4.5 - Co-transport and absorption of glucose in the ileum Flashcards
What helps increase the rate of movement across membranes in epithelial cells
- the epithelial cells lining the ileum posses microvilli
- they’re projections of the CSM, 0.6 micrometers in length, collectively form a ‘brush border’
- they provide more SA for the insertion of carrier proteins, so movement across the membrane can take place
- another mechanism = increased density of protein channels + carrier proteins in any given area of the membrane
Describe the role of diffusion in absorption
- carbohydrates and proteins are being digested continuously
- normally: greater conc. of glucose/amino acids in the ileum than in the blood. (Therefore there’s a conc. gradient that glucose/amino acids move down via facilitated diffusion from ileum to blood)
- because blood is being constantly circulated by the heart, the glucose absorbed into it is being constantly removed by cells as they use it up during respiration
- this helps maintain the concentration gradient between the inside of the ileum and the blood
- this means that the rate of movement by facilitated diffusion across epithelial CSM is increased
Describe the role of active transport in absorption
- diffusion only results in the concs. Either side of the intestinal epithelium becoming equal
- this means that not all the available glucose/amino acids can be absorbed in this way and some may pass out of the body
- the reason why this doesn’t happen, is because glucose/amino acids are being absorbed by active transport
- this means that all the glucose/amino acids should be absorbed into the blood
- the actual mechanism by which they’re absorbed from the small intestine is an example of co-transport
Why is the mechanism by which amino acids/glucose absorbed from the small intestine is an example of co-transport
- either glucose/amino acids are drawn into cells along with sodium ions that have been actively transported out of the sodium-potassium pump
- (go to 4.4 to see how this works)
What are the uses of vesicles
- Active process for mass transport of large molecules
- usually involves transport to/from lysosomes
- done in 2 types of ways: endocytosis or exocytosis
What is endocytosis
- mass transport of large molecules into the cell
- 2 examples:
- phagocytosis (large insoluble molecules or pathogens)
- pinocytosis (smaller soluble molecules in solution)
What is exocytosis
Mass of transport of large molecules out the cell
- exocytosis allows cells to secrete waste substances and molecules (such as hormones and proteins)
- exocytosis is important for chemical signal messaging and cell to cell communication
- exocytosis is used to rebuild the cell membrane by fusing lipids and proteins removed through endocytosis back into the membrane
Give 2 examples of exocytosis
- transport of neurotransmitter into synapse
- release of hormones
What is a co-transporter
A type of carrier protein
How do co-transporters work
- they bind 2 molecules at a time
- the conc. gradient of one of the molecules is used to move the other molecule against its own concentration gradient
Where is glucose absorbed into
Glucose is absorbed into the bloodstream in the small intestine
Describe how the glucose co-transport works
- Na+ ions actively transported out of the ileum epithelial cells —> the lumen of the ileum (by the sodium-potassium pump). Creating concentration gradient — higher conc. Na+ ions in lumen of the ileum, than inside the epithelial cell
- this causes Na+ ions to diffuse from the lumen of the ileum —> epithelial cell, down their concentration gradient. They do this via the sodium-glucose co-transporter proteins
- the co-transporter carriers glucose into the cell with the sodium. As a result the concentration of glucose inside the cell increases
- glucose diffuses out of the cell, into the blood, down its concentration gradient through a protein channel, by facilitated diffusion
Where is glucose being Co-transported
The Mammalian ileum
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