Chapter 25 - The Body Fluid Compartments Flashcards
What are the two major sources of body water?
- Ingested liquid (2.1 L/day)
2. Oxidation of carbohydrates (0.2 L/day)
Intake of water depends on the following variables:
- Climate
- Habit
- Level of Physical Activity
What is insensible water loss?
Water loss that occurs outside of conscious awareness (i.e. 0.7 L/day through respiratory tract and skin). It occurs even in people born without sweat glands.
What is the average rate of water diffusion through the skin?
0.3 - 0.4 L/day
What prevents excessive evaporation through the skin?
Cholesterol-filled cornified layer of the skin.
How much water is lost through the respiratory tract?
0.3 to 0.4 L/day
This may be even greater in colder climates.
What is the amount of water loss from sweat dependent on?
- Physical Activity
2. Environmental Temperature
How much water is normally lost through sweat?
0.1 L/day
1 - 2 L/hour (heavy exercise)
How much water is lost through the feces?
0.1 L/day
What is the most important means by which the body maintains a balance between water intake/output?
Controlling kidney excretion of specific substances
What are the two major compartments that hold the body fluid?
- Extracellular
2. Intracellular
What are the two divisions of the extracellular fluid?
- Interstitial Fluid
2. Blood Plasma
What is transcelllular fluid?
It includes fluid from the synovial, peritoneal, pericardial, spinal cord and intraocular spaces. It constitutes about 1 - 2 L of the body fluid.
In an average 70 kg adult man, what is the body fluid distribution in his body?
Total Body Water: 60% of BW
ICF: 40% of BW
ECF: 20% of BW
Plasma: 5% of BW
Remember 60:40:20:5!
What factors affect the total body water of an individual?
- Age
- Gender
- Obesity
What % BW is water in women and premature and newborn babies?
Women: 50% BW
Premature/Newborn Babies: 70 - 75% BW
The pores of the capillary wall are highly permeable to almost all solutes in the ECF except?
Proteins
Why is blood considered a separate fluid compartments?
Because it is contained within the circulatory system
What is the average blood volume of adults?
7% of BW (~5 L)
60% Plasma
40% RBC
Differentiate: True hematocrit vs. measured hematocrit
True hematocrit is only 96% of measured hematocrit due to residual plasma
What are the average hematocrit values in men and women?
Men: 0.40
Women: 0.36
Severe Anemia: 0.10
Polycythemia: 0.65
Describe the ionic composition of plasma and interstitial fluid?
They are similar due to the highly permeable capillary membrane.
However, there are more proteins in plasma because they are not filtered out.
Define: Donnan effect
It is responsible for the greater concentration of cations in the plasma, as they are attracted to the negatively charged proteins.
Negatively charged ions are thus repelled into the interstitial fluid.
Describe the composition of the ECF
High: Na, Cl and HCO3
Low: K, Ca, Mg, PO3 and organic acid ions
Describe the composition of the ICF
High: Protein (4x plasma), K and PO3
Medium: Mg and SO4
Low: Na, Cl and Ca
What is the indicator-dilution method of measuring a fluid compartment?
It utilises an indicator substances and checks how much it’s diluted to measure the fluid volume.
What are the assumptions of the indicator-dilution method?
- Indicator disperses evenly
- Indicator disperses in a closed compartment
- Indicator is not metabolized/excreted
What substances are used to measure total body water?
- Radiocative Water (Tritium)
- Heavy water (Deuterium)
- Antipyrine
What substances are used to measure the ECF?
- Radioactive Na
- Radioactive Cl
- Radioactive Iothalamate
- Thiosulfate Ion
- Inulin
What substances are used to measure the plasma volume?
- I-albumin
2. Evans blue dye
T/F: Intracellular volume can be measured directly?
False. It is measured indirectly by subtracting ECF volume from TBW.
T/F: Like ICF volume, interstitial fluid volume is also measured indirectly.
True. Subtract the plasma volume from the ECF volume to obtain it.
What is the formula for measuring blood volume?
Plasma volume/(1 - hematocrit)
What substance is commonly used to label red blood cells?
Radiocative Chromium (51Cr)
Relative amounts of fluid between plasma and interstitial spaces is determined by?
Balance of hydrostatic and colloid osmotic forces across the capillary membranes
T/F: The ICF and ECF are isotonic
True. This is because water moves rapidly across the cell membrane.
What is the rate of diffusion of water?
Rate of osmosis
Define: 1 osm
It is equal to 1 mole (6.02 x 10^23) solute particles. Osmolarity accounts for the dissociation of ionic compounds (1 mol NaCl = 2 osm/L)
T/F: Osmolarity and osmolality are interchangeable when body fluids are being talked about.
True. Body fluids are so dilute that the differences are almost negligible.
Osmotic pressure can be calculated if?
The cell membrane is assumed to be impermeable to the solute.
What is the correction factor used in van’t Hoff’s law that accounts for inter ionic attraction?
Osmotic coefficient
About __% of osmolarity of interstitial fluid and plasma is due to ____ and ____?
80; Na ions; Cl ions
What is the approximate total osmolarity of each compartment?
300 mOsm/L
Each mOsm of impermeant solute exerts how much pressure across the cell membrane?
19.3 mmHg
Relatively small changes in the concentration of impermeant solutes cause ____ changes in cell volume.
Large
T/F: 3% glucose solution is isotonic to the body fluid.
False. It’s 5% glucose solution.
Differentiate: Tonicity vs. Osmoticity
Tonicity accounts for impermeable solutes only. It is concerned with changes in cell volume.
Osmoticity is a more general term that considers only the concentration of solutes and not their individual natures.
How long does it take to achieve osmotic equilibrium after drinking water?
Roughly 30 minutes
What factors can cause major volume shifts in the ICF/ECF?
- Water Intake
- Dehydration
- IV Infusion
- Loss of Water through GI Tract
- Loss of Water through Sweating
- Loss of Water through Kidney Excretion
What are the two major governing principles in prescribing therapy for changes in body fluid volume?
- Water moves rapidly across cell membranes.
2. Cell membranes are almost completely impermeable to many solutes.
T/F: Hyponatremia is more common than hypernatremia.
True. Hypernatremia stimulates thirst, which prevents large increases in ECF sodium concentration. However, this may afflict babies and the elderly.
What conditions are prone to intracellular swelling/edema?
- Hyponatremia
- Depression of Metabolic Systems
- Lack of Adequate Cell Nutrition
- Inflammation
What are the causes of extracellular edema?
- Abnormal Leakage of Fluid
2. Failure of Lymphatic Return
What filaria nematode causes the clinical condition known as elephantiasis?
Wucheria bancrofti
What is the most common cause of edema?
Heart failure
What happens in heart failure?
There is an increase in capillary filtration but a decrease in salt and water excretion (due to arterial pressure fall)
