Lesson 2
How does food move down
the oesophagus?
Journey of Food
Peristalsis
The muscles in the wall of the canal cause rhythmic, wave-like contractions called Peristalsis. This process can be visualized as a squeezing action, forcing the food along.
Oesophagus
Food moves on to the stomach by peristalsis.
Any Digestion? No digestion
Motility in the oesophagus The canal has layers of muscles in its walls:
Circular muscles
Longitudinal muscles
Peristalsis When the circular muscle
contracts, the longitudinal muscle relaxes causing the
gut wall to constrict thus squeezing and pushing the food forward.
When the longitudinal muscle contracts, the circular muscle relaxes
and the gut dilates becoming wider for food to enter.
Circular muscles above the bolus contracts
Circular muscles below the bolus relaxes
http://www.westga.edu/~lkral/peristalsis/index.html
Digestion in the stomach
Overview
Role of Digestion Mouth & Oesophagus
Gall Bladder &Pancreas
Stomach
Large Intestine & Others Small Intestine
The last lesson
The physical and chemical digestion in the mouth
The structure of oesphagus and stomach The process of peristalsis
How does the giraffe drink?
Giraffe
Tallest animals in the world Range from 3m -5m tall Drinking – Going against gravity?
Your ideas?
Eat and drink in space?
No gravity Eating and drinking –
possible in the absence of gravity?
If yes, Why? If no, Why?
An astronaut eating a piece of Cornflake in space.
Recall….
A closer look
Ss
Today’s lesson
The chemical digestive process in the stomach
Overview
Role of Digestion Mouth & Oesophagus
Gall Bladder &Pancreas
Stomach
Large Intestine & Others Small Intestine
Digestion in the stomach
The stomach is a muscular bag which contracts and relaxes to mix the food.
In here: Digestion
Of only
PROTEINS
Peristalsis revisited
How does peristalsis play a role in the stomach?
Continual contractions & relaxations of stomach wall muscles result in a churning action
Physical digestion Breaks up food particles
↑ SA / V of ingested food Mixes food well with gastric juice
for efficient enzymatic action
Picture from: http://wwwartsci.clarion.edu/biology/bbarnes/digestivesystem/stomach/stomach_peristalsis.gif
Stomach Main function: store
food turn it into liquid (chyme) release it in small quantities at a time to the rest of the gut
Stores food temporarily for 3 to 4 hours.
Contains gastric glands: secrete gastric juice that mixes with food to form chyme Gastric juice:
water + enzymes + hydrochloric acid pH around 2.0
Function of Hydrochloric acid in the stomachFunctions Actions
Digestion
Anti-bacterial
Neutralisation
Optimal pH
Activates the enzymes pepsin
Kills harmful bacteria ingested with food
Neutralizes the alkaline saliva from the mouth (i.e. stops the action of salivary amylase)
Lowers pH to pH 2 at which the gastric enzymes work best
Conversion of inactive form of enzymes to active form
Both enzymes are secreted are produced as inactive form – pepsinogen & prorennin
Why must both enzymes be secreted in theinactive form?
Pepsinogen
Hydrochloric acidProrennin Rennin
PepsinHydrochloric acid
Enzymes (Proteases) in the stomachEnzymes Enzymatic actions
Substrate Product
Pepsin
(Active) Protein Polypeptide
Rennin Soluble milk protein (caseinogen)
Insoluble protein (casein)
What we have learntOesophagus
Narrow, muscular tube
2 layers of muscles
Longitudinal Circular
is a
with
outer inner
Rhythmic, wave-like contractions
Antagonisticwhich are
producing
Peristalsis
Downward movement of food
Stomach
known as
responsible for
into
What we have learntStomach
Distensible, muscular bag
Gastric glands
Gastric juice
HCl Enzymes
Churning action
Physical digestion
Amylase action
Acidic medium
Bacteria
Pepsin Rennin
Proteins
Polypeptides
Caseinogen
Casein
Chemical digestion
Chyme
Pyloric sphincter
Small intestines
Smaller pieces
is a
with which produces
which secrete
containing
resulting in
breaking food intofor effective action by
stops
creates
kills
responsible for
such as
digests
into
activates
converts
into
making up part of
which passes through
into
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