| The Transfer StationThe Capillary Bed | We have seen in previous lessons that the capillaries are the smallest vessels that connect arteries and veins. | | Capillaries are also very thin, only one cell thick. Why do you think this might be important? | | Let's think back about the size of capillaries. Look back at previous lessons and refresh your memory about their size. Also think about the size of cells. | | In the picture below there is a capillary that lies next to a group of cells. Does this help you think about the interaction between capillaries and cells? | | Now let's look at how the capillaries might lie in the intestines. Remember the animation you saw of the intestines? On the inside the lining of the intestines you could see many folds that are called villi. | |
| Talk this over with your group. | |
| STOP!! Before proceeding be sure students have a model of movement of nutrients out of the intestines into the capillaries. They will use this model in the next lesson. | | Below is a drawing of a few villi. The large circles represent the cells that line the walls of the villi. What do you notice about the cells? How many layers are there? | | Think about your prior ideas about diffusion. Can you think of a way that the nutrients in the interior of the intestines can move through the villi and into the bloodstream? | | Now think about how the blood vessels lie in relation to the villi. | | What is the most efficient placement of the blood vessels so they can pick up the most nutrients? Make a drawing of this. | | Can you think of a reason why this configuration is most efficient for movement of material from the inside of the intestines into the blood stream? Be ready to support your answer. | | Now that you have come up with some of your own ideas about how nutrients get from the inside of the intestines into the circulatory system, draw your model in your lab book. | |
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