chapt 5.5 absorption

• definition

  where digested food substances are absorbed into body cells
• 
  

  water and mineral salts absorbed by the small intestine and colon, small intestine absorbs most water
• 
  

  products of digestion absorbed thru ileum (small intestine) and are absorbed thru cells of s.i into the bloodstream
• adaptations of small intestine for absorption

  inner surface of ileum folded extensively & has numerous finger-like extentions called villi
• villi

  incr the surface area for absorption
• villi

  epithelium (wall of villi) is only 1 cell thick -> lowers diffusion distance for nutrients
• villi

  cells have microvilli further increasing surface area
• villi

  cells also have many mitochondria to provide energy for active transport of nutrients into the villi
• villi

  has many blood capillaries to allow blood to transport absorbed glucose and amino acids, maintaining diffusion gradient
• small intestine

  contains a lacteal to transport absorbed fats away & maintain steep diffusion gradient
• absorbtion of glucose and amino acids

  1. absorbed by diffusion into blood capillaries of villi
  2. also absorbed by active transport if conc. in the lumen is less than that of the blood capillaries
• absorption of glycerol and fatty acids

  1. diffuse into epithelium
  2. combine to form minute fat globules that enter the lacteals
• undigested and unabsorbed matter (egestion)

  1. stored temp in rectum
  2. discharged as faeces thru anus