Exam 2: Hormones of GI Tract Flashcards
(110 cards)
1
Q
What is the largest and most complex endocrine organ in the body?
A
GI tract
2
Q
What percentage of the cells that line the GI tract secrete hormones? What are there cells called?
A
1%; enteroendocrine cells
3
Q
T/F. The GI tract is a sensory organ.
A
True
4
Q
Through what mechanisms is the GI tract a sensory organ?
A
through both hormonal and neural mechanisms
5
Q
What are the three ways the GI tract is a sensory organ through both hormonal and neural mechanisms?
A
- adjusts its own activity (increase or decrease peristalsis)
- alerts body to impending influx of nutrients
- informs brain of need to initiate/terminate feeding
6
Q
How is the GI tract innervated?
A
- with afferent and efferent SNS and PSNS neurons
- ENS (enteric nervous system) = networks of intrinsic nerves
7
Q
About how many neurons does the Enteric Nervous system (ENS) in the GI tract contain? What is this comparable to?
A
~ 100 x 10^6 neurons = number in spinal cord
8
Q
What does the Enteric Nervous system do?
A
transmits info up and down length of GI tract
- sensory, motor, interneurons coordinate secretory, absorptive, and contractile activities
9
Q
What other parts of the nervous system does the Enteric Nervous system communicate with?
A
ENS SNS PSNS ENS
bidirectional communication
10
Q
What do the gut NTs include?
A
- catacholamines (NE, Epi)
- Ach
- peptides
11
Q
What can the peptides from neurons and gut (enteroendocrine cells) act as?
A
- NT
- neurohormones or
- neuromodulates (NM)
12
Q
What nerve provides PSNS innervation to esophagus, stomach, SI, and proximal colon?
A
Vagus nerve
13
Q
What supplies PSNS innervation to the remainder of the colon and rectum?
A
pelvic nerves from sacral cord levels
14
Q
How much of the vagus nerve is sensory? How much is motor?
A
3/4 sensory
1/4 motor
15
Q
What are scattered throughout the stomach and SI that are associated with various vaso-vagal reflexes?
A
Mechano and chemoreceptors
16
Q
Once the Vaso-vagal reflexes in the gut are stimulated, what is in response?
A
integrating centers in brainstem signal secreting or contractile responses
17
Q
T/F. Many responses governed by the vaso-vagal reflexes also are produced by GI hormones.
A
True
18
Q
What occurs with hormonal stimulation of vagal afferent fibers that express receptors for some of the GI hormones?
A
they communicate w/ brainstem w/o having to cross the BBB
GI hormones—-> Target
or GI hormones —> NS –> target
19
Q
Describe the pathway of the GI peptides, hormones.
A
Enteroendocrine cells–> secretion into portal circulation –> liver –> systemic circulation –> target cell
20
Q
Describe the pathway for the GI peptides, Paracrines.
A
Enteroendocrine cell –> diffusion –> target cell
21
Q
Describe the pathway of the GI peptides, Neurocrines.
A
GI tract neuron–> action potential —> target cell
22
Q
What are the 8 GI hormones?
A
- Gastrin
- CCK (cholecystokinin)
- Secretin
- GIP (glucose dependent insulinotropic peptide)
- Motilin
- Ghrelin
- Panreatic polypeptide
- GLP-1 (glucagon like peptides–Enteroglucagon)
23
Q
What are the two incretins of the GI tract?
A
GIP and GLP-1
24
Q
What cells secrete gastrin and where?
A
G (gastrin) cells in antrum of stomach
25
What hormones of the GI tract promotes hydrogen ion secretion? What cells secrete H+ ions?
Gastrin
promotes hydrogen ion secretion by gastric parietal cells
26
What will Gastrin's fxn of stimulating H+ ion secretion do?
lower stomach pH--> and activates pepsinogen (secreted by chief cells)--> which begins process of protein digestion
27
What type of cells secrete pepsinogen?
chief cells
28
When is Gastrin secreted?
in response to eating a meal
29
What are the stimuli for Gastrin release?
- products of protein digestion (phenylalanine and tryptophan)
- Distention of stomach
- stimulation of the Vagus* (via GRP-Gastrin releasing peptide- from vagal nerves)
30
What inhibits Gastrin?
somatostatin and low stomach pH
31
What are the three physiologic effects of Gastrin?
1. stimulate parietal cells to secrete H+ ions
2. stimulate growth of gastric mucosa
3. stimulate gastric emptying
32
What will excess Gastrin do?
- increase H+ ion secretion
| - hypertrophy of gastric mucosa
33
What will deficiency of Gastrin do?
- decrease H+ ion secretion
| - atrophy of gastric mucosa
34
What disease has a Gastrin secreting tumor, "gastrinoma"?
Zollinger-Ellison syndrome
35
Where is the "gastrinoma" in Zollinger-Ellison syndrome typically?
in pancreas (non beta-cell)
36
What will Zollinger-Ellison Syndrome cause?
Gastrin Secretion tumor:
- increase H+ secretion
- hypertrophy of gastric mucosa
- duodenal ulcers due to increase H+ secretion
- acidification of intestinal lumen --> inactiavte pancreatic lipase --> inhibits digestion of fats --> cause steatorrhea (fat in stool)
37
What will the acidificaiton of the intestinal lumen due to Zollinger-Ellison syndrome cause?
inactivation of pancreatic lipase--> inhibits digestion of fats--> leads to steatorrhea (fats in the stool)
38
What is the treatment for Zollinger-Ellison Syndrome?
- H2 receptor blockers (cimetidine)
- Inhibitors of H+ pumps (omeprazole)
- removal of the tumor
39
What GI hormone coordinates and promotes fat digestion and absorption?
CCK (cholecystokinin)
40
What are the two receptors that bind CCK? Which one can also bind gastrin?
1. CCKa--> only bind CCK
| 2. CCKb --> equal affinity for BOTH CCK and gastrin
41
T/F. CCK peptide is structurally related to gastrin and has some gastrin activity.
True
42
What cells secrete CCK and where?
I cells of the duodenal and jejunal mucosa
43
What is CCK secreted in response to?
- monoglycerides and FAs (NOT TGs)
| - small peptides and AAs
44
What type of meal will stimulate release of CCK?
a meal containing fat and protein
45
What will the release of CCK cause coordinated effect of?
to ensure appropriate pancreatic enzymes and bile salts are secreted to aid in digestion and absorption of proteins and fats
46
What are the 5 major actions of CCK?
1. contraction of gallbladder
2. secretion of pancreatic enzymes
3. secretion of bicarbonate from pancreas
4. trophic effect on exocrine pancreas and gallbladder
5. inhibition of gastric emptying
47
With what simultaneous action does contraction of the gallbladder by CCK cause?
with simultaneous relaxation of the sphincter of Oddi (hepatopancreatic sphincter) --> ejects bile from gallbaldder --> into lumen of SI
bile emulsifies and solubilizes dietary lipids
48
What are the pancreatic enzymes that CCK stimulates the pancreas to release? What do they do? (3)
1. Lipases --> digest lipids to FA, monoglycerids, choldesterol
2. Proteases--> digest protein
3. Amylase digest CHO
49
What does the secretion of bicarbonate from the pancreas by CCK effect?
not a major effect, but potentiatiates the effects of secretin on bicarbonate secretion
50
What will the inhibition of gastric emptying of CCK do?
slows gastric emptying which enhances fat digestion and absorption
-- decrease chyme delivery to the SI
51
What is unique about Secretin about its peptide stucutre that is different than CCK and Gastrin?
all 27 AAs are required for biologic activity (NO active fragments like CCK and gastrin)
52
What secretes secretin and where?
secreted by S cells of duodenum
53
What causes secretion of secretin?
in response to H+ (pH<4.5) and FAs in SI
54
What promotes secretion of pancreatic and biliary bicarbonate? What effect does this have?*
Secretin; neutralizes H+ in lumen of SI
| --essential for fat digestion
55
What pH does pancreatic lipases function best at? What pH are the inactivated at?
pH 6-8
inactivated when pH < 3
56
What does Secretin inhibit the effects of?
of gastrin and parietal cells (by neutralizing H+ ions in lumen of SI with bicarbonate)
57
What does GIP stand for?
glucose- dependent insulinotropic peptide
58
What is GIP secreted by and where?
K cells in the duodenal/jejunal mucosa
59
What is GIP secreted in response to?
all three types of nutrients (glucose, AAs, FAs)
60
What is GIP's major effect?
(is it an incretin)
is stimulation of insulin
(hence why oral glucose has greater effect)
61
What has a greater effect, oral glucose or IV glucose and why?
oral glucose greater effect than IV glucose due to oral stimulates both insulin directly and via GIP
62
What does GIP inhibit in animals, but not in humans?
inhibits gastric H+ secretion (hence why used to be called "gastric inhibitory peptide)
63
What hormone is responsible for the migrating motility complex?
Motilin
64
Where is motilin released and what family is it a member of?
secreted from upper duodenum during fasting
member of gastrin-CCK family
65
What does the migrating motility complex that motilin is responsible for do?
brief episodes of contractions about 90mins apart
clears stomach and intestine in preparation for next meal
66
What does motilin stimulate?
- stimulation of enzyme secretion by stomach and pancreas
| - stimulates contraction of gallbladder (like CCK)
67
T/F. The regulation of motilin secretion is unknown.
true
68
What is the only GI hormone that promotes food intake?*
Ghrelin
69
What is Ghrelin mainly secreted by and when?
mainly by stomach mucosa in b/w eating
| other tissues can too; pancreas, brain, ovary, adrenal cortex
70
How does Ghrelin carry out its effect?
released into blood and can cross BBB --> affecting the hypothalamus where it stimulates appetite
71
What are the effects of Ghrelin?
- tells hypothalamus to stimulate appetite
- increase feelings of hunger
- increase gastric acid secretion, gastric motility, gastric emptying
72
What will stimulation of Ghrelin receptors on afferent neurons initiate?
intiates vago-vagal reflexes and local enteric reflexes
73
What is Pancreatic Polypeptide secreted by and in response to what?
PP (F) cells; in response to ingestion of all three types of nutrients (like GIP)
74
What does pancreatic polypeptide inhibit secretion of?*
inhibits pancreatic secretion of bicarbonate and pancreatic enzymes
75
When is Pancreatic polypeptide secretion increased? Decreased?
Increased after:
- a protein rich meal,
- fasting,
- exercise, and
- acute hypoglycemia
Decreased:
- by somatostatin and
- intravenous glucose
76
What does GLP stand for?
Glucagon-like peptides or Enteroglucagon
77
What is GLP secreted by and where?
L cells in the intestinal mucosa
78
What are the most abundant peptide producing cells in the GI tract and what do they produce?*
L cells in intestinal mucosa, producing GLP
79
What are L cells that secrete GLP stimulated by?
enteric neurons and luminal nutrients
80
What are L cells that secrete GLP unresponsive to?
plasma levels of glucose, FA, and insulin
81
What effect on the liver does GLP have?
to increase glycogenolysis and gluconeogenesis (similar to glucagon)
82
What are the two types of GLP (glucagon like peptides) that we have?
GLP-1 and GLP-2
83
Which type of GLP inhibits glucagon secretion?*
GLP-1
84
Which type of GLP stimulates insulin secretion?*
GLP-1
85
Which GLP slows gastric emptying?*
GLP-1
86
Which GLP has trophic effect on intestinal mucosa, therefore proliferation, therefore increases surface area for absorption?*
GLP-2
87
Which GLP produces mucosal repair and decreases inflammatory responses to bowl injury?*
GLP-2
88
What are the functions of GLP-1?
- *inhibits glucagon secretion
- *stimulates insulin secretion
- *slows gastric emptying (feel full)
- inhibits food intake
- inhibits parietal cells and therefore decreases H+ ions
- stimulates D cells to secrete somatostatin and therefore decrease H+ ions
89
What are the functions of GLP-2?
- *trophic effect on intestinal mucosa, increasing proliferation, therefore increasing surface area for absorption
- *produces mucosal repair
- *decreases inflammatory responses to bowel injury
- no effect on insulin secretion
- stimulates AA and glucose transport
- maintains mucosal barrier to bacteria and enterotoxins
- may have use to treat IBD
90
What may GLP-2 may have use to treat?
inflammatory bowl disease (IBD)
- Chrons
- Ulcerative colitis
91
What refers to slowing of gastric and pancreatic exocrine secretion, stomach emptying, and intestinal motility in response to the presence of unabsorbed nutrients in the distal ileum?
Ileal Brake Mechanism
92
What is an important isgnal for the ilieal brake mechanism?
FA b/c no CHO left in chyme at this point
93
The abundance of what cells does a good job of gauging the efficiency of nutrient absorption?
abundance of L cells in distal ileum and colon
94
What feeds back on the stomach to decrease acid secretions, decrease motility, and decrease emptying? What does this result in?*
GLP-1 and peptide YY
will prolong transit time and therefore increase nutrient absorption
95
What is the ileal brake mechanism?
slowing of gastric and pancreatic exocrine secretion, stomach emptying, and intestinal motility in response to presence of unabsorbed nutrients in the distal ileum
96
What are produced in GI endocrine cells and act locally?
paracrines
97
What are two paracrines of the GI tract? What do they do?
Somatostatin--> inhibits stomach acid
and
Histamine--> promotes stomach acid
98
What type of cells secrete Somatostatin and from where? In response to what?
D cells of antral cells (stomach mucosa) in response to decreased luminal pH
also by deta cells of pancreas and hypothalamus
99
When we see somatostatin what should we think?
inhibitory
100
What does somatostatin inhibit?
secretion of gastrin and other GI hormones
| --inhibits gastrin and blocks H+ secretion)
101
What will histamine (a paracrine of the GI tract) cause?
works synergistacally with gastrin and ACh, and will stimulate H+ secretion
102
What cells produce histamine and where?
enteroendocrine cells in Gi mucosa especially in stomach near parietal cells
103
What are the 7 neurocrines of the GI tract?
1. ACh (cholinergic neurons)
2. NE (adrenergic neurons)
3. VIP (neurons of mucosa and smooth muscle)
4. Gastrin releasing peptide (neurons of gastric mucosa)
5. Enkephalins (neurons of mucosa and smooth muscle)
6. Neuropeptide Y (neurson of mucosa and smooth muscle)
7. Substance P (cosecreted with ACh
104
What are the actions of ACh on GI tract?
- contraction of smooth ms in wall
- relaxation of sphincters
- increase: salivary, gastric, and pancreatic secretions
105
What are the actions of NE on GI tract?
- relaxation of smooth ms in wall
- contraction of sphincters
- increase salivary secretion (slightly)
106
What are the actions of VIP on GI tract?
- relaxation of smooth ms
- increase intestinal secretion
- increase pancreatic secretion
107
What are the actions of Gastrin releasing peptide (bombesin) on the GI tract?
- increase gastrin secretion
108
What are the actions of Enkephalins (SNS) on the GI tract?
- contraction of smooth muscle
| - decrease intestinal secretion
109
What are the actions of Neuropeptide Y on the GI tract?
- relaxation of smooth ms
| - decrease intestinal secretion
110
What are the actions of Substance P on the GI tract?
- contraction of smooth ms
| - increase salivary secretion
