Absorption of Products of Digestion

• What are digestion products absorbed by?

  The ileum.
• How is the ileum adapted to its function as an exchange surface?


  It has very thin walls, the walls possess villi, it is lined with epithelial cells that have a rich network of capillaries on their other side.
• How are villi adapted?


  They have very thin walls, contain muscle, are well supplied with blood vessels, and possess microvilli.
• What do villi increase?

  The rate of absorption.
• How do villi increase the efficiency of absorption?

  They increase the surface area for diffusion, reduce the distance over which diffusion takes place, and maintain a diffusion gradient.
• How do villi maintain a diffusion gradient?


  They contain muscle allowing them to move and mix contents of the ileum ensuring that the products are absorbed, and they are well supplied with blood vessels that carry material-rich blood away as well as fresh blood towards.
• What do microvilli do?

  Further increase the surface area for absorption.
• How are amino acids and monosaccharides absorbed in the ileum?

  By diffusion and co-transport.
• How big are micelles?

  4-7nm in diameter.
• What happens to micelles after being emulsified?

  They come into contact with the epithelial cells lining the villi of the ileum.
• How do the micelles come into contact with the epithelial cells?


  Through the movement of material within the lumen of the ileum.
• What happens to the micelles once they come into contact with the epithelial cells lining the villi of the ileum?

  They break down and release the monoglycerides and fatty acids.
• What are micelles?


  Temporary compounds containing monoglycerides and fatty acids in combination with bile salts.
• What is the purpose of micelles?


  To enable lipid digestion products to be transported and absorbed in the ileum as they are soluble whereas lipids are insoluble.
• What happens after the micelles break down into monoglycerides and fatty acids?

  They easily diffuse across the cell-surface membrane into the epithelial cells due to them being non-polar.
• What happens to monoglycerides and fatty acids once in the epithelial cells?

  They are transported to the endoplasmic reticulum.
• What happens to the monoglycerides and fatty acids in the endoplasmic reticulum?

  They are recombined to form triglycerides.
• Where do the triglycerides go after the endoplasmic reticulum?

  Into the golgi apparatus.
• What happens to the triglycerides in the golgi apparatus and why?

  They associate with cholesterol and lipoproteins to form structures called chylomicrons.
• What are chylomicrons?


  Special particles adapted for the transport of lipids.
• What do chylomicrons do after being formed in the golgi?

  Move out of the epithelial cells by exocytosis.
• What do chylomicrons do after moving out of the epithelial cells?


  Enter lymphatic capillaries called lacteals.
• Where are lacteals found?

  At the center of each villus.
• What do chylomicrons do once in the lateals?

  Pass into the blood system.
• What happens once chylomicrons are in the blood system?

  The triglycerides in the chylomicrons are hydrolysed by an enzyme from where they diffuse into cells.
• What is the enzyme that hydrolyses the triglycerides in the chylomicrons in the blood system?

  An enzyme in the endothelial cells of blood capillaries.