202 Flashcards
Hats the formula for the induction method of measuring body fluid compartment volumes
What assumption is this formula based on?
Yes, you’re right! The formula for calculating the volume of a compartment using the indicator solution method can also be expressed as:
F=I/C
Where:
• F = Volume of the compartment (e.g., plasma volume, extracellular fluid volume)
• I = The amount of dye or tracer injected into the body (usually in mg or g)
• C = The concentration of the dye in the sample after distribution (usually in mg/L or g/L)
This formula works under the assumption that the dye is evenly distributed in the compartment and that there’s no significant loss of the dye from the compartment.
Let me know if this makes sense now!
•Indicator dilution method
•If an indicator is mixed with blood with a known injection rate, I (mg/minute)
•And the concentration C (mg/liter) is measured after mixing, then the flow F (liters/minute) is given by
State three characteristics of market substances
Which marker substance is used for:
Plasma
total body water
ECf
-They should be inert: they shouldn’t mix with substances in the body or undergo reactions in the body, they shouldn’t be metabolized, they shouldn’t be absorbed by the body tissues. Shouldn’t be excreted during the measurement period
-They should be harmless
-They should be measurable
Characteristics of Marker Substances:
1. Inert and non-toxic – It should not interfere with body functions or be harmful.
2. Distributes only in the target compartment – It must stay only in the fluid compartment being measured (e.g., plasma, ECF, TBW).
3. Even and rapid distribution – It should quickly and uniformly mix throughout the compartment.
4. Not metabolized or degraded – It should not be chemically altered by the body.
5. Not reabsorbed or secreted – Especially important for renal markers; no loss through urine or uptake by cells during measurement.
6. Easily measurable – Its concentration should be easily detected in body fluids (e.g., blood, urine).
7. Should not bind to proteins or tissues – To avoid being trapped and altering volume estimation.
•
• Examples:
• Evan’s blue and radioactive iodine for plasma.
Methods of Measurement of Body Fluid Volume
•What should be the characteristics of marker substances?
• Examples:
• Evan’s blue and radioactive iodine for plasma.
• D20, T20 and antipyrine for TBW
• Innulin, mannitol and radioactive sodium for ECF
Excellent question! The markers are chosen based on how they behave in the body—specifically, where they distribute and where they don’t. Here’s why each group of markers is used for its respective fluid compartment:
- Plasma Volume (PV)
Markers: Evan’s blue, ¹²⁵I-albumin
Why:
• These substances bind to plasma proteins (like albumin).
• Therefore, they remain confined within the blood vessels (intravascular space) and do not enter interstitial or intracellular fluid.
• This makes them perfect for measuring plasma volume.
- Total Body Water (TBW)
Markers: D₂O (deuterium oxide), T₂O (tritium oxide), antipyrine
Why:
• These substances are small, neutral, and lipophilic, so they can freely cross all cell membranes.
• They distribute throughout both extracellular and intracellular fluids.
• That’s why they reflect total body water.
- Extracellular Fluid (ECF)
Markers: Inulin, mannitol, ²²Na (radioactive sodium)
Why:
• These substances do not enter cells, so they remain in the extracellular space (i.e., plasma + interstitial fluid).
• They are used to measure the volume outside cells, but they still distribute between blood plasma and interstitial fluid.
In short:
• Stays in blood only → Plasma markers
• Crosses into all water spaces → TBW markers
• Doesn’t enter cells → ECF markers
Let me know if you want a visual summary or diagram for easier memorization!
Why don’t we measure ICF and interstitial fluid volume?
Define the following:
Osmolality
Osmolarity
Tonicity
Isosmotic
We don’t measure ICFV because Total body water is made up of ICFV and ECFV so since we can’t measure ICFV directly, we subtract the ECFV from the TBW so we get the ICFV. So TBW-ECfV
So we can’t directly separate the ITFV from the ECF. eCF comprises of plasma, interstitial fluid volume and trans cellular fluid.
So to get ITFV, you subtract the plasma volume from the ECF volume so ECf-PV
Osmolality refers to the concentration o the solute in kilograms of a solution
Osmolarity is the concentration of solute in the volume of a solution
Tonicity is the ability of solute to cause osmosis or cause water to move out of the cell and it depends on the solutes that stay outside the cell. If the solute won’t cause water to go out of the cell, it won’t affect tonicity.
Osmolality vs Osmolarity:
• Osmolality = solute concentration per kilogram of solvent (water) or conc of solute per unit weight(kg) of solvent.
• More accurate inside the body (less affected by temperature/volume changes)
• Osmolarity = solute concentration per liter of solution or conc per unit volume of solution.(mol/litre)
• Easier to calculate in labs
- Tonicity:
• Tonicity is the effect of a solution on cell volume. Or the measure of a solutes ability to cause osmosis
• It depends only on non-permeable solutes (solutes that stay outside the cell).
• These draw water out, making the cell shrink (hypertonic)
• Or allow water in, making the cell swell (hypotonic)
• Or cause no movement, so the cell stays the same (isotonic)
Isosomotic:
So if I understand what you’re saying, isOsmolality is when two solutions have the same concentration or number of particles per kilogram of solvent.
It relates to isotonicity because they have the same isosomolality May or may not cause swelling or shrinking of the cell. That’s why isotonicity is not equal to isosomolality
Yes — you’ve got it exactly right!
Here’s a clearer version of what you just said:
• Isosmolality means two solutions have the same number of solute particles per kilogram of water.
• But just having the same number of particles (isosmolality) doesn’t guarantee the same effect on a cell.
• That’s because tonicity depends on whether those particles can cross the cell membrane or not.
So yes, isosmolality may or may not lead to cell shrinking or swelling, which is why:
Isosmolality ≠ Isotonicity
Great understanding! Want a quick summary table to remember it?
Explain ficks principle in relation to cardiac output and explain the principle ORS works on
Great questions!
- What principle does ORS (Oral Rehydration Solution) work on?
ORS works based on the principle of co-transport of glucose and sodium in the small intestine.
Here’s how it works:
• In the intestine, there’s a special transporter (SGLT-1) that absorbs sodium and glucose together.
• When glucose and sodium are absorbed, water follows due to osmosis.
• This helps rehydrate the body effectively, even during diarrhea when you’re losing water and electrolytes.
So the principle is:
Sodium-glucose co-transport creates an osmotic gradient that pulls water into the body.
That’s why ORS contains both glucose and sodium — without both, it won’t work as well.
- The Fick’s Principle and the equation
Yes! You’re right. The Fick principle focuses on blood flow (F). The equation usually looks like this:
F= oxygen consumption / arterial oxygen- venous oxygen
Or rate of oxygen consumption/ amount of oxygen leaving - amount of oxygen entering the heart
Where:
• F = Blood flow (Cardiac Output) in L/min
• Oxygen consumption = how much oxygen the body uses per minute (measured in mL/min)
• Arterial O₂ = oxygen content in oxygenated blood
• Venous O₂ = oxygen content in deoxygenated blood
Example:
If the body uses 250 mL of oxygen per minute(Oxygen used is mL/min) and the difference in O₂ content between arteries and veins is 50 mL per liter(diff in oxygen is ml/L) , then: F is litres per min.

That means the heart is pumping 5 liters of blood per minute.
Would you like to go over any part with a diagram or real-life example?
Yes, exactly! That’s another way of expressing Fick’s Principle — and it’s actually at the heart of the equation. Let’s break it down:
Fick’s Principle — Concept Simplified:
“The amount of a substance taken up by an organ (like oxygen by the lungs) is equal to the blood flow to the organ multiplied by the difference between the amount entering and leaving the organ.”
So for oxygen and the heart, we say:

Rearranging it gives the formula you’re seeing:

Meaning of “oxygen entering and leaving”:
• Oxygen entering = the amount of O₂ in arterial blood (from lungs to tissues)
• Oxygen leaving = the amount of O₂ in venous blood (after tissues have used some up)
So:
• If you measure how much O₂ the body uses in 1 min (e.g., 250 mL/min),
• And know how much O₂ is in blood before and after it passes through tissues,
• You can calculate how much blood (cardiac output) must have flowed to deliver that oxygen.
Would you like me to explain this with numbers or in a diagram-style breakdown too?
Great! Here’s a simple analogy followed by a clinical example:
Simple Analogy:
Think of your heart as a delivery truck, and oxygen as the cargo.
• The lungs are the loading station where the truck picks up oxygen.
• The body tissues are the delivery locations where the oxygen is dropped off.
Now, if you want to know how many trucks (how much blood) are moving each minute, you can check:
• How much cargo (oxygen) they pick up at the lungs, and
• How much cargo is left after delivery (how much oxygen is left in the blood returning to the lungs).
This is what Fick’s Principle does — by comparing oxygen before and after it’s delivered, it calculates how many “trucks” (i.e., cardiac output) are moving.
Clinical Example:
Let’s say a doctor wants to know how well a patient’s heart is pumping.
1. They measure how much oxygen is in the arteries (O₂ entering) and how much is in the veins (O₂ leaving).
2. They also measure how much oxygen the body is using per minute (VO₂) — maybe with a breathing mask.
3. Using Fick’s equation:
Cardiac output = oxygen used per minute/ arterial oxygen minus venous oxygen
This tells them how much blood the heart is pumping per minute.
If the result is low, it may mean the heart is weak or the tissues aren’t getting enough oxygen — and this helps the doctor know what treatment to give.
Would you like a quick recap in bullet points for easier memorization?
So basically to assess how well your heart is doing, we check the amount of oxygen you’re consuming divided by the amount of oxygen in blood leaving the heart minus the amount entering the heart
Explain the use of blood flow meter as an application of body fluid measurement in health and disease
Sure! Here’s a simple explanation:
Fistula Creation for Dialysis & Blood Flow Measurement
• In patients with kidney failure, hemodialysis is used to filter their blood.
• For this, a strong and wide vein is needed to allow large needles and good blood flow.
• So, doctors create a fistula — they join an artery to a nearby vein (usually in the arm).
• The high pressure from the artery causes the vein to enlarge and thicken over time.
• Blood flow meters are then used to:
• Measure how well blood is flowing through the fistula
• Ensure it’s mature enough for dialysis use
• Detect any blockages or poor flow before complications happen
Let me know if you’d like a quick diagram or summary line to memorize this!
Great questions! Let’s break it down:
Why must they create a fistula for dialysis?
1. Dialysis needs strong blood flow — about 250–400 mL/min.
2. Normal veins are too small and fragile for repeated needle insertion and high blood flow.
3. So, a fistula is created by connecting an artery to a vein.
• The artery’s pressure makes the vein larger and stronger.
• This makes it easier to insert needles and handle the high blood flow needed for dialysis.
How is a blood flow meter an application of body fluid measurement?
1. Blood flow meters measure the rate of blood flow through vessels — this is a form of body fluid (blood) measurement.
2. In the case of a fistula:
• It assesses if the fistula is ready (mature) to be used for dialysis.
• It detects blockages or poor flow, which can prevent effective dialysis.
• It helps guide medical decisions (e.g., whether to redo or repair the fistula).
Summary:
Creating a fistula ensures strong, reliable access to blood for dialysis. Using a blood flow meter is a direct application of body fluid measurement to monitor and maintain this access for effective treatment.
Let me know if you want a quick one-liner to memorize!
What carries what
Sodium or glucose?
In the symport
Na⁺/Glucose Symport (SGLT) – Found in intestines/kidneys:
• Sodium (Na⁺) moves down its concentration gradient into the cell.
• It pulls glucose with it into the cell.
• Both go in the same direction → Symport.
Sodium goes down the electrochemical gradient and easily enters the cell because it’s more outside the cell than inside so naturally it’ll want to move inside. And there’s more negative charge inside the cell than outside so sodium which Is positively charged will want to move inside.
So glucose will ride on sodium’s energy or easy ability to enter the cell using a contransporter called the sodium glucose linked transporter so it enters too.
You’re right! Actually, there is more glucose outside the cell than inside, and I made a mistake earlier. Here’s the corrected explanation:
Why does glucose struggle to enter?
• Glucose concentrations are higher outside the cell (in the bloodstream) compared to inside the cell, so it should naturally move into the cell by diffusion.
• However, glucose cannot easily diffuse across the cell membrane because the membrane is lipid-based, and glucose is a polar molecule, which has difficulty passing through.
So how does glucose enter the cell?
It uses facilitated diffusion or active transport mechanisms (like the SGLT co-transporter I mentioned). Here’s the correct flow:
1. Sodium (Na+) is pumped out of the cell by the sodium-potassium pump, creating a high concentration of sodium outside.
2. Glucose then enters the cell through a co-transporter (SGLT), which uses the energy from sodium moving into the cell (down its gradient) to pull glucose into the cell, even though glucose is already in higher concentration outside. This secondary active transport doesn’t directly use ATP but uses the energy from the sodium gradient.
To summarize:
• More glucose is outside the cell.
• Sodium moves into the cell easily (due to its concentration gradient), and in turn, it helps glucose enter via the co-transporter.
Does this clarify things better?
Yes, you’re correct! There are two main mechanisms for glucose to enter cells: facilitated diffusion and symport (secondary active transport). Both involve transport proteins, but they work in different ways:
- Facilitated Diffusion (GLUT Transporters):
• This process occurs via GLUT transporters (such as GLUT1, GLUT2, GLUT4, etc.).
• Facilitated diffusion allows glucose to enter the cell along its concentration gradient without energy (ATP).
• In this process, glucose moves from an area of high concentration to low concentration, but it needs a carrier protein (GLUT) to help it pass through the cell membrane since it cannot cross the lipid bilayer on its own due to its size and polarity.
• Example: When glucose is present in the blood at higher concentrations, GLUT proteins in cells like those in the liver, muscle, and adipose tissue will allow glucose to diffuse into the cells. - Symport (Sodium-Glucose Transporter - SGLT):
• This mechanism involves SGLT proteins (such as SGLT1 and SGLT2) and is a form of secondary active transport.
• Symport means that two substances move in the same direction across the membrane. In this case, sodium (Na+) and glucose both move into the cell together.
• The key here is that sodium ions are moving down their concentration gradient (from high outside the cell to low inside), and this energy is used to pull glucose into the cell against its concentration gradient (from low inside the cell to high inside).
• Since sodium is moving down its gradient, it doesn’t require direct ATP energy. However, ATP is still involved indirectly because the sodium gradient is maintained by the sodium-potassium pump (which uses ATP to pump sodium out of the cell).
• Example: In the small intestine or kidneys, glucose is absorbed from the lumen into cells via SGLT, driven by the sodium gradient.
Key Differences:
• Facilitated diffusion (GLUT): Moves glucose down its concentration gradient without energy.
• Symport (SGLT): Moves glucose against its concentration gradient by coupling it with sodium moving down its concentration gradient (indirect energy usage).
So, facilitated diffusion is a simpler, energy-free method when the glucose concentration is higher outside the cell, while symport allows glucose to be actively absorbed against its concentration gradient, often in tissues like the small intestine and kidney.
Both processes are important, but they work under different conditions and with different transport mechanisms.
Does that help clarify the two mechanisms?
RBCs lack nucleus and mitochondria. Explain the fluid mosaic model.
State the types of proteins on the cell membrane
•The cell and its organelles
•The cell membrane: the structure is described as fluid mosaic model:
•Fluid because the components are not linked by chemical bonds so can move freely.
•Mosaic because Proteins are dispersed in a hospholipid bilayer
•Components of the cell membrane: Proteins
• Integral Membrane Proteins are embedded within the lipid bilayer
• Transmembrane Proteins span the membrane and function as ion channels, carrier molecules, enzymes, receptors…
• Peripheral proteins: loosely bound to other proteins and phospholipids usually on the cytosolic side. They function mainly as part of the cytoskeleton
