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- In this chapter,

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we're looking at the urinary system.

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Now, we're talking
about the urinary system

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and how the urinary system

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can help with homeostasis,

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but one of the main roles

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of the urinary system is excretion.

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Excretion: removing waste from the body

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or simply excess material.

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Things that you have too much of.

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So, there's four main systems

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that go through excretion.

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We have the digestive system.

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Anything that is extra

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or anything that was a waste product

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from the liver is removed.

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Now, your digestive system is removing

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both solid and liquid waste.

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Respiratory system, well,

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you're removing excess amounts

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of carbon dioxide.

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Now, it's important, your body must

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have certain levels of carbon dioxide,

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but too much becomes a problem.

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So, your lungs can go through excretion.

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Integumentary system,

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well, that's your skin.

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Your skin can excrete water.

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Your skin regularly excretes salt.

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That's why sometimes if you ever get

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sweat in your eyes, it stings.

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That's the salt.

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If he ever get sweat in your mouth,

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it tastes a little salty

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due to the salt content of the water.

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And of course,

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we're talking about the urinary system,

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so we need to make sure the urinary system

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also goes through excretion.

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Nitrogenous wastes, excess solutes,

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waters, pretty much any liquid waste

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or liquid component is
removed by the urinary system.

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Alright, so here we have a figure.

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Let's start with the food intake.

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Food and water intake all starts off

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in the digestive tract.

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Well, if you don't use the food,

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then you have to eliminate it,

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so it comes out as feces,

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but some of it,

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the nutrients and water, are absorbed.

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They're pulled into your system,

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into the circulatory system.

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Well, from the circulatory system,

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you'll head to the
liver, one of the places,

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where you try and go through

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is creates metabolic products.

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Unfortunately, pulling out toxins.

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There's things in your food

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that you wouldn't really
want in your body.

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Well, the liver can get
rid of waste in two ways.

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It can go right back
into the digestive tract

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or head in the circulatory system

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and head out a different way.

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Use your skin (mumbles) water and salt.

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Your respiratory system,

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getting rid of CO2, but picking up oxygen.

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Now, if you notice water just popped up.

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So, both the respiratory system,

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not only are we getting rid of CO2,

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we're also getting rid of water.

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Think about it this way:

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if you've ever been outside on a cool,

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cool day or evening,

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and you exhale through your mouth

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and you see your breath in front of you,

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that's showing you that
there's water content

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in that exhaled breath.

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And the yellow parts your urinary system.

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That's what we need to focus on.

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The urinary system will take excess water,

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excess solutes, which could be salt,

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could be calcium, and any liquid waste

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from the circulatory system,

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filter it out, and excrete it.

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Eliminating all these components

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in a liquid format.

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So, excretion really can occur

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in many different ways,

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but all of these systems

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are all working together.

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Alright, so let's start with the kidneys.

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The kidneys, themselves,

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really help to control
your body's water level.

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Now, they're not the only thing

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to control water levels,

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but they're one of the major ones,

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so anything that you have excess of,

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especially excess water,

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is excreted.

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You can think about it this way:

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the more fluid you drink in a day,

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the more you urinate.

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It's because your body has too much water.

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Now, the output varies
from person to person.

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Depends on environment.

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Is it dry, is it

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hot?

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Depends on person.

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Depends on what their activity levels are.

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It can go anywhere from two

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to 2 1/2 liters a day,

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which isn't that much,

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all the way up to a liter an hour

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if there's a lot of fluid being consumed.

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But besides the water,

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you're also getting rid
of nitrogenous waste.

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You have nitrogen from your amino acids.

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Remember amino acids

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were part of protein.

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So, you get rid of these
nitrogenous wastes.

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You can get rid of other metabolic waste.

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Things along the line of sodium,

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chloride, potassium, calcium,

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even hydrogen.

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All these different components

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can be removed from your
body through your urine.

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So, where do you get your water from?

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Well, you first off, you drink in water.

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The amount of fluid you drink in a day

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is usually about a thousand
milliliters or a liter.

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Some people drink more,

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some people drink less,

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but even if you think,

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"Well, I drink a lot,"

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look at how much water comes in the food.

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There's more water, on average,

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in your food than there
is in the water you drink.

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Well, think about it this way:

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the food you eat,

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is it all completely rock solid?

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No, there's different textures to it,

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different consistencies.

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That's all based on the amount

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of fluid in the food.

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And then metabolic production,

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this is dealing with when your body's

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going through chemical processes.

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Some of these chemical processes

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ending up giving off water

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as a by-product.

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So, all said and done,

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on average you're looking

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at about 2,500 milliliters per day

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or

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2.5 liters gained per day.

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Water loss?

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Well, your water loss

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should hopefully match your water gain,

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so on average the most fluid loss

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comes out of urine.

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Makes sense,

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but look how much you lose

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from just breathing.

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The simple act of breathing

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allows for evaporative loss

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of about 500 milliliters a day

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or about half a liter.

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You lose about a little through the skin

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and of course, you have

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to lose some through the feces.

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Now, depending on the feces,

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the amount changes if it's
more solid, more loose.

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Evaporative loss, the skin,

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the more clothing you have on,

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the more it keeps the fluid on the skin

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or in the skin.

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There are some variables here,

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but on average,

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ya gain 2,500, you lose

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2,500 milliliters per day.

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Looking at the kidneys

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from an anatomical standpoint,

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this could be the primary

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or principal organ of a urinary system.

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In total, there are four different organs

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found in the urinary system.

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We're gonna focus on the
kidney to start with.

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Now, the kidneys have a cortex.

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The cortex, as you can see in the figure,

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is gonna be the outside
area of the kidney.

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So, it's really the outer portion.

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The outer coating.

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But it's not just a shell,

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there's actually some depth to it there.

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Once you go to the inside,

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you get the medulla.

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Can you see those things

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that almost look like triangles

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or guitar picks?

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Well, from there inwards,

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so the whole inner area,

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is the medulla.

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Now, in general, cortex medulla:

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cortex just means outside,

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medulla means inside.

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Now, the two kidneys located

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more in a posterior,

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more towards your back.

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They're just towards the
bottom of the rib cage.

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The kidneys, themselves,

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are fed by what's called the renal artery

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and blood drains the renal vein.

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Well, that renal artery's pretty important

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because that's how all the blood

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gets in the kidney,

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that's how all the blood gets filtered.

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Now, the filtration of your blood

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occurs in the far
right-hand side, you see,

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where you have this
thing called a nephron.

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The nephron will allow the blood

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to be filtered and then we'll change up,

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absorb, reabsorb, secrete

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what's in that filtrate,

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what's in that fluid.

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The whole point of a nephron

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is to make sure

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that the urine that's being released

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has the proper concentration,

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the proper ionic balance.

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So, the nephron is going to add

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and subtract ions as necessary.

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Well, another organ
from the urinary system

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is the ureter.

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The ureter is meant to take the urine

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from the kidney, where it's produced,

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down to the urinary bladder.

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Well, the urinary
bladder stores the urine.

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Now, I have 600 to 1,000 milliliters.

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Again, depends on the person,

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depends on the size of bladder,

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but everyone knows there's that point

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where just the urinary bladder cannot hold

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the urine anymore,

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so there's a variable here.

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And we have the urethra.

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The urethra is what allows the urine

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to carry it from the urinary bladder

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out through an external orifice,

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but the urethra has these two sphincters.

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Sphincters are a ring of muscle

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that allows to be closed
or opened, relaxed.

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So in this case, these sphincters

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are helping to keep the urine

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in the urinary bladder

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or they open up and allow the urine

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to travel through the urethra

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out of the body.

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Now, the male and female system,

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there are some similarities

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and some differences here.

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Both males and females have kidneys.

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No question there.

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Both have ureters.

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Both have urinary bladders.

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The difference comes though,

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from the size and position

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of the urinary bladder and urethra.

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Now, you can see in
the female system here,

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the urinary bladder, a lot of times,

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is a little bit smaller,

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more compressed,

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due to the presence of the uterus.

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But then the pathway
from the urinary bladder

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out through the urethra,

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the female has a much shorter urethra.

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The male has a much longer urethra.

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And this urethra length

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is one of the reasons why,

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a lot of times, females

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have a greater chance of
urinary tract infections.

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It's a shorter distance

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and it's easier for infection

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to get up a short urethra

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than a longer urethra.

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So, the urethra is a major difference

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between male and female,

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but still all four organs are present.