GI 3 Flashcards
1
Q
Nerve supply to the GI tract is
A
extrinsic (sympathetic, parasympathetic) and intrinsic (enteric nervous system)
2
Q
Extrinsic
A
Can modulate the enteric NS
3
Q
Intrinsic
A
Contained in myenteric and submucosal plexuses, back and forth communication
Afferents to the plexuses come from chemo- & mechanoreceptors
4
Q
enteric nervous system is the
A
digestive brain
5
Q
3 layers of smooth muscle
A
Outer longitudinal muscle
Inner circular muscle
Muscularis mucosa
6
Q
layers of GI tract
A
lumen, epithelium, lamina propia, musculares mucosae, submucosa, submucosal plexus, myenteric plexus, serosa, blood
7
Q
submucosal plexus
A
contains GI nervous system,
epithelium, lamina propia, and submucosa
also called Meissner’s secretion
8
Q
myenteric plexus
A
contains GI nervous system
circular muscles and longitudinal muscle
also called Auerbach’s plexus
9
Q
Smooth muscle cells are connected by ___ _______ that form an _______ _________
A
Smooth muscle cells are connected by gap junctions that form an electrical syncytium
10
Q
circular muscles
A
Affects radial dimensions;
Contraction decreases diameter
11
Q
longitudinal muscle
A
Affects anterior-posterior dimensions;
Contraction decreases length
12
Q
Insmooth muscle, there is no _______
A
troponin, rather, the interaction of actin and myosin is controlled by the binding of Ca2+to another protein,calmodulin
13
Q
protein used from muscle contraction in smooth muscle
A
calmodulin
14
Q
tonic contractile activity
A
fairly stable contractions Upper Esophageal Sphincter Lower Esophageal Sphincter Ileocecal sphincter Internal anal sphincter Orad stomach Pylorus
15
Q
phasic contractile activity
A
periodic contractions Pylorus Esophagus Antrum Small intestine Colon
16
Q
which part of the GI tract has both types of contracts activity
A
pylorus
17
Q
Segmentation Contractions
A
contractions in both directions to mix contents
Mix chyme and expose to pancreatic enzymes / secretions
Produce no forward movement
Found in the intestine
18
Q
Peristaltic Contractions
A
proximal muscle contracts, distal muscle relaxes
Propel chyme towards large intestine
Involves several neurotransmitters including Ach and substance P (orad) as well as VIP and nitric oxide (caudad)
Found in esophagus, stomach, intestine
19
Q
contraction
A
Circular muscle contracts, longitudinal muscle relaxes; segment narrows and lengthens
20
Q
relaxation
A
Circular muscle relaxes, longitudinal muscle contracts, segment widens and shortens
21
Q
feces
A
unabsorbed small intestinal content in the large intestine
22
Q
Segmentation Contractions
A
via the haustrations
Occur in the cecum and proximal colon
Serve to mix contents
Associated with haustra
23
Q
Peristalsis in the large intestine
A
propels
24
Q
Mass Movements in the large intestine
A
move contents over longer distances, happen 1-3 times a day final movement is to the rectum to await defecation
Large infrequent peristaltic contractions, 1-3 times a day
25
cyclical pattern is associated with which contractile activity
phasic
26
myogenic contractility is important because
the guy has some contractility without any nervous input whatsoever
27
Luminal contents will cause
basal contractility without any nervous influence at all
28
there is a constant inhibitory tone of
VIP and NO on the gut, to prevent / slow down this contractility
29
Any treatment or condition that removes or inactivates inhibitory motor neurons results in
tonic contracture and continuous uncoordinated activity of the circular muscles
30
example of hyper irritable states cause by inactivation or removal of inhibitory motor neurons
Achalsia, Hirschprung's disease, fecal incontinence
31
MCC phase 1
takes 45 to 60 minutes
0 slow waves with spike
myoelectic activity but no contraction amplitude
32
MMC phase 2
take 30 to 45 minutes
50 % are slow waves with spike
Intermittent, peristaltic, contractions, variable amplitude
33
MMC phase 3
5 to 10 minutes 10 slow waves with spike
Action potentials rapidly propagated along GI axis
Strong peristaltic contractions
34
Interdigestive PeriodMigrating Motility Complex is Initiated during
fasting
Begins in the stomach
Moves undigested material to colon
Repeats every 90-120 min during fasting
35
major complex starches
amylopectin and amylose
| major digestion being in the mouth and they are reduced to disaccharides
36
disaccharides
sucrose, maltose, lactose, trehalose, digestion being in the intestine
37
Digestion and absorption of Carbohydrates
salivary alpha amylase enzyme is active in the mouth and remains active in stomach until acid inactivates it, salivary and pancreatic amylase in the duodenum produce alpha dextrins, maltose and maltostiose
then enzymes on brush border hydrolyze starch products to glucose
38
Enzymes on intestinal brush border
hydrolyze disaccharides to make simple sugars
39
Absorption: Apical Carbs
Na+-glucose cotransport
Na+-galactose cotransport
Fructose facilitated diffusion
40
Absorption: Basolateral Carbs
All by facilitated diffusion with GLUT 2 transporter, glucose, galactose and fructose
41
The function of insulin is to keep the
level of glucose in the blood stream in within a normal range
42
Glucose enters the bloodstream, which stimulates
the pancreas to release insulin in just the right amount
Insulin allows glucose to enter cells throughout the body, where it is used as fuel.
Excess glucose is stored in the liver
43
Incretins are hormones that help
the process of insulin getting glucose into cells
44
Incretin hormones
Glucagon-like peptide-1 (GLP-1)
| Glucose-dependent insulinotropic peptide (GIP).
45
function of (GLP-1) and (GIP)
enhance glucose dependent insulin secretion
suppress postprandial glucagon secretion
slow gastric emptying
reduce food intake and body weight
promote beta cell health
46
GLP-1 is produced
postprandially by intestinal cells
47
GLP-1 in the pancreas
stimulates insulin biosynthesis and secretion
Inhibits glucagon secretion
inhibit beta cell apoptosis
48
GLP-1 ini the heart and brain
has protective effects
increase cardiac output
decreases appetite
49
GLP-1 in the periphery
Insulin sensitivity is increased by improved insulin signaling, insulin sensitivity and reduced gluconeogenesis
50
GLP-1 in the stomach
reduces gastric emptying
51
Digestion and absorption of Proteins- pepsin
begins in the stomach with the activation of gastrointestinal proteases
in a low pH pepsinogen secreted from chief cells becomes pepsin
52
Bulk digestion and Absorption of Proteins
occurs in intestine by the action of the pancreatic enzymes
53
Active forms of protein digestive enzymes also produced in the intestine
enterokinase in the brush border convert trypsinogen into trypsin
Trypsinogen activates pancreatic proezymes to their active form
54
protein final products of digestion to be absorbed
amino acids, dipeptides, tripeptides
55
Absorption: Apical Proteins
Na+-amino acid cotransport
| H+-di/tripeptide cotransport
56
Absorption: Basolateral Proteins
after the H+-di/tripeptide cotransport there is further breakdown to amino acids then
facilitated diffusion OR
Reabsorbed unchanged
57
Digestion and absorption of lipids digestive enzymes
important for fat digestion include lingual lipase, gastric and pancreatic lipases, cholesterol ester hydrolase and phospholipase A2
58
the final digestive product of lipids
monoglycerides, cholesterol, lysolecithin and free fatty acids
59
Absorption of lipids via
micelles and chylomicrons in the jejunum
60
Triglyceride final products
monoglycerides and fatty acids
61
cholesterol esters final products
cholesterol and fatty acids
62
Phospholipid final products
lysolecithin and free fatty acids
63
Lipids are delivered to
liver fat cardiac and skeletal tissue
| locally broken down by lipase
64
what are vitamins
organic compound that cannot be made by the body so we must get from the diet
65
fat soluble vitamins
A, D, E , K
66
Absorption of Water Soluble Vitamins occurs in
the jejunum
67
which vitamins cross apical membrane by the Na+ cotransport
thiamine, riboflavin, vitamin c , biotin, folic acid, niacin, pantothenic acid
68
which water soluble vitamin crossed by simple diffusion
B6 pyridoxine
69
Digestion and Absorption of Fat Soluble Vitamins
Released from food in the small intestine
Processed in the same manner as dietary lipids
Taken up into micelles
Delivered to luminal membrane
Absorbed by simple diffusion
Inside the cell, incorporated into chylomicrons
Extruded by exocytosis into the lymph
70
Fat Soluble Vitamins are passively
absorbed
71
Water absorption by the GI tract
is ______ and in response
to ________
passive and in response to somatic forces
72
water absorbed in duodenum and jejunum
4000 ml
73
water absorbed in ileum
3500 ml
74
water absorbed in colon
1400 ml
75
water lost in feces
100 mk
76
amount of Na+ entering the GI tracts
about 25-35 grams a day from diet and Gi secretions
77
the GI tract is _____ at conserving NA+
very efficient
78
we have ____ _____ mechanisms operating to absorb NA+ through the intestine and colon
Several different
79
intestinal sodium absorption is always
isometric
80
Major site for Na+ absorption
the jejunum
| Absorbs more than ½ of total Na+
81
sodium countertransport in jejunum
Na+-H+
82
sodium coupled absorption in jejunum
Na+-coupled sugar/amino acid absorption
83
Net absorption in jejunum
NaHCO3
84
Net absorption in ileum
NaCl
85
Ileum
HCO3 secretion
86
where does fecal fluid become alkaline
the ileum
87
Intestinal Potassium Absorption
Passive diffusion through tight junctions and lateral intercellular spaces of enterocytes in both the jejunum and ileum
As water is absorbed, luminal K+ increases, resulting in K+ absorption
88
Driving force of Intestinal Potassium Absorption
is K+ concentration difference between lumen and blood.
89
Colonic Absorption net result
fecal fluid tends to be alkaline and has a relatively high K + concentration
90
Aldosterone-sensitive luminal Na+ channel
increase Na+ absorption
91
colonic villus cells
K+ can be absorbed or secreted by colonic villus cells,
| flow rate dependent, more K+ is lost in diarrhea
92
Aldosterone increases _____ and _____ of ____ channels
number and sensitivity of Na+ channels
93
K+ secretion is
flow dependent
94
overall function of intestines
absorption predominates by villus epithelial cells
| there is also secretion by crypt epithelial cells
95
Main electrolyte secreted
chloride
96
how much isotonic alkaline fluid is secreted from crypts of Lieberkϋhn in a day
2 to 3 litters
97
function of isotonic alkaline fluid
main fluidity of chyme and dilute noxious (Poison) substances
98
what makes up isotonic alkaline fluid
water and electrolytes
99
Two channel types in Electrogenic Cl- Secretion from Crypts
Na/K/Cl tritransproter on basolateral membrane
| Cl- channel (CFTR) on luminal membrane
100
Mechanism of Electrogenic Cl- Secretion from Crypts
Na/K pump keeps sodium concentration low; drives Cl- in via Na/K/Cl tritransporter;
Increases CL- concentration which favors efflux on luminal side.
Adds lumen negativity which drives Na+ secretion paracellularly
101
Normally (unstimulated state), crypts secrete very little
Cl- because apical channels are closed or not present
102
Cl- secretion requires activation by
calcium or cAMP
103
What activates cAMP or Ca2+?
Hormones or neurotransmitters
Bacterial endotoxins
Immune cell products
laxatives
104
examples of Bacterial endotoxins that activates Cl- secretion
e coli, and cholera (cAMP)
105
Hormones or neurotransmitters that activates Cl- secretion
```
Ach = cAMP
VIP = Ca2+
```
106
Immune cell products that activates Cl- secretion
histmine cAMP
107
Resulting activation of cAMP or Ca2+ activates
activates preexisting Cl- channels or inserts them into the apical membrane.
End result is increased Cl- secretion
108
laxatives and Cl- secretion
activation of Ca2+
109
Causes of Diarrhea Secretory Diarrhea
cholera
110
Diarrhea
a condition in which feces are discharged from the bowels frequently and in a liquid form
111
Infectious/Inflammatory Diarrhea
Salmonella, rotovirus
| associated with widespread destruction of absorptive epithelium
112
most diarrhea cases are caused by
enteric infections
113
many types of diarrhea are
mixed
114
osmotic diarrhea
an example is lactose intolerant
| Buildup of lactose in GI lumen holds water with it causes diarrhea
115
Deranged Motility causing Diarrhea
an example is hypermotility in some cases of IBS
If food moves too quickly through the GI tract, there is not enough time for sufficient nutrients and water to be absorbed resulting in diarrhea
116
Constipation
a condition in which there is difficulty in emptying the bowels, usually associated with hardened feces
117
causes of constipation
Slow movement of the contents in the large intestine, colon
Fecal evacuation disorder
Combination (slow movement; inability to evacuate)
118
risk factors for constipation
less exercise, sedentary lifestyle, diseases or disabilities that create immobility
use of medications
119
The longer stool remains in the colon
the more water continues to be absorbed, creating hard stools
120
Potential for total body water and electrolyte loss is
enormous when you have diarrhea and cannot properly absorb water
121
Jejunum Na+
Actively absorbed; absorption enhanced by sugars, amino acids
122
Jejunum K+
Passively absorbed when concentration rises because of water absorption
123
Jejunum Cl- and HCO3
absorbed
124
ileum Na+
Actively absorbed
125
Colon Na+
Actively absorbed
126
ileum K+
Passively absorbed when concentration rises because of water absorption
127
Colon K+
net secretion
128
ileum/ colon Cl-
Absorbed, some in exchange for HCO3-
129
ileum/ colon HCO3-
Secreted, partly in exchange for Cl-
130
Dietary cobalamin (B12) released from food by
pepsin
131
B12 is delivered to
liver and red bone marrow
132
a consequence of a gastrectomy is
the loss of intrinsic factor
133
Intestinal Water Transport if 9 L is ingested each day how?
2 L of water and 5 g of sodium are ingested each day (Diet)
| 7 L of salivary, gastric, pancreatic, biliary and intestinal secretions
134
how much water is absorbed
8.8 L of water and 30 g of sodium are absorbed each day
135
where is water absorbed
7 to 8 L absorbed in small intestine
| 1 to 2 L absorbed in colon
136
how much water is excreted
0.1 to 0.2 L excreted in feces
