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MBBS I CPRS > L20– Glomerular Filtration and Tubular Transport > Flashcards

L20– Glomerular Filtration and Tubular Transport Flashcards

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1
Q

How is water content controlled by urine?

A

By urine volume (if water in deficit > concentrated urine > smaller loss of water)

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2
Q

What three things are controlled by urine composition?

A

 Electrolyte balance (Na+, K+, Ca2+, Cl-, PO43-

 Acid/base balance (pH of body fluids)

 Excretion of nitrogenous/metabolic waste

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3
Q

How is blood pressure related to urine production?

A

Indirectly, by blood volume which is related to urine volume

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4
Q

What is the distribution of nephrons in the kidney’s medulla vs cortex?

A

 90% = cortical

 10% = juxtamedullary

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5
Q

Each nephron has which 2 capillary beds?

A

Glomerulus + Peritubular capillary and Vasa Recta (formed from efferent arterioles exiting glomerulus)

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6
Q

In the two types of nephrons, are both renal corpuscles in the cortex?

A

Yes, one in cortex, other in juxtamedullary cortex

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7
Q

Which type of nephron has a longer Loop of Henle?

A

Juxtamedullary

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8
Q

Which two tubules lie adjacent to the glomerulus?

A

PCT and DCT

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9
Q

What are the three basic functions of a nephron?

A

Glomerular filtration

Tubular reabsorption

Tubular secretion

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10
Q

In which vessels do tubular secretion and tubular reabsorption take place?

A

Peritubular capillaries and Vasa Recta

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11
Q

What 2 cells are important in the glomerulus capillaries?

A

Endothelial cells

Mesangial cells

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12
Q

What are the modified cells on the visceral layer of the Bowman’s capsule?

A

podocytes

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13
Q

What is the role of the Mesangial cells in glomerulus?

A

Specialized smooth muscle cells
Do not collapse, structural role
Contract/ relax to control blood flow to glomerulus (contract = reduce filtration rate)

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14
Q

3 components of renal corpuscle filtration barrier?

A

Fenestrated endothelium of glomerular capillaries

Fused basal lamina of endothelial cells and podocytes

Filtration slits of podocytes

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15
Q

What forms filtration slits? What is size of slit?

A

Podocytes’ feet interdigitate

Slits only 20-30nm wide

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16
Q

What is ultrafiltration dependent on? (think properties of what goes through)

A

Molecules ultra-filtrated under HIGH PRESSURE based on SIZE and CHARGE

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17
Q

Glomerular capillaries have fenestrations that does what?

A

Allow macro-molecules to pass

Prevent cells to pass

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18
Q

What component of the renal corpuscle filtration barrier sort molecules by charge?

A
  1. membrane (GBM): made of collagen

negatively charged = repels negatively charged proteins)

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19
Q

What is the role of glomerular basement membrane?

A

 Prevents filtration of large plasma proteins (radius = 7-10nm)
 Slows passage of smaller plasma protein

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20
Q

What is the final glomerular filtration barrier?

A

Glomerular epithelial cells + slit diaphragm

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21
Q

What are some substances that can pass through the glomerular filtration barrier?

A 
ions e.g. Na+, Cl-, H+, K+
Glucose 
Water 
Urea 
Small proteins
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22
Q

Does filtration barrier have much effect on small charged particles

A

No

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23
Q

Are molecules larger than 8nm filtered?

A

No

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24
Q

Why is albumin not filtered?

A

Due to negative charge repelled by GBM and size

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25
What is a sign of chronic kidney disease associated with protein in urine? How does it occur? (think what chronic diseases and how the micro-structure is changed)
Proteinuria/ albuminuria or urine albumin >300mg/24 hours Result from diabetes, hypertension, kidney inflammation... Fusion or collapse of podocyte foot process, splitting of GBM, altered exoskeleton of podocyte
26
How much protein/ time is considered severe nephrotic syndrome?
>3.5g/24 hours
27
Pressure favouring filtration?
Glomerullar blood hydrostatic capillary pressure = 55 mmHg
28
Pressures opposing filtration?
Glomerular capillary oncotic pressure (due to suspension in plasma e.g. albumin) Bowman's capsule hydrostatic pressure ( = 15 mmHg)
29
What does rate of ultrafiltration depend on?
Balance of forces favouring and opposing filtration
30
How is high pressure generated in ultrafiltration?
Blood pressure from Afferent arteriole Efferent arteriole narrower than Afferent arteriole
31
How is net filtration pressure calculated?
``` glomerular capillary blood hydrostatic pressure (GBHP) - Bowman’s capsule hydrostatic pressure (CHP) - Glomerular/blood capillary oncotic pressure (BCOP) ```
32
How does the composition of glomerular filtrate compare to plasma?
 Composition of water, electrolytes, wastes is almost identical to plasma  Exception: proteins, RBCs are kept out from filtrate
33
How much glomerular ultrafiltrate is made each day and how much is reabsorbed?
kidney makes ~180 L of glomerular ultrafiltrate per day | ~179 L is retained
34
What is the normal Glomerular Filtration Rate? GFR
Total volume of filtrate formed by BOTH kidneys per minutes | GFR (90-140 mL/min)
35
How can net filtration pressure (NFP) increase?
Increase by: Vasodilation of AFFERENT arteriole and Vasoconstriction of EFFERENT arteriole
36
What is the effect of vasodilating afferent arteriole?
Increase blood flow to glomerular > increase capillary blood pressure > Increase net filtration pressure
37
What is effect of vasocontricting Efferent arteriole?
Increase capillary pressire | Increase NFP
38
How can NFP be decreased?
Vasoconstrict Afferent arteriole or Vasodilate Efferent arteriole
39
What is the effect of Vasoconstricting afferent arteriole?
Decrease blood flow to glomerulus Decrease glomerular capillary blood pressure Decrease NFP
40
What is the effect of Vasodilating Efferent arteriole?
Decrease glomerular capillary blood pressure | Decrease NFP
41
What 3 things does GFR depend on?
Net filtration pressure Permeability of filtration membrane Surface area available for filtration
42
What are the stages of GFR?
Stage 1 >90mL/min Structural kidney damage with normal function Stage 2 60-89mL/min Kidney damage with mild loss of function Stage 3 30-59mL/min Mild > Moderate> Severe Kidney damage Stage 4 15-29mL/min Severe kidney damage Stage 5 <15mL/min Kidney Failure
43
How can GFR be determined by a substance?
Renal clearance of a substance NEITHER reabsorbed NOR secreted by kidneys can be used to determine GFR
44
How is clearance calculated?
Excretion amount of substance (mass per minute)/ Concentration of substance in body (conc.)
45
What substance is used for good estimating GFR?
Inulin (and sinistrin) Freely filtered, Not reabsorbed nor secreted So diuretic drug would have no effect on inulin clearance
46
Why is creatinine used as a rough measure for eGFR?
Inulin administration is time consuming Creatinine is slightly secreted so eGFR is slightly higher than actual
47
How does excretion relate to filtration, reabsorption and secretion?
Filtration - reabsorption + secretion = excretion
48
What affects GFR?
age, gender, food intake, muscle mass...etc
49
What is the formula for GFR?
GFR= (urine concentration (of inulin) x urine flow)/ Plasma concentration (of inulin)
50
What are the two routes for reabsorption pathways in Renal tubule?
Transcellular route and Paracellular route
51
In which tubule does most reabsorption happen?
70% reabsorption in PCT
52
Sequence of movement in transcellular route? (think what to cross)
Transport across Apical membrane of tubule cell > Diffuse through cytoplasm > Transport across basolateral membrane > Move through interstitial fluid > Move through capillary endothelium
53
Sequence of movement through paracellular route?
Directly bypass cell via leaky tight junctions through lateral intercellular space or Transport through apical membrane > move out of cell to lateral intercellular spaces
54
What is the epithelium of all tubules in kidney except collecting duct (*not collecting tubule)?
Simple cuboidal Collecting duct has simple columnar
55
What transport mechansim for paracelullar route movement? | What substances use paracellular?
Diffusion down concentration gradient e.g. urea, Ca2+, K+...
56
What transport mechanisms for transcellular route?What substances use transcellular?
Primary active transport, secondary a.t. , facillitated diffusion, osmosis e.g. glucose, water, glucose... etc
57
Give examples of symport, antiport on the apical membrane of tubules.
Symport = same direction of transport as Na+ e.g. Glucose and Na+ Antiport: opposite direction to Na+ movement e.g. Na+/ H+ pump
58
What causes Na+ deficiency inside tubule cell and allows apical membrane secondary active transport?
Na+/K+ pump on basolateral membrane generates Na+ concentration gradient inside tubule cell
59
How does glucose move through tubule cell?
Symport at apical membrane Facillitated diffusion at basolateral membrane
60
What is the name of channels involved in glucose movement in tubule cells?
Na+/glucose cotransporter/ symport channel = SGLT2 Facil. diffusion channel/ Uniporter at basolateral membrane = GLUT2
61
What is the anitport channel on apical membrane of tubule cells ?
Na+/H+ exchanger = NHE3
62
What is the primary active transport carrier name on basolateral membrane in tubule cells?
Na+/K+ ATPase
63
What is the name of Cl-/Base exchanger on apical membrane in tubule cells?
Pendrin
64
How does DCT absorb NaCl?
absorbs NaCl mainly via an Na+-Cl- cotransporter
65
In which tubule is paracellular route observed?
PCT only
66
Is the fluid leaving PCT iso-osmotic to plasma?
Yes
67
What follows Na+ movement generated by Na+/K+ ATPase on basolateral membrane?
water
68
What is tubular transport maximum (Tm)?
For substances reabsorbed via transporters (mainly secondary active transport), the number of available carriers determines Tm
69
Relationship between concentration gradient and reabsorption rate for active transport substances?
Completely reabsorbed until all available carriers become | saturated > reach tubular maximum > no further increase in resorption even if concentration gradient increases more
70
What substances are abosorbed by secondary active transport?
Ca2+, Cl-, H+, organic solutes, phosphate
71
How does Glycosuria occur?
Amount of glucose in filtrate exceed maximum number of transporters/Transport maximum of PCT
72
How does filtration rate and conc. grad. relate?
Filtration normally increases in proportion to plasma | concentration (freely filtered)
73
Talk through processes of movement for Na+
Na+ reabsorption Apical: Facillitated Diffusion/ involved in cotransport Basolateral: Active transport with K+
74
Process of mvt. for Water
Osmosis on apical and basolateral | follows Na+
75
Process of mvt. for Ca2+
Diffusion on apical Osmosis on basolateral (Transport of Na+ creates an osmotic gradient > H2O follows (transcellular / paracellular) > leads to concentration gradient for Ca2+ > resorption of Ca2+ (transcellular)
76
Process of mvt. for Cl-?
Apical: Diffusion (mostly paracellular) Basolateral: Electrochemical gradient (with H20 and Na+)
77
Process of mvt. for K+
Reabsorption Apical: Paracellular diffusion Basolateral: Facillitated Diffusion
78
Glucose, amino acid, HPO4_ reabsorption?
Apical: Facillitated co-transport with Na+ Basolateral: Diffusion (Na+/K+ pump)
79
What is transport maximum of glucose in men and women?
Men: 375 mg/ml Women: 300 mg/ml

MBBS I CPRS (78 decks)

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