Understanding Membrane Transport: Mechanisms and Importance

what's up ninja nerds in this video today we're going to be talking about membrane transport before we get started

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so when we talk about membrane transport uh we have a lot of different mechanisms that we have to go through

so the first one that i want us to talk about is simple diffusion simple diffusion it really is

simple and what simple diffusion involves it's a passive process and we'll talk what that means a little bit

later but the first thing you need to know about simple diffusion is that it's a

passive process it kind of means it doesn't involve any energy

so what we'll put next to this is that there's no atp that is utilized in this type of membrane transport

mechanism now that's the first thing that i want you to know the second thing i want you

to know about simple diffusion okay is that this allows for molecules okay particular types of molecules and

we'll discuss which ones to move from areas of high concentration to areas of low concentration

through the cell membrane we have to briefly talk about what the cell membrane is made up of

so with that being said we're taking things and moving it from we're going to abbreviate this a high

concentration gradient to a low concentration gradient that is our concept of simple diffusion

it can just move straight through this cell membrane without having to use a specialized

transport proteins this is going to be things like respiratory gases you know what kind of

respiratory gas is what substance moves from the blood into the cells

do you know which molecule it is this is oxygen oxygen is extremely important because oxygen is carried

on hemoglobin in your red blood cells and taken to the tissues where it's dropped off to the tissue

that's one example so oxygen would be one molecule that moves across the other one is you

know whenever your cells are performing um you know aerobic cellular respiration what's one of the byproducts that is

produced from aerobic cellular respiration co2 so it's a waste product that's actually

produced by what by our cells and this will get pushed out of the cell into the blood

carried by red blood cells to our lungs so that we can exhale them that's one example

so oxygen co2 these are molecules that are going to be examples that move by simple diffusion but we have other ones

really important ones you know we have these hormones very interesting hormones we're going to

draw these hormones like this just a generic structure of them and uh there's no specific thing to this

i'm just kind of doing it for you know the simplicity taker let's say here we have this molecule here

this is a hormone that's derived from cholesterol so we call this a steroid hormone

steroid hormones are lipid soluble and this allows for them to move into the cell without needing a

transport protein or some type of carrier so what kind of molecules can also move

into the cell things that are going to be steroid hormones give me examples

of steroid hormones i know you guys know a bunch of them testosterone estrogen progesterone

aldosterone cortisol vitamin d there's so many different things

one more that i really want you to remember don't forget this one it's also going to be lipid soluble

drugs so i want you to also remember let's kind of do it like this

a little pill here you know drugs that are really really lipid soluble they also have the ability to pass

through the cell membrane without needing a transport carrier so the last thing that

i want you to remember is lipid soluble drug and there's so many of these so with

that being said what are the different molecules that can move by the process of simple diffusion

which is going across this actual cell membrane without needing a transport protein and again it can go into the

cell or out of the cell but it doesn't need a transport protein oxygen co2 steroid hormones

and what else lipid-soluble drugs okay we talked about that there all right now that we understand that

let's talk a little bit more about this if you guys have noticed something about these molecules and how they're

diffusing across the cell membrane they're not needing a transport protein there's a reason why and you have to

know a little bit about the cell membrane let's talk very quickly about the cell membrane

when you look at the cell membrane we have these little red structures here what are these red structures

you have a point here that's like the head of this phospholipid and then you have these little fatty

acid tails very important these are on both sides so they're kind of abutting one another

here so you're going to have these little things here what is this little head

here called this head here is called the phospholipid

okay that's our phospholipid and the big thing to take away from this is that this is a polar

molecule the other component of this is your fatty acid tails so your fatty acid tails now the fatty acids what's

really important to remember out of this is that they are nonpolar now

what's really important is that this phospholipid bilayer really prevents polar molecules

from being able to cross the cell membrane because of these phospholipids you see this phospholipid head

it's on the outside and inside so what it does is it prevents molecules that are really

charged what does that mean that they have like a positive charge or they have like a negative charge

these polar heads these phospholipid heads basically prevent or kind of repel

these charge molecules from getting into the cell or getting out of the cell

that's really important so one reason why these things like oxygen co2 steroid hormones and lipid soluble drugs

can pass freely across the cell membrane is because they're not charged the other reason is that they're

very lipid soluble and guess what fatty acids are very nonpolar

so because they're very nonpolar things like oxygen co2 steroid hormones and lipid soluble

they're also nonpolar so because of that they can dissolve right across the cell membrane because of these fatty acid

tails so two reasons why these things can move across the cell membrane

one is because the phospholipid head repels charged substances and the fatty acid

tails are nonpolar and these things oxygen co2 steroid hormones and lipid soluble drugs

are also non-polar and remember that term they always love to use that like dissolves like so if you have

something that's lipid soluble or nonpolar it's going to dissolve

within a lipid-soluble or nonpolar type of substance so that's important one more thing that

we have to hit off here with this simple diffusion process there's a particular

rate at which these things can diffuse across the actual cell membrane and more particularly

the ones that i really want us to talk about is oxygen and co2 the diffusion the rate of

diffusion of these molecules across the cell membrane is very dependent on a couple different

factors so let's say the rate of diffusion the rate of diffusion and particularly which ones are we talking

about here we're talking about oxygen and co2 this is dependent upon a couple specific

factors one of them is the surface area so you know whenever you have a cell the

larger the surface area of the cell the more diffusion can take place across that cell

and that's going to increase the rate of diffusion so one thing the rate of diffusion will increase with

surface area that's one big thing the next thing that's also going to affect the rate of

diffusion is also going to be the concentration gradient

when the concentration gradient is very high in other words they have a high concentration gradient for example

oxygen is higher outside the cell lower inside the cell co2 is higher inside the cell lower

outside the cell whenever they have a high concentration gradient or big concentration gradient

is going to cause more of these molecules to move in that their corresponding direction okay so the

higher this gradient is here and the lower the co2 is out here the more co2 is going to diffuse across

the more oxygen we have outside the cell and the less oxygen we have inside the cell the more oxygen is going to diffuse

across so the other thing that's also really important here is the concentration

gradient the other really important thing here is going to be the thickness of the cell membrane

you know when the the cell membrane is very very thick that's a farther distance that these

oxygen co2 molecules have to move so if you have a thicker cell membrane it's going to

decrease the rate of diffusion so what i want you to remember is we're going to put here t for thickness

of the actual cell membrane and then one more the last one here is going to be the weight

okay if you have something that's really really heavy the diffusion the rate of diffusion

across the actual cell membrane is going to be a much slower than a substance that's very

light so also we're going to say the weight of that molecule the heavier the weight

is the lower the rate of diffusion so at the end of all this what i want you to take away

the rate of simple diffusion is going to increase with increasing surface area and increasing

concentration gradient the rate of diffusion will decrease with increasing thickness of the cell

membrane and increasing weight of the corresponding molecule

boom roasted we just killed that right so again that should discuss our simple diffusion

process it's molecules moving across the cell membrane down their concentration gradients

and again it's because they're lipid soluble they're non-polar they're not charged that they can do this process

and again we know what things can increase the rate or decrease the rate of these molecules diffusing across the

cell membrane let's now move on to the next part of membrane transport all right so now the

next type of membrane transport mechanism is going to be very very similar to simple diffusion

and what do i mean by this for the most part facilitated diffusion is a passive process again that means

that it doesn't really require any energy it's a passive process so usually for the most part

it is a passive process usually no atp is required directly for these processes to occur

now here's the difference though here we said that things are in the simple diffusion

things are molecules are going from high concentration to low concentration whether that mean that they go from in

the cell to out the cell or out of the cell into the cell it doesn't matter these

molecules that are diffusing across the cell membrane whether it be simple or

facilitated are moving from high concentration gradients to low concentration gradients so that's

not changing here's the difference in simple diffusion do you see any

transport proteins that were allowing those molecules to move across the cell no in facilitated diffusion

you need a protein whether it be a channel or whether it be a carrier to shuttle

those molecules across the cell membrane that is the biggest difference between facilitated

diffusion and simple diffusion so again what does this mean it means you require

two things it requires a channel and we'll talk about the different types of channels

or it requires a particular carrier to mediate that diffusion process that is super

super important okay so now that we know that let's talk about the different types

of facilitated diffusion one of the big one and everybody knows this one is osmosis

osmosis is the movement of water from areas of where high concentration to areas of low concentration so for

example if there was more water outside of the cell

and less water inside of the cell where's the water going to move pretty straightforward it's going to

move from outside the cell to inside the cell this is the process of osmosis but there's another way that

we describe osmosis it's not just dependent upon the concentration of water

but it's also dependent upon the solute concentration let me explain what i mean let's say i take this pink color here

let's say i put a lot of salt so here's a lot of sodium chloride that's in the cell and only a teensy

little bit of sodium chloride is outside the cell where's the sodium chloride

concentration higher it's higher inside the cell and it's lower outside the cell

so water loves to move from areas of high water concentration to low water concentration

but water loves to move from areas of low solute concentration to areas of

high solute concentration and what that means is that there's lots of glucose or sodium usually this is the

perfect example so usually these little molecules we're representing as something like

sodium or glucose so this could be something like sodium or this could be something like glucose

so wherever there's higher amounts of sodium and higher amounts of glucose water is

going to move to that's the important thing and what is this process here called

this process we just described is called osmosis and it's a particular type of facilitated diffusion now

should we know what kind of transport protein really or channel protein that allows

for water to move in or out of the cell depending upon the water concentration

or solute concentration yeah generally these proteins are referred to as aquaporins they're called aqua

porins so this is an important thing to remember and the reason why is that there's many different types of

aquaporins we're not going to go into detail on that but what i want you to know is that

these channels these aquaporin channels are what allows for water to move across the cell membrane

either down its concentration gradient or moving to where there's areas of high

solute concentration boom roasted let's move on to the next type of facilitated diffusion

there's these different channels and we have to discuss these and i like to remember these based upon

their different ways of like mechanism so what we're going to do is we're going to label these these couple channels

here because these are other types of channels that control the movement of ions

this one here in red is called a leaky channel that's the first one i want you to remember the one in

orange is our voltage gated it's our voltage-gated channel so we have different channels we

have a leaky channel we have a voltage gated channel and then here in purple we have

a ligand gated channel what's this next one called

ligand gated so ligand or chemically gated ion channel and then the last one here is going to be the

mechanically gated so the mechanically gated ion channel so again these allow for

you know molecules that are charged to move across the cell membrane utilizing these special transporters so

that's another thing we have to talk about facilitated fusion we know that it's things moving from

high concentration to low concentration utilizing channels and carries like we talked about with water but remember

with simple diffusion what things were not moving across the cell membrane charged molecules why why couldn't

charge molecules move across let's see if you guys remember remember we said that here's the

phospholipid usually phospholipids have a little bit of a negative charge so because of that things like negative

charge or positive charged molecules will be kind of like in some way repelled or

prevented from being able to move across that actual cell membrane right so because of that we need a

channel that will allow for these charged molecules or polar molecules

to move across the cell membrane and that's where these channels are coming in

so the first one is your leaky channels and leaky channels are really really important especially in neurons

you know what is the most important leaky channel that you need to remember your potassium leaky channels these are

super super important now here again we have to understand this high to low

concentration gradient so potassium is really high inside the cell but potassium is really low

outside the cell so whenever these channels are open which is pretty much all the time in neurons where's the

potassium when i want to flow it's a charged molecule it's going to want to move from

inside the high concentration to areas of low concentration so it's going to want

to move from inside the cell to outside the cell these leaky channels again what are they

very very important in they're important what i want you to remember is that these are super

important within neurons and within neurons these leaky potassium channels control

the resting membrane potential in these neurons another reason why we should really

understand these leaky potassium channels so again potassium moving from areas of high

concentration to low concentration utilizing a channel and again it's a charged molecule so it can't diffuse

across the cell membrane it needs this channel to perform it simple right all right next one voltage

gating these are very important especially within neurons

and let's think about these particular with sodium this is the best example you can be calcium it could be sodium it

could be whichever one you want we'll pick both of them frequent right so here we'll have lots of sodium

we'll have lots of calcium and usually the sodium ions are really high and the calcium ions are higher outside

the cell and they're lower inside the cell so whenever there is a

particular voltage what does that mean usually these voltage-gated

sodium or calcium channels you have to hit a specific threshold again it could be a specific threshold

maybe it's like negative 55 millivolts and whenever you hit that threshold boom these channels open because normally if

you're not at that voltage the channel's closed but if we hit a particular voltage like

let's say negative 55 millivolts what's usually threshold potential in neurons what happens this channel will open and

allow for sodium ions to rush into the cell or allow for calcium ions to

rush into the cell and allow for what kind of process well let's explain what that will be significant for

usually these voltage-gated voltage-gated channels usually sodium or calcium

are really important in neurons and guess what they're important for action potentials so usually these are

very important to remember for your action potentials okay all right so we understand this concept

of leaky channels we understand the concept of voltage-gated channels what about the

next one the ligand-gated ion channels again we have to move a

charged molecule across the cell so we need a channel and it needs to be only open when a

particular molecule binds to it let's use the classic example of at the neuromuscular junction you

know the neuromuscular junction your neurons release a particular chemical called acetylcholine and whenever

acetylcholine so let's put here acetylcholine whenever this acetylcholine binds into

this little pocket here that's on the channel usually this channel is closed so no ions are moving across this actual

channel whenever the acetylcholine is not bound to it but when acetylcholine binds into this

little pocket guess what it does usually this kind of gate here is blocking ions from moving

in but when acetylcholine sits down in this pocket it's like a seesaw

it lifts the thing up and now that gate that was blocking the entry is going to open

and it's going to allow for ions to flow in what kind of ions usually this is sodium ions where's

sodium higher in you know sodium is high outside the cell and it's low

inside the cell so because of that where would sodium want to flow when this channel is open because acetylcholine

binds it'll want to go into the cell and when it goes into the cell it's going to do

what it's going to trigger an action potential and lead to muscle contraction

so again where would this channel be very important to know it's important at your

neuromuscular junction because it's going to induce an action potential

and that action potential is going to induce muscle contraction do you see how

something as simple as this little channel can make a difference in our body

okay beautiful another one another channel mediated facilitated diffusion is called

mechanically gated let's say that uh you're you're helping a friend you know you're helping a friend moving something

around his house okay you're picking up a couch all of a sudden he drops one end and then the

couch comes in it falls and smashes your finger that smashing of the finger applies a

particular amount of mechanical stress and you know there's particular nerves pain

receptors that are there in your fingers whenever they get smashed and whenever that actual mechanical

stimulus let's say that it's actually going to be you know a large amount of pressure

is going to stimulate this because again you got your fingers smashed by the couch

that large amount of pressure is going to open up little channels on the pain receptors

and allow for ions to flow in maybe ions like sodium okay maybe ions like sodium will

flow in and as the sodium ions flow into that actual mechanically gate

into that actual pain receptor what's it going to do induce action potentials so again sodium will move from areas of

high concentration to areas of low concentration now you always remember that sodium is always higher

outside the cell and lower inside the cell so whenever you have a particular

pressure that is the stimulus opens up the mechanically gated channels on those pain receptors

when it opens up sodium flows down its concentration gradient into the cell and again why would this be important if

you think about this in like pain receptors right we call them noisy acceptors

this could activate them and then send that actual signal down your pain pathway

and again this could get sent down sensory nerves so this could stimulate the sensory nerves

and induce kind of a pain signal that'll go to your central nervous system right so

something as simple as this that could give us an example of again this facilitated diffusion that is

particularly channel mediated we got one last one for facilitated diffusion that's this carrier-mediated

facilitated diffusion this one is really important i really need you guys to understand this one

okay this last one here for facilitated diffusion is channel mediated and again these

channels are really going to be present sometimes they're present only whenever there's a particular

stimulus and i'll explain what i mean by that or they're present they're open all the

time so what are some examples of these channel mediated molecules well let's say that we take for example the

most classic one glucose you know glucose it's in generally in higher concentrations

outside of our cell and it's going to be in lower concentrations sometimes

inside of our cells okay so because of that if i want to get glucose

particularly in certain types of tissues like maybe your muscle your adipose tissue stuff like that

if i want to get glucose into the cell to utilize it to make atp and generate energy these channels or

these carriers will have to move the glucose into the cell down its concentration

gradient and these little carrier channels are usually referred to as

glut transporters so you're glut transporter you know there's different types of gut transporters

found all over your body we're not going to go into great detail but what's the big ones that i really want you to know

is your glut4 your glut4 transporters are found particularly in what tissues your adipose and it's also found in the

muscle tissue you know what happens with these glut4 transporters if someone needs if someone needs to get glucose

into their tissues you know what hormone regulates the activity of glucose primarily

insulin insulin will stimulate guess what the increased expression in other words

i'm going to put more of these glut transporters into the cell membrane if i have more of these glut

transporters expressed onto the cell membrane what am i going to do i'm going to bring lots of glucose from

outside the cell to lots of glucose into the cell that is why something as simple as this

type of carry-mediated process is important so again facilitated diffusion how can we wrap this up to

describe it again passive usually no atp and that means that in order for that to happen things

need to be moving from high concentration to low concentration but the only way these charged molecules

or large molecules can get across the cell membrane is they need a particular protein channel

or a particular protein carrier that allows for them to cross that so again that's the last thing i want to

mention facilitate diffusion is important for large and charged

molecules whereas simple diffusion is for small and non-charged molecules

right all right so that'll discuss that'll kind of give us the ending that we need for the facilitated diffusion

now let's move into the nitty-gritty stuff like the active transports all right so we talked about facilitated

diffusion now let's hit the primary active transport we have to understand what the heck that is

so primary active transport you can obviously see in this process it is an active process so what the

heck does that mean that means that it directly i want to write that down directly uses

atp in order to move these particular molecules that's the first thing that i need you

to know whenever somebody asks you what's primary active transport it's the direct utilization of

atp to move substances from areas of low concentration

so from a low concentration gradient to a high concentration gradient you're like

what the heck exactly we're going opposite exactly if a

ion or molecule has to move against its concentration gradient like it's going uphill it's going to need energy to

drive that process if it's going downhill it doesn't require much energy it's pretty easy

but if we have to move something against this concentration gradient we need to utilize atp directly to pump

those things against their gradients these are very very important okay and the next thing is we have to talk

about is how do they directly utilize atp there's usually little atp aces so usually these channels have

little enzymes called atp aces on them and what that means is is they take a molecule like

atp and break it down into adp and an inorganic phosphate and when you break this

bond the usually the third phosphate group on atp it creates a lot of energy and that

energy that you generate is what drives the movement of these ions or molecules against their concentration gradient

that's the big thing i want you to take away now the last thing we need to talk about

is what are some of these examples of primary active transport okay the first one that i want you to know about

is the sodium potassium atps if you forget all the other ones just please don't forget this one

this is the most important one the sodium potassium atp aces so again let's use our

understanding of what this primary active transport is moving things against their concentration

gradient okay beautiful where do we say that sodium was higher originally we said that sodium is higher

outside the cell that's something that we knew and we knew that sodium is lower inside the cell that's the first thing

where's potassium generally higher potassium we already know is higher inside the cell and potassium is going

to be lower outside the cell so guess where i'm going to be moving these molecules

i'm going to move sodium from areas of low to high so in other words i'm going to take three sodium molecules

so if sodium sodium sodium and these sodium molecules are going to move

from inside the cell to outside the cell against their concentration so they'll bind onto these little pockets and then

this transporter will flip if you want to think about it like that so that's the first thing with sodium

but then potassium two potassium molecules are going to have to bind to these little pockets of the atpase

and whenever these potassium molecules bind here again they're going to get transported into

the cell against their concentration gradient so in order for me to do that i need a

little pocket here let's say there's a little pocket in this transporter this little atp ace

molecule right what it's going to do is it's going to take that atp in it

and it's going to spit out adp and an inorganic phosphate and by doing that process what is it going to

what is it going to do it's going to flip these things so then it's going to transport three sodium molecules

from inside the cell to outside the cell and it's going to transport two potassium molecules

into the cell and again what are we doing in this process sodium is moving against its

concentration gradient potassium is moving against its concentration gradient

so we need atp directly to power that process straightforward this is one of the most important atp

aces that you can't forget you want to know why there's a lot of things that can

regulate this sodium potassium atps let me quickly mention a couple things and we'll go into a little bit more

detail of them later but the first one that i want you to know is that your sodium potassium

atp aces you know insulin if you have an increased amount of insulin insulin can

increase the activity of the sodium potassium atpases so in other words you're going to

control more of these sodium potassium atpases you're going to increase the activity of the sodium potassium atp

so utilize atp that's one the other one is your thyroid hormone you know t3 t4

if there's an increased amount of t3 and t4 your thyroid hormone that's also going to increase the

activity of the sodium potassium epiaces and you're going to generate more atp utilization and generate more heat

that's why sometimes if people have hyperthyroidism what do they usually have

a high body temperature an increased metabolic rate insulin is going to want to increase

your metabolism so that is the important aspect of these but there's also one more

you know there's a drug that we utilize a lot in heart failure patients called digoxin and digoxin

we'll talk about this later it loves to inhibit the sodium potassium atpases and that

creates this very interesting type of mechanism but we'll talk about that when we get over here

but digoxin is going to increase the contractility of our heart

via inhibiting the sodium potassium atps and we'll talk about that a little bit later but again

i want you to understand how it's relevant to know something at this cellular molecular level at the basic

level how that really builds on your foundation of science and medicine okay beautiful the next one that we have

to talk about here is these calcium pumps these are very very important so again the next

primary active transport is going to be your calcium atp aces okay

now the calcium atp so let me think let me give you an example here because again we're talking about the cell

membrane but i really want you to think about this for a second let's say that pretend this membrane is for the

sarcoplasmic reticulum so what i'm going to do is i'm actually going to draw really quickly another

small mini diagram let's say here is my sarcoplasmic reticulum okay here's going to be my

sarcoplasmic reticulum my sr okay and particularly within what kind of cells is your sarcoplasmic reticulum

really high your muscle cells there's special transporters that are on

this sarcoplasmic reticulum and that's these calcium atp atpases whenever your muscle is going through

relaxation so during the relaxation period so relaxation of the muscle particularly the one that

we really want to focus on here is like your cardiac muscle so during relaxation of the muscle what

happens is the calcium ions we need to get them out of the muscle cytoplasm and into the

sarcoplasmic reticulum why when you're relaxing your muscles we want the calcium to not be there because

calcium is going to continue to induce muscle contraction right so what we need to do is we need to push calcium into

this like little calcium storage center so what you need to remember is that the sarcoplasmic reticulum is a calcium

storage center there's lots of calcium in there and when our muscles are relaxing we

want to push the calcium which is in lower concentrations inside the cytoplasm we want to push it

into the sarcoplasmic reticulum which is where it's going to be in higher concentration in order for that

process to occur if i want to pump it from low concentration to high concentration what do i need

atp so i need atp in this process to pump the calcium from the sarcoplasm right the sarcoplasm which is

basically the cytoplasm of the muscle cell into the sarcoplasmic reticulum and by

doing that we prevent all the calcium from being out here in the sarcoplasm which is going to continue to induce

muscle contraction we don't want that so that's very very important you want to know why this is also another

important thing that we should know for the calcium atp aces you know when our our autonomic nervous

system particularly the sympathetic nervous system is increased let's say that during you have increased

sympathetic nervous system activity and what that means is that you're releasing increased amounts of

norepinephrine and increased amounts of epinephrine what these things do is is they come

over here and they increase an intracellular process through a molecule they increase

the expression of protein kinase a protein kinase a is going to come and stimulate the activity of

these channels it's going to increase the pushing of calcium from the sarcoplasm

into the sarcoplasmic reticulum why so during relaxation we're pushing tons of calcium more calcium than usual with

this sympathetic nervous system activity we're pushing more calcium than usual into the sarcoplasmic reticulum

whenever the next stimulus comes for the muscle to contract guess what we're going to do

we have so much calcium than usual in that sarcoplasmic reticulum that when the next stimulus to the muscle comes

we're going to blast calcium out into that cytoplasm more calcium is going to bind onto those

actual cross bridges that you know the troponin the super change the shape of the

tropomyosin and lead to increase contraction that's why something like that's so

important because increased sympathetic nervous system activity is going to increase the push of calcium

via these calcium atpases into the sarcoplasmic reticulum so whenever you have another muscle

stimulus we can push more calcium out and increase contractility that's important one more pump here one

more type of primary active transport to really drive home the point of this and that's going to be these

proton pumps you know proton pumps are really very important in your stomach you know how

your parietal cells have lots of proton pumps and really we call these proton

potassium atp aces but common you know terminology when you hear these is the proton pumps

and what happens with these is let's say here is going to be where the lumen of the

stomach is okay here's the lumen of the stomach and then this is the cell that's producing

the protons so we're going to call this the parietal cell so here's our parietal

cell and the parietal cell is the one that basically produces

the protons or hydrochloric acid in your stomach well what happens is is i want to push

protons right from inside the parietal cell out here into that actual lumen of the

stomach you know it's really high concentration of lumen of our stomach what do we have lots of in the

stomach we have lots of protons out here right because you know our stomach makes lots

of hydrochloric acid so because of that in the parietal cell there's going to be low amounts of

protons so that's the first thing that you have to remember is that what we need to do here is we need to

pump a proton against its concentration gradient when we push the proton against its

concentration gradient from inside the parietal cell to in the lumen of the stomach

i need to utilize atp so i need to directly break down atp in this process to push this proton

against its concentration gradient now there's another molecule that moves across here it's potassium that's why i

mentioned it but it's not relevant potassium can also kind of move in and out of this cell as

well but again big thing to take home here is that these proton pumps

which are in your stomach they're pumping protons against its concentration gradient so they need atp

why is this relevant well the reason why is these proton pumps these proton potassium atp aces but again mainly

proton pumps inside of your stomach they can be controlled via drugs you know those particular drugs

drugs called proton pump inhibitors and in people who produce a lot of hydrochloric acid they produce

too much of this protons or hydrochloric acid it can cause gerd it can cause peptic ulcer

disease and that's kind of you know could be damaging so what these proton pump inhibitors do is

they inhibit the activity of the proton pumps if you inhibit the proton pumps you

don't produce as much protons or hydrochloric acid into the lumen of the stomach

and that decreases the erosiveness that it can actually cause in the stomach decreasing the severity of

peptic ulcer disease and gastroesophageal reflux disease so again something as simple as

something at the chemical molecular level can be translated into a medical concept it's

it's amazing okay so we understand here i think we've really hit home

the basic scientific and clinical relevance related to primary active transport

mechanisms now let's finish up with secondary active transport all right so let's talk about the next

membrane transport mechanism which is secondary active transport so again pretty straightforward secondary

active transport again you can take away from the name it is an active process but let's be way

more specific remember primary you directly utilized atp in secondary active transport there is

indirect use of atp that's very important we'll kind of

explain what the heck that means in a little bit but for secondary active transport again

what's really happening in this is let's say that we take two molecules so let's say that i take molecule x if

we take molecule x that molecule could be moving from areas of high concentration

right so a high concentration gradient to an area of low concentration so one molecule

could be moving down its concentration gradient but let's take another molecule like

molecule y to areas of high concentration i'm moving it against its concentration

gradient okay now usually this x molecule is what we're going to talk

about for pretty much these examples here is going to be sodium it's going to be

sodium who's going to be moving down his concentration gradient and we'll talk about how

it's able to do that in a second but molecule y is going to be all the other things that

we're going to talk about glucose okay protons you know there's so many things amino

acids a bunch of stuff but other ions that have to move against its concentration gradient

it'll move with sodium whether it's moving in the same direction as sodium what is that called whenever two ions

are moving through the same transporter in the same direction what is that called

there's a particular name for that it's called symport so symport is when both molecules are

moving in the same direction so in other words they're going from outside the cell

to inside the cell both of them x and y antiport is going to be when one molecule is moving

into the cell maybe molecule x and molecule y is moving outside the cell so these are very

important things to remember about secondary active transport is that usually

molecule and x and molecule y can move same direction symport or opposite direction anti-port

okay now that we understand the basics of this let's talk first because this secondary

active transport is truly dependent it's dependent on that sodium potassium atpase

indirectly so let's explain that remember i told you that for pretty much all of these examples i'm going to talk

about sodium is going to be moving it's going to be molecule x it's going to be moving down its concentration

gradient how is sodium able to move down its concentration gradient is the important

aspect here so let's say that we take over here another diagram okay let's have over

here a little diagram and i'm going to have a transporter we've already talked about this

transporter but this transporter is a sodium potassium atpase

and what is it doing it's pumping three sodium ions out of the cell and two potassium ions

into the cell in order for it to do that it needs the utilization of atp we already know that well

this pump what is it doing if this is activating if it's working very very heavily

it's going to be really working hard to push lots of sodium out of the cell okay and so sodium will be in high

concentrations outside the cell so if the sodium is in high concentrations outside the cell

and i want to move something else with it who is going to kind of get to piggyback on him to get into the cell

that is what i'm going to use i'm going to use sodium as my person who's going to help to piggyback me

into the cell because i got to move against my concentration gradient so let's talk about the things that have

to kind of hop on the back of sodium to move into the cell the first one is probably one of my

favorite ones because you're going to see this a lot and this is the sodium

glucose co-transporter or and again you can actually uh uh talk we

can kind of name this a little bit later guess what sodium and glucose are moving in the

same direction so what what else what's another word we could call this sodium glucose symporter so i could also

call sodium glucose imported because that's what sodium and glucose are moving in the same

direction but neither here nor there sodium is going to move from outside the cell

okay to inside the cell and we know this concentration gradient of him is developed by who the sodium

potassium atpase so that sodium potassium atpase is going to build the sodium up

outside the cell glucose is the other molecule i need to get into the cell glucose in a particular example we're

going to use the kidneys glucose is in lower concentration in the kidney tubules

and in higher concentration inside the kidney tubular cells so in order for glucose to get

into the cell going against its concentration gradient who does it have to move with

sodium so sodium is the only way that glucose molecule is going to be able to get into the cell is because

it's piggybacking off the back of sodium who's moving down its concentration gradient

why the heck am i focusing on all this is there a reason yes there's drugs that

target this type of transporter very important drugs use it a lot in diabetes we call these

sodium glucose transporters and technically in the kidneys it's type 2 inhibitors

and the easiest way to remember this is let's say here is our kind of our kidney tubules here's our

kidney tubules and then here's going to be a kidney tubular cell okay let's actually make it

a little bit bigger so here's our kidney tubule and here's our kidney tubular cell and i

want to try to absorb that glucose and that sodium into the blood

okay i use this special transporter normally let's say here's normally here's our transporter

it's going to move sodium across the cell and glucose across the cell into the blood okay we're going to

represent glucose as just like a g and someone who has diabetes guess what they have a lot of

a lot of glucose right in their blood and we're going to filter a lot of glucose out into their actual kidneys

well you know when someone who has diabetes do you want them to have a lot of glucose into their bloodstream

no so guess what i can give a drug like an sglt2 inhibitor it's going to inhibit this channel if i

inhibit this channel will i absorb sodium across the cell no will i absorb glucose across the cell

into the blood no what happens i just pee out tons of glucose into the urine

and that reduces the blood glucose levels in patients with diabetes do you see how something so simple can

apply medically that's important to remember so again why am i mentioning these

the sodium glucose go transporter again one's moving down concentration gradient one's moving against concentration

gradient and again the only way that the sodium is able to move down is because of the

sodium potassium atpase what's the clinical relevance sglt2 inhibitors okay beautiful let's

move on to the next one all right so the next one we talked about sodium glucose let's talk about the next one

the next one is i call it a very special one we're not going to go into crazy i don't want to go crazy because i think

you guys have gotten the point about this one but this next one is called a sodium

potassium two 2-chloride symporter or also known as a

co-transporter again symporta means that they're both moving in the same direction everything is

in this case we've got three molecules that are moving across so again what is the big one that's

moving across down its concentration gradient sodium another one though is chloride so sodium and chloride are

higher outside the cell and lower inside the cell so they're going to move

easily down their concentration gradient well there's another molecule that i need to move another ion i should say

and that is potassium potassium is lower outside the cell and really really high inside the cell so what does that mean

for potassium we're moving it against its concentration gradient but thankfully sodium and chloride are

good friends they're allowing the potassium to piggyback on them

to get them into the cell and so potassium will be able to move as well into the cell why the heck am i

mentioning these again what's an important medical relevance to this

these importers are found in a particular area in the kidneys we've really focused on kidneys pretty heavily

haven't we so in the kidneys there's a very specialized structure here called the

loop of henle okay it's called the loop of henle and this loop of henle

has a lot of these little transporters on them so here what i'll do is i'll draw these little transporters

right here in green okay now normally what they do is is they move the sodium they move the potassium

they move the chloride out here into this little interstitial space so that we can pull water

from this these loop of henle area right but let's say we give a drug a particular drug that's going to inhibit

this you have a drug which are called your loop

diuretics you know you've heard these like lasiks right lasix is your common one

furosemide what these do is they inhibit these little channels the sodium potassium two

chloride co transporters so now what does that mean that means sodium potassium and chloride

can't move into the cells if they can't move into the cells guess where all that stuff builds up in

it builds up inside of the kidney tubules you know what sodium potassium and chloride love to do

what it loves to pull with it water so if sodium potassium and chloride aren't taken up into the cell

they build up in the kidney tubules and whenever they leave they pull with it water and they're going to pull tons and

tons of water out into the urine pulls sodium out into the urine

pull chloride out into the urine and that whole significance of that is that they're going to reduce the

fluid volume in the body in patients who have high volume states like who heart failure patients

who have a lot of edema pulmonary edem in the lungs people with liver failure who have like

who have particularly like ascites and things of that nature we can pull some of that excess fluid off

their body by inhibiting these little transporters isn't that cool all right the next one here

the next one that i want to talk about i forget okay sorry all right remember now

all right what's the next one the next one here really interesting one is called your sodium proton pump

okay and it's a simple thing we are we've already gotten to the point where we should know this now but this is a

sodium proton type of transporter and again you're going to see here it's an

anti-porter so it means that they're moving in opposite directions i wanted to just give you one example of

these so what happens is sodium will move this is again a very important one in the

kidneys sodium will move from areas of high concentration which is outside the cell

to areas of low concentration which is into the kidney cell at the same time i want to move a proton

molecule out of the kidney cell and into the kidney lumen in order for me to do that though

again protons in the kidney lumen are actually going to be higher and then

lower protons inside the cell so again i'm moving sodium down his concentration gradient but i'm

pushing protons against their concentration gradient but thank goodness sodium says hey if i go

in i'll let you go out for free so sodium comes in protons come out this is very very important in your

kidneys particularly in an area of the kidneys called the distal convoluted tubule

again why is this medically relevant you know patients who have uh high levels of aldosterone

guess what it does to these sodium proton pumps it increases the activity of them if you

increase the activity of the sodium proton pump in the distal convoluted tubule

what does that mean i'm going to push more protons out of the kidneys and into the urine

i'm going to pee out more protons if i pee out more protons what's that going to do to the blood the amount of protons

in the blood it's going to decrease them what's that condition called when you have low

protons in the blood or your blood is becoming alkaline alkalosis

and this isn't due to a lung issue it's due to a metabolic issue so this can produce what's called metabolic

alkalosis and then the same concept what if somebody had low aldosterone low aldosterone means

that you have low activity of the sodium proton pumps and that means that i'm not going to

spit as much potassium out into the urine i'm sorry i'm not going to spit as much protons out into the urine

so if i don't spit a lot of protons on the urine a lot of the protons build up in the blood

making the blood more acidic that's called acidosis and we call this metabolic acidosis

so something as simple as that can influence these pumps one last one the last one here

is going to be a sodium calcium exchanger so what is this one called a sodium

calcium exchanger and again this is a anti-porter because they're moving in

opposite directions this is very very important in your cardiac muscle tissue so again where

would this be important this is important in your heart tissue what happens is sodium moves from areas

of high concentrations which is outside the cell tears of low concentration which is into

the heart cell then calcium which is going to be in low concentration inside the cell

has to move out of the cell against its concentration gradient because calcium is higher outside the cell lower inside

the cell now in order for that process to occur in order for me to push the calcium

out of the cell i need sodium to come into the cell down its concentration gradient we

have beat this like a dead horse why is this important though in the heart there's a drug called digoxin

okay we talked about it over there with the sodium potassium episodes watch how this kind of comes together

remember what we said that the digoxin does it inhibits the sodium potassium

atp aces if you inhibit the sodium potassium to pieces what happens to the sodium that builds up so again digoxin