Mammalian Digestion

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Mammalian Digestion
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Mammalian digestion

• In heterotrophic organisms the digestive system
• provides the means by which nutrients are taken
  in
• and broken down. Large insoluble food molecules
• are converted into small soluble ones that can be
  
• absorbed and made available to the body cells.

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Obtaining nutrients

• There are 5 steps involved in heterotrophs
  obtaining nutrients
• Ingestion the intake of food
• Digestion the breakdown of food into smaller,
  soluble chunks that can be easily absorbed. The
  end products of digestion are amino acids (from
  proteins), simple sugars (from carbohydrates) and
  fatty acids (from lipids).

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• 3. Absorption basic units of food are absorbed
  across the digestive tract wall, into the
  bloodstream and into cells.
• 4. Assimilation the end products of digestion
  are built into useful substances as either
  biological material or as an energy source
• 5. Egestion the removal of undigested food as
  waste.

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• Describe the role of teeth in increasing the
  surface area of complex foods for exposure to
  digestive chemicals
• The function of teeth is to physically break down
  food into smaller pieces. Chewing food increases
  the surface area thereby increasing the rate of
  reaction with digestive enzymes (chemical
  breakdown).

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Humans have four types of teeth incisors,
canines, premolars and molars.

• Incisors used to grasp, hold and bite food
• Canines used for ripping and tearing food
• Premolars used for chewing and cutting flesh
• Molars used for grinding and chewing

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Diets

• Herbivores
• Have front teeth (incisors) adapted to tear off
  vegetation and back teeth (molars) to chew on
  plant material. The molars are specially designed
  to help break open the cellulose walls of plant
  cells. Cellulose is extremely hard to break down
  physically and chemically.

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Herbivores cont.

• Herbivores need to chew for a long period of time
  because
• To break down the cellulose
• Large quantities of vegetation is needed to
  provide sufficient energy for the animal
• To further increase the surface area

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• Carnivores
• They have powerful jaws and well developed canine
  teeth designed to hold and kill prey and tear off
  meat.
• The meat is then chewed by the molars to increase
  the surface area before swallowing it.

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• Explain the relationship between the length and
  overall complexity of digestive systems of a
  vertebrate herbivore and a vertebrate carnivore
  with respect to
• the chemical composition of their diet
• the functions of the systems involved

• Herbivores
• Eat plant material that is high in fibre and
  starch and depending on the plant may include
  sugars, proteins, oils and other nutrients.
• Herbivores have adaptations of their digestive
  tract to enable them to digest cellulose.

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Herbivores cont.

• Large herbivores have microbes living in their
  gut who produce an enzyme to break down cellulose
  and release energy. This is called microbial
  fermentation.
• The gut is complex and extremely long providing
  space to hold the large quantity of food that
  must be eaten. It also gives maximum opportunity
  for the microbes to digest cellulose and the
  nutrients to be absorbed.

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Herbivores cont.

• Small herbivores eat plant material with less
  cellulose and their diet is predominately nectar.
• The gut is usually simple and small because their
  diet is easier to digest as it has little or no
  fibre and is high in sugar.

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Carnivores

• Eat animal matter which is more easily digested.
• Their diet is high in protein, low in fibre and
  has more energy than plant material. This means
  that carnivores need to consume lesser quantities
  of food than herbivores.
• Due to the ease at which food can be digested,
  the gut is relatively short. Little undigested
  material is egested due to low fibre diet.

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Herbivore Adaptations

• The microbes living in the gut of animals need to
  be protected from being lost with the passage of
  food. The microbes are present either in the
• Stomach (fore-gut fermenters)
• Caecum (hindgut fermenters)

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Fore-gut Fermentation

• Microbes in the eastern grey kangaroo use
  majority of the dietary glucose and protein but
  release fatty acids as energy for the host
  animal. Some microbes are digested by the host
  and a source of amino acids.

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• Cattle
• They regurgitate the contents of the first part
  of their stomach and re-chew the food to further
  break it down.
• Ruminant fore-gut fermenters meaning they have
  four stomachs two for microbial fermentation,
  one for storage and one which acts as a true
  stomach.
• Food remains in the two fermentation chambers
  for a long period of time so that the microbes
  have enough time to break down the cellulose

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Hindgut Fermenters

• Takes place in the caecum (large intestine)
• The main difference is that the microbes cannot
  be digested by the host animal as a source of
  amino acids. This is because protein digestion
  has already occurred before the large intestine
  and the amino acids are therefore egested.
• This is why rabbits eat their faecal pellets to
  digest the nutrient-rich microbes

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Carnivore Adaptations

• They have a simple stomach and a short intestine
  relative to their body size. The caecum may be
  absent, of if it is present is greatly reduced in
  size.