Glomerular Filtration Rate and Renal Blood Flow Flashcards

1
Q

How do you calculate the amount of filtrate excreted in the urine?

A

amount filtered - amount reabsorbed + amount secreted = amount excreted in urine

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2
Q

Compare and contrast the pressures in the afferent, efferent resistances as well as the pressure in the peritubular capillaries.

A

afferent arterial resistance is less than arteriolar resistance in the systemic arterioles

efferent arteriolar resistance is in series with the afferent arterioles

pressures in the peritubular capillaries is less than a systemic capillary

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3
Q

What is the primary driving force of glumerular filtration?

A

the initial high hydrostatic pressure in the glomerular capillaries drives filtration

this pressure is balanced out by the increased oncotic pressures as filtrate moves through

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4
Q

glomerular filtration rate in humans

A

125 mL/min

represents 20% of renal plasma flow (RPF)

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5
Q

filtration fraction (FF)

A

GFR/RPF

refers to the value of the GFR in relation to renal plasma flow, not renal blood flow

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6
Q

What are the key differences between glomerular filtration and systemic capillary filtration?

A

glomerular capillary permeability x surface area is 100x greater than most systemic capillaries

glomerular capillary hydrostatic pressures is 2 tiems greater than in systemic capillaries

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7
Q

Starling forces favoring glomerular filtration

A

glomerular capillary hydrostatic pressure

Bowman’s space oncotic pressure

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8
Q

Starlin forces impeding glomerular filtration

A

glomerular capillary oncotic pressure

Bowman’s space hydrostatic pressure

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9
Q

What are some of the forces driving net absorptive pressure along the peritubular capillaries?

A

17 mmHg of pressure in the beginning of the capillaries

12 mmHg pressure at the end

constant pressure to reabsorb filtrate

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10
Q

What is the equation that describes renal blood flow (RBF)

A

RBF = (Prenal artery - Prenal vein) / Rrenal vasculature

RBF = 125mL blood/min or 4mL blood/min/gm tissue

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11
Q

Describe the vascularization of the renal cortex, outer medulla, and inner medulla

A

renal cortex = high vascularization (90% RBF)

outer medulla = low vascularization (8% RBF)

inner medulla = very low vascularization (2% RBF)

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12
Q

anatomical distribution of renal capillary beds

A

ratio of cortical nephrons to juxtamedullary nephrons is 7:1

glomerular and peritubular capillaries are confined to the cortex

only vasa recta capillaries dive deep into the renal medulla

blood-flow distribution to various regions is not fixed, but can vary

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13
Q

How does oncotic pressure in the capillaries change thorughout the filtration process?

A

increases in glomerular capillaries

decreases in peritubular capillaries

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14
Q

In terms of pressures and resistances, what is RBF proportional to?

A

mean deltaP/(Raff+Reff) or 1/(Raff+Reff)

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15
Q

In terms of pressures and resistances, what is GFR proportional to?

A

deltaPGC/RGC or Reff/Raff

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16
Q

How does constricting the afferent arteriole affect GFR?

A

decreases due to the fall in both capillary pressure and renal plasma flow

17
Q

How does constriction of the efferent arteriole affect GFR?

A

GFR initially increases because of rising capillary pressure

after a point, GFR begins to decrease because of falling RPF

18
Q

What is the normal range for renal perfusion pressure?

A

80-180 mmHg

19
Q

What are the two theories for renal autoregulation?

A

myogenic theory

tubuloglomerular theory

20
Q

myogenic theory

A

smooth muscle of the afferent arteriole contracts or relaxes during changes in transmural pressure

this change in resistance keeps blood flow and GFR relatively constant

21
Q

tubuloglomerular theory

A

each individual nephron controls its own filtration rate through a sensor located at the macula densa portion of the distal tubule

arterial pressure induced increases in GFR increases solute delivery rate to the macula densa

signal is generated by the macula densa cells that results in afferent arteriolar constriction

conversely, decreases in solute load in the macula densa leads to increases in GFR

22
Q

action of adenosine in the kidney

A

vasoconstrictor

possible signal from the macula densa

23
Q

intrinsic factors affecting blood flow regulation

A

nitric oxide

endothelin

prostaglandins

adenosine

kinins

dopamine

24
Q

extrinsic factors affecting blood flow regulation

A

sympathetic innervation of afferent and efferent arterioles

blood borne substances (angiotensin II, ANP, ADH, ATP, glucocorticoids)

25
Q

factors decreasing RBF and GFR

A

decreased central blood volume (e.g. hemorrhage)

increased circulating renin and angiotensin (e.g. dehydration)

26
Q

RPF

A

renal plasma flow = (RBF x (1-Hct))

27
Q

equations involving load

A

load = mg/min = concentration x flow

kidney input load = Pax x RPFa

kidney output load = (PVx x RPFv) + (Ux x V)

28
Q

What are the three ways that filtered substances may be handled?

A

filtered and secreted

filtered and partially reabsorbed

filtered and reabsorbed

29
Q

clearance

A

volume of plasma from which the kidney completely removes (clears) a particular substance per unit time

Cx = [Ux x Vx]/Px

important for determining how efficient they kidneys clear a certain substance per unit time

30
Q

characteristics of an ideal substance to measure clearance

A

intert

freely filtered

not secreted

not reabsorbed

not synthesized or broken down by the tubules

ex. inulin

31
Q

What are the parameters for using clearance to determine net renal handling of substances?

A

if CQ < GFR, substance Q is filtered and reabsorbed

if CR = GFR, substance R is only filtered

if CS > GFR, substance S is filtered and secreted

32
Q

Why is GFR so important to know?

A

single best estimate of functioning renal mass

serial measurements allow the tracking of the course of the disease

GFR measurement is useful for knowing the appropriate dosage of drugs to use to attain therapeutic levels

GFR varies directly with renal function

33
Q

clearance of creatinine

A

creatinine is an end-product of skeletal-muscle metabolism

GFR = clearance of creatinine (CCR)

decreased functional glomeruli decreases GFR and CCR

decreased CCR can be estimated by an increased PCR

34
Q

What is the relationship between PCR and blood-urea-nitrogen (BUN)?

A

PCR x 10 ~ BUN

PCR is the more accurate estimator of GFR than BUN