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Physiology 2 > 2. GI Part 8 > Flashcards

2. GI Part 8 Flashcards

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

A

movement to the small intestine

22
Q

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

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)

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)

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
Q

motility of the small intestine occurs in 2 distinct phases

A
  1. digestive period – food is present in the gut

2. interdigestive period – little food is present in the gut

26
Q

what are the 2 patterns in the digestive period of small intestine motility

A

propulsive pattern

non propulsive pattern

27
Q

describe the propulsive pattern of the digestive period of small intestine motility

A

peristaltic waves

fast aboral migrating contractions
faster in duodenum, medium in jejunum, slow in ileum

28
Q

describe the non propulsive pattern of the digestive period of small intestine movement

A

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
Q

what is the interdigestive period of small intestine motility

A

time in which stomach and small intestine are empty between meals – typically 80-120 minutes

30
Q

what is the motility pattern of the interdigestive period of small intestine motility called and what does it do

A

migrating motoric complex (MMC)

helps push undigested material out of the intestine

control of the bacterial population

31
Q

what are the 3 phases of MMC of the interdigestive period of small intestine motility

A

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
Q

describe the motility pattern of the large intestine

A

mixing activity is prominent in colon of all species

horses and pigs – colonic segmentation more pronounced and results in formation of sacculations (haustra)

33
Q

main motility patterns observed in large intestine

A

peristaltic waves

anti-peristaltic waves – oral migrating contractions that impede movement of ingesta, causing a more intense mixing activity

34
Q

pathologic contractions

A

giant contractions – high amplitude and long lasting contractions

oral migrating – vomiting
aboral migrating – diarrhea

35
Q

describe vomiting

A

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
Q

stimuli of vomiting an be classified according to when/where they originate (3)

A
  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
Q

vomiting sequence of events (6)

A
  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
Q

describe diarrhea

A

diarrhea refers to an increase in the frequency of defecation or fecal volume

this increase is often due to increased water content

39
Q

what does water in the gut result from that can lead to diarrhea

A

ingested water

water secreted by glands of the GI tract

water secreted or lost directly through the mucosal epithelium

40
Q

why does diarrhea occur

A

occurs when there is a mismatch between secretion and absorption of water

41
Q

what are the 2 types of diarrhea

A

malabsorptive diarrhea

secretory diarrhea

42
Q

when does malabsorptive diarrhea occur and what can cause it

A

occurs when absorption is inadequate to recover secreted water

viral, bacterial, protozoan infections

43
Q

what happens to villi in malabsorptive diarrhea and which cells are more affected

A

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
Q

when does secretory diarrhea occur

A

occurs when the rate of intestinal secretion increases and overwhelms the absorptive capacity

45
Q

how can bacteria cause secretory diarrhea

A

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
Q

what are involved in the defecation reflex and what type of msucle are they

A

internal sphincter – smooth muscle

external sphincter – striated muscle

47
Q

what kind of innervation does the internal sphincter have in regards to the defecation reflex

A

both parasympathetic (sacral spinal segment) and sympathetic (lumbar) innervated

48
Q

what do parasympathetic and sympathetic stimulation of the internal sphincter case in regards to the defecation reflex

A

parasympathetic stimulation – relaxation of the sphincter

sympathetic stimulation – constriction of the sphincter

49
Q

which sphincter is normally tonically contracted (continence)

A

internal sphincter

50
Q

what does voluntary constriction of teh external anal sphincter in trained animals do

A

blocks the reflective activation of defecatin

51
Q

describe the recto sphincteric reflex

A

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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