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Physiology Unit 6 > Intro to GI > Flashcards

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
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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
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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
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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
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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
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6
Q

ileocecal sphincter

A
  • valve like
  • ileum and cecum
  • prevents backflux into ileum
  • IBS from overgrowth
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7
Q

internal and external sphincters

A

-control elimination of waste

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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
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9
Q

parietal/oxyntic cells

A
  • in oxyntic glands
  • acidify contents of stomach
  • promote digestion
  • breakdown of ingested bacteria and antigens
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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

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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
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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
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13
Q

submucosal plexus

A
  • between circular and submucosal
  • secretions
  • absorption and contraction
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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
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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
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16
Q

mechanoreceptors

A
  • stretch

- stimulate contractions

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17
Q

chemoreceptors

A
  • chyme

- regulate motility and secretion of buffers to control luminal pH during influx of acidic chyme into duodenum

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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
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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

Physiology Unit 6 (12 decks)

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