GI System Flashcards
1
Q
How does food go through the body?
A
- mouth
- pharynx
- esophagus
- stomach
- duodenum -> jejunum -> ileum
- ascending -> transverse -> descending -> sigmoid colon
- rectum
- anus
2
Q
4 associated glandular organs that are located outside the GI tract:
A
- salivary glands
- liver
- gall bladder
- pancreas
3
Q
What are the 4 basic layers of the GI tract?
A
- mucosa: innermost layer
- submucosa
- muscularis externa
- serosa
4
Q
T/F: mucosa is not intensely folded
A
F, it is intensely folded to increase SA
5
Q
What makes up the mucosa?
A
- epithelium
- lamina propria
- muscularis mucosa
6
Q
Epithelium of the mucosa is a single…
A
layer of simple columnar cells
- aka enterocytes
7
Q
What do the epithelium of mucosa in the esophagus and anus look like?
A
stratified squamous
8
Q
Function of the lamina propria in the mucosa:
A
CT support for endothelium
9
Q
Description of muscularis mucosa:
A
thin layer of smooth muscle that produces folds and ridges of mucosa
10
Q
Submucosa of the GI tract is made up of…
A
- mainly loose CT (collagen and elastin)
- highly vascular
- submucosal plexus of enteric nervous system
11
Q
Some regions of the submucosa in the GI contain…
A
glands
12
Q
Submucosal plexus is also known as…
A
Meissner’s plexus
13
Q
What are the three parts of muscularis externa?
A
- inner (thicker) circular smooth muscle layer
- outer longitudinal smooth muscle layer
- myenteric plexus of enteric nervous system (between layers)
14
Q
Myenteric plexus is also known as…
A
Auerbach’s plexus
15
Q
Serosa is also known as…
A
adventitia
16
Q
Serosa is the…
A
outermost layer and mainly CT
17
Q
What is the percentage of cardiac output to the GI at rest?
A
25%
18
Q
All venous drainage occurs via…
A
hepatic portal system to the liver lymphatic drainage extensive
19
Q
Venous drainage is important for…
A
- transport of lipid soluble substances
- immunological screening
20
Q
What are the two ways the GI tract can be innervated?
A
- enteric nervous system
- reflexes
21
Q
Is the enteric nervous system intrinsic or extrinsic?
A
intrinsic b/c neurons are located completely w/in GI wall
- network of interconnected neurons w/in GI wall
- integrates motor and secretory activity
22
Q
What are the two major plexuses of the enteric nervous system?
A
- myenteric (between circular and longitudinal muscle layers)
- submucosal (between submucosa and circular muscle)
23
Q
Myenteric plexus innervates…
A
muscle layers
24
Q
Submucosal plexus innervates…
A
mucosa
25
Both plexuses are regulated by...
intrinsic and extrinsic reflexes
26
Examples of intrinsic and extrinsic reflexes:
- sensory neurons
- interneurons
- motor neurons
27
Sensory neurons respond to what kinds of stimuli?
- mechanical
- chemical
- pain
- temperature
28
Sensory neurons can mediate both...
local and central reflex arcs
29
Interneurons in plexi form...
reflex arcs
30
Motor neurons release...
ach onto muscarinic receptors of smooth muscle and secretory cells
31
Enteric nervous system uses neurotransmitters such as...
- Ach
- serotonin (5HT)
- ATP
- NO
- gastrin inhibitory peptide (GIP)
- vasoactive intestinal peptide (VIP)
- somatostatin
32
Examples of excitatory neurotransmitters:
- Ach
- Substance P
- 5HT4 serotonin by stimulating Ach
33
Examples of inhibitory neurotransmitters:
- VIP
- NO
- ATP
- 5HT3 serotonin
- GIP
34
VIP is what type of inhibitor?
non-adrenergic/non-cholinergic
35
How does NO act as an inhibitor?
via protein kinase G
| - reduces intracellular Ca2+
36
How does ATP act as an inhibitor?
inhibits adenylate cyclase
37
How does 5HT3 act as an inhibitor?
inhibits Ach
38
Many of the drugs that affect lower GI function work by...
modulating the enteric nervous system
39
Drugs that affect lower GI function affect levels of...
Ach, 5HT (serotonin), dopamine, enkephalins, motilin and somatostatin (hormones)
40
Short local reflexes are what kind of reflexes?
intrinsic
41
Where do short local reflexes originate and end?
in the ENS
42
For short local reflexes, the submucosal plexus controls...
secretion and blood flow
43
For short local reflexes, the myenteric plexus influences...
motility
44
ANS short and long reflexes are what kind of reflexes?
extrinsic
45
Extrinsic innervations of the ANS short and long reflexes alter the activity of...
enteric (intrinsic) neurons
46
Extrinsic innervations of the ANS short and long reflexes coordinate the activity of...
regions located farther from each other than local reflexes
47
Feedforward reflexes of ANS short/long are based on current status prepare...
forward regions for what is coming
48
Examples of feedforward reflexes:
- cephalic reflexes
| - gastrocolic reflex
49
Function of cephalic reflexes:
increases secretion and motility in response to smell/thought of food
50
Function of gastrocolic reflex:
increases activity in stomach coupled with motor and secretory activity in colon
- it's a central reflex arc
51
SNS terminates on...
enteric neurons, blood vessels, and sphincters
52
Post-ganglionic adrenergic fibers of the SNS release...
norepi, which inhibits activity of muscularis externa
53
What happens when SNS is stimulated?
- digestion inhibited
- decreases slow intrinsic activity, which produces muscle relaxation
- induces contraction of some sphincters and muscularis mucosa
- inhibits GI secretion and alpha 2
- vasoconstriction to redirect blood flow away from GI
54
PNS travels from...
vagus nerve from lower esophagus to transverse colon -> pelvic nerves to colon -> rectum -> anus
55
Post-ganglionic cholinergic neurons are located where and release what?
- in plexi
| - release Ach onto muscarinic receptors
56
What happens when PNS is stimulated?
- increases amplitude of slow intrinsic waves, which produces muscle contraction
- stimulates GI secretions
57
Pre-ganglionic neurons in the PNS release...
Ach to intrinsic neurons
58
GI peptides can regulate...
secretion and motility
59
GI peptides are secreted within the..
GI tract
60
Examples of GI peptides:
- hormones
- neuropeptides
- cytokines
61
T/F: GI peptides can't have action on the CNS
F
- CCK affects satiety
- grehlin affects hunger
62
GI hormone facilitates...
- gastrin family
- secretin family
- motilin and others family
63
How does the gastrin family function?
gastrin and CCK bind to CCKB receptors
64
How does the secretin family function?
secretin, VIP, GIP, GLP-1 all decrease gastric emptying
65
How does the motilin and others family function?
motilin stimulates migrating motor complex
66
Major functions of the GI:
- ingestion
- digestion
- absorption
- secretion
- movement
- excretion
67
Ingestion is the...
entry of food into tract through the mouth
68
Digestion is the...
breakdown of food into absorbable pieces
69
Digestion can occur two ways:
- mechanical: w/ teeth
| - chemical: via digestive enzymes
70
For chemical digestion, there are separate...
enzymes for each major nutrient groups
71
Chemical digestion is regulated by...
hormones
72
Absorption is when...
small nutrient molecules move across GI wall into the vascular system
73
What gets secreted during secretion?
- enzymes
- pH regulating substances
- regulatory hormones
- mucus
74
Movement of food through the GI tract uses the...
longitudinal and inner circular layers of smooth muscle
75
Excretion is the...
elimination of wastes
76
GI system regulates...
secretion and motility
77
Problems GI tract has to overcome to do its job:
- avoiding autodigestion to prevent digestion of body cells
- mass balance of GI fluids
- immune defense exposure to toxins/pathogens as food travels through GI tract
78
What is secreted to protect the GI tract?
mucus
79
Failure of avoiding autodigestion results in...
ulceration
80
GI has to absorb fluid mass equivalent to...
what it secretes but what is also lost in feces and urine
81
Failure of mass balance of the GI occurs when...
one vomits or diarrhea
| - results in dehydration
82
Immune defense of the GI tract is reinforced by...
- mucus
- digestive enzymes
- acidity of stomach
- gut associated lymphoid tissue (GALT)
83
Failure of immune defense of the GI tract results in...
food poisoning/infections
84
What is a major contributor to RMP of GI smooth muscle?
Na+/K+ ATPase
85
What are tonic contractions?
sustained contractions seen in sphincters
86
What are phasic contractions?
pattern of depolarization/repolarization seen in the stomach and small intestine
87
GI smooth muscle has what type of waves?
slow waves (basic electrical rhythm)
88
Slow waves originate from...
pacemaker cells
- interstitial cells of Cajal (modified smooth muscle cells)
- between smooth muscle layers and nerve plexus
89
Because adjacent cells are coupled by gap junctions, the muscle behaves as a...
functional syncitium
90
Amplitude and frequency of slow waves can be modified by...
- activity of extrinsic and intrinsic nerves, hormones, and paracrine substances
- reflexes
- inflammatory mediators
91
Inflammatory mediators are involved in...
GI disorders
- Celiac's
- inflammatory bowel
- Crohn's disease
92
Three major patterns of motility...
- peristalsis
- rhythmic segmentation
- migrating motor complex (MMC)
- tonic contractions
93
What is peristalsis?
propulsive movements forward
| - progressive waves of movement
94
Peristalsis is generated by...
slow waves
95
Peristalsis is altered through...
reflex actions
96
What is rhythmic segmentation?
mixing movements
- breaks food into smaller particles facilitating digestion
- isolated to short segments of tract
- alternating segmental contractions
97
What is the migrating motor complex (MMC)?
movements between meals
| - begins in stomach and sweeps through GI
98
MMC clears GI of...
food remnants and bacteria between meals
99
What is an example of tonic contraction in the GI?
sphincter contraction
100
Tonic contraction limits...
movement into the next segment of GI
| - prevents backflow
101
Chemical and mechanical digestion begins in the...
mouth
102
Saliva is secreted by...
acinar cells of parotid, sublingual, and submandibular glands
103
Function of saliva:
- softens and moistens food
| - dissolves food so it can be tasted
104
Saliva contains...
- amylases, which breaks starch into smaller polysaccharides
| - lysozymes (antibacterial enzyme)
105
What is a bolus?
mass of smaller particles mixed with salivary enzymes
106
What is another word for swallowing?
degluttation
107
Swallowing moves the bolus down...
pharynx and into the esophagus
108
Swallowing is initiated voluntarily by...
the tongue pushing bolus against soft palate
| - remainder is under reflex control
109
Where is the swallowing reflex center located?
medulla
110
Why does nasopharynx close when one swallows?
prevents movement of food into nasal passages
| - under reflex control
111
Why does the epiglottis close when one swallows?
inhibits respiration to prevent inhalation of food
| - under reflex control
112
What relaxes to let food enter the esophagus?
upper esophageal sphincter
113
What do long swallowing reflexes do?
prep stomach for incoming food
114
Steps of movement of food through esophagus by peristalsis:
- peristaltic wave initiated (contracts above bolus, relaxes below bolus)
- wave travels to pharynx
- relaxation of lower esophageal sphincter allows food to enter into stomach
115
How does food enter into the stomach?
by relaxation of lower esophageal sphincter and lowering of pressure to allow food to flow down esophagus
116
Lower esophageal sphincter is normally under...
tonic contraction by extrinsic and intrinsic nerves to prevent gastric contents from entering the esophagus
117
What happens if the lower esophageal sphincter doesn't stay contracted?
GERD/heartburn
118
What is the vomiting reflex?
reverse peristalsis
119
Where is the vomiting center located?
medulla
120
What counts as a strong stimulus for the vomiting reflex?
distention of stomach and duodenum
121
Stomach motility is responsible for...
- storage of food
- mixing of food
- slow emptying of chyme into duodenum
122
What makes up the proximal stomach?
- cardia
- fundus
- superior 1/3 of body
123
When does proximal stomach relax?
- in response to swallowing (under parasympathetic control)
| - in response to food (vagovagal reflex)
124
How does the vagovagal reflex work?
- swallowing and food in stomach picked up by vagal afferents
- signal travels to dorsal vagal complex in brain
- vagal efferents cause receptive relaxation (allows stomach to relax and take in more food)
125
What makes up the distal stomach?
- inferior 2/3 of body
- antrum
- pylorus
126
When is the distal stomach at rest?
in between meals
| - there are periodic contractions to clear stomach
127
What kind of contractions occur in the distal stomach?
- phasic contractions which begin in the body of the stomach
- ends with slow waves
- sometimes intense peristaltic waves
128
What happens during phasic contractions in the distal stomach?
- food is mechanically broken down
- gastric phase: secretions initiated by food
- results in chyme
129
Phasic contractions in the distal stomach are regulated by...
- hormones
- gastrin (+ g cells)
- histamine (+ECF cells)
- somatostatin (-D cells)
130
How do slow waves function in the distal stomach?
- begins at gastric pacemaker
- force and velocity increase as chyme approaches gastroduodenal junction
- moves food through open pyloric sphincter
- if sphincter is closed, bolus is forced back into stomach (retropulsion)
131
What kind of contractions are responsible to emptying the distal stomach?
intense peristaltic waves (pyloric pump)
132
Describe the pyloric sphincter
circular smooth muscle with 2 ring-like thickenings
133
Opening of the pylorus is controlled intramurally by...
contractions in the antrum
134
The pyloric sphincter prevents...
regurgitation of duodenal contents back into stomach
135
The pyloric sphincter has what kind of reflex?
enterogastric reflex (extrinsic)
136
Enterogastric reflex decreases...
emptying rate of gastric contents into duodenum to prevent overwhelming the duodenum
- inhibits antral contractions and stimulates pyloric sphincter to close
137
Enterogastric reflex is activated through...
duodenal mucosal receptors in response to:
- hyperosmotic solution of chyme/nutrients/enzymes
- duodenal pH < 4.5
- fatty acids and monoglycerides
138
Hyperosmotic solution of chyme/nutrients/enzymes work via...
osmoreceptors to inhibit further gastric emptying
139
How does duodenal pH activate enterogastric reflex?
- excess gastric acid gets dumped into duodenum
- sensed by duodenal chemoreceptors
- S-cells of duodenum release secretin
- secretin activates enterogastric reflex
140
What does secretin stimulate?
- release of bicarb from pancreas
| - enterogastric reflex
141
How do fatty acids and monoglycerides activate enterogastric reflex?
- presence of excess fats in duodenum stimulates I cells of duodenum to release hormone cholecystokinin (CCK)
- gastric emptying is slowed, so fat entry doesn't exceed the rate of fat breaking down
142
What is stimulated when CCK is released?
- contraction of pyloric sphincter and gallbladder smooth muscle
- duodenal neurons that initiate vagovagal reflex
- relaxes sphincter of Oddi
143
What is decreased when CCK is released?
rate of stomach emptying
144
When contraction of gallbladder smooth muscle and sphincter of Oddi is relaxed, what happens?
pancreatic juices and bile are able to enter into the duodenum
145
While food is in the small intestine, the majority of _____ and _____ are completed
digestion and absorption
146
What participates in digestion and absorption in the small intestine?
- bicarb from pancreatic duct
- digestive enzymes from intestinal epithelium and exocrine pancreas
- bile from liver via gallbladder
- mucus from intestinal goblet cells
147
Function of bicarb:
neutralize chyme
148
Function of bile from liver:
facilitates emulsification of fats
149
Function of mucus from intestinal goblet cells:
prevents autodigestion
150
Contractility and secretions of the small intestine are regulated by...
neuronal and hormonal clues
151
Chyme in the small intestine activates...
the enteric nervous system
- decreases gastric motility and secretion
- specific nutrients in the chyme can stimulate release of hormones and mechanisms to stimulate release of insulin
152
What type of movement is the most frequent in the small intestine?
segmental contractions
- closely spaced contractions and relaxations of circular muscle
- exposes fresh materials to absorptive surfaces
153
Aside from segmental contractions, what other movement does small intestine have?
- short peristaltic contractions
| - long peristaltic contractions (migrating myoelectric complex)
154
Frequency of short peristaltic contractions of the small intestine:
- regular when there is food
| - few between meals
155
What do long peristaltic contractions of the small intestine do?
empty stomach and small intestine between meals
156
What stimulates long peristaltic contractions of the small intestine?
motilin
157
When is motilin produced?
when there is fat and protein by M cells
158
What inhibits long peristaltic contractions of the small intestine?
- presence of food in stomach
- gastrin
- CCK
159
What is the intestinointestinal reflex of the small intestine?
over-distension of one area leads to the relaxation of the rest of the small intestine
160
What regulates the emptying of the small intestine?
ileocecal valve/sphincter
161
The ileocecal valve/sphincter is normally...
closed
- distention of cecum leads to cecal enteric reflex, which prevents retrograde flow
- distension of ileum promotes relaxation of sphincter
162
The ileocecal valve/sphincter has a reflex called...
gastroileal reflex or gastrocolic reflex
| - same thing, just different name
163
Gastrocolic reflex is initiated by...
- stretch in stomach
- increased motility of stomach
- byproducts of digestion in duodenum
164
Function of gastrocolic reflex:
- increases movement of material through ileocecal sphincter
| - helps make room for more food
165
Motility of the colon is relatively...
slow
- contents can stay here for many hours
- decreased motility causes greater absorption and constipation
166
Colon has an inner band of...
longitudinal smooth muscle, aka taenea coli
167
Contractions of taenea coli causes wall of colon to...
form haustrations (pockets)
168
What occurs within haustrations?
localized segmental contractions similar to segmentation
- mixing function
- compaction of feces
169
T/F: In the colon, peristaltic propulsion occurs in a single direction
F, occurs in both directions
170
T/F: retrograde speeds up progress through colon
F, it slows it down
171
Peristaltic propulsion in the colon is primarily regulated by...
intrinsic enteric reflexes caused by filling and distention
172
What is mass movement in the colon?
wave of contractions that occur 1-3x day
173
How does mass movement in the colon occur?
- large part of internal circular muscle contracts powerfully and propels food distally
- contents get pushed along a significant length of colon, which is mediated through the gastrocolic reflex and/or orthocolic response
174
Colon has what kind of reflex?
defecation reflex: emptying of lower colon initiated by filling of rectum
175
What happens when colon is distended?
- internal anal sphincter is relaxed
- external anal sphincter is constricted
- induces urge to defecate
176
External anal sphincter is under...
voluntary regulation and modulated by higher centers
177
Defecation is aided by...
conscious abdominal contractions against a closed glottis (Valsalva maneuver)
178
What are the major nutrient groups?
- carbohydrates
- proteins
- fats
179
Carbohydrates are ingested as...
- polysaccharides
- disaccharides
- monosaccharides
180
Function of polysaccharides:
storage reservoir for glucose
| - basically large chains of glucose
181
Glycogen is a major...
animal polysaccharide
182
Starch is a polysaccharide that can be found where?
in plants
183
What is a major source of carbs for humans?
starch
184
Starch also has cellulose which is the...
indigestible plant carb, which is a major component of dietary fiber
185
Disaccharides are made up of...
two monosaccharides
186
Examples of disaccharides:
- sucrose
- lactose
- maltose
187
Sucrose is made up of...
glucose and fructose
188
Lactose is made up of...
glucose and galactose
189
Maltose is made up of...
glucose and glucose
190
Examples of monosaccharides:
- glucose
- fructose
- galactose
191
Chemical digestion of carbs begins in the...
mouth w/
- enzyme salivary alpha-amylase (ptyalin)
- ductal cells of salivary glands
192
Salivary alpha-amylase (ptyalin) is made by...
acinar cells of the salivary glands
- parotid
- submandibular
- sublingual
193
What stimulates salivary alpha-amylase (ptyalin)?
PNS (Ach) in response to smell, taste or presence of food in mouth
- aka cephalic phase of digestive regulation
194
What is the optimum pH for salivary alpha-amylase (ptyalin)?
7
195
At what pH is salivary alpha-amylase (ptyalin) inactivated?
< 4
196
Function of salivary alpha-amylase (ptyalin):
break down starch to oligosaccharides
197
Ductal cells of salivary glands modify...
electrolytes in secretions reabsorbing Na+ and Cl- while secreting K+ into saliva
198
Chemical digestion of carbs stops in the...
stomach
199
Why does chemical digestion of carbs stop in the stomach?
when alpha amylase gets mixed with gastric acid, the salivary enzymes are inactivated
200
When does chemical digestion of carbs resume after being stopped in the stomach?
small intestine
201
Initial duodenal digestion of carbs occurs because of...
secretions from the exocrine pancreas
202
Pancreas is organized into...
lobes that have acinar and ductal cells
203
Pancreatic ductal cells contain...
carbonic anhydrase and secretes HCO3-, which neutralizes acid chyme
204
Pancreatic ductal cells are stimulated by...
secretin, which is released by S cells of the duodenum in response to pH <4.5
205
Pancreatic acinar cells are stimulated by...
- Ach
- long vagovago reflexes
- CCK (cholecystokinin)
206
Ach stimulates pancreatic acinar cells in response to...
thinking about food, smell, taste or presence of food in mouth
- this is the cephalic phase of pancreatic secretion
207
Long vagovago reflexes stimulate pancreatic acinar cells in response to what?
presence of food in stomach
| - this is the gastric phase of pancreatic secretion
208
CCK stimulates pancreatic acinar cells in response to what?
presence of fat and protein in duodenum
| - this is the intestinal phase of pancreatic secretion
209
Acinar cells of the pancreas secrete...
pancreatic alpha amylases, which are released by exocytosis
210
Function of pancreatic alpha amylases:
break polysaccharides into smaller oligosaccharides and disaccharides
211
Examples of duodenal secretions:
- sucrase
- lactase
- enterokinase
- peptidase
212
Function of sucrase:
cleaves sucrose into glucose and fructose
213
Function of lactase:
cleaves lactose into glucose and galactose
214
What causes lactose intolerance?
a deficiency of lactase
215
Where does the greatest absorption of monosaccharides occur?
in brush border cells of the duodenum and jejunum
| - they're specialized for absorption
216
Glucose and galactose compete for...
entry into epithelial enterocytes via apical SGLT1 (Na+ glucose transporter 1)
- basolateral Na+/K+ ATPase maintains the Na+ gradient needed for the secondary active transport
217
Glucose and galactose move out of the duodenum and jejunum by...
facilitated diffusion into the ISF by basolateral GLUT 2 transporter
218
Fructose moves in and out of cells via...
facilitated diffusion transporters
- enters apical border on GLUT-5
- exits basolateral by GLUT-2
219
Proteins are...
long chains of amino acids
| - aka polypeptides
220
Proteins are obtained from...
- ingested food
- breakdown of digestive secretions
- exfoliated epithelial cells
221
Amino acids are _____ units
absorbable
222
Chemical digestion of proteins begins in...
stomach due to secretions of gastric pit glands in mucosa
223
Cardiac glands are located...
below lower esophageal sphincter
224
Cardiac glands are made up of...
columnar epithelial cells that secrete mucus gel and alkaline fluid that has HCO3-
225
Function of cardiac glands:
protect epithelium from mechanical and gastric acid injury
226
How does aspirin and other NSAIDs affect cardiac glands?
inhibit mucus and HCO3- secretion
| - prolonged use can result in gastritis or gastric ulcers
227
What can helicobacter pylori affect the mucus gel layer?
can break it down and promote ulcers
228
Oxyntic glands are the acid secreting region in...
fundus and body of stomach
229
What cells make up the oxyntic glands?
- surface mucus cells
- mucous neck cells
- chief cells
- endocrine cells
- parietal/oxyntic cells
230
Surface mucus and mucous neck cells of oxyntic glands secrete...
mucus and bicarb
| - protects stomach from autodigestion
231
Where are chief cells located in oxyntic glands?
bottom of gland
232
Chief cells of oxyntic glands are stimulated by...
acid secretion or Ach
233
What do chief cells of oxyntic glands secrete?
- gastric lipase for fat digestion
| - pepsinogen, which is an inactive enzyme used for protein digestion
234
What activates pepsinogen?
HCl and turns it into pepsin
235
Function of pepsin:
convert about 15% of dietary protein to small peptides and amino acids
236
Examples of endocrine cells:
- ECL (enterochromaffin-like cells)
| - gastrin
237
Function of ECL cells:
secrete histamine
238
ECL cells are triggered by...
- gastrin
| - Ach
239
Gastrin is produced by...
G cells in response to presence of amino acid in stomach
240
Stomach releases acid secretions in response to...
- stomach distension
- presence of amino acids and peptides
- sight, smell, and taste of food
- calcium
- caffeine
- alcohol
241
How do somatostatin from D cells, prostaglandins, and epidermal growth factor inhibit HCl secretion?
inhibits adenylyl cyclase
242
What happens during meals for digestion of proteins?
1. increase in gastric lumen pH to 5/6
2. decreased somatostatin released by D cells
3. increased gastrin secretion
4. increased HCl secretion
243
What happens between meals for digestion of proteins?
1. gastric lumen pH<2
2. increased somatostatin release by D cells
3. decreased gastrin secretion
4. decreased HCl secretion
244
What turns off gastrin production?
somatostatin from D cells
- occurs when pH < 2
- stops when pH > 5
245
What can stimulate gastrin release?
coffee/caffeic acid
246
Where are parietal/oxyntic cells located in oxyntic glands?
deeper and along the sides
247
What is the intrinsic factor that is made in the parietal/oxyntic cells of oxyntic glands?
a glycoprotein that binds vitamin B12 and allows its absorption in small intestine
248
Parietal/oxyntic cells contains...
carbonic anhydrase that's used to produce HCl to lower pH of lumen
- converts CO2 + H2O to carbonic acid
- carbonic acid then dissociates to H+ and HCO3-
249
What is located on the basolateral membrane of parietal/oxyntic cells of oxyntic glands?
HCO3-/Cl- exchanger
- moves HCO3- to ICF by facilitated diffusion, which causes "alkaline tide" (raises pH of blood leaving stomach)
- Cl- enters cell from ECF
250
What is located on the apical membrane of parietal/oxyntic cells of oxyntic glands?
H+/K+ ATPase (aka proton pump)
251
How does the H+/K+ ATPase pump work?
- pumps H+ into lumen and brings K+ into cell
- K+ leaks back out via leak channels on apical border, which in turn increases number and activity of H+/K+ ATPases
- Cl- enters lumen via diffusion
- H+ combines with Cl-
252
Function of HCl:
- kills most ingested microorganisms
- converts inactive pepsinogen to active pepsin
- creates low pH of 1 for optimal action of pepsin
253
HCl secretion is stimulated by...
- Ach via M3 receptors
- gastrin via CCK receptors
- histamine from ECL cells via H2 receptors
- caffeine on adenosine receptors -> cAMP
254
Ach stimulates HCl secretion in response to...
- sight, smell, and taste of food
255
Pathway for Ach:
1. G protein is activated and associated with phospholipase C (PLC)
2. increases DAG, protein kinase C (PKC), IP3
3. increases intracellular [Ca2+]
256
Gastrin stimulates HCl secretion in response to...
- distension of stomach
| - presence of amino acids and peptides
257
What does histamine activate?
- G protein associated with adenylyl cyclase and increases cAMP
- K+ channel on basolateral membrane
258
Histamine is the paracrine agonist with the...
strongest effect compared to gastrin and Ach
259
Effect of caffeine on the stomach:
increases acid production so it can cause ulcers, irritable bowel syndrome, and decrease calcium uptake
260
HCl secretion is inhibited by...
- somatostatin
| - paracrines (prostaglandins (E&I) and epidermal growth factor (EGF))
261
Somatostatin is released from...
D cells in response to pH < 2 in stomach
262
How do paracrine hormones inhibit HCl secretion?
by inhibiting adenylyl cyclase
263
Chemical digestion of proteins continues in the...
duodenum
264
T/F: small intestine has low capacity to process protein
F, has a high capacity and absence of stomach pepsin doesn't impair protein digestion
265
Initial duodenal protein digestion occurs due to...
pancreatic secretions, which are proteases (endopeptidases) secreted in inactive zymogen form
266
Examples of pancreatic secretions:
- trypsinogen (most potent)
- chymotrypsinogen
- proelastase
- procarboxypeptidase
- trypsin inhibitor
267
Procarboxypeptidase is an...
exopeptidase that cleaves terminal amino acid
268
Trypsin inhibitor is made by...
pancreatic acini to prevent premature activation of trypsinogen in pancreas
269
Enterokinase is secreted by...
duodenal mucosa in response to presence of food
270
Function of enterokinase:
convert trypsinogen into trypsin
- trypsin activates chymotrypsin, carboxypeptidase, and elastase
- then proteins are converted to oligopeptides
- also has peptidases that converts oligopeptides to smaller peptides and amino acids
271
50% of protein absorption occurs in the...
duodenum
| - rest are in the jejunum and ileum
272
For absorption of proteins, the apical membranes of the small intestines contain...
transporters for single amino acids and peptides
273
Examples of transporters in the apical membranes of the small intestines:
- single amino acid transporters
- secondary active transport through Na+ driven symporters
- facilitated diffusion at basolateral membranes (moves amino acids into ISF)
274
For absorption of proteins, peptide transporters are what kind of transporters?
- apical secondary active transport through H+ driven symporters
275
Function of peptide transporters in absorption of proteins:
- converts proteins to single amino acids by intracellular peptidases
- helps with facilitated diffusion at basolateral membranes by moving amino acids into ISF
276
During absorption of proteins, small peptides can be moved across the cell via...
transcytosis
277
What are the primary lipids of a normal diet?
triglycerides/fat
278
Chemical digestion of fats begin and end in the...
small intestine
279
Before digestion of fats can occur, they must be...
emulsified by bile to increase SA
280
Where is bile made and stored (two different places)?
- made in liver by hepatocytes
| - stored in gall bladder
281
Bile salts are...
amphipathic, which means they have a hydrophobic area and a hydrophilic area
- can be reabsorbed and recycled
282
Function of bile salts:
- emulsify lipids to increase SA available for enzymatic action
- solubilize cholesterol and phospholipids
283
Digestion of fats occurs due to...
pancreatic secretions
| - mainly pancreatic lipases aided by colipases
284
Pancreatic lipases only have access to...
lipids on surface of fat droplets
285
Function of pancreatic lipases:
1. breaks fat into fatty acids and glycerol
| 2. fatty acids and glycerol form micelles of fat digestive products and fat soluble vitamins
286
What is the benefit of having micelles of fat digestive products and fat soluble vitamins?
- increased transport of lipid digestion products to brush border
- enhanced absorption of lipid products by epithelial cells
287
What are the fat soluble vitamins?
ADEK
288
What are the absorbable units of fats?
- fatty acids
| - glycerol
289
Where do micelles diffuse?
in the brush borders of duodenum and jejunum
290
Fatty acids will bind to ____ to prevent formation of oil droplets
proteins in the cytosol
291
Fat soluble vitamins enter epithelial cells via...
diffusion
292
Cholesterol gets transported into cell on...
brush border transport proteins
| - inhibited by ezetimibe
293
Binding proteins transport lipid digestion products to...
smooth ER and golgi to process and package lipids into chylomicrons
- they then leave by exocytosis
294
T/F: chylomicrons can enter gut capillaries
F, they're too big
| - enter lymphatic capillaries and are transported to veins via lymphatic vessels
295
What stimulates bile production?
CCK in response to presence of fat in duodenum
296
What happens after bile production is stimulated?
1. bile gets emptied into biliary canaliculi that then empties into bile ducts
2. bile gets released into common bile duct
3. bile can then directly enter duodenum at sphincter of Oddi
297
Sphincter of Oddi is usually...
closed and bile gets stored in gallbladder
298
Function of gall bladder:
- stores bile between meals
| - concentrates bile 10-20 fold
299
CCK can stimulate contraction of...
gallbladder smooth muscle, which empties bile into common bile duct
300
Terminal end of the common bile duct empties into..
duodenum through sphincter of Oddi
301
When is sphincter of Oddi is under high contractile tone?
between meals
| - relaxed by CCK
302
What is bilirubin?
bile pigment
- product of degraded RBCs
- makes bile yellow
303
What is cholesterol's only route for secretion?
via bile
304
Too much cholesterol in bile can lead to...
gallstones
305
What is the main site of absorption for micronutrients, water, and electrolytes?
small intestine
| - jejunum is more active than ileum
306
Water absorption in the small intestines depends on...
absorption of ions
| - specifically Na+ and Cl-
307
Na+ is absorbed along...
the entire length of intestine
- moves into epithelial cells with gradient
- Na+ driven transporters facilitate absorption of other substances
308
Ca2+ is absorbed by...
all areas of intestine
- moves into epi cells by passive diffusion w/ gradient through channels
- binds to calbindin inside cell
309
Ca2+ moves across what membrane in the intestine?
basolateral membrane into ISF by Ca2+ ATPase or Na+/Ca2+ exchanger
310
What enhances absorption of Ca2+?
1,25 dihydroxy-vitamin D
311
Vitamin B12 (cobalmin) is absorbed in...
ileum bound to intrinsic factor from stomach
312
Iron is absorbed across...
apical border with H+ on divalent metal transporter 1 (DMTI1)
- heme that got absorbed by apical transporter protein gets converted to Fe2+
- all Fe2+ gets removed from colon cells by transporter ferroportin
313
Transporter ferroportin is regulated by...
hormone hepcidin
| - dependent on body iron levels
314
Iron needs what kind of plasma transporter?
transferrin
315
After absorption, iron travels to...
the liver for storage or carried to bone marrow for RBC production
316
Vitamin C and most of vitamin B is absorbed by...
carrier mediated transport throughout the small intestine
317
What are parts of the large intestine/colon?
- ascending
- transverse
- descending
- sigmoid
318
Colon absorbs the remaining...
water and salt
319
Na+ absorption in the colon is driven by...
a gradient created by Na+/K+ ATPase on basolateral membrane
- are apical Na+ channels in colon
- Na+ can also enter via cotransport with Cl- or Na+/H+ exchanger pump
320
In the large intestine, Cl- follows which gradient?
Na+ electrical gradient into the ISF
- can be cotransported with Na+ or exchanged with HCO3- on apical surface
- also Cl- channels on basolateral surface
321
Immune functions of the GI tract:
- salivary lysozymes
| - extensive lymphatic presence
322
What is the first line of immune defense for the GI tract?
salivary lysozymes
323
Why is there an extensive lymphatic presence in the GI tract?
b/c there is continuous exposure to the external environment
324
Examples of lymphatic presence in the GI tract:
- GALT tissue
| - Peyer's patches in mucosa (M cells here bind antigens)
325
What happens if there is an over-activity of immune response in the GI tract?
- inflammatory bowel disease
| - Chron's disease
