Movement Across the Cell Membrane- Part2 Cell Membranes & Osmosis- S21

Summary

Dr. Kath introduces osmosis, a process critical to water movement across cell membranes. The lecture explains how osmosis, a type of diffusion, regulates water movement in response to solute concentrations inside and outside cells. It highlights the importance of osmosis in maintaining homeostasis, particularly in relation to fluids and electrolytes. Key topics include isotonic, hypotonic, and hypertonic solutions, the role of aquaporins, and examples like hyponatremia. The session emphasizes the relevance of osmotic balance in health, especially regarding brain tissue and its potential medical implications.

Takeaways

• 🧑‍⚕️ Osmosis is a special type of diffusion that describes water movement across the cell membrane.
• 💧 Water moves from areas of low solute concentration to areas of high solute concentration during osmosis.
• 🔬 Intracellular fluid refers to the fluid inside cells, while extracellular fluid refers to fluid outside cells, such as blood plasma.
• 🌊 Aquaporins are special proteins in cell membranes that help water move quickly, particularly in organs like the kidneys.
• ⚖️ Osmosis is essential for maintaining homeostasis, ensuring fluid and electrolyte balance within the body.
• ⚗️ Solutions in the body consist of solvents (like water) and solutes (like sodium ions and glucose). Their concentration can change due to various processes.
• 📏 Osmolarity and osmolality are terms used to measure solute concentration, either by volume (osmolarity) or weight (osmolality).
• 🧠 Osmotic imbalances can lead to medical issues, such as brain swelling or shrinking, depending on the fluid and solute concentrations in and around cells.
• 🥤 Overhydration, like in the example of the hiker, can dilute sodium levels in the extracellular fluid, causing cells to swell.
• 💧 Dehydration and high solute concentration in the extracellular fluid can cause cells to shrink due to water loss, as seen in elderly patients with hypernatremia.

Q & A

What is osmosis, and how does it differ from general diffusion?

Osmosis is the net movement of water across a semi-permeable membrane from an area of low solute concentration to an area of high solute concentration. It is a specific type of diffusion, focusing solely on water movement.

What are intracellular and extracellular fluids?

Intracellular fluid refers to the fluid inside cells, called cytoplasm, while extracellular fluid refers to the fluid outside cells, which surrounds tissues and organs.

What role do aquaporins play in the movement of water across cell membranes?

Aquaporins are special proteins embedded in cell membranes that allow rapid movement of water into and out of cells, which is crucial in organs like the kidneys.

Why does water move from an area of low solute concentration to high solute concentration during osmosis?

Water moves to equalize the concentration of solutes on both sides of a membrane, ensuring a balance of solute and solvent across the membrane.

What is osmotic homeostasis, and why is it important?

Osmotic homeostasis refers to the regulation of water and sodium levels in the body to maintain proper fluid balance. It ensures that cells function correctly by preventing them from swelling or shrinking.

What is the difference between isotonic, hypotonic, and hypertonic fluids?

Isotonic fluids have equal solute concentrations inside and outside cells, causing no net water movement. Hypotonic fluids have a lower solute concentration outside the cell, causing water to enter the cell and swell. Hypertonic fluids have a higher solute concentration outside, causing water to leave the cell and shrink.

What can happen if there's an imbalance in sodium levels in the body?

An imbalance can cause cells to either swell (hyponatremia) or shrink (hypernatremia). This can lead to serious medical issues, especially in sensitive tissues like the brain.

What is hyponatremia, and how does it affect the body?

Hyponatremia is a condition where there is a low sodium concentration in the extracellular fluid, leading to water moving into cells, causing them to swell, which can result in serious health problems.

What is hypernatremia, and what are its effects?

Hypernatremia is a condition where there is a high concentration of sodium in the extracellular fluid, causing water to leave the cells, leading to cell shrinkage and dehydration.

How does osmosis impact brain cells during sodium imbalances?

In cases of hyponatremia, brain cells can swell due to water moving into the cells, while in hypernatremia, brain cells shrink as water moves out, both leading to potentially severe neurological symptoms.

Outlines

00:00

👋 Introduction to Osmosis and Water Movement Across Cell Membranes

Dr. Kath begins by congratulating students on their progress and introduces the topic of water movement across cell membranes through osmosis, a type of diffusion. She explains the importance of osmosis in maintaining homeostasis within the body, which helps balance fluid and electrolyte levels. The discussion focuses on how water crosses cell membranes and the regulation of this process, with an emphasis on diagrams to support learning. She introduces concepts such as intracellular and extracellular fluid and the role of osmosis in maintaining health.

05:03

💧 Defining Osmosis and Its Role in Water Movement

This section focuses on osmosis, defining it as the net movement of water from an area of low solute concentration to an area of high solute concentration. Dr. Kath uses a beaker diagram to explain the process, where water moves into a cell with higher solute concentration, like sodium ions, to balance the solute levels inside and outside the cell. She explains the importance of solutes like electrolytes and glucose in influencing water movement and introduces the concept of solutions, including solutes and solvents.

10:05

🔬 Osmotic Homeostasis: Balancing Sodium and Water in Cells

In this section, Dr. Kath explains osmotic homeostasis, the regulation of sodium and water concentrations in body fluids. She introduces the concept of milliosmoles as a measurement of solute concentration and discusses how the body maintains fluid balance across cell membranes. A diagram shows water movement across the membrane in response to solute concentration differences, demonstrating how imbalances can cause water to move in or out of cells, potentially leading to issues like overhydration or dehydration.

15:07

💡 Neurons and Osmosis: Understanding Fluid Imbalances

Dr. Kath discusses neurons, a special type of nerve cell, and how fluid imbalances affect them through osmosis. She uses examples where solute concentrations differ between the intracellular and extracellular fluids, such as hypotonic conditions (low solute outside the cell) causing the cell to swell, and hypertonic conditions (high solute outside) causing the cell to shrink. Real-life examples, like a hiker experiencing hyponatremia (low sodium), help illustrate the dangers of fluid imbalances, such as cell swelling or dehydration.

20:08

🧠 Brain Osmotic Imbalance: Swelling and Shrinking of Brain Cells

This final section focuses on how osmotic imbalances impact brain tissue, primarily composed of neurons. Dr. Kath explains how water movement across cell membranes, in response to solute concentration differences, can lead to brain swelling (if intracellular solute concentration is higher) or shrinkage (if extracellular concentration is higher). These changes in brain cell size can cause serious medical issues if left untreated. She concludes by inviting students to review the material and ask questions for further clarification.

Keywords

💡Osmosis

Osmosis is the process of water moving across a semi-permeable membrane from an area of low solute concentration to an area of high solute concentration. In the video, it is discussed as the key mechanism for water movement in cells, essential for maintaining homeostasis. This process helps balance fluids inside and outside of cells, preventing cells from swelling or shrinking.

💡Cell Membrane

The cell membrane is a biological barrier that separates the inside of a cell from its external environment. It allows selective passage of substances, including water via osmosis. The video explains how water moves freely across this membrane or through specialized proteins called aquaporins, playing a crucial role in regulating water balance within the body.

💡Aquaporins

Aquaporins are specialized proteins embedded in the cell membrane that facilitate the rapid transport of water in and out of the cell. In the video, these proteins are highlighted in the context of kidneys, where they help regulate water retention and excretion. Aquaporins ensure efficient water movement, especially in organs where water balance is critical.

💡Solute Concentration

Solute concentration refers to the amount of dissolved substances, such as ions or glucose, within a fluid. The video emphasizes how differences in solute concentration across cell membranes drive osmosis. For example, when the solute concentration inside a cell is higher than outside, water moves into the cell to equalize the concentration.

💡Homeostasis

Homeostasis is the body's ability to maintain a stable internal environment despite external changes. The video connects this concept to the regulation of water and solute concentrations in body fluids, highlighting how osmosis is part of maintaining osmotic homeostasis, which is vital for cellular function and overall health.

💡Intracellular Fluid

Intracellular fluid refers to the liquid found inside cells, also known as cytoplasm. It contains solutes like ions and nutrients necessary for cellular processes. In the video, intracellular fluid plays a role in osmosis, where water moves to balance solute concentrations between this fluid and the extracellular fluid.

💡Extracellular Fluid

Extracellular fluid is the fluid outside of cells, including blood plasma and interstitial fluid. The video explains how this fluid bathes cells and interacts with intracellular fluid, particularly in the movement of water during osmosis. Maintaining a balance between extracellular and intracellular fluids is essential for cell function.

💡Hypotonic

Hypotonic refers to a solution that has a lower solute concentration compared to another solution. In the video, a hypotonic extracellular fluid causes water to move into the cell by osmosis, potentially leading to cell swelling or bursting if unchecked. This concept is crucial for understanding how imbalances in solute concentrations affect cell volume.

💡Hypertonic

Hypertonic describes a solution with a higher solute concentration compared to another solution. The video explains that when the extracellular fluid is hypertonic, water moves out of the cell, causing it to shrink. This imbalance can occur in cases of dehydration or other conditions affecting solute levels in the body.

💡Hyponatremia

Hyponatremia is a condition characterized by abnormally low levels of sodium in the blood. The video uses the example of a hiker who drank too much water, diluting her blood sodium levels and causing water to move into cells, leading to swelling. This highlights how electrolyte imbalances can disrupt osmotic balance and cause serious health issues.

Highlights

Introduction to the topic of osmosis, a special type of diffusion related to water movement across cell membranes.

Explanation of intracellular fluid (cytoplasm) and extracellular fluid, and how cells are bathed in extracellular fluid.

Movement of water across the plasma membrane is regulated by proteins called aquaporins, which facilitate rapid water movement.

Osmosis is the movement of water from an area of low solute concentration to an area of high solute concentration.

A hypothetical scenario using a beaker with a semi-permeable membrane is used to explain osmosis and water equalization across cell membranes.

Concept of solutes such as sodium ions and glucose, which influence water movement across membranes.

Introduction to key terms in biological fluid concentration: molarity, osmolarity, and osmolality, which measure solute concentration in solutions.

Discussion of osmotic homeostasis, the regulation of sodium and water concentrations within the body.

Normal fluid concentration is around 285 milliosmoles per kilogram, and water moves across membranes to maintain balance between intra- and extracellular fluids.

The example of a neuron to explain isotonic conditions, where water moves equally into and out of the cell.

Hypotonic and hypertonic conditions are explained using examples where fluid imbalance leads to swelling or shrinking of cells.

A case of hyponatremia, where a hiker experiences low sodium levels due to excessive water intake, leading to cell swelling by osmosis.

A case of hypernatremia, where dehydration causes high extracellular solute concentrations, leading to cell shrinkage.

Brain tissue can be severely affected by osmotic imbalances, either swelling or shrinking, leading to serious medical conditions.

Final thoughts on the significance of maintaining osmotic balance to prevent medical problems such as those affecting the brain or other tissues.

Transcripts

hello everyone dr kath here hope you're

well

uh congratulations on your progress so

far

you're doing a great job what i'd like

to do uh

right now is to introduce you to

uh the topic of movement of water

across the cell membrane this is the

second presentation

in week number seven and what we're

going to be discussing

is the movement of water by a process

called

osmosis and osmosis is just a special

type of diffusion

so we know already that many substances

can move across the cell membrane by

diffusion

but when we're referring to water

movement we call

we use the term osmosis to refer to that

movement of water

and this is a very important topic in

the field

of biology and medicine because our

bodies are constantly

working to maintain a homeostatic

balance

to maintain the correct fluid

electrolyte

to maintain our health and so this is

really a topic that gets

revisited many times

will be revisited many times as you

progress in you in your studies

so what i'd like to do first is

introduce you to the idea

that there are different fluids in

different regions

of a living organism uh we're going to

look at why and how

water crosses cell membranes and we're

also going to look at

why and how water movement is regulated

so let's get started now just to say i

would

we'll be focusing primarily on the

diagrams in this presentation

i'm going to assume that everyone is

going to take the time and

read through the text here so what we're

looking at here is a diagram

showing the location of two fluids

within the living organism

here on the right hand side just to

orient you

we're looking at a collection of cells a

tissue

we don't know what these cells are what

this tissue is but we can

see that they're cells we see the cell

membrane and we can see the nuclei

within each of these cells now we know

already that there is a fluid

within the cells and this fluid is of

course called cytoplasm

another name that's used for cytoplasm

is intracellular fluid intra referring

to inside of

and cellular of course referring to cell

now any fluid that occurs

outside the cell we can call that

extracellular fluid

and it might surprise you to know but

all of the

cells and tissues in our body are bathed

in extracellular fluid and there are a

couple of different types of

extracellular fluid which you'll learn

about later

but basically any fluid that's outside

the cells

uh is called extracellular fluid so if

we look at this blood vessel

here we can see uh the red blood cells

which would contain the intracellular

fluid

the cytoplasm and they would be uh they

are being bathed

in the extracellular fluid which in this

case

is a blood plasma notice in this uh

in-between region between tissues

and blood vessels uh there is a

what seems to be a space but all of this

region here

is full of fluid there's no open spaces

so now we're going to focus on movement

of water across across the membrane

so here we have a depiction of

a phospholipid bilayer here we can see

the two

layers of the phospholipids and what

you're looking at

is water moving freely into and out of

the cell

directly through the plasma membrane

through the cell membrane

now there are also channels which

haven't been discussed called

aquaporins which are present they're

protein special proteins that are

embedded

in some of the cell membranes and there

are occasions

when uh cells need to rapidly

move water either into and out of the

cell and

this is quickly achieved by these

aquaporins

you will find these aquaporins for

example in the kidneys

because our kidneys do a lot of the work

of

um filtering our blood but

uh either allowing us to retain water

or to expel water in the form of urine

now as i mentioned the movement of water

across the membrane

is called osmosis it's a special type of

diffusion and

it is dependent on the concentration

of the solutes now remember

the fluids in our body are not are

water-based but they contain a lot of

electrolytes a lot of ions

they also contain glucose and other

substances dissolved

in in those fluids and it's these uh

solutes that are dictating the movement

of the water

and so um what osmosis is the definition

is the net movement of water from an

area of

low solute concentration

to an area of high solute concentration

let's take a look at this diagram here

what we can see is a beaker of water

divided by a semi-permeable membrane

and what i'd like to you to imagine

is we're looking at a cell let's say

this is the cell

here this is the plasma or cell membrane

and this is the extracellular fluid

and in our imaginary cell we can see

there are there is salt sodium ion

sodium and chloride ions

and this uh these sodium and chloride

ions these

solutes are present within the cell

but absent in the extracellular fluid

now what we're going we're going to make

one small assumption

uh before i go on and that is

um for osmosis to occur the solute in

this case

salt cannot move across that membrane

however the water molecules which

relatively speaking are much smaller can

move back and forth across the membrane

now because the concentration of the

solute is higher

inside the cell in the intracellular

fluid

versus in the extracellular fluid then

water

will pass by osmosis from the outside of

the cell

in to the interior of the cell

and the reason why this happens is that

the

water is going to equalize the

concentrations

uh concentration of fluids here

and also here

so as we look at this diagram this is

just one single

single snapshot in time

you can imagine if water was to continue

to move into the cell

at a certain point it would burst and

that generally does not happen

so earlier on in the semester in unit

number two

oh sorry one we looked at

solutions and what are solutions well

they're really just fluids

that are composed of a solvent

so a liquid that has the ability to

dissolve

things in it and ace

one or many solutes and these are

substances

that can dissolve in the solvent so

examples of solutes would be

sodium ions glucose etc

now when we're thinking about solutions

of fluids within the body we know that

they have varying concentrations

and those concentrations vary because

the amount of solutes in those fluids

vary

we are constantly uh

we're eating we're drinking we're

perspiring

sweating uh we're urinating

and all of these processes that our body

performs

leads to either a gain or a loss of

water

and so there's a constant this constant

change in the concentration of these

fluids

and there is there are a couple of terms

that we use to describe

the concentration of fluids in the body

the first term is a term called molarity

and this is really just a term

that refers to measuring number of moles

of a solute in a certain volume of

solution

but what you'll more likely come across

in the field of biology are these two

terms

osmolarity and osmo morality

sorry osmosis is always a hard one for

me to say

um and these two terms refer

to um the concentration of solute either

within a given volume in this case a

liter

or within a given weight kilogram

weight so please take a minute pause the

video

and uh answer these questions

so this slide walks us through something

called osmotic homeostasis

um basically it's the regulation of

sodium and water

so let's have a look at this slide on

osmotic

homeostasis so the volume and

concentration of our bodies fluids

are normally maintained within a very

narrow range

and that is regulated by um

sodium and water concentrations

and the normal concentration of solute

is as it says here

200 285 milliosmoles

per kilogram so in a normal situation

what you would find uh if we looked at

us

at a cell membrane and the intra

and extracellular fluids is

that the body is constantly working

to maintain this balance of um

on either side of the membrane so if we

see

uh in a quite normal situation

uh water movement occurring both equally

into and out of the cell what we can

assume is the concentration of the

solutes

on this side of the membrane versus this

one is equal

so while we may not be aware or

conscious of

these subtle changes in our body there

are situations

where there can be an imbalance in

sodium ions sodium ion concentration

across the membrane and what can happen

is is shown here in the diagram so let's

imagine a situation

where we have a low concentration of

sodium ions

outside the cell and a high

relatively speaking concentration of

sodium ions into the cell

because of this difference in

concentrations

um across the membrane what will happen

is the water

will move by osmosis from the area of

low solute concentration

to high solute concentration

now let's have a look at this uh with a

specific example

so here we're looking at a a cell it's a

special type of cell called a neuron

uh also known commonly as a nerve cell

they have these

uh kind of law have a kind of long

spindly uh stretched out appearance and

they they carry electrical currents

that they're responsible for the passage

of nerve impulses

now in this situation uh what we're

thinking about still is osmosis

and we're told from the diagram that the

extracellular fluid the ecf

concentration solute concentration is

280 millimoles per liter

and we're also told that the

intracellular

intracellular fluid and intracellular

fluid concentration sorry

is also 280 millimoles per liter

so the the concentration of the solutes

within the cell

and outside the cell are equal and so

what that means

is that water will move equally into and

out of

out of the cell and when these solute

concentrations are the same

as i described we call the extracellular

fluid we call this an isotonic fluid

now there are times where um

as i mentioned before the solute

concentrations

vary between insulin inside and outside

the cell so let's have a look at the

example where that has happened

so here in this example we can see the

concentration of the extracellular fluid

is 250

millimoles per liter however the

intracellular fluid concentration

is 280 millimoles per liter

so there's a higher concentration of

solute within this

neuron versus outside and because of

this higher concentration of solute

water will move by osmosis from the

extracellular fluid

into the intracellular fluid into the

cell

and this cell will over hydrate and it

will swell

we give a name to this extracellular

fluid an extracellular fluid of this

at this concentration we call this

extracellular fluid

hypotonic hypo

meaning below normal it has a

lower than normal concentration

so let's have a look at this example

whereas what causes an imbalance

in water and solute and we're going to

look at an example

the example of hyponatremia

so i always like to go to the diagrams

first and then we'll go back to some of

the texts

so we're looking at a neuron again

and what we're looking at seeing this

time is the extracellular fluid

having a concentration of 250 millimoles

per liter

and the intracellular fluid having a

concentration of 280 millimoles

per liter so the concentration of the

fluid in the cytoplasm

is higher than the concentration of the

fluid

in the extra in the extracellular area

so that means that water is going to

move

by osmosis from this region of lower

solute concentration to this region of

higher solute concentration

and if this continues to happen this

movement continues to happen

then the cell will swell and become over

hydrated

now the situation that's described is

this one we have a hiker

uh she was out at the grand canyon where

temperatures were high

she got to the rest stop she placed a

call

and she reported drinking six litres of

water

in the last three miles of her hike

now because of that massive intake of

water what

happened was her

sodium ion concentrations in her

extracellular fluid

dropped because that sodium got diluted

by all the water that she drank so

this is described the situ situation

sorry

is described as hyponatremia

neutrinia refers to sodium

but hypo this refers to low so she had

low um sodium

ion concentration and because

of that her extracellular fluid

concentration dipped to 250 now

in a somewhat opposite scenario

we have this situation where we have an

older adult

who has to rely on uh assistance

to rehydrate themselves

so they become dehydrated and they

experience something called

hyponatremia and so the extracellular

fluid

um becomes very concentrated and if we

look at the diagram

here in this scenario we've got an

extracellular fluid that's 330

millimoles per liter

but the intracellular fluid is still

280 millimoles per liter

so because we've got this very high

concentration of solute

in the extracellular fluid water is

going to move

by osmosis from

the interior of the cell to the exterior

of the cell

and that cell is going to become

shrunken it's going to become

dehydrated

because they're of the high

concentration of solute

outside the cell the extracellular fluid

is described as hypertonic hyper meaning

above normal

and that term tonicity or tonic that

refers to solute concentration

so this slide here shows a summary of

what i've discussed so please

do pause the video if you need and look

through this information

now let's look at one final example

just to wrap up this topic

so we've looked at imbalances in sodium

uh

and water and you you've seen from what

i've described that

this can lead to swelling of cells and

tissues and shrinking of cells

and this can cause some very serious

problem problems

medical problems if it goes untreated

now

one of the um organs that can be

affected

by osmotic imbalance is the brain

because the brain is

primarily composed of neurons it's

neuronal tissue

and so um in a normal situation a normal

homeostatic situation

what we have is we have if you can

imagine this we have the extracellular

fluid and the intracellular fluid

we have an equal concentration as i

described

previously of solute uh

any intracellular fluid versus the

extracellular fluid

and that means uh water moves by osmosis

equally into and out of these cells and

tissues

however as we saw previously

if the intracellular fluid is very

concentrated so here if we count up

these

these uh circles these sodium ions and

the intracellular fluid we can see that

there's many more

than in the extracellular fluid what

will happen

is the water will move my plasmosis

to the region of higher solute

concentration

and lead to that the brain tissue is

swelling

and conversely if we have a higher

concentration of the solute

in the extracellular fluid high

concentration of sodium

in that extracellular fluid water will

move

by osmosis from the intracellular fluid

to the extracellular

fluid causing the brain tissue

to shrink and there are a range of

symptoms

which can be observed which indicates

uh plus plus other tests and uh various

things

that a person is suffering from osmotic

imbalance so please take

a few minutes take a look through these

questions

and let me know if there's anything that

you don't understand or if you need some

additional guidance

thanks bye