Motility function Motility function of the of the

gastrointestinal gastrointestinal systemsystem

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The 3 major patterns of the digestive tract motility

1. Peristalsis2. Rhythmic segmentation3. Tonic contraction

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• Usually the stimulus for peristalsis is distention• It requires intact enteric nervous system but can be modulated by the autonomic nervous system

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Esophageal Function Esophagus is a collapsible muscular tube. It transports food to stomachSecretes mucus with no digestive or absorptive function.

Upper oesophageal sphincter (UES)

Lower oesophageal sphincter (LES)

Diaphragm

* UES closes in between swallowing to:– Prevent esophageal contents reflux into pharynx–Prevents air entry into the esophagus

LES :–Closed in between swallowing–Prevents stomach content reflux into esophagus

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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 ponsIt involves 3 phases or stages (oral,

pharyngeal & esophageal)

Swallowing or Deglutition

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Phases of SwallowingPhases of Swallowing1. Oral phase:

VoluntaryThe 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

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2. Pharyngeal phase (Involuntary)Phases of SwallowingPhases of Swallowing

• 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

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3. Esophageal Phase (Involuntary)3. Esophageal Phase (Involuntary) Begins once the food bolus enters Begins once the food bolus enters

the esophagusthe esophagus Peristalsis pushes the bolus onwards.Peristalsis pushes the bolus onwards.

Phases of SwallowingPhases of Swallowing

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Esophageal Phase contEsophageal 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

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Functions of the stomach1. Storage of ingested food until

it is emptied into small intestine.

2. Secretion of HCl and enzymes that begin protein digestion.

3. Stomach mixing movements:─ Ingested food is pulverized and

mixed with gastric secretion Chyme

─ Chyme is emptied into the duodenum (gastric emptying)

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Stomach Motility Function Four Aspects of Gastric Motility:

Gastric Filling

Gastric Storage

Gastric Mixing

Gastric Emptying

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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.

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

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

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3. The strong PC propels the chyme forward4. A small portion of the chyme is pushed through the “partially” open sphincter into the duodenum

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

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

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Gastric emptying & mixing:

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Regulation of Gastric Regulation of Gastric emptyingemptying

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

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Distension of the duodenum by chyme, fatty acids

parasympathetic stimulation

Sympathetic stimulation

CCK

Gastric motility

Inhibition of gastric emptying

Enterogastric reflex

Carbohydrates empty > Proteins > fats

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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

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Small intestine Motility Two types of SI movement1. 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.

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Ileocecal sphincterIleocecal sphincterIleocecal 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

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Figure 23.29a

Large Intestine

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Motility of Large Intestine1. 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

2. 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

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Defecation ReflexParasympathetic nerveFibers (pelvic nerve)

Skeletal motor nerve (pudendal 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

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Mass movement

Rectum is distended

Activation of stretch receptors

Signals to sacral spinal cordGives desire to defecate

Through pelvic nerve (parasympthatic) ,relaxation of internal anal sphincter

Defecation Reflex

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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