1
Q
Function of the myenteric plexus and meissner plexus
A
enteric nervous system of GIT
coordinates motility, secretory, and endocrine functions of GIT
2
Q
Function of efferent nerve fibers in the GIT
A
Carry info from brainstem and spinal cord to the GIT
3
Q
Function of afferent nerve fibers in the GIT
A
Carry sensory info from the GIT to the brain stem
4
Q
What type of action does the parasympathetic nervous system have on the GIT
A
Excitatory
5
Q
Which nerves associated with the GIT have parasympathetic function
A
Vagus nerve- upper GIT
Pelvic nerve- lower GIT
6
Q
Which nerve plexus controls GIT motility
A
Myenteric (Auerbach)
7
Q
Which nerve plexus controls GI secretions and blood flow
A
Meissner (submucosal)
8
Q
Source of gastrin secretion
A
G cells
9
Q
Where are G cells located
A
stomach, antrum, duodenum
10
Q
Stimulus for gastrin secretion
A
Small peptides/amino acids
Stomach distension
Vagus nerve
11
Q
What inhibits gastric secretion
A
Hydrogen in the stomach
Somatostatin
12
Q
What actions does gastrin have
A
Increases gastric hydrogen secretion
stimulates GI growth
13
Q
Where are I cells located
A
duodenum, jejunum, ileum
14
Q
What do I cells secrete
A
cholecystokinin (CCK)
15
Q
Stimulus for CCK secretion
A
Small peptides and amino acids
Fatty acides and monoglycerides (NOT TRIGLYCERIDES)
16
Q
Actions of CCK
A
Stimulates GB contraction
Relaxes the sphincter of Oddi
Increases pancreatic enzyme and HCO3 secretion
Increases growth of exocrine pancreas
Inhibits gastric emptying
17
Q
Pacemaker cells for the GIT
A
Interstitial cells of Cajal
18
Q
Location of S cells
A
duodenum
19
Q
What do S cells secrete
A
secretin
20
Q
Stimulus for secretin
A
Hydrogen in duodenum
Fatty acids in the duodenum
21
Q
Actions of secretin
A
Increase pancreatic bicarb secretion (neutralize H+ in duodenum)
Increases hepatic bicarb and H2O secretion
Inhibits secretion of hydrogen from gastric parietal cells
22
Q
Location of K cells
A
duodenum and jejunum
23
Q
What cells secrete gastric inhibitory peptide (GIP)
A
K cells
24
Q
Stimulus for GIP secretion
A
Fatty acids
amino acids
oral glucose
25
Actions of GIP
Increase insulin release
Decrease gastric hydrogen secretion
26
Stimulus for motilin secretion
Fat
Acid
Nervous stimulation
27
Action of motilin
Increase motility
28
What are the GI paracrines
Somatostatin and histamine
29
Stimulus of somatostatin
Hydrogen in the lumen of GIT
30
Action of somatostatin
Inhibits release of all GI hormones
Inhibits hydrogen secretion
31
Effect of insulin on appetite
Suppresses appetite
32
Effect of leptin on appetite
Suppresses appetite
33
Effect of gherkin on appetite
Increases appetite
34
Effect of histamine on GIT
Increases gastric hydrogen secretion
35
Vasoactive intestinal peptide action
Relaxes GI smooth muscle
Stimulates bicarb from pancreas
Inhibits acid secretion
36
Enkephalin
Opioid peptides
Acts as neurotransmitters and neuromodulators in the nervous system
37
Action of enkephalin
Stimulates contraction of GI smooth muscle
Inhibits intestinal secretion of fluid and electrolytes
38
What is the mechanism of slow wave production in the GIT
Cyclic opening of calcium channels (depolarization) followed by opening of potassium channels (repolarization)
39
Swallowing reflex
Upper esophageal sphincter relaxes
40
What mediates relaxation of the lower esophageal sphincter
vagal stimulation and VIP
41
what allows for receptive relaxation of the stomach
vasovagal reflex
CCK
42
what will delay gastric emptying
fats (stimulates CCK secretion)
hydrogen in the duodenum
43
Enterochromaffin cells
enteroendocrine cell found in the lining of the gastrointestinal tract
44
What do enterochromaffin cells secrete
5-hydroxytryptamine (5-HT)
Secreted in the intestinal lumen
45
What is the action of 5-HT
Binds to intrinsic primary afferent neurons
Initiates peristaltic reflex
46
What is the gastroileal reflex
Presence of food in stomach triggers increased peristalsis in ileum
Relaxes the ileocecal sphincter
47
Where is the vomiting center located
The medulla
48
What stimulates the vomiting center
Tickling the back of the throat/gag
Gastric distension
Vestibular stimulation
49
Where is the chemoreceptor trigger zone located
fourth ventricle
50
what stimulates the chemoreceptor trigger zone
emetics, radiation, vestibular stimulation
51
Metoclopramide mechanism of action
D2 dopaminergic antagonist - anti emetic action at the CTZ
5HT4 serotonin agonist- promotility effect on smooth muscle indirectly increases Ach release
Crosses BBB
52
Domperidone mechanism of action
D2 dopaminergic antagonist- anti emetic action at the CTZ
Does not cross BBB
53
Cisapride mechanism of action
5HT4 serotonin agonist
Enhances Act release at myenteric plexus
Stimulates motility
54
Erythromycin mechanism of action
Macrolide antibiotic
Binds 50s ribosome and inhibits protein synthesis (gram + aerobes only)
stimulates motilin receptors to increase smooth muscle activity
55
Ranitidine mechanism of action
H2 antagonist
Suppresses histamine's gastric parietal cell stimulation to decrease gastric acid
Acetylcholinestrase inhibitor
56
Use for cimetidine in acetaminophen toxicity
Inhibition of cP450 reductase
57
Ondansetron mechanism of action
5HT3 serotonin receptor antagonist
During chemotherapy- may be 5HT release from GIT injury which stimulates central vomiting
58
Chlorpromazine mechanism of action
Dopamine antagonist- anti emetic at vomiting center
Phenothiazine tranquilizer
59
Diphenhydramine and meclizine mechanism of action
H1 antihistamines
60
Functions of saliva
Initial starch digestion
Initial triglyceride digestion
Lubrication of food
Buffering foods
61
Composition of saliva at low flow rates
Hypotonic (more NaCl has left ducts at slow rate)
Lowest NaCl, lowest HCo3-, highest K
62
Composition of saliva at high flow rates
More isotonic with plasma
63
What regulates saliva production
Autonomic nervous system (both sympathetic and parasympathetic)
64
What is the most potent stimulus for saliva production
Parasympathetic stimulation
65
What is secreted by parietal cells
HCl
Intrinsic factor
66
What are the stimuli for parietal cell secretion
Gastrin
Ach
Histamine
67
What is secreted by the chief cells
Pepsinogen (converted to pepsin at low pH)
68
What is the stimulus for chief cell secretion
Vagal stimulation (Ach)
69
What is secreted by G cells
Gastrin
70
What is stimulus for G cell secretion
Vagal stimulation (GRP)
Small peptides)
71
What inhibits G cell secretion
Somatostatin
Hydrogen in stomach
72
What is secreted by mucous cells in the antrum of the stomach
Mucus
Pepsinogen
73
Effect of vagal stimulation on gastric hydrogen secretion
Increases hydrogen secretions via muscarinic receptors on parietal cells
Innervation of the G cells to stimulate gastrin secretion, leads to more HCl from the parietal cells
74
What is the stimulus for mucous cell secretion in the antrum of the stomach
Ach (vagal)
75
Where are the H-K ATPase (proton pumps) located in the gastric mucosa
Luminal side of parietal cells
76
How does vomiting result in metabolic alkalosis
Hydrogen does not arrive in the small intestine, so there is no stimulus of pancreatic HCO3 secretion, arterial blood becomes alkaline
77
What is the effect of histamine on Ach and gastrin secretion
potentiates their actions by stimulating hydrogen secretion
78
What is the effect of Ach on gastrin and histamine
Potentiates their actions by stimulating hydrogen secretion
79
What inhibits secretion of hydrogen by the parietal cells
Low pH (<3.0 in stomach) inhibits gastrin somatostatin via G1 protein and decreases cAMP prostaglandins via G1 protein and decrease cAMP
80
What factors contribute to peptic ulcer formation
Hydrogen
pepsin
NSAIDs
stress
81
What is zollinger-ellison syndrome
when a gastrin-secreting tumor of the pancreas causes increased hydrogen secretion
82
what enzymes are in the pancreatic secretions
lipase
amylase
proteases
83
what is the relative bicarbonate concentration of the aqueous component of pancreatic secretion compared to plasma
higher bicarbonate concentration in pancreatic secretion
84
what are the simuli for pancreatic secretion
secretin
CCK
Ach
85
What are the stimuli for HCl secretion
gastrin
histamine
Ach
86
what are bile salts composed of
hydrophilic and hydrophobic portions
bile acids are conjugated with glycine or taurine to form a bile salt
87
what are primary bile acids
cholic acid
chenodoxycholic acid
88
where are primary bile acids synthesized
hepatocytes
89
what are primary bile acids synthesized from
cholesterol
90
where are bile acids conjugated
hepatocytes
91
where are primary bile acids converted into secondary bile acids
duodenum
92
what are secondary bile acids
deoxycholic acid
lithocholic acid
93
what stimulate contraction of the gall bladder
CCK
94
what effect does CCK have on the sphincter of oddi
relaxes it to allow bile to flow out of the GB duct
95
what allows bile acids to be recirculated
Na-bile acid co-transporter in the terminal ileum
96
what are carbohydrates digested into
glucose, galactose, and fructose
97
what degrades lactose, and to what products
lactase
degraded to glucose and galactose
98
what degrade trehalose, and to what products
trehalase
degraded to glucose
99
what degrades sucrose, and to what products
sucrase
degraded to glucose and fructose
100
how are glucose and galactose transported from the intestinal lumen into cells
Na-dependent co-transport (SGLT1) into the luminal membrane
101
what transports glucose and galactose from the cell to the blood
GLUT2 transporters
102
what method of transport occurs to move fructose into the cell
facilitated diffusion
103
Function of endopeptidases
degradation of proteins by hydrolyzing interior peptide bonds
104
what is the function of expopeptidases
hydrolyze one amino acid at a time from C terminus of proteins and peptides
105
what cells secrete pepsinogen
chief cells in the stomach
106
how is pepsinogen activated to pepsin
gastric hydrogen (optimum pH is 1-3)
107
what is the function of enterokinase in the small intestinal brush border
activates trypsinogen into trypsin
108
what are functions of trypsin
conversion of chymotrypsinogen, proelastase, and procarboxypeptidase A and B into active forms
109
How are proteins abosrbed
digestive products can be absorbed as amino acids, dipeptides, or tripeptides via hydrogen or sodium dependent transporters
110
how are lipids digested
Mixing in stomach
Lingual lipases in the mouth
CCK slows the gastric emptying to allow adequate time for digestion
Pancreatic lipases in the small intestines
Bile acids in the small intestines emulsify lipids
111
How are hydrophobic products of lipid digestion absorbed
in micelles by bile acids
112
function of pancreatic lipase
Hydrolyze lipids to fatty acids, monoglycerides, cholesterol, and lysolecithin
113
what are causes for the malabsorption of lipids
Pancreatic disease (pancreas cannot synthesize lipases)
Hypersecretion of gastrin (low gastric acid/pH inactivates pancreatic lipase)
Ileal resection (depletion of bile acid pool since no enterohepatic recirculation can take place)
Bacterial overgrowth (deconjugate bile acids in SI)
Decrease synthesis of apoprotein B (leads to inability to form chylomicrons)
114
what are chylomicrons
products of lipid digestion where intestinal cells reesterfy lipids to triglycerides, cholesterol ester, and phospholipids
115
Absorption of Na in the small intestines
Na-glucose cotransport
Na-amino acid cotransport
Na-H exchange
116
Absorption of Cl in the small intestines
Passive diffusion
Na-Cl cotransport
Cl-HCO3 exchange
117
where is dietary potassium absorbed
small intestines
118
how is dietary potassium absorbed
passive diffusion
119
where is potassium secreted in the GIT
in the colon (similar to distal tubules in renal physiology)
120
what happens to potassium levels with diarrhea
Excessive potassium loss in diarrheal fluid
Causes hypokalemia
121
How is water absorbed
Isoosmotic with small intestine and gall bladder- water follows solutes
122
where is water permeability low in the GIT
colon
123
what is the function of the crypts in the intestines
secretion
124
what is the function of the villi in the intestines
absorption
125
what is the primary ion secreted into the intestinal lumen
chloride
126
how are the calcium channels regulated in the intestines
cAMP
127
how can E. coli cause secretory diarrhea
catalyzes ADP ribosylation leading to increased cAMP and chloride channel opening
128
how are fat soluble vitamins absorbed
incorporated into micelles
129
what are the fat soluble vitamins
A, D, E, K
130
how are water soluble vitamins absorbed
Na-dependent cotransport
131
where is vitamin B12 absorbed
ileum
132
what is required for B12 absorption
intrinsic factor
133
what is required for absorption of calcium in the small intestines
vitamin D and calbindin
134
how is iron absorbed
Heme iron (bound to Hb or Mb), or as free Fe2+
135
how is iron transported from the intestinal cells to the blood
free Fe2+ binds to apoferritin and transported to blood
136
how is free Fe2+ transported through the blood
transferrin
137
what is bilirubin
degradation product of Hb
138
how is bilirubin carried in blood
bound to albumin
139
where is bilirubin conjugated
in the liver
140
what is bilirubin conjugated to
glucoruonic acid via UDP glycuronyl transferase
141
what is conjugated bilirubin converted to in the intestines
Urobilinogen which is returned via enterohepatic circulation
Also urobilin and stercobilin, which are excreted in feces
142
what role does liver play in carbohydrate metabolism
Gluconeogenesis
Storage of glucose as glycogen
Releases glucose into circulation
143
what roles does liver play in protein metabolism
Synthesizes nonessential amino acids
Synthesizes plasma proteins
144
what role does liver play in lipid metabolism
Fatty acid oxidation
Synthesizes lipoproteins, cholesterol, phospholipids
145
what enzyme phosphorylates glucose in the liver
Glucokinase - phosphorylates glucose into glucose 6 phosphate (which is necessary for glycogen storage)
146
what substances activate glycogenolysis via phosphorylase activation
glucagon and epinephrine
147
where does glycolysis occur
in the cytoplasm
148
how many ATP are generated for each molecule of glucose
38
149
what is the main component of chylomicrons
triglycerides
150
which lipoprotein has highest concentration of triglycerides
very low density lipoproteins
151
which lipoprotein has the highest concentration of protein
high density lipoproteins
152
which lipoprotein has the highest concentration of cholesterol
low density lipoproteins
153
which lipoprotein transfers triglycerides from liver to adipose tissue
very low density lipoproteins
154
what effect do catecholamines have on fat metabolism
activate hormone sensitive lipase to promote fat breakdown and mobilization
155
what effect does growth hormone and cortisol have on fat metabolism
activates hormone sensitive lipase to promote fat mobilization
156
what effect does insulin have on fat metabolism
inhibits hormone sensitive lipase
157
what effect does insulin have on fat metabolism
inhibit hormone sensitive lipase
158
which B vitamin affects aminotransferases during protein formation
vitamin B6 (pyridoxine)
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