Renal Physiology I Flashcards
60/40/20 rule
60% of body weight is total body water
40% of body weight, or 2/3 of total body water is intracellular fluid
20% of body weight, or 1/3 of total body water is extracellular fluid
Intracellular fluid ion levels - Na, phosphate, K, protein anions
Low Na High K High phosphate Higher protein anions than ECF No HCO3
Interstitial fluid ion levels - Na, phosphate, K, Cl, HCO3
High Na
High Cl
Low K
Medium HCO3
Plasma fluid ion levels- Na, Cl, HCO3, K, protein anions
High Na High Cl Medium HCO3 Low K Low protein anions
Electrolytes
Eg.. NaCl - molecules that can dissociate into two ions
Have greater ability to cause fluid shift
Normal serum osmolality
285-295
Water diuresis
Increased water excretion without corresponding increase in salt excretion
- Primary cause is increased water intake
- also polydipsia, diabetes insipidus
Solute diuresis
Increased water excretion concurrent with increased salt excretion
Primary cause- significant increase in salt present in tubular fluid
–IV NaCl, hyperglycemia, high protein intake, recovery from AKI
Free water clearance
If free water clearance is positive - excess water Is being excreted
If it is negative, excess solutes are being removed from blood by kidneys and water is being conserved
–Whenever urine osmolarity is greater than plasma osmolarity, free water clearance is negative, indicating water conservation
Free water clearance equation
FWC= V - Cosm = V - (Uosm x V)/(Posm) Cosm- osmolar clearance V- urine flow rate U- urine osmolarity P- plasma osmolarity
Indicators for total body water volume
radioactive H2O (D2O), antipyrine
Indicators for EC fluid volume
Na, I-iothalamate, thiosulfate, insulin
Indicators for IC fluid volume
Total body water - EC fluid volume
Indicators for plasma volume
Albumin, evans blue dye
Indicators for blood volume
Plasma volume/1-hematocrit
Indicators for interstitial fluid
EC fluid volume - plasma volume
Plasma osmolarity equation
(Na x2) + Glucose/18 + BUN/2.8
Eyeballing: 2x plasma sodium
Gibbs donnan effect
Negatively charged proteins inside capillary generates both osmotic and electrochemical gradient favoring fluid and positive charge flow inwards
What would happen if gibbs donnan effect was not countered
IC proteins would result in an influx of water into cell- cell swelling and death
Na/K exchanger counteracts the effect, preventing water influx
ICF volume lost/gained effect on RBC
ICF loss leads to decreased hematocrit because of RBC shrinkage
ICF gain is opposite
Cyrstalloids replacement therapy
Organic or inorganic salts dissolved in sterile water
Do not cross plasma membrane- remain in ECF
Distributed evenly in ECF b/w intravascular and interstitial
Glucose and NaCl commonly used as solutes
Colloids
Contain large molecules that don’t pass through semipermeable membranes
Remain in intravascular compartment and expand intravascular volume by drawing fluid from extravascular spaces
-Hydroxyethyl starches HES, albumin
Body fluid volumes are regulated by
Changes in Na balance
Serum osmolality and Na concentration regulated by
Changes in H2O balance
Hyponatremic dehydration
Loss of sodium is greater than loss of water in ECF
Serum Na concentration in the ICF is greater than that of ECF
Water shifts from ECF to ICF to establish equilibrium
Serum Na and serum osmolality will be less than normal range
Brain swelling, confusion, weakness, hypotension, tachycardia
Hypernatremic dehydration
Loss of water is greater than loss of sodium in ECF
Serum Na concentration in the ECF is greater than in the ICF, water shifts from ICF to ECF
Serum osmolality exceeds 300mOsm/kg
Serum Na will be more than 150mEq/L
Edema, increased BP, muscle weakness, hyperreflexia
Isosmotic volume contraction
Acute fluid loss conditions hemorrhage, diarrhea and vomiting
Diarrhea causes loss of isosmotic fluid from the GI tract
Decrease in ECF volume and no change in body osmolality or ICF volume
Hyperosmotic volume contraction
Hypotonic fluid loss conditions - Dehydration, diabetes insipidus, alcoholism
Insensible water loss from ECF, solute is left behind and becomes concentrated
Decrease in ECF and ICF volume but increase in body osmolality
Hyposmotic volume contraction
ICF volume increases, ECF volume decreases, osmolarity decreases
Adrenal insufficiency due to loss of aldosterone leading to excessive loss of NaCl in urine
Transient response is that ECF osmolarity decreases and fluid shifts to ICF until equilibrium
Isosmotic volume expansion
ECF volume increases, ICF volume stays the same, osmolarity stays the same, hematocrit and plasma protein decrease
Hypertonic volume expansion
ECF volume increases ICF volume decreases Osmolarity increases Fluid shift from intracellular to extracellular until equilibrium -mimics high salt intake
Hyposmotic volume expansion
Gain of hypotonic fluid
Conditions like excess water drinking and syndrome of inappropriate ADH secretion cause this
Increase in ECF and ICF volume, decrease in body osmolality
Congestive heart failure
Low effective circulating volume due to decreased cardiac output
Sensed as low pressure
Na and fluid retention resulting in edema in which venous and capillary hydrostatic pressures increase
Patients continue to retain Na, increasing ECF volume without correcting the effective circulating volume
Renin is stimulated by
Drop in blood pressure and B1 adrenergic receptor activation
Renal vasoconstrictors
Sympathetics
Endothelin
ATP/adenosine
Angiotensin II
Renal vasodilators
Prostaglandins Bradykinin NO Dopamine ANP ACE-inhibitor
Angiotensin II constricts which arteriole
Efferent arteriole, raising GFR during diminished renal perfusion pressure
ACE inhibitors will lower GFR but blocking angiotensin II production
Sympathetic effect on RBF/GFR
Sympathetic stimulation will vasoconstrict many renal blood vessels, but there is a particularly high level of a-1 receptors on the afferent arteriole, meaning there will be a decrease in RBF/GFR
