Intro to Renal

Question 1

regulatory functions of the kidney

Answer 1

• extracellular fluid volume
• extracellular fluid osmolarity
• extracellular fluid ion composition
• clearance of metabolic end products, toxins and drugs
• endocrine- erythropoietin, active vitamin D, renin

Question 2

body fluid compartments

Answer 2

• total body fluid decreases with age from approx 75% of BW to 50%
• ECF contracts from 50% of BW to 33% in adults
• TBW is inversely proportional to % body fat and TBW decreases as a % of BW with an increased % of body fat- puberty increases body fat in women and decreases TBW
• solute comp of ICF/ECF different, osm is the same

Question 3

body fluid balance

Answer 3

• kidneys monitor and maintain plasma volume and osm
• in turn maintains total body water and osm due to water and solute exchange between the ECF and ICF compartments
• kidneys are only effector organs of regulated water and salt excretion
• unregulated water and salt loss from TBW occurs in sweat, feces, insensible skin and lung loss
• kidneys are the effector organ compensating for the effects of variable consumption of solutes and water on ECF volume and osm by increasing or decreasing the excretion of solutes and water in the urine

Question 4

fluid and solute distribution between plasma and ISF

Answer 4

• fluid distribution between plasma and ISF is driven by the balance between hydrostatic pressure and osmotic pressure differences across the cap wall
• filtration out of intravascular compartment into the extravascular compartment (ISF) and reabsorption is driven by opposing forces
• rate =lp [(Pc-Pi)-(piC-piI)], lp is hydraulic conductivity coefficient

P is hydrostatic, pi is oncotic
-filtration driving is hydrostatic, absorption is driven by oncotic pressure

Question 5

solute distribution

Answer 5

• solute concentration is similar between ISF and plasma with the exception of negatively charged plasma proteins
• impermeable to cap wall and remain in intravascular compartment
• therefore, osmotic pressure is higher in plasma than ISF (osm higher)

Question 6

edema

Answer 6

• excess accumulation of fluid in the interstitial space due to cardiac, renal, hepatic, or endocrine dysfunction
• localized or generalized imbalance of hydrostatic and osmotic pressure across the cap wall induces a fluid shit from the intra to extravascular space
• CHF, nephrotic syndrome, liver disease can cause an isotonic retention of sodium and water as well as decreased circulating volume, which may decrease renal perfusion pressure and activate the R-A-A system, further increasing the sodium retention and maintaining edema
• an increase or decrease in edema can be assessed clinically by the patients weight

Question 7

fluid and solute distribution between ICF and ECF

Answer 7

• net movement of water between ICF and ECF is driven only by osmotic pressure differences across the cell membrane
• permeating and non permeating solute concentrations in ICF and ECF determine water movement
• water moves passively across the cell membrane down its concentration gradient
• water follows solute

Question 8

isosmotic fluid expansion

Answer 8

• IV isosmotic fluid gain to ECF
• increase ECF vol
• ECF osm stays
• no DF
• no change in ICF vol/ osm
• dilution of plasma proteins and decrease Hct

Question 9

isosmotic volume contraction

Answer 9

• diarrhea, isosmotic fluid loss
• decrease in ECF vol
• no change in ECF osm
• no DF, no change in ICF vol/ osm
• concentration of protein and increased Hct

Question 10

hyperosmotic volume contraction

Answer 10

• profuse sweating and/or water deprivation
• decrease in ECF vol and increase in ECF osm
• water moves from ICF to ECF
• decrease ICF vol and inc ICF osm

Question 11

hyperosmotic volume expansion

Answer 11

• high NaCl intake without fluids, gain of solute
• increase ECF osm
• water moves to ECF
• decrease ICF vol and increase ICF osm
• increase ECF vol
• ICF Na concentration remains unchanged due to Na-K pump activity balancing Na entry

Question 12

hypoosmotic volume expansion

Answer 12

• syndrome of inapproprate ADH (gain of water)
• excess water reabsorption from collecting ducts into ECF causes:
• increased ECF vol and decreased osm
• water moves to ICF
• inc ICF vol and dec ICF osm

Question 13

hypoosmotic volume contraction

Answer 13

• aldosterone insufficiency and decreased renal NaCl reabsorption (loss of solute in excess of water)
• dec in ECF osm
• water moves to ICF
• increase ICF vol and dec osm
• decrease ECF vol

Question 14

solute distribution 2

Answer 14

• ECF and ICF different due to Na/K pumo
• exchanges intracellular Na and extracellular K
• K high inside and Na low
• K low outside and Na high
• sum is same so osm is still 300

Question 15

cells shrinking

Answer 15

• if cells shrink in response to an increase in ECF osm (water to ECF)
• cells activate solute uptake mechanisms to inc ECF osm
• drives water back into cells to restore volume to normal
• regulatory volume increase

Question 16

cells swelling

Answer 16

• dec in ECF osm, water to ICF
• cells activate solute efflux mechanisms to decrease ICF osm
• drives water out and volume back to norma
• regulatory volume decrease

Question 17

restoring ECF osm

Answer 17

• caution
• don’t go too fast
• causes dangerous cell swelling or shrinking

Question 18

filtration

Answer 18

• anatomical separation of an ultrafiltrate from the blood
• ultrafiltration of blood through glomerular caps excluding cells and large proteins from the filtrate
• not urine
• ultrafiltrate collected in Bowman’s space and contains organic and inorganic solultes
• GFR is 125 ml/min, 180 L/day
• sum of filtration across all glomeruli of 1 million nephrons

Question 19

reabsorption

Answer 19

-directional movement of solutes and water from the lumen of the kidney tubule to the peritubular surface (blood side)

Question 20

secretion

Answer 20

-directional movement of solutes form the peritubular side of the kidney tubule to the lumenal surface

Question 21

synthesis

Answer 21

• metabolism within the kidney cells degrading and creating organic solutes or hormones appearing in the blood or in the urine
• NH4, HCO3, renin, erythropoietin and active vitamin D

Question 22

excretion

Answer 22

• final result of above processes
• amt of solute and water eliminated in the urine
• excretion is not a renal process

Question 23

handling of solutes

Answer 23

• excreted=filtered+ secreted+synthesized- reabsorbed

- if not metabolized- just filterd+secreted-reabsorbed

Question 24

components of renal function

Answer 24

1. glomerular filtration
2. tubular secretion
3. tubular reabsorption
   - all happen and reabsorption goes to same blood supply as the afferent arteriole coming in
   - separate plasma from blood and filter it to form an ultrafiltrate
   - ultrafiltrate changes in volume and solute comp as it passes down the nephron by reabsorption and secretion of solutes and reabsorption of water
   - proximal tubule to collecting duct