digestive system

• Mechanical digestion

  Involves physical breakdown of food like using teeth to grind food and muscles of the stomach to churn up food.
• Chemical Digestion

  Enzymes help break down food
• Food has to be digested as the molecules are large/insoluble, so cannot fir through the intestinal wall to be absorbed into the blood.
• Digestive system organs:

  A) mouth

  B) oesophagus

  C) stomach

  D) liver

  E) gallbladder

  F) pancreas

  G) small intestine

  H) large intestine

  I) anus

  
• gut


  gastrointestinal system (digestive system)
• The digestive system is an organ system that consists of a group of organs that work together to perform the roles of:

  • Digestion - process of breaking down large food molecules into smaller molecules.
  • Absorption - process of absorbing these small food molecules into the body.

  For e.g: the pancreas releases digestive enzymes (helps break down the food molecules) to the small intestine, so it absorbs the nutrients.
• Mouth

  Teeth physically break the food into smaller pieces.

  • It increases the surface area for enzymes to act on.
  • It makes the food easier to swallow.

  Salivary glands release saliva, which lubricates the food to make it easier to swallow.

  • the saliva contains amylase enzymes, which ONLY breaks starch into maltose.
• Oesophagus



  carries food from the mouth to the stomach through muscular contractions called peristalsis.

  • Peristalsis - the squeezing action of muscles that is used to move food along the gut.

  
• Stomach


  • Contracts its muscular walls to churns and mix food.
  • It produces pepsin (a type of protease enzyme) to ONLY break proteins down into amino acids.
  • It produces hydrochloric acid, makes the breakdown of food faster:
  • By providing the optimum pH for pepsin to function. (pH 2)
  • It kills microorganisms, since it's so acidic. When it's not, then you are sick.

  
• Bile


  A yellow-greenish liquid, produced by the liver and stored in the gall bladder and released into the small intestine.

  
• When Bile is released into the small intestine it:

  • Emulsify lipids, where large lipid droplets are broken down into tiny lipid droplets to increases the surface area of the lipid droplets for lipase enzymes to break them down; this helps lipid digestion.


  Bile neutralises the acid from the stomach, so enzymes aren't in too acidic conditions and gets affected by the pH and denature, bile can do this, because it's alkaline.

  
• Pancreas


  Produces most of the digestive enzymes like:

  • protease enzymes
  • carbohydrase enzymes
  • lipase enzymes

  And pushes these into the small intestine, in the form of pancreatic juices.

  
• Liver



  Filters blood and breaks down poisonous substances like alcohol and drugs.

  • It also produces bile that neutralises HCI acids and emulsifies fats.

  
• Gallbladder



  Stores the bile produced by the liver and releases it to the small intestine.

  
• Small intestine


  Produces digestive enzymes to break down food like:

  • protease enzymes
  • carbohydrase enzymes
  • lipase enzymes

  Where food is digested into tiny pieces and it's absorbed across the lining of the intestine into the bloodstream, this is an exchange surface.

  • The rest is moved to the large intestine.

  
• Villi


  Finger-like protrusions of the small intestine that are responsible for absorbing nutrients into the body.

  
• Large intestine


  • Absorbs excess water from the secretions of the pancreas, stomach and gall bladder and leaves behind faeces.
  • Waste is stored in the rectum and exited through the anus

  
• Adaptations of the villi in the small intestine:

  • Covered in lots of villi to increase the surface area, so more nutrients can be absorbed into the blood, quickly.
  • It has a single layer of surface cells, for a short diffusion path for a quicker absorption of nutrients.
  • Good blood supply to maintain a strong concentration gradient between the lumen and the blood.
  • The cells lining the villi have microvilli on their surface, to increase the surface area, so more nutrients can diffuse.
  • Surfaces are permeable, so nutrients can diffuse across.

  
• A Good blood supply in villi helps main concentration gradient:

  1. Glucose is absorbed into blood.
  2. Blood will be taken away.
  3. replaced with blood that doesn't yet have lots of glucose.

  
• • The concentration of glucose in the small intestine increases between 100 and 300 cm, because carbohydrates are broken down by carbohydrase or amylase and are digested into sugars.
  • The concentration of glucose in the small intestine decreases between 300 and 700 cm, because of absorption of glucose into blood, by active transport.