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Digestion and alimentary canal

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* * P14 The gut Handout C2 the human gut Moving food- peristalsis- VIDEO Feeding ... with HCL Absorption in stomach None major nutrients ... From plants which make ... – PowerPoint PPT presentation

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Title: Digestion and alimentary canal


1
Standard Grade Biology
Topic 3 Animal Survival
2
Animal Survival is divided into
A- The need for food B- Reproduction C- Water and
waste D- Responding to the environment
Colour key
3
Learning Objectives (aims)
1. Explain why food is required by animals
2. Know the chemical elements and simple
structures of carbohydrates, proteins and fats
3. Define digestion and explain why it happens
(absorption and solubility)
4. Know about teeth types in a herbivore,
carnivore and an omnivore
5. Identify the main parts of the mammalian
alimentary canal and know the sites of production
of the digestive juices
4
6. State that different enzymes are responsible
for the breakdown of carbohydrates, proteins and
fats and give specific examples
7. Explain the mechanism of peristalsis
8. Explain how the contractions of the stomach
help in the chemical breakdown of food
9. Explain how the structure of the small
intestine is related to what it does
10. Explain how the structures of a villus are
related to the absorption and transport of food
11. Describe how the large intestine absorbs and
eliminates water
5
Why do we need food?
  • For a source of energy
  • For a source of raw materials for growth /
    repair

Where do we get it from?
  • From plants which make their own food by
    photosynthesis (producers)
  • By eating other plants and animals (food
    chains / webs)

6
What do we need from food?
Food Group containing Elements Made from basic units of Function
Carbohydrates Simple sugars (eg glucose)
Proteins
Fatty acids glycerol Store energy, insulate body, in cell membranes
7
Food Group containing Elements Made from basic units of Function
Carbohydrates Carbon, oxygen hydrogen Simple sugars (eg glucose) Provide energy
Proteins Carbon, oxygen, hydrogen, nitrogen Amino acids Growth and repair
Fats Carbon, oxygen hydrogen Fatty acids glycerol Store energy, insulate body, in cell membranes
8
Food types (groups)
Carbohydrates
Proteins
Long chains made from more than 20 different
amino acids
Fats
Glycerol molecule joined to 3 fatty acids
9
What is in different foods?
Watch and do the activities in the
presentation Digestion and Balanced Diets
10
Food Research
Healthy living websites http//www.eatwell.gov.uk
and http//www.lifebytes.gov.uk
  • Get information on
  • What is 5-a-day?
  • What should you be eating lots of and little
    of?
  • How do different food groups/minerals/vitamins
    help your body?
  • Any other interesting things youve found out?

11
How do we get these things from food?
Through the process of digestion
What is it? The breakdown of large insoluble food
molecules into small, soluble food molecules.
Why? So that they can be absorbed into the blood
stream (through the lining of the small
intestine) for our bodies to use.
12
The gut as a production line
13
Digestion falls into two main types
1. Mechanical breakdown by teeth which is
followed by
2. Chemical breakdown by enzymes
14
Mammalian diets
How could you investigate which foods a certain
animal eats?
Observation (plusses, minuses?)
Collecting, dissecting faeces (plusses, minuses?)
Look at their teeth (plusses, minuses?)
Teeth
15
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16
1. Teeth stuff (mechanical)
17
Herbivores- sheep skull
Male deer
18
Carnivores- note carnassial teeth (specialised
molar)
Tooth from Dire Wolf, N.USA, fossil from last Ice
Age (est 10,000 years old)
19
Omnivores- humans
20
Looking After Your Teeth
Find out what you should do to look after your
teeth. You could try http//www.lifebytes.gov.uk
Find out about nutrition for teenagers,
especially for healthy teeth and bones
  • Note the addresses of any websites you use.
  • You can use written resources (eg. library,
    Home Economics, PSE leaflets, science books).
  • Take short notes

21
2. Chemical breakdown of food
Ingestion Digestion Absorption Egestion
22
The digestive system
23
Salivary glands
mouth
gullet
tongue
windpipe
liver
stomach
Gall bladder Bile duct
pancreas
small intestine
colon
Large intestine
rectum
appendix
anus
24
Peristalsis
Explain the mechanism of peristalsis
Peristalsis is a wave-like motion as muscles
alternately contract and relax, pushing the food
along the tube.
Watch the Feeding Video
25
The Journey So Far
  • The food has been made physically smaller in
    the mouth by chewing and mixed with saliva.
  • Saliva softens and lubricates food. It also
    contains an enzyme (carbohydrase) which starts
    chemically breaking down carbohydrates.
  • The food moves down the oesophagus by
    peristalsis and reaches the stomach, passing
    through a ring of muscle on its way in.

26
Stomach
Explain how the contractions of the stomach help
in the chemical breakdown of food
  • The stomach is a muscular bag which contracts
    in both directions, churning the food.
  • Churning helps to physically break it down and
    also mixes it with gastric juices released by the
    stomach lining.

27
What is happening inside?
  • Gastric juices contain protease enzymes
    (including pepsin) and hydrochloric acid.
  • Enzymes are substances which break down (or
    combine) specific chemicals.
  • Pepsin breaks down proteins.
  • It works best in acidic conditions.
  • Churning and enzyme action continue the
    breakdown of the food that has been eaten.

28
No major nutrients are absorbed in the stomach.
Aspirin and alcohol (small, fat soluble
substances) can pass into bloodstream.
The Next Steps in the Journey
  • Food squirts through the lower ring of muscle
    into the small intestine.
  • This happens each time the stomach relaxes
    between contractions.
  • Nutrients have to be small and soluble so they
    can pass through the wall of the small intestine
    and enter the bloodstream of your body.

29
Further breakdown of food is helped by the
Liver- produces bile which neutralises stomach
acid and enzymes which break down fat (lipases).
Bile is stored in the Gall Bladder and when
released passes through the bile duct into the
small intestine.
Pancreas- produces enzymes which break down all 3
food groups. These pancreatic juices break down
the food in the small intestine.
30
The Small Intestine
Main role is absorption of food nutrients.
Explain how the structure of the small intestine
is related to its function
31
Small Intestine - Structure
Key Points
  • Good blood supply to carry nutrients around
    body
  • Large surface area for digestion and
    absorption as it is folded into villi
  • Villi have finger-like projections
    (microvilli) on them with a thin lining for
    absorption

32
More on breakdown of food
Food contains many large, insoluble molecules.
You have made them a bit smaller mechanically by
  • teeth
  • churning by the stomach

BUT they are still to big and insoluble to pass
into the bloodstream
SO chemicals called enzymes can break them down
into small molecules.
Enzymes are specific and different types break
down each food group
33
What are these enzymes?
The main enzymes in your digestive system are
Enzyme Break down Products
Carbohydrase Carbohydrates Maltose, Glucose
Protease Proteins Amino acids
Lipase Fats and oils Fatty acids Glycerol
The main organs producing enzymes in mammals are
salivary glands, stomach, pancreas, liver, small
intestine
34
Where are they found?
Enzymes are produced in the digestive juices.
  • Carbohydrate (starch) is broken down into
    glucose in the mouth and small intestine

Example of a carbohydrase- salivary amylase in
salivary glands in the mouth
  • Proteins are broken down into amino acids in
    the stomach and small intestine

Example of a protease- pepsin in stomach
  • Fats are broken down into fatty acids and
    glycerol in the small intestine

Example of a lipase- pancreatic lipase in pancreas
35
More about the Small Intestine
36
Small Intestine - digestion
Explain how the structures of a villus, including
the lacteal and blood capillaries, are related to
the absorption and transport of food - collect
handout -
  • Wall of villus is only one cell thick
  • Villus contains a dense network of capillaries
  • Capillaries absorb the products of protein
    digestion (amino acids) and carbohydrate
    digestion (glucose) and carry it round the whole
    body
  • Central lacteal absorbs the products of fat
    digestion (fatty acids and glycerol) and drains
    into lymphatic system, carrying it round the
    whole body

37
Large Intestine
Describe the role of the large intestine in water
absorption and elimination
  • Any food which hasnt already been absorbed
    reaches here (indigestible material)
  • The main function of the large intestine is to
    absorb water and salts
  • The remaining food is temporarily stored in
    the rectum then released through the anus-
    excretion.

38
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