Elements of renal function Flashcards

Question 1

Q

What other body systems are the kidneys integrated with? In what way?

Answer

A

Ion balance: endocrine, gastrointestinal
Water balance: CNS
Blood pressure, Na+, K+: autonomic NS
Acid-base balance: respiratory, CNS
Blood pressure: cardiovascular
Elimination of wastes, toxins: liver

Question 2

Q

What percent of CO is dedicated to renal supply?

Question 3

Q

High pressure in the _____________________ causes filtration of blood. Lower pressure in the _____________________ permits fluid reabsorption

How can pressure in both capillary beds be regulated?

Answer

A

Glomerular capillaries

peritubular capillaries

can be regulated by resistance changes in afferent and efferent arterioles

Question 4

Q

What are the two types of nephrons?

Answer

A

Juxtamedullary and superficial cortical

Question 5

Q

What are the loops of henle like in cortical nephrons?

Answer

A

Short loops of henle, surrounded by peritubular capillaries

Question 6

Q

What are the juxtamedullary loops of henle like? What are their long efferent arterioles divided into? What do these function to do?

Answer

A

long loops of Henle
long efferent arterioles are divided into specialized peritubular capillaries (vasa recta)
functions to concentrate urine

Question 7

Q

Detail the steps of renal microcirculation

Answer

A

Afferent arteriole
Glomerular capillaries
Efferent arteriole
Peritubular capillaries
Interlobular vein
Arcuate vein
Interlobar vein
Renal vein

Question 8

Q

Describe the first and second capillary networks

Answer

A

First capillary network (glomerular capillaries): high hydrostatic pressure; large fluid volume filtered into Bowman’s capsule
Second capillary network (peritubular capillaries): low hydrostatic pressure; large amounts of water and solute are reabsorbed

Question 9

Q

How does a slow blood flow rate through the medulla enable us to concentrate our urine?

Question 10

Q

•Does renal fraction (of CO) change during exercise?

Question 11

Q

In afferent arterioles, sympathetic neurons synapse on:

1.

2.

Causing?

Answer

A

•Smooth muscle causing arteriolar constriction
–Protective during increased BP
•Granular cells causing renin secretion

Question 12

Q

Sympathetic stimulation causes powerful constriction of afferent and efferent arterioles (afferent > efferent). this leads to?

Answer

A

‒Decreases renal blood flow
‒Diverts the renal fraction to vital organs

Question 13

Q

Apart from constriction of arterioles, what other effects does sympathetic stimulation have?

Answer

A

Stimulates renin release from granular cells.

•Stimulates Na+ reabsorption in proximal tubule, thick ascending limb of Henle’s loop, distal convoluted tubule, collecting duct

Question 14

Q

What is glomerular filtration?

Answer

A

•Filtration of plasma from glomerular capillaries into Bowman’s capsule

Question 15

Q

What is tubular reabsorption?

Answer

A

•Transfer of substances from tubular lumen to peritubular capillaries

Question 16

Q

What is tubular secretion?

Answer

A

•Transfer of substances from peritubular capillaries to tubular lumen

Question 17

Q

Define excretion

Answer

A

•Voiding of substances in the urine

Question 18

Q

What are the basic processes of urine formation?

Answer

A

Glomerular filtration

tubular reabsorption

tubular secretion

excretion

Question 19

Q

•Urinary excretion = ?

Answer

A

amount filtered – amount reabsorbed + amount secreted

Question 20

Q

•Tubular reabsorption = ?

Answer

A

glomerular filtration - urinary excretion

Question 21

Q

•For most substances, the rate of their filtration and reabsorption are?

Answer

A

large relative to rate of excretion

Question 22

Q

–Small changes in filtration or reabsorption can lead to?

Answer

A

large changes in excretion

Question 23

Q

–Increasing plasma Na+ increases its filtration rate, and a smaller fraction of the filtrate is reabsorbed, leading to an?

Answer

A

increased excretion

Question 24

Q

What is the glomerular filtration rate?

Answer

A

•volume of plasma filtered into the combined nephrons of both kidneys per unit time (e.g. ml/min)

Question 25

Q

GFR is an index of?

Answer

A

functioning renal mass

Question 26

Q

–GRF is determined by?

Answer

A

Starling forces in the glomerulus and glomerular capillary permeability

Question 27

Q

•Reductions in GFR in disease states are most often due to?

Answer

A

a decrease in net permeability resulting from a loss of filtration surface area induced by glomerular injury

Question 28

Q

•In normal subjects, GFR is primarily regulated by?

Answer

A

alterations in glomerular hydrostatic pressure that are mediated by changes in arteriolar resistance

Question 29

Q

•Filtration rate of any freely filtered substance =

Answer

A

•Filtration rate of any freely filtered substance = GFR x plasma concentration of substance

Question 30

Q

What is filtration fraction? What is NL?

Answer

A

•Filtration fraction is the part of the renal plasma flow (RPF) that is filtered into the tubules
–Normally about 20% (GFR/RPF)

Question 31

Q

What does FF change with? (filtration fraction)

What happens with an increased FF?

Answer

A

ultrafiltration pressure

–With an increased FF, the oncotic pressure of the efferent arterioles increases, aiding reabsorption of tubular fluid

Question 32

Q

ØNet rate of reabsorption or secretion of a substance =

Answer

A

ØNet rate of reabsorption or secretion of a substance = difference between glomerular filtration and urinary excretion (assuming substance is not produced or metabolized by the kidneys)

Question 33

Q

–If excretion < filtration,

Answer

A

net reabsorption occurred

Question 34

Q

–If excretion > filtration,

Answer

A

net secretion occurred

Question 35

Q

What is the urinary excretion rate?

Answer

A

•Product of urine flow rate x concentration of substance “a” in the urine (i.e., Ua x V)

Question 36

Q

Define renal clearance

Answer

A

•the volume of plasma from which a substance is completely removed (cleared) by the kidneys in a given time period
–Units are volume/time, e.g. ml/min, l/hr, etc.

Question 37

Q

Renal clearance describes how effectively the kidneys…

Answer

A

remove a substance from the bloodstream and excrete it in the urine; different substances have different clearances.

Question 38

Q

What is the formula for clearance?

Answer

A

Clearance = (Urine concentration of x ×Urine flow rate)/(Plasma concentration of x) = (U×V)/P

Question 39

Q

Calculate the clearance of urea…

P_urea = 20 mM

U_urea = 400 mM

V = 1 ml/min

Answer

A

Curea = (400 mM · 1 ml/min) / 20 mM = 20 ml/min

Question 40

Q

What compound is the gold standard for measuring GFR? How do you administer?

Answer

A

Inulin

I.V.

Question 41

Q

What is another method of estimating GFR that is not so invasive?

Answer

A

measure creatinine

Question 42

Q

Where is creatinine produced?

Answer

A

•endogenously from metabolism of creatine by skeletal muscle.

Question 43

Q

•Normally, creatinine excretion = ?

Answer

A

creatinine production

Question 44

Q

•P_creatinine inversely proportional to?

Question 45

Q

•Theoretically, if GFR falls to 25% of normal, Pcreatinine should?

Answer

A

increase 4x over a few days

Question 46

Q

Theoretically, if GFR falls to 25% of normal, Pcreatinine should increase 4x over a few days
In reality, this inverse relationship isn’t perfect, due to?

Answer

A

–Differences in lean muscle mass among patients, meat intake
–Compensatory increased proximal tubule secretion

Question 47

Q

What is creatinine useful for?

Answer

A

Long-term monitoring of renal fx

Question 48

Q

What is important to keep in mind regardin creatinine monitoring?

Answer

A

•Significant disease progression can occur with little or no elevation in plasma creatinine, especially in patients with GFR > 60 mL/min

Question 49

Q

–In glomerular disease (drop in glomerular permeability due to decreased surface area available for filtration), a drop in GFR is counteracted by?

Answer

A

tubuloglomerular feedback to maintain GFR at near-normal levels

Question 50

Q

–Nephron loss may be compensated for by?

Answer

A

remaining nephrons (25-30% loss can still appear normal)

Question 51

Q

–Once GFR does fall, the rise in plasma creatinine will be minimized?

Answer

A

by increased creatinine secretion in proximal tubule

Question 52

Q

If BUN/Cr is >20/1 then?

Describe the mechanism

Answer

A

Problem is Prerenal.

BUN reabsorption is increased. BUN is disproportionately elevated relative to creatinine in serum. Reduced renal perfusion due to hypovolemia

Question 53

Q

If BUN/Cr is 10-20/1?

Describe mechanism

Answer

A

Normal range or postrenal

Normal range. Can also be postrenal disease (obstruction) BUN reabsorption is within normal limits

Question 54

Q

If BUN/Cr is <10/1?

Describe mechanism

Answer

A

Intrarenal

Renal damage causes reduced reabsorption of BUN and a lower BUN:Cr ratio.

Question 55

Q

The principle behind the BUN/Cr ratio is the fact that both urea (BUN) and creatinine are freely filtered by the glomerulus, however…

Answer

A

urea reabsorbed by the tubules can be regulated (increased or decreased) whereas creatinine reabsorption remains the same (minimal reabsorption).

Question 56

Q

What is Cystatin C?

Answer

A

•Cystatin C is a 13 kilodalton protein that is continuously produced by all nucleated cells in the body, and is freely filtered by the glomerulus.

Another marker for GFR

Question 57

Q

•Similar to creatinine, serum levels of cystatin C become elevated when…

Answer

A

GFR declines.

Question 58

Q

What is an advantage of Cystatin C for measuring GFR?

Answer

A

•Advantage of Cystatin C is that levels not affected by muscle mass, age, or gender

Question 59

Q

What is used to estimate RPF? Why?

Answer

A

•Para-aminohippuric acid (PAH)
–Freely filtered
–Avidly secreted in proximal tubule

Question 60

Q

•PAH: completely cleared from plasma of ___________________when plasma PAH concentraion is low

Answer

A

peritubular capillaries

Question 61

Q

•RPF ~ CPAH = ?

Answer

A

•RPF ~ CPAH = (UPAH· V)/PPAH

Question 62

Q

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Elements of renal function Flashcards

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