Intro to GI Flashcards
1
Q
GI tract
A
- consists of s series of hollow tubes stretching from mouth to anus
- with accessory exocrine glands and organ functions to promote digestion, absorption, and removal of waste products
- motility
- secretion
- absorption
- excretion
- digestion
2
Q
ingestion of food
A
and smell
- initiate the process through an integrated series of endocrine, paracrine, and neural responses
- blood flow increases from vasodilators
- absorbed nutrients initially circulate through liver to be processed before entering systemic circulation
- sedentary adult needs 30kcal/ kg per day
3
Q
upper esophageal sphincter
A
- highest resting pressure
- prevents air from entering the esophagus
- striated muscle
- under control of swallowing center in medulla
- relaxes during swallowing
4
Q
lower esophageal sphincter
A
- separates esophagus and stomach
- smooth muscle that relaxes during swallowing
- coordinates passage of food into the stomach
- prevents reflux
5
Q
pyloric sphincter
A
- separates stomach from duodenum
- regulation of gastric emptying and prevention of duodenal reflux
- reflux can lead to gastritis, ulcer formation, and risk of perf
6
Q
ileocecal sphincter
A
- valve like
- ileum and cecum
- prevents backflux into ileum
- IBS from overgrowth
7
Q
internal and external sphincters
A
-control elimination of waste
8
Q
fluid shifts
A
- 7-9L of fluids secreted per day but absorb most of it to maintain balance
- pH changes needed to promote functions
- ingest 2 L
- only 100-200 ml excreted in feces
9
Q
parietal/oxyntic cells
A
- in oxyntic glands
- acidify contents of stomach
- promote digestion
- breakdown of ingested bacteria and antigens
10
Q
chyme
A
- pH reaches 1-2
- secretion of HCO3 into the lumen of the duodenum by the exocrine pancreas neutralizes the acidic chyme delivered to it
11
Q
enteric nervous system
A
- branch of ANS
- myenteric plexus (motility), b/n longitudinal and circular layers
- submucosal (secretory) b/n circular and submucosal
12
Q
myenteric plexus
A
- between longitudinal and circular muscle
- proximal end of esophagus to rectum
- increases tone in gut
- rhythmic/phasic contractions and velocity of conduction of excitatory waves
13
Q
submucosal plexus
A
- between circular and submucosal
- secretions
- absorption and contraction
14
Q
enteric nervous system 2
A
- can function independently
- responds to input from local environment (chemo, osmo, mechanoreceptors)
- even in absence of extrinsic innervation
- processing sensory signals is primary function
- sensory neurons, interneurons, and motor neurons intrinsic to END connect for efficient bidirectional flow of info
- musculomotor and secretomotor neurons can alter smooth muscle activity, secretion, absorption of fluid or electrolytes by epithelium
- can alter endocrine cells, submucosal blood vessels
- modulated by ANS
15
Q
intrinsic and extrinsic connections in ENS
A
- multiple pre programmed responses, initiated by sensory inputs
- afferent neurons monitor changes in luminal activity
- they activate interneurons, which relay signals that activate efferent secretomotor neurons
- efferent neurons stimulate or inhibit a range of effector cells, including blood vessels, smooth muscle cells, epi cells, enteric endocrine cells
- ANS modifies these responses b/c sensory neurons relay info to CNS and can trigger vagovagal reflexes
16
Q
mechanoreceptors
A
- stretch
- stimulate contractions
17
Q
chemoreceptors
A
- chyme
- regulate motility and secretion of buffers to control luminal pH during influx of acidic chyme into duodenum
18
Q
osmoreceptors
A
- osmolarity of chyme
- only a one cell barrier between chyme and lumen of small intestine and the capillaries
- hypertonic chyme can exert an osmotic force, pull fluid out of the cell
19
Q
para pre gang fibers
A
- vagal and pelvic nerves
- terminate on post gang cholinergic or peptidergic neurons in plexi
- PNS activation leads to increased motility, relaxation of sphincters, enhanced secretions
20
Q
vagovagal reflexes
A
- prominent in coordinating GI function
- long reflexes
- afferent and efferent impulses are carried by neurons in mixed vagus nerve
21
Q
PNS action
A
- increases motility
- vagus is proximal 2/3
- pelvic bottom 1/3
- Ach is major nt
- some have peptides
- increases secretions and relaxes sphincters
- relaxes sphincter of Oddi (cephalic and gastric phases)
22
Q
SNS action
A
- via post gang from celiac plexus, hypogastric, superior and inferior mesenteric ganglia
- norepi is major nt
- relaxes gut wall and reduces contractions and contracts sphincters
- diverts blood flow from GI tract
23
Q
cephalic phase
A
- salivation on seeing, smelling, tasting food
- facial, and IX
24
Q
cephalic and gastric phases
A
- acid production in gastric acid secretion
- pancreatic enzyme secretion
- X
25
Q
intestinal phase
A
- pancreatic enzyme and buffer secretion
- X
26
Q
interstitial cells of cajal
A
- pacemaker cells
- slow spike waves
- spread in three dimensions
- slow waves 5-15 mV
- spike potentials-40 mV, when threshold is reached, triggers phasic contractions
- 10-40 times longer than neural APs
- ca entry through L type channels
- ENS controls distance and direction of spread of electrical activity in muscle with excitatory (Ach) and inhibitory (VIP) motor neurons
- tonic contractions maintain tone
27
Q
slow waves
A
- influenced by hormones, paracrine factors, and ANS
- slow wave freq highest in small intestine, intermediate in the colon and lowest in the stomach
- maximal contractile frequency does not exceed freq of slow waves
- failure of ENS can lead to disordered motility including spasm and abd cramping
28
Q
segmental/mixing/non-propulsive contractions
A
- chyme enters SI
- distends the wall
- elicits local contractions and mixes chyme with intestinal secretions
- contractions are local
- occur in different segments at a freq of 2-3 per minute
- max 12/min
29
Q
peristaltic contractions
A
- move material from mouth to color
- relatively weak and move material through SI at 1 cm/min
- 3-5 hours to move chyme from pylorus to ileocecal valve
- intensified after a meal by stretch of duodenal wall
- gastroenteric reflex enhances
- gastroileal relex triggers opening of ileocecal valve to permit passage from small to large intestine
- then colon distends to close sphincter
- enterogastric reflex decreases mobility and stimulates contraction of pyloric sphincter to inhibit chyme from going to duodenum if its full
30
Q
peristalsis and segmentation
A
- motility in SI under control of the myenteric plexus and consists of peristalsis and segmentation
- segmentation forms pockets of chyme and mixes and propels it
31
Q
myenteric reflex (peristalsis)
A
- contractile ring forms on the orad side of the distended segment and pushes the contents toward the anus (contraction of longitudinal muscle)
- receptive relaxation occurs downstream and aids unidirectional movement
- law of the gut
- propulsive and receiving segment
- reflex control
- circular muscle around bolus, longitudinal muscle farther down
32
Q
neural activity on peristalsis
A
- coordinated excitatory and inhibitory motor neurons in response to distension of the intestinal wall
- afferents from mechano and chemo receptors
- relax in front of bolus, contract behind it
33
Q
physiological ileus
A
- absence of motility in the small and large intestine
- output of a motor program stored in ENS
- normal state
- remains in effect for varying periods of time in different intestinal regions
- inhibitory neurons active and suppress the response of the circular muscle to slow waves
34
Q
pathological ileus
A
- normal periods of not moving are much longer
- inhibitory neurons abnormally active
- cramping pain, nausea, vomiting
- common after operations, anti cholinergic or opiate treatment
35
Q
fasting
A
- long periods of quiescence in conjunction with short rhythmic waves of strong propulsive contractions that pass down the distal stomach and small intestine
- Migrating motor complex (MMC)
- quiescence, little activity, strong activity
36
Q
MMC
A
- sweep stomach and SI of residue
- pyloric sphincter is inhibited and particles larger than 2 mm can pass into the duodenum
- 3 hours after meal and cyclic intervals of 90 min
- begins in the distal 1/3 of the stomach and continues to terminal ileum
- when it doesn’t work, bezoars accumulate and can obstruct lumen
- intrinsic property of the GI tract
- vagotomy reduces activity, so PNS is important
37
Q
motilin
A
- synthesized in duodenal Mo cells, released into circulation and stimulates contractions seen during the active stage
- acts through ENS and ANS
38
Q
deglutition
A
-voluntary movement of food to the pharynx activates swallowing reflexes including a primary peristaltic wave in the esophagus
39
Q
voluntary stage of swallowing
A
- shaping of food into a bolus
- collection on the tongue
- raising of the tongue against the hard palate to create a pressure gradient that pushes the bolus into the pharynx
40
Q
involuntary stage of swallowing
A
- food activates sensory neurons that project via the vagus and IX nerves to the swallowing center in medulla
- efferents back to pharynx, esophagus, and sphincters and stomach causing the soft palate to pull up, epiglottis to close, and relaxation of the UES
- steps 1 and 2 are pharyngeal phase
- swallowing also initiates primary peristaltic wave that propels food through the open UES, closure of the UES, and peristalsis that goes to the LES
- receptive relaxation of the stomach
- that’s esophageal phase^
- secondary wave if needed
41
Q
pharyngeal phase
A
- tactile areas near the pharyngeal opening sent afferents through V and IX to medulla
- activates V, IX, X, XII
- 6 sec
- pharynx and upper 1/3 of esophagus is striated ctrlled by IX and X
- can damage CN, medulla, muscles
42
Q
primary peristalsis
A
- swallowing initiates an intraluminal pressure wave
- receptive relaxation of the stomach
- vasovagal reflex (VIP)
- in stomach receptive relaxation results in an inc in intragastric volume but not pressure
- gradual relaxation of the entire stomach called accommodation
43
Q
gastric accommodation
A
- adaptive relaxation of the fundus in response to gastric filling
- emptying is effected by the contents of the meal- slower after high fat meal, and rapid after liquid
- feedback from duodenum and delays emptying
- small squirts of gastric juices
- chemo and mechano sense whats in the contents
- signals are vagal nerve, secretin, CCK, GIP
44
Q
LES 2
A
- maintains relatively high pressure in the distal 3-5 cm of the esophagus to prevent reflux of stomach contents
- during swallowing, tone relaxes to allow food into the stomach
- achalasia is failure of LES to relax-can’t send signal for receptive relaxation
- GERD when LES tone isn’t maintained
45
Q
proximal gastric resevoir
A
- fundus and 1/3 of body
- continuous contractile tone
- accommodate arrival of a meal
- without increasing pressure
- maintains compressive forces which pushes contents to antral pump reagion
46
Q
distal antral pump
A
- caudal 2/3 of body, antrum, pyloris
- contract phasically
- propels chyme toward the gastroduodenal junction
- 3/min
- propulsive and retropropulsive forces serve to grind the contents
- APs are myogenic
- nt change amplitude of plateau phase of AP and strength of muscle contraction
- PNS inc, SNS dec
- gastric pacemaker
- grinding in antrum
- smaller than 2 mm through pylorus
