Renal Homeostasis Flashcards
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?
Muscle:
• 43% Total Body Weight
• 76% of tissue is H2O
Skeleton:
• 16% Total Body Weight
• 22% of tissue is H2O
Organs:
• 6% Total Body Weight
• 75% of tissue is H2O
Adipose:
• 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?
- 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 - 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?
Plasma:
• 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?
- Non Toxic at concentration employed
- Neither Synthesized or Metabolized
- Disperses Evenly in the Fluid
- Disperses ONLY in the compartment of interest
- Do not influence fluid compartment volume
What happens if the tracer used to do the dilution principle is endogenously synthesized or metabolized?
Synthesized:
• Measured Conc. will be higher than it should be making the Vol. of the compartment “smaller”
Metabolized:
• 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)
ISF = ECFV - PV
