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Flashcards in Renal Homeostasis Deck (37)
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What is the normal percent total body weight of water?

• 60% (42L in a 70kg adult)


What percentage of Total Body Water is found in:
• Muscle
• Skeleton
• Organs
• Adipose Tissue

***What is the % or water in these tissues?

• 43% Total Body Weight
• 76% of tissue is H2O

• 16% Total Body Weight
• 22% of tissue is H2O

• 6% Total Body Weight
• 75% of tissue is H2O

• 10% Total Body Weight
• ~10% of tissue is H2O


What is the relationship between body fat and Water?
• why is this an important relationship?

• Increased % body fat causes Decreased percentage of H2O (a direct inverse proportion)

• Important because you need a high % H2O to maintain a normal metabolic rate


What are the 3 general methods of food intake?
• variable for constant?
• amount taken in?
• Relative Abundance?

2.5 L a day are taken in via:
• Oxidative Metabolism (0.3 L)
• Water Content of Food (2.2 L a day from both
• Drink


What are the 3 predominant methods of output?

• Urine (most fluid eliminated this way)
• Insensible Water Loss (second most)
• Feces (less H2O loss)


T or F: like fluid intake, urinary fluid output is highly variable.

False, urinary fluid output is highly regulated


What is referred to by insensible water loss?
• when can this loss become excessive?

• H2O lost through skin and lungs without knowing its happening

• BURN patients may loos up to 5L per day.


What are the primary metabolic waste products taken care of by the kidney?

• Urea
• Uric Acid
• Creatinine


Non-Filtration (endocrine) functions performed by the kidney.
• how is homeostasis maintained by each of these?

• EPO production - RBC produciton
• 1,25-dihydroxyvitamin D3 - Calcium and Phosphate Balance
• Renin and Angiotensin II production - sodium balance
• GLUCONEOGENESIS - in fasting via amino acids


Why is sodium balance by RAAS important?

• Because Blood Volume is critical in cardiac function


What are the body's 4 open systems?
• what makes them open?
• does fluid leak occur?

• Lung
• Kidney
• GI tract
• Skin

***Open because they are in direct contact with the external environment

***Fluid doesn't necessarily leak out because these tissues have barrier function


What are the two fluid compartment?
• amount of body fluid in each of them?
• Sub-compartments?

Intra cellular fluid (ICF)
• 40% of body H2O (~25L)
• % of H2O is almost the same in every cell and every tissue

Extra cellular fluid (ECF) (20%/15L) consists of:
• Plasma - ~3L in blood vessels
• Interstitial Fluid - ~12L outside of blood vessels


What is the normal blood volume?
• % of body wt?
• Composition (plasma and hct)?
• factors causing variability?

5L (ECF + ICF), 8% of body wt.
60% plasma and 40% RBC (Hct)
• age, sex, pathophysiology affect these values


What are the 2 main barriers to fluid flow?
• what do they separate?
• how do they differ?

1. Capillaries
• Separate Plasma from interstitial fluid
• HIGHLY permeable so composition of Plasma and Interstitial fluid are similar
• HOWEVER there is a HIGHER protein content in the plasma than interstitial fluid

2. Cell Membrane
• separates Interstitial/Extracellular Fluid from Intracellular Fluid
• NOT very permeable
• H2O, Cl-, Urea, lipophilic substances = only things that can go


What is the major cation in the plasma and interstitial fluid? Intracellular Fluid?
• Anion?

Plasma AND interstitial fluid = ECF
• Sodium = major cation
• Chloride, HCO3-, and *Pr- = major anions

*note: proteins are in plasma only

Intracellular Fluid
• Potassium = major cation
• Phosphates, Bicarbonate, and Protein = major anions


What is the difference in composition of the two components of extracellular fluid?

• contains 2% more SODIUM (Na+) because of sodium binding to anionic proteins in the Plasma that can't pass through to the capillaries


Where are the following ions most likely to be found?
• Mg2+
• Ca2+
• PO4

Mg2+ = HIGH in the ICF

Ca2+ = ABSENT in in the ICF (b/c you don't want it activating proteins) - so found mostly in ECF

PO4 = HIGH in ICF (make sense b/c of use of phosphates for intracellular signaling, DNA, etc.)


What is the idea behind the Dilution Principle?

To determine the FLUID VOLUME in a compartment you inject a KNOWN AMOUNT of a tracing agent that is permeable to the layers of interest. CONCENTRATION can be measured later.
• using M = mass injected / Volume to find the volume

**Formula Given: V = Q/(Q/V)


What are the 5 criteria that must be met in order to use the dilution principle?

1. Non Toxic at concentration employed
2. Neither Synthesized or Metabolized
3. Disperses Evenly in the Fluid
4. Disperses ONLY in the compartment of interest
5. Do not influence fluid compartment volume


What happens if the tracer used to do the dilution principle is endogenously synthesized or metabolized?

• Measured Conc. will be higher than it should be making the Vol. of the compartment "smaller"

• Measured Conc. will be more dilute than it should be making the Vol. of the compartment "bigger"


What characteristics would you look for in a probe that is meant to measure plasma volume?
• what are two tracers that satisfy this criteria?

• To measure PLASMA VOLUME you want a probe that DOES NOT cross the Capillary wall

• Therefore it must be a protein or something that rides on a protein

Two Probes: 131-I-Albumin and Evans Blue Dye (attaches to protein)


What are the formulas for Plasma Vol. (PV) measurement?
• what other information can be extrapolated from measuring PV? Formula?

PV = Q / (Q/V)

BLOOD VOLUME: can be extrapolated by

BV = PV / (1 - hct)


What characteristics would you look for in a probe that is meant to measure Extracellular Volume (i.e. plasma vol. + interstitial vol.)?
• what are three tracers that satisfy this criteria?

• To measure ECFV you want a probe that PENETRATES CAPILLARIES but CANNOT cross Cell Membranes

• Insulin, thiosulfate, and Na+ satisfy this criteria

(remember for cell membrane: H2O, Cl-, Urea, lipophilic substances = only things that can go)


What is the formula for ECFV measurement?
• how can it be used to find ISF?

ECFV = Q / (Q/V)



How can you correct for loss of probe in urine (in the case of markers that are permeable into capillaries)?

VOLUME = (Q - Q-lost-in-urine) / (Q/V)


What are the predominant forces governing fluid movement between PLASMA and INTERSTITIAL Fluid?

Plasma Interstitial Fluid
• Starling Forces (Hydrostatic and ONCOTIC pressure)
• note: Oncotic pressure is important but osmotic pressure is not because ions can travel freely across capillaries

Interstitial Fluid Intracellular Fluid
• Osmotic Pressure


What is the relative permeability of cell membranes to:
• Sodium
• Urea
• H2O
• Glycerol

Sodium - impermeable

Urea - permeable

H2O - permeable

Glycerol - slowly permeable


What is the difference between 1 oslmolal and 1 oslmolar glucose in solution?

1 osmolal = 1 Osmole per Kg H2O
1 osmolar = 1 Osmole per L H2O


what pressure does 1 mOsmole of gradient correspond to?

19.3 mmHg


T or F: Osmolarity of body fluids in different compartments is the same.

True, this is 295 mOsmole/L - this happens because water is FREELY PERMEABLE through the barriers and equilibrium is achieved