1. FOOD & DIGESTION
DIGESTION

2. Functions of Digestive System
Breaks down food into molecules
Molecules are absorbed into blood and carried throughout the body
Wastes are eliminated from the body

3. VIDEO

4. Parts of the digestive system

6. Task- 2.6
Draw and label the parts of the human digestive system.

7. Parts of the digestive system
Two main parts:
Alimentary canal – continuous coiled hollow tube
Accessory digestive organs

8. Organs of the alimentary canal
Mouth
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
Anus

9. Accessory digestive organs
Salivary glands
Tongue
Gall Bladder
Liver
Pancreas

10. Processes of the Mouth Mastication (chewing) of food
Mixing masticated food with saliva
Initiation of swallowing by the tongue
Allowing for the sense of taste
Slide 14.7
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

11. Saliva Saliva helps break down starch into simple sugars.
It also moistens the food allowing easier passage through the gastrointestinal tract.
Saliva is secreted from glands found under the tongue and at the back of the mouth.
The sight, smell, taste or even the thought of food will start to increase the amount of saliva secreted.

12. Pharynx Function Serves as a passageway for air and food
Food movement is by alternating contractions of the muscle layers (peristalsis)
Epiglottis shuts the air passage while swallowing.

13. Esophagus Runs from pharynx to stomach through the diaphragm
Conducts food by peristalsis (slow rhythmic squeezing)
Passageway for food only (respiratory system branches off after the pharynx)
Slide 14.10
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

14. Stomach Functions Acts as a storage tank for food
Site of food breakdown
Chemical breakdown of protein begins
Delivers chyme (processed food) to the small intestine
Slide 14.18
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

15. Small Intestine The body’s major digestive organ
Site of nutrient absorption into the blood
Duodenum
Attached to the stomach
Curves around the head of the pancreas
Slide 14.21
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

16. Large Intestine
Larger in diameter, but shorter than the small intestine
Frames the internal abdomen
Slide 14.28
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

17. Functions of the Large Intestine
Absorption of water
Eliminates indigestible food from the body as feces
Does not participate in digestion of food
Slide 14.29
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

18. Structures of the Large Intestine
Colon
Rectum
Anus – external
Body opening
Slide 14.30b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

19. Digestion
Process by which the body breaks down food into small nutrient molecules

20. Two Kinds of Digestion
Mechanical
And
Chemical

21. Mechanical Digestion
Foods are physically broken down into smaller pieces.
Begins when you take your first bite of food
Your teeth are the first stage in mechanical digestion

22. Chemical Digestion
Chemicals produced by the body break foods into smaller chemical building blocks.
Begins in the mouth
Accomplished by enzymes

23. What are enzymes?
Catalysts speed up a reaction by providing an alternate path for the reaction(short cut route so that the reaction happens fast)
Enzymes – protein that speeds up chemical reactions in the body.
Enzymes are highly substrate specific.
Names end with an ‘–ase’

25. Our food is made up of: Carbohydrates: Bread, Pasta, Potato
Protein: Meat, Nuts, Lentils
Fats: Butter, Milk
Our body needs to digest them – turn them into a form that can be absorbed into the blood and used by cells. Enzymes make this possible.

26. Look closely at the 3 digestion equations:
Enzymes that work on carbohydrates:
Amylase + Starch Maltose
Enzyme (in pasta, bread (a form of sugar that can be (in saliva) carbohydrate) absorbed by the body )

27. Enzymes that work on Proteins:
Protease + Proteins Amino Acids
Enzyme (eg. In meat, nuts) (the body can absorb (in stomach) them and use them)

28. Enzymes that work on Fats:
Lipase enzyme + Fats Fatty Acids + Glycerol
(secreted by pancreas) (Butter, Milk) (can be absorbed into body)
Enzyme action animation

29. Task-2.8 Complete the table: Sl.No: Name of the enzyme Substrate
Reaction it aids/ function
Found in
Carbohydrase
Amylase
Protease
Lipase
Peptidase
Sucrase
Pepsin
Maltase
lactase

30. What is digestion?
Digestion is the breakdown of large insoluble molecules into smaller soluble molecules which can pass through the wall of the gut into the blood.

31. How does it start?
Well first you chew something with your teeth. Which makes it have a larger surface area, then and enzyme in your saliva called amylase starts breaking the carbohydrate into sugar. The food is then pushed down the oesophagus to the stomach by PERISTALSIS.
What’s that???

32. Peristalsis is the contraction and relaxation of the circular muscles
in the wall of the gut.
When the muscle relaxes
the food drops down and
when it contracts at the
top the food at the
bottom is pushed down

33. The food is then in the
stomach, the food is
churned around by more
waves of peristalsis to make
it into mush, and it mixes
with gastric juice. Gastric
juice contains and enzyme called Protease which breaks down, yup you guessed it, protein, into amino acids.

34. It also contains hydrochloric acid which kill bacteria and makes the optimum PH for this enzyme, meaning it will work at its best at a lower PH. The food is then released a little bit at a time into the duodenum, which is the first part of the small intestine.
The duodenum DOES NOT produce any digestive juices, but has 2 poured into it!
*Did you know the small intestine is 6m long?*
Whoa that’s really long!

35. One of the juices comes from the pancreas
One of the juices comes from the pancreas. Pancreatic juice, It contains carbohydrase, protease and lipase.
What does each one do?
The other digestive juice is call bile. Which is made by the liver and stored in a bag called the gall bladder. It is NOT AN ENZYME, but it neutralises the acid that was added in the stomach. This helps the small intestine work more effectively.

36. Bile also helps emulsify the fats.
What’s emulsify mean?
It means to make the fats into smaller blobs to make their surface area larger. So that the lipase can digest quicker.

37. The food is now a semi-liquid like a smoothie
The food is now a semi-liquid like a smoothie! And it passes into the second part of the small intestine called the ileum.
The walls of the ileum make a digestive juice which contains
carbohydrase, protease and lipase.

38. These enzymes complete the digestion of fats to fatty acids, glycerol, (carbohydrate) to simple sugars and protein to amino acids.
The ileum is specially adapted for absorption, passing digested food into the blood. It is very long to allow time for digestion.It has a very large surface area due to the presence of villi (finger like projections) and microvilli.

39. This allows rapid diffusion of the products of digestion
This allows rapid diffusion of the products of digestion.Since villi walls are only one cell thick, this helps speed up the diffusion.

40. Each Villus has a blood vessel and a lymph vessel to carry the food away.
All the food which cannot be digested ends up in the large intestine. It enters into the colon where most of the water is reabsorbed into the blood. The indigestible remains form a semi solid faeces which is stored in the rectum. Eventually it is passed out the anus.

41. Absorption Occurs after food has been digested.
Process by which nutrient molecules pass through the wall of the digestive system into the blood

42. Summary of the phases of digestion
Ingestion - this is the physical intake of foodstuffs into the gastrointestinal tract.
Digestion - a series of physical and chemical processes which begin in the mouth, but take place mainly in the stomach and small intestine.
Absorption - the passage of the digested food substances across the gastro-intestinal lining, or mucosa, into the blood and lymph.
Elimination - the excretion, or elimination, of those food substances that cannot be digested (such as cellulose) or without any nutritional value in the faeces.

44. Some interesting facts on digestive system
People do not have conscious control over the muscles in the oesophagus. Even if someone is upside down, the food will be passed on to the stomach.
The stomach is an expandable sack made up of three different layers of muscles where the bolus will be churned for a few minutes or up to 2 or 3 hours.
The duodenum is about 25 centimetres long and in the shape of a horse shoe.
Fat can take from 3 to 5 hours to be broken down and absorbed.
Dietary fibre aids peristalsis because it increases the bulk of the bolus or chyme being moved along.
The villi have a surface area of about 30m2, this is equivalent to the size of a tennis court!

45. Task-2.8
Describe step wise the digestion of a chicken sandwich.