A secretes bile which helps in emulsification of fats. B is the hepatic portal vein. C (i) Urea. (ii) Urea is formed from the breakdown of excess amino acids in the liver. The amino acids are deaminated and the ammonia produced is converted to urea. D The liver plays an important role in assimilation. It receives nutrients like glucose and amino acids from the hepatic portal vein after digestion and absorption in the small intestine. It converts excess glucose to glycogen for storage. It also converts excess amino acids into urea which is excreted in urine. This prevents toxic build up of ammonia in the body.

1. Nutrition in Humans
From Gums to Bums

2. What did you had for lunch just now?

4. Learning Objectives
1. Describe the functions of main regions of the
alimentary canal and the associated organs:
• Mouth, salivary glands, oesophagus, stomach,
duodenum, pancreas, gall bladder, liver,
ileum, colon, rectum, anus, in relation to ingestion,
digestion, absorption, assimilation and egestion
of food
2. Describe peristalsis in terms of rhythmic wave-like
contractions of the muscles to mix and propel the
contents of the alimentary canal

5. Learning Objectives
3. Describe the functions of enzymes (e.g. amylase,
maltase, protease, lipase) in digestion, listing the
substrates and end-products
4. Describe the structure of a villus and its role,
including the role of capillaries and lacteals
in absorption
5.State the function of the hepatic portal vein as the
transport of blood rich in absorbed nutrients from
the small intestine to the liver

6. 6. State the role of the liver in
• carbohydrate metabolism
• fat digestion
• breakdown of red blood cells
• metabolism of amino acids and the formation of urea
• breakdown of alcohol
7. Describe the effects of excessive consumption of
alcohol: reduced self-control, depressant, effect on
reaction times, damage to liver and social implications

7. Some important words…
Digestion
Ingestion
Assimilation
Egestion
Process whereby food is taken into
the body
Process whereby large, insoluble food
molecules is broken down into
smaller, simpler products
Digested Food substances transport
to liver via the hepatic portal vein
Removal of undigested food from the
body via the anus

8. MicroQuestion
1. Differentiate between egestion and excretion.
Egestion: Removal of undigested food from the body
via the anus
Excretion: The process by which metabolic waste
products and toxic substances are removed from the
body of an organism
Eg: Carbon dioxide, urea, excess water

9. What happens to the food that we
eat?...
1. Ingestion
2. Digestion
3. Absorption
4. Assimilation
5. Egestion

10. Digestion in the MOUTH
Mechanical Digestion
• Food is broken down into
smaller pieces
• Tearing, chewing, slicing , biting
• Makes use of the teeth
• Purpose?:
• Increase the surface area for
enzymes to work on

11. What Organism is this?

12. What Organism is this?

13. What Organism is this?

14. What Organism is this?

15. Did you know that!!??
By looking at the animal’s teeth we can
understand what they feed on

16. Digestion in the MOUTH
Chemical Digestion
• Starch is broken down into
maltose
• By Salivary amylase
• No digestion of proteins and fats
in the mouth
starch  maltose

17. MOUTH  OESOPHAGUS
The Tongue
• Helps to roll the food into a
bolus
• Push it towards the back of
the mouth for swallowing
• Saliva helps to moisten the
food

18. Down the Oesophagus
Peristalsis
• Moves the food down the
oesophagus
• 2 layers of muscles causes
rhythmic, wave-like
contraction
• No enzyme secreted in the
oesophagus

19. Down the Oesophagus
Peristalsis
• Antagonistic muscles work
together to move the food
through the gut
• Circular muscles &
Longitudinal muscles
• Circular muscles contract,
longitudinal muscles relax  push
food forward
• Circular muscles relax, longitudinal
muscles contract lumen widens

20. Digestion in the STOMACH
Chemical Digestion
• Stomach release gastric juices:
i) Hydrochloric acid
ii) Enzyme proteases
• Pepsin
• Rennin (Pure bio)

21. Digestion in the STOMACH
Chemical Digestion
i) Hydrochloric acid
• Stops action of salivary amylase
• Kills harmful microogranisms in food
• Activate pepsin
• pH: 1 – 2 (highly acidic environment)
What prevents the acid from ‘burning’
our stomach walls?

22. Digestion in the STOMACH
Chemical Digestion
ii) Pepsin
• Pepsinogen  Pepsin
(Inactive) (active)
• Catalyses the hydrolysis of proteins
into polypeptides)
Hydrochloric acid

23. Digestion in the STOMACH
Chemical Digestion
iii) Rennin
• A type of enzyme that catalyses
Soluble caseinogen  insoluble casein
• Casein is more easily digested by
pepsin

24. Digestion in the STOMACH
Mechanical Digestion
• Stomach churns and mix the
food (chyme) with the gastric
juices

25. What is going on in
our body when…
‘Heartburn’
Indigestion felt as a burning
sensation in the chest,
caused by acid reflux into
the oesophagus

26. Digestion in the SMALL INTESTINE
Chemical Digestion
Digestive juices are secreted into
the small intestines to complete the
process of digestion
i) Bile (liver)
ii) Pancreatic juice (pancreas)
iii) Intestinal juice (small intestine)

27. Digestion in the SMALL INTESTINE
Chemical Digestion
i) Bile
• Produced in the liver
• Stored in the gal bladder
• Does not contain enzymes
Function:
Breaks up fats  into tiny fat
droplets  to Increase surface area
for lipase action
Emulsification of fats

29. Bile Action
Emulsification of
fats

30. Digestion in the SMALL INTESTINE
Chemical Digestion
ii) Pancreatic juice
• Produced in the pancreas
a. Pancreatic amylase
b. Trypsin
c. Pancreatic lipase
All 3 fluids are alkaline
 Neutralise the acidic chyme
 Suitable pH for the pancreatic
enzymes

31. Digestion in the SMALL INTESTINE
Carbohydrate Digestion:
Starch maltose glucose
Lactose glucose + galactose
Sucrose glucose + fructose
Pancreatic amylase
lactase
sucrase

32. Digestion in the SMALL INTESTINE
Protein Digestion:
Proteins polypeptides
Polypeptides amino acids
trypsin
peptidases

33. Digestion in the SMALL INTESTINE
Fat Digestion:
Fats fatty acids + glycerol
Pancreatic &
intestinal lipases

34. Digestion in the SMALL INTESTINE
Chemical Digestion
ii) Intestinal juice
• Walls of the small intestine
secretes
a. Intestinal amylase
b. Intestinal protease
c. Intestinal lipase
All digestion is completed in the
small intestine nutrients
absorbed by the small intestine

35. • Where do the digested food go to?
Digestion in the SMALL INTESTINE
Glucose
Absorbed into the
blood stream
Amino
acids
Fatty acids

36. Enzymes Actions
Pepsin Protein  polypeptide
Lipase Fats  Glycerol + fatty acids
Amylase Starch  Maltose
Trypsin Polypeptide  Amino Acids
Peptidases Polypeptide  Amino Acids
Sucrase** Sucrose  Glucose + Glucose
Maltase Maltose  Glucose
lactase Lactose  Glucose + Galactose
Amylase Starch  Maltose
Lipase Fats  Glycerol + fatty acids

37. Let Recap!

38. 2(i) Identify three organs that produce enzymes that
digest proteins.
......................................................................................
microQuestion
Stomach, Pancreas, Small intestine

39. • 2(ii) Complete the following table
microQuestion
Nutrients: Enzymes involved: End of product
digestion:
1.Carbohydrates
(starch)
Amylase
2.Protein Protease
3. Fats
maltose
polypeptide
Lipase Glycerol
+
Fatty acids

40. 3. Describe the function of the digestive tract in terms of
digestion of fat.
……….…...…………………………………………………………………………
………………………………………………………………………………………
……………………………………………….
4. If the bile duct is blocked, a man may have difficulty in
the digestion of
A.carbohydrates.
B.fats.
C.proteins.
D. vitamins. ( )
microQuestion
It helps to break down big, insoluble and complex fats
molecules into small, soluble, and diffusible molecules
such as glycerol and fatty acids
B

41. 5.The diagram below shows the human alimentary canal.
A. 1 and 2. B. 2 and 3. C. 1, 2 and 3 D. All the above. ( )
microQuestion
Digestion of
carbohydrates takes
place at parts
B

42. • Soluble food molecules, diffuse though
the intestinal wall into the blood
stream
Absorption in the SMALL INTESTINE
Glucose
Absorbed into the
blood stream
Amino
acids
Fatty acids,
Glycerol

43. Absorption in the SMALL INTESTINE

44. Adaptations of the SMALL INTESTINE
Adaptations of villi Function:
a) inner walls lined with villi
To further increase surface area for absorption of
digested food materials
b) numerous microvilli on the
epithelium
c) one-cell thick wall of
epithelium
Allow efficient diffusion
d) rich network of blood
capillaries & lacteals
Continual transport of digested food substances
maintains the concentration gradient between
the lumen of small intestines and blood capillaries.
??What other cell types you could
find similar types of adaptations??

45. Absorption in the SMALL INTESTINE

46. Absorption in the SMALL INTESTINE
Under the electron
microscope

47. Where are we now??
What’s next?
The Large Intestine

48. • No food digestion occurs here
• Absorption of water & mineral salts
• Compacts solid waste
Absorption in the LARGE INTESTINE

49. What is going on in
our body when…
‘Lactose intolerant’
Body cannot easily digest
lactose, a type of natural
sugar found in milk and
dairy products
Bloating, Cramps, Gas,
Diarrhoea, Vomiting

50. What is going on in
our body when…
‘Diarrhoea’
Condition of having at least
three loose or liquid bowel
Might be due to infection
of the intestine…WHY?
Not enough water is
absorbed by the large
intestine.

51. Definition:
Distribution and use of the
products of digestion as an
energy source and conversion
into other substances required
for growth.
Assimilation in the LIVER

52. Assimilation in the LIVER

53. Assimilation in the LIVER
1. Nutrients
absorbed
through the
villi
2. Blood
capillaries
merges to form
the Hepatic
portal vein
3. Transports
glucose & amino
acid to the liver

54. 8.The diagram shows part of the circulatory system.
After a meal, which blood vessel will contain blood with
the most glucose?
( )
microQuestion
B

55. 9.The diagram below shows a section of the human
alimentary system.
a) Identify structures X, Y and Z.
b) Describe the function of Y
microQuestion
Hepatic arteryHepatic Vein
Hepatic portal
vein

56. Function of the LIVER
1.Metabolism of glucose
• When glucose concentration is high, excess glucose is
converted to glycogen for storage by hormone insulin.
• When glucose concentration is low, glycogen is
converted to glucose for cellular respiration by
hormone glucagon.

57. Function of the LIVER
2. Metabolism of amino acids
• Excess amino acids cannot be stored
• They are converted (deaminated) to urea to be
excreted in the urine through the kidney
urea
urea
urea
urea

58. Function of the LIVER
3. Breakdown of alcohol
• Alcohol is broken down by the enzyme:
• Alcohol dehydrogenase
• Converts Alcohol  acetaldehyde (harmless)
• Acetaldehyde can be broken-down further to
compounds  used in cellular respiration

59. ‘Asian’ Flush
Alcohol Rash/
Flush
• Because 80 per cent Asians have an overactive
alcohol dehydrogenase
• Break down alcohol into acetaldehyde faster up
to 100 times faster.
• Making things worse, most Asians have an
inactive variant of the liver enzyme ALDH2, which
means that acetaldehyde takes much longer to
clear from their blood.

61. Function of the LIVER
4. Iron Storage
• RBC are broken down in the spleen,
Haemoglobin  Transported to liver  broken
down  iron
• Iron is then stored in the liver

62. Function of the LIVER
5. Production of bile (recap)
• Bile pigments are formed from the breakdown of
haemoglobin
• Function of bile?
• Emulsify large fat droplets into smaller ones
• To?....

63. 10.The diagram below shows part of the human
alimentary canal, some blood vessels and the liver.
(a) State the function of A and the fluid which is secreted into
the duodenum.
microQuestion

64. 10.The diagram below shows part of the human
alimentary canal, some blood vessels and the liver.
(b) Name blood vessel B.
microQuestion

65. 10.The diagram below shows part of the human
alimentary canal, some blood vessels and the liver.
(c) (i) Name a metabolic waste product from the liver
(ii) Explain how this metabolic waste product is formed.
microQuestion

66. 10.The diagram below shows part of the human
alimentary canal, some blood vessels and the liver.
(d) Describe the function of liver in assimilation.
microQuestion