Absorption

• Where are all products of digestion absorbed.

  Across cells lining the ileum.
• Describe the structure of the ileum

  The ileum wall is covered in villi, which have thin walls surrounded by a network of capillaries and epithelial cells which have even smaller microvilli.
• Why does the ileum have so many folding's?

  Maximises absorption by increasing the surface area, decreasing the diffusion distance
• Why is there a network of capillaries in the villi?

  To maintain the concentration gradient.
• How are monosaccharides and amino acids absorbed?

  Co-transport
• What is the first step of monosaccharide/amino acid absorption?

  Sodium ions are actively transported from the epithelial cell into the blood via a sodium-potassium pump, decreasing the concentration of sodium ions in the epithelial cell.
• What does the first step of absorption by co-transport achieve?

  The sodium ion gradient
• What is the second stage of absorption by co-transport?

  Sodium ions move down their concentration gradient from the intestine into the epithelial cell, carrying an amino acid/glucose is transported at the same time by the co-transported protein.
• What is the 3rd stage of absorption by co-transport

  The concentration of amino acids/glucose in the epithelial cell increases, and amino acids diffuse down their concentration gradient via facilitated diffusion into the blood.
• Why is absorption by co-transport necessary?

  To absorb glucose/amino acids from the lumen to the gut there must be a higher concentration in the lumen compared to the epithelial cell- for facilitated diffusion. Though there is usually more in the epithelial cells.
• What is the first stage of Lipid absorption?

  Micelles diffuse across the cell surface membrane entering epithelial cells.
• What is the second stage of lipid absorption?

  Micelles are modified back into triglycerides inside of the endoplasmic reticulum and Golgi body.
• What often happens as the third stage of lipid absorption?

  Triglycerides/fatty globules combine with proteins to form chylomicrons- inside the Golgi apparatus
• What is the fourth stage of lipid absorption?

  Chylomicron is then released inside of a Golgi vesicle- moves to other end of epithelial cell, released by exocytosis.
• What is the fifth stage of lipid absorption?

  Lymph in the lacteal transports chylomicron- eventually drains into the capillary.