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CardioRespiratory Year 1 > Renal Structure and Function Part 1 > Flashcards

Renal Structure and Function Part 1 Flashcards

1
Q

where do renal arteries branch from

A

the abdominal artery

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2
Q

what does the ureter do

A

it is the tube carrying urine to the bladder

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3
Q

what does the urethra do

A

the tube carrying the urine from the bladder to the outside

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4
Q

describe what the renal arteries pass into and divide into

A

the renal arteries pass into the interloper vessel and divide into the small arcuate arteries in the renal cortex

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5
Q

where do the arcuate arteries end

A

= they terminate in a clump of capillaries in a cortex in a structure called the glomerulus

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6
Q

what is each capillary glomerulus enclosed by

A
  • it is enclosed inside a bag of tissue called the bowman capsule
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7
Q

what are the stages of urine formation

A
  • plasma is filtered from the glomerular capillaries into the space of the capsule
    1. blood enters the glomerulus of the nephron int he afferent arteriole and leaves through the efferent arterioles, afferent has a larger diameter than efferent this causes a drop in pressure between eh afferent and efferent arterioles and this makes the filtration pressure which forces the fluid through the endothelium into the capsular space
    2. the fluid leaves bowman capsule and enters the proximal convoluted tubule then it enters the loop of gene then the distal convoluted tubule and then the collecting duct which drains in the ureter
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8
Q

what is the difference between the afferent arterioles and efferent arterioles

A
  • afferent has a larger diameter than efferent

- afferent brings blood in whereas efferent removes the blood

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9
Q

what is the filtration fraction

A

it is normally 20%
- this is the proportion of the blood plasma that is filtered through glomerulus into the bowman capsule which enters in the proximal tubule

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10
Q

a greater filtration fraction will…

A
  • make the blood in the efferent arteriole too viscous as it would have too high a haematocrit
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11
Q

describe the capillary structure in the glomerulus

A
  • they are fenestrated - this means that they have gaps between the endothelial cells
  • covered on the outside by podocytes
  • podocytes have gaps between them which help form the filtration mechanism this allows certain molecules to enter the urine and certain molecules to stay in the plasma
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12
Q

what happens to the podocytes in renal disease

A
  • in renal disease - the podocytes become inflamed and enlarged therefore the gaps between them get larger which enables more solutes to enter the urine
  • proteinuria is therefore a sign of glomerular inflammation
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13
Q

what is the nephron

A
  • this is the complete set of tubes from the bowman capsule to the collecting duct
  • it is the unit of kidney function
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14
Q

what supplies oxygenated blood to the glomerulus

A
  • efferent arterioles

- wraps around and forms a plexus

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15
Q

what part of the nephron is in the medulla

A
  • loop of Henle
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16
Q

what part of the nephron is in the cortex

A
  • glomerulus

- proximal convoluted tubule

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17
Q

several distal tubules….

A

enter into one collecting duct

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18
Q

what part of the nephron can vary in size

A
  • loop of Henle
  • in desert animals it is long so they don’t loose much water but have heavily concentrated urine
  • in water animals it is short so they loose a lot of water and don’t have heavily concerted urine
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19
Q

what happens int he proximal convoluted tubule

A
  1. reabsorption into the pertiubular capillaries
  2. substances are transported out of the capillaries and secreted into the tubular fluid
  3. filtration
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20
Q

How do you work out the amount of material excreted

A

amount filtered + amount secreted - amount reabsorbed

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21
Q

what is the filtration of water into the capsule controlled by in an healthy individual

A
  • balance between constriction of the afferent and efferent arterioles
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22
Q

what is the normal physical pressure in the glomerular capillaries

A

55 mmHg

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23
Q

How do you work out the net filtration

A

hydrostatic pressure - osmotic pressure

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24
Q

what is the net filtration pressure

A

10 mmHg

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25
Q

describe cardiac output to the kidneys

A
  • just under a quarter of CO goes to the capillary, this is 1.2 Lt/min
26
Q

Define the glomerular filtration rate

A
  • this is the total amount of fluid filtered through all the glomeruli in both kidneys
  • usually 120-125 ml/min
27
Q

what is urine flow

A

1ml/min

- almost all of the fluid filtered by the glomeruli is reabsorbed

28
Q

what is the renal plasma flow

A
  • 680 ml/min
29
Q

what is used clinically to assess the health of the kidney

A

Glomerular filtration ate GFR

30
Q

where is the water reabsorbed

A
  • 2/3 reabsorbed int he proximal tubule

- some reabsorbed in the collecting duct

31
Q

how does reabsorption of water in the proximal tubule happen

A
  • tubule is lined with epithelial cells and the basal membranes of these cells contain sodium pumps that move the sodium from the proximal tubule into the interstitial fluid against the concentration gradient this creates a low concentration gradient in the proximal tubule
  • in the luminal membrane of the proximal tubule there are sodium channels and sodium therefore diffuses down the concentration gradient into the proximal tubule (this is a symport mechanism and brings glucose with it)
  • water is then reabsorbed down an osmotic gradient from the lumen into the cells and then out into the interstitial fluid (it flows the sodium pathway)
  • when the sodium is taken out of the proximal tubule there is a negative voltage so the chloride is pulled out as well
32
Q

How do you measure GFR

A
  • Measured by clearance
33
Q

define clearance

A
  • it is the effective volume of plasma completely cleared of a substance per minute
34
Q

if 100% blood component is filtered through the glomerulus ..

A
  • this means that material goes into the proximal tubule at the same rate as the water in the plasma, therefore the clearance of the substance will be the same as the glomerular filtration rate which is 125 ml/min
35
Q

if 100% of the blood component is filtered through the glomerulus and all of it is reabsorbed ..

A
  • no blood will be cleared of the material

- clearance is o

36
Q

that 100 % of the material is filtered and in addition all of the material in the efferent arteriolar blood is secreted into the urine

A
  • renal venous blood will have no material in it and all the blood passing through the kidney will have been cleared of the material
  • the clearance will then equal the renal plasma flow
37
Q

what can clearance be equal to

A

Not removed at all by kidney: Clearance = zero

Removed at same rate as water passes through glomeruli: Clearance = GFR

Completely removed from blood passing through kidney: Clearance = RPF

38
Q

what happens to the GFR and RPF if the kidney is damaged

A

GFR will decrease

RPF will be normal

39
Q

what is the formula of clearance

A

urine concentration/ plasma concentration x urine flow (volume of urine per minute)

40
Q

how do you measure the clearance of a substance

A
  1. measure the concentration of the substance in the plasma
  2. collect the urine for a fixed period to get the urine flow
  3. measure the concentration of the substance in the collected urine
41
Q

what do you use to measure GFR

A
  • inulin - completely filtered from the plasma and is not reabsorbed, have to iV inulin over a period of hours until you reach a steady plasma concentration - not clinically practical as it takes too long
  • Clinically use creatinine to measure GFR, produced naturally by the Body and is filtered by the glomerulus and is also secreted by the peritubular capillaries in the small amounts, it is already at a steady state concentration in the blood so it takes much shorter to measure
42
Q

what does the secretion of creatinine by the peritubular capillaries do

A
  • means that the creatinine clearance overestimates the GFR by 10-20%
43
Q

what is creatinine

A

it is the product of creatine metabolism

44
Q

how does urine collection work

A
  • a 24 hour urine collection is usually undertaken from empty bladder one morning to the contents of the bladder the following morning
  • blood test for creatinine then taken
45
Q

how can you get an approximation of kidney function

A

from blood creatinine concentration

46
Q

what can clearance also be used to measure

A

renal plasma flow

47
Q

how can clearance be used to measure renal plasma flow

A

if all of a particular substance is filtered along with water and addition of all material int he efferent arteriolar blood is secreted into the urine than the renal venous blood will have no material in it

  • all the blood passion through the kidney will have been cleared of the material
  • therefore ether clearance will then equal the renal plasma flow
48
Q

what material is used to use clearance to measure the renal plasma flow

A
  • PAH
  • PAH infused until steady concentration in arterial blood is reached
  • urine is collected for 24 hours and urien flow and PAH concentration is measured
49
Q

what is the normal GFR

A

120-125 ml/min

50
Q

What is the norml RPF

A

600-700 ml/min

51
Q

name the 5 stages of chronic kidney disease

A 
stage 1 greater but equal to 90 
stage 2 (mild) 60-89
stage 3 (moderate) 30-59
stage 4 (severe) 15-29
stage 5 (kidney failure) less than 15
52
Q

the GFR in kidneys is…

A

autoregulated which means that it does not change over a wide range of blood pressures

53
Q

what does auto regulation of the GFR mean

A
  • means the the GFR does not change over a wide range of blood pressures
54
Q

why are the EPO relasing cells in the kidney

A
  • the renal blood flow is constant and the oxygen consumption of the kidney is constant the oxygen saturation of kidney interstitum is a measure of the oxygen delivery to the kidney and therefore the oxygen carrying capacity of the blood
55
Q

how is the GFR auto regulated

A
  • by the balance of constriction in the smooth muscle of the afferent and efferent arterioles
56
Q

what happens if the afferents relax and what happens if the afferents constrict

A
  • if the afferents relax and dilate this increases the filtration pressure and increases the GFR
  • if the afferents constrict this lowers the filtration pressure and the GFR
57
Q

what is auto regulation of the GFR controlled by

A
  • the Juxtaglomerular apparatus
  • this is the point at where the distal tubules folds back and contacts the glomerulus at the point where the afferent and efferent arterioles enter
58
Q

what are the 3 structures of the juxtaglomerular apparatus

A
  • afferent arteriole
  • efferent arteriole
  • distal tubule
59
Q

what lines the wall of the distal tubules

A
  • macula densa
60
Q

what are macula densa

A
  • sodium sensors

- release local chemicals which modulate the contraction of smooth muscle around the afferent arteriole

61
Q

why does a low sodium level indicate a low GFR

A

Sodium is removed (by reuptake) from the proximal tubule at a fixed rate.
If the flow is slow (low GFR) , more sodium has been removed by time the fluid has reached the end of the tubule and the remaining concentration will be low . Conversely, if the flow is fast (high GFR) , more sodium is flowing past the uptake sites than they can manage, so the concentration remains high.

With low distal tubule sodium, the macula densa cells release local chemical factors which relax the smooth muscle in the afferent arteriole, thus increasing the filtration pressure and increasing GFR. Conversely, if the sodium level is too high, the macula densa cells release chemical factors which constrict the the afferent arteriole, decrease filtration pressure and reduce GFR.

CardioRespiratory Year 1 (28 decks)

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