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Urinary > Renal Blood Flow and GFR > Flashcards

Renal Blood Flow and GFR Flashcards

1
Q

Where does the input of blood into the kidney come from?

A

The Renal Artery

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2
Q

What is Renal Blood FLow (RBF)

A

1.1L/min

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3
Q

How much blood flows through the glomerulus?

A

All the blood goes throught the glomeruli in the cortex, but only 20% is filtered at any one time

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4
Q

What is haematocrit?

A

A measurement of the proportion (%) of blood that is made up of RBCs (or the erythrocyte volume fraction EVF).
Normally ~0.45

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5
Q

Using the Haematocrit or EVF value of 0.45 and RBF of 1.1L/min
What is Renal Plasma Flow?

A

100-45= 55

0.55 X 1.1L/min= 0.605L/min

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6
Q

What is filtered through the glomeruli?

A

Renal plasma ONLY

RBC dont fit through

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7
Q

What is the blood supply to the kidney?

A

Renal Artery –> Segmental Arteries –> Interlobar Arteries –> Arcuate Arteries –> Interlobular Arteries –>Afferent Arterioles => Glomerulus => efferent arteriole –> peritubular capillaries or Vasa recta

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8
Q

What are Vasa Rectas?

A

A type of peritubular capillary associated with juxtamedullary nephroins responsible for concentrating urine

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9
Q

What are the two types of nephrons?

A

Cortical and Juxtamedullary

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10
Q

Where are the two types of nephron located?

A

Cortical - in the outer part of the cortex

Juxtamedullary - in the inner part of the cortex

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11
Q

Compare the sizes of the glomerulus in the two types of nephron.

A

Cortical- small

Juxtamedullary - Big

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12
Q

Which nephron has the longer loop of henle?

A

The juxtamedullary nephron

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13
Q

Compare the diameters of the Afferent arterioles to the efferent arterioles in each type of nephron.

A

In the Cortical the AA>EA

In the juxtamedullary the AA = EA

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14
Q

What does the efferent arteriole go on to form in the juxtamedullary nephron?

A

Vasa Recta

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15
Q

What is the sympathetic innervation in each type of nephron like?

A

In Cortical- Rich

In Juxtamedullary- Poor

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16
Q

What is the concentration of renin in each type of nephron like?

A

In Cortical- High

In Juxtamedullary- Almost none

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17
Q

What is the percentage of cortical nephrons compared to juxtamedullary?

A

90% vs 10%

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18
Q

What does the Glomerulus do?

A

Filters 20% of the plasma from the renal artery, 80% leaves via EA.
Always the same despite the type of nephron

19
Q

What can pass through the filtration barrier?

A

H20, salts, glucose, urea, creatinine (small molecules)

Cells and large proteins do not get filtered

20
Q

What 3 layers form the filtration barrier?

A
  1. Capillary Endothelium
  2. Basement Membrane
  3. Podocyte Layer
21
Q

What is the basement membrane of the filtration barrier? What is it permeable and what is it impermeable to?

A

Acellular gelatinous layer of collage/glycoproteins
Permeable to small proteins
impermeable to large charged proteins

22
Q

What effect do glycoproteins in the basement membrane have?

A

Glycoproteins are negatively charged and therefore repel positively charged proteins, making the membrane impermeable to them

23
Q

What forms filtration slits in the podocyte layer?

A

Pseudopodia interdigitate forming filtration slits

24
Q

What is used to estimate GFR and why?

A

Inulin (5200 MW, 1.48nm- effective molecular radius) just small enough to fit through the glomeruli filtration barrier

25
Q

What molecules will fit through the filtration barrier? (MW and radius)

A

small MW wt and effective radius less than 1.48nm

26
Q

What are the two selective requirements of the filtration barrier?

A
  1. Perm-selectivity barrier: MW and radius

2. Effect of charge (positively charged molecules will be repelled)

27
Q

What is proteinuria? What could be the cause?

A

The presence of abnormal quantities of protein in the urine, which may indicate damage to the kidneys.
The loss of the negative charge on the filtration barrier, proteins are more readily filtered

28
Q

What 3 forces are involved in the filtering of plasma?

A
  1. Hydrostatic pressure in the capillary- regulated (Pgc)
  2. Hydrostatic pressure in the Bowman’s capsule (Pbc)
  3. Oncotic pressure difference between the capillary and tubular lumen
29
Q

Which of the 3 forces involved in filtering of plasma favour filtration?

A

Hydrostatic pressure in the plasma (50mmHg)

30
Q

What is the net filtration pressure?

A-(B+C)

A 
50mmHg (hydrostatic pressure in plasma) 
15 mmHg (hydrostatic pressure in tubule) 
25 mmHg (oncotic pressure in glomerulus)

Net filtration pressure = 10 mmHg

31
Q

How is pGC regulated?
Tip:
Afferent/efferent vessels

A

The golmerullary capillary hydrostatic pressure is regulated by auto-regulation- myogenic response.
SMC oppose whatever is inflicted on them.
Increasing flow= Increasing pressure/ increasing resistance

32
Q

What affect does increasing flow have on the afferent arterioles?

A

Increase in BP –> increasing afferent arteriole resistance, therefore less blood entering, limiting hydrostatic force and decreasing pressure.
–> GFR is unchanged

33
Q

What affect does decreasing blood flow have on the afferent and efferent arterioles?

A

Decrease in BP –> Afferent arteriole dilation –> increasing blood flow entering.
The efferent arterioles are constricted, increasing the pressure within and therefore increasing filtration rate

–> GFR unchanged

34
Q

Equation for the auto-regulation of Pgc?

A

(increasing) Flow= (increasing) pressure/ (increasing) Resistance

35
Q

Autoregulation is able to maintain ___ when BP is within _____?

A

Autoregulation is able to maintain GFR when BP is within normal limits 80-180mmHg

36
Q

What arteriole (afferent of efferent) are most changes due to in myogenic autoregulation of the Pgc?

A 
Afferent arteriole 
(increase in BP --> increase in arteriole resistance --> GFR unchanged)
(decrease in BP --> afferent arteriole dilation --> GFR unchanged)
37
Q

Other than the changes in afferent and efferent arteriole SMC, what helps with the autoregulation of Pgc?

A

Tubular Glomerular feedback (TG-Feedback)

38
Q

Describe Tubular Glomerular Feedback (TG) in helping the autoregulation of Pgc
Only in acute changes

A

Changes in tubular flow rate as a result of changes in GFR. The change in the amount of NaCl that reaches the DCT.
increase in arterial pressure = increase in glomerular capillary pressure and an increase in renal plasma flow and therefore increase in GFR
And increase in GFR leads to an increase in [Na+] and [Cl-] in the DCT (i.e. increase in the filtered load)
Macula Densa cells respond to changes in NaCl arriving in the DCT
- MD is a sensor of the DCT lumincal [NaCl]
- works via conc-dependent salt uptake through the NaK2Cl cotransporter
- Regulation of arterial tone and therby filtration rate
- stim juxtaglomerular apparatus to release chemicals which have different actions: (To reduce GFR: adenosine released = vasodilation of EA, to increase GFR: PG vasodilator of AA)

39
Q

Summarise the TGF response if NaCl increases i.e Increase in BP (therefore increase in GFR)

A

Need to decrease GFR:
Adenosine is released causing vasodilation of the efferent arteriole
Reduces pressure gradient across the golmerulus and thus slows GFR

40
Q

Summarise the TGF response if NaCl decreases (i.e Decrease in BP and therefore a decrease in GFR)

A

Needs to increase GFR

Prostaglandins are released, causing vasodilation of the Afferent arterioles

41
Q

Why is it called tubular reasborption?

A

Because substances have already been absorbed once in the SI

42
Q

What is reabsorption in the PCT driven by?

A

Na+ active

43
Q

What kind of Na+ transporters are present in the;

(1) PCT
(2) Loop of H
(3) Early DCT
(4) Late DCT and CD?

A

(1) PCT: Na-H antiporter & Na-Glucose symporter
(2) Loop of H: Na-K2Cl symporter
(3) Early Na-Cl symporter
(4) Late DCT and CD - ENaC

44
Q

Describe the location of the DCT

A

The DCT comes back and nestles between own afferent and efferent arterioles of its own glomerulus.
The macula densa of the DCT can therefore sit closest to the arterioles and chemically signal to change GFR

Urinary (7 decks)

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