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Lecture 1 GI Flashcards

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1
Q

Components of the GI tract:

A
  1. mouth/pharynx
  2. esophagus
  3. stomach
  4. small intestine duodenum, jejunum, ileum
  5. large intestine
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2
Q

Accessory organs of the GI system

A

salivary glands
pancreas
liver
gallbladder

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3
Q

Function of the sphincters?

A

Sphincters are specialized muscle structures that control movement of material between regions of the GI tract

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4
Q

What are the sphincters in the GI system?

A

Upper and lower esophageal sphincters

pyloric sphincter

ileocecal sphincter

internal and external anal sphincter

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5
Q

organization of the GI tract wall

A
  1. mucosa
  2. submucosa
  3. muscularis externa
  4. serosa (adventitia)
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6
Q

Components of the mucosa

A
  1. epithelium
  2. exocrine glands
  3. lamina propria
  4. muscularis mucosa
  5. villi and microvilli (brush border)
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7
Q

Components of the epithelium (in the mucosa of the GI tract wall)

A 
absorptive cells
mucous cells
endocrine cells
exocrine cells
stem cells
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8
Q

Components of the lamina propria (of the mucosa in the GI tract wall)

A

Blood vessels

lymphatic vessels

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9
Q

components of the submucosa

A

major blood vessels and lymphatic vessels

submucosa nerve plexus

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10
Q

Components of the muscularis externa

A

inner circular and outer longitudinal layers of smooth muscle

myenteric nerve plexus

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11
Q

Describe the serosa layer

A

it is the outermost layer made of connective tissue

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12
Q

Primary function of the GI system

A

to obtain nutrients and water from the external environment

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13
Q

Subsidiary functions of the GI tract

A

contractility and motility

secretion

digestion

absorption-reabsorption

excretion

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14
Q

Describe the function of contractility and motility

A

contractile activity of the smooth muscles surrounding the GI tract. Mixes GI contents and propels them in a controlled manner down the GI tract.

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15
Q

Describe the function of secretion

A

Exocrine secretion of the digestive and lubricative substances into the lumen of the GI tract and endocrine secretion of hormones to regulate various GI functions

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16
Q

Describe the function of digestion

A

Breakdown of macromolecule complexes into smaller components.

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17
Q

Describe the function of absorption-reabsorption

A

Transfer of nutrients, fluids, and electrolytes from the lumen of the GI tract to the portal circulation and-or lymphatics

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18
Q

Describe the function of excretion

A

Elimination of non-digestible and unusable substances from the GI tract

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19
Q

Regulation of GI function:

A

Neural
hormonal
Paracrine

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20
Q

Components of neural regulation of GI

A
  1. enteric nerve plexus

2. Extrinsic nerves

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21
Q

Enteric Nerve plexus (neural regulation of GI) includes ___ and ___.

A

submucosal plexus and myenteric plexus

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22
Q

Enteric nerve plexus (ENP) mediates ____ which …

A

ENP mediates short reflexes which regulate GI contractile and secretory activities via pathways that are totally contained within the GI tract.

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23
Q

neural component of GU function regulation: Extrinsic Nerves (para/sympathetic) mediate ____

A

Long reflexes

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24
Q

Most extrinsic nerves (neural part of GI fxn) to the GI tract synapse with ___ and ____

A

Most extrinsic nerves to the GI tract synapse with cells in the enteric nerve plexus and smooth muscles

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25
Extrinsic nerves/long reflexes coordinate activities over ___ and they ____
long distances in the GI tract regulate activities of the glands associated with the GI tract
26
Endocrine cells (present mostly in the distal stomach and proximal small intestine) do what function?
secrete hormones in response to intralumenal stimuli and reflexes in the ENP
27
Hormones secreted by endocrine cells help regulate....
activities of the GI tract and associated glands
28
What are the hormones involved in GI function?
Gastrin cholecystokinin secretin motilin
29
Gastrin is secreted by ___ of the antrum of the stomach in response to ___ and the presence of ____
Gastrin is secreted by G cells of the antrum of the stomach in response to neural reflexes and the presence of protein digestion products in teh stomach
30
Gastrin stimulates ___ and ___
gastric motility and HCI secretion
31
Cholecystokinin (CCK) is secreted by ___ of the upper small intestine in response to _____ in the lumen of the small intestine
I cells fat, peptides, and amino acids
32
Cholecystokinin stimulates ___ and ___
pancreatic enzyme secretion and gallbladder contraction
33
Secretin is secreted by ___ of the upper small intestine in response to ___ in the lumen of the small intestine
S Cells acid
34
Secretin stimulates ___
pancreatic bicarbonate secretion
35
Motilin is secreted by ____ of the upper small intestin
endocrine cells
36
Motilin regulates ____
the migrating mobility complex (MMC)
37
Paracrine component of GI function regulation (the basic statement and two parts)
the chemical signals that affect local cells histamine and somatostatin
38
Histamine is secreted by ___ in the stomach in response to ___ and ___
Histamine is secreted by ECL cells in the stomach in response to neural reflexes and gastrin
39
Histamine stimulates ____
histamine stimulates gastric secretion of HCl
40
Somatostatin is secreted by ___ in the stomach in response to ____
Somatostatin is secreted by D cells in the stomach in response to acidic gastric contents
41
Somatostatin inhibits secretion of
gastrin and histamine
42
What are the phases of GI function
cephalic phase gastric phase intestinal phase
43
Cephalic phase: gastric phase: intestinal phase:
cephalic: time when meal is in the mouth and chewing/swallowing occurs Gastric: time when meal is in the stomach Intestinal: time when meal is the small intestine
44
What are the functions of mastication?
mixes ingested material with saliva and lubricates to make it easier to swallow breaks up large solids - easier to swallow begins digestion of starches with amylase in saliva
45
Function of deglutition
convey ingested material from the oral cavity to the stomach
46
Oropharyngeal phase 3 parts
initiation inhibition or respiration relaxation of UES
47
Describe initiation of oropharyngeal phase
wave -like contraction of tongue propels bolus to oropharynx - stimulation of pressure receptors and initiation of swallowing reflex
48
Inhibition of respiration
closure of air passageways sequential contraction of pharyngeal muscles propels bolus toward esophagus
49
Describe relaxation of the UES at end of oropharyngeal phase
UES is normally closed. UES reflexes during oropharyngeal phase of swallowing to allow the bolus to pass into the esophagus and then closes. It acts to minimize reflux back into the pharynx.
50
Components of the esophageal phase of swallowing
primary peristalsis LES Secondary peristalsis
51
Primary peristalsis (esophageal phase)
initiated by swallowing. A ring of smooth muscle constricts proximal to the bolus and propagates distally - propelling the bolus toward the stomach
52
Lower esophageal Sphincter (LES)
its closed at rest and acts to minimize reflux of gastric contents into the esophagus. The LES relaxes to allow the bolus to proceed into the stomach
53
Secondary peristalsis (esophageal phase)
initiated by distention. Once initiated, it proceeds like primary peristalsis 2 peristalsis functions to remove material left behind by an ineffective primary peristaltic contraction and to return material refluxed up into the esophagus.
54
LES and heartburn | 3 things
1. increased intra-abdominal pressure - increased LES tone 2. Ethanol, chocolate, and peppermint - decreased LES tone 3. Progesterone - decreased LES tone
55
Functions of the stomach:
store ingested material, convert ingested material into chyme, controlled release of chyme into the upper small intestine
56
Gastric Mobility regions
1. proximal | 2. Distal
57
Proximal (gastric mobility region):
fundus and upper body thin layers of smooth muscle
58
Distal (gastric mobility region)
lower body and antrum thick layers of smooth muscle
59
2 components of the proximal stomach
receptive relaxation and accommodation and sustained contractions
60
Proximal stomach Receptive relaxation and accommodation pressure ___ in the proximal stomach during swallowing.
pressure decreases
61
Proximal stomach Receptive relaxation and accommodation relaxation of the proximal stomach is stimulated by the ____
entrance of the bolus from the esophagus the relaxation facilitates receipt of the meal
62
Proximal stomach Receptive relaxation and accommodation After relaxation, the stomach can hold ____ (how much?)
1.5 L
63
Proximal stomach Receptive relaxation and accommodation Relaxation is mediated by ___
inhibitory vagal neurons
64
Proximal stomach Sustained contractions contractures of the proximal stomach increase ___
gastric pressure
65
Proximal stomach Sustained contractions the pressure gradient between the stomach and duodenum does what?
moves the bolus into the distal stomach
66
Proximal stomach Sustained contractions These contractions also aid in ...
emptying of liquids and solids Proximal sustained contractions also promote emptying of lids and small solids
67
Proximal stomach Sustained contractions Sustained contractions occur once all of the meal has been swallowed and are stimulated by ____
distention of the proximal stomach
68
Distal Stomach components
1. Slow wave depolarization or basic electrical rhythm 2. spike potentials superimposed upon the plateau fo the slow wave contraction and initiate peristaltic contractions 3. contractions 4. distention stimulates gastric contractions
69
Distal Stomach Slow wave depolarization (SWD) or basic electrical rhythm Myogenic. SWD originates at ____, occur at a frequency of ___ and propagated ____
Myogenic. SWD originates at pacemaker region, occur at a frequency of ~3/min and propagated distally
70
Distal Stomach Slow wave depolarization (SWD) or basic electrical rhythm SWD are not...
sufficient by themselves to cause significant contractile activity
71
Distal Stomach - spike potentials superimposed upon the plateau fo the slow wave contraction and initiate peristaltic contractions Spike potentials are initiated through ___ and __ during ___
Spike potentials are initiated through parasympathetic and endocrine stimuli during ingestion of the meal
72
Distal Stomach - Contractions Peristalsis??
begins as a ring of contraction in the body of the stomach and propagates distally toward the antrum
73
Distal Stomach - Contractions Antral Systole??
as the peristaltic contraction enters the antrum, the antrum contracts as a unit (antral systole) and the pyloric sphincter constricts
74
Distal Stomach - Distention Stimulates gastric contractions 2 parts
long (vago-vagal) and short cholinergic reflexes gastrin
75
Gastric mixing and emptying Distal peristaltic contractions do what?
break up solids to a small size so they can be empties
76
Gastric mixing and emptying Distal peristaltic contractions propel solids into the ___
antrum
77
Gastric mixing and emptying Distal peristaltic contractions - as the antrum begins to contract, what happens?
some liquid and small solids squirt through the pyloric sphincter into the duodenum (antral pump)
78
Gastric mixing and emptying Distal peristaltic contractions - as the antrum continues to contract, the ___ closes and ____
the pyloric sphincter closes and traps the solids in the antrum and grinds them together.
79
Gastric mixing and emptying Distal peristaltic contractions - The solids (after being ground) are then...
retropelled back into the stomach and the process begins again
80
Gastric mixing and emptying Distal peristaltic contractionS - The continual propulsion, grinding, and retropulsion serve to...
break up solids and mix them with the gastric secretions
81
Gastric mixing and emptying Distal peristaltic contractions - Sustained contractions and the antral pump contribute to ___. Gastric emptying takes how long after a mixed meal?
emptying 3-5 hours
82
Regulation of emptying 5 components
size of material volume composition control of gastric emptying by duodenum other hormones
83
Size of material - liquids> solids Solids must be ... non-digestible solids larger than 2 mm diameter are not emptied during ___
solids must be reduced in size before they can be emptied ...not emptied during the postprandial period
84
Regulation of emptying For liquid meals, the greater the ___, the greater the rate of emptying
volume
85
Regulation of emptying Composition ___>___>___ High ___ and low ___ slow emptying
carbs>protein>fat high osmolality and low pH slow emptying
86
Regulation of emptying Control of gastric emptying by duodenum ___ and ___ reaching the small intestine stimulate secretion of CCK that slows emptying by ______
fats and amino acids reaching the small intestine stimulate secretion of CCK that slows emptying by inhibiting proximal contractions
87
Regulation of emptying Other hormones Glucagon-like peptide 1 (GLP-1) ___ gastric emptying and GI motility
inhibits
88
Emesis is usually preceded by?
Nausea, increased salivation, and retching
89
Reverse peristalsis in small intestine moves interstitial content into the ___
Stomach
90
The ___ and ___ contract, preventing contents from moving back into the intestine
pyloric sphincter, antrum
91
Retching - what happens?
1. inspiration against a closed glottis and reduction of esophageal pressure 2. LES relaxes 3. ab muscles contract and force gastric contents into esophagus 4. stimulate 2 peristalsis to move contents back into stomach
92
Vomiting - same as retching plus:
increased force of ab muscle contraction Hyoid bone is elevated to relax the UES Evacuation of gastric content
93
Vomiting reflex is controlled by vomiting center in the __
medulla
94
Stimulants of vomiting?
1. GI tract irritation 2. pain 3. dizziness (uneven vestibular stim) 4. chemical stimulation of receptors in chemoreceptor trigger one in the brain 5. distressing emotions, visual, and olfactory stimuli
95
Motility of the small intestine Functions:
1. mixes chyme with exocrine secretions 2. reduces particle size more 3. circulates chyme along intestinal wall for absorption 4. slowly propels chyme toward large intestine
96
Sm Intestine motility Peristalsis: Occurs ___. Travels only a short distance before ___
occurs infrequently dying out. Supposed to be drying?
97
Sm Intestine motility Segmentation: Most frequent ___ in the small intestine.
type of contractile activity
98
Sm Intestine motility Segmentation: Functions both to ___ and ___
mix small intestine contents and propel contents distally
99
Sm Intestine motility Segmentation: ___ of contractions decreases from proximal to distal sections. Major stimulus:
frequency this causes the contents to move down the GI tract major stimulus - distention (mechanical and short reflexes)
100
Sm Intestine motility Intestinal sphincters and reflexes (3)
1. intestino-intestinal reflex 2. ileocecal sphincter 3. gastroileal reflex
101
Sm Intestine motility Intestino-intestinal reflex: gross distention or irritation of a portion of the small intestine results in ___
inhibition of contractions of the entire small intestine
102
Sm Intestine motility Intestino-intestinal reflex is mediated by:
extrinsic nerves
103
Sm Intestine motility ileocecal sphincter is normally ____. This slows emptying of small intestine and _____.
closed minimizes bacterial reflux from the colon
104
Sm Intestine motility ileocecal sphincter ___ - relaxation of the sphincter
distend ileum
105
Sm Intestine motility Gastroileal reflex: ____ in distal ileum and relaxation of ileocecal sphincter during or shortly after a meal.
increased motility
106
Sm Intestine motility Gastroileal reflex: ____ of intestinal contents. Mediated by ___
increases emptying increased levels of circulating gastrin
107
Motility of large intestine Functions: Movement of material through is very ___
Functions: mix chyme and propel it toward rectum slow - 24 hr
108
Anatomy of large intestine
``` Cecum ascending colon transverse colon descending colon sigmoid colon rectum haustrum ```
109
Large intestine mobility Segmentation type contractions (haustrum) mix contents - frequency and stimuli??
Slower than small intestine (~ once every 30 min) distention of the colon is the major stimulus
110
Large intestine mobility Mass movement description
propulsive, ring of contraction elongates distally moving contents toward the rectum
111
Large intestine mobility Mass movement occurs when?
3-4x/day usually after a meal
112
Large intestine mobility Mass movement gastrocolic reflex is?
ingestion of a meal and distention of stomach stimulates colonic mass movement through neural reflexes or hormonal mechanisms
113
Large intestine mobility Defecation Defecation reflex??
1. Distention of rectum - movement of material into rectum by mass movement triggers reflex.
114
Large intestine mobility Defecation reflex - relaxation of _____(smooth muscle) and transient contraction of ____(skeletal muscle) and awareness of the need to defecate.
internal anal sphincter external anal sphincter
115
Defecation voluntary movements - contraction of ___ and relaxation of ext anal sphincter
abdominal muscles
116
Defecation Involuntary movements - contraction of ____and relaxation of ___
distal colon internal anal sphincter
117
Motility during the interdigestive period: the migrating motility complex (MMC) Function:
House cleaning during fasting
118
Migration of the MMC | 2 parts
1. The MMC occurs 1st in the stomach, then in the proximal small intestine and progresses distally to the ileum. 2. Repeats at ~90 min intervals
119
Motility during the interdigestive period: the migrating motility complex (MMC) Contractions: 2 parts
1. Stomach - powerful peristaltic contractions (Pyloric sphincter remains open) and functions to remove non-digestible 2. Intestine - peristaltic contraction. Functions remove mucous, sloughed cells and bacteria. Defect - bacterial overgrowth.
120
Motility during the interdigestive period: the migrating motility complex (MMC) Regulation
The MMC is initiated in the stomach by increased circulated motilin
121
salivary secretion two functions of saliva
protection and digestion
122
How does saliva protect?
1. antibacterial (Lysozyme, lactoferrin) 2. neutralize acid - bicarb neutralizes acid secreted by bacteria in the mouth) 3. lubrication (water and mucus)
123
Xerostomia is?
dry mouth - inability to produce saliva
124
Sjogren Syndrome
Autoimmune disease that destroys salivary glands and lacrimal glands
125
How does saliva aid in digestion?
salivary gland amylase begins digestion of carbs
126
Secretion of saliva secreted by? basic unit is?
secreted by a variety of salivary glands (Parotid, sublingual, submandibular, and minor salivary glands) basic unit is the salivon that consists of ACINAR cells and DUCT cells
127
Acinar cells secrete ____along with ____
Acinar cells secrete organic components of saliva alone with a fluid that has ~ the same ionic composition as plasma
128
As saliva passes down he duct (in secretion), its composition is altered by ___
duct cells
129
Duct cells absorb____ out of the fluid and secrete ____ into it
Duct cells absorb Na and Cl out of the fluid and secrete K and HCO3 into it
130
The saliva that enters the oral cavity is __ to plasma and contains higher concentration of ____ and lower concentrations of ___ than plasma
The saliva that enters the oral cavity is hypotonic to plasma and contains higher concentration of K and HCO3 and lower concentrations of Na and Cl than plasma
131
Control of saliva How much is secreted per day? Stimulated by? Stimulation is mediated entirely by?
1-2 L/day is secreted thought of food, smell, mechanical stimulation of oral mucosa, taste (acid) entirely by neural mechanisms
132
stimulation of salivary glands and neural control parasympathetic - ___ stimulation of secretion and vasodilation of vessels to salivary gland. Parasympathetic is the ____
parasympathetic - cholinergic stimulation of secretion and vasodilation of vessels to salivary gland. Parasympathetic is the most important control of salivary secretion
133
stimulation of salivary glands and neural control Sympathetic - ___ stimulation of salivation
small, transient
134
Gastric secretion of HCl 6 components of gastric glands
gastric glands (oxyntic glands) - found in the body of the stomach 1. surface epithelial cells 2. mucous neck cells 3. parietal cells (oxyntic cells) 4. chief cells 5. enterochromaffin-like cells (ECL cells) 6. D cells
135
1. surface epithelial cells - 2. mucous neck cells - 3. parietal cells (oxyntic cells) - 4. chief cells - 5. enterochromaffin-like cells (ECL cells) - 6. D cells -
1. secrete thick mucus 2. secrete thin mucus 3. secrete HCl and intrinsic factor 4. secrete pepsinogen 5. secrete histamine 6. secrete somatostatin
136
Functions of HCl
antibacterial - kills bacteria we swallow provides appropriate pH for pepsin activity denatures proteins
137
Cellular mechanisms of HCl secretion by parietal cells 1st - H/K-ATPase in lumenal membrane actively transports ___ into gastric lumen in exchange for ___
H/K-ATPase in lumenal membrane actively transports H into gastric lumen in exchange for K
138
Cellular mechanisms of HCl secretion by parietal cells 2nd - The H is derived from ____. Secretion of H into the lumen leaves an ____ behind.
2nd - The H is derived from dissociation of H20. Secretion of H into the lumen leaves an OH behind.
139
Cellular mechanisms of HCl secretion by parietal cells 3rd - The OH is ____ by ____, derived from reaction of CO2 with H2O.
The OH is neutralized by H2CO3, derived from reaction of CO2 with H2O.
140
Cellular mechanisms of HCl secretion by parietal cells 4th - the reaction of CO2 with ____ (catalyzed by carbonic anhydrase), producing H2O and ___
4th - the reaction of CO2 with H2O (catalyzed by carbonic anhydrase), producing H2O and HCO3
141
Cellular mechanisms of HCl secretion by parietal cells 5th - The HCO3 is transported across the ____ membrane in exchange for ___. The HCO3 enters the blood producing the ___
5th - The HCO3 is transported across the basolateral membrane in exchange for Cl. The HCO3 enters the blood producing the alkaline tide
142
Cellular mechanisms of HCl secretion by parietal cells 6th - The Cl- diffuses through Cl- channels into the lumen. The net results is _____
6th - The Cl- diffuses through Cl- channels into the lumen. The net results is secretion of HCl into the lumen and bicarb into the blood
143
Stimulation of HCl secretion Stimulation of ____ cells. they can be stimulated to secrete H by Acetylcholine, gastrin, and histamine
parietal cells
144
Stimulation of HCl secretion Stimulation of ____: they can be stimulated to secrete histamine by acetylcholine and gastrin
enterochromaffin-like ECL cells
145
Stimulation of HCl secretion inhibitors:
H2-receptor blockers, (cimetidine, pepcid) H+/K+-ATPase inhibitors (omeprazole)
146
Regulation of HCl secretion Cephalic phase (___% of response) Vagal reflexes initiated during the cephalic phase stimulate acid secretion by ___
30-40% parietal cells
147
Regulation of HCl secretion Cephalic phase - 1. These "long" reflexes, acting though cholinergic neurons on the enteric nerve plexus, stimulate secretion of ___ by ____ and secretion of ___ by ___cells
1. These "long" reflexes, acting though cholinergic neurons o the enteric nerve plexus, stimulate secretion of HCl by parietal cells and secretion of histamine by ECL cells
148
Regulation of HCl secretion Cephalic phase - 2. Histamine, in turn stimulates parietal cell secretion of ___. In addition, vagal reflexes to the antrum stimulate secretion of ____ from G cells
Cephalic phase - 2. Histamine, in turn stimulates parietal cell secretion of acid. In addition, vagal reflexes to the antrum stimulate secretion of gastrin from G cells
149
Regulation of HCl secretion Cephalic phase - 3. Elevated levels of circulating gastrin increase _____ by direct stimulation of ____ and by stimulating histamine secretion from ECL cells.
Cephalic phase - 3. Elevated levels of circulating gastrin increase acid secretion by direct stimulation of parietal cells and by stimulating histamine secretion from ECL cells.
150
Regulation of HCl secretion Gastric phase - (__% of response to the meal)
50-60%
151
Regulation of HCl secretion Gastric phase - stimulation: During the gastric phase, _____ stimulates acid secretion via long vago-vagal reflexes and short reflexes mediated by the _____. The reflexes enhance acid secretion by doing three things (On the next few cards)
Gastric phase - stimulation: During the gastric phase, distention of the stomach stimulates acid secretion via long vago-vagal reflexes and short reflexes mediated by the enteric nerve plexus. The reflexes enhance acid secretion by doing three things
152
Regulation of HCl secretion Gastric phase - stimulation: reflexes enhance secretion by - 1. 2. 3.
1. cholinergic stimulation of parietal cells 2. stimulation of histamine secretion by ECL cells 3. stimulation of gastrin secretion by G cells
153
Regulation of HCl secretion Gastric phase - stimulation: ____ stimulates acid secretion by direct stimulation of parietal cells and by stimulating histamine secretion by ECL cells. If the meal contains protein, protein digestion products (peptides) produced by the activity of ___ and ___ will stimulate G cells secretion of gastrin further enhancing acid secretion
Gastric phase - stimulation: Gastrin stimulates acid secretion by direct stimulation of parietal cells and by stimulating histamine secretion by ECL cells. If the meal contains protein, protein digestion products(peptides) produced by the activity of acid and pepsin will stimulate G cells secretion of gastrin further enhancing acid secretion
154
Regulation of HCl secretion Gastric phase - Inhibition As acid is secreted, the pH of the lumenal contents ____. Reduction of the pH to less than 2.0 will stimulate secretion of ____
Gastric phase - Inhibition As acid is secreted, the pH of the lumenal contents decreases. Reduction of the pH to less than 2.0 will stimulate secretion fo somatostatin from D cells in the stomach.
155
Regulation of HCl secretion Gastric phase - Inhibition Somatostatin acts to prevent ____ by inhibiting secretion of ___ from G cells and ___ from ECL cells
Somatostatin acts to prevent excessive production of acid by inhibiting secretion of gastrin from G cells and histamine from ECL cells
156
Regulation of HCl secretion Intestinal phase The presence of acidic of hyperosmotic chyme or chyme containing fat in the small intestine causes a _____. Part of this inhibition is d/t short loop neural reflexes and part is the result of secretion of hormones collectively known as ____
Intestinal phase The presence of acidic of hyperosmotic chyme or chyme containing fat in the small intestine causes a reduction in gastric secretion of acid from parietal cells. Part of this inhibition is d/t short loop neural reflexes and part is the result of secretion of hormones collectively known as ENTEROGASTRONES
157
Gastric secretions Intrinsic Factor (IF) is secreted by parietal cells and is required for efficient absorption of ____. Secretion parallels ____. Lack of IF results in _____.
Intrinsic Factor (IF) is secreted by parietal cells and is required for efficient absorption of Vit B12. Secretion parallels HCl secretion. Lack of IF results in a pernicious anemia
158
Gastric secretions Pepsinogen is synthesized on the ____ of chief cells and passes into the ____. It then migrates to smooth vesicles and then condensing vacuoles of the Golgi Apparatus.
Pepsinogen is synthesized on the RER of chief cells and passes into the cisternae. It then migrates to smooth vesicles and then condensing vacuoles of the Golgi Apparatus.
159
Gastric secretions Pepsinogen- Zymogen granules bud off and are stored in the cytoplasm until the cells are stimulated to secrete. When stimulated, zymogen granules _________.
Zymogen granules bud off and are stored in the cytoplasm until the cells are stimulated to secrete. When stimulated, zymogen granules migrate to and fuse with the lumenal membrane dumping pepsinogen into the lumen.
160
Gastric secretions Pepsinogen- In the lumen some pepsinogen is converted to ___ by ____. Once some pepsin is formed, it can convert additional pepsinogen to pepsin.
In the lumen some pepsinogen is converted to pepsin by gastric acid. Once some pepsin is formed, it can convert additional pepsinogen to pepsin.
161
Gastric secretions Pepsinogen- ___ and ____ stimulate secretion during cephalic and gastric phases.
Pepsinogen- | Short and long cholinergic reflexes stimulate secretion during cephalic and gastric phases.
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Gastric secretions Mucus is secreted by ___ and _____ in response to mechanical stimulation and cholinergic reflexes during cephalic and gastric phases. It forms a 1-2 mm layer over surface of stomach and serves a ____
Mucus is secreted by mucus neck cells and surface epithelial cells in response to mechanical stimulation and cholinergic reflexes during cephalic and gastric phases. It forms a 1-2 mm layer over surface of stomach and serves a protective function.
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Gastric mucosal barrier -
mucus with HCO3 and tight junctions
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Summary of gastric secretions 1. Parietal cells secrete ___ 2. Chief cells secrete ___ 3. Surface epithelial cells secrete ___ & ___ 4. Mucus neck cells secrete ____ 5. G cells secrete ____ 6. ECL cells secrete ____ 7. D cells secrete ____
1. Parietal cells secrete HCl and intrinsic factor 2. Chief cells secrete pepsinogen 3. Surface epithelial cells secrete mucus and HCO3 4. Mucus neck cells secrete mucus 5. G cells secrete gastrin 6. ECL cells secrete histamine 7. D cells secrete somatostatin
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Pancreatic secretion functions
neutralize gastric acid and digest macromolecules
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Composition (pancreatic secretions) 1. Acinar cell contribution = _____ 2. Ductal cell contribution = _____
1. Acinar cell contribution = digestive enzymes | 2. Ductal cell contribution = H2O, bicarbonate (HCO3-) and ions
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Regulation of pancreatic secretion Cephalic and Gastric phases (~__% of response to a meal) Vagal stimulation of ___ causes ___
Cephalic and Gastric phases (~20% of response to a meal) Vagal stimulation of acinar cells causes enzyme secretion.
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Regulation of pancreatic secretion 2. Intestinal phase (~__% of response to a meal) a. H+ stimulates S cell to release____, which stimulates ____ and causes release of HCO3- and volume. The HCO3- does what?
2. Intestinal phase (~80% of response to a meal) a. H+ stimulates S cell to release secretin. Secretin stimulates ductal cell and causes release of HCO3- and volume. The HCO3- neutralizes acid in the duodenum.
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Regulation of pancreatic secretion 2. Intestinal phase (~80% of response to a meal) b. Fat and amino acids (AA) stimulate I cells to secrete ____ which stimulates ____ to release enzymes to digest macromolecules.
b. Fat and amino acids (AA) stimulate I cells to secrete cholecystokinin (CCK). CCK stimulates acinar cell to release enzymes to digest macromolecules.
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Bile funcitons?
facilitate i) digestion and absorption of fat-soluble substances and ii) excretion of bile pigments
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Anatomy of the bile system
1. Liver 2. Gall Bladder 3. Ducts a. Common hepatic duct b. Common bile duct 4. Sphincter of Oddi 5. Bile Canaliculi 6. Hepatic portal vein
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Hepatic secretion of bile components of bile (5)
a. bile salts b. cholesterol c. phosphatidylcholine (lecithin) d. bicarbonate and salts e. bile pigment f. trace metals
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The liver synthesizes bile salts (acids) from ____ and actively secretes them into the ____.
The liver synthesizes bile salts (acids) from cholesterol and actively secretes them into the bile canaliculus.
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Bile salts in bile are above the critical micellar concentration and form ____. Micelles are cylinders 2 bile salts high. Bile salts are arranged on the ___ of the cylinder with their ____ facing out. ___ & ____ are sequestered in the interior of the micelle.
Bile salts in bile are above the critical micellar concentration and form micelles. Micelles are cylinders two bile salts high. Bile salts are arranged on the outside of the cylinder with their hydrophilic groups facing out. Cholesterol and phosphatidylcholine are sequestered in the interior of the micelle.
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When fasting, the sphincter of Oddi is ___ and bile is diverted into the ___ where it is stored and concentrated. When ___ containing fat or peptides enters the small intestine it stimulates secretion of ___ from I cells. CCK causes ___ and contraction of the ____ expelling bile into the ____
When fasting the sphincter of Oddi is closed and bile is diverted into the gallbladder where it is stored and concentrated. When chyme containing fat or peptides enters the small intestine it stimulates secretion of CCK from I cells. CCK causes relaxation of sphincter of Oddi and contraction of the gallbladder expelling bile into the upper small intestine.
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The bile salts aid in the digestion of ___
The bile salts aid in the digestion of fats in the small intestine.
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``` When the bile salts reach the ___ they are efficiently reabsorbed by a Na+- dependent secondary active transport. The reabsorbed bile salts are returned to the ____ in the portal circulation. ```
``` When the bile salts reach the ileum they are efficiently reabsorbed by a Na+- dependent secondary active transport. The reabsorbed bile salts are returned to the liver in the portal circulation. ```
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The ___ extracts the bile salts from the ____ and secretes them back into the bile canaliculus thereby completing the enterohepatic circulation of bile salts. Once the fat and peptides have been absorbed, CCK levels ____, the____closes and bile is again diverted to the ____ to be stored and concentrated.
The liver extracts the bile salts from the portal blood and secretes them back into the bile canaliculus thereby completing the enterohepatic circulation of bile salts. Once the fat and peptides have been absorbed, CCK levels decrease, the sphincter of Oddi closes and bile is again diverted to the gallbladder to be stored and concentrated.
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Ninety-five percent (95%) of the bile salts are ____ and enter the ____ while 5% are excreted in the ____. Thus, the liver only synthesizes the 5% that is lost in the feces.
Ninety-five percent (95%) of the bile salts are reabsorbed and enter the enterohepatic circulation while 5% are excreted in the feces. Thus, the liver only synthesizes the 5% that is lost in the feces.
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The bile pigment, ____, is a breakdown product of ___ and is found in the circulation bound to ____.
The bile pigment, bilirubin, is a breakdown product of hemoglobin and is found in the circulation bound to albumin.
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Bile pigments - The liver extracts ____ from the blood, conjugates it with two molecules of ____ and secretes the bilirubin-diglucuronide into the bile.
The liver extracts bilirubin from the blood, conjugates it with two molecules of glucuronic acid and secretes the bilirubin-diglucuronide into the bile.
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Bile pigments When the bile enters the small intestine, the bilirubin is not reabsorbed but passes into the ___ and is excreted in the feces. The ____ is the major route for elimination of bilirubin. Failure to eliminate bilirubin results in ____.
When the bile enters the small intestine, the bilirubin is not reabsorbed but passes into the colon and is excreted in the feces. The GI tract is the major route for elimination of bilirubin. Failure to eliminate bilirubin results in jaundice.
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Causes for jaundice include:
Causes for jaundice include: 1. Increased destruction of red blood cells 2. Lack of glucuronidation enzymes 3. neonates 4. liver disease 5. Obstruction of bile duct
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Most (80%) gallstones are composed primarily of ____
Most (80%) gallstones are composed primarily of cholesterol.
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Normally cholesterol is solubilized in the bile by incorporation into ____. Gallstones form when the bile has more ____ than can be solubilized and the cholesterol precipitates out of solution, usually in the ____.
Normally cholesterol is solubilized in the bile by incorporation into micelles. Gallstones form when the bile has more cholesterol than can be solubilized and the cholesterol precipitates out of solution, usually in the gallbladder.
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Gall stones may be due to an increase in the amount of ____ or a decrease in the amounts of ___ and/or ___ in the bile.
Gall stones may be due to an increase in the amount of cholesterol or a decrease in the amounts of bile salts and/or phosphatidylcholine in the bile.
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Some (approximately 20%) gallstones are pigmented and contain ___. These stones form when bilirubin-diglucuronide is ____in the ___ or ___ and precipitates out of solution forming a stone.
Some (approximately 20%) gallstones are pigmented and contain bilirubin. These stones form when bilirubin-diglucuronide is deconjugated in the bile duct or gallbladder and precipitates out of solution forming a stone.

Physiology (8 decks)

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