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Physiology 2 > 2. GI Part 8 > Flashcards

2. GI Part 8 Flashcards

(51 cards)

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1
Q

what are the 3 types of GI reflexes essential to GI function

A
  1. reflexes that are integrated entirely within the gut wall
  2. reflexes form the gut to the prevertebral sympathetic ganglia and then back to the GI tract
  3. reflexes form the gut to the spinal cord/brainstem and then back to the GI tract
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2
Q

reflexes that are integrated entirely within the gut wall – what does it do

A

control of GI secretions, peristalsis, formation of mixing contractions, local inhibitory effects

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3
Q

reflexes form the gut to the prevertebral sympathetic ganglia and then back to the GI tract – what do they do

A

transmit signals long distances to other areas of the GI tract

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4
Q

reflexes form the gut to the prevertebral sympathetic ganglia and then back to the GI tract – 3 different types

A
  1. gastrocolic reflex – signals from stomach that cause evacuation of colon
  2. enterogastric reflex – signals from the colon and small intestine inhibit stomach motility and stomach secretion
  3. colonoileal reflex – signals from the colon that inhibit emptying of ileal contents into the colon
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5
Q

reflexes form the gut to the spinal cord/brainstem and then back to the GI tract – 3 different types

A
  1. reflexes from the stomach and duodenum to the brainstem and then back to the stomach to control gastric motor and secretory activity
  2. pain reflexes that cause general inhibition of the entire GI tract –> happens in colic
  3. the defecation reflex which travels from the colon and the rectum to the spinal cord and back again to produce the colonic, rectal, and abdominal contractions required for defecation
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6
Q

describe the peristaltic reflex

A

stretching of the intestinal wall during passage of bolus triggers a reflex that constricts the lumen behind the bolus and dilates the lumen ahead of it

coordination of longitudinal and circular musculature

propulsive movement of the chyme

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7
Q

what muscles are contracted and what muscles are relaxed in the constricted and dilated areas during peristalsis

A

constricted – longitudinal muscle relaxation and circular muscle contraction

dilated – longitudinal msucle contraction and circular msucle relaxation

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8
Q

what does stretch of the intestinal wall stimulate in the peristaltic reflex

A

afferent neurons (mechanoreceptors) –> interneurons –> motor neurons

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9
Q

what is the direction of propulsion in the peristaltic reflex

A

oral to aboral

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10
Q

what neurotransmitters do excitatory motor neurons release and what do they cause

A

release Ach and SP

causes smooth muscle contraction

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11
Q

what neurotransmitters do inhibitory motor neurons release and what do they cause

A

release NO, ATP, VIP

cause smooth msucle relaxation

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12
Q

what does the term vagovagal reflex refer to

A

gastrointestinal tract reflex circuits where afferent and efferent fibers of the vagus nerve coordinate responses to gut stimuli via the dorsal vagal complex in the brain

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13
Q

what stimulates the vagus afferent fibers in the vagovagal reflex

A

stimulation of the mechanical receptors located in the gastric mucosa

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14
Q

what does the vagovagal reflex control

A

motility the gastrointestinal muscle layers in response to distension of the CI tract by chyme like receptive relaxation of the stomach in response to mastication of food and deglutition

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15
Q

describe the distal region of the stomach in terms of motility

A

the gastric pump

grinding and sieving function

breaks solid pieces of food down into particles small enough for small intestine digestion

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16
Q

describe the proximal region of the stomach in terms of motility

A

gastric reservoir

stores and retains food as it awaits eventual entry into the small intestine

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17
Q

what are the 4 main steps of the inflow into the gastric pump

A
  1. gastric reservoir (tonic relaxation and tonic contraction)
  2. a strong peristalsis wave in the corpus
  3. passage into the grinder (mixing and braking down into small particles)
  4. pylorus
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18
Q

motoric of the stomach – gastric reservoir (tonic relaxation and tonic contraction)

A

maintain tone without increasing pressure – allows storage of lots of food

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19
Q

motoric of the stomach – a strong peristalsis wave in the corpus

A

food moves to distal part for mixing and grinding

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20
Q

motoric of the stomach – passage into the grinder (mixing and braking down into small particles)

A

passage into the grinder, might need to be mixed/ground multiple times

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21
Q

motoric of the stomach – pylorus

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A

movement to the small intestine

22
Q

inflow into the gastric pump happens due to the following sequence (4)

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A
  1. tonic contractions of the fundus (gastric store)
  2. strong peristalsis wave in the corpus
  3. passage into the grinder and then into the pylorus
  4. emptying of fluid and predigested particles into the duodenum (fluids empty faster than solids)
23
Q

increased pressure (moderate) after stomach filling induces a reflective relaxation of the stomach (3)

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A
  1. receptive relaxation (vagovagal reflexes) – through mastication and deglutition, mechanical stimulation of the pharynx
  2. adaptive relaxation (gastro-gastric reflexes) – food, expanding stomach
  3. feed back relaxation – nutrients
24
Q

functions of intestinal motility (3)

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A
  1. mixing food with digestive juices (GI secretions)
  2. enhancing contact between intestinal wall and food
  3. peristalsis, the propulsive movement of the chyme to the distal (aboral) direction
25
motility of the small intestine occurs in 2 distinct phases
1. digestive period -- food is present in the gut | 2. interdigestive period -- little food is present in the gut
26
what are the 2 patterns in the digestive period of small intestine motility
propulsive pattern non propulsive pattern
27
describe the propulsive pattern of the digestive period of small intestine motility
peristaltic waves | fast aboral migrating contractions faster in duodenum, medium in jejunum, slow in ileum
28
describe the non propulsive pattern of the digestive period of small intestine movement
segmentation contractions localized contractions of circular msucle small segments of the small intestine contract tightly dividing the gut into 2 segments of constricted and dilates lumen doesn't contribute significantly to the net aboral propulsion of ingesta, but is important when nutrient concentration is high
29
what is the interdigestive period of small intestine motility
time in which stomach and small intestine are empty between meals -- typically 80-120 minutes
30
what is the motility pattern of the interdigestive period of small intestine motility called and what does it do
migrating motoric complex (MMC) helps push undigested material out of the intestine control of the bacterial population
31
what are the 3 phases of MMC of the interdigestive period of small intestine motility
phase 1 -- motoric rest, no contractions (GI all quiet, 60-70 minutes) phase 2 -- intermittent and irregular contractions, sometimes isolated stronger ones (20-30 minutes) phase 3 -- strong peristaltic contractions starting from stomach and migrating distally to reach colon (3-10 minutes)
32
describe the motility pattern of the large intestine
mixing activity is prominent in colon of all species horses and pigs -- colonic segmentation more pronounced and results in formation of sacculations (haustra)
33
main motility patterns observed in large intestine
peristaltic waves anti-peristaltic waves -- oral migrating contractions that impede movement of ingesta, causing a more intense mixing activity
34
pathologic contractions
giant contractions -- high amplitude and long lasting contractions oral migrating -- vomiting aboral migrating -- diarrhea
35
describe vomiting
defense mechanism and important clinical sign activated in order to eliminate gastrointestinal content complex reflex involving many striated muscle groups and other structures outside the GI tract coordinated in the brainstem
36
stimuli of vomiting an be classified according to when/where they originate (3)
1. before food intake -- color, smell, emotions, appearance 2. after food intake (particles in intestinal lumen) -- visceral afferents, vomiting center 3. after absorption (particles in blood) -- drugs, toxins -- stimulate Chemoreceptor trigger zone (CTZ) in the area postrema
37
vomiting sequence of events (6)
1. antiperistaptic wave originates in duodenum (vomiting may contain ingesta of intestinal origin) 2. propulsions of ingesta toward stomach 3. contraction of abdominal musculature increasing the intrabdominal pressure 4. expansion of the chest cavity while the glottis remains closed in order to lower the intrathoracic pressure 5. relaxation of the lower esophageal sphincter 6. opening of the upper esophageal sphincter
38
describe diarrhea
diarrhea refers to an increase in the frequency of defecation or fecal volume this increase is often due to increased water content
39
what does water in the gut result from that can lead to diarrhea
ingested water water secreted by glands of the GI tract water secreted or lost directly through the mucosal epithelium
40
why does diarrhea occur
occurs when there is a mismatch between secretion and absorption of water
41
what are the 2 types of diarrhea
malabsorptive diarrhea secretory diarrhea
42
when does malabsorptive diarrhea occur and what can cause it
occurs when absorption is inadequate to recover secreted water viral, bacterial, protozoan infections
43
what happens to villi in malabsorptive diarrhea and which cells are more affected
destruction of the villi and reduced length of villi shortened villi causes a loss of absorptive intestinal surface area more affected are mature enterocytes that possess the enzymes of the brush border and transport proteins
44
when does secretory diarrhea occur
occurs when the rate of intestinal secretion increases and overwhelms the absorptive capacity
45
how can bacteria cause secretory diarrhea
some pathogenic bacteria produce enterotoxins enterotoxins bind to enterocytes and stimulate adenylyl cyclase activity and cAMP production leads to opening of chloride channels -- water and other electrolytes follow
46
what are involved in the defecation reflex and what type of msucle are they
internal sphincter -- smooth muscle external sphincter -- striated muscle
47
what kind of innervation does the internal sphincter have in regards to the defecation reflex
both parasympathetic (sacral spinal segment) and sympathetic (lumbar) innervated
48
what do parasympathetic and sympathetic stimulation of the internal sphincter case in regards to the defecation reflex
parasympathetic stimulation -- relaxation of the sphincter sympathetic stimulation -- constriction of the sphincter
49
which sphincter is normally tonically contracted (continence)
internal sphincter
50
what does voluntary constriction of teh external anal sphincter in trained animals do
blocks the reflective activation of defecatin
51
describe the recto sphincteric reflex
feces accumulate in the rectum (reservoir) peristaltic movement of feces into the rectum and relaxation of the internal anal sphincter urge to defecate -- contraction of descending colon and rectum as well as increase of intraabdominal pressure

Physiology 2 (11 decks)

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