Ch6. GI Flashcards
(123 cards)
1
Q
What is the difference between circular muscle vs longitudinal muscle in the GI tract?
A
circular muscle contraction– causes a decrease in diameter of the lumen
Longitudinal muscle– contraction causes shortening of a segment of GI
2
Q
What make up the enteric nervous system of the GI tract?
A
submucosal plexus (Meissner plexus) an dmyenteric plexus
3
Q
The extrinsic innervation of the GI tract has (parasymp/symp) efferent fibers carried from the
A
brain stem and spinal cord to the GI tract
4
Q
The extrinsic innervation of the GI tract has (parasymp/symp) afferent fibers carry what information?
A
sensory info from chemo receptors and mechanoreceptors in the GIT to the brain stem and spinal cord
5
Q
Parasympathetic nervous system is usually excitatory or inhibitory on the funcitons of the GIT
A
excitatory
6
Q
The parasympathetic nervous system innervation of the GIT is carried by what nerves?
A
vagus & pelvic nerves
7
Q
Where do preganglionic parasympathetic fibers synapse where in the GIT?
A
myenteric and submucosal plexuses
8
Q
The sympathetic nervous system is typically excitatory or inhibitory on the functions of the GIT?
A
inhibitory
9
Q
Where do sympathetic nerves orginate in what portion of the spinal cord?
A
between T8 and 12
10
Q
what is the function of myenteric plexus (Auerbach plexus)?
A
controls the motility of the GI smooth muscle
11
Q
what is the function of the submucosal plexus (Meissner plexus)
A
primarily secretion and blood flow
**receives info from chemoreceptors & mechanoreceptors in the GI tract
12
Q
Site of secretion: Gastrin
A
G cells of stomach
13
Q
Site of secretion: CCK
A
I cells of duodenum and jejunum
14
Q
Site of secretion: secretin
A
S cells of duodenum
15
Q
Site of secretion: GIP
A
duodenum & jejunum
16
Q
What is the stimulus for secretion of Gastrin?
A
-small peptides & amino acids
-distention of the stomach
-vagus (via GRP)
-inhibited by H in stomach
-inhibited by somatostatin
17
Q
What is the stimulus for secretion of CCK?
A
small peptides & fatty acids (monoglycerides; triglycerides cannot cross intestinal cell membranes)
18
Q
What is the stimulus for secretion of secretin?
A
-H in duodenum
-fatty acids in duodenum
19
Q
What is the stimulus for secretion of GIP?
A
fatty acids, amino acids and oral glucose
20
Q
GI hormone, what is the action of: Gastrin
A
INC Gastric H secretion
stimulates growth of gastric mucosa
21
Q
GI hormone, what is the action of: CCK
A
-stims contraction of gallbladder and relaxation of sphincter of Oddi
-INC pancreatic enzyme and HCO3 secretion
-INC growth of exocrine pancreas/gallbladder
-inhibits gastric emptying
22
Q
GI hormone, what is the action of: secretin
A
INC pancreatic HCO3 secretion
INC biliary HCO3 secretion
DEC gastric H secretion
23
Q
GI hormone, what is the action of: GIP
A
INC insulin secretion
DEC Gastric H secretion
24
Q
Gastrin works on what cells of the GI tract?
A
gastric parietal cells
25
What cells secrete gastrin?
G cells of the gastric antrum
**in response to a meal
26
What is the most potent stimuli for secretion of gastrin?
pheylalanine
tryptophan
27
What are mechanisms that inhibit gastrin secretion?
-H in the lumen of the stomach (negative feeback control)
-somatostatin
28
CCK is released from what cells of the duodenal and jejunal mucosa?
I cells
29
Secretin is released from what cells of the duodenum?
S cells
30
MOA of motilin
INC GI motility and is involved in interdigestive myoelectric complexes
31
MOA of pancreatic peptide
inhibits pancreatic secretions
32
MOA of glucagon-like peptide (GLP-1)
binds pancreatic Beta-cells and sitmulates insulien secretion
33
MOA leptin
decreases appetite
34
MOA Ghrelin
increases appetite
35
What are the GI paracrines?
somatostatin
histamine
36
Somatostatin is secreted by cells throughout the GI tract in response to
H in the lumen
37
Somatostatin secretion is inhibited by
vagal stimulation
38
MOA of somatostatin
inhibits release of all GI hormones
and
inhibits gastric H secretion
39
Histamine is secreted by what cells of the gastric mucosa?
Mast cells
40
What is the effect of histamine on the GI tract?
increases gastric H secretion
**directly potentiates the effects of gastrin & vagal stimulation
41
What are Neurocrines of the GI tract?
synthesized in neurons of the GI tract, moved by axonal transport down the axons & released by action potentials in the nerves
--> neurocrines then diffuse across teh synaptic cleft to a target cell
42
List the GI neurocrines
vasoactive intestinal peptide (VIP)
neuropeptide Y
nitric oxide (NO)
GRP (bombesin)
enkephalins
43
Vasoactive intestinal peptide (VIP) is released from neurons in what part of the GI tract?
mucosa & smooth muscle
44
what is the effect of vasoactive intestinal peptide (VIP)?
produces relaxation of GI smooth muscle, including the lower esophageal sphincter
45
What is the MOA of vasoactive intestinal peptide (VIP)?
stimulates pancreatic HCO3 secretion and inhibits gastric H secretion
**resembles secretin
46
GRP (Bombesin) is released from where?
vagus nerves tha tinnervate the G cells
47
GRP (bombesin) MOA
stimulates gastrin release from G cells
48
What are the actions of enkephalins?
-stimulate contraction of GI smooth muscle (particularly lower esophageal, pyloric & ileocecal sphincters)
-inhibit intestinal secretion of fluid & electrolytes
49
Where is the satiety center located?
-inhibits appetite
**located in the ventromedial nucleus of the hypothalamus
50
Where do the oscillating membrane potentials in GI smooth muscle originate?
interstitial cells of cajal
**serves as the pacemaker for GI smooth mm
**not action potentials
51
What is the mechanism of slow wave production in the GI smooth muscle?
-cyclic opening of Ca channels (depolarization) followed by opening of K channels (repolarization)
52
What initiates the vagovagal reflex?
distention of the stomach
53
The rate of gastric emptying is fastest when?
-when stomach contents are isotonic
54
When is gastric emptying inhibited?
-hypertonic or hypotonic
-fat (by stim CCK)
-H in the duodenum
55
Food in the intestinal lumen is sensed by enterochromaffin cells, which release what hormone?
serotonin (5-HT)
56
Describe the gastroileal reflex
presence of food in the stomach triggers increased peristalsis in the ileum & relaxation of the ileocecal sphincter
**intestinal contents are delivered to large intestine
57
Describe the gastrocolic reflux
presence of food in the stomach increases motility in the colon & increases frequency of mass movements
58
What neuronal functions mediate the gastrocolic reflex?
-rapid parasympathetic component-- initiated when stomach is stretched by food
-slower, hormonal component mediated by CCK & gastrin
59
What are the functions of saliva?
-initial starch digestion by alpha-amylase and initial triglyeride digestion by lingual lipase
-lubrication of ingested food by mucus
-protection of mouth & esophagus by dilution and buffering of ingested food
60
The composition of saliva is characterized by:
-high volume
-high K and HCO3 concentrations
-low Na and Cl concentrations
-hypotonicity
-presence of alpha-amylase, lingual lipase & kallikrein
61
What stimulates gastric secretion?
gastrin
parasympathetic nervous system
histamine
62
Pancreatic secretion is stimulated by:
secretin
CCK (potentiates secretin)
Parasympathetic nervous system
CCK
63
What stimulates bile secretion?
-CCK (causes contraction of gallbladder and relaxation of sphincter of Oddi)
-Parasympathetic nervous system (causes contraction of gall bladder)
64
Initially saliva has the same concentration as plasma, which part of the salivary duct produces this?
acinus
65
Where is saliva modified and how is it modified (from initial concentrations)?
-the ducts
--> reabsorb Na and Cl
--> secrete K and HCO3
66
What is the effect of aldosterone on saliva?
-acts on ductal cells
- increases reabsorption of Na and secretion of K (analagous to the actions on renal distal tubule)
67
Parasympathetic stimulation of saliva glands increased transport via what cranial nerves?
CN VII & IX
68
What do the parietal cells secrete?
HCL & intrinsic factor
69
What hormones stimulate parietal cells?
-gastrin
-vagal stimulation (ACh)
-histamine
70
Chief cells secrete what?
pepsinogen (converted to pepsin at low pH)
71
What stimulate chief cells?
vagal stimulation (ACh)
72
What do G cells of the stomach produce?
gastrin
73
What stimulates G cells for secretion?
vagal stimulation (via GRP)
small peptides
74
What inhibits G cell secretion?
somatostatin
H in stomach (via stimulation of somatostatin release)
75
Mucous production in the cells is stimulated by?
vagal stimulation (ACh)
76
What cells are produced by the body (fundus) of the stomach?
parietal cells
chief cells
77
what cells are produced by the antrum of the stomach?
G cells
mucous cells
78
What are the steps in which the parietal cells secrete HCL in the stomach?
1. parietal cells, CO2 & water converted to H and HCO3, catalyzed by carbonic anhydrase
2. H secreted into the lumen of the stomach by H-K pump (H,K AtPase)
3. HCO3 produced in cells absorbed into the bloodstream in exhcange for CL (CL-HCO3 exchange); pH of blood increases (alkaline tide)
79
omeprazole MOA
proton pump inhibitor
**inhibits H, K ATPase and blocks blocks H secretion
80
Gastrin stimulates H secretion by interacting with...
CCK on the parietal cells
81
Histamine stimulates H secretion by activating what receptors on parietal cells?
H2 receptors
82
What is the second messenger for histamine?
cAMP
83
What hormones work to stimulate H secretion?
-histamine potentiates the actions of ACh and gastrin
-AcH potentiates the actions of histamine & gastrin
84
What work as negative feed back mechanisms, for inhibition of gastric H secretion?
low pH of stomach (inhibits gastrin secretion)
somatostatin
prostaglandins
85
What is the mechanism by which prostaglandins inhibit gastric H+ secretion?
-activate Gi proteins, inhibiting adenylyl cyclase & dec cAMP levels
86
What is the direct pathway by which somatostatin inhibits gastric H secretion?
-binds receptors on parietal cells, Gi protein, thus inhibiting adnylyl cyclase & decreasing cAMP levels
87
What is the indirect pathway by which somatostatin inhibits gastric H secretion?
inhibits the release of gastrin and histamine, thus decreasing H secretion indirectly
88
Pancreatic secretion has higher concentration of what electrolyte?
HCO3
**has lower Cl concen than plasma
89
Acinar cells produce the pancreatic secretion, then how do ductal cells modify pancreatic secretion?
-secreting HCO3 and absorbing Cl via CL-HCO3 exchange
90
What is the secondary messenger for secretin?
cAMP
91
What is the effect of CCK on pancreatic acinar cells?
increase enzyme secretion (amylase, lipases, proteases)
92
CCK potentiates the effect of what on pancreatic ductal cells?
secretin on ductal cells to stimulate HCO3- secretion
93
What are the second messengers of CCK?
IP3 and increased intracellular Ca
94
What are the contents of bile?
bile salts
phospholipids
cholesterol
bile pigments (bilirubin)
95
How do bile salts aid in intestinal digestion and absorption of lipids?
By emulsifying them and solubilizing them in micelles
96
What is the effect of CCK on the gall bladder?
-contraction of the gall bladder & relaxation of the sphincter of Oddi
97
Where are bile acids reabsorbed to recirculate bile acids to the liver?
terminal ileum
**via Na-bile acid cotransporter
98
How are carbohydrates absorbed in the small intestine?
via monosaccharides (glucose, galactose, fructose) via Na-dependent cotransport (glucose, galactose) and facilitated diffusion (fructose)
99
How are proteins absorbed in the small intestine?
amino acids, dipeptides, tripeptides via Na-depednent cotransport (aa) and H-dependent cotransport (di & tri-peptides)
100
How are lipids absorbed in the small intestine?
to fatty acids, monoglycerides and cholesterol via micelles form with bile salts in intestinal lumen
-->diffusion of fatty acids, monocglycerides and cholesterol into cell
-->re-esterification in cell to triglycerides & phospholipids and chylomicrons form in cell and are transferred to lymph
101
How is vitamin B12 absorbed in the small intestine and ileum?
SI: Na-dependent cotransport
ileum: intrinsic factor- Vit B12 complex
102
How is calcium absorbed in the small intestine?
Vit D dependent (calbindin D-28K)
103
How is Fe absorbed in the small intestine?
-Fe3+ is reduced to Fe2+
- binds to apoferritin in cell
104
when Fe is absorbed from small intestine, it circulates in blood bound to?
transferrin
105
pancreatic proteases (trypsin, chymotrypsin, etc), are secreted in inactive forms that are activated in the small intestine as follows:
1. trypsinogen is activated to trypsin by brush border enzyme: enterokinase
2. trypsin then converts chymotrypsinogen, proelastase and procarboxypeptidase A and B to active forms
106
What is the effect of lipids on gastric emptying?
slows b/c CCK slows gastric emptying
107
What is the effect of pancreatic lipases on the lilpids?
hydrolyze lipids to fatty acids, monoglycerides, cholesterol & lysolecithin
108
List pancreatic enzymes
pancreatic lipase
cholesterol est hydrolase
phospholipase A2
109
How are chylomicrons transported out of the intestinal cells
by exocytosis
110
lack of what protein leads to the inability to transport chylomicrons out of the intestineal cells
apoprotein B
111
Potassium is absorbed in what part of the GIT and secreted in what part of the GIT?
absorbed: SI
secreted: colon
112
In diarrhea why do we see hypokalemia?
K secretion by the colon is increased b/c of flow rate-depedent mechanism similar to renal distal tubule
113
Where are the secretory vs absorptive mechanisms located in the small intestine?
secretory: crypts
absorptive: villi
114
list fat soluble vitamins
A, D, E and K
**incorporated into micelles and absorbed along with other lipids
115
How are water soluble vitamins absorbed?
Na-dependent cotrnasport emchanisms
116
absorption of vitamin B12 in the ileum requires what?
intrinsic factor
**secreted by the stomach
117
The absorption of calcium is dependent on what?
adequate amounts of active form of vitamin D, 1,25 dihydroxycholecalciferol
118
How is iron absorbed?
as heme iron (iron bound to hemoglobin or myoglobin) or as free Fe2+
119
bilirubin is carried in circulation bound to?
albumin
120
IN the liver, wha tis bilirubin conjugated with
glucronic acid via the enzyme UDP glucuronyl transferase
121
Where is conjugated bilirubin excreted?
** in urine and bile
122
In the intestine, conjugated bilirubin is converted to
urobilinogen
**returned to the liver via enterohepatic circulation
--urobilin and stercobilin secreted in feces
123
In the liver describe phase 1 and 2 reactions
phase I: catalyzed by cytochrome p450 enzymes, followed by
phase II: conjugate substances
