Digestive System Flashcards
(25 cards)
Two purposes of the digestive system
• break down complex food substances
• provides very large surface area for maximum food adsorption
Function of the mouth in digestion
• mechanically breaks down food
Salivary glands
• produce amylase enzyme in the saliva
Gullet (oesophagus)
• food travels down
Stomach function
• pummels the food with its muscular walls
• produces the protease enzyme, pepsin
• produces hydrochloric acid for two reasons:
To kill bacteria
To give the right pH for the protease enzyme to work (pH 2 - acidic)
Pancreas function
• produces protease, amylase and lipase enzyme
• releases these into the small intestine
Small intestine function
• produces protease, amylase and lipase enzymes to complete digestion
• this is where the digested food is absorbed out of the digestive system into the blood
Liver function
• where bile is produced
• main metabolic organ of the body
• detoxifies poisons, e.g. ethanol
• urea production
• breaks down red blood cells and storing the iron
• passage of breakdown product to blood for excreation via kidney
• removal of lactic acid, re conversion to glucose and glycogen
Gall bladder function
• where bile is stored before it’s released into the small intestine
Large intestine function
Where excess water is absorbed from the food
Rectum function
Where faeces are stored before they are excreted from the anus
What is the function of digestive enzymes?
• starch, proteins and fats are BIG molecules - too big to pass through walls of digestive system
• digestive break these BIG molecules into smaller ones like sugars (glucose and maltose) amino acids, glycerol and fatty acids
• smaller, soluble molecules can pass easily through walls of the digestive system, allowing them to be absorbed into the bloodstream
Amylase converts carbohydrates into simple sugars
• amylase breaks down starch
• into maltose (and other sugars, e.g. dextrins)
• made in salivary glands, the small intestine and the pancreas
Proteases convert proteins into amino acids
• proteases are made in three places - stomach (called pepsin here), pancreas and the small intestine
Lipases convert lipids into glycerol and fatty acids
• lipids = fats and oils
• made in pancreas and small intestine
Food tests for sugars
Benedict’s Test
• Prepare a food sample and transfer to test tube.
• Prepare a water bath set to 75•C
• Add some Benedict’s solution to the test tube (10 drops) with pipette
• place test tube in water bath using a test tube holder and leave for 5 mins - make sure tube is pointing away from you
• if sample turns brick red, positive
Food test for starch
• make a food sample and transfer to test tube
• add a few drops of iodine solution and gently shake
• positive test - blue/black
Food test for proteins
• prepare sample of food and transfer to a test tube
• add some biuret solution (2cmcubed) and mix contents of tube by gently shaking
• turns purple if positive
Food test for lipids
• prepare a sample and transfer to test tube
• use pipette and add 3 drops of Sudan III stain solution to test tube and gently shake
• positive - mixture separates into two layers - top layer will be bright red
Enzymes
• biological catalysts
• control rate of reactions
• large protein molecules
• each enzyme acts with a particular substrate
• shape is vital for enzymes to function
Lock and key theory
• substrate fits into the specific active site of an enzyme
• substrate splits into products which leave the active site
Types of metabolic reactions sped up by enzymes
• building large molecules from smaller ones - starch, glycogen or cellulose from glucose, lipids from fatty acids, proteins from amino acids
• changing one molecule to another, e.g. glucose to fructose
• breaking down large molecules to small ones during digestion - e.g. carbohydrates, proteins, lipids
Enzymes make sure each specific reaction doesn’t interfere with another
Factors effecting enzyme action
• temperature - higher rate increases at first, but once optimum temp is surpassed the enzymes will become denatured (37degrees)
• pH - if too high/low, pH interferes with bonds holding enzymes together - changes shape of active sight and denatures the enzyme (optimum is usually 7 - but for pepsin (for proteins) in the stomach, it is pH 2
Best conditions for enzymes
• acidic in stomach (protease)
• produce hydrochloric acid to maintain low pH
• enzymes made in pancreas and small intestine - alkaline
