Gastrointestinal Physiology Flashcards
(178 cards)
1
Q
colorectal cancer is the __ deadliest cancer in US
A
2nd
2
Q
Diarrhea is the __ leading cause of death worldwide
A
3rd
3
Q
segments of the GI tract
A
mouth, pharynx, esophagus, stomach, small intestine, large intestine, sphincters between segments
4
Q
GI tract accessory organs
A
salivary glands, liver, gallbladder, pancreas
5
Q
layers of the GI tract (outside to inside)
A
- serosa (outerlining)
- longitudinal muscle
- myenteric (Auerbach’s) nerve plexus
- circular muscle
- submucosa
- submucosa (Meissner’s) nerve plexus
- muscularis mucosae
- mucosa
- epithelial linging
6
Q
major functions of the digestive system
A
- motility
- digestion
- absorption
- secretion
7
Q
2 processes of digestion
A
- mechanical (chewing/mastication)
- chemical (action of enzymes)
7
Q
absorption
A
- mechanism of the nutrients being digested are then being absorbed from the GI lumen into the blood stream
8
Q
___ helps with digestion and absorption
A
secretions
9
Q
where does most absorption occur?
A
small intestine
10
Q
once the nutrients are absorbed from the GI lumen, where do the nutrients in the blood stream go?
A
to the liver
11
Q
motility
A
food keeps moving along the GI tract through this process, aided by contractions of the smooth muscle in the GI tract
12
Q
HPV connects the __ as well as the __ to the liver, where the liver gets nutrients first
A
small intestine; colon
13
Q
endocrines (hormones)
A
all GI hormones are peptides released into the blood to act on the distant target cells
14
Q
GI hormones
A
-gastrin
-secretin
-cholecystokinin (CCK)
-glucose-dependent insulinotropic peptide (GLIP) or gastric inhibitory peptide (GIP)
-motilin
15
Q
paracrines
A
some are peptides (somatostatin), and some are not (exp. histamine)
16
Q
histamine
A
- gastrin and ACh cause release from cells in stomach
- stimulates acid secretion
17
Q
what does a Histamine H2 receptor blocker do?
A
- decreases acid secretion
18
Q
exp. of histamine H2 blockers
A
Cimetidine (Tagamet), Ranitidine (Zantac)
18
Q
Neurocrines (neurotransmitters)
A
- some are peptides (VIP - vasoactive intestinal peptide), some are not (ACh, NE)
- nerves release –> diffuse to target cells
19
Q
site of production gastrin
A
antrum of stomach
20
Q
site fo production CCK
A
small intestine
21
Q
site of production secretin
A
small intestine
22
Q
Gastrin does what to stomach 1.) acid secretion 2.) motility
A
stimulates, stimulates
23
CCK does what to stomach 1.) acid secretion 2.) motility
inhibits, inhibits
24
secretin does what to stomach 1.) acid secretion 2.) motility
inhibits, inhibits
25
intrinsic control
enteric nervous system
26
enteric nervous system (ENS)
- myenteric (Auerbach's) plexus
- submucosal (Meissner's) plexus
27
extrinsic control
autonomic nervous system
- PNS (rest & digest)
- SNS
28
what stimulates the PNS?
ACh
29
what stimulates the SNS?
mainly inhibits via NE
30
GI reflexes
- local within (ENS)
- long loop
31
local reflexes
- afferent fibers from gut terminates in ENS
- affects (+ or -) secretion, peristalsis, mixing movement
32
long loop reflex
gut --> afferent nerve --> prevertebral ganglia --> efferent nerve --> gut
reflexes: gastrocolic, enterogastric, colonoileal
33
Vagovaval reflexes
stomach/ duodenum --> aff. N. --> brain stem --> Eff. N. --> stomach/duodenum
controls gastric motor and secretory activity
34
defecation reflexes
colon/rectum --> aff. N. --> spinal cord --> Eff. N. --> colon/rectum
35
pain reflexes - overall
inhibition of GI tract
36
GI regulation of smooth muscle
- unitary (single-unit) smooth muscle
- slow waves
- spike potentials
- muscle contractions (helps with motility)
37
unitary (single unit) smooth muscle
- functions as a syncytium
- gap junctions
38
functions as a syncytium
- nucleated mass of protoplasm produced by merging of cells
- large areas of sm contract as a single unit
39
gap junctions
- low resistance pathways for ion movement
- between bundles of cells and layers of SM
- signal propagation - AP spreads from cell to cell
- within and between muscle layers
40
slow waves and spike potentials are caused by
rhythmical changes in membrane potential caused by variations in sodium conductance
41
slow waves
- interstitial cells of Cajal - pacemaker cells
- dictates maximum frequency of SM contraction
- independent of nervous/hormonal stimuli
- increase in amplitude leads to increase spike potential frequency which leads to increase in strength of contraction
42
Spike potentials (or APs)
- occurs when slow waves reach threshold (-40 mV)
- casuse SM contraction
- Ca++ entry leads to contraction
- affected by nervous/hormonal stimuli
- increase in frequency leads to stonger contraction
43
what is required for peristalsis?
Myenteric plexus
43
gastrointesinal movements
peristalsis
44
T/F atropine (blcoks ACh receptors) which increases peristalsis
FALSE
44
segmentation contractions also called?
rhythmic segmentation (local)
44
where does segmentation contractions occur?
small and large intestines
45
blood flow proportional to local activity, what happens when you eat a meal?
increase in blood flow (2-3 fold) for 3-6 hours
46
causes of activity-induced blood flow?
- vasodilator hormones: gastrin, secretin, CCK
- vasodilator kinins
- low oxygen (high adenosine)
47
what effects the nervous control of blood flow?
- PNS increases gut activity which leads to increased blood flow
- SNS directly decreases blood flow (Autoregulatory escape, exercise, shock)
48
voluntary
initiates swallowing process
49
3 stages of swallowing
- voluntary
- pharyngeal
- esophageal
50
pharyngeal
passage of food through the pharynx into esohagus
51
esophageal
passage of food from pharynx to stomach
52
primary peristalsis
swallow-induced peristalsis
53
secondary peristalsis
elicited by esophageal distention
54
disorders that could effect swallowing
- CVA (stroke)
- cranial nerve damage
- muscular dx (MG, polio, botulism)
- anesthesia can have an effect
55
aspiration
UES and pharyngeal contrations are not coordinated
(effect is primary peristalsis)
56
GERD
backwash of acid, pepsin, and bile into esophagus
57
heartburn/acid indestion effects (_/10) people
1
58
GERD can lead to
- stricture of esophagus (scar tissue)
- aspiration
- chronic sinus infection (reflex into throat)
- barrett's esophagus (lead to esophageal cancer)
59
what helps with regualtion of gastric emptying?
chyme
60
what is chyme
- food bous mixed with acid
- must enter duodenuma at a proper rate
- pH must be optimal (7) for enzyme function
- slow enough for nutrient absorption
61
Immediately after a meal
emptying does not occur before onset of gastric contractions
62
small intestinal motility contributes to digestion and absorption by
- mixing chyme: with digestive enzymes and other secretions
- circulation of chyme: to achieve optimal exposure to mucosa
- propulsion of chyme: in an aboral direction
63
two types of movements in small intestine following a meal
- peristalsis: a propulsive movement recall "Law of Gut"
- segmentation: a mixing movement
(regulated by slow waves)
64
functions of large intestine SM
- mixes chyme: enhances fluid/electrolyte absorption (haustral contractions)
- propels fecal material: mass movements
65
Musculature of large intestine
- longitudinal SM: 3 groups
- circular SM - continuous to anus
- internal anal sphincter - a thickening of circular SM
- external anal sphincter - striated muscle, that surrounds internal anal sphincter
- haustra (Haustrations) - not fixed, appear & disappear
66
lists of sphincters
- UES (pharyngoesophageal)
- LES (gastroesophageal)
- pyloric sphincter (gastroduodenal)
- Ileocecal valve/sphincter
- internal anal sphincter
- external anal sphincter
66
3 levels to control defecation
- intrinsic reflex
- spinal cord reflex
- involvement of higher centers
67
peristaltic reflex
stretch bowel, proximal of contraction, distal relaxation
68
enterogastric reflex
from duodenum to regulate gastric emptying
69
gastroileal reflex (gastroenteric)
gastric distention relaxes ileocecal sphincter
70
intestino-intestinal reflex
over-distention or injury of the bowel segment causes entire bowel to relax
71
gastro- duodenocolic reflex
distension of the stomach/duodenum initiates mass movements
72
defecation reflex (rectospincteric)
rectal distention initiates defecation
73
types of secretory glands
single cell: mucous or goblet cells
simple: indentations in the epithelium (crypts of lieberkühn)
Tubular: acid-secreting oxyntic gland
complex: salivary, pancreas
74
control of secretions
- local: tactile, distention, irritation
- reflex: nervous input
- hormonal: GI input
75
mucus composition properties
- thick secretion that is mainly water, electrolytes and glycoproteins
76
mucus is essential for digestion because
- adherent: sticks to food
- body: coats well
- low resistance (for slippage): lubrication
- self-adherent: sticks together
77
mucus is resistant to __ by the GI enzymes, buffering capacity (glycoproteins) to _____
digestion, neutralize acid
78
2 types of saliva
serous - water secretion, contains alpha-amylase (ptyalin) --> carbohydrate digestion
mucous - contains mucin (lubrication)
79
how much saliva is secreted a day
800-1500 mL/day
max rate of secretion is 4 mL/min
80
salivary glands (4)
parotid (serous)
submandibular (mucous/serous)
sublingual (mucous/serous)
buccal (mucous)
81
what 2 glands contribute to 90% of total saliva secreted?
parotid & submandibular
82
ionic composition of saliva
K+ 7x the plasma
HCO-3 3x the plasma
83
T/F saliva is hypotonic
true
84
effect of loss of saliva?
cal lead to K+ depletion
85
functions of saliva
- lubrication and binding
- solubilizes dry food
- initiates starch digestion
86
clinical correlation to saliva
oral hygiene, xerostomia (dry mouth), drooling
87
functions of the stomach
- short-term storage reservoir
- secretion of intrinsic factor
- chemical and enzymatic digestion is initiated, particularly of proteins
- liquefication of food
- slowly released into small intestine for further processing
88
Gastric (oxytonic) gland cell types
mucous neck cells: mucus
peptic cells (chief cells): pepsinogen, renin
parietal cells: HCl, intrinsic factor
G-cells: release gastrin
Enterochromaffin-like (ECL) cells: release histamine
89
what increases HCl production?
gastrin
histamine
ACh
90
what decreases HCl production?
somatostatin
91
the gastric mucosa has a ___ and an __ basis to prevent back-leak of hydrogen ions
physiological, anatomical
92
what strengthens gastric mucosal barrier?
mucus, HCO3- secretion, gastrin, PGs, epidermal growth factor
93
what weakens gastric mucosal barrier?
H. pylori, aspirin, ethanol, NSAIDs, bile salts
94
peptic ulcers
occur when damaging effects of acid and pepsin overcome the ability of mucosa to protect itself
1. high acid and peptic content
2. irritation
3. poor blood supply
4. poor secretion of mucus
5. infection of H. pylori
95
gastic ulcers
main problem is decreased ability of mucosa to protect itself
96
duodenal ulcers
main problem is exposure to increased amounts of acid and pepsin
97
treatment of peptic ulcers
antacids; (H2 antagonists, PPIs)
98
pancreas
- as chyme floods into small intestine 2 things must happen
1.) Acid must be neutralized to prevent damage to duodenal mucosa
2.) Macromolecular nutrients - proteins, fats, and starch must be broken down much further so their constituents can be absorbed
BIG THINGS PANCREAS DOES
- digestive enzymes for all food types
- bicarb solution to neutralize acid chyme
99
Where is bile stored?
gall bladder
100
Where is bile made?
liver
101
What is bile?
emulsification NOT breaking it down
102
Pancreatic secretions
- Trypsin, chymotrypsin, elastase
- Carboxypeptidase
- Lipase
- Amylase
103
Trypsin, chymotrypsin, elastase
what is there substate and action?
substrate: proteins
action: break peptide bonds in proteins to form peptide fragments
104
Carboxypeptidase
what is the substate and action?
substrate: Proteins
action: splits off terminal amino acid from carboxyl end of protein
105
Lipase
what is the substate and action?
substrate: fats
action: splits off 2 fatty acids from triglycerides, forming 3 fatty acids and monoglycerides
106
Amylase
what is the substate and action?
substrate: polysaccharides
action: splits polysaccharides into glucose and maltose
107
what helps activate the proteolytic enzymes and where are they located?
enterokinases, located on the intestinal mucosal cells
108
control of pancreatic secretion
- increase in acid from stomach
- increase in secretin secretion from SI
- increase in plasma secretin
- increase in bicarb secretion from the pancreas
- increase in flow of bicarb into SM
- neutralization of intestinal acid in SI
109
T/F Secretin is nature's antacid
true
110
liver & its major function
severs as a secretory organ, major function is to secrete bile
111
other critical functions fo the liver
- processes and stores nutrients
- serves as a filter and functions in the removal of old RBCs which leads to Hgb processing and generation of bilirubin
- responsible for the synthesis of plasma proteins (albumin, clotting proteins, angiotensinogen, steroid binding proteins)
112
bile secretion and liver function flow
- increase in CCK secretion from the fatty acids in the duodenum
- increase in plasma CCK
- 1.) leads to contraction of gall bladder --> increases bile flow into CBD
- 2.) leads to relaxation of sphincter of oddi --> increase in bile flow into the duodenum
112
causes of gallstones:
1. too much absorption of water from bile
2. too much absorption of bile acids from bile
3. too much cholesterol in bile
4. inflammation of epithelium
112
effects of gallstones on the body
- causes intense pain
- inflammation issues
- obstruction issues
- make fat digestion a bigger problem b/c lack of bile flowing into the duodenum
113
small intestine secretions
brunner's glands: secrete an alkaline mucus
- compound mucus gland in duodenum
- protects the mucosa from acid chyme
- stimulated by local irritation - vagus (ACh)
- inhibited by sympathetic NE
Crypts of Lieberkühn: mostly secrete waterlike fluid
114
Basis of digestion
involves the breakdown or hydrolysis (addition of water molecule) of nutrients to smaller molecules that can be absorbed in SI
114
Large intestine secretions
- contains Crypts of Lieberkühn but there are no villi or enzymes
- crypts mainly secrete alkaline mucus
- mucus secretion increase by PNS stimulation
115
T/F pepsinogen only gets converted to pepsin in the presence of bicarb
False
presence of HCl
115
4 mechanisms are critical for the transport of substances across the intestinal cell membrane
1. active transport: primary and secondary
2. passive diffusion
3. facilitated diffusion: carrier mediated
4. endocytosis: this allows large proteins (immunoglobulins) to be absorbed in babies. does NOT occur in adults
116
a nutrient must cross how many barriers to be absorbed by blood or lymph?
8
117
What gets absorbed in the stomach?
ethanol, NSAIDs, aspirin
118
what gets absorbed in the duodenum and jejunum?
nutrients, vitamins, various ions, water and electrolytes
119
what gets absorbed in the ileum?
bile salts and vitamin B12
120
what gets absorbed in the colon?
water and electrolytes
121
what gets absorbed in the rectum
drugs such as steroids and salicylates
122
starch digestion
- begins with alpha-amylase in saliva (5% digestion in mouth, up to 40% in stomach)
- continues in SI with pancreatic amylase
- final digestion occurs at brush border
123
disaccharides
maltose
surcrose
lactose
124
final products of carbohydrate digestion are all monosaccharides, mostly ___
glucose 80%
fructose 10%
galactose 10%
125
glucose and galactose require what for absorption?
secondary active transport
compete fro membrane carriers (SGLUT-1)
energy from Na K APTase
125
what could be a problem with carbohydrate digestion and absorption?
lactose intolerance
126
fructose requires what for absorption?
facilitated diffusion by (GLUT-5)
does not require energy
requires concentration gradient
127
digestion of proteins occurs in 3 locations
intestinal lumen - stomach (pepsin digests collagen) & SI (endopeptidases -trypsin/chymotrypsin, exopeptidase - carboxypeptidase)
brush border - oligopeptidases, dipeptidases
cytoplasm of mucosal cells - di- tri- peptidases
128
enterokinase activates
trypsinogen
129
proteolytic enzymes are __ and __ very rapidly
activated; destroyed
130
trypsin is
autocatalytic and activates other proenzymes
131
Proteolytic enzymes __ themselves
digest
132
luminal digestion produces __ amino acids and __ small peptides
40%; 60%
133
abnormalities of protein absorption?
pancreatic insufficiency
hartnup dx (malabsorption of tryptophan)
134
digestion of triglycerides
- triglyceride introduced in duodenum
- fatty acid/ 2-monoglyceride by enterocyte
- triglyceride is repackaged to form chylomicron
135
3 main processes must occur for triglyceride to be absorbed into blood
- emulsification: large aggregates of dietary triglyceride are broken down
- enzymatic digestion: to yield monoglyceride and fatty acids. both can diffuse into enterocyte
- reconstitution of triglyceride and chylomicron formation
136
liver has __ densisty cholestrol
low
137
statins traget
LDL, plaque formation form endogenous cholestrol
138
chylomicrons life cycle
- formed in enterocyte in SI and packaged by GA
- secreted by exocytosis into interstitial space
- enter central lacteal* of villi and transported to venous system via thoracic duct
- lipoprotein lipase (on capillary endothelial cells) works with apolipoprotein C to degrade triglyceride to FFA and glycerol within chylomicron
1.) FFA and glycerol respired by cells or resynthesized to triglycerides for storage
2.) chylomicron remnant is phagocytized in hepatocytes(liver)
139
cholesterol is an important precursor for all __ hormones
steroid
139
familial lipoprotein lipase deficiency would lead to..
increase chylomicron, increase in triglyceride = triglycerideenemia
exp. propofol
140
malaborption
as a general phenomenon is defined clinically in terms of fat malabsorption because fat can be measured easily ins tool, unlike carbohydrates and proteins
141
motility disorders
moving through too rapidly
141
digestion disorder
pancreatitis (not enough lipase)
142
absorption disorders
sprue
resection of SI
steatorrhea
143
when chyme is "hypotonic"
water is absorbed
144
when chyme is "hypertonic"
water enters intestine
144
chyme is usually
isotonic
145
sodium absorption causes __ absorption
water
146
sodium is absorbed by ___ of SI
epithelial cells (enterocytes)
147
Sodium uptake creates ___ electrical potential in gut lumen, that provides gradient for ___ uptake
negative; chloride
148
water follows Na and Cl in accordance with ..
osmotic forces
149
what percentage of total body Na is absorbed each day by the intestine
15%
150
___ absorption of Na can lead to rapid Na __ and death
decreased; depletion
151
2 processes establish an osmotic gradient that pulls water into lumen of the intestine:
1.) increased osmotic pressure resulting form the digestion of foodstuffs
2.) Crypt cells actively secrete electrolytes, leading to water secretion
152
water secretion by crypt cells is driven by
chloride secretion
153
the apical (luminal) membrane contains a ___ chloride channel- "cystic fibrosis transmembrane conductance regulator" or CFTR
cyclic AMP-dependent
154
when chloride exits cells through chloride channels
sodium and water follow
155
mutations in gene for ion channel CFTR result in
cystic fibrosis
156
innervation of the vomiting center
sensory signals:
- originate in the pharynx, esophagus, and upper small intestine
- afferent signals transmitted via vagal and sympathetic nerves
motor impulses:
- to upper GI tract via CN VII, IX, X, XII
- to lower GI tract via vagal and sympathetic nerves
- to diaphragm and abdominal muscles via spinal nerves
157
antiperistalsis
- can begin as low as the ileum
- prelude to vomiting
- pushes GI contents into the duodenum
- this distention excites the vomiting act
158
Vomiting act steps
1. deep breath
2. UES open
3. glottic closes
4. elevation of soft palate
5. contraction of diaphragm (a downward motion) and muscles increases pressure in the stomach
6. LES relaxes
7. Gi contents force out mouth
159
Obstruction at pylorus
acidic vomitus - can lead to metbaolic acidosis
160
Obstruction below duodenum
neutral or basic vomitus, usually little change in whole body acid-base status
161
obstruction at distal large intestine
severe constipation can cause vomiting when contents of SI accumulate
162
causes of obstruction
1. cancer
2. ulcer
3. spasm
4. paralytic use
5. adhesions
163
low obstruction causes extreme __ with __ vomiting
constipation; less
164
high obstruction causes extreme
vomiting
