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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
Why is absorption in kidney called reabsorption?
• Already been absorbed once by GI tract
26
Give three mechanisms by which reabsorption occurs
* Osmosis * Diffusion * Active transport
27
What is tubular secretion?
• Substances secreted into renal tubular lumen from peritubular capillaries
28
By what mechanism are substances secreted into the tubular lumen?
• Active transport
29
What two main types of substances are secreted into the tubular lumen?
* Those present in great excess | * Natural poisons
30
What does secretion help to maintain?
• Blood pH
31
Give three examples of things actively secreted
* Protons * Potassium * Creatinine
32
What are two methods of secretion into the PCT?
* Entry by passive carrier | * Secretion into the lumen
33
What is entry by passive carrier?
• Diffusion across basolateral membrane down conc grad created by Na+/K+ ATPase
34
How does entry by active secretion differ to passive?
• Directly uses ATM and H+ gradient creat by Na+-H+ antiporter
35
Give two forms of reabsorption?
* Transcellular | * Paracellular
36
How easy is it for a cation to get through the filter compared to an anion?
• Positive charge of cation allows slighty bigger molecules through than anions
37
What is reabsorption in PCT driven by?
• Sodium uptake
38
How is Na+ reabsorbed in tubular cells
* 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
39
In what way do solutes move in the PCT?
• Tubular lumen -> Intersticium -> Capillaries
40
What are the three mechanisms via which tubular reabsorption occurs?
* Osmosis * Diffusion * Active transport
41
What does iso-osmotic mean when applied to reabsorption?
• Osmosis does not take effect
42
Where does unregulated absorption occur?
• Proximal convoluted tubule
43
What is the method via which reabsorption occurs?
• Co-transport, following active transport
44
What is the transport maximum?
• If plasma conc exceeds Tm, the rest spills over into urine
45
What is the reabsorption path?
• Lumen -> Intersticium -> Peritubular capillaries
46
How is reabsorption different from glomerula filtration?
• Occurs primarily through cells
47
What 7 main substances are secreted into glomerula filtrate?
* Protons * Potassium * Ammonium ions * Creatinine * Urea * Some hormones * Some drugs
48
Why do we need kidney secretion?
• Only 20% of plasma filtered in renal corpuscle each time
49
From where does tubular secretion occur?
• From the epithelial cells that line the renal tubules and collecting duct into the glomerular filtrate
50
How are organic cations secreted?
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
Name three endogenous cations
* Dopamine * Adrenaline * Histamine
52
Name three cationic drugs
* Morphine * Atropine * Sulfonamides
53
Name three endogenous anions
* Urate * Bile salts * Fatty acids
54
Name two anionic drugs
* Penicillin | * Salicylate
55
What is secondary active transport?
• Na+/K+ ATPase used to generate Na+ gradient
56
Where is glucose reabsorbed in the nephron?
• Proximal convoluted tubule
57
Through what transporter is glucose reabsorbed in the proximal convoluted tubule?
SGLUT
58
What is SGLUT?
* 2 Na+ ions and 1 glucose * Glucose travels from lumen of tubule to the peritubular capillaries (moves into peritubular capillaries by facillitated diffussion
59
What is Tm?
• Transport maximum from tubule to capillaries
60
What is the renal threshold for glucose?
• 200mg/100ml
61
What occurs if transport maximum for glucose exceeded?
* Rest of glucose spills over into urine | * Causes polyuria
62
Where does reabsorption of amino acids occur?
• Proximal convoluted tubule via Na+ co-transporters
63
What is clearance?
• The volume of plasma from which any substance is completely removed by the kidney in a given amount of time (usually 1 minute)
64
What is the clearance calculation?
• Clearance rate = Urine concentration of substance x Urine flow rate / Plasma concentration of the substance
65
What is excretion rate?
• Amount in urine x Urine flow rate
66
When are the inputs and outputs of the kidney?
* One input - Renal artery | * Two outputs - Renal vein and Ureter
67
What can we measure from the rate at which a substance appears in the urine, provided that that substance is completely cleared
• The GFR
68
What is the Tm for glucose in males and females?
* Males - 375mg/min | * Female 300 mg/min females
69
What is glomerular filtration rate?
• The volume of plasma from which any substance (X) is completely removed by the kidney in a given amount of time
70
What is GFR a measure of?
• Kidneys ability to filter a substance (overall function)
71
What does a fall in GFR indicate?
• Kidney disease is progressing
72
In order to measure GFR, what properties must a substance have?
* Must be freely filtered across the glomerulus * Must not be reabsorbed, secreted or metabolised * Must pass directly into the urine
73
What is standard renal blood flow?
• 1.1l/min
74
How can we find out renal plasma flow?
* Heamatocrit is the volume (%) of RBC in blood * Normally 45% * 0.55 x 1.1 (RBF) = 605ml - Plasma flow
75
What is the filtration fraction of 605 ml plasma?
• 605ml x 0.2 = 125ml (20% blood processed per minute)
76
What is GFR for males?
• 115-125 ml/min
77
What is GFR in females?
• 90/100 mi/min
78
Outline the GFR of inulin, glucose and para-aminohippurate
Inulin - 125ml/min - Not reabsorbed, not secreted Glucose - 0 - Completely reabsorbed Para-aminohippurate - 625 ml/min (Secreted!)
79
Outline use of urea
• Used as an active osmol by the kidney
80
What is filtration fraction?
* 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
What is autoregulation?
• Auto-regulatory mechanisms keep GFR within normal limits when arterial BP within physiological limits (80-120 average BP)
82
What is myogenic autoregulation?
• Smooth muscles of afferent capillaries of glomerulus (those going in) contract to increase or decrease pressure
83
What are the limits of myogenic autoregulation?
• Normal average blood pressure between 80-120 mmHG
84
What is GFR?
* Glomerular filtration rate | * A measure of the kidney's ability to filter a substance
85
Give two mechanisms of controlling blood flow to glomerulosa
a • Smooth muscle control in afferent and efferent arterioles • Tubular Glomerular feedback
86
What happens to smooth muscle in afferent arterioles to glomerulosa if blood pressure drops?
Vasodilation
87
What happens to smooth muscle in afferent arterioles to glomerulosa if blood pressure increases
• Vasoconstriction
88
Outline tubular glomeruola feedback
* 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
How do the macula densa cells in the JGA oppose high GFR
• Release adenosine (vasoconstrictor) or prostaglandin (Vasodilator)
90
How much blood is received by the kidney each minute?
• 1.1 litres of blood
91
What is general overflow aminoaciduria?
* All amino acids present in urine | * Due to inadequate deamination in the liver, or increased GFR
92
When is general overflow aminaciduria often seen?
• Early pregnancy
93
What is specific overflow aminoaciduria?
* 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
How can kidney stones develop as a result of renal aminoaciduria?
* 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
What is the difference between clearance rate and GFR?
GFR does not take into account secreted ions, but clearance rate does.

Semester 3 - Urinary (33 decks)

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