Lecture 1 (Anatomy, GFR and Clearance, Glucose Handling)

balance in renal system

ingestion + production = excretion + consumption

label section of human kidney diagram

renal corpuscle consists of

glomerular capillaries and Bowman’s capsule

order of filtered fluid flow:

1. proximal tubule

2. loop of henle

3. distal tube

4. late distal tubule/connecting tubule

5. collecting duct

cortical nephron (%, function, where it resides)

• 80-85% of nephrons

• main function is reabsorption/secretion

• most of the tubular segments are within the cortex

juxtamedullary nephron (% and function)

• 15-20% of nephrons

• main function is establishing hypertonic medullary ISF

• loop of henle in renal medulla

label what happens in each part

excreted equation

filtered + secreted - reabsorbed

what is the functional unit of the kidney

nephron

what is the site of filtration down the pressure gradient

glomerulus

what brings blood flow into the glomerulus

afferent arteriole

what brings blood flow out of the glomerulus

efferent arteriole

peritubular vs vasa recta capillaries

• peritubular = osmotic reabsorption (pressure driven)

• vasa recta = important for generating hypertonic renal medulla

how do we describe filtrate

“plasma-like”: cells are not filtered, and very little protein is filtered, but small molecules are in the same concentration as in plasma

does filtration occur by bulk flow or by diffusion and/or active transport

bulk flow

does reabsorption occur by bulk flow or by diffusion and/or active transport

active transport, diffusion, facilitated diffusion

does secretion occur by bulk flow or by diffusion and/or active transport

active transport, diffusion, facilitated diffusion

does excretion occur by bulk flow or by diffusion and/or active transport

bulk flow

glomerular filtration rate (GFR)

volume of fluid filtered into Bowman’s space per unit time (125 ml/min = 180 L/day)

equation for filtered load

[X]p x GFR

equation for amount excreted

[X]u * urine flow rate (V-dot)

clearance

the rate of removal of substance (X) from the plasma compartment

clearance equation

Cx = ([X]u * V-dot)/[X]p

the clearance of what substances can be used to calculate GFR? and which one is exogenous and endogenous?

inulin (exogenous) and creatinine (endogenous)

what happens to Pgc and GFR is you constrict the afferent arteriole?

Pgc and GFR decreases

what happens to Pgc and GFR is you constrict the efferent arteriole?

Pgc and GFR increases

what happens to Pgc and GFR is you dilate the efferent arteriole?

Pgc and GFR decreases

what happens to Pgc and GFR is you dilate the afferent arteriole?

Pgc and GFR increases

if amount excreted < filtered load, then

net reabsorption

if amount excreted > filtered load,

net excretion

if amount excreted = filtered load

no net reabsorption or excretion

where is the only location of kidneys where glucose can be reabsorbed

proximal tubule

what is the primary glucose transporter in the apical membrane and describe the movement of ions

• SGLT-2 (Na+/glucose transporter type 2) — secondary active transporter

• Na+ gradient is used as an energy source to move glucose against its concentration gradient

what is the primary glucose transporter in the basolateral membrane and describe the movement of ions

• Glut-2 (passive facilitated diffusion transporter)

• Na+/K+ ATPases to generate Na+ gradient (keeps [Na+] very low within the tubule epithelial cell)

  

apical membrane is in contact with

tubular fluid

basolateral membrane is in contact with

corticol ISF

what is normal plasma glucose

~90-100 mg/dL

what does threshold indicate for renal handling of glucose?

is plasma [glucose] at which glucosuria (glucose in urine) begins (~170-200 mg/dL)

what does the transport maximum indicate for renal handling of glucose

highest constant maximal rate for glucose reabsorption. all SGLTs are saturated. (= 375 mg/dL)