1. Motility function of the gastrointestinal system

2. The 3 major patterns of the digestive tract motility
Peristalsis
Rhythmic segmentation
Tonic contraction

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

4. 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

5. 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)

6. 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

7. 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

8. Phases of Swallowing 3. Esophageal Phase (Involuntary)
Begins once the food bolus enters the esophagus
Peristalsis pushes the bolus onwards.

9. 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

10. 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) 10

11. Four Aspects of Gastric Motility:
Stomach Motility Function
Four Aspects of Gastric Motility:
Gastric Filling
Gastric Storage
Gastric Mixing
Gastric Emptying 11

12. 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.

13. 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 13

14. 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

15. Carbohydrates empty > Proteins > fats
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

16. 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

17. 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.

18. 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

19. Large Intestine
Figure 23.29a

20. 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 20

21. Defecation Reflex Two anal sphincters:
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)

22. 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