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Let's say that you've got a blood vessel

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here, and it's a longish blood vessel

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and we'll give it a resistance of eight, and it has three branches

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say two big ones, and a tiny one in the middle

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and this goes straight across, and this has a resistance

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of ten, and these biggish ones, they

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have resistance of say, half that, so they're about

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five, and on this side, they all come together again

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and enter a short vessel, this has a resistance of three

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so my question to you is what is the total resistance of blood going in here

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and out here? So, again, it's going to have to go through this eight bit, and then it has three choices here

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here, here or here, but eventually they all come together again into that three bit, and then exit out the other side

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So, what is the total resistance, so what is Rt resistance, that's the question, and

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what I'm going to do is to divide this into two parts: part one

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i'm going to figure out in part one, what the resistance is for this part, right in here

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so I can do that using an equation I introduced in the last video, which was you can basically take

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Rt, which is the total resistance for that yellow box, equals one over, one over five plus one over ten plus one over five

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and i can look at that and tell you that the common denominator is going to be ten

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Right? For all three, and in the numerator, we got two, one and two.

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So, putting it all together, I got one over..., what is that, five over ten.

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And that equals, ten over five, which equals two

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So that tells me that the resistance in this middle, yellow box is two

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and that makes sense with our rule, because we said that when things are in parallel, the total resistance

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is going to be less than any components, and in fact two is less than five, ten and five, right?

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It's less than any of those numbers individually.

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So, we've got now in part two, we have three things in series, right?

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We basically have something like this, we have eight, and we have two, and we have three.

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So, we've got basically three things in the series, and so we simply add those up

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and i'm going to say Rt now equals eight plus two plus three

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And so Rt equals thirteen, so if I wanted to know what is my total Rt, my total resistance

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I would say it is thirteen, so that's the answer to this problem

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And, what I wanted to get you thinking about is total resistance for the body, the human body

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, which has obviously more than just a few vessels, unlike I have in this diagram here

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LIterally, thousands and thousands of vessels