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Semester 3 - Urinary > Session 3 - Filtration > Flashcards

Session 3 - Filtration Flashcards

1
Q

Outline the sequence of arteries leading into the kidney

A

• Renal Artery -> Segmental Arteries -> Interlobar Arteries -> Arcuate Arteries -> Interlobular Arteries -> Afferent Arterioles

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2
Q

Give one way in which the structure of the renal arteries increases pressure in the glomerulus

A

• The diameter of each afferent arteriole is slightly greater than the diameter of the associated efferent arteriole

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3
Q

What is the size limit and effective molecular radius for filtration?

A
  • Size limit - 5,200

* Effective molecular radius - 1.48 nm

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4
Q

Why are proteins not usually filtered into the kidney?

A
  • Size

* Basement membrane and podocyte glycocalyx have many negatively charged glycoproteins which repel protein movement

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5
Q

How much blood is filtered by the renal artery at any one time?

A

• 20%

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6
Q

What happens to blood not filtered by the glomerulus?

A

• Exits via efferent arteriole

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7
Q

What are the two types of kidney nephron?

A
  • Cortical

* Juxtamedullary

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8
Q

Why is a juxtamedullary nephron named thus?

A

• Glomeruli located in cortex, but next to medullary bounds

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9
Q

Give two differences between cortical and juxtamedullary nephrons

A
  • Juxtamedullary has longer loops of henle
    • Arrangement of peritubular capillaries around cortical nephrons messy
    • Structured and organised arrangement of capillaries in juxtamedullary nephron
    • Countercurrent flow in organised juxtamedullary nephron
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10
Q

How is filtration a selective process?

A
  • Cells and large proteins do not get filtered through
    • Water, salts and small molecules pass through
    • Thanks to filtration mesh provided by podocytes
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11
Q

Where do the glomerula tufts always lie?

A

• In the cortex

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12
Q

Where does blood to be filtered arrive in the kidney?

A

• Glomerula tuft

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13
Q

What are the three layers in the filtration barrier?

A

• Capillary endothelium
○ Water, salts, glucose
• Basement membrane
○ Acellular gelatinous layer of collagen/glycoprotein
○ Permeable to small proteins
○ -‘ve charge to repel protein movement
• Podocyte layer
○ Pseudopods interdigitate and form filtration slits

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14
Q

It is more difficult for a positive protein to pass through membrane than a negative. Do you agree?

A

• No, negative repelled by -vely charged basement membrane

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15
Q

What happens if a clinical conditions results in negative proteins being stripped of their charge?

A

• They will be filtered and appear in the urine

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16
Q

Give conc of following in plasma and ultrafiltrate

A
  • Glucose 100
    • Na+ mmol/l 140
    • Urea mg/dl 15
    • Creatinine umol/l 60-120
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17
Q

Give three physical forces involved in plasma filtration

A
  • Hydrostatic pressure in the capillary (regulated) (capillary -> tubule)
    • Hydrostatic pressure in bowman’s capsule (tubule -> capillary)
    • Osmotic (oncotic) pressure differences between the capillary and tubular (tubular -> Capillary)
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18
Q

What is the net filtration pressure in the glomerulosa?

A

• 10mmHg

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19
Q

What is the average hydrostatic pressure between capillaries and tubule?

A

• 50mmHG (about half of normal pressure)

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20
Q

What is the effect of charge on filtration?

A
  • Neutral molecule - The bigger it is, the less likely to get through
    • Anions - Negative charge also repels, more difficult to get through
    • Cations - Positive charge allows slightly bigger molecules through
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21
Q

How is blood in afferent arteriole (going out) different to efferent (going in)?

A
  • Oncotic (protein) pressure higher

* Blood is more concentrated

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22
Q

Give one cause of proteinuria involving filtration forces

A

• In many disease processes the negative charge is lost on the filtration barrier, so proteins are more readily filtered

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23
Q

What is osmotic pressure?

A

• Force generated because of solute within solvent

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24
Q

What is oncotic pressure?

A

• Oncotic force in generated because of protein within solute

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25
Q

Why is absorption in kidney called reabsorption?

A

• Already been absorbed once by GI tract

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26
Q

Give three mechanisms by which reabsorption occurs

A
  • Osmosis
    • Diffusion
    • Active transport
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27
Q

What is tubular secretion?

A

• Substances secreted into renal tubular lumen from peritubular capillaries

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28
Q

By what mechanism are substances secreted into the tubular lumen?

A

• Active transport

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29
Q

What two main types of substances are secreted into the tubular lumen?

A
  • Those present in great excess

* Natural poisons

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30
Q

What does secretion help to maintain?

A

• Blood pH

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31
Q

Give three examples of things actively secreted

A
  • Protons
    • Potassium
    • Creatinine
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32
Q

What are two methods of secretion into the PCT?

A
  • Entry by passive carrier

* Secretion into the lumen

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33
Q

What is entry by passive carrier?

A

• Diffusion across basolateral membrane down conc grad created by Na+/K+ ATPase

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34
Q

How does entry by active secretion differ to passive?

A

• Directly uses ATM and H+ gradient creat by Na+-H+ antiporter

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35
Q

Give two forms of reabsorption?

A
  • Transcellular

* Paracellular

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36
Q

How easy is it for a cation to get through the filter compared to an anion?

A

• Positive charge of cation allows slighty bigger molecules through than anions

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37
Q

What is reabsorption in PCT driven by?

A

• Sodium uptake

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38
Q

How is Na+ reabsorbed in tubular cells

A
  • 3Na-2K-ATPase (Na into ECF, K+ into cell)
    • Na+ moves across the apical membrane from tubule lumen down its concentration gradient
    • Water follows into cell
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39
Q

In what way do solutes move in the PCT?

A

• Tubular lumen -> Intersticium -> Capillaries

40
Q

What are the three mechanisms via which tubular reabsorption occurs?

A
  • Osmosis
    • Diffusion
    • Active transport
41
Q

What does iso-osmotic mean when applied to reabsorption?

A

• Osmosis does not take effect

42
Q

Where does unregulated absorption occur?

A

• Proximal convoluted tubule

43
Q

What is the method via which reabsorption occurs?

A

• Co-transport, following active transport

44
Q

What is the transport maximum?

A

• If plasma conc exceeds Tm, the rest spills over into urine

45
Q

What is the reabsorption path?

A

• Lumen -> Intersticium -> Peritubular capillaries

46
Q

How is reabsorption different from glomerula filtration?

A

• Occurs primarily through cells

47
Q

What 7 main substances are secreted into glomerula filtrate?

A
  • Protons
    • Potassium
    • Ammonium ions
    • Creatinine
    • Urea
    • Some hormones
    • Some drugs
48
Q

Why do we need kidney secretion?

A

• Only 20% of plasma filtered in renal corpuscle each time

49
Q

From where does tubular secretion occur?

A

• From the epithelial cells that line the renal tubules and collecting duct into the glomerular filtrate

50
Q

How are organic cations secreted?

A

1) Entry by passive carrier into tubular lumen cell
a. Positive cation from ECF moves into negative cell down electrical gradient. This is as a result of basolateral 3 Na+/2 K+ ATPase
2) Secretion into the lumen
a. H-OC exchanger driven by H+ gradient created by the Na+-H+ antiporter
b. Na+ into cell from lumen, H+ out cell into lumen
c. Drives H+ into cell from lumen by creating conc grad
d. Organic Cation out by active transporter

51
Q

Name three endogenous cations

A
  • Dopamine
    • Adrenaline
    • Histamine
52
Q

Name three cationic drugs

A
  • Morphine
    • Atropine
    • Sulfonamides
53
Q

Name three endogenous anions

A
  • Urate
    • Bile salts
    • Fatty acids
54
Q

Name two anionic drugs

A
  • Penicillin

* Salicylate

55
Q

What is secondary active transport?

A

• Na+/K+ ATPase used to generate Na+ gradient

56
Q

Where is glucose reabsorbed in the nephron?

A

• Proximal convoluted tubule

57
Q

Through what transporter is glucose reabsorbed in the proximal convoluted tubule?

A

SGLUT

58
Q

What is SGLUT?

A
  • 2 Na+ ions and 1 glucose
    • Glucose travels from lumen of tubule to the peritubular capillaries (moves into peritubular capillaries by facillitated diffussion
59
Q

What is Tm?

A

• Transport maximum from tubule to capillaries

60
Q

What is the renal threshold for glucose?

A

• 200mg/100ml

61
Q

What occurs if transport maximum for glucose exceeded?

A
  • Rest of glucose spills over into urine

* Causes polyuria

62
Q

Where does reabsorption of amino acids occur?

A

• Proximal convoluted tubule via Na+ co-transporters

63
Q

What is clearance?

A

• The volume of plasma from which any substance is completely removed by the kidney in a given amount of time (usually 1 minute)

64
Q

What is the clearance calculation?

A

• Clearance rate = Urine concentration of substance x Urine flow rate / Plasma concentration of the substance

65
Q

What is excretion rate?

A

• Amount in urine x Urine flow rate

66
Q

When are the inputs and outputs of the kidney?

A
  • One input - Renal artery

* Two outputs - Renal vein and Ureter

67
Q

What can we measure from the rate at which a substance appears in the urine, provided that that substance is completely cleared

A

• The GFR

68
Q

What is the Tm for glucose in males and females?

A
  • Males - 375mg/min

* Female 300 mg/min females

69
Q

What is glomerular filtration rate?

A

• The volume of plasma from which any substance (X) is completely removed by the kidney in a given amount of time

70
Q

What is GFR a measure of?

A

• Kidneys ability to filter a substance (overall function)

71
Q

What does a fall in GFR indicate?

A

• Kidney disease is progressing

72
Q

In order to measure GFR, what properties must a substance have?

A
  • Must be freely filtered across the glomerulus
    • Must not be reabsorbed, secreted or metabolised
    • Must pass directly into the urine
73
Q

What is standard renal blood flow?

A

• 1.1l/min

74
Q

How can we find out renal plasma flow?

A
  • Heamatocrit is the volume (%) of RBC in blood
    • Normally 45%
    • 0.55 x 1.1 (RBF) = 605ml - Plasma flow
75
Q

What is the filtration fraction of 605 ml plasma?

A

• 605ml x 0.2 = 125ml (20% blood processed per minute)

76
Q

What is GFR for males?

A

• 115-125 ml/min

77
Q

What is GFR in females?

A

• 90/100 mi/min

78
Q

Outline the GFR of inulin, glucose and para-aminohippurate

A

Inulin - 125ml/min - Not reabsorbed, not secreted
Glucose - 0 - Completely reabsorbed
Para-aminohippurate - 625 ml/min (Secreted!)

79
Q

Outline use of urea

A

• Used as an active osmol by the kidney

80
Q

What is filtration fraction?

A
  • Proportion of a substance actually filtered
    • If renal plasma flow is 605ml/min, 20% of all plasma is filtered, 125ml filtered through into bowman’s space and 480ml passes through into peritubular capillaries
    • Filtration fraction = Glomerular filtration rate/Renal plasma flow
    • Filtration fraction about 20%
81
Q

What is autoregulation?

A

• Auto-regulatory mechanisms keep GFR within normal limits when arterial BP within physiological limits (80-120 average BP)

82
Q

What is myogenic autoregulation?

A

• Smooth muscles of afferent capillaries of glomerulus (those going in) contract to increase or decrease pressure

83
Q

What are the limits of myogenic autoregulation?

A

• Normal average blood pressure between 80-120 mmHG

84
Q

What is GFR?

A
  • Glomerular filtration rate

* A measure of the kidney’s ability to filter a substance

85
Q

Give two mechanisms of controlling blood flow to glomerulosa

A

a
• Smooth muscle control in afferent and efferent arterioles
• Tubular Glomerular feedback

86
Q

What happens to smooth muscle in afferent arterioles to glomerulosa if blood pressure drops?

A

Vasodilation

87
Q

What happens to smooth muscle in afferent arterioles to glomerulosa if blood pressure increases

A

• Vasoconstriction

88
Q

Outline tubular glomeruola feedback

A
  • If arterial pressure too high
    • Increases glomerular capillary pressure
    • Increased glomerula filtration rate
    • More Na+ and Cl- in distal convoluted tubule
    • Macula densa cell in the JGA respond
89
Q

How do the macula densa cells in the JGA oppose high GFR

A

• Release adenosine (vasoconstrictor) or prostaglandin (Vasodilator)

90
Q

How much blood is received by the kidney each minute?

A

• 1.1 litres of blood

91
Q

What is general overflow aminoaciduria?

A
  • All amino acids present in urine

* Due to inadequate deamination in the liver, or increased GFR

92
Q

When is general overflow aminaciduria often seen?

A

• Early pregnancy

93
Q

What is specific overflow aminoaciduria?

A
  • Only a specific AA is present in the urine.
    • This is usually do to a genetic inability to break down one AA
    • PKU
    • Homocysteinuria
94
Q

How can kidney stones develop as a result of renal aminoaciduria?

A
  • Caused by dibasic acids, due to failure of transport system
    • Cystein abnormally insoluble, and is strongly associated with kidney stone formation
    • Cysteinuria associated with stone formation

FUN FACT

95
Q

What is the difference between clearance rate and GFR?

A

GFR does not take into account secreted ions, but clearance rate does.

Semester 3 - Urinary (33 decks)

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