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Renal IVF > Renal anatomy, filtration and blood flow > Flashcards

Renal anatomy, filtration and blood flow Flashcards

1
Q

What % of cardiac output does the kidney get?

A

22%

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2
Q

What is the GFR

A

125ml/min

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3
Q

What 2 types of nephrons are there

A

Cortical
Juxtamedullary

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4
Q

What is in the renal corpuscule

A

Bowmans capsule
Glomerulus

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5
Q

what type of cells are in the PCT

A

Cuboidal cells with microvilli

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6
Q

What cells are in the loop of Henle

A

Thin segmented cells to assist water absorption

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7
Q

What cells are in the collecting tubule

A

Intercalated cells
Principle cells

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8
Q

What type of cell structure do you find in the DCT

A

Regular cuboidal cells

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9
Q

What is the purpose of a podocyte

A
  • Podocytes secrete and maintain the basement membrane
  • The pedicels interdigitate —> loss of this or effacement is what contirbutes to minimal change disease and cause proteinuria
  • The gap between these is known as slit diaphragms or slit pores
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10
Q

How does perfusion pressure affect GFR??

A
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11
Q

What % of CO is renal blood flow? How much of this is actually needed for metabolic supply?

A

20% of cardiac output
This is 10x what is needed

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12
Q

How does medullary blood flow compare to cortical blood flow

A

10x in cortex

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13
Q

How is renal blood flow regulated? Which areas of the kidney have the capacity to regulate and which do not?

A
  1. Myogenic autoregulation via Afferent and efferent arteriole resisatnce changes - especially afferent arteriole
  2. Tubuloglomerular feedback
    MAP 75-70 GFR is regulated as constant

Juxtamedullary nephrons do not have self regulation

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14
Q

Explain tubuloglomerular feedback

A

2 elements
- Change in afferent tone
- Alteration in renin secretion

Macula densa (ascending LOH/earlyDCT) detects changing tubular flow rate via sodium flux causing cellylar swelling. As basolateral membrane has contact with arterioles or extrraglomerular mesangial cells local feedback

Reduced GFR = reduced flow –> reduced adenosine release and prompting NO release and renin release with afferent limb dilation

Increased flow –> increased perfusion pressure –> adnosine release –> reduces GFR

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15
Q

Describe the subdivisions of the renal artery

A
  • Renal artery / interlobar artery / arcuate artery / interlobular artery / afferent artery / efferent artery
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16
Q

What renal blood flow grossly going to be controlled by (Ohns law)

A
  • RBF = (MAP – CVP) / RVR

 - MAP ~100mmHg

 - CVP ~2mmHg

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17
Q

What does decreased glomeular filtration lead to as part of tubuloglomerular feedback

A

↓ Filtration results in reflex afferent arteriolar relaxation

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18
Q

What 3 mechanisms regulated renal blood flow intrinsically

A

RAAS (hormonal)
Myogenic autoregulation
Tubuloglomerular feedback

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19
Q

Neuronal control of renal blood flow occurs how?

A

Sympthetic nerves causing vasoconstriction via alpha mechanism

Afferent AND efferent constriction

Efferent > afferent. i.e. GFR is preserved MORE than renal blood flow

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20
Q

What effect does SNS have on GFR

A

Overall slight reduction in GFR

Efferent > afferent constriction
Increased capillary hydrostatic pressure
Reduced filtered load of Na though
Also triggers renin seccretion
Directly triggers Na/H exchange in PCT

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21
Q

Where is renin released from

A

Granular cells from juxtaglomerular apparatus

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22
Q

Triggers for renin release

A

Beta 1 stimulation directly from SNS
Macula densa secondary to reduced Na content in DCT
Reduced perfusion/hypotension

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23
Q

Angiotensin 2 effects 5

A
  1. Direct vasoconstriction of peripheral vasculature
  2. Afferent > efferent vasoconstriction reducing renal blood flow markedly more than SNS
  3. Mesangial cell constriction reducing surface area for filtration
  4. Increased ADH/aldosterone secretion
  5. Thirst
  6. Increased Na reabsorption
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24
Q

What vasodilates in the afferent arterioles

A

ANP (dilates afferent, constricts efferent)
PGE2 and PGI2
NO

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25
Q

Normal renal blood flow

A

1.1L/min

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26
Q

Normal plasma blood flow

A

600ml/min

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27
Q

Filtration fraction

A

20%

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28
Q

Filtrate is?

A

Plasma - oplasma proteins/plasma bound substances

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29
Q

How much is filtered per day in the kidney

A

172L

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30
Q

Urinary output at baseline

A

1ml/kg/hr

1ml/min

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31
Q

GFR equation

A

net filtration pressure x filtration coefficient

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32
Q

Average capillary net filtration pressure

A

17mmHg

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33
Q

What is glomerular hydrostatic pressure

A

55-60mmHg

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34
Q

What is capsular hydrostatic pressure

A

16mmHg

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35
Q

What is blood colloid osmotic pressure

A

30mmHg

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36
Q

What is bowmans capsule oncotic pressure

A

0

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37
Q

What affects the hydrostatic pressure in Bowmans capsule

A

MAP
Catecholamine
Local autoregulation - myogenic, tubuloglomerular feedback, hormones (AT2 and PGE2)

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38
Q

How does osmotic pressure change along the capillary in bowmans capsule

A

Increases with filtration as protein free fluid is filtered a higher proportion of protein remains

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39
Q

What is filtered

A

Water
Electrolytes
Glucose
Small amount of uncharged molecules

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40
Q

What separates tubular content from blood flow in the nephron

A

single layer of epithelial cells and a basement membrane

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41
Q

What is the main purpose of a cortical nephron

A

Filtration

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42
Q

What is the main purpose of a juxtamedullary nephron

A

concentration

43
Q

What is Kf? What dose it depend on?

A

Glomemrular filtration

Permeability and surface area

44
Q

What factors contribute to the filtration membrane

A
  1. Capillary endothelium
  2. Basemment membrane negatively charged
  3. Foot processes
45
Q

What size molecule can not be filtered

A

> 7000 Daltons

46
Q

What 3 cells are part of the juxtaglomerular apparatus

A
  1. JG cells of the afferent arterioles/granular cells
  2. Macula densa
  3. Mesangial cells
47
Q

What constricts the afferent arteriole

A

Catecholamine and SNS
2. Adenosine via tubuloglomerular feedback
3. Endothelin 1

48
Q

What factors increased efferent arterioles constriction

A

ANP
SNS and catecholamines
AT2

49
Q

What happens to renal blood flow, GFR and filtration fraction with afferent constriction

A
50
Q

What happens to renal blood flow, GFR and filtration fraction with afferent dilation

A
51
Q

What happens to renal blood flow, GFR and filtration fraction with efferent dilation

A
52
Q

What happens to renal blood flow, GFR and filtration fraction with efferent constriction

A
53
Q

Clearance =

A

The VOLUME of a drug cleared per unit of time

urine concentration x urine volume / plasma concentration

54
Q

Urine concentration x urine volume / plasma concentration =

A

renal clearance

55
Q

How can you calculate GFR

A
  1. Inulin clearance
  2. Creatinine clearance
56
Q

What propoerties favour calculation of GFR using clearance

A
  1. Freely filtered
  2. Not reabsorbed
  3. Not secreted
57
Q

What is inulin

A

Natural polysacchardie

58
Q

How do you use inulin to measure GFR

A

Continuous infusion of the natural polysacchardie and constant plasma concentration –> where clearance = infusion volume

59
Q

Creatinine is?

A

A byproduct of muscle metabolism

60
Q

What factors make creatinine a good marker for GFR measurement? What makes it a poor one?

A

Relatively cnostantly produced
Not metabolised
Free filtered
Not reabsorbed
Does have some secretion which relatively becomes more important with reducing GFR (overestimates GFR when low)

Problems
- Variation in race, muscle mass, age, sex and diet
- Can only use it when production and clearance are in steady state

61
Q

What is the eqaution for direct measurement fo creatinine clearance

A

Urine concentration x volume / plasma concentration

Therefore 24 hour creatinine urine collection must be done

62
Q

What estimates of GFR are instead used

A

Creatinine clearance via Cockroft Gault equation

◦ Cockcroft Gault formula (0.83 correlation with creatinine clearance)
	‣ Clearance = (140-age) x weight x sex (1 for male, 0.85 for female)/72 x creatinine in micromol/L
63
Q

What is the Cockroft Gault equation

A

◦ Cockcroft Gault formula (0.83 correlation with creatinine clearance)
‣ Clearance = (140-age) x weight x sex (1 for male, 0.85 for female)/72 x creatinine in micromol/L

64
Q

What are 2 alternative creatinine clearance calculations other than Cockroft Gault

A

CKD EPI

MDRF

65
Q

What are the flaws in estimating creatinine clearance based on plasma creatinine

A

Rely on stable Cr measurements less reliable in critically ill

Less reliable with low GFR overestimating it

Inaccuracy with large muscle mass, older age, malignancy, diet

66
Q

What is a normal GFR value

A
  • GFR 90-120 ml/min/1.73m^2 or 125ml/min
67
Q

What are the factors determining GFR

A

◦ GFR = filtration coefficient x (Glomerular capillary pressure - bowman’s capsule hydrostatic pressure) - reflection coefficient for blood protein x (glomerular capillary oncotic pressure - bowman’s capsule oncotic pressure)

68
Q

How big is the afferent to efferent pressure drop passing through the glomerulus

A

2mmHg form 60 –> 58

69
Q

What 3 factors will determine renal afferent arterial flow

A

CO
Renal blood flow
Local vasoconstriction

70
Q

What is the hydrostatic pressure in Bowmans capsule

A

15mmHg

71
Q

What happens to oncotic pressure along the capillary? Why? What values

A

Increases
‣ Increases along the capillary, as protein free-fluid is filtered leaving a higher concentration of protein within the capillary. This change in capillary oncotic pressure is proportional to the filtration fraction - a greater filtration fraction will cause a higher oncotic pressure of fluid in the capillary.
‣ Dependent on plasma protein concentration - increased concentration increases oncotic pressure, dropping GFR
‣ Oncotic pressure at afferent end ~21mmHg, and 33mmHg by the efferent end
‣ As protein is not filtered in normal states, the oncotic pressure in Bowman’s Space is usually assumed to be 0mmHg

72
Q

What is capillary oncotic pressure in Bowmans capsule

A

21mmHg –> 33mmHg

73
Q

What is the net filtration pressure in the glomerulus

A

24mmHg at afferent, 17mmHG mean, 10mmHg at efferent

74
Q

What is the filtration coeffiicent of the kids determined by?

A

Surface area and membrane permeability

75
Q

Surface area is dependent on?

A

Gloemrular mesangial contraction
Age and number of gloemruli

76
Q

Glomerular membrane is composed of what factors> What is not filtered? Why?

A
  • fenestrated capillary endothelium freely filtering molecules <7000 daltons, with variable filtration up to 70 000 daltons - the endothelial Glycocalyx mainly filters proteins, fenestration mainly filter cells (60-80nm)
    * Mesangial cells - contract in response to angiotensin 2 reducing surface area for filtration —>reduced GFR
    * Negatively charged basemement membrane reducing filtration of negatively charged molecules
    * Negatively charged podocyte foot processes with 3-4nm slits filtering mainly proteins
77
Q

What is the reflection coefficient of the glomerular basement membrane

A
  • Reflection coefficient = 1 as the glomerular membrane is essentially completely impermeable to protein
78
Q

Draw a graph relating serum creatinine to renal function

A
79
Q

What is creatinine

A
  • Small endogenous molecule from skeletal muscle metabolism, eliminated by glomerular filtration and tubular secretion only (no reabsorption)
    ◦ Generally produced in a steady state
80
Q

Define creatinine clearance

A
  • Creatinine clearance is volume of plasma cleared of creatinine per unit of time (measured in mL/min or L/day)
81
Q

Measurement of creatinine clearance relys on which principle>

A
  • Measurement of creatinine clearance utilises Fick’s principle
    ◦ Renal clearance = amount of substance in urine per unit of time / plasma concentration of substance P
    ◦ Where amount of substance in urine per unit of time = urine concentration x urine flow
    ◦ Plasma concentration is stable and therefore arteriovenous differences do not need to be measured
82
Q

What are the issues with measured creatinine clearance in the critically ill (2)

A

◦ Time delay in being able to calculate GFR especially in dynamically changing environments
◦ As creatinine is secreted into the PCT (10-20% at baselin) creatinine clearance will overestimate GFR; with declining kidney function secretion often remains intact and represents a greater proportion of measured creatinine clearance resulting in overestimation of GFR when low

83
Q

Cockroft Gault equation

A
  • CG (Cockcroft-Gault Equation): common method which has a correlation of ~0.83 with CrCl:
    ◦ CrCl = [(140−A) × W x S)] / (814 × Cr) , where:
    ‣ Cl = Clearance (mL/min), A = Age, W = Lean body Wt (kg)
    ‣ S = Sex coefficient (Male = 1, Female = 0.85)
    ‣ Cr = Creatinine in mmol/L (if mg/dL then use 72 instead of 814)
84
Q

Problems with Cockroft Gault is divided into 3 factors

A
  1. Problems with the generalisations about weight and age
  2. Applying to critically ill
    - Extra corpereal circuits
    - Fluid resuscitation
    - Muscle injury, sarcopenia, steriods, nutrition
  3. Serum creatinine has a non linear association with Cr
85
Q

What Formula average problems can you forsee with Cockroft Gault

A

◦ extremes of age
◦ different ethnicities,
◦ Extremes of muscle mass
◦ malignancy
◦ diet - increased Cr with increased dietary protein consumption, decreased with fasting and vegetarian diet
◦ drugs affecting tubular secretion

86
Q

What critical illness factors influence Cr

A

◦ the amount of creatinine produced varies with muscle mass, nutrition, steroid use, muscle injury
◦ are modified by aggressive fluid resuscitation
‣ Dilutes serum creatinine making things appear better
◦ Extra-corpereal circuits e.g. CRRT and ECMO can mask raised creatinine by dilution, dialysing or adsorbing

87
Q

Non linear association of Cr and renal function

A
  1. Where renal function is changing rapidly
  2. Cr only rises once >50% of renal function is lost
  3. More inaccurate the worse renal function is
88
Q

Draw a graph representing a loss of renal function and rise in Cr

A
89
Q

What is the range of molecular size able to be filtered at the glomerulus

A

‣ Capillary endothelium - large fenestrations
* <7000 daltons freely filtered
* 7000 - 70, 000 variably filtered
* Above 70k daltons cannot pass

90
Q

Where are the kidneys from a surface anatomy perspective

A

T12 - L3

91
Q

Gross anatomy of a kidney

A

◦ Paired, solid, bean shaped abdominal (retroperitoneal) organ
◦ Hilum on the medial side –> renal artery and vein, lymphatic supply, nerves and ureter
◦ Tough fibrous capsule - perirenal fat - renal fascia and pararenal fascia

92
Q

Main substructural elements of a kidney

A

◦ Cortex:
‣ cortical labyrinth
‣ medullary rays/renal columns which ar extensions of the cortex penetrating into the medulla
◦ Outer medulla: inner stripe and outer stripe; multiple pyramids with the base at the corticomedullary junction and apices - the papilla - at the hilum draining into the ureters

93
Q

What is the blood supply of the kidney

A
  • Blood supply - paired arteries off the abdominal aorta renal arteries; R longer than left
    ◦ Venous drainage via renal veins into IVC
94
Q

What is the innervation of the kidney

A

◦ efferent is strictly sympathetic, from T9-T13
◦ afferent (pain) via the least splanchnic nerve (T12)

95
Q

Nephrons
- Number
- Types

A

◦ Functional unit of the kidney - 1 million/kidney
◦ Functional unit consists of glomerulus, proximal tubule, loop of Henle, dital tubule and collecting ducts
◦ Cortical nephrons: short-looped in the cortex
◦ Juxtaglomerular nephrons: have long loops of Henle, contribute the most to the process of producing concentrated urine and the efferent arteriole forms the vasa recta

96
Q

Constant renal artery flow maintained between what ranges

A

MAP 70 -170

97
Q

Where does the blood flow go in distribution in the kidney

A

95% cortex
5% to medullar

98
Q

What is the renal oxygen extraction

A

10-15%

99
Q

Renal oxygen extraction vs blood flow?

A

Stable as with increasing renal blood flow there is increasing function

Renal oxygen consumption is proportional to renal filtraiton and tubular sodium delivery

100
Q

What % of the autoregulatory function of blood flow to the kidney does each unit do

A

50/35/15
Myogenic
tubuloglomerular feedback
Renin

101
Q

How does the myogenic feedback system work

A

◦ Vasoconstriction in response to wall stretch (increased transmural pressure –> increased intracelular calcium concentration due to mechanically gated non-specific cation channels) –> membrane depolarisation –> vasoconstriction
◦ Constriction prooperotional to increase in pressure keeping flow constant
* This is a stereotyped vascular smooth muscle response, not unique to the kidney

102
Q

How does tubuloglomerular feedback work

A
  • Sensory - macula densa in the junction of the ascending limb of the loop of Henle/DCT
    ◦ Detects change int ubular flow rate via changing Na flux across its membrane
    * Increased flow = increased perfusion pressure = release of adenosine and afferent arteriole constriction via extraglomerular Mesangial + granular cells in the walls of the afferent arteriole releasing renin
    * Decreased flow leads to reduced adenosine release and subsequent NO release and renin
103
Q

What escape mechanisms does the kidney have for reduced blood flow

A

‣ PGE2 + PGI2 act as escape mechanisms where renal blood flow is chronically reduced in times of stress to vasodilation and oppose the systemic vasoconstrictors

Renal IVF (7 decks)

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