digestion

• Lipase is an enzyme that breaks down fats into fatty acids and glycerol.
• Pancreatic juice contains:

  Sodium hydrogen carbonate – an alkaline

  salt that neutralises the acidic chyme in the

  duodenum and raises the pH to 8
• Pancreatic Lipase

  Pancreatic lipase is a lipid digesting enzyme

  It is produced in the pancreas

  It acts in the duodenum

  It breaks down lipids into fatty acid and glycerol

  It’s ideal temperature is 37oC

  It’s ideal pH is pH 8
• Nutrition is the way organisms obtain and use

  food.
• Autotrophic – organisms can

  make their own food

  E.g. plants and some bacteria
• Heterotrophic – organisms

  cannot make their own food.

  E.g. humans, dogs, badger.
• Heterotrophic organisms (heterotrophs) can be classified as:

  Herbivores – eat plants only. E.g. rabbit

  Carnivores – eat animals only. E.g. fox

  Omnivores – eat plants and animals. E.g. badger
• Digestion is the breaking down of

  food into smaller particles that can

  be absorbed by the body
• Digestion is necessary to:

  Make the food soluble

  Make the food easier to absorb

  Make it easier to transport
• Chemical – breaking down of food

  using enzymes
• Mechanical – physical breaking down

  of food
• Ingestion – taking food into the mouth
• Digestion – breaking down of food
• Egestion – removal of undigested waste

  from the body
• Absorption – the passage of the digested

  food into the blood or lymph
• The mouth has many different functions:

  It grinds the food ( masticates it)

  It mixes the food with saliva to soften it

  It swallows the food
• Saliva contains enzyme amylase that breaks down starch molecules into smaller sugar molecules.
• Mechanical digestion is carried out by the action

  of the teeth
• Chemical digestion is carried out by the enzyme

  salivary amylase
• Saliva consists of water, salts, mucous

  and the enzyme amylase.
• Saliva helps to soften and dissolve the

  food so we can taste and swallow it.
• Salivary Amylase

  Salivary amylase is a carbohydrate digesting enzyme.

  It breaks down starch into maltose.

  It is produced by the salivary glands and acts in the mouth.

  Its ideal temperature is 37oC

  Its ideal pH is 7 (the pH in the mouth)
• Peristalsis – muscular contractions that

  pushes food along the alimentary canal
• The oesophagus is a muscular tube about

  25cm in length

  It connects the throat (pharynx) to the

  stomach

  It pushes food along by a process called

  peristalsis
• The stomach is a muscular bag that stores

  and digests food

  The stomach holds approx. 1 ½ L of food

  that mixes with gastric juice.

  The mixture is churned for 3-4 hours

  becoming a semi liquid called chyme
• Food enters the stomach via the

  cardiac sphincter.

  The gastric mucosa covers the internal

  surface of the stomach – which is

  heavily folded

  Glands in the mucosa produce a range

  of secretions, collectively called

  gastric juice.
• Hydrochloric Acid (HCl)

  HCl kills microorganisms on food.

  The acid lowers the pH to pH2.

  It activates pepsinogen to pepsin

  It denatures salivary amylase
• Pepsinogen

  Pepsinogen is an inactive enzyme ( so it does not digest the stomach lining)

  It is converted to the active enzyme pepsin by the HCl, that digests proteins.
• Mucous

  protects the inner surface of the stomach from acid and digestive enzymes (

  prevents gastric ulcers)
• Pepsin

  Pepsin is protein digestive enzyme – a protease

  It is produced by gastric glands in the stomach wall

  It acts in the stomach

  It breaks down proteins into peptides and amino acids

  Its ideal temperature is 37oC

  Its ideal pH is pH 2
• Mechanical Digestion – The churning of

  the food with gastric juice breaks down the

  food physically.
• Digestion in the Stomach

  Mechanical Digestion – The churning of

  the food with gastric juice breaks down the

  food physically.

  Chemical Digestion – The enzyme pepsin

  breaks down proteins into peptides.
• The food leaves the stomach to

  enter the duodenum via the

  pyloric sphincter
• The main function is digestion

  The duodenum gets secretions from

  3 sources:

  Bile from the Gall Bladder

  Pancreatic Juice from the pancreas

  Intestinal juice from the walls of the

  duodenum
• Intestinal glands in the wall of the

  duodenum produce intestinal juice

  This contains:

  Mucous – protects the walls from

  acidic food leaving the stomach

  Enzymes
• The pancreas is both an exocrine and an

  endocrine gland
• Pancreatic juice contains:

  Sodium hydrogen carbonate – an alkaline

  salt that neutralises the acidic chyme in the

  duodenum and raises the pH to 8

  Pancreatic lipase – breaks down lipids into

  fatty acids and glycerol

  Other enzymes
• The juice enters the duodenum via the

  pancreatic duct
• Bile salts emulsify fats
• Pancreatic Lipase

  Pancreatic lipase is a lipid digesting enzyme

  It is produced in the pancreas

  It acts in the duodenum

  It breaks down lipids into fatty acid and glycerol

  It’s ideal temperature is 37oC

  It’s ideal pH is pH 8