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