Costanzo Renal Physiology: Reabsorption and Secretion Flashcards
What is reabsorption or secretion rate?
The reabsorption or secretion rate is the difference between the amount filtered across the glomerular capillaries (filtration load) and the amount excreted.
How is reabsorption differentiated from secretion?
If filtered load is greater than amount excreted then there is net reabsorption. If the filtration load is smaller than the amount excreted then there is net secretion.
What determines the glucose filtration load?
The glucose filtration load is directly proportional to the plasma glucose concentration.
How is glucose reabsorbed?
Glucose is reabsorbed by Na+ glucose cotransport pumps in the proximal tubule.
What is the transport capacity for glucose?
Glucose concentrations less than 250 mg/dL are completely reabsorbed.
concentrations greater than 350 mg/dL have saturated all the the glucose transporters (Tm)
What is the glucose excretion threshold?
Glucose must reach concentrations of 250 mg/dL or greater before it will appear in the urine. Above 350 mg/dL all extra glucose is excreted because there are no more transporters (Tm)
What is splay?
The splay is the region of the glucose curve between the threshold and the Tm
How is the excretion of secreted substances such as para-aminohippuric acid calculated?
The excretion of PAH is the sum of the filtration across the glomerulus plus the amount secreted in the proximal tubule.
How are weak acids and bases excreted?
Weak acids and bases are filtered. However, they are not reabsorbed and can only diffuse back to the blood in their non ionized form. Therefore the pH of the urine directly impacts which weak acids and base can diffuse back into the blood stream.
