Body Fluids II Flashcards
What percentage of body mass consists of water for the standard reference individual?
60% of body mass
State the major compartments and subcompartments that make up body water.
2 major compartments: intracellular fluid (ICF), extracellular fluid (ECF)
ECF is subdivided into 2 major subcompartments and 2 minor subcompartments:
- Plasma (major)
- Interstitial fluid (ISF) (major)
- Lymph (minor)
- Transcellular fluid (minor)
What is the difference between intracellular fluid and extracellular fluid?
Intracellular fluid is all the fluid inside the cells of the body and extracellular fluid is the fluid that is moving around between cells of the body.
What proportion of total body water and total body mass do intracellular fluid and extracellular fluid make up (for the standard reference individual)?
ICF occupies 2/3 of total body water. Since total body water makes up 60% of body mass, ICF is 40% of body mass. ECF occupies 1/3 of total body water and therefore 20% of total body mass.
In an individual with 42 L of body water total, how many litres of intracellular fluid and extracellular fluid are in their body?
ICF = 2/3 of total body water, so 2/3 of 42 = ~28 L
ECF = 1/3 of total body water, so 1/3 of 42 = ~14 L
What is plasma?
Plasma is the fluid medium in which blood cells are suspended.
What are the components of blood? How can we isolate them?
The three components of blood are red blood cells (erythrocytes), the buffy layer (consisting of white blood cells and platelets), and plasma. To isolate these things, we have to centrifuge blood.
What is hematocrit (Ht)?
It is the percentage of blood volume that is occupied by red blood cells, also known as the packed cell volume. It can be thought of as the height of the erythrocyte column in centrifuged blood.
What is the formula to calculate hematocrit?
Height of erythrocyte column/height of whole blood column.
How can the hematocrit value be used?
It can be used to calculate how much of the blood is composed of plasma. Plasma (% of blood) = 100% - hematocrit (%)
What is the normal hematocrit value?
Around 45%
What is the percent breakdown (% body mass) of the different compartments of extracellular fluid?
Of the 20% of body mass occupied by extracellular fluid, 15% is interstitial fluid and 5% is plasma.
What is interstitial fluid?
It is the fluid that moves between cells in the body, making it the true “milieu interieur”.
In a 70 kg male with 60% body water, how much interstitial fluid and plasma does he have?
0.6 x 70 kg = 42 L of body water total
ISF: 0.15 x 42 = 10.5 :
Plasma; 0.05 x 42 = 3.5 L
Explain the interaction between the fluid in the capillaries, lymphatic system, and interstitial space.
The blood (plasma) flows through the capillaries and exits into the interstitial space, where it becomes interstitial fluid. Some interstitial fluid reenters the capillaries. Excess fluid gets picked up by the lymphatic system, at which point it becomes lymph (lymph does not exit at this point again - drains into the chest later).
Explain what the lymphatic system is (briefly).
It is a network of terminal tubules that form larger lymphatic vessels, which themselves form lymphatic ducts. These ducts drain into the large veins in the chest.
What proportion of the ECF does lymph volume make up?
About 1-2% of the ECF volume.
What is trancellular fluid?
It is an aggregate of fluid found in specific areas of the body, secreted by specific epithelial cells and with specialized functions depending on the body part.
Give 3 examples of trancellular fluid.
- Intraocular fluid (in the eye)
- Cochlear fluid (in the ear)
- Synovial fluid (in joints)
What proportion of the ECF does transcellular fluid make up? How significant is transcellular fluid in the body as a whole?
It makes up less than 1-2% of the ECF volume. While it does not contribute significantly to overlal water, however, it is very important in local function.
How does the total body fluid volume and the relative distribution of compartments vary within an individual (not over a long period of time)?
They both remain constant to remain in good health. That being said, there is always water movement between the compartments.
What method is used to determine body fluid compartment volumes in an individual?
The indicator dilution method.
Explain how the indicator dilution method works, including the formula.
You add a known quantity of some agent, allow time for it to equilibrate in the body, and then calculate its concentration. The formula for the volume of the body compartment (ml) is quantity of indicator (g)/concentration of indicator after equilibration (g/ml)
Describe the 5 steps of the indicator dilution procedure
- Introduce a known quantity (Q) of indicator into the vein
- Allow time to equilibrate
- Remove known volume of blood, and centrifuge to obtain plasma
- Measure concentration (c) in unit volume of plasma
- Calculation V = Q/c