31- Calculations & Glucose Handling

equation for RPF

RPF= (U _PAH x V) / P _PAH

equation for GFR

GFR = (U _Inulin x V) / P _inulin

FF equation

FF = GFR/ RPF

P _Inulin Is used to calculate what

GFR

P _PAH is used to calculate what

RPF (Renal Plasma Flow)

describe what the workload of kidneys entails

• glomerular filtration

  • no energy consumed in filtering plasma

• reabsorption and secretion of solutes and water 

  • requires energy

what if reabsorption by the kidneys didnt occur?

• massive loss of water and solutes

  • 180 L filtered so loss of 180 L water, 25,200 mEq Na, 19,800 Cl , 4, 320 HCO3, 14, 400 glucose

the degree of reabsorption and secretion of filtered substances will determine what?

final excretion amounts in urine

describe reabsorption in the kidney

water and solutes REABSORBED from tubular fluid

• Na

• Cl

• HCO3

• glucose

• AA

• urea

• Ca

• Mg

• Phosphage

• lactate

• citrate 

describe renal secretion

organic acids and bases, K typically secreted into tubular fluid from peritubular capillaries

what is filtered load and whats the equation

amt of substrate in plasma

filtered load = GFR x [P]_x

what is excretion rate and whats the equation 

amt of substrate in urine

excretion rate = V x [U]_x

reabsorption or secretion rate =

filtered load - excretion rate

if filtered load is GREATER THAN excretion rate….

net reabsorption of substance

if filtered load LESS THAN excretion rate…

net secretion of substance

where does glucose reabsorption occur?

in the proximal convoluted tubule

facilitated glucose transport across occurs

across peritubular membrane side using GLUT1 and GLUT2

why is there a transport maximum for glucose reabsorption?

due to limited # of glucose transporters

what does the glucose titration curve show

• relationship bt plasma glucose concentration and glucose reabsorption

  • shows reabsorption rate of glucose as plasma concentration increases

  • freely filtered load

as plasma gluc increases, filtered load

increases linearly

describe glucose reabsorption

at plasma gluc < 200, all reabsorb = filtration

> 350 = transporters are saturated and levels off at Tmax

whats Splay indicate

reabsorption approaching saturation. gluc shows up in urine before tmax is reached

describe excretion values on the glucose titration curve 

below 200 mg/dL all filtered glucose reabsorbed, none excreted

above 200 carriers near saturations, some glucose not reabsorbed

describe threshold on the glucose titration curve

plasma conc at which glc appears in urine

above 350, curve inc linearly

define glucosuria 

excretion/spilling of glucose into urine 

why can glucosuria occur in uncontrolled diabetes mellitus

due to high plasma glucose/hyperglycemia

• filtered glucose load exceeds reabsorptive capacity (plasma glucose above Tmax)

why can glucosuria occur in preg

GFR inc which increases filtered glucose load

why can glucosuria occur due to abnormalities/defects

due to issues w Na/glucose co-transporter

• can allow glucose to spill into urine at lower than normal plasma conc

whats the renal threshold for glucosuria in dogs and cats 

dogs- 200mg/dL

cats- 280-300 mg/dL

when can cats get hyperglycemia 

high stress times 

what syndrome can occur even with normal glycemia

primary renal glucosuria

fanconi syndrome

• can occur from disorder w proximal tubule, issues with gluc transport

describe fanconi syndrome

problems w absroping glucose, bicarb, phosphates, urea, potassium, certain AA and can spill into urine.

• can be caused by exposure to certain drugs or exposure to heavy metals, vit d deficiency, kidney transport

what breed can have autosomal recessive fanconi syndrome since it is hereditary

basenji

describe acquired fanconi syndrome

caused by beef jerky treats imported from china

-affect small breeds more

-lethargy, v/d, pu/pd

-urine dipstick showed glucosuria, aminoaciduria, liver enzymes inc