Animal Physiology

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Animal Physiology

• Mammalian Nutrition

Mr G R Davidson
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Composition of Food

• Humans are adapted for feeding and digestion so
  that food molecules can reach the body cells.
• The main groups of food we eat are
• Carbohydrates
• Fats
• Proteins
• Vitamins
• Minerals

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Composition of Food

• Carbohydrates contain the elements carbon,
  hydrogen oxygen
• Fats contain the elements carbon, hydrogen
  oxygen
• Proteins contain the elements carbon, hydrogen,
  oxygen nitrogen

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Carbohydrates

• Carbohydrates provide us with energy for our
  normal activities.
• They consist of long chains of glucose molecules.

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Fats

• Fats release some energy for our use if required
  while the rest is stored in adipose tissue
  beneath the skin.
• This is used as insulation.
• Each fat is made up of a glycerol molecule joined
  to 3 fatty acid molecules.

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Proteins

• Our body requires protein to build it up and for
  growth and repairing damaged tissue.
• Proteins are built up from long chains of amino
  acids.
• There are only about 20 different amino acids.

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Vitamins

• Vitamins are required for good health.
• They do not provide energy.
• They act as coenzymes which are required in the
  various biochemical activities within cells.
• Some examples of vitamins, their source and the
  deficiency disease are given in the table.

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Vitamins
Vitamin Source Deficiency Disease
A Milk, fresh veg. Night Blindness
B1 (Thiamine) Cereal grains Beri beri
B3 (Niacin) Cereal, lean meat Pellagra
C (Ascorbic acid) Citrus fruits Scurvy
D Liver, fish, milk Rickets
E Wheat germ Reproductive Disorders
K Green veg. Blood doesnt clot
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Minerals

• Minerals are chemical elements which are required
  in very small quantities.
• They have a whole variety of functions, some of
  which are shown in the following table.

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Minerals
Mineral Required For
Iron Haemoglobin in Red Blood Cells
Iodine Thyroxine
Sodium All cells
Calcium Healthy teeth bones
Potassium Contraction of muscles
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Alimentary Canal

• The food we eat passes from the mouth to the anus
  through the alimentary canal or gut.
• As food passes through this canal it is processed
  in a number of ways and by a number of organs.
• Other organs, such as the salivary glands, liver
  and gall bladder are attached to the alimentary
  canal by ducts, and these are called associated
  organs.

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Alimentary Canal
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The Mouth

• The food is physically broken down into
  manageable sizes by the teeth.
• It is mixed with a fluid called saliva, which
  contains the enzyme salivary amylase, to digest
  starch.

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The Mouth

• Saliva also contains mucus which makes the food
  easier to swallow.
• The food is then moved through the gullet
  (oesophagus) to the stomach by a process called
  peristalsis.

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Peristalsis
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Stomach

• The stomach is a muscular bag with a valve at
  either end.
• The CARDIAC sphincter at the top allows food in.
• The PYLORIC sphincter at the bottom allows food
  to leave.

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Stomach

• The stomach wall produces digestive juices from
  gastric glands which secrete mucus, acid and
  enzymes.
• For digestion to work properly the food must be
  well mixed with these juices.
• The stomach muscles contract and relax to mix up
  the juices and food.

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Gastric Gland
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Gastric Glands

• The mucus-secreting cells release a slimy mucus
  which sticks to the wall of the stomach and
  protects it from damage by the strong digestive
  enzymes.

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Gastric Glands

• The acid-secreting cells release hydrochloric
  acid which has 2 functions
• It creates conditions needed to produce active
  pepsin.
• It provides the optimum pH for the enzymes to
  work.

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Gastric Glands

• The enzyme-secreting cells release an inactive
  enzyme called pepsinogen.
• Once the pepsinogen comes in contact with the
  acid, it is converted to an active enzyme called
  pepsin.
• The pepsin can now break down proteins in the
  stomach to peptides, which will later be broken
  down further into amino acids.

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Stomach

• The longitudinal muscles contract to make the
  stomach shorter and fatter.
• The circular muscles contract to squeeze the
  stomach.
• Once the food has been in the stomach for a
  while, it is released slowly, small drops at a
  time into the small intestine.

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Small Intestine

• The food enters the small intestine from the
  stomach and is moved along by peristalsis.
• A number of digestive enzymes break down the
  large insoluble food molecules to small soluble
  food molecules before they are absorbed out of
  the intestine.

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Small Intestine

• The small intestines function is to absorb
  soluble food molecules and it is well suited to
  this job in a number of ways.
• It is very long (About 6m). The inner surface is
  folded into thousands of finger-like villi.
• The lining of each villus is very thin. (Only one
  cell thick)
• Each villus has a network of vessels for
  absorbing the food, both blood capillaries and
  lymphatic vessels. (Lacteals)

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A Villus
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Absorption

• The glucose and the amino acids are absorbed into
  the blood capillaries.
• These tiny blood capillaries all join up to form
  the hepatic portal vein and transport the
  absorbed food to the liver.

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Absorption

• The liver stores most of the glucose as glycogen
  until it is required, but some glucose remains in
  the blood.
• The amino acids are used in the body for growth
  and repair, but if there are any excess amino
  acids, these are broken down by the liver into
  urea.

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Absorption

• This is later removed by the kidneys and released
  in the urine.
• Vitamins and minerals are transported to cells
  where they have special functions which help to
  keep the body healthy.
• Any excess vitamins and minerals are either
  stored or excreted.

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Absorption

• Fats and fatty acids are absorbed by the lacteals
  which contain a fluid called lymph.
• This lymph is transported in the lymph vessels
  which will eventually drain into the blood
  system.
• The products of fat digestion can be used for
  energy, as insulation or simply stored until
  required.

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Large Intestine

• When the food eventually reaches the large
  intestine (Colon), it is mainly water and
  indigestible waste materials.
• The function of the large intestine is to absorb
  water back into the bloodstream leaving a
  semi-solid called faeces.
• The faeces is passed into the rectum (bowel)
  where it is stored until it is eventually
  eliminated through the anus.