ and phosphate ions prevent demineralization of teeth.
26
How do different salivary glands vary in secretion composition?
Parotid gland: More amylase than mucus.
Submandibular gland: More mucus than amylase.
Sublingual & minor mucous glands: Only mucus.
27
Which gland has the highest flow rate in different conditions?
Basal condition: Submandibular gland.
Stimulated condition: Parotid gland.
28
How does the autonomic nervous system (ANS) regulate salivary secretion?
Parasympathetic (PS) stimulation → Increases fluid and electrolyte secretion.
Sympathetic (S) stimulation → Increases macromolecular component secretion.
29
What do oesophageal secretions consist of?
Only mucus, produced by widespread minor glands.
30
How is oesophageal secretion regulated?
It is neutrally controlled
31
What triggers the cephalic phase of digestion?
Thinking about food
Presence of food in the mouth
32
What happens during the cephalic phase?
Salivary and gastric secretions increase.
Chewing breaks food into smaller particles.
Amylase in saliva initiates starch digestion.
33
What type of control regulates the cephalic phase?
Neural (extrinsic control).
34
What triggers the gastric phase of digestion?
Food entering the stomach.
35
What happens during the gastric phase?
Secretion of acid and pepsinogen.
Gastric motility increases, breaking down food mechanically.
Protein digestion begins.
36
What type of control regulates the gastric phase?
Neural (extrinsic and enteric nervous system [ENS]).
Hormonal regulation.
37
What triggers the intestinal phase of digestion?
Food entering the small intestine.
38
What happens during the intestinal phase?
Hormones released that inhibit gastric secretion and motility.
Biliary and pancreatic secretions are released into the duodenum.
Most digestion and nutrient absorption occur.
39
What type of control regulates the intestinal phase?
Neural (extrinsic and ENS).
Hormonal regulation.
40
What do chief (peptic) cells secrete?
Pepsinogen
41
What do parietal (oxyntic) cells secrete?
Hydrochloric acid (HCl)
Intrinsic factor
42
What additional components are secreted in the stomach?
Mucus from surface enterocytes
Gastric lipase
Water
43
What enzyme facilitates acid secretion in parietal cells?
Carbonic anhydrase
44
What reaction does carbonic anhydrase catalyze?
CO₂ + H₂O → H₂CO₃ (carbonic acid)
H₂CO₃ then dissociates into H⁺ and HCO₃⁻
45
How is H⁺ secreted into the gastric lumen?
H⁺ is pumped out via the H⁺/K⁺ ATPase pump
This process requires ATP because it moves H⁺ against its concentration gradient
46
How is Cl⁻ obtained for secretion into the gastric lumen?
Cl⁻ is absorbed from blood via an exchanger on the basolateral side of the cell
This exchanger exchanges HCO₃⁻ for Cl⁻
47
What is the net effect of H⁺ secretion on the blood?
HCO₃⁻ is moved into the blood
This is known as the alkaline tide (temporary increase in blood pH after a meal)
48
What happens to water during acid secretion?
Water follows ion movement into the gastric lumen via osmosis
49
Where are most proton pumps located in a resting (basal secretion) state?
Confined within intracellular tubulovesicles
50
What happens to tubulovesicles upon stimulation?
Tubulovesicles rearrange and fuse with canaliculi
Canaliculi become continuous with the luminal membrane
This increases the surface area for HCl secretion
51
What are the three mechanisms regulating acid secretion?
Neural regulation
Endocrine regulation
Paracrine regulation
52
What stimulates gastrin release from the pyloric antrum?
Proteins, coffee, alcohol, etc.
53
What inhibits gastrin release?
Low gastric pH
54
What are the effects of gastrin?
Induces gastric secretions and increases motility
55
Where is CCK (Cholecystokinin) released from, and what stimulates its release?
Released from the duodenal wall, stimulated by fats
56
What is the effect of CCK on the stomach?
Depresses gastric motility and secretion
57
What stimulates secretin release?
Acid in the duodenum
58
What is the effect of secretin?
Inhibits gastric secretion
59
Where are GIP and GLP-1 secreted from?
GIP from the small intestine (SI)
GLP-1 from the ileum/colon
60
What stimulates the release of GIP and GLP-1?
Fat and chyme in the lumen
61
What are the effects of GIP and GLP-1 on the stomach?
Inhibit gastric motility and secretion
62
What is the main function of the small intestine?
Absorption
63
What are the three main secretions of the small intestine?
Mucus (from goblet cells)
Isotonic saline (from crypt cells)
Alkaline mucus (from Brunner’s glands)
64
Where is mucus in the small intestine secreted from?
Goblet cells
65
Which small intestine cells secrete isotonic saline?
Crypt cells
66
What is the function of Brunner’s glands in the small intestine?
Secretion of alkaline mucus
67
What do surface enterocytes on villi produce?
Digestive enzymes embedded in the glycocalyx of their brush border
Bicarbonate-rich fluid
68
Where are pancreatic and biliary secretions discharged?
Into the duodenum
69
How are pancreatic and biliary secretions released into the duodenum?
Relaxation of the sphincter of Oddi
70
What are the two main components of pancreatic exocrine secretions?
Alkaline fluid rich in HCO₃⁻
Digestive enzymes
71
What is the function of the bicarbonate (HCO₃⁻) in pancreatic secretions?
neutralizes acidic chyme entering the small intestine from the stomach
72
Which pancreatic cells produce the alkaline fluid rich in HCO₃⁻?
Cells of the pancreatic duct
73
What 4 types of digestive enzymes are secreted by the pancreas?
Endopeptidases
Carboxypeptidase
Amylase
Lipase
74
Which pancreatic cells produce digestive enzymes?
Acinar cells
75
ow are digestive enzymes stored before being released?
Stored as inactive precursors in 'zymogen' granules inside acinar cells
76
How are pancreatic digestive enzymes released?
By exocytosis
77
What is the function of pancreatic digestive enzymes?
To break down macromolecules in food for digestion
78
What are the main hormones regulating pancreatic exocrine secretion?
Cholecystokinin (CCK) and Secretin
79
What stimulates the release of CCK?
Fats in the duodenum
80
What is the function of CCK in pancreatic secretion?
Induces release of enzyme-rich pancreatic secretions
81
What stimulates the release of Secretin?
Acidic chyme in the duodenum
82
What is the function of Secretin in pancreatic secretion?
Induces release of bicarbonate-rich pancreatic secretions
83
What is the source of bicarbonate (HCO₃⁻) in pancreatic duct cells?
CO₂ from blood forms H₂CO₃, catalyzed by carbonic anhydrase.
84
What provides energy for bicarbonate secretion in pancreatic duct cells?
The Na⁺/K⁺ ATPase pump on the basal (blood) side of the cell.
85
How does bicarbonate (HCO₃⁻) exit into the duct lumen?
Via an anion exchanger that swaps HCO₃⁻ for Cl⁻
86
What condition results from a defect in the CFTR Cl⁻ channel?
Cystic fibrosis, leading to failure of bicarbonate secretion and no enzyme delivery.
87
What triggers the release of secretin from the duodenal wall?
Acid chyme from the stomach.
88
What does secretin stimulate after being released?
Increases plasma secretin levels.
89
How does secretin affect the pancreas?
It stimulates bicarbonate secretion from pancreatic duct cells.
90
What is the role of bicarbonate in the small intestine?
It neutralizes acid in the small intestine.
91
What stimulates the release of CCK from the duodenal wall?
Fats and protein products entering the duodenum
92
What happens after CCK is released from the duodenal wall?
Plasma CCK levels increase.
93
How does CCK affect the pancreas?
CCK acts on pancreatic acinar cells to stimulate enzyme secretion.
94
What is the role of pancreatic juice secretion in digestion?
It delivers pancreatic and biliary secretions into the duodenum.
95
What is the final outcome of this process?
Digestion of fat and protein in the small intestine.
96
Where is bile primarily secreted?
Bile is made in the liver by hepatocytes.
97
What is the role of bile salts/acids?
They are essential for emulsification of fats in the small intestine (SI).
98
What is the main bile pigment and its function?
Bilirubin (a breakdown product of hemoglobin) is excreted in bile.
99
What other components are present in bile?
Cholesterol and lecithin.
100
How is bile fluid modified as it passes along bile ducts?
Water and HCO₃⁻ are added, stimulated by secretin.
101
What hormone stimulates gallbladder contraction?
CCK causes the gallbladder to contract and the sphincter of Oddi to relax.
102
idk what to do for this
103
What hormone from the small intestine stimulates insulin release in response to food?
GIP (Glucose-dependent Insulinotropic Peptide) stimulates insulin release in a feedforward manner.
104
Which hormone from the ileum/colon inhibits glucagon release and promotes satiety?
GLP-1 (Glucagon-Like Peptide-1)
105
What is the function of CCK (Cholecystokinin) in metabolism?
CCK promotes satiety after food digestion.
106
Which hormone is known as the "hunger hormone"?
Ghrelin, released from the stomach and other GI tract parts, promotes appetite and feeding behavior.
107
How is ghrelin secretion affected by food digestion?
Ghrelin release is inhibited when food is digested.
108
What is the primary function of the colon?
The main function of the colon is the absorption of water
109
What are the three main secretions of the colon?
Mucus - for lubrication.
HCO₃⁻ (bicarbonate) - secreted in exchange for Cl⁻.
K⁺ (potassium) - some K⁺ secretion occurs.
110
How does the colon absorb water?
Sodium (Na⁺) is absorbed via luminal Na⁺ channels.
More Na⁺ is absorbed than Cl⁻, leaving the lumen with a negative potential.
This drives K⁺ secretion into the lumen via the paracellular pathway.
Water follows Na⁺ absorption via osmosis.
111
What are the effects of inadequate salivary production (dry mouth)?
Difficulty swallowing
Enamel damage
Reduced microbiological protection
112
What condition results from a lack of intrinsic factor in gastric atrophy?
Pernicious anemia
113
How can H. pylori infection affect gastric secretions?
Causes gastritis by breaking down the mucosal barrier
Leads to exposure of acid & proteases
Can result in gastric and duodenal ulcers
114
What are the consequences of excess gastric acid production?
Duodenal ulcers
Small intestine (SI) malabsorption
Diarrhea
115
Why does pancreatitis lead to malabsorption?
pancreatitis reduces the production of digestive enzymes, leading to inefficient digestion and nutrient absorption.
116
How does cystic fibrosis affect pancreatic secretions?
Reduced Cl⁻ conductance
Decreased formation of alkaline pancreatic juice
Reduced enzyme delivery to the duodenum
117
What happens when bile is not adequately produced or delivered to the duodenum?
Fat malabsorption
Inadequate fat digestion
