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6. SUGAR > The Kidneys > Flashcards

The Kidneys Flashcards

1
Q

What are the 3 major functions of the kidneys?

A
  1. Endocrine function (secreting hormones)
  2. Maintain balance of water, Salt and pH
  3. Excrete waste products
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2
Q

How much cardiac output does each kidney receive?

A

20% of cardiac output

5L/min

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3
Q

What is total renal blood flow?

A

1L/min

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4
Q

What is total urine flow?

A

1L/min

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5
Q

What is the pathway of renal blood supply from the renal artery?

A 
Renal artery
Segmental artery
Interlobar artery
Arcuate artery
Interlobular artery
Afferent arteriole
(Nephron) glomerular capillary
Efferent arteriole
(Nephron) peritubular capillary
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6
Q

Each nephron has how many capillary beds and where?

A

2 capillary beds

One at the glomerulus and one of the peritubular area

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7
Q

Within each nephron, how many sets of capillaries are there and which ones?

A

2 sets of capillaries
Glomerular capillaries (glomeruli)
Peritubular capillaries

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8
Q

How are the 2 capillaries connected together?

A

By an efferent arteriole, the vessel that allows blood to leave the glomerulus

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9
Q

What is unusual about renal circulation?

A

2 sets of arterioles and capillaries

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10
Q

Where do peritubular capillaries supply blood to and why?

A

Supply the tubules with blood

Many of the tubular processes of secretion and reabsorption so are active (thus require oxygen and energy) so blood supply is crucial

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11
Q

Where do the peritubular capillaries go after?

A

Form the veins and blood leaves the kidneys

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12
Q

What is the entire capillary covered by?

A

Podocytes

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13
Q

What happens in glomerular filtration?

Where does fluid go from and to?

A

Passage of fluid from the blood into Bowman’s space to form filtrate

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14
Q

What is the distal part of the nephron (tubule) responsible for?

A

Secretion and reabsorption

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15
Q

What are the layers of the glomerular filtration barrier?

A 
Capillary 
Capillary endothelium 
Basement membrane (basal lamina)
Podocytes
Bowman’s capsule
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16
Q

What factors determine what crosses the filtration barrier?

A

Pressure
Size and charge of molecule
Rate of blood flow
Binding to plasma proteins eg. Calcium, hormones such as thyroxine

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17
Q

What can pass the filtration barrier?

A

Small molecules and ions up to 10 kDa can pass freely eg. Glucose, Uric acid, potassium and creatine

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18
Q

What molecules are restricted?

A

Larger molecules are increasingly restricted

19
Q

What charges are able to pass?

A

Fixed negative charge in the glomerular basement membrane repels negatively charges anions eg, albumin

20
Q

Can albumin pass into the tubule and why?

A

Albumin has a molecular weight around 66kDa and is negatively charged so it cannot pass into the tubule easily

21
Q

Is protein found in the filtered fluid in the tubules?

A

It is protein free

Only protein found is Tamm horsfall protein in urine which is produced by tubule

22
Q

What can pressure determine in the kidneys?

A

Glomerular filtration rate

23
Q

What are the 2 types of pressure found in the glomerular filtration?

A 
Hydrostatic pressure (of glomerular capillary and bowman’s space - GC and BS)
P(gc) bigger & P(bs) smaller

Osmotic pressure
ℼ(gc) - increases as you go along glomerular capillary ad proteins become more concentrated
ℼ(bs) - no osmotic pressure as there are no proteins = 0

24
Q

What is the glomerular filtration rate?

A

It is the filtration volume from glomeruli into Bowman’s space per unit time (minutes)

25
Q

What is the equation for GFR?

A

GFR = Kf [P(gc) - P(bs) - ℼ(gc)]

26
Q

What does Kf stand for?

A

Filtration coefficient

The product of permeability of the filtration barrier and the SA available for filtration

27
Q

In a 70kg person, the average GFR =

A

125ml/min

28
Q

How can GFR be increased and decreased?

A

By constricting and increasing blood flow to afferent and efferent arterioles

29
Q

What happens when afferent arterioles are constricted?

A

Decreased hydrostatic pressure in the glomerular capillaries P(gc)
Decreasing GFR

30
Q

What happens when efferent arterioles are constricted?

A

Increases hydrostatic pressure in glomerular capillaries P(gc)
Increasing GFR

31
Q

What happens when afferent arterioles are dilated?

A

Increases the P(gc) and thus GFR

32
Q

What happens when efferent arterioles are dilated?

A

Decreases the P(gc) and thus GFR

33
Q

What is GFR measured by?

A

Calculated by measuring the excretion of a marker substance (M)

34
Q

What must the marker be? (3)

A

Freely filtered (same conc in blood and tubular fluid)
Not secreted or absorbed in the tubules
Not metabolised

35
Q

Amount excreted per min =

A

Amount filtered per min

36
Q

Equation for amount of M in fluid?

A

Conc in fluid x vol of fluid

37
Q

Equation for GFR including conc of M in urine and plasma?

A

GFR = Um x urine flow rate / Pm

38
Q

What is used to estimate GFR clinically and why?

A 
Creatine
Muscle metabolite, constant production
Serum creatinine conc will vary with muscle mass
Freely filtered by glomerulus
Some additional secretion by the tubules
39
Q

What is the filtration fraction? And equation?

A

It’s the Proportion of renal blood flow that gets filtered

GFR / renal plasma flow

40
Q

Renal blood flow=1000ml/min
40% of blood is cells and rest is plasma
Renal plasma flow = ?
If GFR is 120ml/min then what is the filtration fraction?

A

Renal plasma flow=600ml/min

Fraction= 120/600 = 0.2 = 20%

41
Q

What is renal clearance?

A

The vol of plasma from which a substance is completely removed from the kidney per unit time (usually a minute)

42
Q

Why is substance M used?

A

It is freely filtered at the glomerulus and is neither reabsorbed nor secreted in the tubule
All the M that is filtered will end up in the urine

43
Q

What is the clearance of substance M!

A

125ml/min

Equal to GFR

44
Q

What is the equation for for clearance?

A

Urine conc x urine vol / plasma conc

6. SUGAR (14 decks)

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