GI Secretions Flashcards
(121 cards)
1
Q
What are the functions of saliva?
A
- initial digestion
- dilution and buffering
- lubrication with mucus
- oral hygiene
- evaporative cooling in dogs
2
Q
Higher salivary pH may increase susceptibility to what?
A
gingivitis due to more calculus
3
Q
How does saliva function for intial digestion?
A
- contains amylase for starch breakdown and lipase for lipid breakdown
4
Q
The dilution and buffering function of saliva is important for what?
A
rumination
5
Q
Saliva functioning to provide lubrication with mucus helps form what?
A
bolus
6
Q
How does saliva help with oral hygiene?
A
- flush oral cavity of food debris
- lysozomes in saliva to lyse bacteria
7
Q
What are the major salivary glands?
A
- parotid glands
- submandibular glands
- sublingual glands
8
Q
Initial saliva passes through which duct before the striated duct?
A
intercalated duct
9
Q
What structure is lined with acinar cells?
A
acinus
10
Q
What structure is responsible for producing initial saliva?
A
acinus
11
Q
Which duct is lined with ductal cells to alter the ion concentration of saliva?
A
striated duct
12
Q
What causes myoepithelial cells to contract and eject saliva?
A
neural stimulation
13
Q
Acinar and ductal cells have what type of innervation?
A
SNS and PSNS, but usually PSNS dominates
14
Q
Do salivary glands have high or low blood flow?
A
high
15
Q
Blood flow of salivary glands increases when what is stimulated?
A
saliva production
16
Q
What is saliva composed of?
A
- water
- electrolytes
- amylase (some species)
- lingual lipase
- kallikrein
- mucus
17
Q
What enzyme regulates local vasodilation associated with secretions?
A
kallikrein
18
Q
Saliva is _____ compared with plasma.
A
hypotonic
19
Q
Saliva is formed in a two step process. What are they?
A
- formation of isotonic solution by acinar cells
- modification of solution by ductal cells to become hypotonic
20
Q
Modification of saliva involves transporters where?
A
on the luminal and basolateral membranes
21
Q
What are the luminal membrane transporters for saliva formation?
A
- Na+/H+ exchange
- Cl-/HCO3- exchange
- H+/K+ exchange
22
Q
What are the basolateral membrane transporters for saliva formation?
A
-Na+/K+ ATPase
- Cl- channels
23
Q
Low concentrations in saliva mean what?
A
- Absorption of Na+ and Cl- into blood
- Secretion of K+ and HCO3- into saliva
24
Q
How is saliva hypotonic?
A
- ductal cells impermeable to water (not reabsorbing water)
25
Acing cells secrete what organic components?
- alpha-amylase (pig and human only)
- lingual lipase
- mucin glycoproteins
- IgA
- Kallikrein
26
At high flow rates (4mL/min), final saliva resembles what?
plasma
27
At low flow rates (<1mL/min), final saliva is what?
hypotonic
28
Final composition of saliva depends on wha?
Contact time with ductal cells
29
What is the exception to final composition being contact dependent? Why?
HCO3- concentration lowest at low flow rates and highest at hgh flow rates because its secretion is selectively stimulated by PSNS when saliva production is stimulated
30
What are the two features of salivary secretion regulation?
- salivary secretion is exclusively under neural control
- Salivary secretion stimulated by BOTH PSNS and SNS (usually PSNS dominant)
31
What is the PSNS innervation of salivary secretion regulation?
- carried on facial and glossopharyngeal nerves
- postganglionic neurons release acetylcholine
32
Acetylcholine released by postganglionic neurons of the PSNS for salivary regulation does what?
- acts on muscarinic receptors on acinar and ductal cells to increase volume and enzymes in saliva
33
What is the SNS innervation of salivary secretion regulation?
- originates in T1 to T3, synapse on superior cervical ganglion
- postganglionic neurons release NE
34
Norepinephrine released by postganglionic neurons of the SNS for salivary secretion regulation does what?
- acts on beta adrenergic receptors to increase secretions
35
What are the components of gastric juice?
- HCl
- pepsinogen
- intrinsic factor
- mucus
36
What components of gastric juice initiate protein digestion?
- HCl
pepsinogen
37
What component of gastric juice is essential for absorption of vitamin B12 in ileum?
intrinsic factor
38
What component of gastric juice protects gastric mucosa from HCl and lubricates?
mucus
39
The body of the stomach contains what glands?
oxyntic glands
40
Oxyntic glands empty products via ducts into where?
stomach lumen
41
The openings (aka pits) of oxyntic glands are lined with?
epithelial cells
42
Mucous neck cells of oxyntic glands secrete what?
mucus
43
Parietal cells of oxyntic glands secrete what?
- intrinsic factor
- HCl
44
Chief cells of oxyntic glands secrete what?
pepsinogen
45
What glands can be found in the antrum of the stomach?
pyloric glands
46
G cells of pyloric glands secrete what?
gastrin into circulation
47
Mucous neck cells of pyloric glands secrete what?
- mucous
- bicarbonate
- pepsinogen
48
What is the brief general mechanism of HCl secretion?
- by parietal cells
- apical (luminal) membrane has H+/K+ ATPase and Cl- channels
- basolateral membrane has Na+/K+ ATPase and Cl-/HCO3- exchangers
- cells contain carbonic anhydrase
49
What is the detailed mechanism of HCl secretion?
- CO2 combines with water to form H2CO3, which dissociates into H+ and HCO3-. Hydrogen goes to lumen of stomach via H+/K+ ATPase. Bicarb absorbed into blood via bicarbonate/Cl- exchanger.
- Cl- follows H+ into lumen by diffusing through Cl- channels
- Absorbed bicarbonate responsible for "alkaline tide" in gastric venous blood after meal. Alkaline tide eventually secreted back to GI tract via pancreatic secretions.
- net secretion of HCl and net absorption of bicarbonate
50
In order to alter HCl secretion, we can alter H+ secretion. What substances stimulate H+ secretion?
- histamine (paracrine)
- acetylcholine (neurocrine)
- gastrin (hormone)
51
Strong interaction of histamine with either acetylcholine or gastrin is called?
potentiation
- sum of two stimuli causes a greater response than individual responses alone
52
What drug will block histamine action on parietal cells? How?
Cimetidine blocks H2 receptors to block histamine action
53
Describe the action of histamine to stimulate H+ secretion.
- released from ECL cells in gastric mucosa
- binds to H2 receptors on parietal cells
- cAMP is second messenger
54
Describe the action of acetylcholine to stimulate H+ secretion.
- released from vagus nerves innervating gastric mucosa
- binds muscarinic receptors in parietal cells
- IP3/Ca2+ are second messengers
- Ach also stimulates ECL cells to release histamine
55
Describe the action of gastrin to stimulate H+ secretion.
- secreted by G cells in stomach antrum
- binds CCKB receptors on parietal cells
- IP3/Ca2+ are second messengers
- gastrin also stimulates ECL cells to release histamine
56
What drug mostly blocks H+ secretion, no matter the stimulus?
omeprazole
57
What are the two direct paths of vagal stimulation for HCl secretion?
1. vagus nerve --> parietal cells --> Ach --> HCl
2. vagus nerve --> GRP --> G cells --> gastrin
58
What is the indirect path of vagal stimulation for HCl secretion?
gastrin from G cells --> systemic circulation --> HCl from parietal cells
59
Atropine will not block HCl secretion completely. Why?
Because it cannot affect the second direct pathway at all
60
What are the phases of HCl secretion?
- cephalic phase
- gastric phase
- intestinal phase
61
The cephalic phase accounts for how much HCl secretion?
30%
62
The gastric phase accounts for how much HCl secretion?
60%
63
The intestinal phase accounts for how much HCl secretion?
10%
64
What are the two mechanisms to promote HCl secretion in cephalic phase?
- direct stimulation of parietal cells by vagus nerve to relase Ach
- indirect stimulation via gastrin
65
What are the four mechanisms to promote HCl secretion in gastric phase?
- distention --> vagal stimulation --> parietal cells
- indirect via gastrin
- distension of antrum --> gastrin
- amino acids and peptides --> gastrin
66
Alcohol and caffeine stimulate HCl in what phase?
gastric phase
67
The intestinal phase is stimulated by what?
products of protein digestion
68
The gastric phase is stimulated by what?
distension of stomach and presence of AA and peptides
69
The cephalic phase is stimulated by what?
- smelling
- tasting
- chewing
- swallowing
- conditioned reflexes
70
When is HCl secretion inhibited?
When it is no longer needed for conversion of pepsinogen to pepsin
71
What three things trigger inhibition of HCl secretion?
- decreased pH of gastric contents
- somatostatin (directly and indirectly)
- prostaglandins antagonize histamine by reducing cAMP
72
What is peptic ulcer disease?
- ulcerative lesion of gastric or duodenal mucosa caused by loss of mucus, have excessive H+ and pepsin secretion, or ombination of both
- can be classified as either gastric or duodenal ulcers
- other damaging factors include H pylori infection and stress
73
What are the barriers to acid and pepsin damage to mucosa?
- bicarbonate
- mucus
74
How does bicarbonate provide a barrier to mucosa?
gets trapped in mucus and neutralizes acid/deactivates protein
75
How does mucus provide a barrier to mucosa?
forms barriers between cells and luminal contents
76
Why do gastric ulcers form?
because mucosal barrier is defective which allows H+ ions to penetrate and pepsin is able to digest mucosa
77
How does H. pylori cause gastric ulcers?
colonizes gastric mucus and attaches to epithalial cells and releases cytotoxins which help breakdown the mucus barrier
78
How does H pylori colonize gastric mucus?
because it has urease enzyme which allows it to survive the acidic environment
79
Whaat syndrome has high rates of H+ secretion due to high gastrin, delivers high H+ to duodenum, and causes steatorrhea?
gastrinoma (Zollinger-Ellison syndrome)
80
The aqueous component of the exocrine pancreas is high in what?
bicarbonate
81
The enzymatic component of the exocrine pancreas digests what?
- carbs
- protein
- fat
82
The exocrine pancreas comprises ____% of the pancreas.
90%
83
What is the structure of exocrine glands?
- acinus lined with acinar cells
- ducts lined with ductal cells
- centroacinar cells
84
What cells of the exocrine pancreas are responsible for secreting the aqueous portion?
- ducts lined with ductal cells
- centroacinar cells
85
What part of the exocrine pancreas secretes enzymes?
- acinus
86
Does the PSNS stimulate or inhibit the exocrine pancreas?
stimulates
87
Does the SNS stimulate or inhibit the exocrine pancreas?
inhibits
88
Enzymes secreted from the pancreas are synthesized where?
rough er of acinar cells
89
Amylase and lipase are secreted as what?
active enzymes
90
Proteases are secreted in what form?
inactive known as zymogens
91
The juice of the aqueous component of pancreatic secretions is what and contains what?
- isotonic
- contains Na+, Cl-, K+, HCO3-
92
For the aqueous component of pancreatic secretions, what cells make the intiial secretion that is then modified by transport processes in ductal cells?
centroacinar and ductal cells
93
What ions of pancreatic secretions have a constant flow rate?
- Na+
- K+
94
The bicarbonate concentration of pancreatic secretions increases with high or low flow rates?
high
95
The The Cl- concentration of pancreatic secretions decreases with high or low flow rates?
high
96
Why does bicarb secretion increase with high flow rates?
Because at high flow rates, secretions are mostly Na+, HCO3-, and water
97
Why does Cl- secretion increase with low flow rates?
because at low flow rates, solution contains mostly Na+, Cl-, and water
98
The aqueous portion of pancreatic secretion is stimulated by what?
H+ in duodenum
99
The enzymatic portion of pancreatic secretion is stimulated by what?
products of digestion
100
Acinar cells are receptors for what?
- CCK
- Ach
101
Ductal cells are receptors for what?
- CCK
- Ach
- secretin
102
Bile secretion is needed for what?
digestion and absorption of lipids
103
What is bile?
a mixture of bile salts, bile pigments, cholesterol, phospholipids, ions, water
104
Why do we need bile salts?
to emulsify lipids for digestion which makes them water soluble
105
The biliary system includes what?
- liver
- gallbladder
- bile duct
- duodenum
- ileum
- portal circulation
106
What synthesizes the components of bile?
hepatocytes
107
Bile flows out of the bile ducts and into where?
gallbladder
108
What stimulates contraction of the gallbladder and relaxes the sphincter of Oddi?
CCK
109
After lipid absorption, bile salts are recirculated to liver via?
reabsorption in ileum (enterohepatic circulation)
110
Liver conjugates bile acids with amino acids to form what?
bile salts
111
What are the two primary bile acids formed by hepatocytes?
- cholic acid
- chenodeoxycholic acid
112
What are the two amino acids that can conjugate with bile acids?
- glycine
- taurine
113
Bile salts have what charge?
Negative
114
Bile salts bind products of lipid digestion to form what?
micelles
115
Bile salts assist in absorption of what products?
lipid products
116
What is the product of hemoglobin degradation?
bilirubin
117
What is the function of the gallbladder?
stores, concentrates, and ejects bile
118
Ejection of bile occurs how long after ingestion of a meal?
30 minutes
119
Is bile constantly ejected or ejected in spurts?
spurts
120
Is bile constantly made or only as it is needed?
constantly made and stored in gallbladder
121
Describe the enterohepatic circulation of the ileum.
- bile salts transported from small intestine lumen into portal blood by Na+/bile salt co-transporters
- portal blood carries to liver
- liver extracts bile salts and add to hepatic bile salt/bile acid pool
- fecal loss of bile salts approximately 600mg / day
