Physiology of Gastrointestinal Motility
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Questions and Answers

What distinguishes the proximal stomach from the distal stomach in terms of contraction type?

  • The proximal stomach has peristaltic contractions.
  • The proximal stomach has slow tonic contractions. (correct)
  • Both regions exhibit tonic contractions.
  • The distal stomach has high distensibility.

Which factor influences the rate of gastric emptying the most?

  • The type of liquid consumed.
  • The total volume of the meal.
  • The macronutrient composition of the meal. (correct)
  • The presence of digested solids.

Which hormone is primarily responsible for inhibiting gastric motility upon stimulation by stomach distension?

  • Gastric inhibitory peptide (GIP)
  • Secretin
  • Gastrin (correct)
  • Cholecystokinin (CCK)

Which of the following is TRUE about the gastric emptying of different substances?

<p>Carbohydrates empty faster than proteins. (A)</p> Signup and view all the answers

Which of the following statements regarding the effects of secretin is accurate?

<p>Secretin is secreted by S cells in the duodenum in response to acid. (A)</p> Signup and view all the answers

What primarily regulates the progress of intestinal contents along the small and large intestines?

<p>Enteric nervous system activity (B)</p> Signup and view all the answers

Which motor pattern is mainly responsible for mixing and segmentation in the small intestine during the fed state?

<p>Segmentation (D)</p> Signup and view all the answers

What is the function of the ileocecal valve?

<p>Prevents reflux of colonic contents into the ileum (C)</p> Signup and view all the answers

What stimulates Phase III of the migrating motor complex (MMC)?

<p>Motilin (A)</p> Signup and view all the answers

How do motility patterns and transit times correlate with meal content?

<p>They are directly proportional to caloric content (B)</p> Signup and view all the answers

What primarily triggers peristalsis in the gastrointestinal tract?

<p>Elicited by mechanical distension (D)</p> Signup and view all the answers

Which neurotransmitters are primarily involved in stimulating motility proximal to a food bolus during peristalsis?

<p>Ach and Substance P (D)</p> Signup and view all the answers

What is the primary role of segmentation in the gastrointestinal tract?

<p>Mixing food with digestive secretions (D)</p> Signup and view all the answers

What initiates the basic electrical rhythm (BER) in gastrointestinal smooth muscles?

<p>Influx of Ca+ ions (B)</p> Signup and view all the answers

During fasting, what change occurs in gastrointestinal motility?

<p>Inhibition of peristalsis (D)</p> Signup and view all the answers

Which component of the enteric nervous system is most closely associated with peristalsis?

<p>Myenteric plexus (A)</p> Signup and view all the answers

Which factor does NOT govern gastric emptying?

<p>Hormonal response to stress (B)</p> Signup and view all the answers

How do interstitial cells of Cajal influence gastrointestinal motility?

<p>They generate and regulate the basic electrical rhythm. (C)</p> Signup and view all the answers

What triggers the relaxation of the ileocecal sphincter during digestion?

<p>Ileal distension due to chyme (B)</p> Signup and view all the answers

Which process primarily aids in the movement of contents through the colon?

<p>Haustral shuttling (A)</p> Signup and view all the answers

How does the intrinsic reflex associated with defecation operate in the rectum?

<p>Contracts the rectum due to stretch receptors (D)</p> Signup and view all the answers

What role do the enteric nervous system (ENS) and extrinsic nerves play in gastrointestinal reflexes?

<p>They assist in both reflex and voluntary movements (D)</p> Signup and view all the answers

What occurs during the gastro-ileal reflex in the gastrointestinal tract?

<p>Chyme moves into the ileum and empties it (A)</p> Signup and view all the answers

What is a key function of the motility patterns in the intestines?

<p>Mixing contents with digestive enzymes and juices (D)</p> Signup and view all the answers

During the process of defecation, what is the effect of the extrinsic reflex?

<p>Intensifies peristaltic waves in the colon (B)</p> Signup and view all the answers

In terms of baselines, what is the basic electrical rhythm (BER) frequency of the duodenum?

<p>12/min (A)</p> Signup and view all the answers

What is an essential feature of cecal distension in relation to the ileocecal sphincter?

<p>It causes the sphincter to contract (C)</p> Signup and view all the answers

What is the primary function of the migrating motor complex (MMC)?

<p>Clears stomach contents during fasting periods (B)</p> Signup and view all the answers

Which factors stimulate the release of motilin?

<p>Neural input, fat, and acidic conditions (A)</p> Signup and view all the answers

How do parasympathetics influence motility in the gastrointestinal tract?

<p>Enhance peristalsis (A)</p> Signup and view all the answers

What is the purpose of chewing in the digestive process?

<p>To prepare food for swallowing and enhance enzymatic activity (C)</p> Signup and view all the answers

What role do tonic contractions play in the gastrointestinal tract?

<p>They stabilize sphincters and prevent backflow (B)</p> Signup and view all the answers

What is the average basal electrical rhythm (BER) in the ileum?

<p>8 contractions per minute (A)</p> Signup and view all the answers

What initiates reflex inhibition of chewing muscles?

<p>Pressure against the mouth lining (B)</p> Signup and view all the answers

What is the role of the swallowing center located in the medulla?

<p>Coordinates the muscular contractions for deglutition (B)</p> Signup and view all the answers

Flashcards

Gastrointestinal Motility

The movement of food through the digestive system, crucial for digestion and excretion.

Peristalsis

Wave-like muscle contractions that propel food through the digestive tract.

Segmentation

Mixing contractions that break down food and mix it with digestive juices.

Basic Electrical Rhythm (BER)

Slow, spontaneous electrical signals in smooth muscle cells that initiate contractions.

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Interstitial Cells of Cajal

Specialized cells that generate the basic electrical rhythm.

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Submucosal Plexus

Part of the enteric nervous system; controls secretions.

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Myenteric Plexus

Part of the enteric nervous system; controls peristalsis.

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Gastric Emptying

The rate at which food leaves the stomach.

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Stomach Segments

The stomach is divided into two segments: the proximal orad stomach and the distal caudad stomach. The orad stomach is a reservoir for food and is characterized by slow tonic contractions and high distensibility. The caudad stomach is responsible for grinding solids and exhibits strong peristaltic contractions with lower distensibility.

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Gastric Emptying Determinants

The rate at which food leaves the stomach depends on factors such as the type of food (liquids empty faster than solids), the volume of food, and the tonicity of the food. For example, isotonic saline empties faster than hypotonic or hypertonic saline.

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Gastric Emptying Time

A normal mixed meal (1500 ml) typically takes around 3 hours to empty into the duodenum.

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Emptying Rates: Carbohydrates, Proteins, and Fats

Different food groups empty at different rates. Carbohydrates are emptied fastest, followed by proteins, and then fats.

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Hormonal Control of Gastric Motility

Hormones like secretin, cholecystokinin (CCK), and gastrin regulate gastric emptying. Secretin inhibits gastric motility in response to acid in the duodenum, CCK inhibits gastric motility in response to fats and amino acids, and gastrin promotes gastric emptying in response to stomach distension.

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Duodenum BER

The basic electrical rhythm (BER) in the duodenum is approximately 12 cycles per minute, meaning muscle contractions happen about 12 times a minute.

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Ileum BER

The basic electrical rhythm (BER) slows down to about 8 cycles per minute in the ileum, the last part of the small intestine.

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Parasympathetics & GI Motility

The parasympathetic nervous system increases peristalsis (food movement) and decreases sphincter tone (relaxation of muscle rings), aiding digestion.

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Sympathetics & GI Motility

The sympathetic nervous system, involved in 'fight or flight', decreases peristalsis and increases sphincter tone, slowing digestion.

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Migrating Motor Complex (MMC)

A powerful wave of muscle contractions that sweeps through the digestive tract every 90 minutes, cleaning out any remaining food and debris.

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Motilin: Where?

Motilin, a hormone crucial for the MMC, is secreted by specialized cells (M-cells) in the duodenum and jejunum (the first parts of the small intestine).

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Motilin: Stimuli

Motilin release is triggered by neural input (nerve signals) and the presence of fat and acid in the digestive tract.

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Motilin: Actions

Motilin stimulates gastric and intestinal motility, essentially kickstarting the MMC 'housekeeping' function.

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What does the ileocecal valve prevent?

The ileocecal valve prevents the reflux of colonic contents back into the ileum, maintaining the sterility of the small intestine.

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Small Intestine Motility in Fed State

During digestion, the small intestine primarily engages in segmentation and mixing movements to break down and mix food, with some propulsive movement both forward and backward.

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MMC Phase III

The propulsive phase of the MMC, driven by the hormone motilin, is responsible for the powerful contractions that sweep through the small intestine.

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Colon: Salvage and Reservoir

The colon's main functions are to absorb water and further process waste materials, acting as a reservoir for stool before defecation.

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Small Intestine BER Gradient

The Basic Electrical Rhythm (BER) in the small intestine gradually decreases from the duodenum (12 cycles/min) to the ileum (8 cycles/min).

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Ileocecal Valve Function

The ileocecal valve acts as a sphincter, regulating the flow of chyme from the ileum into the colon. It prevents reflux of cecal contents back into the ileum.

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What triggers ileocecal valve relaxation?

Ileal distension by chyme during a meal relaxes the ileocecal valve, allowing passage of chyme into the colon.

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What triggers ileocecal valve contraction?

Cecal distension, caused by the accumulation of chyme in the cecum, contracts the ileocecal valve, preventing further chyme entry.

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Gastro-ileal reflex

A reflex stimulated by a meal, which empties the ileum by relaxing the ileocecal valve, allowing chyme to move into the colon.

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Haustral Shuttling

Segmental contractions in the colon, creating a slow and erratic movement of chyme through the haustra.

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Defecation Intrinsic Reflex

A short reflex triggered by rectal distension, leading to rectum contraction, internal sphincter relaxation, and external sphincter contraction.

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Defecation Extrinsic Reflex

A long reflex, mediated by parasympathetics, intensifying the intrinsic defecation reflex, promoting stronger peristaltic waves and internal sphincter relaxation.

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Rectal Accommodation

The ability of the rectum to adapt to increasing distension by gradually accommodating more stool

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Why are intestinal motility patterns important?

Motility patterns in the small and large intestines serve not only to propel intestinal contents but also to mix them with digestive juices, and to retain them in a given segment long enough for optimal absorption to occur.

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Study Notes

Physiology of Gastrointestinal Motility

  • Gastrointestinal motility encompasses the movement of food through the digestive tract.
  • Motility aids digestion and excretion.
  • Peristalsis moves food forward, while segmentation mixes it.
  • Basic Electrical Rhythm (BER) governs contraction patterns.
  • Motility changes during fasting.
  • Factors affecting gastric emptying and vomiting are defined.
  • Colon motility's role in stool desiccation and evacuation is described.
  • Intrinsic nerve plexuses and extrinsic nerves control motility.

Objectives

  • List major motility forms in the gastrointestinal tract and their functions in digestion/excretion.
  • Differentiate peristalsis from segmentation.
  • Describe the electrical basis of GI tract contractions and BER's role.
  • Detail how GI motility changes during fasting.
  • Explain how food is swallowed and transferred to the stomach.
  • Identify factors governing gastric emptying and vomiting.
  • Describe how colon motility functions to desiccate and evacuate stool.

Gastrointestinal Physiology: Motility

  • Motility is influenced by external factors and local changes in the digestive tract.
  • Receptors in the digestive tract activate intrinsic/extrinsic nerves and hormones.
  • Intrinsic autonomic nerves and extrinsic autonomic nerves regulate motility.
  • Gastrointestinal hormones further modulate motility.
  • Exocrine gland cells secrete digestive juices.
  • Endocrine gland cells secrete gastrointestinal and pancreatic hormones.

Electrical Activity of GI Smooth Muscles

  • Slow waves (BER) initiate contractions in GI smooth muscles.
  • Depolarization occurs due to Ca2+ influx, followed by K+ efflux.
  • Interstitial cells of Cajal (ICC) act as pacemakers.
  • ICCs generate slow waves that cause smooth muscle cell contractions.
  • The intrinsic system includes the submucosal plexus and myenteric plexus.
  • Submucosal plexus controls secretion; myenteric plexus controls peristalsis.

Electrophysiology of Gastrointestinal Smooth Muscle

  • Basic Electrical Rhythm (BER) is the electrical activity of smooth muscle that underlies the slow, spontaneous, rhythmic contractions of the gut.
  • Spike potentials are superimposed on BER and trigger contractions.
  • Neurotransmitters like acetylcholine and epinephrine can modulate the BER.

Segment - Specific Patterns

Mouth & Esophagus

  • Chewing increases food surface area for enzyme action.
  • Chewing is controlled by nuclei in the brain stem.
  • Chewing reflexes control jaw muscles.
  • Swallowing is a coordinated reflex initiated by the swallowing center in the medulla oblongata.
  • Esophageal pressure changes during swallowing.

Stomach

  • Proximal stomach accommodates food through relaxation.
  • Stomach empties based on food composition; liquids empty faster.
  • The migrating motor complex (MMC) removes undigested material between meals.
  • Gastric motility is influenced by hormones such as gastrin, secretin and CCK.

Hormonal Control of Stomach

  • Hormones like secretin, CCK, gastrin, and GIP regulate stomach motility and secretions.
  • These hormones respond to stimuli like acid, fats, proteins, and distension.
  • These hormones can promote or inhibit stomach motility.

Vomiting

  • Vomiting is a protective reflex triggered by the brain stem.
  • Nausea is often a symptom and feeling of illness or discomfort precedes vomiting.
  • Irritants, drugs and emotions can stimulate vomiting.

Small Intestine

  • Slow waves and peristalsis mix and propel chyme.
  • The migrating motor complex (MMC) removes undigested materials between meals.
  • Motility is controlled by enteric nervous system, hormones, and neural input.

Colon

  • Haustral shuttling mixes and moves intestinal contents. (smooth contractions).
  • Colon is responsible for water resorption; it also stores and compacts fecal material to prepare for elimination.

Rectum & Defecation

  • Intrinsic defecation reflex -- Internal sphincter relaxes when rectal pressure increases and external sphincter is consciously controlled.
  • External sphincter relaxes for defecation (extrinsic reflex; conscious).

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GI Motility Physiology PDF

Description

Explore the fascinating concepts behind gastrointestinal motility in this quiz. Learn about the different movements that aid in digestion and excretion, such as peristalsis and segmentation, and their controlling mechanisms. Delve into how motility is affected by fasting and the role of electrical rhythms in contraction patterns.

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