Motility function of the gastrointestinal system
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Motility function of the gastrointestinal system. The 3 major patterns of the digestive tract motility. Peristalsis Rhythmic segmentation Tonic contraction. Usually the stimulus for peristalsis is distention It requires intact enteric nervous system but can

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Motility function of the gastrointestinal system

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Motility function of the gastrointestinal system

Motility function of the gastrointestinal system


Motility function of the gastrointestinal system

The 3 major patterns of the digestive tract motility

  • Peristalsis

  • Rhythmic segmentation

  • Tonic contraction


Motility function of the gastrointestinal system

  • Usually the stimulus for peristalsis is distention

  • It requires intact enteric nervous system but can

  • be modulated by the autonomic nervous system


Motility function of the gastrointestinal system

Esophageal Function

  • Esophagus is a collapsible muscular tube.

  • It transports food to stomach

  • Secretes mucus with no digestive or absorptive function.

Upper oesophageal

sphincter (UES)

  • UES closes in between swallowing to:

  • Prevent esophageal contents reflux

  • into pharynx

  • Prevents air entry into the esophagus

Diaphragm

Lower oesophageal

sphincter (LES)

  • LES:

  • Closed in between swallowing

  • Prevents stomach content reflux into esophagus


Motility function of the gastrointestinal system

Swallowing or Deglutition

  • Swallowing is the movement of food from mouth into the Stomach

  • It is facilitated by secretion of saliva and mucus

  • It involves mouth, pharynx and esophagus

  • It is coordinated by the swallowing center in medulla oblongata and lower pons

  • It involves 3 phases or stages (oral, pharyngeal & esophageal)


Phases of swallowing

Phases of Swallowing

  • Oral phase: Voluntary

    The swallowing starts when the food bolus is forced to the back of the oral cavity and into the pharynx by the movement of the tongue upward and backward against the palate


Phases of swallowing1

Phases of Swallowing

2.Pharyngeal phase (Involuntary)

  • Tongue sweeps backward → bolus into the oro-pharynx

  • Elevation of soft palate and contraction of the upper constrictor muscle of the pharynx to close nasopharynx.

  • Epiglotis and vocal cords

  • shut off the larynx

  • Reflex apnea

  • Relaxation of UES

  • Peristatic contraction begins in the upper constrictor muscle → middle & inferior constrictor muscle


Phases of swallowing2

Phases of Swallowing

3. Esophageal Phase (Involuntary)

  • Begins once the food bolus enters the esophagus

  • Peristalsis pushes the bolus onwards.


Esophageal phase cont

Esophageal Phase cont…

  • At the lower of the oesophagus

    • LES (Cardiac sphincter) relaxes to allow the bolus to enter the stomach

    • It is usually closed to prevent gastric reflux


Motility function of the gastrointestinal system

Functions of the stomach

  • Storage of ingested food until it is emptied into small intestine.

  • Secretion of HCl and enzymes that begin protein digestion.

  • Stomach mixing movements:

  • Ingested food is pulverized and mixed with gastric secretion Chyme

  • Chyme is emptied into the duodenum (gastric emptying)


Motility function of the gastrointestinal system

Stomach Motility Function

  • Four Aspects of Gastric Motility:

    • Gastric Filling

    • Gastric Storage

    • Gastric Mixing

    • Gastric Emptying


Gastric filling and storage

Gastric Filling and storage:

  • The stomach is able to accommodate such a 20-fold change in its volume

  • Question: HOW?

  • Answer: Receptive Relaxation

    • During a meal stomach relaxes slightly with each mouthful RECEPTIVE RELAXATION

    • Receptive relaxation enhances the stomach ability to accommodate with extra volume of food.


Motility function of the gastrointestinal system

Gastric emptying & mixing:

1

1. Peristaltic contraction (PC) originates in the upper fundus → the pyloric sphincter

2. The PC becomes more vigorous as it reaches the antrum.

3

4

2

3. The strong PC propels the chyme forward

4. A small portion of the chyme is pushed through the “partially” open sphincter into the duodenum

5

5. When PC reaches the pyloric sphincter, the sphincter closes tightly → No further emptying

6

  • 6. The chyme that was not delivered in to the duodenum is forced backward into the stomach for further mixing


Regulation of gastric emptying

Regulation of Gastric emptying

Distension of the stomach by the presence of food

Secretion of gastrin and increase parasympathetic impulses

Stimulate contraction of lower esophageal sphincter,

increase motility of the stomach

Relax of the pyloric sphincter

Gastric

emptying


Motility function of the gastrointestinal system

Distension of the duodenum by chyme, fatty acids

Enterogastric reflex

parasympathetic stimulation

Sympathetic stimulation

CCK

Gastric motility

Carbohydrates empty > Proteins > fats

Inhibition of gastric

emptying


Motility function of the gastrointestinal system

Small Intestine

  • Site of digestion and absorption

  • Divided into 3 regions: duodenum, jejunum, ileum

  • Joins the large intestine at ileocecal sphincter

  • Stomach chyme must be transported from duodenum down the full length of the small intestine for digestion and absorption to take place efficiently.

  • Chyme is chopped, churned and mixed with small intestine secretions


Small intestine motility

Small intestine Motility

  • Two types of SI movement

    1. Segmentations

  • Mix contents with the digestive juices and bring the particles of food into contact with the mucosa for absorption

  • They do not push the intestinal contents along the tract.

2. Migrating motility complexes (MMC)

  • It is type of peristalsis

  • It starts in the lower stomach and pushes chyme forward along the small intestine.


Ileocecal sphincter

Ileocecal sphincter

  • Ileocecal juncture prevents contamination of the small intestine by large intestine contents.

  • Normally remain partially closed.

  • After a meal gastroileal reflex intensifies ileum peristalsis and forces chyme into caecum.

  • Gastrin cause sphincter relaxation.

  • When caecum distended the contraction of ileocaecal sphincter intensifies


Motility function of the gastrointestinal system

Large Intestine

Figure 23.29a


Motility function of the gastrointestinal system

Motility of Large Intestine

  • Haustration (segmentation in colon)

    • Slow segmenting movements that move the contents of the colon (occur every 30 min)

    • Controlled by the intrinsic plexuses

    • Stimulated by distension

    • Movement are slow → absorptive and storage functions

  • Mass movements (propulsive movements)

    • ↑↑↑ motility in ascending and transverse colon occurring after a meal

    • Drive the colonic contents to the distal portion of large intestine

    • Triggered by:

    • ─ Gastrocolic and duodenocolic reflexes

    • ─ Irritation

    • ─ Intense parasympathetic stimulation


Defecation reflex

Defecation Reflex

Parasympathetic nerve

Fibers (pelvic nerve)

  • Two anal sphincters:

    • Internal anal sphincter: smooth muscle & NOT under voluntary control.

    • External anal sphincter: striated muscle, under voluntary control & is innervated by the pudendal nerve

Skeletal motor nerve (pudendal nerve)


Defecation reflex1

Defecation Reflex

Mass movement

Rectum is distended

Activation of stretch receptors

Signals to sacral spinal cord

Gives desire to defecate

Through pelvic nerve (parasympthatic),

relaxation of internal anal sphincter

If the conditions are right:

Voluntarily relaxation of external anal sphincter allows defecation.

Otherwise, the reflex subsides until the rectum is filled again


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