GI Physiology Flashcards
[from BRS physiology]
1
Q
Meissner’s plexus
A
submucosal plexus, primarily conrtols the secretion and blood flow
2
Q
Parasympathetics on the GI tract
A
usually excitatory, carried via vagus and pelvic nerves
3
Q
Vagus nerve- GI organs
A
Esophagus, Stomach, Pancreas and upper large intestine
4
Q
Pelvic Nerve - GI organs
A
lower large intestine, rectum and anus
5
Q
Sympathetics on the GI tract
A
inhibitory
6
Q
Auerbach’s plexus
A
Myenteric plexus, controls motility of GI smooth muscle
7
Q
G cells
A
in antrum of stomach, secrete gastrin in response to a meal
8
Q
Actions of gastrin
A
increases H+ from parietal cells
stimulates gastric mucosal growth
9
Q
Most important stimuli for gastrin secretion
A
phenylalanine and tryptophan
others: distention of stomach, vagal stimulation mediated by GRP
10
Q
gastrin inhibitors
A
H+ in stomach lumen (negative feedback)
somatostatin
11
Q
gastrin is secreted by non-beta cell tumors of pancreas
A
Zollinger-Ellison Syndrome
12
Q
Peptide that is homologous to gastrin
A
CCK
13
Q
Actions of CCK
A
1) contract GB and relaxes sphincter of Oddi
2) pancreatic enzyme secretion
3) growth of exocrine pancreas
4) potentiates HCO3- from pancreas
5) inhibits gastric emptying
14
Q
I cells of duodenal and jejunal mucosa
A
secrete CCK
15
Q
Stimuli for CCK
A
small peptides, AA, FAs and monoglycerides
16
Q
homologous to glucagon
A
secretin
17
Q
Actions of secretin
A
stim panc HCO3- secretion and increase exocrine pancreatic growth
increase bile production
inhibits H+ from parietal cells
18
Q
S cells
A
In duodenum, Secrete secretin in response to H+ and FAs in duodenum
19
Q
Actions of GIP
A
Insulin release in response to ORAL glucose
inhibits H+ secretion
20
Q
hormone secreted in response to carbs, fats and protien
A
GIP
21
Q
Somatostatin
A
secreted by cells throughtout the GI tract in response to H+ in lumen
inhibits release of ALL GI hormones
inhibits gastric H+ secretion
22
Q
Histamine
A
Secreted by mast cells of the gastric mucosa
increases gastric H+ secretion directly and potentiating gastrin and vagal stimulation
23
Q
VIP
A
relaxes the lower esophageal sphincter
stimulates the pancreatic HCO3- secretion and inhibits gastric H+ secretion
24
Q
secreted by pancreatic islet cell tumors
A
VIP
presumed to mediate pancreatic cholera
25
Bombesin
GRP, release from vagus nerves that innervate the G cells
| stim gastrin release from G cells
26
Stimulate the contraction of GI smooth muscle, particularly the LES, pyloric and ileocecal sphincter
Inhibit intestinal secretion
Enkephalins
27
Opiate use in GI tract
Tx diarrhea
28
Tonic contractions
LES, orad stomach, ileocecal and internal anal sphincter
| always closed unless stimulated to open
29
Phasic contraction
esophagus, stomach, gastric antrum, small intestine. contract and relax periodically
30
oscillating membrane potentials inherent to smooth muscle of GI tract
Slow waves
31
Pacemaker of GI tract
interstitial cells of Cajal
32
Mechanism of Slow Wave production
Cyclic calcium channels open (depolarization) which brings mem potential closer to threshold
followed by K channels opening (repolarization)
33
Slow wave frequency
lowest in stomach (3 slow waves/min)
| highest in duodenum (12 slow waves/min)
34
Swallowing coordination
Medulla
35
Sequence of Events in Swallowing
Nasopharynx closes, breathing inhibited
Glottis is closed and larynx is elevated
peristalsis in pharynx and UES relaxes
36
Primary vs Secondary Peristaltic Contraction
1 - high pressure behind bolus to move it down
| 2 - clears esophagus of remaining food
37
Receptive relaxation
food in upper part of GI tract will relax GI tract further down to allow passage of food, Vagovagal reflex
38
Gastroesophageal Reflux
tone of LES is decreased and gastric content reflux into esophagus
39
Achalasia
LES does not relax during swallowing and food accumulates in esophagus
40
Contractions of GI tract during fasting
migrating myoelectric complex, occurs at 90 minute intervals
| Mediated by Motilin
41
How fats inhibit gastric emptying
fat stimulates CCK release which inhibits gastric emptying
42
How H+ in duodenum inhibit gastric emptying
direct neural reflexes
43
Segmentation contractions
mix intestinal contents
| back-and-forth movement
44
peristaltic contractions in small intesting
propel the chyme
contraction behind bolus and relaxation in front
coordinated by enteric nervous system
45
Gastroileal Reflex
mediated by extrinsic ANS and possibly gastrin
| prescence of food in the stomach triggers increased peristalsis in the ileum and relaxation of ileocecal sphincter
46
Haustra
sac-like segments, contracts of large intestine
47
Frequency of Mass movements in large intestine
1-3x/day
| cause colonic contents to move distally
48
Rectosphincteric reflex
rectum fills, it contracts and the internal anal sphincter relaxes
49
urge to defecate
when rectum is filled ~25%
50
Gastrocolic Reflex
food in stomach increases motility of the colon and increases the frequecy of mass movements
has a rapid PS component
51
Hirschsprung's Disease
absence of the colonic enteric nervous system resulting in constriction of involved segment
52
reverse peristalsis beginning in small intesting
Vomiting
53
Vomiting center of medulla
stimulated by tickling bac kof throat, gastric distention and vestibular stimulation (motion sickness)
54
Chemoreceptor trigger zone
in 4th ventricle, activated by emetics, radiation and vestibular stimulation
55
Composition of Saliva
High K and HCO3-
Low Na Cl
hypotonic
alpha-amylase, lingual lipase, and kallikrein
56
Slow Flow rate for Saliva
lowest osmolarity, lowest Na, Cl and HCO3-
| highest K conc
57
High Flow rate for Saliva
highest osmolarity, closest to that of plasma
58
Acinus for Saliva production
produces initial saliva, composition is similar to plasma
| isotonic
59
Ducts for Saliva production
modifies initial saliva, reabsorbs NaCl, secretes K and HCO3-
Aldosterone acts on these
Saliva becomes hypotoniic
60
Parasympathetic Stimulation of Saliva
CN VII and IX
increases saliva production by causing vasodilation
Muscarinic - IP3/Ca
61
Sympathetic Stimulation of Saliva
beta-adrenergic receptors
| cAMP
62
Parietal Cells
located in the body of stomach, secrete HCl and intrinsic factors
Stimulus is gastrin, Ach, Histamine
63
Chief Cells
located in body of stomach, secretes pepsinogen, stimulated by vagal stimulation
64
Mucous Cells
Antrum of Stomach, secretes mucus and pepsinogen
| stimulus is ACh
65
Alkaline Tide
pH of blood increases around the stomach due to Cl/HCO3-exchange when making acid for the stomach
66
Cimetidine
H2 receptor blocker, inhibits H+ secretion
67
ECL cells
inhibits histamine
68
messenger for histamine
Gs/cAMP
69
messenger for somatostatin to inhibit H+
Gi thus decreasing cAMP
| indirect pathway to inhibit H+ secreteion is inhibiting the release of gastrin and histamine
70
Protective factors for Peptic Ulcer Disease
mucus, HCO3, prostaglandins, mucosal blood flow, GFs
71
Gastric Ulcers
H+ secretion is decreased
Gastrin is increased
major cause = H. pylori
72
Duodenal Ulcer
H+ secretion is increased
gastrin in response to a meal is increased
major cause = H. pylori
73
3 Drugs that block gastric H+ secretion
Atropine, Cimetidine, Omeprazole
74
Low Flow Rates - Pancreas
isotonic fluid primarily of Na and Cl
75
High Flow Rates - Pancreas
isotonic fluid, primarily Na and HCO3-
76
Acinar cells - Pancreas
small volume, mainly Na and Cl
77
Ductal cells - Pancreas
secreting HCO3 and absorbing Cl through HCO3/Cl-exchange
78
Bile Salts
amphipathic
| surround lipid droplets (emulsification) and aid in intestinal digestino and absorption of lipis into micells
79
Micelle
contains FFAs and monoglycerides
80
conjugates with bile acids to make bile salts
glycine or taurine
81
where are bile acids reabsorbed
terminal ileum, Na-Bile acid cotransporter
82
alpha-amylase
hydrolyze 1,4-glycosidic bonds in starch, yields maltose, ,altotriose and alpha-limit dextrans
83
maltase, alpha-dextrinase and sucrase
part of intestinal brush border which hydrolyze oligosaccharides into glucose
84
lactase
lactose to glucose and galactose
85
trehalase
trehalose to glucose
86
sucrase
sucrose into glucose and fructose
87
SGLT1
Na-dependent cotransport with glucose in lumen of intestine
| sugar transported uphill, Na transported downhill
88
GLUT2
facilitated diffuse from inside enterocyte to blood
89
Fructose
transported by facilitated diffusion
90
Lactose intolerance
causes osmotic diarrhea
| lack lactase in brush border
91
Endopeptidases
hydrolyze interior peptide bonds
92
Exopeptidases
hydrolyzes 1 AA at a time from C terminus
93
Pepsin
optimal pH 1-3
94
enterokinase
a brush border anzyme that makes trypsin from trypsinogen
95
Trypsin
converts chymotrypsinogen, proelastase and procarboxypeptidase A and B to their active forms
also makes more trypsin
96
Free AA
Na-dependent amino acid cotransport
then facilitated diffusion into blood
4 separate carrier for neutral, acidic, basic, and imino amino acids
97
Dipeptides and Tripeptides
absorbed faster than free AA
H+-dependent cotransport of dipeptides and tripeptides on luminal memrbane
cytoplasmic peptidases make them into AA
facilitated transport into blood
98
Chylomicrons
re-esterfied products of TGs, cholesterol ester, phospholipids with apoprotein attached so it can leave the intestinal cells
99
Lymph Vessels
Where chylomicrons are exocytosed into and travel in until thoracic duct (then goes to blood)
100
How dietary postassium is absorbed
small intestine by passive diffusion through the paracellular route
101
Potassium in the Colon
K is secreted in the colon, sitmulated by aldosterone
| Diarrhea = hypokalemia
102
Primary ion secreted into the intestinal lumen
Chloride, regulated by cAMP
103
Cholera toxin (from vibrio cholerae)
catalyzes ADP ribosylation of alpha-s of Gs coupled to AC, permanently activating it
chloride is excreted
SECRETORY DIARRHEA
104
Fat Soluble Vitamins
A, D, E, K
| incorporated into micelles
105
Water Soluble Vitamins
absorbed by Na-dependent cotransport mechanisms
106
Vit B12 absorption
Ileum, requires intrinsic factor
107
Gastrectomy
loss of parietal cells, the source of intrinsic factor, lead to loss of vit B12, causes pernicious anemia
108
Calcium
Need 1,25-dihydroxycholecalciferol from kidney to induce syn of calcium-binding protein calbindin D-28K
109
Apoferritin
Free Fe2+ binds this to be transported into the blood
110
Transferrin
Fe2+ bound protein in the blood taking Fe from intestine to liver or from liver to BM
111
Most common cause of anemia
Iron deficiency
112
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