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GERR > Glomerular filtration rate > Flashcards

Glomerular filtration rate Flashcards

1
Q

Define glomerular filtration?

A

Process by which water and some solutes pass from the glomerular capillary to the bowman capsule

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2
Q

Give example of molecules which can’t fit through the podocyte slits?

A
  • Albumin
  • WBCs
  • RBCs
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3
Q

What can freely flow through the the podocyte epithelium?

A
  • Plasma protein (smaller ones)
  • H2O
  • Glucose
  • electrolytes
  • Amino Acids
  • Fatty-acids
  • Nitrogenous waste
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4
Q

When may Proteinuria or hematuria occur?

A
  • caused by glomerular damage

- e.g. in Diabetes or hypertension or infection

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5
Q

When might you see leukocytes in the urine?

A

In UTIs

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6
Q

What forces will push fluid out of the capillaries?

A
  • Blood flow

- Blood pressure

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7
Q

What forces will push fluid into the capillaries?

A
  • Protein and salt sitting in the blood vessels which create concentration gradient (colloid osmotic pressure)
  • fluid sucked back in
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8
Q

Where in the capillary will pressure be forcing fluid in and out?

A

Arterial forcing fluid out by hydrostatic pressure

Venous forcing fluid in due to decrease in hydrostatic pressure but no drop in colloid osmotic pressure

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9
Q

How do you calculate Net filtration pressure?

A

Hydrostatic pressure = HP Colloid osmotic pressure = Pi
Capillary = c
Interstital fluid = if
(HPc-HPif) - (Pi c - Pi if)

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10
Q

What affects hydrostatic pressure in the glomerulus?

A
  • Arterial pressure

- Higher arteriolar resistance in efferent than afferent

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11
Q

What affects hydrostatic pressure in bowmans capsule?

A
  • pressure of filtrate in the capsule, higher in bowman than glomerulus
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12
Q

How do you calculate net filtration pressure in the glomerulus?

A

(HPgc - HPbc) - (Pi gc - Pi bc)

Overall fluid forced out into bowman capsule

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13
Q

What determines the colloid osmotic pressure in bowmans and glomerulus?

A

Proteins in plasma and filtrate

more proteins in plasma than filtrate

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14
Q

What is GFR determined by?

A
  • Net filtration pressure

- Ease of fluid to move through slits (Kf - constant of hydraulic conductivity and surface area of capillaries)

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15
Q

What unit is GFR expressed in?

A

mL/min or mL/min/1.73 m(squared)

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16
Q

Define glomerular filtration rate?

A

Clearance rate of a substance from the blood into the urine when any substance is freely filtered and is neither reabsorbed nor secreted by the kidneys

17
Q

How can GFR be calculated?

A

(Urine concentration x Urine flow) / Plasma concentration

18
Q

What substances can be used to work out GFR?

A

1) Inulin - given as continuous IV infusion, multiple blood and urine samples over 24h (invasive and can be inaccurate if incomplete bladder voiding)
2) Creatinine - clearance based on serum creatinine level used to estimate GFR (tends to overestimate due to peritubular secretion of creatinine)

19
Q

How is creatinine naturally produced in the body?

A

Breakdown of creatinine phosphate in the muscles

20
Q

How can renal function be estimated without blood tests?

A

Test urine for creatinine clearance then estimate plasma creatinine from this and so renal function

21
Q

What lifestyle factors are also accounted for when estimating GFR?

A

Age, sex, weight and body SA

22
Q

What factors may affect GFR?

A
  • Kidney disease (reduced GFR)
  • Hypertension (damage to glomeruli reduces GFR)
  • Sleep (due to hormone and oncotic variation)
  • Exercise (BF diverted to muscles)
  • Renal BF - in renal stenosis less BF to kidney so GFR lower
23
Q

What substance is used to measure Renal Blood Flow?

A
  • Para-aminohippuric acid
  • almost all extracted in one circuit and doesn’t affect kidney function
  • PAH only in plasma so doesn’t directly measure renal BF
24
Q

Why is it essential renal BF is maintained?

A

Need constant BF to keep constant GFR

25
Q

What blood vessel would need to constrict and relax to increase BF

A

afferent constricts

26
Q

What blood vessel would need to constrict to increase filtration?

A

afferent constricts to increase blood pressure

27
Q

What characteristics does substance used in measurement of Renal blood flow need to have?

A
  • Cleared in one circuit through kidney

- doesn’t affect kidney function

28
Q

How is Para-aminohippuric acid used to estimate renal BF

A
  • Clearance of PAH is equal to volume of plasma delivered to kidney which is equal to renal plasma flow
  • Renal BF = renal plasma flow / (1 - haematocrit)
29
Q

What is the formula used to calculate clearance of PAH?

A

clearance of PAH = PAH concentration in urine x urine flow rate (ml/min) / arterial plasma concentration PAH
concentration measured in millimol per millilitre

30
Q

What is the difference between renal plasma flow and renal blood flow?

A
  • PAH more dilute in the plasma

- need to take into account haematocrit in blood flow

GERR (49 decks)

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