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Physiology > GIT-2 > Flashcards

GIT-2 Flashcards

1
Q

What is motility?

A

The action of the muscles of the GI tract that mix and propel its contents from mouth to anus

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2
Q

What is peristalsis?

A

The involuntary constriction and relaxation of the muscles of the intestine or another canal, creating wavelike movements that push the contents of the canal forward

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3
Q

What is segmentation?

A

Contractions are a common type of mixing motility seen especially in the small intestine-segmental rings of contraction chop and mix the ingests. Alternating contraction and relaxation of the longitudinal muscle in the wall of the gut also provides effective mixing of its contents

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4
Q

Describe the big picture of enteric motility

A

Gastrointestinal (GI) motility focuses on digestive motor function and the transit of ingested material within the GI tract

  • Motility involves the coordination of smooth muscle and nerve function to mix, titrate, and propel products of digestion
  • While the esophagus, stomach, small bowel, and large intestine has its own specialized functions, all work collaboratively to aid in digestion and motility
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5
Q

What are the types of motility patterns?

A

Tonic contractions

Phasic contractions

Depolarization of circular or longitudinal muscle leads to a contraction that alters diameter or length

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6
Q

Define What are tonic contractions?

A

Maintain constant level of contraction without regular relaxation(sustained)

-Lower esophageal, pyloric, Ileocecal, internal anal sphincters

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7
Q

What are phasic contractions?

A
  • Periodic contractions followed by relaxation; seconds

- Esophagus, gastric antrum, small intestine- colicky contractions

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8
Q

Describe in depth what are tonic and phasic contractions

A

The time course of contractions among smooth muscles in the GI tract varies. Some muscles such as those found in the esophagus, small intestines and gastric antrum contract and relax in a matter of seconds (phasic contractions) other smooth muscles as those found in the lower esophageal sphincter, oral stomach, ileocecal and internal anal spchincters show slow sustained contractions that last from minutes to hours. These are called tonic contractions. The type of contraction is governed by the smooth muscle itself or the interstitial cells of Cajal located in them

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9
Q

What are tonic contractions governed by?

A

By smooth muscle itself or the interstitial cells of Cajal located in them

Generate the slow waves, act as intrinsic pacemaker cells for enteric motility

Located mostly between circular and longitudinal muscles, but also within each muscle layer (different subtypes of ICC)

ICCs form and electrical synctium
-electrically coupled by gap junctions to each other, the ENS and to neighboring SM cells, enabling motor coordination

Integrate gut mechanics (stretch) into motility pattern
Bolus/chyme distends the gut, stretching the walls
ICCs are stretch sensitive and their membrane potential in the stretched section becomes more depolarized
when a slow wave passes over this area of sensitized smooth muscle a contraction is more likely, aiding peristalsis and segmental contractions

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10
Q

Do phasic and tonic contractions depend on neural or hormonal input?

A

They don’t. Neurocrines, endocrine and paracrine are important because they modulate them basic contractile activity, so that the amplitude of the contractions of phasic muscle varies and the tone of the tonic muscle increases or decreases

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11
Q

What are some uses of phasic contractions?

A

Peristalsis, segmentation, MMCs

Peristaltic contractions create forward movement

Propulsive segment- relaxation of longitudinal muscle; contraction of circular muscle

Receiving segment- Contraction of longitudinal muscle; inhibition of circular muscle

There are also Segmental contractions: which result in mixing with no net forward movement

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12
Q

What helps the basic processes to occur?

A

Slow waves

Slow waves are oscillating membrane potentials

  • occur spontaneously
  • originate in the interstitialcells of Cajal,(pacemaker for GI smooth muscle)
  • not action potentials
  • Determine pattern of contraction
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13
Q

What helps the basic processes to occur?

A

ICCs cause cyclic opening of Ca2+ channels(depolarization) opening of K+ (repolarization)

  • Depolarization during each slow wave brings the membrane potential of smooth muscle to threshold
  • therefore, increases the probability that action potentials will occur
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14
Q

What helps the basic processes to occur?

A

When the bolus distends the gut, stretching stimulates nerves in the wall of the gut to release neurotransmitters into smooth muscle at the site of distension

Neurotransmitters increase the intracellular Ca++ via voltage gated channels

  • When these channels are activated, rapid transients in membrane potential causing the membrane potential of the section smooth muscle becomes “more depolarized”
  • Each time the peak of the slow waves temporarily become more positive than -40mv, spike potentials appear on those peaks
  • The higher the slow wave potential rises, the greater the frequency of the spike potentials, ranges between 1-10 spikes/seconds
  • Action potentials, produced on top of the background of slow waves, then initiate phasic
  • Results in contractions of the smooth muscle

When a slow wave passes over this area of sensitized smooth muscle, spike potentials form and contraction results

  • The contraction moves around and along the gut in the coordinated manner because the muscle cells are electrically coupled through gap junctions
  • However, sympathetics cause hyperpolarization (down-regulation)
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15
Q

Describe the frequency of slow waves

A
  • Varies along the GI tract but is constant and characteristic for each part of the GI tract
  • is not influenced by neural or hormonal output. In contrast, the frequency of the action
  • Potentials that occur on top of the slow waves is modified by neural and hormonal influences
  • sets the maximum frequency of contractions for each part of the GIbtract.
  • is lowest in the stomach (3 slow waves/min) and highest in the duodenum (12 slow waves/min)
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16
Q

What type of motility pattern is expected to be seen in oral cavity and esophagus?

A

Swallowing, chewing
-primary and secondary peristalsis

  • Role of Sphincters
  • Clinical correlation - GERD(heart burn), Achalsia
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17
Q

What types of motility pattern do you expect to see in the stomach?

A

Peristaltic mixing and propulsion

Fed state:

  • Receptive relaxation
  • Mixing and digestion
  • gastric emptying

Fasting state: MMCs

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18
Q

What types of motility pattern do you expect to see in the small intestine?

A

Mixing and propulsion primarily by segmentation:

  • Segmentation contractions
  • Peristaltic contractions

-Gastroileal reflex

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19
Q

What types of motility pattern do you expect to see in the large intestine?

A

Segmental Mixing ; mass movement for propulsion

  • Role of sphincters
  • Segmentation, mass movements
  • Defecation
  • Reflexes

Clinical correlation

  • Constipation/Diarrhea
  • Hirschsprung disease
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20
Q

Describe the motility of oral cavity

A

The mouth serves as the first site of mechanical and chemical digestion of food

Mastication/chewing:

  • Mixing, reducing particle size and aiding in digestion
  • Controlled by voluntary and involuntary nerves
  • pressure of food in the mouth triggers the chewing
  • Size of the swallowed particle has no effect on the digestive process
  • Mixes the food with saliva
  • Pattern of chewing is based on input from the medulla
  • BUT increases taste pleasure
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21
Q

Describe the stages of esophagus motility

A

Swallowing reflex- coordinated by CN X and X; to/from the medulla

The act of swallowing is coordinated largely initiated voluntarily and becomes involuntary initiated

  1. Voluntary stage- Tongue pushes bolus against soft palate and back of mouth, triggering swallowing reflex
  2. Pharyngeal stage- upper esophageal sphincter relaxes while epiglottis closes to keep swallowed material out of the airways
  3. Esophageal stage- Food moves downward into the esophagus, propelled by peristaltic waves and aided by gravity
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22
Q

What is the effect of the nervous system on esophagus motility?

A

A parasympathetic response involves afferent feedback to the swallowing center followed by efferent response through other nuclei.

  • This coordination allows muscle to be contracted in a proximal-distal manner down the esophagus. (Primary peristaltic wave)
  • The pressure in the thoracic esophagus is below atmospheric and stomach pressure. Therefore, must have sphincters.
  • The upper 1/3 is skeletal muscle, the lower 2/3 is smooth muscle
  • Non-vagal- coordinates the activity of CN V, VII, XII
  • Nucleus Ambiguus- somatic nerves regulate the pharynx and striated areas of the esophagus
  • Dorsal Motor Nucleus- Autonomic nerves, visceral motor type to the smooth muscle of esophagus via ENS
23
Q

Differentiate primary and secondary peristalsis of the esophagus

A

Primary peristalsis
-Once the bolus passes the UES, series of coordinated movement sends a positive pressure wave to propel the bolus into the stomach

  • Contraction occurs proximal to bolus, relaxation caudal to bolus.
  • This propels the bolus to the stomach and opens the LES as it approaches. Gravity accelerates the movement
  • this takes about 6-1 0 seconds
  • Relaxation of LES- mediated by Vagus, nitric oxide and Vasoactive intestinal peptide

Secondary Peristaltic valve

  • IF bolus not propelled to stomach in first wave:
    • Stretch of esophagus by bolus
    • Activated pressure receptors
    • Second peristaltic wave
24
Q

What is GERD?

A
  • Reflux of gastric contents into the lower esophagus
  • Decreased lower esophageal sphincter tone
  • Barium swallow or upper endoscopy with biopsy
25
Q

What is Achalasia?

A
  • Bird beak appearance
  • Failure of smooth muscle fibers to relax especially at LES
  • Lack of peristalsis
26
Q

What are the esophageal motility disorders?

A
  • GERD

- Achalasia

27
Q

Describe the reservoir (receptive relaxation)

A

Gastric motor activity has the components:
Reservoir, mixing and emptying

Reservoir:

When food arrives at the stomach receptive relaxation (vagovagal) and accommodation (Vagus and ENS)

Increases in vol. not increasing pressure until a threshold is reached - Stomach volume may increase from 0.05 to 1.5 L

Weak peristaltic constrictor(mixing) waves from the gastric pacemaker cells (smooth muscle located on greater curve, proximal to middle part) of the stomach

Frequency of slow waves ~3 min

28
Q

Explain the mixing and digestion of in the stomach

A
  1. Propulsion: peristaltic waves move from the fundus toward the pylorous
  2. Grinding: the most vigorous peristalsis and mixing action occur close to the pylorous

The constrictor waves move into the atrium

-more powerful and food trapped near the antrum undergoes grinding

29
Q

Explain the emptying during gastric motility of the stomach

A

Particles greater in size than 2 do not leave the stomach during the immediate post prandial period

Rate of emptying: water > acidic and caloric fluids> fatty foods even slower

What will promote gastric emptying?

Pyloric sphincter

  • Contraction of the antral portion of the stomach leads to closure
  • This keeps the contents within the stomach
  • Small amounts food only are transferred to the duodenum
  1. Retropulsion: the pyloric end of the stomach acts as a pump that delivers small amounts of chyme into the duodenum, simultaneously forcing most of its contained material backward into the stomach
30
Q

What inhibits gastric motility in the stomach?

A
  • Enterogastric nervous reflexes via ENS, Sympathetics and Parasymoathetics
  • Hornonal factors mainly via CCK and Secretin
  • The presence of acid, proteins, fats, hypertonicity and distension of the duodenum all lead to a decrease in gastric motility
31
Q

Explain accommodation as a function of gastric motility

A

The primary function of the upper half of the stomach is to accommodate food from the esophagus. During swallowing, the LES relaxes and allows food to move into the low-pressure area of this stomach. The stomach is prepared for the bolus by relaxing the upper part of the stomach. This relaxation is termed receptive relaxation and is mediated NO and VIP. This is mediated by the vagus nerve and us called the vago -vagal reflex

32
Q

Explain mixing of gastric motility

A

The lower half of the stomach has slow waves. This propagate towards the pylorus. The slow waves move faster than thee food bolus and as such some of the bolus is propelled through the pylorus and some of the food is pushed backward (retropulsion). This thoroughly mixes and breaks up the food. Contents can remain relatively undisturbed for almost an hour or more after eating.

33
Q

Explain the gastric emptying as a function of the stomach

A

Is accomplished by coordinated contractile activity of the stomach, pylorus and proximal small intestine. Emptying is regulated to aid optimal digestion and absorption. Solids empty only after periods when they are reduced in size by the retropulsive activity of the caudal stomach. Only foods smaller than 2 mm are readily emptied into the intestines. Liquids empty almost immediately.

34
Q

Rate if emptying of the stomach depends on…

A

The chemical composition. Isotonic fluids before hypertonic fluids. Carbohydrates then proteins then fats. Inhibition of emptying is regulated by the changes in the duodenum. Presence of acidic chyme of substrate stimulate enterogastric reflexes

35
Q

Describe the fed state/digestive state

A

Migrating motor complex “rumble in my tummy”

  • Intense periodic contractions, few minutes time, and moves from stomach to ileum
  • Every 90 mins (overnight about 6-8 of these complexes)
  • Cleans out gut because it relaxes the pyloric sphincter to empty stomach.
  • Mediaated by Motilin, integrated by ENS
36
Q

What is the migrating motor complex ?

A

A distinct pattern of electrochemical activity observed in gastrointestinal smooth muscle during the periods between meals. It is thought to serve a “housekeeping “ role and sweep residual undefeated material through digestive tube. As studied in dogs and man, the cycle recurs every 1.5 to 2 hours and consists of 4 phases:

  1. A period of smooth muscle quiescence lasting 45 to 60 minutes, during which there are the only rare action potentials and contractions
  2. A period of roughly 30 minutes in which peristaltic contractions occur and progressively increase in frequency. Peristalsis originates in the stomach and propagates through the small intestine
  3. The phase lasting 5 to 15 minutes in which rapid, evenly spaced peristaltic contractions occur. In contrast to the digestive period, the pylorous remains open during these peristaltic contractions, allowing many indigestible materials to pass into the small intestine
  4. A short period of transition between the barrage of contractions in phase 3 and the inactivity of phase 1. An increase in gastric, biliary and pancreatic secretion is also seen in conjunction with motor activity
37
Q

An increase in gastric, biliary and pancreatic secretion is also seen in conjunction with…

A

The motor activity.

These secretions probably aid in the cleansing activity of the migrating motor complex and assist in preventing a buildup of bacterial populations in the proximal segments of the digestive tube

38
Q

The periodic nature of the migratory motor complex …

A

Is thought to be controlled from the CNS and may be implemented in part by the enteric hormone motilin. Like real housekeeping, the migrating motor complex is readily overridden by “more important” and restore a digestive pattern of motility

39
Q

What are the therapeutic and social implications implications of the migrating motor complex?

A

Blood levels of drugs that are differentially absorbed in the stomach and small intestine may very unpredictably depending on whether they are taken during digestive or in digestive phases, when mechanisms of gastric emptying are different - this is reflected in the recommendation accompanying many drugs to ingest before or with meals

Migrating motor complexes can be noisy and are the cause of “growling”. fortunately, you can usually squelch a migrating motor complex by ingesting some food, allowing transition into a quiet, digestive pattern of motility. If food is not available (let’s say you’re undergoing a job interview or waiting in line with your date at a concert), you can explain the phenomenon and gain points for intellect

40
Q

Describe the fed state/digestive phase motility in the small intestines

A

Parasympathetic- increased smooth muscle contraction
Sympathetic- decreased smooth muscle contraction

Slow waves set the BER, at frequency- 12 waves/ minute
Action potentials occur on top leading to contractions

-frequency reduces as you move caudally

Segmentation= primary form of motility, mixes up the chyme, back and forth movement

Peristaltic movement= propels the chyme, coordinated by the enteric nervous system

Gastroileal reflex-

  • Extrinsic ANS, Gastrin
  • Food in the stomach triggers increased peristalsis in the ileum and relaxation of the ilococcal sphincter
  • Move intestinal contents into large intestine
41
Q

What are the villi? What are there purpose?

A

Villi are the tiny finger like projections that line the small intestines to increase the surface area for absorption

Local nervous reflex in response to chyme

Mucosal mucosa- filament of the smooth muscle fiber

Lashing type- mixing
Villus pump- blood flow

42
Q

What are haustra?

A

Sac-like segments, appear after the contractions of the colon

43
Q

What are the Cecum and Proximal colon?

A

Distention of material in ileum relaxes ileocecal sphincter

Distention of cecum with fetal material closes sphincter

44
Q

Define austral shuttling and mass movements

A

Haustral shuttling- mixes the contents (segmentation), intrinsic nerves, slow, bacterial growth

Mass movements- move fecal material dismally for long distances, gastronomic reflex, responds to Gastrin and ENS 1-3 times usually

45
Q

What occurs in the distal colon?

A

Water absorption, fecal material is semisolid, mass movements push it into rectum

46
Q

How much do we defecate?

A

About 150 gm excreted each

100 mls water, 50 g solids

47
Q

Summarize what happens to rectum before defecation

A

Rectum fills with fecal material, rectum contracts, internal anal sphincter relaxes (recto-sphincteric reflex)

  • Urge to defecate is felt hen rectum is 25% filled.
  • External anal sphincter remains closed
  • When convenient-then external is relaxed voluntarily, rectum contracts, Valsalva maneuver increase intra-abdominal pressure
48
Q

How are the internal and external anal sphincters involved in the defecation reflex?

A

Rectum empty: internal sphincter tonically contracted

Rectum fills with feces—> rectosphincteric reflex which causes the internal sphincter relaxes(along with the urge to defecate) prompts the suppression of voluntary contraction of the external sphincter

Internal sphincter regains tone and rectum accommodates to the distension

This leads to rectal wall relaxation- pressure returns to normal

The process starts again and rectum can store large amount of feces

When appropriate defecation takes place

49
Q

Explain the feedforward reflex of motility

A
  1. Gastrocolic reflex- food in stomach increases frequency of massmovements
  2. Colocolic/ duodenocolic- Propels stool caudally by proximal muscle constriction-distension and
  3. Gastroileal reflex - Stomach distension leading to increased ideal peristalsis and relaxation of the ileocecal sphincter, extrinsic ANS, Gastrin
50
Q

Explain the feedback of reflex motility

A
  1. Enterogastric/ileogastric- Distension and irritation of small intestine results in suppression of secretion and motor activity in the stomach
  2. Ileana brake-Lipid in intestines slows gastric motility
  3. Rectocolic- Colonic peristalsis due to stimulation of rectum
51
Q

Summarize the motility reflex

A

Feedforward:
-Gastrocolic- food in stomach increases frequency of mass movements *babies

  • Colocolic/duodenocolic- propels stool caudally by proximal muscle constriction distention and distal distention
  • Gastroileal- stomach distention leading to increased ideal peristalsis and relaxation of the ileocecal sphincter, extrinsic ANS, Gastrin & CCK

Feedback

Enterogastric/ileogastric- distention and irritation of small intestine results in suppression of secretion and motor activity in the stomach ENS and ANS

Ileal brake- lipid in intestines slows gastric motility -GLP-1 and peptide YY

Rectocolic- colonic peristalsis due to stimulation of rectum

52
Q

What are sphincters(specialized skeletal muscles) and segments they separate?

A

Upper esophageal sphincter( UES)- pharynx/upper part of the esophagus

Lower esophageal sphincter(LES)- esophagus/stomach

Pyloric sphincter- stomach/duodenum

Sphincter of Oddi- Common duct/duodenum

Ileocecal- ileum/cecum

Anal- internal & external= rectum/external environment

53
Q

Why is vomitting both good and bad? How does it occur?

A

A wave of reverse peristalsis begins in the small intestine, moving the GI in the orad direction

  • The gastric contents are eventually pushed into the esophagus. If the upper esophageal sphincter remains closed, retching occurs. If the pressure in the esophagus becomes high enough to open the upper esophageal sphincter, vomitting occur
  • The vomitting center in the medulla is stimulated by tickling the back of the throat, gastric distention, and vestibular stimulation (motion sickness)
  • The chemoreceptor trigger zone in the fourth ventricle is activated by emetics, radiation, and vestibular stimulation

Physiology (36 decks)

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