Ch 21

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Ch 21
Human Digestive System
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Need to know

• The definition of Autotroph, heterotroph,
  herbivore, carnivore, omnivore and examples of
  each
• Understand the need for digestion and a
  digestive system
• Know the definition of ingestion, digestion,
  absorption, egestion.

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Nutrition
The way an organism obtains and uses its food
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Autotrophic

• Heterotrophic

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Herbivores
Animals that feed only on plants e.g. rabbit

• Carnivores

Animals that feed onother animals e.g. fox
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Omnivores
Animals that feed on plants and animals e.g.
Badger
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Digestion definition The physical and chemical
breakdown of food into soluble particles small
enough to pass into body cells Need for
Digestion To breakdown large food particles until
they are small enough to pass into body cells
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Stages in Human Nutrition
Ingestion
Food is taken into the mouth
Food is broken down into smaller soluble pieces
Digestion
The movement of digested from the alimentary
canal into the blood stream
Absorption
Egestion
Removal of undigested /unabsorbed food as faeces
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• Digestion 1.

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Learning check

• Define
• Autotroph,
• heterotroph,
• Herbivore,
• Carnivore,
• Omnivore Give an examples of each
• Explain (a) the need for digestion
  (b) the need for a digestive system
• Define ingestion,
• digestion,
• absorption,
• egestion

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Need to know

1. The functions of the main parts of the
   alimentary canal and the associated glands
2. Function of teeth .
3. The human dental formula
4. Role of mechanical digestion and peristalsis
5. Details of chemical digestion by one amylase, one
   protease and one lipase .
6. Role of bile salts
7. Symbiotic bacteria functions in the large
   intestine
8. Benefits of fibre

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The Digestive System
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• Diagram label

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Mechanical breakdown of food

• Teeth
• Contractions in stomach wall
• Peristalsis
• Rhythmic muscular contraction and relaxation in
  the wall of the alimentary canal causing the food
  to move along the canal

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The Mouth
Contains a muscular tongue and a set of teeth.
Secretes a juice called saliva from the salivary
glands. Saliva contains water, salts, and the
enzyme Salivary amylase.
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Baby Teeth!

• First set of teeth in humans are milk teeth
• no molars present

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The Mouth Physical Digestion

• Physical digestion by chewing action of teeth
  results in smaller particles of food, easier to
  swallow greater surface area for digestion

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Human Teeth
Incisors Cutting Canines Tearing

Crushing and grinding
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4 types of teeth

• Incisors sharp edges, cuts, slices and bites
• Canines Long and pointed, grip, stab and tear
  food
• Premolars Have cusps they crush and chew food
• Molars- Large teeth at the back also crush and
  chew food

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Human dental Formula
The number of each type of tooth in the upper
jaw one side of the mouth
Incisors
Canines
Pre molars
Molars
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The Mouth Chemical Digestion

• Chemical digestion takes place due to the
  presence of the enzyme salivary amylase
• This is found in saliva which is secreted by 3
  pairs of salivary glands

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Saliva

• Consists of water, salt and Salivary amylase
• The water lubricates the food.
• The salt provides a slightly alkaline medium (pH
  8) which Salivary Amylase works best at
• Salivary Amylase breaks down starch into maltose

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Learning check 1
Name four types of teeth
Write down the human dental formula
State the function of each of the four types of
teeth
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Learning check 2

1. Mechanical breakdown of food involves what 3
   things?
2. Explain how the mouth is involved in Physical
   Digestion
3. Name the 4 types of teeth give their functions.
4. What is the Human dental Formula?
5. Explain how the mouth is involved in Chemical
   Digestion.
6. Define peristalsis.
7. What is saliva?

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Oesophagus
A hollow muscular tube, 25 cm long that connects
the mouth to the anus. The walls of the
Oesophagus secrete mucus and the food is moved by
Peristalsis
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Oesophagus (Food Pipe)
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Stomach

• J shaped muscular bag
• Stores food for about 4 hours
• Chemical Physical digestion takes place in the
  stomach

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Sphincter Muscle Location
Cardiac Sphincter Muscle Circular muscle which
contracts to close entry from oesophagus to
stomach Pyloric Sphincter Muscle Circular muscle
which contracts to close the entry to duodenum
from the stomach. (Open when relaxed )
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Digestion in the Stomach

• Mechanical Digestion Peristalsis physically
  mixes up the food with gastric juices
• Chemical Digestion using
• Gastric Juice containing
• Mucus
• HCL
• Pepsin

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Lining of the Stomach

• The lining of the stomach is very muscular and
  highly folded
• Millions of gastric glands line the stomach
• producing
• gastric juice

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Functions of gastric juice

• Mucus - Lines and protects the stomach wall from
  HCL pepsin
• HCL a. Kills bacteria
• b. Activates pepsin, by lowering
  the pH
• Pepsin - Pepsin is an enzyme produced by the
  cells lining the stomach. Pepsin breaks downs
  protein into peptides

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Hydrochloric acid

• This gives stomach a pH of 1 to 2!
• Very acidic
• This acidity kills many bacteria, loosens fibrous
  and cellular foods,
• activates pepsin and
• denatures amylase from saliva
• too much acid in the stomach leads to heartburn
  can be neutralised with alkalis such as alka
  seltzers or Rennies

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Ulcers

• If gastric juice does manage to digest the
  stomach wall ulcers can result
• If ulcer becomes perforated bacteria could get
  into body and cause death

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Learning check 3

1. What is the Oesophagus?
2. What is involved in Mechanical Digestion in the
   stomach?
3. What is involved in Chemical Digestion in the
   stomach?
4. What is the lining of the stomach made up off?
5. Why are gastric juices made up off?
6. Why is the function of HCL in the stomach?

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Small Intestine

• Muscular tube 5-6m long
• Functions
• Digestion
• Absorption
• Has three parts

1. duodenum
2. jejunum
3. ileum
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Duodenum
25cm muscular tube Most digestion takes place in
the duodenum
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• Food / acid chyme arrives in from the stomach
• This stimulates the production of pancreatic
  juice from the pancreas, bile gall bladder
• Cells that line the duodenum produce
• Digestive juices
• Enzymes
• These all mix together.

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Pancreas

• Lies beneath the stomach
• Produces pancreatic juices which contain
• water
• sodium bicarbonate salt to neutralise chyme from
  the stomach and
• enzymes
• The pancreatic duct leads from the pancreas to
  the duodenum

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Pancreatic Enzymes

• Contain enzymes which break down food
• Pancreatic amylase which converts starch to
  maltose
• Pancreatic lipase which converts lipids to fatty
  acids glycerol
• Pancreatic protease / trypsin which converts
  proteins to peptides

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Bile

• Made in the Liver stored in the gall bladder
• Passes into the duodenum via the bile duct
• It contains
• Sodium bicarbonate neutralises the acid chyme
  from the stomach provides an alkaline
  environment
• Organic salts which emulsifies fats.

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The Ileum - Absorption

• In the duodenum
• Lipids were broken down
• into fatty acids
• Carbohydrates into monosaccharides
• Proteins into amino acids.
• These digested food then pass through the ileum
  wall and are absorbed into the blood and lymph
  systems.

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The lining of the Ileum - Villi
Villi are tiny infoldings in the lining of the
ileum, which consist of smaller infoldings
microvilli Function Increase the surface area
for absorption of digested food.
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• Villi details

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• The products of fat breakdown - Fatty acids and
  Glycerol are reconverted to tiny fat droplets
• They pass into the lymph vessels / Lacteals,
  found inside each villi, which are part of the
  lymphatic system.
• Eventually the return to the bloodstream
• And then to the Liver.

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• Fat digestion absorption
• Absorption 1
• Absorption 2

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• The products of
• Carbohydrates (monosaccharides) and
• Proteins (amino acids) breakdown
• Mineral
• Vitamins
• Pass via the villi from the small intestine to
  the the bloodstream
• They are then carried via the Hepatic portal vein
  to the Liver

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• Digestion 5

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Learning check 4

1. The Small Intestine is made up 3 parts?
2. State two ways in which the small intestine is
   adapted to absorb digested food
3. Cells that line the duodenum produce ?
4. How are the products of fat digestion transported
   away from the small intestine

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The Liver
Digested food material except fats are brought to
the Liver via the Hepatic portal vein. The
Hepatic artery brings oxygenated blood from the
heart. The Hepatic vein brings blood from the
Liver to the heart.
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Functions of the Liver

• Detoxifies the body breaks down poisons such as
  alcohol and drugs
• Breaks down excess amino acids to form urea
• Converts glucose to glycogen for storage
• Converts excess carbohydrate to fat
• Produces Bile
• Stores vitamins (e.g. vit D)
• Stores minerals (e.g. Iron)
• Produces heat to warm
• the blood and the body

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Large Intestine
1m Long
Colon
Caecum
Appendix
Rectum
Anus
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Functions of the Large Intestine Colon

• Reabsorb water mineral salts into the blood
• Symbiotic Bacteria live in the colon
• produce Vitamins B K
• Prevent growth of pathogenic bacteria

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• Digestion 4

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Learning check 4
State two ways in which the small intestine is
adapted to absorb digested food
What are the main functions of the large intestine
How are the products of fat digestion transported
away from the small intestine
Give the function of the liver in digestion
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Fibre
The remaining undigested food eventually passes
into the Large Intestine. Fibre (Roughage)
consists of cellulose from plant cell walls which
humans cannot digest Stimulates peristalsis in
the colon by providing bulk against which muscles
of the gut wall push against. Helps prevent
constipation
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Function unknown in humans
Rectum
Stores faeces bacteria, unabsorbed food, cells
from the intestine wall, bile pigments and mucus
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• Caecum and Appendix are Vestigial organs in
  humans - they have lost their function
• Sometimes bacteria gather and grow in the
  appendix, bacterial waste builds up and causes
  pain if appendix ruptures it can be very serious

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• The capillaries carry the nutrients to the
  hepatic portal vein which takes them to the liver
• The Liver acts like a giant warehouse allowing
  some nutrients out and storing others
• Amino acids cannot be stored in the body so any
  that are not needed are broken down in a process
  called Deamination
• This forms urea which is excreted in urine
• Urea leaves through the Hepatic portal vein along
  with other wastes and goes to the kidneys

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Learning check 3

1. State ONE way in which the small intestine is
   adapted to absorbing digested food
2. How are the products of fat digestion transported
   away from the small intestine?
3. What are the main functions of the large
   intestine?

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Need to know

• Understand the term balanced diet
• Learn the main human food groups
• Understand how variety and moderation are
  important in having a balanced diet
• Draw a human food pyramid
• Relate human diet to age, gender and activity
  level
• Learn the recommended daily servings of each of
  the main food groups

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Balanced Diet
Taking the correct amounts of all the essential
nutrients in the diet
Water
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A Balanced Diet

• Seven components
• Carbohydrate
• Lipid
• Protein
• Minerals
• Vitamins
• Fibre
• Water

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• The amount of food a person requires
• depends on age, activity, gender and
• Health
• Four food groups are
• Cereals breads and potatoes
• Fruit and Vegetables
• Milk cheese and yoghurt
• Meat, fish and poultry

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Build a Food Pyramid
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Food Pyramid
The daily food portions types an average adult
should eat
Very few
6 - 11
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A Balanced Diet
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Learning check

1. Define Balanced diet
2. List the five main food groups
3. Give two general ways to ensure a balanced diet
4. Draw a human food pyramid
5. State the recommended daily average number of
   servings of each food groups

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Three enzymes involved in digestion
Enzymes are biological catalysts
1 Amylase
2 Pepsin
3 Lipase
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Salivary amylase
Digest starch
Role
Production site
Salivary glands
Where it acts
Mouth
pH in mouth
Alkaline, pH 8
Digestion product
Maltose
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Pepsin
Digest protein
Role
Production site
Gastric glands in Stomach wall
Where it acts
Stomach
pH in mouth
Acid, pH 2
Digestion product
Peptides
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Lipase
Digest fat
Role
Production site
Pancreas
Where it acts
Dudenum
pH in mouth
Alkaline, pH 8
Digestion product
Fatty acids Glycerol
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Learning check 4
Explain the benefits of fibre in the diet
Name a protease enzyme
Give the site of action of the protease and state
the pH at this location
What is the product of the action of the protease
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End