Absorption

Question 1

How is the ileum adapted for absorption?

Answer 1

• 5 metres long
• Walls contain lots of villi to increase surface area
• Lined with microvilli to increase surface area further
• Short diffusion distance due to thin walls
• Muscular walls can contract to maintain diffusion gradient
• Cell membrane of epithelial cells have many transport proteins
• Many RER, golgi apparatus and mitochondria to synthesise proteins

Question 2

What are epithelial cells?

Answer 2

Cells that layer the outside of an organ

Question 3

What are endothelial cells?

Answer 3

Cells that provide the inner layer of an organ

Question 4

How do monosaccharides absorb?

Answer 4

• Active co-transport of sodium and glucose from lumen of SI to the epithelial cell of SI
• Glucose is transported via facilitated diffusion from epithelial cells of SI into capillary
  -Sodium is transported via sodium potassium pump out of the epithelial cell into the blood capillary
• Potassium leaves from blood capillary to the epithelial cell
• Sodium is transported alongside glucose to maintain a high concentration of glucose within the epithelial cell

Question 5

How are amino acids absorbed?

Answer 5

• Active co-transport of sodium and amino acids from lumen of SI to the epithelial cell of SI
• Amino acids are transported via facilitated diffusion from epithelial cells of SI into capillary
  -Sodium is transported via sodium potassium pump out of the epithelial cell into the blood capillary
• Potassium leaves from blood capillary to the epithelial cell
• Sodium is transported alongside amino acids to maintain a high concentration of amino acids within the epithelial cell

Question 6

What are micelles are why are they important?

Answer 6

• Micelles = monoglycerides and fatty acids + bile salts
• Monoglycerides and fatty acids are not soluble and too large, so micelles allow them to reach the surface of the epithelial cells
• Micelles break down and add to a pool of fatty acids and monoglycerides that are dissolved in the SI solution surrounding epithelial cells
• These freely dissolved molecules enter the epithelial cell via diffusion
• Non-polar so can diffuse through the phospholipid bilayer

Question 7

How do lipids then absorb?

Answer 7

• Short FA chains can move directly into blood via diffusion
• Longer FA chains link with monoglycerides and glycerol to form triglycerides
• Triglycerides are packaged into lipoproteins called chylomicrons
• Chylomicrons are then transported to a lacteal via exocytosis
• Lymph in lacteal transport chylomicrons away from SI and into the bloodstream

Question 8

How do you calculate magnification?

Answer 8

Image size ÷ actual size