Co-transport and absorption of glucose

1. Co-transport and absorption of glucose • How is the small intestine adapted to adsorb digested materials? • Write down as many ways as you can think of • Hint: think about Fick’s law

2. Adaptations of the small intestine for absorption • Long... Large SA for efficient absorption and give time for exchange to occur

3. Adaptations of the small intestine for absorption • Folded...further increases SA

4. Adaptations of the small intestine for absorption • Villi...finger-like projections which increase SA

5. Adaptations of the small intestine for absorption • Epithelial cells have micro-villi to provide a large surface area

6. Adaptations of the small intestine for absorption • Thin epithelium (inner layer)...one cell thick • This creates a short diffusion pathway

7. Adaptations of the small intestine for absorption • The villi have a good blood supply – takes away products of digestion and maintains a concentration gradient

8. Absorption occurs via 3 processes • Diffusion (for small/non polar molecules only) • Facilitated diffusion e.g. glucose, amino acids • Active transport e.g. glucose, amino acids

9. Diffusion • The net movement of substances from an area of high concentration to an area of low concentration. • Passive process • Reaches an equilibrium

10. Facilitated diffusion • Involves a carrier protein or channel protein • Is a passive process • Equilibrium is reached

11. Active Transport • Substances are moved against a concentration gradient • This requires a supply of energy • This energy comes from ATP • Ensures that all glucose from food is absorbed

12. Co-transport • Glucose must be moved from the lumen of the gut into the epithelial cells • But the concentration of glucose can be higher in the epithelial cells than in the gut • Transport into the cell requires energy • Glucose is drawn into the cells along with sodium ions that have been actively transported out of the cells

13. Na+ high concentration Glucose Lumen of small Intestine Co Transport Na+ low concentration Glucose Epithelial Cell K+ Active Transport Facilitated Diffusion Blood Capillary Glucose K+

14. Co-transport • Sodium ions are actively transported out of the epithelial cells and into the blood. • This maintains a lower concentration of sodium in the cells than in the lumen • Sodium ions (Na⁺) then diffuse into the cells from the lumen through a co-transport protein. • Glucose is carried into the cells with the sodium ions • Na⁺ ions move along a conc. gradient whereas glucose molecules move against their conc. gradient

16. Movement of glucose into the blood • Glucose molecules move into the blood via facilitated diffusion (high concentration in epithelial cells to low concentration in the blood)

17. Co-transport • It is the sodium ion concentration gradient, rather than ATP directly, that powers the movement of glucose (and amino acids) into cells. • Indirect form of active transport

18. Extended Writing • Describe how substances move in and out of cells (10 marks) • 5 minutes to plan your answer

19. Extended Writing • Describe how substances move in and out of cells (10 marks) • 15 minutes to write your answer

20. Peer Marking • Swap your work with someone else • Get three colours: red, yellow and green. • In the margin put a… Green dot next to any good points or effective use of key words Yellow dot next to any errors in English Red dot next to any errors in science