Body Fluid Compartments | ICF | ECF | General Physiology

Summary

This video explains the different body fluid compartments in the human body, which is composed of 50-70% water. It discusses the intracellular fluid (ICF) and extracellular fluid (ECF), separated by cell membranes, with two-thirds of the water inside cells and one-third outside. The ECF is further divided into plasma and interstitial fluid. The video also highlights solutes and proteins in these compartments, the role of osmolarity, and how water movement between compartments maintains balance. The indicator-dilution principle is introduced to measure fluid volumes in the body.

Takeaways

• 💧 The human body is composed of 50-70% water, with variations based on factors like age and body fat percentage.
• 🔄 Body water is distributed between intracellular fluid (ICF) inside cells and extracellular fluid (ECF) outside cells.
• 🧫 Two-thirds of the body's water is in the ICF, while one-third is in the ECF.
• ⚖️ In an average body, 60% of the body weight is water: 40% is ICF and 20% is ECF (60-40-20 rule).
• 🩸 The ECF is divided into plasma (inside vessels) and interstitial fluid (outside vessels), with interstitial fluid making up three-quarters of the ECF.
• 💡 Plasma and interstitial fluid are separated by the capillary membrane, while ICF and ECF are separated by the cell membrane.
• 🔬 The major cation in the ECF is sodium, while the major cations in the ICF are potassium and magnesium.
• ⚗️ Proteins are present in plasma and ICF, but the interstitial fluid contains very little protein due to the capillary membrane.
• 📏 Body water compartments can be measured using the indicator-dilution principle, with different indicators used for total body water, ECF, and plasma volume.
• 🔄 Osmosis maintains equilibrium between the ICF and ECF, as water moves across the cell membrane in response to solute concentration differences.

Q & A

What percentage of the human body is composed of water?

The human body is composed of 50 to 70 percent water, depending on factors like age and body fat percentage.

How is total body water distributed in the body?

Total body water is distributed inside the cells (intracellular fluid or ICF) and outside the cells (extracellular fluid or ECF).

What separates the intracellular fluid (ICF) and extracellular fluid (ECF)?

The cell membrane separates the intracellular fluid (ICF) from the extracellular fluid (ECF).

What fraction of total body water is intracellular fluid (ICF) and extracellular fluid (ECF)?

Two-thirds of total body water is intracellular fluid (ICF), and the remaining one-third is extracellular fluid (ECF).

How is extracellular fluid (ECF) further divided?

Extracellular fluid is divided into plasma (inside vessels) and interstitial fluid (outside vessels).

What is the main difference between plasma and interstitial fluid in terms of composition?

Plasma contains more proteins, which are too large to pass through the capillary membrane, while the interstitial fluid has very little protein.

What are the predominant cations and anions in the extracellular fluid (ECF)?

The predominant cation in the ECF is sodium, and the predominant anions are chloride and bicarbonate.

What are the major cations and anions in the intracellular fluid (ICF)?

The major cations in the ICF are potassium and magnesium, and the major anions are organic phosphates and proteins.

What principle is used to measure total body water, extracellular fluid, and plasma volume?

The indicator-dilution principle is used, where an indicator is placed in the compartment and its dilution is measured.

How does the movement of water between compartments help maintain osmotic balance?

Water moves across the semi-permeable cell membrane by osmosis to ensure that the osmolarity of the ECF and ICF remains equal.

Outlines

00:00

💧 Understanding Body Fluid Compartments

This paragraph introduces the concept of body fluid compartments. It explains that the human body consists of 50-70% water, which varies based on factors like age and body fat. The water is distributed across two main compartments: intracellular fluid (ICF), which is within cells, and extracellular fluid (ECF), which is outside cells. The cell membrane separates these two compartments. The majority of the body's water (two-thirds) is in the ICF, with the remaining one-third in the ECF. The ECF is further divided into plasma (inside vessels) and interstitial fluid (outside vessels). Plasma makes up one-quarter of the ECF, while interstitial fluid accounts for three-quarters. Blood also contains both ECF and ICF within its plasma and red blood cells (RBCs), and the proportion of RBCs is called the hematocrit. Additionally, there are small transcellular compartments, such as cerebrospinal and peritoneal fluids, which are also part of the ECF.

05:02

🌊 Fluid Composition and Membranes

This section delves into the composition and role of membranes in body fluids. It explains that both the ICF and ECF contain solutes. The capillary membrane separates plasma from interstitial fluid, and while water and solutes can move across it, large proteins cannot. The interstitial fluid is an ultrafiltrate of plasma, lacking significant protein. Cations (positively charged ions) like sodium dominate the ECF, while potassium is more prevalent in the ICF. Plasma contains proteins, but interstitial fluid does not. Despite differences in ion concentrations, both compartments remain electrically neutral. The cell membrane is selectively permeable to water but impermeable to many solutes, creating distinct compositions in the ICF and ECF. The ICF primarily contains potassium and magnesium, while the ECF contains sodium and chloride.

🧪 Measuring Fluid Volumes Using Indicators

This paragraph explains the methods used to measure the volumes of body fluids through the indicator-dilution principle. Total body water, ECF, and plasma volumes can be measured by placing an indicator in a compartment and assessing its distribution after equilibration. For total body water, the indicator must cross the cell membrane, while for the ECF, it should not. For plasma, the indicator should not cross the capillary membrane or enter red blood cells. The volumes of interstitial fluid and intracellular fluid are calculated indirectly. Blood volume can be determined if both plasma volume and hematocrit are known, using the formula: plasma volume / (1 - hematocrit).

⚖️ Osmotic Equilibrium Between Compartments

This section highlights the importance of osmolarity and equilibrium between body compartments. The ECF and ICF must have the same osmolarity, and any imbalance in solute concentration results in water moving through the semi-permeable cell membrane to restore balance through osmosis. This movement of water helps maintain osmotic equilibrium across compartments, ensuring the stability of fluid distribution in the body.

👍 Conclusion and Thank You

In this final part, the video concludes by briefly summarizing the key points about body fluid compartments. The speaker encourages viewers to give the video a thumbs up if they found it helpful and to subscribe to the channel for more content in the future. The paragraph ends on a friendly note, thanking viewers and expressing eagerness for future engagements.

Keywords

💡Total Body Water (TBW)

Total Body Water (TBW) refers to the amount of water in a human body, which makes up 50-70% of body weight. This value varies based on factors like age and body fat percentage. In the video, TBW is divided into intracellular and extracellular compartments, forming the basis for understanding body fluid distribution.

💡Intracellular Fluid (ICF)

Intracellular Fluid (ICF) is the water contained within the cells, accounting for about two-thirds of the total body water. This fluid is separated from the extracellular fluid by the cell membrane, and the ICF is rich in potassium and proteins. It plays a crucial role in maintaining cell function and overall fluid balance.

💡Extracellular Fluid (ECF)

Extracellular Fluid (ECF) refers to the water outside of cells, making up one-third of total body water. It is further divided into interstitial fluid and plasma. The ECF is vital for transporting nutrients and waste between cells and the bloodstream, with sodium being the primary cation in this compartment.

💡Interstitial Fluid

Interstitial Fluid is the fluid located between cells and outside the blood vessels, making up about three-quarters of the ECF. It acts as a medium for nutrient and waste exchange between cells and blood. The video highlights that the interstitial fluid is an ultrafiltrate of plasma, lacking large proteins.

💡Plasma

Plasma is the fluid component of blood that resides within blood vessels, accounting for one-quarter of the ECF. Plasma contains proteins and plays a role in nutrient transport and waste removal. In the video, the plasma is described as being separated from interstitial fluid by the capillary membrane.

💡Capillary Membrane

The capillary membrane is a thin barrier that separates plasma from the interstitial fluid. It allows the movement of small solutes and water while restricting the passage of larger molecules like proteins. This selective permeability helps maintain the composition difference between plasma and interstitial fluid.

💡Hematocrit

Hematocrit is the fraction of blood volume that is occupied by red blood cells (RBCs). It helps in determining blood volume, which can be calculated using the plasma volume and hematocrit. The video emphasizes its importance in differentiating between the fluid in blood (ICF and ECF) and solid components.

💡Osmolarity

Osmolarity refers to the concentration of solutes in a solution. In the body, osmolarity must be balanced between the ICF and ECF to prevent excessive water movement across the cell membrane. The video discusses how water moves via osmosis to equalize osmolarity across compartments when imbalances occur.

💡Indicator-Dilution Principle

The Indicator-Dilution Principle is a method used to measure fluid volumes within body compartments. By introducing an indicator substance that distributes evenly in a compartment, the dilution of the indicator is measured to calculate volume. The video explains how this method is applied to measure TBW, ECF, and plasma volumes.

💡Transcellular Fluid

Transcellular Fluid is a small, specialized portion of the ECF found in spaces such as the pericardial, peritoneal, and cerebrospinal cavities. Although minor in volume, these fluids play crucial roles in specific bodily functions. The video briefly mentions transcellular fluid as a distinct compartment of body water.

Highlights

The human body is composed of 50 to 70 percent water, depending on factors like age and body fat percentage.

Total body water is divided into intracellular fluid (ICF) and extracellular fluid (ECF).

ICF makes up two-thirds of the total body water, while ECF accounts for one-third.

60 percent of body weight is total body water, of which 40 percent is ICF and 20 percent is ECF (60-40-20 rule).

ECF is further divided into plasma (inside vessels) and interstitial fluid (outside vessels), with interstitial fluid making up three-quarters of ECF.

The capillary membrane separates plasma and interstitial fluid, with plasma proteins unable to pass through the membrane.

Blood consists of both ECF and ICF, as it contains plasma (ECF) and red blood cells (ICF).

The fraction of blood that is red blood cells is known as the hematocrit.

A small part of the ECF is known as the transcellular compartment, which includes fluids in areas like the cerebrospinal fluid and pericardial cavity.

The cell membrane separates the ICF from the ECF and is selectively permeable, allowing water but restricting solutes.

ICF has higher levels of potassium and magnesium, while ECF has higher sodium and chloride levels.

The total body water can be calculated by summing the volumes of ICF and ECF.

Interstitial fluid is considered an ultrafiltrate of plasma and has a similar composition, minus proteins.

The indicator-dilution principle is used to measure the total body water, ECF, and plasma volumes.

Osmolarity must be balanced across the cell membrane, and water moves via osmosis to maintain equilibrium between ECF and ICF.

Transcripts

Hello. Welcome to Byte Size Med. This video  is on the different body fluid compartments.  

The human body is around 50 to 70 percent water. Now  this number isn't fixed because the amount of  

water would vary depending upon different factors,  like age, body fat percentage and things like that.  

This water content of the body is the total body  water and it gets distributed inside cells and  

outside cells. If we consider the water  content of the insides of all the cells  

of the body as one compartment, that  is the intracellular fluid or the ICF.  

And all of the water outside the cells  together forms the extracellular fluid,  

that's the ECF. And what's between the two? A cell  membrane. So the cell membrane is what separates  

the intracellular fluid from the extracellular  fluid. Most of the fluid is inside the cells, that's  

two-thirds the total body water. So the remaining  one-third would be the extracellular fluid.  

If we assume an average of 60 percent  of the body weight is total body water,  

then 40 percent is the intracellular fluid and  20 percent is the extracellular fluid. 60-40-20.

The ECF is further divided into fluid  inside vessels and fluid outside vessels.  

Inside the vessels would be the plasma,  outside is the interstitial fluid. The  

interstitial fluid is larger, being around three  quarters of the ECF. So the plasma is a quarter.  

Now what's between these two? A capillary membrane.

Now blood can be considered to be a compartment of  its own, because it has both an ECF and an ICF. It  

has plasma and it has cells, like red blood cells.  The fluid inside the RBCs is the ICF and the fluid  

in the plasma, that's the ECF. The fraction  of blood that's RBCs is called the hematocrit.

There's also fluid in the pericardial  cavity, the peritoneal cavity,  

there's the cerebrospinal fluid. Now these kinds  of fluids, they form another compartment called  

the transcellular compartment, which should  be a small part of the extracellular fluid.  

For now, we're going to focus on the ICF, the ECF,  the interstitial fluid, and the plasma. So yes,  

these compartments have water, but they also  have solutes. So between the ECF and the ICF  

is the cell membrane and between the plasma and  the interstitial fluid is the capillary membrane.  

Fluid from the plasma gets filtered  through the capillary membrane to form  

the interstitial fluid. So the interstitial  fluid is an ultrafiltrate of the plasma,  

and its composition is similar to the plasma.  The capillary membrane, it has pores which lets  

solutes through, except for proteins. Proteins are  too large and so don't pass through the membrane.  

They stay in the plasma. So the interstitial  fluid has very little protein. Cations are  

positively charged, anions are negatively charged.  Proteins are negatively charged. Because they  

can't move across the capillary membrane, by  the Gibbs-Donnan effect to maintain balance,  

the plasma will have more smaller cations like  sodium and lesser smaller anions like chloride.  

But this effect isn't much. So the composition of  the two is quite similar, making the predominant  

cation in the ECF sodium, the predominant  anions would be chloride and bicarbonate.  

Along with plasma proteins in the plasma, the  cell membrane is selectively permeable. It's  

freely permeable to water, but is impermeable to  a lot of solutes. So the composition of the ICF  

and the ECF are different. In the ICF, the major  cations are potassium and magnesium, versus sodium  

of the ECF. Here inside the cell, the anions are  organic phosphates like ATP and ADP, and proteins,  

So proteins are inside the cells and in the plasma,  but the interstitial fluid has very little protein.  

Potassium is higher inside the cells, while sodium  is higher outside. But in both compartments, the  

concentration of cations and anions are equal,  keeping them overall electrically neutral.

So the volume of total body water is equal to the  volume of the ICF plus that of the ECF, while the  

ECF volume is equal to the volume of interstitial  fluid plus the plasma volume. These three, that's  

the total body water, the ECF and the plasma volume  can be measured by placing an indicator in the  

compartment and allowing it to distribute evenly.  Then its dilution is assessed. That's the indicator- 

dilution principle. Different indicators are used  depending upon what we're choosing to measure.  

Like for total body water, it would be something  that crosses the cell membrane and so gets  

distributed between the two compartments. For  the ECF, it should not cross the cell membrane  

and for the plasma volume, it should not cross the  capillary membrane nor should it enter the RBCs.  

But these two, the interstitial fluid and  the intracellular fluid, they are calculated  

indirectly. The ICF will be the total body  water minus the ECF, and the interstitial  

fluid is the ECF minus the plasma volume. If  we have the plasma volume and the hematocrit,  

then we can calculate the blood volume. That's  the plasma volume over one minus the hematocrits.

So the compartments have solutes and a solvent.  Now these solutions, across the cell membrane,  

have to be at equilibrium. The ECF osmolarity  has to be equal to the ICF osmolarity.  

The cell membrane is semi-permeable. It's freely  permeable to water, but is impermeable to most  

solutes. So if there's any imbalance, water will  move across the membrane to bring back equilibrium.  

This movement of water is by osmosis.

So those are the different body fluid  compartments. If this video helped you, give  

it a thumbs up and subscribe to my channel. Thanks  for watching and I'll see you in the next one! :)