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Physiology > Gastrointestinal > Flashcards

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

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2
Q

Where do sympathetic fibers to the GI tract first synapse?

A

In prevertebral ganglion

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3
Q

What is the neurotransmitter at the postganglionic synapse for sympathetic innervation of the gut?

A

Norepinephrine

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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

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5
Q

Does the enteric nervous system have more or fewer neurons than the spinal cord?

A

Many more

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6
Q

Which plexuses contain the cell bodies of the enteric nervous system?

A

Meissner’s plexuses (submucosal)

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7
Q

What effect does nitric oxide have on the GI tract?

A

Sphincter relaxation

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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

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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

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10
Q

Are G-cells in the proximal or distal part of the stomach?

A

Distal

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11
Q

What receptor does gastrin bind to?

A

CCK receptor-B

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12
Q

How is gastrin release inhibited? What cells release this modulator?

A

By somatostatin released from D cells

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13
Q

What three regulators will stimulate acid production by the parietal cell?

A

Gastrin, histamine, and Ach

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14
Q

What does the prefix cholecysto- refer to?

A

Gall bladder

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15
Q

Cholecystokinin stimulates contaction of what organ, and secretion of what enzymes?

A

Gallbladder contraction; pancreatic enyme secretion

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16
Q

Both secretin and CCK induce secretion of what ion?

A

Bicarbonate: HCO3-

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17
Q

Both secretin and somatostatin inhibit release of what hormone that acts on the stomach?

A

Gastrin

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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)

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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

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20
Q

What antibiotic is an agonist for motilin? What side effect does this cause?

A

Erythromycin; overactive gut

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21
Q

Where is ghrelin made? What is its principle effect?

A

In the fundus of the stomach; it increases food intake

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22
Q

What stimulates the release of somatostatin? What inhibits its release?

A

Gastric acid in the lumen; inhibited by high luminal pH

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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.

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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

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25
Q

What two digestive enzymes is saliva rich in?

A

Salivary amylase and lingual lipase (although this is only significantly active for infants)

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26
Q

What is the difference in function between the proximal and distal stomach?

A

The proximal is primarily a secretion reservoir, while the distal is responsible for mixing and griding.

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27
Q

When vagal activity of the stomach increases, what two cell types in the fundic glands are stimulated?

A

Parietal cells and chief cells

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28
Q

Where are chief cells concentrated in the fundic gland?

A

Primarily toward the interior

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29
Q

What enzyme do chief cells secrete?

A

Pepsinogen

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30
Q

What are two classes of drugs that can be used to inhibit the function of parietal cells?

A

Proton pump inhibitors, acting on the H+/K+ATPase, and H2blockers acting on the histamine receptors

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31
Q

What regulatory mechanism is used to activate and deactivate proton pumps in parietal cells?

A

Sequestering of the membrane-bound pumps into vesicles, and then fusion of these vesicles with the canaliculi on activation

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32
Q

Does histamine released by ECL cells in the fundic gland activate chief cells, parietal cells, or both?

A

Both

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33
Q

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?

A

Somatostatin; D cells, in response to low pH

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34
Q

What neurotransmitter influences ECL cells in the stomach? What other cell type does it affect?

A

Acetylcholine from vagal stimulation; Parietal cells

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35
Q

Pancreatic juice is very alkaline, with lots of bicarbonate; what does this neutralize?

A

Gastric acid

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36
Q

What channels face the luminal side of the pancreatic duct cell?

A

A Cl-/HCO3-exchanger and a CFTR that passes Cl-ions

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37
Q

What hormone influences the activity of the luminal channels of the pancreatic duct cells, along with the HCO3-/Na+symporter?

A

Secretin

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38
Q

Which intracellular messenger is used by secretin stimulation to induce fusion of zymogenic granules in the pancreatic acinar cell?

A

cAMP

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39
Q

What amino acids are conjugated onto primary bile acids in order to get them into bile? Why are they necessary?

A

Glycine and taurine, which make the bile acid more hydrophilic (bile is watery)

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40
Q

Where are primary bile acids reabsorbed?

A

The terminal ileum

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41
Q

Bile acid is comparable to which household cleaning product?

A

Soap or detergent

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42
Q

Bile acids surround fatty acids in spherical structures called…

A

Micelles

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43
Q

Primary and secondary bile salts are mixed with what other components to make bile?

A

Phospholipids, cholesterol, and a little bit of protein, electrolytes and bilirubin.

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44
Q

What hormone controls smooth muscle contraction of the gall bladder?

A

Cholecystikinin

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45
Q

What innervation causes smooth muscle contraction in the bile duct, and what sphincter is relaxed by this innervation using which neurotransmitter?

A

Vagal innervation releasing Ach causes contraction; NO and VIP released to relax the sphincter of Oddi at the head of the bile tract

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46
Q

Besides the muscle or the nerve, where else can the problem in a GI motility order manifest?

A

The brain-gut axis (signalling)

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47
Q

What cells usually produce gas and distension of the bowel tract?

A

Bacteria

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48
Q

There are slow waves of electrical activity in the GI tract; in which part are these waves most frequent?

A

The small intestine

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49
Q

Besides slow waves, what other electrical activity can be propagated through the GI tract?

A

Spike activity, caused by reaching the threshold for an action potential

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50
Q

What function do interstitial cells of Cajal serve in the GI tract?

A

Electrical pacemakers of slow wave activity

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51
Q

What parts of the GI tract are tonically contracted (normally closed or constricted)?

A

storage organs like the gastric fundus and cecum, and sphincters

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52
Q

What does the “intestinal housekeeper” do?

A

They are waves of peristalsis that flush out the GI tract between meals

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53
Q

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?

A

Segmentation; the small and large intestine

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54
Q

Does peristalsis require contraction, relaxation, or both?

A

Both

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55
Q

Which neurotransmitters are important for peristalsis?

A

Serotonin (5-HT), acetylcholine, and nitric oxide

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56
Q

Where do the retrograde contractions of vomiting begin?

A

In the duodenum

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57
Q

Where is the vomiting reflex controlled?

A

In the central vomiting center of the medulla of the brain

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58
Q

Can cortical input cause vomiting? Can input from the vestibular system (balance) cause vomiting?

A

Yes to both

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59
Q

Is the lower esophageal sphincter a true sphincter?

A

No

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60
Q

Which neurotransmitter relaxes GI sphincters?

A

Nitric oxide

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61
Q

Which two GI sphincters are under voluntary contral?

A

The upper esophageal sphincter and the external anal sphincter

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62
Q

Does vasoactive intestinal polypeptide (VIP) promote or inhibit the smooth muscle relaxation caused by nitric oxide?

A

Promote

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63
Q

Do the laryngeal muscles contract after or before the nasopharynx closes during swallowing?

A

Generally, the larynx elevates after the nasopharynx closes

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64
Q

Once the bolus gets into the esophagus during swallowing, what contracts to prevent food from refluxing into the pharynx?

A

The upper esophageal sphincter

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65
Q

How long does it take food to reach the stomach from the pharynx during swallowing?

A

5-6 seconds

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66
Q

When does the lower esophageal sphincter begin to relax during swallowing?

A

When the pharynx contracts, well before the bolus has reached it; this is vagally mediated

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67
Q

What muscular structure surrounds the lower esophageal sphincter (that is not within the esophageal wall)?

A

The diaphragm

68
Q

What is the basal lower esophageal pressure at rest?

A

20mmHg

69
Q

What innervation mediates the antrum’s action of grinding and retropulsing food?

A

Vagal innervation

70
Q

What is the normal “rhythm” of the stomach?

A

3 cycles per minute

71
Q

What causes the housekeeping waves of the GI tract? What is the audible signal of its action? What happens to it during a meal?

A

The migrating motor complex; stomach rumbling noises; it is inhibited during meals

72
Q

A special stain was used to highlight the pacemaker cells of the GI tract. What are they called?

A

Interstitial cells of Cajal

73
Q

What is the storage area of the colon for liquids?

A

The cecum

74
Q

Does the colon perform more peristalsis or segmenting contractions?

A

Segmenting

75
Q

Which are more common in the colon: low amplitude contractions, or high amplitude contractions?

A

Low amplitude (>100/day)

76
Q

High amplitude contractions of the colon are concurrent with what GI process?

A

Defecation

77
Q

What is the gastrocolic reflex?

A

When the stomach is distended, we tend to want to have a bowel movement right away (to clear out the GI tract)

78
Q

What hormones are used in the efferent limb of the gastrocolic reflex?

A

Cholecystokinin (CCK) and gastrin

79
Q

Why do you need to squat (or at least sit) to defecate?

A

To straighten the anorectal angle

80
Q

What skeletal muscle wraps around the anal canal like a sling and creates the anorectal angle?

A

The puborectalis muscle

81
Q

What maintains more of the resting tone of the anal sphincter: the internal or the external sphincter?

A

The internal anal sphincter

82
Q

Why does watery stool potentially cause incontinence?

A

The volume of the stool and the sensation of this by the anal canal are part of the physiology of continence

83
Q

Secretion is most often associated with the […] of intestinal epithelia, while absorption is associated with […].

A

Secretion is most often associated with the crypts of intestinal epithelia, while absorption is associated with villi.

84
Q

About how much water is excreted as saliva, gastric, biliary, and pancreatic juices per day?

A

Saliva and biliary juice: 1L/d eachGastric and pancreatic juice: 2L/d each

85
Q

What fraction of the water content of the food passing through the small intestine is absorbed in the small intestine?

A

80%, from ~8L/d to ~1.5L/d presented to the proximal colon.

86
Q

How much water is normally excreted in the feces each day?

A

~100-200mL

87
Q

What is the typical maximum capacity of the colon to absorb water, in the course of a day?

A

About 5L

88
Q

What happens when colonic H2O absorption is maxed out?

A

Diarrhea

89
Q

Where does fluid being absorbed through an epithelium accumulate in the absorptive state?

A

Between the tight junctions and the basement membrane

90
Q

What solute is used to facilitate osmotic transport of water in the colon?

A

Na+

91
Q

What kind of pressure moves water from the absorptive spaces between epithelial cells into the capillaries?

A

Hydrostatic pressure

92
Q

Are tight junctions leakier (allowing larger molecules to diffuse through them) in the jejunum or the colon?

A

Leakier in the jejunum

93
Q

What are the three main methods by which sodium is transported in the intestines to drive fluid absorption?

A

1) solute-coupled sodium transport2) sodium hydrogen exchangers3) electrogenic sodium transport

94
Q

During nutrient-coupled sodium transport in the intestine, what drives Na+out of the basolateral membrane? What imports Na+via the apical membrane?

A

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
Q

What is oral rehydration therapy?

A

A solution of salts and sugars given by mouth that facilitates reabsorption of water by the intestines and decreasing diarrhea

96
Q

In sodium-hydrogen exchange, what transporter on the apical membrane is used to move Na+into the cell?

A

An Na+/H+exchanger

97
Q

In sodium-hydrogen exchange within the intestines, what transporter on the apical membrane is used to maintain acid/base balance?

A

A Cl-/HCO3-exchanger, which pumps out bicarbonate and Cl-into the cell.

98
Q

In electrogenic sodium absorption in the intestines, is the Na+transported across the apical membrane using an ATPase?

A

No, it uses a channel and follows an electric gradient created by a basolateral Na+/K+ATPase

99
Q

In which part of the small intestine does electrogenic Na+transport become more important?

A

The distal part (the ileum and some of the duodenum)

100
Q

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

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
Q

Cl-is absorbed during absorption of Na+and water in the intestinal lumen. Does it typically drive fluid absorption?

A

No, it typically drives fluid secretion

102
Q

What Cl-channel in the apical membrane allows it to exit into the lumen during chloride secretion?

A

CFTR

103
Q

What is the second messenger for VIP, secretin, PGE1, and bradykinin?

A

cAMP

104
Q

What second messengers do many bacterial toxins use to promote intestinal secretions?

A

cAMP and cGMP

105
Q

What causes osmotic diarrhea?

A

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
Q

What carbohydrates can cause osmotic diarrhea?

A

Lactose (e.g. from a lactase deficiency), sorbitol and aspartame (chewing gum or diet sodas)

107
Q

What minerals can you use to cause osmotic diarrhea? When is this an appropriate treatment?

A

Sodium sulfate, magnesium citrate; typically used before an endoscopy to clear out the bowels

108
Q

With osmotic diarrhea, will stool volume decrease and symptoms improve with fasting?

A

Yes

109
Q

What things can cause secretory diarrhea?

A

Secretagogues that increase cAMP, cGMP, and Ca++: bacterial toxins, hormones, bile acids, drugs (caffeine, methylxanthines), or inflammatory mediators (histamine)

110
Q

Why is caffeine a natural laxative?

A

It increases levels of cAMP, stimulating secretory processes in the bowel.

111
Q

In secretory diarrhea, does fasting cause relief from the symptoms?

A

No

112
Q

What is the major symptom of people with cholera that causes them to die? What is the treatment?

A

Dehydration from secretory diarrhea; treated with IV fluids

113
Q

Why do changes in motility cause diarrhea?

A

The bowel needs time to absorb water, so moving contents too quickly (hypermotility) can inhibit water absorption

114
Q

How do most common antidiarrheals (e.g. Immodium) function to decrease diarrhea? What is the common side effect that can result?

A

They slow down movement of the bowel, allowing more time for water absorption; this can cause constipation

115
Q

Besides neural transmitters and endocrine signalling, what other two forms of cellular communication affect GI control?

A

Paracrine communication: release of chemicals into interstital spaceAutocrine communication: type of paracrine communication providing feedback inhibition

116
Q

Why are GI hormone-secreting cells called enterochromaffin cells? Where are they found?

A

Called enterochrommafin cells based on their histological staining properties; found in pancreatic islets and between mucosal cells of columnar cell epithelia

117
Q

What sensation in the gut is correlated with the release of the tachykinin Substance P?

A

Pain

118
Q

What effect does the hormone motilin have on the gut?

A

It binds to receptors on smooth muscle, increasing motility and phase III contractions of the migrating motor complex

119
Q

What endocrine hormone is the “global inhibitor” of the GI control system?

A

Somatostatin

120
Q

What receptors does distension of the stomach activate, leading to a reflex response that increases gastric acid production?

A

Stretch receptors

121
Q

Both pancreatic juice and salivary juice contain a higher concentration of what anion as their flow increases?

A

Bicarbonate: HCO3-

122
Q

Which receptor type is most important for the stimulated release of digestive enzymes from pancreatic acinar cells?

A

CCK-B receptors

123
Q

When physicians say “malabsorption” what other process besides absorption can they also mean to be broken?

A

Digestion

124
Q

Are the lingual lipases and gastric lipases significantly contributory toward breakdown of lipids in an adult?

A

No

125
Q

Which lipases in the GI tract are most significant in an adult?

A

Pancreatic lipases

126
Q

What does the suffix -ogen and the prefix pro- both signify with regard to enzyme naming?

A

It is an inactive form that is later activated (usually by cleavage)

127
Q

Which amylase is secreted by the pancreas?

A

α-amylase

128
Q

What class of molecules is not broken downby pancreatic digestive enzymes?

A

Disaccharides, which are digested in the small intestine

129
Q

Where are minerals (e.g., iron, magnesium) chiefly absorbed in the GI tract?

A

Duodenum

130
Q

When EtOH is ingested, which part of the GI tract is chiefly responsible for its absorption?

A

The stomach

131
Q

Which four vitamins are fat soluble and must be solubilized in lipids to be absorbed?

A

Vitamins A, D, E, and K

132
Q

Can disaccharides by absorbed by the intestinal epithelia?

A

No, only monosaccharides

133
Q

What enzyme is used to break down starch?Where is it secreted?What are the products of this cleavage?

A

Amylase;pancreas and saliva;the disaccharide maltose, trisaccharide maltotriose, and α-dextrins and oligosaccharides—short chains of glucose

134
Q

What converts the products of amylase breakdown (maltose and α-dextrins) into glucose? Where is it secreted?

A

Maltase; from the intestinal brush border membrane

135
Q

What enzyme breaks down sucrose and where is it secreted?

A

Sucrase-isomaltase, which is secreted from the intestinal brush border membrane

136
Q

Where is lactose broken down in the GI tract? Which enzyme is responsible for this?

A

The small intestine; lactase

137
Q

What two monosaccharides are known to be actively transported (either by an ATPase or via symport with an ion gradient) into the intestinal epithelium?

A

Glucose and galactose. (Fructose transport is thought to be facilitated diffusion but it is not yet clear.)

138
Q

What two monosaccharides form sucrose?

A

Glucose and fructose

139
Q

What two monosaccharides form lactose?

A

Glucose and galactose

140
Q

Can small oligopeptides be absorbed across the intestinal epithelium?

A

Yes

141
Q

Where does protein digestion begin? What enzyme initiates this?

A

Stomach; pepsin, assisted by gastric acid

142
Q

How are the pancreatic enzyme precursors activated in the duodenal lumen (and only there)?

A

Enterokinase, which lives on the brush-border of the duodenum, activates trypsinogen → trypsin, which then activates the other enzymes (chymotrypsin, elastase, and carboxypeptidase)

143
Q

If the parietal cells are not making acid, will pepsinogen be activated in the stomach?

A

No

144
Q

Do the pancreatic proteases cleave proteins indiscriminately or at specific sites?

A

At specific sites, dependent on the enzyme

145
Q

What do pancreatic lipase and co-lipase do to triglycerides?

A

Break them down into monoglycerides and free fatty acids

146
Q

What is the composition of a mixed micelle?

A

Monoglycerides and free fatty acids inside, bile salts on the outside

147
Q

What must FFAs be repackaged into by intestinal epithelia to leave the cells and enter the lymphatic system?

A

Chylomicrons and VLDLs

148
Q

What’s the definition of a medium chain fatty acid?

A

6-8 carbons in the chain

149
Q

What proteins are needed to form chylomicrons in intestinal epithelia?

A

Lipoproteins

150
Q

What is this metabolic disorder? What is it caused by?

A

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
Q

Which circulatory network is used to get bile salts back to the liver from the ileum?

A

The portal system

152
Q

Are vitamin B, vitamin C, and niacin fat solubule or water soluble?

A

Water soluble

153
Q

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.

A

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
Q

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.

A

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
Q

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.

A

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
Q

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].

A

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
Q

Does vitamin B12bind immediately to intrinsic factor in the stomach?

A

No, it only associates with it in the distal duodenum, after pancreatic proteases separate vitamin B12from R factors (haptocorrin)

158
Q

What is another name for vitamin B12?

A

Cobalamin

159
Q

What biochemically rare mineral is contained in vitamin B12?

A

Cobalt

160
Q

What tissue can be permanently damaged by hypocobalaminemia? What metabolic substance is deficient in this disease?

A

Neural tissue; vitamin B12(also called cobalamin)

161
Q

If you do not absorb sufficient protein, what is the typical clinical finding? Why?

A

Edema; water accumulates in the interstitial spaces because of hypoalbuminemia

162
Q

If you are malabsorptive for fat, what are the typical clinical findings?

A

Steatorrhea (fatty stool), and sometimes weight loss

163
Q

When you are malabsorptive for carbohydrates, what clinical findings result and why?

A

Diarrhea, bloating and gas because the microbes of the distal gut get more carbs then they usually do, and proliferate

164
Q

What clinical problems result from a vitamin K deficiency, and why?

A

Bruising, because vitamin K is needed for posttranslational modification of coagulation proteins

165
Q

Besides neuropathy, what is another clinical finding associated with vitamin B12deficiency, common with folate or iron malabsorption? What is the difference in the histological presentation of these anemias and why?

A

Anemia; however, iron-deficiency anemia is microcytic (a heme production issue), while vitamin B12and folate deficiencies are megaloblastic (indicating DNA synthesis problems).

166
Q

What effects does gastrin have on the GI tract? What cells are stimulated? What receptor does it bind to?

A

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.

Physiology (3 decks)

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