digestion

• define digestion

  Digestion is a process whereby food is broken down into small particles, small enough to be carried by the blood around the body.
• define ingestion


  when the food is broken down in the mouth by the teeth. the teeth are used to break the food into small pieces. The pieces are mixed with a liquid called saliva and swallowed.
• define absorption

  Liquid food passes through the gut wall into the bloodstream
• define assimilation 


  Food is taken in by the cells, and used for energy, growth, and repair.
• define defecation

  Fibre and other food which cannot be digested pass out through the anus
• the alimentary canal

  a tube running through the body.

  (also known as the gut)

  -the alimentary canal has two layers of muscles:

  • longitudinal muscle: fibres of this muscle run along its length
  • circular muscle: fibres run around the canal. when the muscles contract, they make the alimentary canal narrow in that region.

  
• describe peristalsis.

  A contraction in one region of the alimentary canal is followed by another contraction just below it so that a wave of contraction passes along the canal pushing food in front of it. The wave of contraction, called peristalsis.

  
• describe the functions of the epithelium

  It makes new cells to replace the old ones worn out by food passing through.

  The goblet cells secrete mucus which lubricates the food and the lining of the canal, protecting it from wear and tear.

  Other cells produce digestive enzymes which digest the food.
• state the order of digestion in the body parts.

  1. mouth
  2. oesophagus
  3. stomach
  4. small intestine
  5. caecum and appendix
  6. large intestine
  7. rectum

  
• what is saliva made from?

  -mucus: moistens the food so that it slides down the oesophagus when it is swallowed. it also binds food together to form a bolus.

  -salivary amylase: an enzyme that acts on starch and starts changing it to maltose.

  -water: helps to dissolve substances in the food.
• describe the function of the epiglottis.

  covers the entrance to the trachea, and this stops food from entering the lungs.
• list the characteristics of the stomach

  functions:

  ➢ store food

  ➢ digest proteins in the food

  • elastic walls which contract and relax to churn the food
  • food mixes with the mucus and enzymes to produce chyme, known as gastric juice
  • secretes pepsin to break down protein into becoming polypeptides
• describe the characteristics of the small intestine

  -made up of two parts:

  • duodenum: closest part to the stomach. digestion is completed
  • ileum: closest to the large intestine. absorption of food occurs.

  small intestine receives fluids from three different places:

  1. liver: produces bile -> stored in the gall bladder
  2. pancreas: pancreatic juice -> pancreatic amylase, trypsin, lipase
  3. intestinal walls of the small intestine
• describe the characteristics of the intestinal glands

  -inner walls are covered with villi

  -enzymes secreted by the intestinal glands don't enter the lumen of the small intestine but stay close to the cells in the walls.

  -cells found in the part of the small intestine = ileum

  -enzymes secreted by these cells =

  • maltase
  • lactase
  • sucrase
  • lipase
• describe the characteristics of the villi

  -one cell thick

  -increased surface area = allowing nutrients to be absorbed faster

  -very thin walls = digested food can pass rapidly through it to reach blood capillaries and lacteals

  -dense network of blood capillaries

  -lacteals in each villus