Gastrointestinal Flashcards
1
Q
Where do parasympathetic nerves to the GI tract have their first extracranial synapse? What are the neurotransmitters and receptors at this synapse?
A
In gangion surrounding the gut; Ach on nicotinic Ach receptors
2
Q
Where do sympathetic fibers to the GI tract first synapse?
A
In prevertebral ganglion
3
Q
What is the neurotransmitter at the postganglionic synapse for sympathetic innervation of the gut?
A
Norepinephrine
4
Q
Which layer of the GI tract contains the ganglia that hold the first synapses for parasympathetic fibers coming from the brain?
A
Auerbach’s plexuses in the muscularis externa
5
Q
Does the enteric nervous system have more or fewer neurons than the spinal cord?
A
Many more
6
Q
Which plexuses contain the cell bodies of the enteric nervous system?
A
Meissner’s plexuses (submucosal)
7
Q
What effect does nitric oxide have on the GI tract?
A
Sphincter relaxation
8
Q
For each of the following, do they act mostly as hormones or neuropeptides in the GI tract?
– Gastrin
– Secretin
– Gastrin-releasing peptide (GRP)
– GIP
– Glucagon, GLP-1, GLP-2
– VIP
– Motilin
A
– Gastrin: hormone
– Secretin: hormone
– Gastrin-releasing peptide (GRP): neuropeptide
– GIP: hormone
– Glucagon, GLP-1, GLP-2: hormone
– VIP: neuropeptide
– Motilin: hormone
9
Q
For each of the following, do they act mostly as hormones or neuropeptides in the GI tract?
– Substance P; tachykinins
– Pancreatic polypeptide
– Peptide YY
– Ghrelin
A
– Substance P; tachykinins: neuropeptides
– Pancreatic polypeptide: hormone
– Peptide YY: hormone
– Ghrelin: hormone
10
Q
Are G-cells in the proximal or distal part of the stomach?
A
Distal
11
Q
What receptor does gastrin bind to?
A
CCK receptor-B
12
Q
How is gastrin release inhibited? What cells release this modulator?
A
By somatostatin released from D cells
13
Q
What three regulators will stimulate acid production by the parietal cell?
A
Gastrin, histamine, and Ach
14
Q
What does the prefix cholecysto- refer to?
A
Gall bladder
15
Q
Cholecystokinin stimulates contaction of what organ, and secretion of what enzymes?
A
Gallbladder contraction; pancreatic enyme secretion
16
Q
Both secretin and CCK induce secretion of what ion?
A
Bicarbonate: HCO3-
17
Q
Both secretin and somatostatin inhibit release of what hormone that acts on the stomach?
A
Gastrin
18
Q
What are the major actions of vasoactive intestinal peptide (VIP)?
A
Epithelial cell secretion and smooth muscle relaxation (in the sphincter of Oddi)
19
Q
What are the three effects of the tachykinin Gastrin Releasing Peptide (GRP)?
A
Mediates of the vagal release of gastrin, stimulates pancreatic secretion, and increases GI motility
20
Q
What antibiotic is an agonist for motilin? What side effect does this cause?
A
Erythromycin; overactive gut
21
Q
Where is ghrelin made? What is its principle effect?
A
In the fundus of the stomach; it increases food intake
22
Q
What stimulates the release of somatostatin? What inhibits its release?
A
Gastric acid in the lumen; inhibited by high luminal pH
23
Q
What are ECL cells in the gut? What do they release to promote gastric acid release?
A
They are a type of neuroendocrine cell found in the gastric glands of the gastric mucosa beneath the epithelium in the vicinity of parietal cells. They release histamine in response to gastrin.
24
Q
Saliva contains what major ion? What is its principal function in the distal esophagus?
A
Bicarbonate; neutralizes gastric acid to protect distal esophagus
25
What two digestive enzymes is saliva rich in?
Salivary amylase and lingual lipase (although this is only significantly active for infants)
26
What is the difference in function between the proximal and distal stomach?
The proximal is primarily a secretion reservoir, while the distal is responsible for mixing and griding.
27
When vagal activity of the stomach increases, what two cell types in the fundic glands are stimulated?
Parietal cells and chief cells
28
Where are chief cells concentrated in the fundic gland?
Primarily toward the interior
29
What enzyme do chief cells secrete?
Pepsinogen
30
What are two classes of drugs that can be used to inhibit the function of parietal cells?
Proton pump inhibitors, acting on the H+/K+ ATPase, and H2 blockers acting on the histamine receptors
31
What regulatory mechanism is used to activate and deactivate proton pumps in parietal cells?
Sequestering of the membrane-bound pumps into vesicles, and then fusion of these vesicles with the canaliculi on activation
32
Does histamine released by ECL cells in the fundic gland activate chief cells, parietal cells, or both?
Both
33
What hormone inhibits the action of G-cells in the antrum? Which cell type secretes it, and what do those cells secrete it in response to?
Somatostatin; D cells, in response to low pH
34
What neurotransmitter influences ECL cells in the stomach? What other cell type does it affect?
Acetylcholine from vagal stimulation; Parietal cells
35
Pancreatic juice is very alkaline, with lots of bicarbonate; what does this neutralize?
Gastric acid
36
What channels face the luminal side of the pancreatic duct cell?
A Cl-/HCO3- exchanger and a CFTR that passes Cl- ions
37
What hormone influences the activity of the luminal channels of the pancreatic duct cells, along with the HCO3-/Na+ symporter?
Secretin
38
Which intracellular messenger is used by secretin stimulation to induce fusion of zymogenic granules in the pancreatic acinar cell?
cAMP
39
What amino acids are conjugated onto primary bile acids in order to get them into bile? Why are they necessary?
Glycine and taurine, which make the bile acid more hydrophilic (bile is watery)
40
Where are primary bile acids reabsorbed?
The terminal ileum
41
Bile acid is comparable to which household cleaning product?
Soap or detergent
42
Bile acids surround fatty acids in spherical structures called...
Micelles
43
Primary and secondary bile salts are mixed with what other components to make bile?
Phospholipids, cholesterol, and a little bit of protein, electrolytes and bilirubin.
44
What hormone controls smooth muscle contraction of the gall bladder?
Cholecystikinin
45
What innervation causes smooth muscle contraction in the bile duct, and what sphincter is relaxed by this innervation using which neurotransmitter?
Vagal innervation releasing Ach causes contraction; NO and VIP released to relax the sphincter of Oddi at the head of the bile tract
46
Besides the muscle or the nerve, where else can the problem in a GI motility order manifest?
The brain-gut axis (signalling)
47
What cells usually produce gas and distension of the bowel tract?
Bacteria
48
There are slow waves of electrical activity in the GI tract; in which part are these waves most frequent?
The small intestine
49
Besides slow waves, what other electrical activity can be propagated through the GI tract?
Spike activity, caused by reaching the threshold for an action potential
50
What function do interstitial cells of Cajal serve in the GI tract?
Electrical pacemakers of slow wave activity
51
What parts of the GI tract are tonically contracted (normally closed or constricted)?
storage organs like the gastric fundus and cecum, and sphincters
52
What does the "intestinal housekeeper" do?
They are waves of peristalsis that flush out the GI tract between meals
53
What is the kind of GI contraction that does not result in a proximal-to-distal gradient called? In which part of the GI tract is this the major contractile process?
Segmentation; the small and large intestine
54
Does peristalsis require contraction, relaxation, or both?
Both
55
Which neurotransmitters are important for peristalsis?
Serotonin (5-HT), acetylcholine, and nitric oxide
56
Where do the retrograde contractions of vomiting begin?
In the duodenum
57
Where is the vomiting reflex controlled?
In the central vomiting center of the medulla of the brain
58
Can cortical input cause vomiting? Can input from the vestibular system (balance) cause vomiting?
Yes to both
59
Is the lower esophageal sphincter a true sphincter?
No
60
Which neurotransmitter relaxes GI sphincters?
Nitric oxide
61
Which two GI sphincters are under voluntary contral?
The upper esophageal sphincter and the external anal sphincter
62
Does vasoactive intestinal polypeptide (VIP) promote or inhibit the smooth muscle relaxation caused by nitric oxide?
Promote
63
Do the laryngeal muscles contract after or before the nasopharynx closes during swallowing?
Generally, the larynx elevates **after** the nasopharynx closes
64
Once the bolus gets into the esophagus during swallowing, what contracts to prevent food from refluxing into the pharynx?
The upper esophageal sphincter
65
How long does it take food to reach the stomach from the pharynx during swallowing?
5-6 seconds
66
When does the lower esophageal sphincter begin to relax during swallowing?
When the pharynx contracts, well before the bolus has reached it; this is vagally mediated
67
What muscular structure surrounds the lower esophageal sphincter (that is not within the esophageal wall)?
The diaphragm
68
What is the basal lower esophageal pressure at rest?
20mmHg
69
What innervation mediates the antrum's action of grinding and retropulsing food?
Vagal innervation
70
What is the normal "rhythm" of the stomach?
3 cycles per minute
71
What causes the housekeeping waves of the GI tract? What is the audible signal of its action? What happens to it during a meal?
The migrating motor complex; stomach rumbling noises; it is inhibited during meals
72
A special stain was used to highlight the pacemaker cells of the GI tract. What are they called?
Interstitial cells of Cajal
73
What is the storage area of the colon for liquids?
The cecum
74
Does the colon perform more peristalsis or segmenting contractions?
Segmenting
75
Which are more common in the colon: low amplitude contractions, or high amplitude contractions?
Low amplitude (\>100/day)
76
High amplitude contractions of the colon are concurrent with what GI process?
Defecation
77
What is the gastrocolic reflex?
When the stomach is distended, we tend to want to have a bowel movement right away (to clear out the GI tract)
78
What hormones are used in the efferent limb of the gastrocolic reflex?
Cholecystokinin (CCK) and gastrin
79
Why do you need to squat (or at least sit) to defecate?
To straighten the anorectal angle
80
What skeletal muscle wraps around the anal canal like a sling and creates the anorectal angle?
The puborectalis muscle
81
What maintains more of the resting tone of the anal sphincter: the internal or the external sphincter?
The internal anal sphincter
82
Why does watery stool potentially cause incontinence?
The volume of the stool and the sensation of this by the anal canal are part of the physiology of continence
83
Secretion is most often associated with the [...] of intestinal epithelia, while absorption is associated with [...].
Secretion is most often associated with the crypts of intestinal epithelia, while absorption is associated with villi.
84
About how much water is excreted as saliva, gastric, biliary, and pancreatic juices per day?
Saliva and biliary juice: 1L/d each
Gastric and pancreatic juice: 2L/d each
85
What fraction of the water content of the food passing through the small intestine is absorbed in the small intestine?
80%, from ~8L/d to ~1.5L/d presented to the proximal colon.
86
How much water is normally excreted in the feces each day?
~100-200mL
87
What is the typical maximum capacity of the colon to absorb water, in the course of a day?
About 5L
88
What happens when colonic H2O absorption is maxed out?
Diarrhea
89
Where does fluid being absorbed through an epithelium accumulate in the absorptive state?
Between the tight junctions and the basement membrane
90
What solute is used to facilitate osmotic transport of water in the colon?
Na+
91
What kind of pressure moves water from the absorptive spaces between epithelial cells into the capillaries?
Hydrostatic pressure
92
Are tight junctions leakier (allowing larger molecules to diffuse through them) in the jejunum or the colon?
Leakier in the jejunum
93
What are the three main methods by which sodium is transported in the intestines to drive fluid absorption?
1) solute-coupled sodium transport
2) sodium hydrogen exchangers
3) electrogenic sodium transport
94
During nutrient-coupled sodium transport in the intestine, what drives Na+ out of the basolateral membrane? What imports Na+ via the apical membrane?
An Na+/K+ ATPase expels Na+ from the basolateral membrane.
An Na+/glucose symporter, e.g. SGLT-1, imports Na+ on the apical membrane.
95
What is oral rehydration therapy?
A solution of salts and sugars given by mouth that facilitates reabsorption of water by the intestines and decreasing diarrhea
96
In sodium-hydrogen exchange, what transporter on the apical membrane is used to move Na+ into the cell?
An Na+/H+ exchanger
97
In sodium-hydrogen exchange within the intestines, what transporter on the apical membrane is used to maintain acid/base balance?
A Cl-/HCO3- exchanger, which pumps out bicarbonate and Cl- into the cell.
98
In electrogenic sodium absorption in the intestines, is the Na+ transported across the apical membrane using an ATPase?
No, it uses a channel and follows an electric gradient created by a basolateral Na+/K+ ATPase
99
In which part of the small intestine does electrogenic Na+ transport become more important?
The distal part (the ileum and some of the duodenum)
100
Because of Na+ transport, does the intestinal lumen have a net negative or positive charge? What ion can this draw into the lumen? Therefore, what ion imbalance can be caused by uncontrolled diarrhea?
A net negative charge due to the exit of positive ions; K+ may be drawn into the lumen; hypokalemia can result from uncontrolled diarrhea
101
Cl- is absorbed during absorption of Na+ and water in the intestinal lumen. Does it typically drive fluid absorption?
No, it typically drives fluid secretion
102
What Cl- channel in the apical membrane allows it to exit into the lumen during chloride secretion?
CFTR
103
What is the second messenger for VIP, secretin, PGE1, and bradykinin?
cAMP
104
What second messengers do many bacterial toxins use to promote intestinal secretions?
cAMP and cGMP
105
What causes osmotic diarrhea?
A nonabsorbable solute in the bowel lumen causes water to enter the lumen (mostly in the small bowel) and the water load exceeds colonic absorptive capacity
106
What carbohydrates can cause osmotic diarrhea?
Lactose (e.g. from a lactase deficiency), sorbitol and aspartame (chewing gum or diet sodas)
107
What minerals can you use to cause osmotic diarrhea? When is this an appropriate treatment?
Sodium sulfate, magnesium citrate; typically used before an endoscopy to clear out the bowels
108
With osmotic diarrhea, will stool volume decrease and symptoms improve with fasting?
Yes
109
What things can cause secretory diarrhea?
Secretagogues that increase cAMP, cGMP, and Ca++: bacterial toxins, hormones, bile acids, drugs (caffeine, methylxanthines), or inflammatory mediators (histamine)
110
Why is caffeine a natural laxative?
It increases levels of cAMP, stimulating secretory processes in the bowel.
111
In secretory diarrhea, does fasting cause relief from the symptoms?
No
112
What is the major symptom of people with cholera that causes them to die? What is the treatment?
Dehydration from secretory diarrhea; treated with IV fluids
113
Why do changes in motility cause diarrhea?
The bowel needs time to absorb water, so moving contents too quickly (hypermotility) can inhibit water absorption
114
How do most common antidiarrheals (e.g. Immodium) function to decrease diarrhea? What is the common side effect that can result?
They slow down movement of the bowel, allowing more time for water absorption; this can cause constipation
115
Besides neural transmitters and endocrine signalling, what other two forms of cellular communication affect GI control?
Paracrine communication: release of chemicals into interstital space
Autocrine communication: type of paracrine communication providing feedback inhibition
116
Why are GI hormone-secreting cells called enterochromaffin cells? Where are they found?
Called enterochrommafin cells based on their histological staining properties; found in pancreatic islets and between mucosal cells of columnar cell epithelia
117
What sensation in the gut is correlated with the release of the tachykinin Substance P?
Pain
118
What effect does the hormone motilin have on the gut?
It binds to receptors on smooth muscle, increasing motility and phase III contractions of the migrating motor complex
119
What endocrine hormone is the "global inhibitor" of the GI control system?
Somatostatin
120
What receptors does distension of the stomach activate, leading to a reflex response that increases gastric acid production?
Stretch receptors
121
Both pancreatic juice and salivary juice contain a higher concentration of what anion as their flow increases?
Bicarbonate: HCO3-
122
Which receptor type is most important for the stimulated release of digestive enzymes from pancreatic acinar cells?
CCK-B receptors
123
When physicians say "malabsorption" what other process besides absorption can they also mean to be broken?
Digestion
124
Are the lingual lipases and gastric lipases significantly contributory toward breakdown of lipids in an adult?
No
125
Which lipases in the GI tract are most significant in an adult?
Pancreatic lipases
126
What does the suffix -ogen and the prefix pro- both signify with regard to enzyme naming?
It is an inactive form that is later activated (usually by cleavage)
127
Which amylase is secreted by the pancreas?
α-amylase
128
What class of molecules is *not* broken down by pancreatic digestive enzymes?
Disaccharides, which are digested in the small intestine
129
Where are minerals (e.g., iron, magnesium) chiefly absorbed in the GI tract?
Duodenum
130
When EtOH is ingested, which part of the GI tract is chiefly responsible for its absorption?
The stomach
131
Which four vitamins are fat soluble and must be solubilized in lipids to be absorbed?
Vitamins A, D, E, and K
132
Can disaccharides by absorbed by the intestinal epithelia?
No, only monosaccharides
133
What enzyme is used to break down starch?
Where is it secreted?
What are the products of this cleavage?
Amylase;
pancreas and saliva;
the disaccharide maltose, trisaccharide maltotriose, and α-dextrins and oligosaccharides—short chains of glucose
134
What converts the products of amylase breakdown (maltose and α-dextrins) into glucose? Where is it secreted?
Maltase; from the intestinal brush border membrane
135
What enzyme breaks down sucrose and where is it secreted?
Sucrase-isomaltase, which is secreted from the intestinal brush border membrane
136
Where is lactose broken down in the GI tract? Which enzyme is responsible for this?
The small intestine; lactase
137
What two monosaccharides are known to be actively transported (either by an ATPase or via symport with an ion gradient) into the intestinal epithelium?
Glucose and galactose. (Fructose transport is thought to be facilitated diffusion but it is not yet clear.)
138
What two monosaccharides form sucrose?
Glucose and fructose
139
What two monosaccharides form lactose?
Glucose and galactose
140
Can small oligopeptides be absorbed across the intestinal epithelium?
Yes
141
Where does protein digestion begin? What enzyme initiates this?
Stomach; pepsin, assisted by gastric acid
142
How are the pancreatic enzyme precursors activated in the duodenal lumen (and only there)?
Enterokinase, which lives on the brush-border of the duodenum, activates trypsinogen → trypsin, which then activates the other enzymes (chymotrypsin, elastase, and carboxypeptidase)
143
If the parietal cells are not making acid, will pepsinogen be activated in the stomach?
No
144
Do the pancreatic proteases cleave proteins indiscriminately or at specific sites?
At specific sites, dependent on the enzyme
145
What do pancreatic lipase and co-lipase do to triglycerides?
Break them down into monoglycerides and free fatty acids
146
What is the composition of a mixed micelle?
Monoglycerides and free fatty acids inside, bile salts on the outside
147
What must FFAs be repackaged into by intestinal epithelia to leave the cells and enter the lymphatic system?
Chylomicrons and VLDLs
148
What's the definition of a medium chain fatty acid?
6-8 carbons in the chain
149
What proteins are needed to form chylomicrons in intestinal epithelia?
Lipoproteins
150
What is this metabolic disorder? What is it caused by?
Aβ-lipoproteinemia; there is an accumulation of fat in the intestinal epithelia because lipoprotein β cannot be synthesized to form chylomicrons for lipid export
151
Which circulatory network is used to get bile salts back to the liver from the ileum?
The portal system
152
Are vitamin B, vitamin C, and niacin fat solubule or water soluble?
Water soluble
153
Before binding to [substance] in the duodenum, secreted from parietal cells in the stomach, vitamin B12 is bound to R-factors like haptocorrin found in saliva and gastric juice.
Before binding to intrinsic factor in the duodenum, secreted from parietal cells in the stomach, vitamin B12 is bound to R-factors like haptocorrin found in saliva and gastric juice.
154
Before binding to intrinsic factor in the duodenum, secreted from [cell type] in the [organ], vitamin B12 is bound to R-factors like haptocorrin found in saliva and gastric juice.
Before binding to intrinsic factor in the duodenum, secreted from parietal cells in the stomach, vitamin B12 is bound to R-factors like haptocorrin found in saliva and gastric juice.
155
Before binding to intrinsic factor in the duodenum, secreted from parietal cells in the stomach, vitamin B12 is bound to [...] found in saliva and gastric juice.
Before binding to intrinsic factor in the duodenum, secreted from parietal cells in the stomach, vitamin B12 is bound to R-factors like haptocorrin found in saliva and gastric juice.
156
Before binding to intrinsic factor in the duodenum, secreted from parietal cells in the stomach, vitamin B12 is bound to R-factors like haptocorrin found in [digestive juice types].
Before binding to intrinsic factor in the duodenum, secreted from parietal cells in the stomach, vitamin B12 is bound to R-factors like haptocorrin found in saliva and gastric juice.
157
Does vitamin B12 bind immediately to intrinsic factor in the stomach?
No, it only associates with it in the distal duodenum, after pancreatic proteases separate vitamin B12 from R factors (haptocorrin)
158
What is another name for vitamin B12?
Cobalamin
159
What biochemically rare mineral is contained in vitamin B12?
Cobalt
160
What tissue can be permanently damaged by hypocobalaminemia? What metabolic substance is deficient in this disease?
Neural tissue; vitamin B12 (also called cobalamin)
161
If you do not absorb sufficient protein, what is the typical clinical finding? Why?
Edema; water accumulates in the interstitial spaces because of hypoalbuminemia
162
If you are malabsorptive for fat, what are the typical clinical findings?
Steatorrhea (fatty stool), and sometimes weight loss
163
When you are malabsorptive for carbohydrates, what clinical findings result and why?
Diarrhea, bloating and gas because the microbes of the distal gut get more carbs then they usually do, and proliferate
164
What clinical problems result from a vitamin K deficiency, and why?
Bruising, because vitamin K is needed for posttranslational modification of coagulation proteins
165
Besides neuropathy, what is another clinical finding associated with vitamin B12 deficiency, common with folate or iron malabsorption? What is the difference in the histological presentation of these anemias and why?
Anemia; however, iron-deficiency anemia is microcytic (a heme production issue), while vitamin B12 and folate deficiencies are megaloblastic (indicating DNA synthesis problems).
166
What effects does gastrin have on the GI tract? What cells are stimulated? What receptor does it bind to?
It stimulates secretion of gastric acid and pepsinogen, and hypertrophy of the gastric mucosa; the parietal cells and chief cells; the CCK-B receptor is used.
