PHYS20008 Lecture Notes - Lecture 30: Esophagus, Sphincter, Chyme
12 Jun 2018
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Lecture 30
PHYS20008 - HUMAN PHYSIOLOGY
LECTURE 30
DIGESTION 2:UPPER GASTROINTESTINAL SYSTEM
TODAY
•Cephalic phase
•Gastric phase
•Diverse roles of stomach
•Acid production
GASTROINTESTINAL STRUCTURES/FUNCTIONS
•Mouth, Pharynx - chewing, swallowing
•Oesophagus - peristalsis
•Stomach - mixing, digestion, controlled delivery of chyme from
stomach into small intestine
•Small Intestine - digestion, absorption, propulsion
•Large Intestine - reclamation, expulsion
•Digestive System Accessory Organs include:
•Pancreas - digestive enzymes, hormones
•Liver - excretory, digestion, absorption
THE CEPHALIC PHASE
•Digestive reflexes triggered by stimuli received in the brain e.g.
sight, sound smell of food.
•Recall tip: Cephalo means “head”
•Enteric plexus = enteric NS. Signals sent to effector cells, which
affect secretion or motility of chyme within GI tract.
•In the stomach there is mechanical breakdown, whereby the
muscular walls churn the food, and there is also chemical
breakdown, whereby the enzyme pepsin breaks down protein.
•Mechanical and Chemical digestion begins in the mouth
•Mechanical digestion (mastication): Chewing involves slicing,
tearing, grinding and mixing of food by the teeth
•Chemical digestion: Saliva (water, electrolytes, enzymes, and protein)
•softens and lubricates food
•mucus, provides lubrication
•lysozyme, destroys bacteria
•chemical
•amylase, begins carbohydrate digestion
•some lipase, begins fat digestion
•During swallowing, respiration must be inhibited, the glottis and epiglottis must close and the
lower esophageal sphincter relaxes. The upper esophageal sphincter won’t close.
•Lower sphincter is what allows food to move into the stomach.
SWALLOWING REFLEX
•Upper sphincter is keeping oesophagus closed.
•Tongue pushed balls of food to back of throat, triggering the swallowing reels. Epiglottis is closed
off, preventing food from entering trachea, and the upper sphincter relaxes so the food can move
into the oesophagus.
•Diagram on the page below top right.
Lecture 30
PHYS20008 - HUMAN PHYSIOLOGY
PERISTALSIS
•Once we’ve swallowed, a
pressure wave builds at the
top of the oesophagus and moves down.
•Oesophageal intraluminal pressures at different sites
during swallowing.
•After a swallow, the “pressure wave” moves sequentially
down the oesophagus.
•Gastro-oesophageal Sphincter is normally closed to
prevent gastric contents from refluxing into the
oesophagus.
GASTRO-OESOPHAGEAL SPHINCTER
•Separates oesophagus from stomach
•Prevents reflux of stomach contents
•Relaxes to allow entry of food
•Disorders:
•Failure of relaxation-swallowing difficulties
•Ineffectiveness-reflux oesophagitis (heartburn)
THE GASTRIC PHASE
•The stomach has three general functions:
•Storage (and control of exit)
•Protection from both outside environment and itself.
•Acid environment destroys bacteria and other
pathogens.
•Stomach must also protect itself from “auto-
digestion”
•Digestion
•Enzymes
•Acid assists
•The stomach is able to peans as it receives food because
there is lots of loose tissue in the form of rugue, and
increased vagal stimulation during filling of the stomach
decreases the tone of the gastric smooth muscle.
•Broken into 3 sections: Fundus, body and antrum.
•Storage: (Body)
•Digestion: (Mostly Antrum)
Document Summary
Today: cephalic phase, gastric phase, diverse roles of stomach, acid production. The cephalic phase: digestive reflexes triggered by stimuli received in the brain e. g. sight, sound smell of food, recall tip: cephalo means head , enteric plexus = enteric ns. The upper esophageal sphincter won"t close: lower sphincter is what allows food to move into the stomach. Swallowing reflex: upper sphincter is keeping oesophagus closed, tongue pushed balls of food to back of throat, triggering the swallowing reels. Epiglottis is closed off, preventing food from entering trachea, and the upper sphincter relaxes so the food can move into the oesophagus: diagram on the page below top right. Gastro-oesophageal sphincter: separates oesophagus from stomach, prevents reflux of stomach contents, relaxes to allow entry of food, disorders, failure of relaxation-swallowing difficulties, ineffectiveness-reflux oesophagitis (heartburn) Phys20008 - human physiology: mechanical: mixing (peristaltic waves, chemical: enzymes; acid assists, absorption: no food, a few lipid soluble substances eg. alcohol, aspirin.
