Lecture 6: Calculations and Glucose Flashcards
What contributes to final excretion of substances in urine?
Degree of reabsorption and secretion of filtered substances
Reabsorption
Water and solutes such as Na, Cl, HCO3, glucose, AA, urea, Ca, Mg, phosphate, lactate, citrate are all reabsorbed
Secretion
Organic acids and bases, K, some urea, typically secreted into tubular fluid from peritubular capillaries
If filtered load is greater than excretion rate
Net absorption of substance
If filtered load less than excretion rate
Net secretion of substance
Reabsorption or secretion rate =
Filtered load - excretion rate
Where does glucose reabsorption occur
Proximal convoluted tubule
How does glucose get across luminal membrane?
Na+/glucose co-transporter (aka SGLT 1)
How does glucose get reabsorbed from proximal tubule cell into blood?
GLUT1 or GLUT2
Glucose titration curve shows relationship between?
Plasma glucose concentration (x axis) and reabsorption (y axis)
As plasma glucose increases
Filtered load increases linearly
Why does filtered load increase linearly as plasma glucose increases?
It is a freely filtered substance
At what plasma glucose concentration is all filtered glucose reabsorbed up to? (So less than this concentration)
< 200 mg/dl
Above what value of glucose concentration are transporters limiting and the glucose curve starts to bend?
Above 200 mg/dl
At what glucose concentration are all transporters saturated and curve levels off?
Above 350 mg/dl
What is Tmax?
ALL transporters are saturated, where curve begins to level off
Splay
Reabsorption approaching saturation glucose level to show up in urine before Tmax reached
Excretion occurs at what concentrations of glucose
Above 200 mg/dl, not all carriers saturated but some excretion due to a lot of them being sautrated
Above 350 mg/dl the excretion curve
Increases linearly
Glucosuria
Excretion/spilling of glucose in urine
Why does glucosuria occur in diabetes mellitus?
Due to high plasma glucose/hyperglycemia
Hyperglycemia
High plasma glucose
Pregnancy
Glucosuria can occur during pregnancy
In what glucose transport system can glucosuria occur?
Abnormalities/defects in Na+/glucose co-transporter
Abnormalities/defects in Na+/glucose co-transporter cause what?
Tmax decreases, so takes less saturation of glucose to cause all carriers to be booked
Name all conditions that can cause Glucosuria
Diabetes mellitus
Pregnancy
Defects in Na+/glucose co-transporter
High stress
Fanconi syndrome
Fanconi syndrome, disorder in what part of renal tubule?
Proximal convoluted tubule
Symptoms of Fanconi syndrome
Normal glycemia and primary renal glucosuria
How is Fanconi syndrome acquired?
Certain drugs, exposure to heavy metals, Vitamin D deficient, Kidney transplant
How is Fanconi syndrome congenital?
Basenji dogs - autosomal recessive trait
