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Renal > 1.7: Physiology 3 > Flashcards

1.7: Physiology 3 Flashcards

1
Q

What is glomerular filtration?

A

This is process by which some of the plasma in the capillaries is filtered across to Bowman’s capsule to produce the tubular filtrate

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2
Q

Where does modification of the filtrate occur?

A

Modification occurs along the length of the nephron including the collecting duct.

After filtrate leaves the collecting duct, no more modification occurs (this is the final product, urine)

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3
Q

What are the barriers to glomerular filtration?

A

Glomerular Capillary Endothelium

Basement Membrane/Basal Lamina

Podocytes

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4
Q

What is the barrier to the red blood cells?

A

The endothelial cells

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5
Q

What is the barrier to plasma proteins?

A

The filtration slits of the podocytes

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6
Q

Describe the pores of the endothelium of the glomerular capillaries?

A

These pores (tight junctions) are much larger than the pores of capillaries elsewhere in the body

They are much more leaky

Allows subtances to pass through

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7
Q

Describe how the basement membrane/basal lamina is a barrier to filtration?

A

There are no cells here

This is negatively charged

This repels the negatively charged plasma proteins

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8
Q

Describe how the podocytes are a barrier to glomerular filtration?

A

They have finger like projections

Interdigitating projections from neighbouring podocytes form filtration slits

Only small molecules can pass through these filtration slits

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9
Q

Collectively, the three barriers (Endothelial cells, basal lamina and podocytes) are refered to as the…?

A

Glomerular Membrane

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10
Q

Name two substances that are retained within the glomerulus and cannot pass into the lumen of Bowman’s capsule?

A

Red Blood Cells
Plasma Proteins

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11
Q

Describe the intial tubular filtrate?

A

This is a modified filtrate of the blood
Components (eg: Salt, fluid) are in roughly the same concentrations in the filtrate as they are in the plasma

The red blood cells and plasma proteins are missing

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12
Q

Is the process of glomerular filtration passive or active?

A

The process of glomerular filitration is completley passive

Requires no active transport or energy expenditure

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13
Q

The process of glomerular filtration requires no energy. What does it rely on?

A

Relies on 4 individual pressures that act on the glomerular capillaries

  • Glomerular capillary blood pressure
  • Capillary oncotic Pressure
  • Bowman’s capsule hydrostatic pressure
  • Bowman’s capsule oncotic pressure
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14
Q

Describe glomerular capillary blood pressure?

A

This is caused by the pressure of the blood in the capillary

This pressure is constant along the capillary

This pressure FAVOURS filtration

About 55mm Hg

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15
Q

What is the major determinant of net filtration pressure?

A

Glomerular Capillary Blood Pressure

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16
Q

What is the pressure of the glomerular capillary blood pressure?

A

55 mm Hg

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17
Q

Why is the blood pressure along the glomerular capillary constant along the whole length?

A

The afferent arteriole is much larger than the efferent

This causes a back pressure of blood

Leads to constant BP along capillary

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18
Q

Describe capillary oncotic pressure?

A

This is set up by the abundance of plasma proteins in the capillary

There is no plasma proteins in Bowman’s capsule

Sets up a gradient

Fluid moves from Bowman’s capsule to the capillaries

OPPOSES FILTRATION

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19
Q

Describe Bowman’s capsule hydrostatic pressure?

A

Filtration causes fluid build up in Bowman’s capsule

Exerts hydrostatic pressure

Opposes filtration

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20
Q

Describe Bowman’s capsule oncotic pressure?

A

There are no plasma proteins in Bowman’s capsule

This means the oncotic pressure is 0

This favours filtration

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21
Q

Match these forces to their movement (very simplified)

A) Hydrostatic

B) Oncotic

1 = Pushes it out

2 = Pulls it in

A

Hydrostatic (A) = Pushes it out

(Eg: Bowman’s Capsule hydrostatic pressure opposes filtration and pushes fluid back into glomerulus)

Oncotic (B) = Pulls it in

(Eg: Capillary Osmotic pressure opposes filtration as it pulls fluid back into glomerulus)

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22
Q

Give the pressure value for Bowman’s capsule hydrostatic pressure?

A

15 mm Hg

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23
Q

Give the pressure value for glomerular capillary osmotic pressure?

A

30 mm Hg

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24
Q

Give the pressure value for Bowman’s capsule oncotic pressure?

A

0 mm Hg

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25
Q

What is the net filtration pressure of the Starling forces (acting on glomerulus and Bowman’s capsule)?

A

10 mm Hg (Favours filtration)

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26
Q

What is glomerular filtration rate?

A

This is the rate protein-free plasma is filtered from the Glomerulus into Bowman’s Capsule

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27
Q

Label this diagram A, C, D, E, F (No B!)

A

A = Glomerular Capillary Blood Pressure (Hydrostatic)

C = Capillary Oncotic Pressure

D = Bowman’s Capsule Hydrostatic Pressure

E = Bowman’s Capsule Oncotic Pressure

F = Net Filtration pressure is 10 mmHg

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28
Q

What is the equation for GFR (Glomerular Filtration Rate)?

A

GFR = Kf x Net Filtration Pressure

Kf is the filtration coeffecient (measures how holey/leaky) the membrane is

29
Q

Describe the effect of changing the net filtration pressure on GFR:

  • Increasing net filtration pressure?
  • Decreasing net filtration pressure?
A

INCREASING net filtration pressure will INCREASE GFR

DECREASING net filtration pressure will DECREASE GFR

30
Q

What is the main determinant of GFR?

*Hint: GFR = Filtration coeffiecient x net filtration pressure

What is the main determinant of net filtration pressure?*

A

The main determinant of GFR is the glomerular capillary blood pressure

31
Q

If there is a change to the capillary blood pressure what will happen to the:

  • Net Filtration Pressure?
  • GFR?
  • Urine output?
A

If the capillary blood pressure changes, this will affec the net filtration pressure (Increase in BP increases net filtration pressure, decrease in BP decreases net filtration pressure)

Change to the capillary blood pressure affects net filtration pressure and therefore GFR (Increased BP = Increased GFR, Decreased BP = Decreased GFR)

Change to the capillary blood pressure affects net filtration, GFR and hence rate of kidney filtration and urine output. Increased BP = Increased Urine. Decreased BP = Decreased urine

32
Q

How the renal blood flow (and hence GFR) regulated?

A
  • Extrinsic Mechanisms
  • Intrinsic Mechanisms (Myogenic and Tubuloglomerular Feedback)
33
Q

Describe the extrinisic regulation of renal blood flow and GFR?

A

Sympathetic control via the baroreceptor reflex

34
Q

Describe extrinsic regulation if the arterial BP fell? (Eg: Due to haemorrhage)

A
  • Drop in BP
  • Detected by carotid sinus and aortic baroreceptors
  • Increased sympathetic activity
  • Vasoconstriction of afferent arteriols
  • Decreased blood flow into glomerulus
  • Decreased glomerular capillary blood pressure (Hydrostatic)
  • Decreased net filtration pressure
  • Decreased GFR
  • Retention of fluids (compensates for loss)
35
Q

Describe the extrinsic regulation if arterial BP increased?

A
  • Detected by baroreceptors
  • Decreased sympathetic activity
  • Causes afferent arteriole vasodilation
  • More blood flow into glomerulus
  • Increased glomerular capillary blood flow
  • Increased net filtration pressure
  • Increased GFR
  • More urine output (compensate for excess)
36
Q

What is the affect of:

  • Vasodilation
  • Vasoconstriction

of the afferent arteriole?

A

Vasodilation = More blood flow in glomerulus, increased glomerular capillary blood pressure, increased net filtration pressure, increased GFR, increased urine output

Vasoconstriction = Less blood flow in glomerulus, decreased glomerular capillary blood pressure, decreased net filtration pressure, decreased GFR, decreased urine output

37
Q

Describe intrisic regulation of renal blood flow and GFR?

A

This is autoregulation

This prevents short term changes in arterial blood pressure affecting GFR

38
Q

What is the equation for MAP?

A

1/3 (Systolic - Diastolic) + Diastolic

39
Q

What is the MAP (Mean Arterial Pressure) of someone with a blood pressure of 120/80?

A

MAP = 1/3 (Systolic - Diastolic) + Diastolic

MAP = 1/3 (120-80) + 80

MAP = 13.3 + 80

MAP = 93.3

40
Q

Why do we have autoregulation?

A

This is to prevent short term changes to mean arterial blood pressure affecting the GFR
This could lead to salt/fluid imbalance

41
Q

Describe myogenic autoregulation?

A

This is related to stretch

Vascular smooth muscle is stretched when arterial blood pressure increases (Eg; Exercise)

Smooth muscle contracts to oppose this

Arteriole constricts

Decreases GFR

42
Q

Describe tubuloglomerular feedback?

A

This is done by the juxtaglmerular apparatus

This examines the contents of the distal tubule as it passes between the afferent and efferent arterioles

If the salt content is too high, it causes afferent arteriole constriction to decrease GFR

Negative feedback

43
Q

What cells of the juxtaglomerular apparatus sense the salt content of the tubules?

What cells of the juxtaglomerular apparatus secrete the vasoactive chemicals?

A

Macula Densa

Granular Cells

44
Q

The intrinsic mechanism can override the extrinsic

True or False?

A

False

The extrinsic (sympathetic) mechanism can override the intrinsic at times of great stress (Eg; Haemorrhage)

45
Q

Describe the effect of kidney stones on GFR?

A

Kidney stones cause a blockage and fluid build up

Increases hydrostatic pressure in Bowman’s capsule

Leads to decrease in net filtration rate

Decreased GFR

46
Q

Describe the effect of diarrhoea on GFR?

A

Becomes dehydrated

Increased concentration of plasma proteins

Increased capillary oncotic pressure (lack of fluid)

Causes decreased net filtration pressure

Causes decreased GFR

47
Q

Describe the effect of severe burns on GFR?

A

Lose plasma proteins from site of injury

Decreased capillary oncotic pressure

Increased net filtration pressure

Increased GFR

48
Q

Describe the effect of changing the filtration coefficient?

A

Decreased filtration coeffiecient (membrane is less leaky)

Less permeable membrane

Decrease in GFR

49
Q

Out of this list, which would decrease GFR? Which would increase GFR?

  • Kidney Stone
  • Diarrhoea
  • Burns Patients
  • Damage to membrane (leading to decrease in filtration coeffecient)
A

Decrease GFR:

  • Kidney Stone
  • Diarrhoea
  • Decreased filtration coefficient

Increase GFR:

  • Burns patient
50
Q

What is plasma clearance?

A

This is a measure of how effectively the kidneys can ‘clean’ the blood

This is the volume of plasma that can be compleltey cleared of a subtance in one minute

Measured in millilitres per minute

51
Q

Equation for plasma clearance?

A

Plasma Clearance = Rate of Excretion of X

Plasma Concentration of X

Given in millilitres per minute

52
Q

What is the equation for rate of excretion?

A

Rate of Excretion = Urine concentration of (X) x Urine Flow Rate

53
Q

Describe inulin and its clearance?

A

Inulin is an exogenous compound found in onion and garlic

It is freely filtered at the glomerulus

It is neither absorbed or secreted

Therefore Insulin Excretion = GFR

Clearance of inulin is about 125ml/min

54
Q

What is the normal value for GFR?

A

125ml/min

55
Q

What can be used to give an approximation of GFR instead of Inulin?
Why is this just an approximation?

A

Creatinine clearance can be used instead of inulin

Creatinine is not reabsorbed like inulin however there is a small amount of secretion. This means it can give an approximation of GFR but isn’t exact (unlike inulin)

56
Q

Describe the clearance of a substance that is filtered freely then completly reabsorbed and not secreted?

Give an example?

A

The clearance is 0

An example is glucose

Glucose is freely filtered, completley reabsorbed and not secreted (NONE IS PRESENT IN URINE)

57
Q

For a substance that is freely filtered, partly reabsorbed and not secreted:

Is the clearance GREATER or LESS than GFR?

Give an example?

A

The clearance is LESS than GFR (some is reabsorbed)
Example is urea

58
Q

For a substance that is freely filtered, secreted and not reasborbed:

Is clearance GREATER or LESS than GFR?

Give an example?

A

The clearance is GREATER than GFR

Example is Hydrogen

59
Q

For each example, say if the substance has been reabsorbed, secreted or neither:

  • Clearance > GFR?
  • Clearance = GFR
  • Clearance < GFR?
A

Clearance > GFR then SECRETION

Clearance = GFR then no secretion or reabsorption

Clearance < GFR then REABSORPTION

60
Q

What is PAH?

Describe filtration/clearance?

What is it used for clinically?

A

Para-amino Hippuric Acid (PAH)

This is an exogenous compound

This is freely filtered, secreted and not re-absorbed (fully cleared)
Used clinically to measure renal plasma flow

61
Q

What is renal plasma flow for a healthy adult?

A

650ml/min

62
Q

Give the normal clearance values for:

  • Glucose?
  • Inulin?
  • Creatinine?
  • PAH?
A

Glucose = 0

Inulin = 125ml/min (GFR)

Creatinine = ABOUT 125ml/min (GFR)

PAH = 625 ml/min (RPF)

63
Q

PAH gives a measure of the XXXX?

What is the normal clearance value of PAH and therefore the normal value of XXXX?

A

PAH gives a measure of the renal plasma flow

The normal clearance value of PAH (and therefore the normal value of renal plasma flow) is 625ml/min

64
Q

Describe the properties that a clearance marker should have:

  • In general?
  • For GFR?
  • For RPF?
A

General: Non toxic, not broken down, easily measured in urine and plasma

GFR: Freely filtered, not absorbed or secreted

RPF: Freely filtered, compleltey secreted, not absorbed

65
Q

What is the filtration fraction?

Value for filtration fraction?

A

This is the fraction of plasma flowing through the glomeruli that is filtered into the tubules

The filtration fraction is about 20% (20% filtered, 80% moves on to peritubular capillaries)

66
Q

Equation for filtration fraction?

A

GFR/Renal Plasma Flow

67
Q

Roughly, how much plasma is filtered by the glomeruli every day?

A

180litres/day

68
Q

What is the renal blood flow?

A

1200ml/min

(About 20-25% of cardiac output)

69
Q

How much is cardiac output (in litres per minute)?

A

CO = 5l/min

Renal (34 decks)

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