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Renal Week 2 2017/18 > 1: Physiology 4 & 5 > Flashcards

1: Physiology 4 & 5 Flashcards

1
Q

Where does the majority of reabsorption occur?

A

Proximal tubule

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2
Q

What is a normal healthy GFR?

A

125 ml/min

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3
Q

Why is reabsorption specific?

A

Specific transport proteins

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4
Q

What is the osmolarity of the fluid at the start of the proximal tubules compared to that at the end?

A

The same

no change in osmolarity

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5
Q

Which process mainly occurs in the proximal tubule?

A

Reabsorption

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6
Q

Does secretion occur in the proximal tubule?

A

Some secretion

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7
Q

By which two means can substances be reabsorbed into peritubular capillaries?

A

Transcellular (through cell membranes)

Paracellular (through tight junctions)

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8
Q

What is primary active transport?

A

Energy used to transport a substance against its concentration gradient using a carrier

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9
Q

What is secondary active transport?

A

Active transport of a substance by carriers COUPLED to the concentration gradient of another ion

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10
Q

Secondary active transport usually occurs using the concentration gradient of which ion?

A

Sodium

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11
Q

What is facilitated diffusion?

A

Passive transport WITH A CARRIER

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12
Q

Where is 2/3rds of filtered sodium reabsorbed?

A

Proximal tubules

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13
Q

Where are NaKATPases found on the tubular cells of the proximal tubules?

A

Basolateral

empties into capillaries

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14
Q

What is the function of NaKATPases on the basolateral membrane of the tubular cells?

What does this achieve?

A

Active transport of 3 Na OUT and 2 K IN

Maintains concentration gradient of sodium

So it can diffuse in (be reabsorbed) at the apical membrane

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15
Q

Where do sodium ions go once they have been secreted OUT of tubular cells by NaKATPase?

A

Peritubular capillaries

leaving conc gradient from filtrate to tubular cells

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16
Q

The transport of sodium from the filtrate to the capillaries sets up which types of gradient?

A

CONCENTRATION GRADIENT FOR SODIUM (so more is reabsorbed from proximal tubules)

OSMOTIC GRADIENT FOR WATER (following sodium)

ELECTROCHEMICAL GRADIENT FOR CHLORINE (so it’s reabsorbed by the PARACELLULAR route)

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17
Q

By which routes are sodium and chlorine reabsorbed?

A

Sodium - transcellular

Chlorine - paracellular

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18
Q

Why doesn’t the osmolarity of the proximal tubules decrease as you go along?

A

Water and salt reabsorbed equally

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19
Q

By which means does glucose leave proximal tubules?

A

Co-transport with sodium (SGLT2)

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20
Q

How does glucose leave the tubular cells by the basolateral membrane?

A

FACILITATED DIFFUSION down its concentration gradient

GLUT2?

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21
Q

How does water follow sodium and glucose into the peritubular capillaries?

A

Paracellular reabsorption

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22
Q

Which two substances are reabsorbed via the paracellular route?

A

Water

Chloride ions

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23
Q

What proportion of glucose is reabsorbed in the proximal tubules?

A

100% normally

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24
Q

What is the equation for rate of filtration?

A

Rate of filtration = [substance]plasma x GFR

25
Q

Does the rate of reabsorption of glucose increase in proportion with its rate of filtration?

A

Yes, up to the point where all the carriers are saturated

26
Q

Which transporter is saturated when the rate of filtration of glucose is too high?

A

SGLT2

co-transporter

27
Q

Which rate starts to increase if you pass the maximum rate of reabsorption of glucose?

A

Rate of excretion

glycosuria

28
Q

What is the TM of glucose?

A

Transport maximum of glucose

RATE OF FILTRATION AFTER WHICH YOU START TO EXCRETE GLUCOSE

2 mmol/min

29
Q

What is the

a) rate of filtration
b) plasma concentration

of glucose after which you start to get glycosuria?

A

a) 2 mmol/min, transport maximum

b) Around 12 mmol/L

30
Q

After you reach the transport maximum for glucose, glucose is excreted by the kidneys, producing which sign?

A

Glycosuria

31
Q

What value is

a) inulin/creatinine
b) PAH

used to determine?

A

a) GFR (because their clearance = GFR)

b) Renal blood flow (because its clearance = RBF)

32
Q

100% of which substances are reabsorbed in the proximal tubules?

A

Glucose

Amino acids

33
Q

What is the osmolarity of the proximal tubules all the way along it?

Why?

A

300 mosmol/L

Same volumes of water and NaCl reabsorbed, so osmolarity doesn’t change

34
Q

What are the two parts of the Loop of Henle?

A

Descending limb

Ascending limb

35
Q

What is the function of the Loop of Henle?

A

Generates solute concentration gradient between the renal cortex and medulla

36
Q

The Loop of Henle allows for the production of (hypertonic / hypotonic) urine which is (dilute / concentrated) in solute.

A

hypertonic

high solute concentration (concentrated)

37
Q

What process occurs in the Loop of Henle to produce concentrated urine?

A

Countercurrent multiplication

38
Q

Which blood vessel, found in juxtamedullary nephrons, help concentrate the urine along with the Loop of Henle?

A

Vasa recta

39
Q

What is reabsorbed in the descending limb of the Loop of Henle?

A

WATER

NOT NaCl

40
Q

What is reabsorbed in the ascending limb of the Loop of Henle?

A

NaCl

NOT WATER

41
Q

The descending limb reabsorbs ___.

The ascending limb reabsorbs ___.

A

descending limb = WATER

ascending limb = NaCl

42
Q

What transporter is found at the basolateral membrane of every cell in the body?

A

NaKATPase

43
Q

Which transporter, found on the luminal membrane of the cells of the ascending limb, transports ions across the membrane?

A

Na-K-2Cl co-transporter

44
Q

Does water follow salt into the tubular cells in the ascending limb?

A

No

Can’t, tight junctions won’t let it through

45
Q

What ions are absorbed into the interstitial fluid, then the capillaries at the ascending limb?

A

Na

Cl

46
Q

Which drugs block the triple transporter in the ascending limb?

A

Loop diuretics

e.g furosemide

47
Q

As a result of the action of the triple transporter and NaCl reabsorption in the ascending limb, what happens to the osmolarity of the ascending limb?

A

Osmolarity decreases

48
Q

Interstitial fluid osmolarity (increases / decreases) as a result of NaCl reabsorption by the ascending limb.

A

increases

49
Q

What happens when osmolarity of a compartment increases?

A

Osmosis of water from another compartment

50
Q

As a result of osmosis into the interstitial space from the DESCENDING LIMB, what happens to the descending limb’s osmolarity?

A

Increases

runs round into ascending limb, NaCl reabsorbed, ascending limb’s osmolarity decreases, interstitium’s osmolarity increases so water reabsorbed from descending limb, descending limb’s osmolarity increases…

accumulates and accumulates, concentrating tubular fluid many many times

51
Q

What process occurs in the Loop of Henle?

A

Countercurrent multiplication

Distal tubule’s fluid has a much higher osmolarity compared to proximal tubule

Establishes concentration gradient between cortex and medulla

52
Q

What three substances contribute to the concentration gradient between the renal cortex and medulla?

A

Water

NaCl by countercurrent multiplication in Loop of Henle

Urea recycling

53
Q

Which part of the kidney has the higher osmolarity?

A

Renal medulla

where countercurrent multiplication occurs

54
Q

Which hormone requires there to be a concentration gradient between the renal cortex and medulla?

A

ADH

55
Q

What is the purpose of ADH?

A

Controls water concentration by changing permeability of collecting ducts to water

Altering urine output and concentration

Allowing kidneys to produce hypertonic, concentrated urine if dehydrated or hypotonic, dilute urine if overloaded

56
Q

Keeping in mind the osmolarities of the renal cortex and medulla, what happens to the osmolarity of the vasa recta as it goes

down into the medulla

back up into the cortex?

A

down - osmolarity INCREASES (water diffuses out down conc gradient, solute diffuses in down conc gradient)

up - the opposite, as osmolarity of interstitium DECREASES going back up to cortex

57
Q

How is the vasa recta adapted so it doesn’t take up solute and urea and wash it out of the adrenal medulla?

A

Hairpin loops

Endothelium is freely permeable to NaCl and H20

Low volume blood flow

58
Q

What two structures maintain the concentration gradient between the renal cortex and medulla?

A

Loop of Henle (via countercurrent multiplication and urea cycle)

Vasa recta

Renal Week 2 2017/18 (11 decks)

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