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Urinary > Glomerular Filtration > Flashcards

Glomerular Filtration Flashcards

0
Q

What can pass through the glomerular filter?

A 
Water
Salts
Small proteins
Glucose
Urea
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1
Q

What percentage of the blood which passes through the renal artery is filtered?

A

20%

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2
Q

What cannot pass through the filter?

A

Large proteins

Cells

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3
Q

What causes the pressure to be increased inside the glomerulus?

A

Afferent arteriole has a slightly larger diameter than the efferent

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4
Q

What repels proteins from being filtered?

A

The podocyte glycocalyx and the basement membrane have negatively charged glycoproteins

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5
Q

What is the ultrafiltrate?

A

The water and solutes forced through the filter

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6
Q

What are the physical forces involved in filtering of plasma and where are they? Do they favour or oppose filtration?

A

Hydrostatic pressure in the capillary - favours filtration
Hydrostatic pressure in Bowman’s capsule - opposes filtration
Osmotic pressure difference between capillary and tubular lumen - opposes filtration

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7
Q

Structure of the basement membrane of the filter?

A

Acellular
Gelatinous
Layer of collagen and glycoproteins

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8
Q

What are the three layers of the filtration barrier?

A

Capillary endothelium
Basement membrane
Podocytes

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9
Q

If you get loss of the negative charge on the glycoproteins, what can this lead to?

A

Proteinuria

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10
Q

What is clearance?

A

The volume of plasma from which a substance can be completely cleared to the urine per unit of time

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11
Q

What is renal blood flow? Value?

A

Volume of blood delivered to kidneys per unit of time

1.1L/min

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12
Q

Define renal plasma flow. Value?

A

Volume of blood plasma delivered to kidneys per unit time

605ml

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13
Q

What is measured to calculate renal plasma flow?

A

Haematocrit (volume percentage of red blood cells in blood)
This = 0.55
1.1 x 0.55 = 605ml/min

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14
Q

Value of the glomerular filtration rate?

A

125ml

20% of renal plasma flow

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15
Q

What is the filtration fraction?

A

Proportion of a substance that is actually filtered

16
Q

How is the filtration fraction calculated?

A

GFR / RPF

17
Q

What do you use to calculate a patient’s GFR?

A

Clearance of something eg urea

18
Q

How is clearance rate worked out? (Equation)

A

Clearance rate =
{urine conc of P x urine flow (ml/min)} /
plasma conc of p

(so if a compound is completely cleared from the plasma that is filtered, then the rate it appears in the urine is the GFR)

19
Q

Define glomerular filtration rate

A

Volume of plasma from which any substance is completely removed by the kidney in a given amount of time

20
Q

Normal GFR for males and females?

A 
Males = 115-125 ml/min
Females = 90-100 ml/min
21
Q

What conditions must there be when choosing a substance to use to measure the GFR?

A

Must be freely filtered across the glomerulus

Must not be reabsorbed, secreted or metabolised by cells of the nephron

Must pass directly into the urine

22
Q

What are substances that can be used to measure GFR?

A

Creatinine and inulin

23
Q

What is autoregulation used for?

A

To keep the GFR within normal limits when arterial BP is within the physiological limit

24
Q

What is the myogenic response in autoregulation?

A

If arterial blood pressure rises, get afferent arteriole constriction.

If it falls, get afferent arteriole dilation

25
Q

How does tubular glomerular feedback occur

A

Changes in GFR causes changes in tubular flow rate

This causes a change in the amount of NaCl reaching the distal tubule

26
Q

If there is an increase in arterial pressure, what happens in tubular glomerular feedback?

A

Increase in arterial pressure - increase in GFR - increase in [Na] and [Cl] in distal tubule
Macula densa cells respond - cause release in adenosine which causes vasoconstriction of afferent arteriole

27
Q

What happens if NaCl concentration decreases in distal tubule (for tubular glomerular feedback)

A

Macula densa cells cause release of prostaglandins which cause vasodilation of afferent arteriole

28
Q

What is general overflow aminoacidura?

A

All amino acids are present in the urine.

29
Q

What can general overflow aminoacidura be caused by?

A
  • Inadequate deamination in the liver
  • Increased GFR
  • Often seen in early pregnancy
30
Q

What is specific overflow aminoacidura?

A

Only a specific amino acid is in the urine

31
Q

What can cause specific overflow aminoacidura?

A

Genetic inability to break down an amino acid

Eg phenylalanine in PKU due to lack of phenylalanine hydroxylase

32
Q

Which amino acid is usually associated with renal stone formation? Why?

A

Cysteine (cystinuria)

It is an insoluble amino acid, especially in acidic urine

Urinary (19 decks)

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