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Physiology VI- GI System > GI Intro and Motility > Flashcards

GI Intro and Motility Flashcards

1
Q

Role of stomach?

A
  • Specialized for storage of food and slow contractions to mix food to become chyme
  • Chemical breakfdown of food by acid and enzymes
  • mechanical breakdown via muscular contractions
  • pyloric sphincter regulates release of chyme into small intestine
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2
Q

3 parts of small intestine? Roles

A
  • Duodenum- short, only 1’ in length. At start we have common bile duct where secretions from organs associated with GI tract enter GI tract. Slurry of chyme is met with secretions from common bile duct immediately
  • Jejunum- 8 feet long, majority of absorption occurs here by pancreatic enzyme. Very efficient. Halfway through jejunum, more than half of chyme absorbed
  • Ileum- continues reabsorption of chyme. 10 feet long.
    • terminal part is site of vit b12 absorption and recycline of bile
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3
Q

What is the ileocecal sphincter?

A
  • Spincter from small intestine to large intestine
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4
Q

What role does large intestine play in GI tract?

A
  • Storage and very slow movement of chyme so final reclamation of salt/water can come out of chyme to make feces
  • Does not have brush border
  • consists of- cecum, appendix, colon, rectum, anal canal
  • at end, we have internal and external anal sphincter
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5
Q

What is role of liver in GI tract?

A
  • Secretion of bile
  • storage of nutrients
  • production of cellular fuels
  • plasma proteins
  • clotting factors
  • detoxification
  • phagocytosis
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6
Q

Role of pancreas in GI tract?

A
  • Secretion of buffers and digestive enzymes by exocrine cells
  • secretion of hormones by endocrine cells to regulate digestion
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7
Q

Role of gall bladder?

A

storage and concentration of bile

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8
Q

What digestion begins in the mouth?

A
  • Mechanical digestion occurs through mastication
  • chemical digestion begins on predominant dietary carb (starch), and a small degree on lipids
  • aso secretes saliva so food can be swallowed
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9
Q

Where does skeletal muscle exist in GI tract?

A
  • Mouth
  • Upper esophagus
  • external anal sphincter

Allows voluntary control of both input and output

  • The rest of the GI tract has smooth muscle (longitudinal and circular bands)
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10
Q

What makes up lining of villi?

A
  • Enterocytes- epithelial cells that make up lining of small intestine
  • only one cell thick, very narrow barrier. easy access to blood
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11
Q

What is role of lymph system in GI tract?

A
  • Absorbs fat into system
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12
Q

GI tract is highly _____

A

vascularized

We need lots of nutrients, blood sent here in order to get job done

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13
Q

What are the 2 smooth muscle typs in GI tract? What’s the 3rd one in the stomach as well?

A

Longitudinal (outside) and circular (inside)

Stomach also has oblique layer to twist and mx food

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14
Q

What are the plexi of the GI tract?

A
  • Submucosal plexus- secretions
  • Myenteric plexus- muscle movement

Compose enteric nervous system

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15
Q

What is the enteric nervous system?

A

Composed of myenteric and submucosal plexus

Gi tract can function intrinsically without autonomic input

-Receive signals from luminal receptors (mechanoreceptor, chemoreceptor) can stimulate nerves

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16
Q

What is an ileus?

A

Where area of GI tract is anganglionic and everything stops in that area

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17
Q

What do goblet cells produce?

A

Mucus

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18
Q

How often do intestinal cells turn over? What produces them?

A
  • Each cell only last 3-6 days
  • replaced by cells that differentiate from stem/progenitor cells.
    • migrate up the crypt of lieberkuhn when needed
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19
Q

What circulation encases intestine?

A

Splanchnic

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20
Q

Where does the splanchnic plexus empty into?

A

Portal vein

This is what constitues the first past effect through liver.

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21
Q

What nutrients do not go through first pass effect?

A

Lipids

  • Inside enterocytes, lipids are packaged into chylomicrons, absorbed into lymph, bypassing first pass effect, empties into systemic circulation FIRST and then the lipids go to the liver for processing
  • takes hours to process lipids
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22
Q

Functions of GI tract

A
  • Digestion- enzymes and HCl
  • Endocrine- LOTS of hormones which act on GI tract
  • Elimination- rids body of undigested waste
  • Protection- HCl, IgA, opsonins, and other immune cells
  • Motility- propels and mixes chyme
  • Absorption- of almost everything you eat
  • Secretion- buffers mucus, hormones, enzymes
  • Storage- stomach and colon
23
Q

How much fluid does Gi tract secrete? How much will it absorb?

A
  • Secretes 7-8 L
  • Absorb 9-10L of fluid each day
    • secretions help to lubricate, digest (HCl, enzymes) and buffer (HCO3 buffers the acid) the chyme
24
Q

What are sounds produced by GI tract called?

A

Borborygmi

25
Q

Why does chyme need to be buffered?

A

VERY acidic chyme coming out of pyloric sphincter. Buffers need to immediately neutralize acid so that chyme doesn’t burn a hole thorugh duodenal wall

26
Q

Where is majority of GI fluid absorbed?

A

Small intestine (8500 mL/day)

Colon absorbs only 400 mL/dau

27
Q

What are the changes in pH through Gi tract?

A
  • Stomach acid around 1.5
  • Up to 3 at duodenum
  • Up to 7 by the time chyme at jejunum (only 1’ later)

Important to get pH of chyme up to 7 so that pancreatic enzymes can work!

28
Q

What type of receptors are on enteric nervous system?

A

Lumenal chemo, mechano, and osmoreceptors

29
Q

What is main innervation of GI tract?

A
  • PSNS- mainly vagal to transverse colon, then pelvic to anus
    • think pro-motility want to make you digest, absorb, move chyme
  • SNS- post-ganglionic adrenergic fibers from celica, sup and inf mesenteric and hypogastric plexes
    • think slow- slows activity if running from bear
  • CNS
    • sensory input to CNS provides initial stimulus for salivary and gastric acid secretion. Seeing/smelling food triggers central response
30
Q

What is the MMC?

A
  • Interdigestive state (between eating)
  • Housekeeping movement- sweeps undigested material and bacteria into colon
  • active mid-stomach through the terminal ileum
  • has 4 phases
    • Phase I, II, IV have minor, disregulated contractions. Entire cycle last 75-120 min
    • Phase III is most imporant part of cycle
      • only 10 min
      • series of contractions sweep material lower in the tract
      • Stimulated by hormone motilin that is secreted into blood from M cells of small intestine
  • MMC stops once you start eating
31
Q

What is benefit of MMC?

A

Helps cells last longer

32
Q

What kind of action is swallowing?

A

Both voluntary (skeletal muscle in upper esophagus/pharynx) and involuntary as enteric/ANS takes over

33
Q

What are 2 types of propulsion in esophagus?

A

Primary and secondary peistalsis

34
Q

What is primary peristalsis?

A
  • More about moving food bolus down esophagus
  • Little contraction- controlled by swallowing center in medulla
    • more vagal/PSNS resposne
  • helps contraction move food down
35
Q

What is secondary peristalsis?

A
  • When dry food stuck in esophagus, causes pressure and pain/cramp in esophagus
  • Mediated via enteric nerves (stretch receptors) through myoteric plexus causes secretion of mucus
  • more local through ENS
36
Q

What is achalasia?

A
  • Lack of ENS innervation in lower part of esophagus
  • Don’t sense stretch of dry food bolus, and food gets stuck.
  • Even if food gets down, esophageal sphincter does not realize food is there, doesn’t know to relax, so the food gets stuck in esophagus.
  • Eventually, esophagus can start dilating.
    • very painful
  • Smooth muscle d/o
37
Q

What allows gastic accomodation?

A

Vagus nerve

aka receptive realxation

38
Q

What is gastric accomodation

A
  • Can fill stomach with 1L food before you start feeling full based on intraluminal pressure
  • progressive relaxation/stretch of smooth muscle of stomach in order to allow more food to enter
39
Q

What does a vagotomy do?

A
  • Prevent receptive relaxation to stomach
  • whole principle behind how bariatic sx works
  • feel full quicker
40
Q

Speed of gastric emptying based on what you’re eating?

A
  • Carbs digested very quickly
  • Acidic meal (protein)- medium length
  • Oleate meal (fat)- slow because it goes through special digestive pathway
41
Q

What is synonymous with resting membrane potential in GI tract? How is it different from normal?

A
  • Slow waves (basic electrical rhythm or BER)
  • Undulating electrical rhythm caused by SIP syncytium regulated by K channels and receptor-mediated process
  • Waves do not cause contraction! only depolarization above -40 mV
  • -70-80 mV BER with -40mV being threshold potential
42
Q

What increases depolarization/spike potentials in GI tract? What causes hyperpolarization?

A
  • Depolarization
    • ACh/PSNS
    • Gastrin
    • Serotonin
    • Substance P (tachykinin)
    • stretch
  • Hyperpolarization
    • NE,
    • Sympathetics
    • VIP
    • NO
43
Q

Are slow waves at same rate throughout GI tract?

A

No

Stomach 3 slow waves/min (Q20 SEC squish)

Small intestine 10-12/min (q 5 sec contracting)

44
Q

What causes contraction in smooth muscle?

A
  • AP generated by depolarization of slow waves are caused by entry of Ca into smooth muscle via voltage-gated channels
  • Ca- calmodulin binding and cross-bridge formation
45
Q

What are 2 types of propulsion in small intestine?

A
  • Peristalsis
    • vagus/gastrin/some stimuli goes to enteric nerves.
    • at back of bolus, depolarize slow wave, contracts circular muscle
    • ahead of bolus have VIP motor neuron that relaxes circular muscle ahead of bolus
    • moves chyme but does not move it hugely/efficiently
  • Segmentation
    • more intrinsic control (enteric nerve)
    • pretty effiicient
    • constrict and moves down tract in “paired couplings”
    • mixing and moving
    • makes up more propulsion movement than peristalsis
46
Q

When does gallbladder contract? What causes it?

A
  • Releases bile via contraction as soon as chyme into duodenum
    • bile facilitates lipid absorption
  • Vagal stimulation relaxes sphincter of Oddi (into duodenum) and later in digestion (during intestinal phase) the hormne CCK will stimulate gallbladder contraction
47
Q

What kind of propulsion is in colon?

A

Segmental propulsion

  • NOT segmentation
  • very slow in order to absorb water
  • makes pockets called haustrae (taneia coli contract to form)
  • designed for dehydration of chyme into feces and storage.
  • a couple times of day, have mass movmeents
48
Q

What are mass movements?

A
  • 3-4 times day haustrae relax
  • allow peristaltic movements
  • allows chyme to move forward in colon and down
  • starts collecting in rectum
  • when it gets to rectum, causes rectal stretch and causes rectosphincteric reflex
49
Q

What is rectosphincteric reflex?

A
  • Rectal stretch causes reflex arc to signal urge to defecate
  • enteric nerves relaxing internal anal sphincter
  • voluntary contract external anal sphincter
    • can abate over time, causing relaxation of colon and abating signal and allowing relaxaiton of external anal sphincter
    • if more feces get pushed into colon, then signal will refire again. continue to happen until able to go to bathroom
50
Q

Mass movements coincide with ____

A

feeding

51
Q

What is gastocolic reflex?

A
  • Chyme in stomach stimulates colonic mass movmenet
  • stimulation fo PNS and hormone gastin, are stimulated very early in feeding
  • Vagus and gastin both stimulate depolarization of slow waves in lower GI tract
  • initiates peristaltic-type movement
  • moves chyme out of the lower GI tract and prepares the area for more chyme
  • so, eating helps evacuate the lower GI tract via this reflex
52
Q

What is ileogastric reflex?

A

Slows emptying of chyme into duodenum based on presense of chyme in ileum

53
Q

What is hirschsprung disease?

A
  • Aganglionic area in colon
  • can’t sense need to void
  • colon slowly dilates out (aka megacolon)
  • will cut out part of colon that is aganglionic and reattach
  • will retrain how to defecate

Physiology VI- GI System (1 decks)

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