1
Q
Layers of GI wall?
A
- Mucosa (lamina propia, muscularis mucosa)
- Submucosa (Meissners plexus)
- Muscularis externa (inner circular, outer longitudinal)
- Auerbacks plexus (myenteric) - Serosa/Adventitia
2
Q
Why do SM fibers of GI tract contract in rhythmic cycles?
A
syncytium of gap junctions
3
Q
Slow waves?
A
not action potentials
-cyclic opening of calcium channels that increases probability of AP as it gets closer to threshold
4
Q
Spike potentials?
A
- true action potentials
- large influx of calcium
5
Q
Factors that depolarize smooth muscle?
A
- stretching
- ACh from parasympathetics
- hormones
6
Q
Factors that hyper polarize smooth muscle?
A
- NE/EPI
2. sympathetics
7
Q
Role of myenteric plexus (auerbachs)?
A
motility
8
Q
Role of submucosal plexus (meissners)?
A
secretion and blood flow
9
Q
Vasodilators released from GI mucosa?
A
- CCK
- VIP
- Gastrin
- Secretin
- Kinins
10
Q
Sympathetic effect on blood flow?
A
vasoconstrictor to decrease blood flow
11
Q
Jaw muscles innervated by?
A
Trigeminal III branch
12
Q
Salivary gland secretion?
A
- Amylase (serous)
2. Mucin (not parotid)
13
Q
Composition of saliva relative to plasma?
A
- hypotonic
- high bicarbonate
14
Q
Innervation to salivary glands?
A
Parasympathetic
- Glossopharyngeal to parotid
- Facial (chorda tympani) to submand/sublingual
15
Q
T/F
Sympathetic stimulation increases salivation.
A
True
-but less than parasympathetic
16
Q
How does salivation dilate blood vessels?
A
Kallikrein splits alpha2 globulin to form bradykinin
17
Q
Swallowing reflex?
A
- Sensory from vagus and glossopharyngeal to medulla
- medulla sends motor to striated muscle to voluntarily swallow
- then involuntary reflex
18
Q
What regulates entrance of food into stomach?
A
LES
- normally tonically constricted
- relaxes as peristaltic wave passes down esophagus
19
Q
Vomiting reflex?
A
- vagus and sympathetic afferent to brainstem
- motor through spinal nerves to diaphragm and abdominals
- strong duodenum and stomach contractions
- LES relaxation
- deep breath and raise hyoid bone
- close glottis
- lift soft palate
- downward contraction of diaphragm builds pressure
20
Q
How does the stomach empty?
A
intense antral peristaltic contractions
21
Q
Factors that promote gastric emptying?
A
- food volume
- stomach stretch
- Gastrin
- Ghrelin
22
Q
Factors that inhibit gastric emptying?
A
- duodenum distention
- duodenal irritation
- acidity
- osmolarity
- proteins and fats
- CCK
- GIP
- Secretin
23
Q
CCK?
A
- most potent block on stomach motility (pyloric constriction)
- pancreatic enzyme secretion from acinar cells
- GB contraction
- relaxes sphincter of oddi
- secreted by I cells
24
Q
Role of mucous secreting cells in stomach?
A
- mucous
- alkaline environment
25
Cells of tubular gastric glands (oxyntic) and function?
1. mucous neck secrete mucous
2. chief cells secrete pepsinogen
3. parietal cells secrete HCl and Intrinsic factor
26
Cells of pyloric glands and functions?
1. mucous cells
2. G cells secrete Gastrin
3. D cells secrete somatostatin
27
Pepsinogen function?
activated by HCl to degrade proteins into peptides
28
Intrinsic factor function?
absorption of Vitamins B12 which helps stimulate bone marrow
29
Role of acetylcholine in stomach?
1. pepsinogen secretion
2. HCl secretion
3. mucous
30
Role of Gastrin?
1. Stimulates ECL to release histamine
2. H binds H2 on parietal cells
3. increases cAMP
4. stimulates H/K ATPase and secretes HCl
5. bicarbonate secreted into plasma
- Gastrin also directly stimulates parietal cells at CCKb receptor
31
Role of somatostatin in stomach?
responds to acid to inhibit parietal cells, G cells, and ECL cells
32
What determines amount of HCl secreted?
amount of histamine from ECL
| -gastrin and ACh (M3) plays smaller role
33
Phases of gastric secretion?
1. Cephalic
- dorsal motor nuclei of vagus by sight, smell
- 30% of secretion
2. Gastrin
- 60% of secretion
3. Intestinal
- presence of food in duodenum
- 10%
- secretion is then inhibited by reverse enterogastric reflex
34
Secretin function?
- inhibits parietal cells
- bicarbonate
- adds Na/bicarb to bile
- secreted by S cells, activated at low pH
35
GIP?
- increase insulin
| - inhibit gastric secretion (also VIP and somatostatin)
36
Brunners glands?
- located in duodenum
- stimulated by secretin
- release bicarbonate
37
Crypts of lieberkuhn cells?
1. goblet cells
- mucous
2. enterocytes
- water and electrolytes
38
Paneth cells functions?
1. lysozyme
| 2. defensins
39
Active secretions of small intestines?
1. chloride
2. bicarbonate
Others:
- peptidases
- lactases and other ases
- lipase
40
Substances absorbed by stomach?
- OH
- Aspirin
- highly lipid soluble
41
How does SI absorb water?
osmosis through paracellular and transcellular
- enhanced by aldosterone
- reverse if hyper osmotic chyme
42
Transport of Na and glucose?
1. Na actively transported into ISF from basolateral Na/K ATPase
2. creates a gradient for Na to transport from lumen as secondary active
3. Na/glucose cotransport
4. Na/AA cotransport
5. Na/H exchanger
43
Where is bicarbonate reabsorbed? secreted?
- actively reabsorbed in duodenum and jejunum
| - secreted in ileum and colon to neutralize bacterial acid
44
Reabsorption of calcium?
- actively reabsorbed from duodenum
- enhanced by Vit D which is activated by PTH
- calbindin enhances
45
Absorption of fatty acids?
directly into portal blood
46
What mixes chyme with digestive juices in SI?
segmentation contractions propelling it
| -gastroileal reflex
47
How long to get from pylorus to ileocecal valve?
3-5 hours
48
Hormonal increase in intestinal motility?
- Gastrin
- CCK
- Insulin
- Motilin
- Serotonin
49
Hormonal inhibition of intestinal motility?
- Secretin
| - Glucagon
50
What sweeps inside of intestines clean between meals?
Migrating motility complex regulated by Motilin
| -inhibited by feeding
51
Function of ileocecal sphincter?
prevents contamination of SI by bacteria
52
Function of acinar cells of pancreas?
secrete digestive enzymes
53
Function of duct cells of pancreas?
secrete Na, Bicarb, H2O
- protects duodenum
- higher pH needed to activate enzymes
54
Activation of Trypsin?
1. secreted as zymogen
2. cleaved by enteropeptidase
3. Trypsin activates other enzymes
- trypsin inhibitor made in acini
55
Phases of pancreatic secretion of bicarb?
1. Cephalic (ACh-20%)
2. Gastric (5-10%)
3. Intestinal (secretin)
56
What forms bile?
Liver (600-1000 mL/day)
57
Precursor to bile salts?
Cholesterol
| -7a-hydroxylase
58
Where does 95% of bile salts come from?
reabsorbed by enterohepatic circulation
59
Cause of cholesterol gallstones?
bile salts combine with cholesterol to form micelles
- obesity
- estrogen
- too thin
- female
Upper GI
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