GFR, renal flow, clearance

180, 1.5

Kidneys filter __ L of plasma daily and excrete about __ L of urine daily

Filtration, reabsorption, secretion, excretion

Renal Stages

• __ notes blood to lumen

• __ notes lumen to blood

• __ notes blood to lumen

• __ notes lumen to external environment

20, non-selective

Renal Filtration

• __% of plasma in glomerular capillaries is filtered into Bowman’s capsule

• Filtration is __ (selective vs non-selective)

  • Filtrate composition resembles plasma minus most proteins

filtrate, peritubular, conserves

Renal Reabsorption

• Many solutes and 99% of fluid reabsorbed from __ into the __ capillaries

• Action __ substances (i.e. Na+, glucose, water)

Peritubular, lumen, excretion

Renal Secretion

• Selective transfer of substances from __ capillaries to tubule __

• Enhances __ (i.e. waste products, foreign substances, regulation of H+ and K+)

Mass, artery input, -, +, excreted

Fick’s Principle

• __ is conserved in and out

• Renal __ __ = ureter output + renal vein input

• Amount filtered _ (+/-) amount reabsorbed _ (+/-) amount secreted = Amount of solute __

Membrane protein, not

• Reabsorption and secretion of many solutes is mediated by __ __ transporters

• Filtration __ (is/not) mediated by transport proteins

Low, transport, concentration, maximal transport rate

• At __ (high/low) concentrations, the __ rate of substrate is proportional to the __ gradient

• __ __ __ (Tmax): Occurs when all carriers are occupied (saturated)

Threshold, rate of transport

• Renal __: Plasma concentration of substrate at which saturation occurs

  • When past threshold = No longer able to increase __ of __

200 mg/dL

Renal threshold for glucose reabsorption

SGLT, Tmax, excreted

Glucose Handling

• When plasma [glucose] rises above threshold, __ transporter in nephron is saturated and reaches __

• Glucose that could not be reabsorbed is __ in urine

Glomerular Filtration Rate (GFR)

Volume of fluid that enters Bowman’s capsules per unit time

All, hydrostatic, oncotic, surface area, glomeruli

GFR is a sum of filtration rate of __ nephrons

• Net Filtration Pressure (deltaP) = Net __ and __ forces in glomerular capillary and Bowman’s capsule

• Filtration Coefficient (Kf) = __ __ and permeability

  • More __ area = more filtration

Net filtration pressure x Kf

GFR Equation

Increase, increase, decrease, decrease, increase, decrease, decrease, increase

Answer 1-4

RBF (increase/decrease), GFR (increase/decrease)

Net, relative

• The effects on RBF depend on __ changes in renal resistance

• The effects of GFR depend on __ rates of glomerular inflow vs outflow

(relative/net)

Dilate, constrict, dilate

Factors increasing renal blood flow

• ANP and BNP

  • __ afferent arterioles; __ efferent arterioles

• Prostaglandins

  • __ afferent arterioles (and efferent a. to lesser degree)

Afferent, efferent, hypotension, stenosis

Factors decreasing renal blood flow

• Sympathetic system

  • Constricts both efferent < __

• Angiotensin II

  • Constricts both __ > afferent

• Severe __ - outside myogenic autoregulation zone

• Renal artery __

Increase, increase, decrease, increase, decrease, decrease

How does each stimulus affect GFR?

• ANP + BNP __ GFR

• Prostaglandins __ GFR

• Sympathetic NS __ GFR

• Angiotensin II __ GFR at steady levels, at high levels __ GFR

• Severe hypotension or renal stenosis __ GFR

Sympathetic, high

Renal vasculature has little __ tone

• Renal sympathetic activity must be __ in order to reduce renal blood flow

Filtration fraction (FF), 0.17, increase

__ __ is the fraction of renal plasma flow that is filtered

• Normally around __

• Increase in glomerular capillary pressure, __ in FF

GFR / RPF

Filtration fraction formula

Renal Clearance

Rate at which solute is removed from plasma by kidneys

• Affected by GFR, reabsorption, and secretion

Renal clearance of solute X

Inulin, filtered

__ is a plant polysaccharide that is freely__, NOT reabsorbed, NOT secreted

Excreted, tubules, GFR

Inulin

• 100% of filtered inulin is __ → Inulin Excretion = Inulin Filtration

• All fluid reabsorbed from __ is “cleared” of inulin

• Therefore Inulin = __ (rate which plasma is filtered)

0.02, 100, 126, 600

Renal clearance numbers

• Glucose: __  mL/min (largely reabsorbed) 

• Inulin: __ mL/min

• Creatinine: __ mL/min

• PAH: __ mL/min (largely secreted)

Creatinine (Cr)

Endogenous substance that is freely filtered

Reabsorbed, muscle, constant, increases

Creatine

• Not __ (filtered/reabsorbed) → Small amount secreted to tubules

• Byproduct of __ metabolism; produced at steady state

• Plasma [Cr] remains relatively __ for given muscle mass

• Small amount of creatinine secretion __ (increases/decreases) clearance rate

Rise (increase)

What will happen to plasma [Cr] over time if GFR falls?

young, lean, serum

Creatinine clearance

• directly proportional to __ age and __ body weight

• inversely proportional to __ creatinine levels

Secreted, reabsorbed

Determining net renal handling of solutes

• If amount excreted > filtered → difference was __

• If amount excreted < filtered → difference was __

Filtration only

Filtration, partial reabsorption

Filtration, complete reabsorption

Filtration, secretion

Reabsorbed, 0

Renal clearance of glucose

• All glucose is __

• No plasma is “cleared” of glucose → Glucose clearance = _

clearance of solute / clearance of inulin

Clearance ratio formula

greater, secretion

Clearance ratio > 1

• Clearance of solute __ than GFR

• Solute undergoes net __

less, reabsorption

Clearance ratio < 1

• Clearance of solute __ than clearance of inulin

• Solute undergoes net __

PAH

__ clearance can be used to estimate renal plasma flow (RPF)

• nearly 100% of renal plasma flow is cleared of this

RPF = C PAH

Rate which PAH enters (via artery) ~ rate which PAH leaves (as urine)

(Equation)

RPF / (1-HCT)

Renal blood flow formula

Hematocrit, 1-HCT

RBF Components

• __ is the fraction of blood composed of blood cells

• Fraction of blood composed of plasma = ___ (formula)