Homeostasis of Body Fluids Flashcards
How much of normal body weight is water?
60% (42 L)- total body water is less in women than men, and decreases with age
Most of the body water is in tissue. Which tissues carry the most?
Second %= percent of the tissue that is water
muscle- 43% (76%)
skeleton- 16% (22% )
adipose- 10% (75%)
other- 6% (10%)
What is the relationship between % total body water (y) and fat content (x)?
inversely proportional- as the fat content increases, % total body water decreases linearly
What are the main sources of water intake?
- drink
- water from food
- oxidative metabolism (300ml/day)
What are the main sources of water output?
- urine
- insensible water (perspiration and sweat)
- feces
How much water is lost daily through insensible water?
perspiration (skin and lung)- 700 ml/day (up to 5L/day burn)
sweat- 100 ml/day (up to 1-2L day exercise)
What is the minimum urinary output?
0.5L/day- this is the minimum requirement to excrete the metabolic waste products produced by our body daily
What important hormone is produced in the kidneys?
EPO
What other hormones are produced/processed in the kidneys?
- conversion of 25-hydroxyvitamin D is converted to 1,25-dihydrovitamin D3
- renin production
- gluconeogenesis during fasting primarily for the brain
Intracellular fluid represents what percentage of our body wgt? Plasma? Interstitial fluid?
- 25L (40% of body weight)
- 3L plasma
- 12L
Notes on composition of blood.
- 8% of BW, 5L (ECF + ICF)
- 60% plasma and 40% RBC (hematocrit)
What separates plasma from interstitial fluid?
capillary walls (very permeable so their contents are very similar)
What does plasma have higher protein content and interstitial fluid have very low protein content?
capillary walls are impermeable to large proteins such as albumin and cells
What are the main contents of plasma and interstitial fluid?
Na+ is the major cation (very little K+ present) and Cl- is the major anion with some HCO3- present (and Protein in plasma)
Why is Na+ a little (2%) higher in plasma compared to interstitial fluid?
Because proteins which are negatively charged bind them to retain them in plasma while Cl-/HCO3- is propelled from the plasma and thus has a slightly higher content in interstitial fluid
What separates extracellular fluid from intracellular fluid?
impermeable cell membranes
What are the main contents of intracellular fluid?
Main cation is K+ with very little Na+ and
the main anions are phosphates, Pr-, and some HCO3- with very little Cl- is present
Ratio of components of intracellular vs. extracellular fluids (mM).
Na+- 14:140 K+- 140:4 Ca2+- 0:1.3 HCO3- 10:26 Protein: 4:1 Mg2+ 20: 0.75 PO4 11:2
How to measure volume of body fluid compartments.
volume= quantity of dye injected/concentration
What are the criteria for probe selection for body fluid measurements?
- non toxic
- neither synthesized nor metabolized
- disperses evenly and only in the compartment of interest
- does not influence compartment volume
What probe is used to measure PLASMA volume?
131I-albumin, Evans blue dye (binds to plasma proteins well)
Why is this a good probe?