Overview of GIT Flashcards
1
Q
what is the main function of GIT?
A
digestion and absorption of nutrients
2
Q
what does the GIT system achieves its function?
A
motility
secretions –> digestive juices to aid in digestion and absorption
digestion –> biochemical break down
absorption –> small absorbable units transferred into the blood or lymph
3
Q
describe the motility process?
A
muscular contraction
propulsive
mixing
4
Q
why is the motility rate regulated?
A
optimize digestion and absorption
5
Q
what is the function of oral cavity?
A
mixing food with saliva to form a bolus
6
Q
describe the canal arrangement of GIT system?
A
mouth
pharynx
esophagus
stomach
small intestine ( duodenum , jejunum, ileum )
large intestine ( cecum , appendix, colon, rectum )
anal canal
7
Q
what is the function oral cavity , teeth, tongue?
A
chewing
moistening
push the bolus backwards
8
Q
what is function of salivary glands?
A
saliva with the enzymes to breakdown carbohydrate
lubricate food in the mouth
9
Q
what is the function of pharynx ?
A
pharyngeal muscles propel food in esophagus
10
Q
what is the function of esophagus?
A
transport of materials to stomach
11
Q
what is the function of stomach?
A
chemical breakdown of materials via acid and enzymes , muscular contractions breakdown food
12
Q
what is the function pancreas?
A
exocrine cells secrete digestive enzymes and endocrine cells secrete hormones
13
Q
what is the function of small intestine?
A
enzymatic digestion
absorption of water, organic substances, ions and vitamins
14
Q
what is the function of large intestine?
A
water absorption
compactions of indigestible material in preparation of elimination
15
Q
what is the function of gall bladder?
A
storage and concentration of bile
16
Q
what is the function of liver?
A
secretion of bile
storage of nutrients
17
Q
what are the layers of GI wall?
A
lumen
mucosa
submucosa
muscularis externa
Serosa
18
Q
what are the 2 layers of muscularis externa?
A
Outer longitudinal muscle
inner circular muscle
19
Q
what is the nervous system of the Gut?
A
Enteric nervous system
20
Q
what does enteric nervous system consist of ?
A
myenteric plexus
submucosal plexus
21
Q
where is the myenteric plexus present?
A
between the longitudinal and circular layer
22
Q
where is the submucosal plexus present?
A
in the submucosa between submucosa and circular layer
23
Q
what does the mucosa consist of?
A
epithelium
lamina propria
muscularis mucosa
24
Q
what is the function of epithelium of mucosa?
A
absorb and secrete
25
what is the function of lamina propria of the mucosa?
contains connective tissue with blood and lymph vessels
26
what is the function of muscularis mucosa of the mucosa?
smooth muscle cell contraction
changes the shape and surface area of the epithelial cell layer
27
what is the function of submucosa?
collagen
elastin
glands
blood vessels
28
what is function of muscularis externa?
inner : circular muscle layer is thick and more densely innervated
outer : longitudinal muscle layer is thin with few nerve fibers
between both we have the myenteric plexus
29
what is the function of submucosal plexus?
control secretion
blood flow
between submucosa and circular muscles
30
what is the other name of submucosal plexus ?
meissners plexus
( submucosal = meissners = secretion )
31
what is the function myenteric plexus?
controls the GIT movement
Generally excitatory
inhibitory at splincters ?
Release VIP ( vasoactive intestinal polypeptide )
Found between circular and longitudinal muscles
32
what is the other name of myenteric plexus?
auerbachs plexus
(myenteric = motility )
33
where does the enteric nervous system of the gut lie?
lies the entire wall of the gut
from esophagus till anus
100 million neurons
Control movement and secretions
34
what are the components of enteric nervous system?
extrinsic --> sympathetic and parasympathetic fibers that connect both myenteric and submucosal plexus
Intrinsic ---> enteric nervous system ---> can function independently but communicates with extrinsic component
35
describe the myenteric plexus?
linear chain of interconnecting neurons
it is concerned mainly with controlling muscles activity along the length of the gut ( M = motility )
36
what does the stimulation of myenteric plexus lead to?
increased muscle tone of the gut wall
increase the intensity of rhythmic contractions
increase the rate of rhythm of contraction
Velocity of conduction of excitatory waves causing rapid peristaltic waves
It is not entirely excitatory some of it is neurons are inhibitory and release vasoactive intestinal polypeptide and inhibit some intestinal sphincters such as pyloric sphincters and sphincter of ileocecal vavle to control emptying of stomach into duodenum and emptying of small intestine
37
what is the function of submucosal plexus?
mainly concerned with controlling function within the inner wall of each minute segment of intestine
many sensory signals originating from gastrointestinal epithelium and are then integrated in the submucosal plexus to control local intestinal secretion and local absorption and local contraction of submucosal muscle
38
what is the cranial division of parasympathetic fibers?
vagus nerve
39
where does the sacral division originate from?
S2 , S3 ,S4 segment of spinal cord
39
what is the sacral division of parasympathetic fibers?
pelvic nerves
40
what does the parasympathetic fibers innervate?
Cranial division --->upper GIT , esophagus , stomach, pancreas, small intestine and ascending colon
Sacral division -----> lower GIT, muscle of external anal canal and transverse and descending and sigmoid colon wall
41
what is the function of parasympathic fibers?
increase activity of enteric nervous system ---> submucosal and myenteric plexus
increase the activity of the enteric nervous system ----> increase the activity of GIT
42
where does the sympathetic fibers originate from?
spinal cord segment T5- L2
43
describe the course of the sympathetic fibers?
preganglionic fibers enter sympathetic chain that lie lateral to the spinal column and many of these fibers then pass through the chains outlying ganglion
like CELIAC ganglia and various mesenteric ganglia , the postganglionic neuron bodies are in these ganglions
then the post ganglionic fibers then spread to all parts of the gut
44
what does the sympathetic nerve endings secrete?
norepinephrine which inhibit smooth muscles and also inhibit the enteric nervous system
45
what is the function of sympathetic fibers?
inhibit the activity of GIT
46
describe the electrical activity of GI smooth muscles
individuals muscle fibers are arranged in bundles
muscle fibers are electrically connected through gap junctions
each muscle layer function as syncytium ( flat sheet contract together )
electrical activity are either in slow waves or SPIKES
slow waves dont create contraction because its not a full action potential it only produce rhythm in the gut
spikes potentials actually cause muscle contraction
action potential strengthen the contraction
47
describe the slow waves?
not action potential
slow undulating changes in the resting membrane potential
intensity varies between 5 and 15 mV
frequency of slow waves is from 3 to 12 per minute
caused by complex interactions between smooth muscle cells and interstitial cells of cajal ( pacemakers for smooth muscle )
48
what initiates the electrical activity and the basic electrical rhythm of GIT?
cells of cajal ---> pacemaker cells
49
how do cells of cajal produce electrical activity and rhythm?
they have unique ion channels that open and produce currents that may generate slow wave activity
slow waves usually do not by themselves cause muscle contraction in most parts of the gastrointestinal tract , they mainly cause appearance of spike potentials
50
what are basic electrical rhythm in different parts of GIT?
stomach - 4/min
duodenum 12/min
distal ileum 8/ min
cecum 2/min
sigmoid 6/min
51
what is the function cells of cajal?
coordinate peristaltic and other motor activity
spike potentials superimposed on BER cause muscle contraction
52
describe spikes?
true action potentials
RMP is -50 to -60 mv
Frequency is 1 and 10 spikes per second
generated by the opening of slow channels that allow the entry of both sodium and calcium
occur when RMPG of GI smooth muscles become more positive than -40 mV
53
what are the 3 types of gi reflexes?
integrated within gut wall enteric nervous system
From the gut to prevertebral sympathetic ganglia and back to GIT
from the GUT to spinal cord / brain stem and back to the GIT
54
what is an example of reflexes integrated within gut wall enteric nervous system?
secretions
peristalsis
mixing contraction
local inhibition
55
what is an example of reflexes from the Gut to the prevertebral sympathetic ganglia and back to the GIT ?
Gastrocolic - evacuation of colon
Enterogastric - inhibit stomach motility and secretion
colonoileal - inhibit emptying of ileum into colon
These reflexes transmit signals long distances to other areas of gastrointestinal tract
56
what is an example of reflex from the gut to spinal cord/brain stem and back to GIT?
gastric motor and secretory activity is controlled by vagus through reflexes from stomach and duodenum to brain stem and back to stomach
pain reflex - inhibition of entire GIT
defecation reflex - travel from colon and rectum to spinal cord and back again to cause colonic , rectal , abdominal contraction for defecation
57
describe the function of Gastrin
stimulated by : protein , distension , nervous system
secreted by G cells of antrum , duodenum and jejunum
Action : increase gastric acid secretion
growth of gastric mucosa
57
what are the 3 types of regulating signals released by GIT?
hormones -- peptide released from endocrine cells of GIT ( Gastrin, CCK, cholecystokinin, secretin, glucose )
Paracrines - peptides secreted by GIT endocrine cells and act locally - Somatostatin
Neurocrines - peptides synthesized in GIT neurons and released following an action potential ( ACH, norepinephrine , VIP , NO )
58
describe the action of CCK ?
stimulated by Fats , protein, acid
Released by I cells of duodenum, jejunum, ileum
actions :
increase Pancreatic enzyme secretion
increase pancreatic bicarbonate secretion
increase gall bladder contraction
increase growth of exocrine pancreas
inhibit gastric emptying
59
describe the action of GIP?
stimulated by fats , protein, carbohydrates
Released by K cells of duodenum and jejunum
Actions
increase insulin release
inhibit gastric acid secretion
60
describe the actions of Secretin?
Stimulated by fats and acid
Released by S cells of duodenum , jejunum, ileum
Action :
increase pepsin secretion
increase pancreatic bicarbonate secretion
increase biliary bicarbonate secretion
increase growth of exocrine pancreas
inhibit gastrin release and gastric acid
61
describe the actions of motilin?
stimulated by Fats, acid , nervous system
Released by M cells of duodenum and jejunum
actions : Increase git motility and intestinal motility
62
describe the actions of ACH?
released by : cholinergic neurons
increase the contraction of smooth muscles wall
increase salivary, gastric ,pancreatic secretions
63
describe the actions of Norepinephrine?
released by adrenergic neurons
increase relaxations of smooth muscles in wall
increased salivary secretions
64
describe the actions of Vasoactive intestinal peptide? ( VIP )
released by neurons of mucosa and smooth muscles
increase relaxations of smooth muscles
increase intestinal and pancreatic secretion
65
describe the actions of GRP?
released by neurons of gastric mucosa
increase gastrin secretions
66
describe the actions of enkephalins?
released by neurons and mucosa and smooth muscles
increase contraction of smooth muscles
decrease intestinal secretions
67
describe the actions of NPY?
released by neurons and mucosa of smooth muscles
relaxations of smooth muscles
Decrease intestinal secretions
68
describe the actions of substance P?
secreted with ACH from cholinergic neurons
contraction of smooth muscles
increase salivary secretions
69
describe propulsive movement?
cause food to move forward along the tract at an appropriate rate to accommodate digestion and absorption
70
what are the 2 types of propulsive movement?
peristalsis
mass movement
71
describe the mixing movement?
to keep the intestinal contents thoroughly mixed at all times
72
what are the 2 types of mixing movement?
segmentations contractions
haustrations
73
what stimulates peristalsis ?
distensions of gut ----> stimulates enteric nervous system and ring is formed
74
describe the process of peristalsis ?
a contractile ring appear around the gut and initiates peristalsis
75
what is necessary for peristalsis to occur?
intact myenteric plexus
76
what law does peristalsis follow?
law of gut - from esophagus all the way to anal directions is the movement of peristalsis
77
describe the mixing movement?
vary in different parts of the gut
in some areas peristaltic contractions cause mixing --> the forward projection is blocked by sphincters so the peristalsis wave only churn contents
in other locations , local constrictive contractions occur every few cms in gut wall and last for 5-30 seconds thus chopping and shearing the content
78
what are the phases of migrating motor complex?
phase 1 -- no spike potentials - no contractions
phase 2 - irregular spike potentials and contractions
phase 3- regular spike potentials and contractions
79
when is migrating motor complex seen?
seen during fasting between periods of digestions
occurs interval of 90 minutes
80
what initiates migrating motor complex?
motilin
81
where do the motor activity migrate to?
motor activity migrates from the stomach to distal ileum
