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Chapter 33: The human digestive system


Chapter 33: The human digestive system Leaving Certificate Biology Higher Level Macrostructure of Digestive System Rectum: Stores faeces as it arrives from the colon ... – PowerPoint PPT presentation

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Title: Chapter 33: The human digestive system

Chapter 33 The human digestive system
  • Leaving Certificate Biology
  • Higher Level

  • Autotrophic
  • Green plants use light
  • Some photosynthetic bacteria use light
  • Some chemosynthetic bacteria use chemicals
  • Heterotrophic
  • Organisms that have to obtain their energy from
    preformed food in the environment (animals
    fungi most bacteria)

Heterotrophic Nutrition
  • Omnivore
  • Eat both plant and animal material e.g. human,
    bears, badgers
  • Carnivore
  • Eat only animal material e.g. dogs, cats
  • Herbivore
  • Eat only plant material e.g. cattle, sheep

Human Nutrition
  • Digestion is the physical and chemical breakdown
    of food into its constituent molecules so that
    they can pass into cells
  • Need for digestion in heterotrophs they acquire
    preformed food from environment. Preformed food
    particles, such as carbohydrate, protein, and
    fats are too big to pass directly into the bodys
    cells and so must be broken down into smallest
    possible particles in order to travel across cell

Digestion and Digestive System
  • Need for digestion and digestive system
  • Digestion heterotrophs acquire preformed food
    from environment, such as carbohydrate, protein,
    and fat particles that are too big to pass
    directly into the bodys cells and so must be
    broken down into smallest possible particles in
    order to travel across cell membranes
  • Digestive system heterotrophs have sophisticated
    digestive systems that break down food particles
    and are designed to extract all the nutrients
    from ingested food and transport them into the
    bloodstream, while at the same time ensuring that
    microorganisms are killed and do not infect the

Human Nutrition
  • Ingestion taking in of food into the mouth
  • Digestion physical and chemical breakdown of
    food particles into their constituent molecules
  • Absorption constituent molecules of the food are
    absorbed into cells that line the digestive tract
    and transported into the bloodstream for
    transport to the liver via the hepatic portal
  • Egestion removal of undigested and unabsorbed
    material from the digestive system

Digestive System Anatomy
Macrostructure of Digestive System
  • Mouth
  • Physical/mechanical (teeth) digestion of food
  • Teeth
  • Human dental formula 2(I2/2 C1/1 PM2/2 M3/3)
  • Incisors (8 in total) cutting food
  • Canines (4 in total) tearing food
  • Premolars (8in total) grinding/crushing food
  • Molars (12 in total) grinding/crushing food
  • Chemical digestion of food salivary glands
    secrete amylase which has an optimal pH of 7
  • Starch Amylase pH7 ? Maltose Amylase
  • Mouths forms a bolus of food that is then

Dental Decay
  • Dental decay is the destruction of tooth structure

Dental Decay
  • Symptoms
  • Small holes (caries and/or cavities) appear in
    the teeth especially in areas that are
    difficult to clean with a tooth brush such as the
    grooved surfaces of the premolars and molars and
    between the teeth
  • Toothache only occurs when the cavity has
    reached the dentine and pulp areas of the tooth
    where a bacterial infection of the tooth occurs
    and the tooth has to be removed

Dental Decay
  • Cause
  • occurs when foods containing carbohydrates
    (sugars and starches) such as breads, cereals,
    milk, fizzy drinks, fruits, cakes, sweets are
    left on the teeth
  • Bacteria that live in the mouth digest these
    foods, turning them into acids
  • The bacteria, acid, food debris, and saliva
    combine to form plaque, which clings to the teeth
  • The acids in plaque dissolve the enamel surface
    of the teeth, creating holes in the teeth called
    cavities, or caries

Dental Decay
  • Treatment
  • Depends on how bad the tooth decay is
  • Use of fluoride can prevent further decay within
    a cavity
  • Fillings cavities can be filled with a
    substances such as metals, metal alloys, plastic,
    porcelain, or a combination of materials
    (composite fillings)
  • Severe tooth decay may need a crown or root canal
  • Extreme tooth decay may result in the tooth
    having to be removed

Dental Decay
  • Prevention
  • Regular brushing (at least 2 times/day) with
    fluoride toothpaste
  • Regular flossing (at least daily)
  • Healthy diet
  • Avoid snacking on high sugar snacks
  • Avoid fizzy drinks and alcohol
  • Include foods rich in calcium and vitamin D
  • Chew gum after a meal

Macrostructure of Digestive System
  • Oesophagus
  • Carries food (bolus) from the mouth to the
    stomach by a process called peristalsis
  • Peristalsis is the rhythmical contractions of
    smooth muscle of the alimentary canal that has
    the effect of moving food along
  • Peristalsis is also a form of mechanical
  • Fibre stimulates peristalsis thereby preventing
  • Good movement of food along the alimentary canal
    is important in decreasing the chance of
    contracting colon cancer

Macrostructure of Digestive System
  • Stomach
  • Receives food from mouth via oesophagus and
    stores food while the cells of the gastric glands
  • HCl (parietal cells) kills bacteria and
    denatures protein
  • Pepsinogen (chief cells) is zymogen that is
    activated by HCl to pepsin (optimal pH12) which
    then digests proteins to peptides
  • Mucous (goblet cells) is slightly alkaline and
    protects the stomach lining
  • Cardiac sphincter found at entrance to stomach
    opens when food enters the stomach
  • Pyloric sphincter controls the amount of chyme
    that leaves stomach

Stomach (Peptic) Ulcer
  • A peptic ulcer is a small lesion in the lining of
    the stomach wall
  • A duodenal ulcer is a small lesion in the
    duodenal wall
  • A perforated ulcer is a complete lesion in the
    wall of the stomach/duodenum where the contents
    can leak into the body cavity

Stomach (Peptic) Ulcer
  • Symptoms of an ulcer
  • Persistent or intermittent pain in the upper
    abdomen that is relieved by eating or taking
  • Vomiting
  • Fatigue (due to loss of blood due to internal
  • In the case of a perforated ulcer, internal
    bleeding and bacterial infection of body cavity
    (possibly fatal)

Stomach (Peptic) Ulcer
  • Cause
  • Lack of mucous or excess HCl is likely to cause
    peptic ulcers
  • Ulcers can also be caused by the bacterium
    Helicobacter pylori which if untreated can go
    on to cause stomach cancer
  • Ulcers in the digestive system are more likely to
    occur in people who
  • Take anti-inflammatory drugs such as aspirin,
    ibuprofen, and naproxen
  • Drink alcohol
  • Smoke
  • Feel stressed

Stomach (Peptic) Ulcer
  • Treatment
  • If bacterial, then antibiotics are administered
  • If stress-related then time-out and exercise
  • If diet-related, then a special diet is made out
    by a dietician
  • If too much acid is being produced, then antacids
    are administered
  • Stop smoking and/or drinking

Stomach (Peptic) Ulcer
  • Prevention
  • Prevention of stomach ulcers would involve
    ensuring good hygiene when preparing food to
    reduce risk of bacterial infection
  • Eating balanced, nutritious meals several small
    meals are generally better than 3 big meals
  • Exercise as it combats the effects of emotional
  • Avoid overuse of anti-inflammatory drugs
  • Do not smoke
  • Avoid alcohol

Macrostructure of Digestive System
  • The small intestine
  • Consists of three parts
  • Duodenum (25 cm) digestion
  • Jejunum absorption
  • Ileum absorption

Macrostructure of Digestive System
  • Duodenum
  • Receives chyme from stomach
  • Further digestion occurs
  • Secretions from the pancreas (pancreatic juice)
    and gall bladder (bile) are released into
  • Pancreatic amylase, lipase and bile salts are
    responsible for digestion within the duodenum

Macrostructure of Digestive System
  • Pancreas
  • Secretes pancreatic juice into the duodenum
  • Pancreatic juice contains
  • Sodium bicarbonate neutralises stomach acid
  • Lipase acts on lipids and converts it into fatty
    acids and glycerol (optimal pH of lipase 7)
  • Amylase acts on starch and converts it into
    maltose (optimal pH of amylase 7)
  • Starch amylase pH7 ? maltose amylase

Macrostructure of Digestive System
  • The liver and its functions in digestion
  • Produces bile which is stored in gall bladder
  • Bile consists of
  • Bile salts secreted into duodenum and emulsifies
  • Sodium bicarbonate secreted into duodenum and
    neutralises acidic chyme
  • Bilirubin and biliverdin breakdown products of
    haem from the haemoglobin of red blood cells

Macrostructure of Digestive System
  • The liver and its other functions
  • Receives blood from the jejunum and ileum
    (hepatic portal vein) detoxifies toxins (e.g.
  • Breaks down excess amino acids into urea which
    is then excreted via the kidneys
  • Converts excess glucose to glycogen which it then
  • Stores fat-soluble vitamin (A, D, E, and K) and
    trace minerals (iron, copper, zinc)
  • Synthesises clotting factors (e.g. fibrinogen)
  • Synthesises cholesterol key component of cell

Macrostructure of Digestive System
  • Jejunum and ileum
  • Absorption of nutrient occurs in this 6 m section
    of the small intestine
  • Monosaccharides (breakdown products of starch)
    glucose, fructose, galactose are absorbed
    directly into bloodstream as they are
  • Amino acids (breakdown products of protein) are
    also absorbed into bloodstream as they are
  • Fatty acids and glycerol (breakdown products of
    starch) are absorbed into the lacteals and
    combine with proteins to form lipoproteins which
    are then transported in the lymph to the blood

Macrostructure of Digestive System
  • Small intestine
  • Small intestine is very well-adapted for
    digestion and absorption due to
  • Length of small intestine (67 m long)
  • Internal epithelium is structured into villi and
    microvilli to increase the surface area for
  • The surface of the villi are only one-cell thick
    in order that absorption into the bloodstream and
    lacteals is very rapid
  • Small intestine has a very good blood supply

Macrostructure of Digestive System
  • Large intestine
  • The large intestine is 1.5 m long and consists
  • Caecum
  • Colon
  • Rectum

Macrostructure of Digestive System
  • Caecum
  • Separated from the ileum by the ileocaecal valve
  • It is the beginning of the large intestine
  • In humans, the caecum's main functions are to
    absorb fluids and salts that remain after
    completion of intestinal digestion and absorption
    and to mix its contents with mucous

Macrostructure of Digestive System
  • Appendix
  • The appendix is a small branch of the caecum
  • Its average length is 10 cm
  • The appendix is rich in infection fighting cell
    (white cells) suggesting that it may have an
    immune function
  • However, the appendix has no function officially

  • Appendicitis is painful inflammation and swelling
    of the appendix
  • Symptoms
  • Severe and localised pain in the right, lower
  • Cause
  • Bacterial growth and build up of toxins and waste
  • Treatment
  • Surgical removal of the entire appendix
  • Prevention
  • No known preventative measure

Macrostructure of Digestive System
  • Colon
  • The colon consists of three parts
  • Ascending, transverse, and descending colons
  • The function of the colon is to absorb water
    converting the semi-solid waste that changes into
  • The colour of faeces is due to the bile pigments
    bilirubin and biliverdin
  • Symbiotic bacteria (300 1000 different species
    of bacteria live in the colon!) produce biotin (a
    B-vitamin) and K which are then absorbed through
    the colon wall
  • Symbiotic bacteria also help to break down unused
    energy substrates such as small amounts of

Macrostructure of Digestive System
  • Importance of dietary fibre for the colon
  • Dietary fibre (also called roughage) is necessary
    to keep the gut healthy by stimulating
    peristalsis and ensuring that the undigested
    material moves along freely without becoming
  • Constipation results if there is not enough fibre
    in the diet
  • Persistent constipation increases the risk of
    colon cancer later in life as the undigested
    material begins to fester due to bacterial action
    and toxins can build up

Macrostructure of Digestive System
  • Rectum
  • Stores faeces as it arrives from the colon and
    until it is egested from the body via the anus
  • Egestion from the rectum through the anus is not
    excretion as faeces is not a waste product of
    metabolism faeces is the undigested food
  • REMEMBER Excretion is defined as the removal of
    the waste products of metabolism from the body
    via the kidneys, skin, and lungs

Vitamin A Deficiency
  • Symptoms
  • Night-blindness dry, scaly skin mental
    retardation and retarded growth in children
  • Cause
  • Inadequate intake of food high in vitamin A
  • Treatment
  • Increase intake of foods rich in vitamin A such
    as milk, cheese, cream, liver, cod liver oil,
    leafy green vegetable, carrots
  • Prevention
  • Eat adequate amounts of milk, cheese, cream,
    leafy green vegetables, carrots

Balanced Human Diet
  • A balanced diet is one in which a person receives
    all the essential nutrients in the correct
    proportions to maintain homeostasis
  • A variety of foods should be include in the diet
    to maintain good health
  • No one group of foods should be taken in excess

Balanced Human Diet
  • An individuals diet will depend on
  • Age adolescents, adults and pregnant and
    lactating women will require the largest amount
    of nutrients
  • Sex generally males require more calories than
    females (except during pregnancy and lactation)
  • Occupation labourers will require more calories
    per day than someone with a desk job
  • Activity sports people will require many more
    calories than a sedentary person

Food Pyramid
Slimming Disorders
  • Anorexia nervosa
  • Psychological condition found mostly in women
  • They have a perception that they are fat
  • They eat very small amounts of food and go on
    strict diets or even go long periods of time
    without eating
  • Can be fatal
  • Bulimia
  • Psychological condition similar to anorexia,
    however, these people generally eat normally
  • Difference is that bulimics will induce vomiting
    after a meal
  • Harder to treat as they appear normal because of
    their eating patterns
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