Unit 7 - Introduction to Renal Physiology

Question 1

what are regulatory functions of the kidneys?

Answer 1

• extracellular fluid volume, oxmolarity, and ion composition
• clearance of metabolic end products, toxins, and drugs
• endocrine (erythropoietin, active vit D, renin

Question 2

how does solute composition VS concentration differ in ICF and ECF?

Answer 2

composition of solute is different (Na more outside, K inside), but concentration/osmolarity is the same (~300 mOsm/L)

Question 3

how does total body water change with age? with body fat?

Answer 3

decreases (75% in neonates, 50% in aged adults)

• ECF contracts from 50% in neonates to 33% in adults
• TBW is inversely proportional to % body fat, as well as decreases percentage of TBW of body weight (puberty)

Question 4

what are kidneys the only effector organs of?

Answer 4

regulated water and salt excretion
-compensate for effects of variable consumption of solutes and water on ECF volume and osmolarity by increasing/decreasing excretion of solutes and water in urine

Question 5

what does unregulated water and salt loss from TBW cause?

Answer 5

sweat, feces, and insensible skin and lung loss (H2O only)

Question 6

what is fluid distribution between plasma and ISF driven by?

Answer 6

balance between hydrostatic pressure and osmotic pressure differences across capillary wall (opposing Starling forces)

Question 7

what is the filtration or reabsorption rate formula? their variables?

Answer 7

rate = Lp [(Pc - Pi) - (πc - πi)

• Pc = capillary hydrostatic pressure (filtration)
• Pi = interstitial hydrostatic pressure
• Pc - Pi = push out
• πc = capillary oncotic pressure (reabsorption)
• πi = interstitial oncotic pressure
• πc - πi = pull in

Question 8

what is oncotic pressure?

Answer 8

osmotic pressure inside and outside the capillary attributable to presence or absence of negatively charged PRO

Question 9

solute distribution

Answer 9

solute concentration is similar between ISF and plasma, with exception of negatively charged plasma PRO, which are impermeable to capillary wall and remain within intravascular compartment
-osmotic pressure is higher in plasma than ISF due to absence of PRO in ISF

Question 10

what is Gibbs-Donnan equilibrium?

Answer 10

state of electro-chemical equilibrium with diffusible cation and anion concentration

Question 11

what is edema?

Answer 11

excess accumulation in interstitial space due to cardiac, renal, hepatic, or endocrine dysfunction
-localized/generalized imbalance of hydrostatic and osmotic pressure across capillary wall, inducing a shift in fluid distribution from intravascular to extravascular space

Question 12

what can CHF, nephrotic syndrome, and liver disease edema all cause?

Answer 12

isotonic retention of sodium and water, as well as decreased circulating volume
-decreases renal perfusion pressure and activates RAA system, further increasing Na retention maintaining the edema

Question 13

what is the mechanism of CHF edema VS that of nephrotic syndrome and liver disease?

Answer 13

CHF is increases of capillary hydrostatic pressure (increase filtration), while nephrotic syndrome and liver disease are decreases in plasma PRO concentration, thus capillary oncotic pressure (decrease reabsorption)

Question 14

what is the only thing that drives net movement of water between ICF and ECF?

Answer 14

osmotic pressure differences across the cell membrane

Question 15

what is tonicity and what does this determine?

Answer 15

permeating and non-permeating solute concentrations in ICF and ECF; determines water movement

Question 16

what happens in IV isosmotic fluid gain to ECF?

Answer 16

isosmotic fluid expansion

• increase ECF volume
• no change in ECF osmolarity, osmotic driving force between ICF and ECF, ICF volume or osmolarity
• dilution of plasma PRO
• decreased Hct

Question 17

what happens in diarrhea (isosmotic fluid loss)?

Answer 17

isosmotic volume contraction

• decreased ECF volume
• no change in ECF osmolarity, ICF volume or osmloraity
• no osmotic driving force between ICF and ECF
• increased PRO concentration and Hct

Question 18

what happens in profuse sweating and/or water deprivation?

Answer 18

hyperosmotic volume contraction (loss of water in excess of solute from ECF)

• decreased ECF volume
• increased ECF osmolarity
• water moves from ICF to ECF
• -causes decreased ICF volume and increased ICF osmolarity

Question 19

what happens in high NaCl intake without fluids?

Answer 19

hyperosmotic volume expansion (gain of solute in excess of water)

• increased ECF osmolarity
• ICF NaCl concentration remains unchanged due to Na-K pump activity (Na extrusion) balancing Na entry
• water moves from ICF to ECF
• -causes decreased ICF volume and increased ICF osmolarity
• -increased ECF volume

Question 20

what happens if syndrome of inappropriate antidiuretic hormone (SIADH)?

Answer 20

hypoosmotic volume expansion (gain of water in excess of solute)

• inappropriate water reabsorption from collecting ducts into ECF causes:
• -increased ECF volume and decreased ECF osmolarity
• -water moves from ECF to ICF
• -increased ICF volume and decreased ICF osmolarity

Question 21

what happens if adrenal (aldosterone) insufficiency?

Answer 21

hypoosmotic volume contraction; decreased renal NaCl reabsorption causing loss of solute in excess of water

• decreased ECF osmolarity
• water moves from ECF to ICF
• increased ICF volume and decreased ICF osmolarity
• decreased ECF volume

Question 22

how do cells respond to osmotically driven changes in ICF volume?

Answer 22

activating solute transport mechanisms

-remember that water transport follows solute transport

Question 23

what is regulatory volume increase (RVI)?

Answer 23

if a cell is shrunk in response to an increase in ECF osmolarity
-cells activate solute uptake mechanisms to increase ICF osmolarity, driving water into cells to restore volume to normal

Question 24

what is regulatory volume decrease (RVD)?

Answer 24

if a cell has swelled in response to a decrease in ECF osmolarity
-cells activate solute efflux mechanisms to decrease ICF osmolarity, driving water out of cells to restore volume to normal

Question 25

why should you be cautious when restoring ECF osmolarity?

Answer 25

in cells where RVI or RVD ocured, a rapid correction of ECF osmolarity (giving either hypertonic or hypotonic) at high rate of infusion may cause dangerous cell shrinking or swelling

Question 26

what are the 5 basic processes of the kidney?

Answer 26

• filtration
• reabsorption
• secretion
• synthesis
• excretion

Question 27

kidney filtration

Answer 27

ultrafiltration of blood through glomerular capillaries excludes cells and large proteins from filtrate
-ultrafiltrate is collected in Bowman’s space, and contains organic and inorganic solutes at concentrations similar to plasma

Question 28

what is GFR usually?

Answer 28

125 ml/min or 180 L/day

-sum filtration across all glomeruli of 1 million nephrons in each kidney

Question 29

kidney reabsorption

Answer 29

movement of solutes and water from tubular fluid in the lumen of the kidney tubule to peritubular surface (blood side) and into peritubular capillaries

Question 30

kidney secretion

Answer 30

movement of solutes (but NOT water) from peritubular (blood) side of kidney tubule to tubular fluid in lumen of kidney tubule

Question 31

kidney synthesis

Answer 31

metabolism within kidney cells degrading and creating organic solutes or hormones appearing in blood or urine
-NH4+, HCO3-, renin erythopoietin, active vit D

Question 32

kidney excretion

Answer 32

final result of kidney filtration, reabsorption, secretion, and synthesis

• amount of solute and water eliminated in urine
• excretion is not a renal process, but is the final result of kidney processes

Question 33

what are the 3 components off renal function?

Answer 33

1. glomerular filtration
2. tubular secretion
3. tubular reabsorption