Normal GI Physiology Flashcards
1
Q
What is the function of alpha cells in the pancreas?
A
secretes glucagon, leading to increased circulation of glucose and gluconeogenesis (mobilizes fat)
2
Q
What is the effect of sympathetic innervation on salivary glands?
A
vasoconstriction
viscous secretions (protein secretion)
3
Q
What is the gross structure of the stomach lining?
A
rugae - folds that flatten to allow the stomach to distend
4
Q
How is food ground up and mixed in the stomach?
A
the stomach propels material towards the pylorus and then most of it is squeezed back to the body by the antrum
5
Q
How is bicarbonate transported by parietal cells?
A
bicarbonate produced from OH- and CO2
it diffuses out of the cell, making gastric venous blood alkaline
6
Q
What is the cellular structure of liver tissue?
A
hepatocytes form branching plates of cells between sinusoids that connect portal tracts to central veins
7
Q
What is the parasympathetic innervation of sublingual and submandibular glands?
A
preganglionic fibers arise in pons and brainstem
travels via facial nerve to submandibular and sublingual ganglion
8
Q
What are amylytic enzymes? Lipolytic enzymes? Proteolytic enzymes?
A
amylytic: break bonds in carbohydrates
lipolytic: lipases and esterases for fats
proteolytic: trypsinogen and chymotrypsinogens
9
Q
How many layers of smooth muscle are present in the muscularis propria in the small intestine?
A
two layers of smooth muscle
10
Q
What is the mechanism of primary peristalsis?
A
CNS generated activity (vagus nerve)
orderly progression of contractions of the circular muscle layer (smooth and striated) of the esophagus
orderly progression is intrinsic to esophagus
11
Q
What is this?
A
ileum of small intestine
can tell because of Peyer’s patches
12
Q
How are fat soluble vitamins absorbed?
A
incorporated into micelles and absorbed by simple diffusion
enter general circulation via lymphatics
13
Q
What signals generate peristalsis?
A
myenteric plexus stimulation on top of slwo waves
autonomic nervous system not required
14
Q
What are the major inputs to the enteric nervous system?
A
inputs from sympathetic and parasympathetic nerves
inputs from chemo- and mechano-receptors in gut muscle and mucosa
inputs from GI hormones
15
Q
What is the net secretion of ions from acinar cells?
A
secretion of NaCl is driven by Na/K ATPase (Na transported out, K transported in)
there is also secretion of HCO3
- more Na transported than K, which creates a gradient to drive Cl- into the cell*
- Cl- builds up in cell, which leads to Cl- leaving the cells*
- Cl- secretion drives Na+ to enter the lumen between the cells*
16
Q
What do G-cells produce?
A
gastrin
17
Q
What is the efferent control of swallowing?
A
includes motorneurons (innervating striated muscle) and autonomic preganglionic neurons
located in the trigeminal, hypoglossal, facial, and vagal motor nuclei (going to 20+ separate muscles)
also includes parasympathetic and sympathetic innervation
18
Q
What are the variations in slow wave frequency along the GI tract?
A
stomach lower frequency than intestine
oral regions have highest frequencies
19
Q
What activates the cephalic phase of GI activity? What happens in this phase?
A
activated by: presence of food perceived by sensory receptors (ex. sight, smell, etc.)
events: activates widespread CNS reflexes (salivary, gastric, pancreatic secretions), mediated entirely by CNS
20
Q
What do endocrine cells produce?
A
hormones (ex. histamine)
21
Q
What cells make up the endocrine components of the pancreas?
A
beta/B cells (secrete insulin)
alpha/A cells (secrete glucagon)
delta/D cells (secrete somatostatin)
22
Q
What is the effect of hydrochloric acid on ions in the small intestine?
A
it solubilizes Ca2+ and Fe3+ so they are more readily absorbed
23
Q
What are migrating motor complexes?
A
periodic wave activity that occurs in the fasting state
clears GI tract of debris
does not require ANS and is abolished by feeding
24
Q
How are myoepithelial cells stimulated for salivary secretions?
A
stimulated by alpha adrenergic and muscarinic receptors
25
How is gastric secretion inhibited in the intestinal phase of secretion?
inhibited by acid, digests of fats, proteins, and carbohydrates
26
What is the mechanism of secondary peristalsis?
reflex activated by distension of the esophagus
mediated by a CNS reflex (vagovagal reflex) or by intrinsic reflex mechanisms (lower part of esophagus)
27
In the small intestine, Na+ is absorbed by each of the following processes except:
a) diffusion
b) coupled to amino acid absorption
c) coupled to galactose absorption
d) coupled to transport of H+ in the opposite direction
e) coupled to the absorption of HCO3-
e) coupled to the absorption of HCO3-
## Footnote
*this is coupled to Cl-*
28
What are the histologic layers of the stomach?
mucosa
submucosa
muscularis propria/externa
serosa
29
How is food broken down in the stomach?
chemically (by gastric secretions) and mechanically (contractions of smooth muscle in the stomach)
30
What is this?
antrum of the stomach
## Footnote
*you can tell because of the stain for gastrin*
31
How does potassium transport change along the GI tract?
jejunum/ileum: passive K+ absorption
proximal colon: passive and active K+ secretion
distal colon: passive and active K+ secretion, active K+ absorption
32
In the distal portion of the ileum:
a) most fatty acids are absorbed
b) Cl- is absorbed in exchange for HCO3-
c) Na+ absorption occurs primarily coupled to glucose and amino acids
d) intrinsic factor is secreted
e) K+ is absorbed in exchange for Na+
a) most fatty acids are absorbed
33
What is the effect of distension in the gastric phase of secretion?
it stimulates vaso-vagal reflexes and intrinsic nerve reflexes
vagal reflexes activate parietal cells
intrinsic reflexes activate parietal cells (via acetylcholine) and stimulate gastrin release
34
How is H+ transported in parietal cells?
H+ is actively pumped out of cells in exchange for K+
## Footnote
*proton pump*
35
What is absorptive/protective mucosa?
mucosa that specializes in water absorption and mucous secretion
## Footnote
* contains deep crypts but no villi*
* found in large intestine*
36
What is the motor activity of the large intestine?
propels contents towards anus slowly with little net propulsion
haustral contractions (similar to segmentation) mix and move contents slowly
* long transit time = more absorption of water and electrolytes*
* 1-3 mass movements into sigmoid colon per day*
37
What are the four layers of the hollow GI organs?
mucosa
submucosa
muscularis propria/externa (smooth muscle)
adventitia/serosa
38
What is this?
large intestine
39
What are the main transporters on the lumen side of acinar cells?
K+ (into lumen)
Cl-/HCO3- cotransport (into lumen)
40
What is this?
pancreas
41
How is the swallowing reflex produced?
produced by a brainstem central pattern generator in the medullary reticular formation (gets input from the nucleus tractus solitarius)
42
What is the muscular makeup of the esophagus? How is it innervated?
top 1/5 = striated muscle, innervated by **axons of cranial nerve motorneurons directly**
middle = mixed
bottom 1/2 = smooth muscle, innervated by **vagal preganglionic axons indirectly** via innervation of intrinsic neurons of esophageal wall
43
What are the major electrolytes of saliva?
Na+, K+, Ca2+, Cl-, HCO-, HPO3-
44
What ion changes create action potentials in GI muscle?
increased permeability of membrane to Na+ and Ca2+
45
Which of the following transporters is not found on the apical membrane of intestinal cells?
a) HCO3/Cl exchange
b) H/Na exchange
c) Na/K exchange
d) glucose/Na cotransport
c) Na/K exchange
## Footnote
*found on basolateral membrane, facilitates sodium absorption*
46
47
What is the change in the tonicity of saliva at high secretion rates?
high secretion rates reduces the amount of time for reabsorption, so it becomes more isotonic
48
What is absorptive mucosa?
mucosa that is responsible for absorbing digested nutrients and hormone production
## Footnote
* contains villi and crypts that increase surface area*
* found in small intestine*
49
What are the digestive functions of saliva?
lubricates/washes oral cavity
alpha amylase breaks down starch
50
What is an upper esophageal sphincter?
an area that keeps the opening to the esophagus closed under normal conditions
composed of cricopharyngeus and part of the thyropharyngeus muscles
51
What factors affect the acid output in gastric juice?
dependent on the number of parietal cells secreting H+ (each one secretes a constant amount of acid)
52
How is pancreatic secretion regulated in the gastric phase?
vagally mediated due to distention of the stomach
vagus activates pancreas in cephalic phase, some stimulation by gastrin from the stomach
53
What are the four junctions of the GI tract with changes in mucosal lining?
gastro-esophageal junction
gastro-duodenal junction
ileo-cecal junction
recto-anal junction
54
What is secretory mucosa?
GI mucosa with cells that are responsible for secretion of digestive enzymes
## Footnote
*found exclusively in the stomach*
55
What is the effect of hydrochloric acid on stomach enzymes?
it activates pepsinogens to activate pepsins
it also creates an acidic environment that boosts enzyme activity and denatures non-enzymatic proteins
56
What is the effect of parasympathetic innervation on salivary secretions?
vasodilation in glands
increase in serous secretion
painful stimuli
57
What are the contents of gastric juice in the interdigestive period?
low in acid and pepsin (mostly non-parietal cell secretion)
basal secretions follow a circadian pattern and are influenced by emotional factors
58
What are the components of the muscularis propria/externa?
inner circle and outer longitudinal muscle
striated muscle (upper 1/3), smooth muscle (lower 1/3), and mixed in the middle
59
What type of tissue comprises the majority of the liver?
epithelium (hepatocytes)
60
A 70 year old woman undergoes a gastrectomy for Zollinger-Ellison syndrome. Her physician informs her that she will need to take intramuscular vitamin B12 shots for the rest of her life. Absence of which of the following cell types is responsible for this vitamin replacement requirement?
a) chief cells
b) G cells
c) goblet cells
d) mucous neck cells
e) parietal cells
e) parietal cells
61
Gastrin stimulates the secretion of hydrochloric acid from parietal cells. The stimulatory effects of gastrin on acid secretion are mediated in part by gastrin-induced secretion of which substance?
a) acetylcholine
b) amino acids
c) gastrin-releasing peptide
d) histamine
e) somatostatin
d) histamine
62
What is this?
liver
## Footnote
*portal tract on the right side, central vein in the center*
63
What is the structure of the muscularis propria/externa?
inner circular layer of smooth muscle, outer longitudinal layer
*muscles allow for peristalsis*
64
How are monosaccharides absorbed in the GI tract?
absorbed into cell with SGLT1 (cotransport with Na) or GLUT5, transported out of basolateral membrane via GLUT2
65
What activates the interdigestive phase of GI activity? What happens in this phase?
activated by: between meals (empty stomach)
events: minimal secretory and motor activity, periodic contractions of the migrating motor complex
66
What are the histological layers of the large intestine?
mucosa
submucosa
muscularis externa
serosa
67
How does acid in the duodenum inhibit gastric acid secretion?
acid stimulates release of secretin, which inhibits gastrin secretionn
acid also stimulates a local inhibitory reflex (enterogastric reflex)
68
What is the mechanism of segmentation in the stomach?
circular contractions separated by relaxed segments
longitudinal muscle stays relaxed
69
What are the three layers of the mucosa of the hollow organs of the digestive system?
epithelium (stratified squamous, simple columnar)
lamina propria (loose connective tissue and vessels)
muscularis mucosae (thin double layer of smooth muscle)
70
What reflexes control ileocecal sphincter opening?
cecal-ileal reflex: keeps sphincter closed by distending cecum
gastro-ileal reflex: promotes ileal emptying during gastric secretion/emptying
*distension of stomach leads to sphincter opening*
71
What is the tonicity of gastric juice?
almost isotonic
## Footnote
*due to H2O diffusion passively*
72
What are the histologic layers of the esophagus?
mucosa
submucosa
muscularis propria/externa
adventitia
73
Where are water and fluids largely absorbed along the GI tract?
mostly within the small intestine (90-95%)
water is also absorbed in the colon
74
How is iron absorbed in the GI tract?
it is absorbed actively
it is taken up by mucosal cells by binding to apoferritin (creating ferritin) and is stored
ferritin is slowly removed/absorbed via binding to a transferrin carrier
75
What happens during the esophageal phase of swallowing?
bolus enters the esophagus
bolus propelled downard by peristalsis
lower esophageal sphincter relaxes to let the bolus enter the stomach
76
How are pepsinogens activated?
they can be converted to pepsins at a pH of less than 5 or by other pepsins
77
How are acinar cells stimulated?
electronically coupled
stimulation spreads cell to cell
78
GI hormones:
a) stimulate their target cells from the luminal side of the gut
b) are for the most part inactivated as they pass through the liver
c) are released from discrete glands within the mucosa of the GI tract
d) pass through the liver and heart before reaching their targets
e) are bound to plasma proteins in the blood
d) pass through the liver and heart before reaching their targets
79
What are the protective functions of saliva?
alkaline --\> protects against acid
bicarbonate --\> saliva buffering of pH
antimicrobial/immunological functions
80
How are water soluble vitamins absorbed in the GI tract? How is Vitamin B12 absorbed?
non-B12: passive, facilitated, or active transport (co-transport with Na+)
B12: binding to intrinsic factor for uptake in the distal ileum
81
How do fatty acids, proteins, and carbohydrates cause gastric secretion inhibition?
they cause release of gastric inhibitory peptide (and other peptides) that reduce gastrin stimulated secretion and histamine stimulated secretion
fatty acids and amino acids also cause release of cholecystokinin (CCK) that binds to gastrin receptors and is a partial agonist (blocks binding of gastrin)
82
What is the composition of pancreatic juice?
alkaline pH (to neutralize gastric acid)
composition varies with rate of secretion: Na+ and K+ consistently iso-osmotic with plasma, low secretion rates = Cl- and HCO3- iso-osmotic with plasma, high secretion rates = high HCO3-, low Cl-
83
What secretogogues stimulate enzyme release from pancreatic acinar cells?
VIP, secretin, GRP, ACh, and CCK
84
How is Cl- secreted in the small intestine and colon?
it enters the cell by transport with K and Na (2Cl/K/Na tranpsorter) and is transported out of the cell via an apical transporter into the lumen
## Footnote
*it can also be exchanged for HCO3- on the apical surface*
85
Which of the following is the most important factor in stimulating bicarbonate secretion from the pancreas?
a) acetylcholine
b) CCK
c) GIP
d) gastrin
e) secretin
e) secretin
86
What are the variations in the mucosa between different parts of the stomach?
cardia: mucus-secreting glands only
fundus: parietal cells, chief cells, endocrine cells
antrum/pylorus: mucus-secreting glands and endocrine glands (G-Cells)
87
How is iron absorption regulated in the GI tract?
iron is stored in epithelial cells and only is released when there is high iron demand
if iron demand is low, the epithelial cells fill with iron and slough off
if iron demand is high, there is increased transferrin which leads to more iron uptake from the gut
88
Describe the secretion of surface epithelial cells.
they secrete slightly alkaline isotonic fluid
secretions constant in composition and volume
active secretion of bicarbonate
89
What is the source of sympathetic innervation of salivary secretion?
preganglionic fibers from T1-T4
postganglionic fibers from superior cervical ganglion
*innervates acinar, duct and myoepithelial cells, blood vessels*
90
What determines the frequency of segmentation activity in the stomach? What does it do?
slow waves determine frequency
segmentation mixes lumenal contents and facilitates absorption
91
92
What is chyme?
the semi-fluid partially digested food that passes into the duodenum
93
What is the function of beta cells in the pancreas?
they secrete insulin, leading to uptake of glucose from the bloodstream (and its utilization and storage)
94
What is the ileocecal sphincter?
a one-way valve that is regulated by intrinsic reflexes
wave of relaxation precedes ileal peristalsis
contraction closes sphincter after peristalsis
95
How does depolarization spread across GI muscles?
it travels down the longitudinal layer (via gap junctions) and then spreads to the circular layer
96
A region of the intestine contracts weakly upon stimulation of its extrinsic nerves. Distention of the region elicits a peristaltic reflex, but with weak contractions. Slow wave activity is absent. Taken together, these findings suggest a disorder of which of the following?
a) enteric nerves
b) parasympathetic nerves
c) release of motilin
d) smooth muscle cells
e) symapthetic nerves
d) smooth muscle cells
97
What is the pathway of bile thorough the gall bladder?
bile is stored in the gall bladder and gets expelled through the common bile duct into the duodenum
98
How is contraction and relaxation of the lower esophageal sphincter mediated?
tone is maintained by tonic intrinsic neural activity and myogenic mechanisms
99
What are the major components of gastric juice?
water, electrolytes, mucus, intrinsic factor, and enzymes
100
What happens during the pharyngeal phase of swallowing?
bolus reaches pharynx and activates sensory receptors to trigger the swallowing reflex (not under voluntary control)
airway, mouth, and nasopharynx are closed
progressive wave of contractions propel the bolus towards the upper esophageal sphincter (which opens)
101
How is Cl- and K+ transported in parietal cells?
Cl- leaves via a chloride channel due to an electrochemical gradient from an Na/K transporter
K+ (high concentration in the cell) diffuses into lumen following Cl-
102
How do slow waves cause smooth muscle activity in the GI tract?
they cannot on their own
slow wave must be paired with a depolarizing input (ex. acetylcholine release from vagus or intrinsic plexus) in order to produce an action potential and muscle contractions
*slow waves determine the frequency at which contraction may occur and the speed of propagation*
103
What is the effect of HCl secretion in the stomach? How is secretion controlled?
effect: stimulates pepsinogen, mucus, and intrinsic factor secretion
stimulated by: histamine, acetylcholine, and gastrin
104
What happens in response to acid in the small intestine?
causes the release of secretin that inhibits gastric motility
## Footnote
*also stimulates pancreatic HCO3 secretion)*
105
How is pancreatic secretion regulated in the cephalic phase?
stimuli from food activates vagal innervation of pancreas
vagal postganglionic fibers release acetylcholine --\> excites acinar cells to secrete enzymes, excites duct and centroacinar cells to secrete fluid and electrolytes, sensitizes pancreatic response to secretin and CCK
106
How is CCK release stimulated? What is the effect of CCK stimulation on acinar cells?
release: fatty acid and protein digests stimulate CCK release in duodenum
effect: stimulates acinar cells to secrete enzymes
107
A patient experiences a rapid rate of transit of contents from the duodenum to the cecum. What characteristic would contractions recorded at various loci of the small intestine exhibit during this time?
a) frequency greater than that of slow wave
b) low in force
c) mostly peristaltic
d) mostly segmenting
e) mostly tonic
c) mostly peristaltic
108
What is the effect of sympathetic stimulation on alpha and beta receptors on salivary secretion?
alpha: vasoconstriction
beta: stimulation of acinar secretion
109
What is this?
stomach
110
What are the three layers of the mucosa?
epithelium, lamina propria, and muscularis mucosae
111
What is the relationship between acetylcholine, histamine, and gastrin?
they act synergystically to promote gastric secretion
112
What are the four major types of mucosa in the GI tract?
protective mucosa, secretory mucosa, absorptive mucosa, absorptive/protective mucosa
113
What signal inhibits gastric secretion?
somatostatin (via inhibiton of histamine release from ECL)
acid also self-inhibits and stimulates somatostatin
114
What common feature is present in the regions of the digestive system covered by stratified squamous epithelium?
the regions covered by stratified squamous epithelium are those most closely associated with the outside environment/stressors
115
Which regions of the GI tract have somatic innervation?
oropharynx and external anal sphincter (skeletal muscles)
116
What activates the gastric phase of GI activity? What happens in this phase?
activated by: food in stomach activating chemo- and mechano-receptors in gastric mucosa
events: initiates CNS and intrinsic reflexes and hormonal release mainly to increase gastric secretory and motor activity
117
What is the direct pathway of stimulation of gastric secretion? Indirect pathway?
direct: acetylcholine, gastrin, and histamine stimulate the parietal cell (triggers acid secretion into lumen)
indirect: acetylcholine and gastrin stimulate the ECL cell resulting in secretion of histamine, that acts on the parietal cell
118
Which of the following is most true about segmental contractions of the colon?
a) increase inf requency in response to increased circulating levels of epinephrine
b) occur more often than do peristaltic contractions of the colon
c) occur at a higher frequency in the sigmoid colon than in the rectum
d) occur at a frequency that is higher than that for slow waves in the same region
e) are accompanied by the loss of haustral markings
b) occur more often than do peristaltic contractions of the colon
119
What factors determine gastric emptying?
volume (distends stomach, triggering reflexes)
osmolarity (hyperosmolar = slower)
pH (acid in small intestine slows emptying)
chemical composition (fatty acids in small intestine slows emptying)
quality of chyme (solids move slower but empty faster)
120
What is the gross structure of the small intestine?
large circular folds (plicae circulares)
smaller folds (villi)
fine projections (microvilli)
121
What is the effect of VIP and ACh on salivary secretion?
It leads to vasodilation
## Footnote
*interacts with parasympathetic post-ganglionic nerves*
122
How is pancreatic secretion regulated in the intestinal phase?
mostly due to presence of acid and digestion products in the intestine
gastric acid stimulates S cells in the duodenum and jejunum to release secretin
secretin stimulates duct and centroacinar cells to secrete HCO- and fluid
123
What activates the intestinal phase of GI activity? What happens in this phase?
activated by: chyme in intestine stimulates chemo- and mechano-receptors in intestinal mucosa
events: initiates CNS and intrinsic reflexes and hormonal release to regulate gastric, intestinal, and pancreatic secretions
124
Which regions of the stomach secrete acid?
fundus and body (because they have parietal cells)
## Footnote
*pyloric antrum does not produce acid, but has gastrin cells that stimulate parietal cells in the body of the stomach*
125
What are the controls of gastric phase secretion?
gastric juice volume, acid, and pepsinogen secretion is increased by distention and chemical stimulation of mucus (by chyme)
126
What stimuli increase gastric motor activity? Decrease?
increase: distention of stomach (activates reflexes, increases gastrin release), gastrin secretion
decrease: norepinephrine (from sympathetics), secretin and CCK (from duodenum in response to chyme in duodenum)
127
What regions of the GI tract are innervated by the pelvic nerve?
mid-transverse colon to internal anal sphincter
128
How are Na+ and Cl- ions transported into cells before absorption?
Na/K pump on basolateral surface provides a driving force for Na+ diffusion into the cell down its gradient
Cl- follows passively (with water) paracellularly
129
How is K+ absorbed in the GI tract?
mostly passively (diffusion through tight junctions driven by electrochemical gradient)
some active transport also happens
*mostly occurs in small intestine, some in colon*
130
What is the general effect of sympathetic innervation on salivary glands?
increased secretion, decreased blood flow
131
Which organ contains secretory mucosa?
a) small intestine
b) stomach
c) liver
d) large intestine
e) esophagus
b) stomach
132
What is the effect of atropine on salivary secretion?
it blocks secretion and gland contraction
## Footnote
*secretion and contraction are due to muscarinic stimulation*
133
What is the structure of liver sinusoids?
they are lined by phagocytic Kuppfer cells and sinusoidal lining cells
## Footnote
*sinusoids connect portal tracts to the central vein*
134
What is the tonicity of fluid secreted by acinar cells relative to plasma?
isotonic
135
What are the major outputs and functional roles of the enteric nervous system?
innervation of GI smooth muscle, mucosal cells, and glands
functional roles: stores and generates intrinsic motor and secretory patterns
*can be modulated by extrinsic nerves*
136
How does salivary composition change with secretory rate?
higher flow rate = higher Na, HCO3, and Cl concentration, lower K concentration
137
What determines frequency of peristalsis?
slow waves
138
Which GI regions are innervated by the vagus nerve?
mid-esophagus to mid-transverse colon
139
Where do the pancreas and liver deliver secretions into the small intestine?
duodenum
140
what is the structure of the mucosa of the large intestine?
thick mucosa with deep crypts and no villi
formed from columnar absorptive cells with scattered goblet cells
lamina propria contains inflammatory cells
141
Where are preganglionic neurons for the pelvic nerve located? Postganglionic neurons?
preganglionic: sacral segments 2-4
postganglionic: pelvic ganglia or intrinsic ganglia of colon
142
What happens in response to fatty acids in the small intestine?
stimulates release of CCK, which inhibits gastric motility
## Footnote
*also stimulates pancreatic enzyme secretion and gall bladder contraction*
143
What is this?
esophagus
144
What is the resting state of the upper esophageal sphincter? Esophagus? Lower esophageal sphincter?
UES: resting tone (closes off esophagus)
esophagus: flaccid at rest
LES: resting tone (closes off stomach)
145
What is the adventitia/serosa of the hollow GI organs?
serosa: connective tissue in organs lined by mesothelium
adventitia: connective tissue without surrounding mesothelium (retroperitoneal organs, esophagus, blood vessels)
146
What happens to water exchange in different parts of the small intestine?
upper duodenum: net movement into lumen (due to hyperosmolarity of chyme)
jejunum: net movement out of lumen (paracellularly) as solutes are absorbed
* absorptiondriven by NaCl transport*
147
What do parietal cells produce?
acid and intrinsic factor
148
In the small intestine, each of the following is true regarding Cl- absorption except that:
a) it occurs in exchange for Na+
b) it occurs in exchange for HCO3-
c) it will result in absorption of water
d) it occurs along the entire length of the small bowel
a) it occurs in exchange for Na+
149
What is the parasympathetic innervation of the parotid glands?
preganglionic fibers from the medulla that travel via glossopharyngeal nerve to the otic ganglion
innervates all cell types of parotid glands
150
What is the main difference between secretory contens of acinar cells vs. ductule cells?
acinar cells secrete nearly isotonic fluids
ductule cells modify the ionic content of that fluid
151
What neurotransmitters control the tone of the lower esophageal sphincter?
excitatory: acetylcholine
inhibitor: nitric oxide
152
How is fluid secreted from duct or centroacinar cells?
Na+, K+ diffuse passively into the lumen
HCO3- enters lumen via exchange (with Cl-)
Cl- enters lumen through channels
H2O flows into the lumen passively following electrolytes
153
How does alpha amylase get secreted?
it is stored in zymogen granules in salivary duct cells and is released by exocytosis
154
What is the primary driving force of secretion from duct/centroacinar cells?
Na/K ATPase on the basal surface of duct or centroacinar cells
## Footnote
*provides an electrochemical gradient for sodium to enter the cell, which pumps out H+*
155
What is the blood supply to the liver?
supplied by the hepatic artery and hepatic portal vein
## Footnote
*both leave and enter the liver at the porta hepatis*
156
What is the functional role of sympathetic innervation to the GI tract?
mostly adrenergic and inhibitory to GI activity, constricts blood vessels
157
Stimulation of an intrinsic nerve in the intestine usually causes contraction of an intestinal muscle cell through the release of which neurotransmitter?
a) acetylcholine
b) nitric oxide
c) norepinephrine
d) somatostatin
e) vasoactive intestinal peptide
a) acetylcholine
158
What is this?
jejunum
## Footnote
*no peyer's patches*
159
How is Ca2+ absorbed in the GI tract?
controlled actively (deficiency increases absorption)
Ca2+ is solubilized by gastric acid and binds to calcium binding protein (CBP)
CBP sequesters intracellular Ca2+
Ca2+ is transported out of the cell by a Ca-ATPase on the basolateral surface
160
How is contraction and relaxation of the upper esophageal sphincter controlled?
normally contracted due to tonic neural activity
relaxes at end of pharyngeal stage due to inhibition of neural input
161
Most of the acid response to a meal occurs during which pase?
a) cephalic phase
b) esophageal phase
c) gastric phase
d) intestinal phase
c) gastric phase
162
CCK:
a) stimulates gastric emptying
b) is released by vagal stimulation
c) is released by protein and fat in the proximal small bowel
d) is inhibited by distention when food enters the small bowel
e) is an important stimulator of gastric acid secretion
c) is released by protein and fat in the proximal small bowel
163
How does Na+ get absorbed in the colon?
driven by Na/K pump on basolateral side that pumps Na out
## Footnote
* Na enters the cell via diffusion (also paracellularly) or via transport channels*
* it can also be exchanged for H+ on the apical surface*
164
What is protective mucosa?
stratified squamous epithelium that provides protection in areas with little digestion/absorption
## Footnote
*found in oral cavity, esophagus, anal canal*
165
What do chief cells produce?
pepsinogen and lipase
166
What is the structure of the exocrine part of the pancreas?
serous acini that produce enzyme filled fluid
167
What are the histologic layers of the small intestine?
mucosa
submucosa
muscularis externa
serosa
168
What is this?
gall bladder
169
What is the effect of secretin on duct and centroacinar cells?
It stimulates them to secrete HCO- and fluid
170
What is the organization of GI smooth muscle?
small cells, high surface area to volume ratio, organized in bundles
organized grossly into longitudinal (outer) and circular (inner) layers
171
Where are preganglionic neurons for the vagus nerve located? Postganglionic neurons?
preganglionic: brainstem
postganglionic: intrinsic ganglia of gut wall
172
How is water transported in the small intestine?
driven by electrolyte absorption (mostly Na+)
water moves in both directions, but net movement is out
diffuses out passively by osmotic forces
173
What is the structure of the mucosa in the small intestine?
simple columnar epithelial cells including enterocytes and goblet cells
structure: villi, crypts
underlined by the lamina propria
174
What is the relationship of Na+ exchange in the small intestine and acid concentration?
Na+ is exchanged for H+ on the apical surface of the cell to promote acid excretion and sodium reabsorption
175
Where are preganglionic neurons for the sympathetic nerves to the GI tract located? Postganglionic neurons? Where do postganglionics synapse?
preganglionic: spinal cord from T5-L1
postganglionic: sympathetic chain or prevertebral ganglia
synapse: on smooth muscle cells of arterioles and neurons of intrinsic plexus
176
Where in the GI tract does double exchange of Na/H and Cl/HCO3 mostly occur?
ileum of small intestine
177
What is the sympathetic control of swallowing?
derives from the upper thoracic spinal cord
178
In a patient in whom resting tone of the internal anal sphincter is normal, distention of the rectum induces normal relaxation of the internal anal sphincter, no change in tone of the external anal sphincter, and no sensation of the urge to defecate. These findings are consistent with the findings of damage to which of the following?
a) enteric nerves
b) internal anal sphincter
c) vagus nerve
d) spinal cord
e) transverse colon
d) spinal cord
179
What happens during the oral phase of swallowing?
mouth closed, tongue pushes bolus towards pharynx
under voluntary control, dependent on sensory information from oral cavity
180
How is Na+ transported by parietal cells?
transported with an Na/K ATPase
some leaks across mucosa into lumen
181
What factors control pepsinogen secretion?
increased directly by acetylcholine and secretin
increased indirectly by gastrin and histamine
182
The electrical activities of smooth muscle cells of the orad stomach, proximal and distal antrum, and proximal duodenum are monitored in a fasted subject. Compared with the period of minimal contractions, the period of intense contractions of the migrating motor complex ischaracterized by which of the following?
a) a decrease in the apparent propagation velocity of antral slow waves
b) a decrease in the frequency of duodenal slow waves
c) an increase in the amplitude of antral slow waves
d) an increase in the frequency of antral slow waves
e) the occurrence of slow waves in the orad stomach
c) an increase in the amplitude of antral slow waves
183
What are the major proteins of saliva?
alpha amylase, glycoproteins
184
What causes stimulus-induced salivary secretion?
increases in cAMP or Ca2+
## Footnote
* beta adrenergic stimulation leads to cAMP, ACh, and peptide increases*
* alpha adrenergic stimulation leads to increased Ca2+*
185
What is a lower esophageal sphincter?
a region at the intersection of the esophagus and stomach
normally, provides a barrier for the passage of material from the stomach to the esophagus
186
What is the functional role of parasympathetic nerves to the GI tract?
increases/modifies motor and/or secretory activity
## Footnote
*there are some inhibitory parasympathetic activities*
187
How is gastric secretion controlled in the cephalic phases?
mediated by the vagus nerve
vagal activity excites parietal cells via muscarinic receptors
vagal activity excites G cells (via GRP)
188
What mechanisms prevent the stomach from digesting itself?
HCl secretion is mostly secreted when there is food to buffer
gastric mucosal barrier of tight junction surface epithelium
high blood flow washes away HCl quickly
insoluble mucus covers the stomach surface and contains alkaline fluid that buffers
gastric cells are turned over quickley
189
How is H+ produced in parietalcells?
it is produced from the hydrolysis of water through the cytochrome chain (requires glucose and O2)
190
How is intrinsic factor secreted? What does it do?
secreted by parietal cells
it binds vitamin B12 and transports it to the ileum to facilitate absorption of B12
191
What are the major plexuses of the enteric nervous system?
Myenteric/Auerbach's plexus --\> between longitudinal and circular muscle layers
Submucosal/Meissner's plexus --\> within the submucosa
192
What is the afferent control of swallowing?
afferents travel in superior laryngeal nerve
triggers swallowing reflex (by mechanical and chemical stimulation)
afferents terminate in the nucleus of the tractus solarius (NTS) in the medulla
193
What is the relationship betwen Ca2+, CBP, vitamin D, and parathyroid hormone?
CBP and Ca2+ ATPase synthesis is driven by vitamin D3
synthesis of vitamin D3 is stimulated by PTH
PTH levels rise when calcium levels fall
*low Ca --\> high PTH --\> high vitamin D3 --\> high CBP and Ca-ATPase --\> more Ca absorbed*
194
What is the function of delta cells in the pancreas?
secretes somatostatin, leading to inhibition of A and B cells and inhibition of exocrine pancreas secretions
195
What are the causes of chemical stimulation of mucus in the gastric phase?
gastrin release stimulated by proteins, calcium, caffiene, and alcohol
196
What are the general components of gastric juices?
hydrochloric acid, mucus, pepsin, and lipase
## Footnote
*produced by gastric mucosal glands*
197
What is the parasympathetic innervation of swallowing?
derives from vagus nerve
cell bodies located in the dorsal motor nucleus of the vagus and nucleus ambiguus
