Renal Physiology I

Question 1

60/40/20 rule

Answer 1

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

Question 2

Intracellular fluid ion levels - Na, phosphate, K, protein anions

Answer 2

Low Na
High K
High phosphate
Higher protein anions than ECF
No HCO3

Question 3

Interstitial fluid ion levels - Na, phosphate, K, Cl, HCO3

Answer 3

High Na
High Cl
Low K
Medium HCO3

Question 4

Plasma fluid ion levels- Na, Cl, HCO3, K, protein anions

Answer 4

High Na
High Cl
Medium HCO3
Low K
Low protein anions

Question 5

Electrolytes

Answer 5

Eg.. NaCl - molecules that can dissociate into two ions

Have greater ability to cause fluid shift

Question 6

Normal serum osmolality

Answer 6

285-295

Question 7

Water diuresis

Answer 7

Increased water excretion without corresponding increase in salt excretion

• Primary cause is increased water intake
• also polydipsia, diabetes insipidus

Question 8

Solute diuresis

Answer 8

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

Question 9

Free water clearance

Answer 9

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

Question 10

Free water clearance equation

Answer 10

FWC= V - Cosm = V - (Uosm x V)/(Posm)
Cosm- osmolar clearance
V- urine flow rate
U- urine osmolarity
P- plasma osmolarity

Question 11

Indicators for total body water volume

Answer 11

radioactive H2O (D2O), antipyrine

Question 12

Indicators for EC fluid volume

Answer 12

Na, I-iothalamate, thiosulfate, insulin

Question 13

Indicators for IC fluid volume

Answer 13

Total body water - EC fluid volume

Question 14

Indicators for plasma volume

Answer 14

Albumin, evans blue dye

Question 15

Indicators for blood volume

Answer 15

Plasma volume/1-hematocrit

Question 16

Indicators for interstitial fluid

Answer 16

EC fluid volume - plasma volume

Question 17

Plasma osmolarity equation

Answer 17

(Na x2) + Glucose/18 + BUN/2.8

Eyeballing: 2x plasma sodium

Question 18

Gibbs donnan effect

Answer 18

Negatively charged proteins inside capillary generates both osmotic and electrochemical gradient favoring fluid and positive charge flow inwards

Question 19

What would happen if gibbs donnan effect was not countered

Answer 19

IC proteins would result in an influx of water into cell- cell swelling and death
Na/K exchanger counteracts the effect, preventing water influx

Question 20

ICF volume lost/gained effect on RBC

Answer 20

ICF loss leads to decreased hematocrit because of RBC shrinkage
ICF gain is opposite

Question 21

Cyrstalloids replacement therapy

Answer 21

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

Question 22

Colloids

Answer 22

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

Question 23

Body fluid volumes are regulated by

Answer 23

Changes in Na balance

Question 24

Serum osmolality and Na concentration regulated by

Answer 24

Changes in H2O balance

Question 25

Hyponatremic dehydration

Answer 25

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

Question 26

Hypernatremic dehydration

Answer 26

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

Question 27

Isosmotic volume contraction

Answer 27

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

Question 28

Hyperosmotic volume contraction

Answer 28

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

Question 29

Hyposmotic volume contraction

Answer 29

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

Question 30

Isosmotic volume expansion

Answer 30

ECF volume increases, ICF volume stays the same, osmolarity stays the same, hematocrit and plasma protein decrease

Question 31

Hypertonic volume expansion

Answer 31

``` ECF volume increases ICF volume decreases Osmolarity increases Fluid shift from intracellular to extracellular until equilibrium -mimics high salt intake ```

Question 32

Hyposmotic volume expansion

Answer 32

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

Question 33

Congestive heart failure

Answer 33

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

Question 34

Renin is stimulated by

Answer 34

Drop in blood pressure and B1 adrenergic receptor activation

Question 35

Renal vasoconstrictors

Answer 35

Sympathetics Endothelin ATP/adenosine Angiotensin II

Question 36

Renal vasodilators

Answer 36

``` Prostaglandins Bradykinin NO Dopamine ANP ACE-inhibitor ```

Question 37

Angiotensin II constricts which arteriole

Answer 37

Efferent arteriole, raising GFR during diminished renal perfusion pressure ACE inhibitors will lower GFR but blocking angiotensin II production

Question 38

Sympathetic effect on RBF/GFR

Answer 38

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