Lesson 2 How does food move down the

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 n Food moves on to the stomach by peristalsis. Any Digestion? n No digestion

Motility in the oesophagus n The canal has layers of muscles in its walls: n Circular muscles n Longitudinal muscles

Peristalsis circular muscle contracts, the longitudinal muscle relaxes causing the gut wall to constrict thus n When the squeezing and pushing the food forward. longitudinal muscle contracts, the circular muscle relaxes and the gut dilates becoming wider for n When the 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 Large Intestine & Others Mouth & Oesophagus Gall Bladder &Pancreas Stomach Small Intestine

The last lesson n The physical and chemical digestion in the mouth n The structure of oesphagus and stomach n The process of peristalsis

How does the giraffe drink?

Giraffe n Tallest animals in the world n Range from 3 m -5 m tall n Drinking – Going against gravity? Your ideas?

Eat and drink in space? n No gravity n Eating and drinking – possible in the absence of gravity? n If yes, Why? n 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 Large Intestine & Others Mouth & Oesophagus Gall Bladder &Pancreas Stomach Small Intestine

Digestion in the stomach n The stomach is a muscular bag which contracts and relaxes to mix the food. n In here: n Digestion n Of only PROTEINS

Peristalsis revisited n How does peristalsis play a role in the stomach? n Continual contractions & relaxations of stomach wall muscles result in a churning action n Physical digestion n Breaks up food particles ↑ SA / V of ingested food n Mixes food well with gastric juice for efficient enzymatic action Picture from: http: //wwwartsci. clarion. edu/biology/bbarnes/digestivesystem/stomach_peristalsis. gif

Stomach n Main function: store food turn it into liquid (chyme) release it in small quantities at a time to the rest of the gut n Stores food temporarily for 3 to 4 hours.

n Contains gastric glands: secrete gastric juice that mixes with food to form chyme n Gastric juice: n water + enzymes + hydrochloric acid Ø p. H around 2. 0

Function of Hydrochloric acid in the stomach Functions Actions Digestion Activates the enzymes pepsin Anti-bacterial Kills harmful bacteria ingested with food Neutralisation Neutralizes the alkaline saliva from the mouth (i. e. stops the action of salivary amylase) Optimal p. H Lowers p. H to p. H 2 at which the gastric enzymes work best

Conversion of inactive form of enzymes to active form n Both enzymes are secreted are produced as inactive form – pepsinogen & prorennin Pepsinogen Prorennin Hydrochloric acid Pepsin Hydrochloric acid Rennin Why must both enzymes be secreted in the inactive form?

Enzymes (Proteases) in the stomach Enzymes Enzymatic actions Substrate Rennin Pepsin (Active) Soluble milk protein (caseinogen) Protein Product Insoluble protein (casein) Polypeptide

What we have learnt Oesophagus is a Narrow, muscular tube with 2 layers of muscles outer inner Longitudinal Circular which are Antagonistic producing Rhythmic, wave-like contractions known as Peristalsis responsible for Downward movement of food into Stomach

What we have learnt Stomach is a Distensible, muscular bag with which produces Gastric glands Churning action which secrete resulting in Gastric juice Physical digestion containing HCl activates Enzymes stops Amylase action kills Bacteria breaking food into Smaller pieces responsible for Chemical digestion such as creates Acidic medium for effective action by Pepsin digests Proteins into Polypeptides Rennin Small intestines converts Caseinogen into Pyloric sphincter into Casein making up part of which passes through Chyme