Secretions of GI Tract & Pancreas Flashcards
1
Q
What are the main components of saliva?
A
water, electrolytes, alpha-amylase, lingual lipase, kallikrein, mucus
2
Q
What is the tonic relation of saliva (upon secretion) to blood plasma?
A
hypotonic
3
Q
What ions are in high concentration in saliva?
A
Potassium
Bicarbonate
4
Q
What ions are in low concentration in saliva?
A
Sodium
Chloride
5
Q
What is the role of alpha-amylase?
A
breakdown of carbohydrates
- only in the saliva
- inactive once the environmental pH decreases
6
Q
What is the role of lingual lipase?
A
breakdown of lipids
- active throughout the GI tract
- not sensitive to pH changes
7
Q
What is the role of kallikrein?
A
-makes bradykinin from kininogen
–bradykinin is a vasodilator that increases bloodflow locally during periods of increased salivatory activity
8
Q
How do ductal cells modify primary acinar secretions in order to create the final saliva product?
A
- increased absorption of sodium and chloride from lumen into blood
- increased secretion of potassium and bicarbonate into the lumen from the blood
9
Q
True or False: ductal cells in salivatory glands are permeable to water
A
False
10
Q
In salivatory ductal cells, what are important cellular mechanisms for secreting potassium and bicarbonate into the lumen?
A
chloride-bicarb exchanger = apical side
CFTR (secretes bicarb) = apical side
hydrogen-potassium exchanger = apical side
sodium-bicarb symporter = basal side
11
Q
In salivatory ductal glands, what are important cellular mechanisms for absorbing sodium and chloride?
A
sodium-potassium ATPase = basal side
chloride channels = basal side
sodium-hydrogen exchanger = apical side
12
Q
What is the parasympathetic innervation to the salivatory glands?
A
CN VII to the submandibular and sublingual glands
–synapse at the submandibular and otic ganglia
CN IX to the parotid gland
13
Q
What is the neurotransmitter used in the parasympathetic innervation of the salivatory glands?
A
Ach
14
Q
What is the sympathetic innervation to the salivatory glands?
A
T1-T3 spinal nerves
- -synapse at the cervical ganglion
- -nerves travel on the arteries (periarterial) to get to the salivatory glands
15
Q
What is the neurotransmitter used in the sympathetic innervation of the salivatory glands?
A
NE
16
Q
What environmental factors stimulate saliva production?
A
conditioning
smell
taste
nausea
17
Q
What environmental factors inhibit saliva production?
A
fear
sleep
dehydration
18
Q
What receptor and pathway does Ach activate in parasympathetic stimulation of saliva production?
A
M3 receptor
(IP3 and DAG pathway)
-increases intracellular calcium
19
Q
What receptor and pathway does NE activate in sympathetic stimulation of saliva production?
A
Beta-adrenergic receptor
cAMP pathway
20
Q
True or False: parasympathetic and sympathetic innervation both stimulate saliva production
A
True; parasympathetic stimulation dominates while sympathetic stimulation just helps
21
Q
What two major hormones modify saliva composition?
A
ADH and aldosterone
- -decrease sodium
- -increase potassium
22
Q
What cells are responsible for the mechanical part of saliva secretion?
A
myoepithelial cells contract to secrete saliva
23
Q
What are the main components of gastric juice?
A
HCl Pepsin Mucus IF Water
24
Q
What is the role of HCl as a part of the gastric juice?
A
- initiates protein digestion
- kills a large number of bacteria
-required to create low pH that converts pepsinogen to pepsin
25
What is the role of pepsinogen (pepsin) as a part of the gastric juice?
-protease
26
What is the role of mucus as a part of the gastric juice?
- lines stomach wall and protects from damage
- lubricant
- neutralizes acid
- maintains neutral pH of the surface mucosa
27
What is the role of intrinsic factor as a part of the gastric juice?
-req'd for the absorption of vitamin B12 (cobalamin) in the ileum
28
What is the role of water as a part of the gastric juice?
- serves as a medium for the action of HCl and enzymes
| - solubilizes much of the ingested material
29
Where are the oxyntic glands in the stomach?
-in the body and fundus of the stomach
30
What cells comprise the oxyntic glands?
- parietal cells
- mucus neck cells
- chief cells
- enterochromaffin-like cells
- D cells
- Enterochromaffin Cells
31
What is the role of parietal cells in the gastric glands?
- secrete HCl
- secrete IF
-HCl is formed at the villus-like membranes of the canaliculi
32
What is the role of mucus neck cells in the gastric glands?
- secrete mucus, bicarbonate, and pepsinogen
| - -protective neutralizing effect on the gastric mucosa
33
What is the role of chief cells in the gastric glands?
-secrete pepsinogen
34
What is the role of enterochromaffin-like cells in the gastric glands?
- secrete histamine
| - -histamine binds to H2 receptors on parietal cells and increases secretion of acid
35
What is the role of D cells in the gastric glands?
-secrete somatostatin
36
What is the direct pathway for the action of somatostatin on acid secretion?
-somatostatin binds to a receptor on parietal cells and inhibits secretion of acid
37
What are the two types of indirect pathways for the action of somatostatin on acid secretion?
- somatostatin inhibits ECL cells from releasing histamine
| - inhibits G cells from releasing gastrin
38
What is the role of enterochromaffin cells in the gastric glands?
- secretes serotonin
- -senses secretions and ctx of the gastric wall
- relays messages to IPAN
39
Where are the pyloric glands in the stomach?
-in the antrum
40
What types of cells comprise the pyloric glands?
- D cells
- enterochromaffin cells
- G cells
- mucus cells
41
What is the role of G cells in the gastric glands?
- secretes gastrin into systemic circulation
- -gastrin is delivered back to the stomach
- -binds to CCKB receptors on parietal cells
- -stimulates acid secretion
42
What is the required environment for pepsinogen to be converted to pepsin?
- low pH
- ideal pH (1.8-3.5)
- reversible inactivation (3.5-5.0)
- irreversible inactivation (>5.0)
43
What is the major enzyme responsible for generating the acid and the bicarb components in the creation of gastric juice?
carbonic anyhdrase
44
What transporters are responsible for the acid secretion into the stomach?
```
hydrogen-potassium ATPase (apical side)
chloride channels (apical side)
chloride-bicarb exchanger (basal side)
```
45
How does CN X stimulate gastric secretion via Ach?
- Ach binds to the M3 receptor on parietal cells and stimulates acid secretion via the IP3 and DAG pathway
- Ach also has potentiation effects on G cells and ECL cells, stimulating release of gastrin and histamine
46
How does CN X stimulate gastric secretion via GRP?
GRP binds to G cells which secrete gastrin
- gastrin binds to CCKB receptors
- activates IP3 and DAG pathway
- stimulates acid secretion
- gastrin also potentiates histamine from ECL cells
47
How do ECL cells affect gastric secretion?
ECL cells secrete histamine
- binds to H2 receptors
- stimulates cAMP pathway
- stimulates acid secretion
- acid secreted via H+-K+ ATPase
48
How does somatostatin affect gastric aid secretion?
- inhibits the cAMP pathway
- inhibits the ECL cells from secreting histamine
- inhibits G cells from secreting gastrin
49
How do prostaglandins affect gastric acid secretion?
- inhibit ECL cells from secreting histamine
| - inhibit cAMP pathway
50
What membrane transporter is responsible for the secretion of H+?
H+-K+ ATPase
51
How does atropine (an Ach receptor antagonist) block gastric acid secretion?
- blocks the M3 receptor that normally responds to Ach
- does not block the effects of gastrin d/t GRP
-blocks the potentiation effects of Ach on gastrin and histamine via G cells and ECL cells
52
How does the duodenal environment impact gastric secretion?
-acid secretion is stimulated due to:
- -distention of the small intestines
- -presence of digested proteins
53
How does cimetidine work to decrease gastric acid secretions?
- H2 receptor antagonist
- blocks the H2 receptor from binding histamine
-thus, also blocks the potentiated effects on ECL cells from gastin and Ach
54
How does cimetidine work to decrease gastric acid secretions?
-inhibits the H+-K+ ATPase
55
What are the three phases of gastric acid secretion?
- cephalic
- gastric
- intestine
56
How much of the gastric acid secretion is the cephalic phase responsible for?
30%
57
What are the stimuli that affect the cephalic phase?
- smell and taste
- chewing and swallowing
- conditioned reflexes
58
What are the events (mechanisms) that cause gastric secretions during the cephalic phase?
- CN X releases Ach to parietal cells that secrete H+
- CN X releases GRP to G Cells which release gastrin into the bloodstream; the gastrin is delivered back to the stomach and stimulates parietal cells to secrete H+
59
True or False: a vagotomy completely abolishes the cephalic phase of gastric acid secretion
True
60
How much of the gastric acid secretion is the gastric phase responsible for?
-60%
61
What are the stimuli that affect the gastric phase of gastric acid secretion?
- stomach distention
| - presence of breakdown of proteins, amino acids, and small peptides
62
What are the events (mechanisms) of CN X that cause gastric acid secretions during the gastric phase?
- CN X releases Ach to parietal cells that secreted H+
- CN X releases GRP to G cells that secrete gastrin into the bloodstream; the gastrin is delivered back to the stomach and stimulates parietal cells to secrete H+
63
What are the mechanical events and/or mechanisms that cause gastric acid secretions during the gastric phase?
- distention of the stomach antrum causes local reflexes to stimulate G cells to release gastrin
- amino acids and small peptides stimulate G Cells to release gastrin
64
How much of the gastric acid secretions is the intestinal phase responsible for?
-10%
65
What are the stimuli that affect the intestinal phase of gastric acid secretion?
- distention of the small intestine
| - presence of digested protein
66
What are the events (mechanisms) that cause gastric acid secretion in the intestinal phase?
- parietal cells secrete HCl
| - intestinal G Cells secrete gastrin into the bloodstream
67
What is a gastrinoma?
duodenal or pancreatic neuroendocrine tumor that secretes large amounts of gastrin
68
What syndrome is characterized by the presence of gastrinoma(s)?
Zollinger-Ellison Syndrome
69
How does Zollinger-Ellison Syndrome affect parietal cells?
- causes increased H+ secretion
| - increases parietal cell mass
70
How does Zollinger-Ellison Syndrome affect absorption in the small intestines?
- absorption of sodium and water is inhibited by the excess of gastrin
- causes secretory diarrhea
71
How does Zollinger-Ellison Syndrome affect the structural integrity of the small intestines?
- excess H+ in the duodenum overwhelms the buffering capacity of bicarbonate in the pancreatic juice
- causes ulcers
72
What are the effects of the abnormally low pH in the intestines that is caused by Zollinger-Ellison Syndrome?
- inactivates pancreatic digestive enzymes
- interferes w/ emulsification of fats by bile acids
- damages intestinal epithelial cells and villie
- leads to maldigestion and malabsorption
- -steatorrhea
73
What is the Secretin Stimulation Test?
- under normal conditions, secretin inhibits release of gastrin
- in gastrinomas, injection of secretin causes a paradoxical increase of gastrin
74
What are the products secreted by parietal cells?
- HCl
| - Intrinsic Factor
75
What is the importance of Intrinsic Factor?
- IF is req'd for absorption of B12 in the ileum
| - IF is a mucoprotein that binds to B12
76
Why is pernicious anemia hard to detect in the early development of the condition?
-the liver stores enough B12 to last for several years
77
What are possible causes of pernicious anemia?
- atrophic gastritis = chronic inflammation of stomach mucosa leads to loss of parietal cells
- autoimmune metaplastic atrophic gastritis = immune system attacks IF protein or gastric parietal cells
78
How does a gastrectomy or gastric bypass affect B12?
- creates a loss of parietal cells that secrete IF which is req'd for B12 absorption
- exclusion of stomach, duodenum, and proximal jejunum alters B12 absorption
79
What types of mucosal cells are present in the stomach and how do they contribute to gastric defense?
- mucus neck cells secrete mucus
| - surface mucus cells secrete bicarbonate
80
List some protective factors of the gastric mucosa.
bicarbonate, mucus, prostaglandins, mucosal bloodflow, gastrin (stimulates somatostatin), and growth factors
-protects gastric mucosa from H+ and pepsin
81
List some damaging factors of the gastric mucosa.
acid, pepsin, NSAID's (ex: aspirin), Helicobacter pylori, alcohol, bile, and stress
82
What are some characteristics of gastric ulcers?
- form on stomach lining
| - form mainly b/c mucosal barrier is defective, not b/c of acid
83
What are some characteristics of duodenal ulcers?
- form on lining of duodenum, not malignant
- more common than gastric ulcers
- increased H+ secretion rates and more parietal cells
84
How are H+ and gastrin levels in the presence of a gastric ulcer?
- decreased H+
| - increased gastrin
85
How are H+ and gastrin levels in the presence of a duodenal ulcer?
- increased H+
| - increased gastrin
86
How are the H+ and gastrin levels in the presence of a gastrinoma?
- markedly increased H+
| - markedly increased gastrin
87
What are the two main components of pancreatic juice and which cell types secrete them?
- enzymatic secretion (amylase, lipase, protease)
- -secreted by acinar cells
- aqueous secretion (bicarb fluid)
- -secreted by centroacinar and ductal cells
88
True or False: amylases are secreted from the pancreas in their active form
True
89
True or False: lipases are secreted from the pancreas in their active form
True
90
True or False: proteases are secreted from the pancreas in their active form
False; proteases are secreted as zymogens and converted into their active form in the lumen of the duodenum
91
What is the enzyme responsible for providing the bicarb that is secreted into the pancreatic juice?
carbonic anhydrase
92
What are the intracellular mechanisms for bicarb secretion into the pancreatic juice?
- CFTR
| - chloride bicarb exchanger
93
What is the mechanism by which pancreatic zymogens are secreted into the small intestine?
- peptides and fatty acids activate I cells
- I cells release CCK
- CCK causes release of pancreatic enzymes
94
How are the zymogens activated in the small intestine?
- trypsinogen is activated by enterokinase (a brush border enzyme)
- active trypsin automatically catalyzes the rest of the trypsinogen and other pancreatic proteases
95
What is the role of cystic fibrosis transmembrane regulator (CFTR) in the production of pancreatic juice?
-CFTR secretes chloride into the lumen so that the chloride-bicarb exchanger can exchange the chloride back into the cell and secrete bicarb into the lumen
96
What is the purpose of the aqueous bicarb solution in the duodenum?
-aqueous bicarb solution flushes enzymes into the duodenum
97
What happens if the cystic fibrosis transmembrane regulator (CFTR) is impaired?
- mucus is thick and enzymes cannot be properly flushed into the small intestine
- enzymes become prematurely activated in the enzyme and digest it; leads to recurrent pancreatitis
98
What is the mechanism behind why the pancreatic enzymes are prematurely activated?
-trypsin inhibitor is overwhelmed by the accumulation of enzymes
99
List factors that stimulate secretion of saliva.
- parasympathetic stimulation dominates
| - stimulated by smell, taste, chewing, swallowing)
100
List factors that decrease secretion of saliva.
- sleep
- dehydration
- fear
- atropine
101
List factors that stimulate gastric secretion.
- gastrin
- histamine
- parasympathetics (Ach)
102
List factors that decrease gastric secretion.
- H+ in stomach
- chyme in the small intestine
- somatostatin
- atropine, cimetidine, omeprazole
103
List factors that stimulate pancreatic secretion.
- secretin
- CCK
- parasympathetics
104
What is the mechanism by which the aqueous bicarb solution is secreted into the intestines?
-presence of H+ in the intestinal lumen stimulates S Cells in the intestine to secrete secretin which activates the cAMP pathway and initiates secretion of bicarb
