Renal Physiology ( 15% ) Flashcards

Question 1

Q

Which of the following regarding the nephron is true

The capillary endothelium has 4nm pores.
Filtration slits are approximately 8nm wide
Filtration slits formed by podocytes are closed by a thin membrane
Mesangial cells are located between the basal lamina and the podocytes.
Mesangial cells function only as flow regulation.

Answer

A

Filtration slits formed by podocytes are closed by a thin membrane

The capillary endothelium has 70-90nm pores
Filtration slits are approximately 25nm wide.
- 8nm is the maximum size of filtered particles
Mesangial cells are located between the basal lamina and the endothelium
Mesangial cells function as flow regulation, Secrete BL/ECM, and take up immune complexes

Question 2

Q

regarding the tubules of the nephron which is false

the DCT has a thick brush border
the PCT is approximately 15mm long
the collecting duct epithelium contains intercalated cells
the longest loops of henle are in juxtamedullary nephrons
the juxtaglomerular apparatus contains 3 types of cells

Answer

A

the DCT has no brush border

3 cells in the JGA are Juxtaglomerular cells, lacis cells, and macula densa

Question 3

Q

Which of the following is false regarding the renal circulation

The lymph drainage is into the superior mesenteric vein
The descending vasa recta is non-fenestrated
The pressure drop across the glomerulus is in the order of 1-3mmHg
The kidneys receive approximately 25% of CO
Renal blood flow exhibit autoregulation across a perfusion pressure range of approximately 90-220mmHg

Answer

A

The lymph drainage is into the thoracic duct

Question 4

Q

Which of the following effects on the renal blood flow is true

Increased by NA
Increased by high protein diet
Increased by angiotensin II
Decreased by ACh
Decreased by DA

Answer

A

Increased by high protein diet

increases blood flow

decreased by NA (constricts vessels)
reduced by angiotensin II (arteriolar constrictor)
increased by ACh (venodilation)
increased by DA (renal venodilation)
Prostaglandins increase cortical flow, reduce medullary.

Question 5

Q

In the normal structure of the kidney

Mesangial cells can assist in the regulation of glomerular function
Basal lamina has filtration slits of 25nm
DCT has a less obvious brush border than the PCT.
The macula densa is located in walls of the afferent arteriole near the termination of the thick ascending loop of Henle.
The collecting ducts commence at the corticomedullary junction.

Answer

A

Mesangial cells can assist in the regulation of glomerular function

podocytes have filtration slits of 25nm.
- endothelial cells have slits of 70-90nm
- functionally 8nm is the size that can pass due to negative charge inside cells
DCT has no brush border (only in the PCT)
The macula densa is located in walls of the juxtaglomerular appartus, closely related to the a**fferent arteriole, near the termination of the thick ascending loop of Henle.
The collecting ducts commence in the cortex

Question 6

Q

Renal blood flow

Glomerular capillaries drain into peritubular veins.
Renal autoregulation is prevented by denervation.
Oxygen extraction is higher in the cortex than the medulla.
Kidney’s receive approximately 15% CO.
Angiotensin II causes greater constriction of the efferent than the afferent arteriole

Answer

A

Angiotensin II causes greater constriction of the efferent than the afferent arteriole

efferent arterioles drain into peritubular veins. Glom caps drain into efferent arterioles.
Renal autoregulation is maintained in denervation.
Oxygen extraction is higher in the medulla than the cortex.
- Due to all the glomeruli, cortical blood flow is high, but as filtration is a passive process, oxygen extraction is low. The opposite applies to the medulla, which needs low blood flow to maintain its osmotic gradient, but has a high oxygen extraction
Kidney’s receive approximately 20-25% of CO

Question 7

Q

What is the GFR (ml/min) if the urinary concentration of inulin is 40mg/mL, the urinary flow rate is 60mL/h and the plasma concentration is 0.4mg/ml

0.6
2.6
100
160
1000

Answer

A

100

GFR = ([urinary] / [serum]) x flow rate

= (40 / 0.4) x 1

=100

60ml/h = 1 ml/mon

Question 8

Q

The filtration fraction of the kidney is

0.1
0.2
0.3
0.4
0.5

Answer

A

0.2

GFR/RPF

Total blood flow to kidneys 1.2-1.3L/min

RPF usually 700ml/min

GFR ~125ml/min

Question 9

Q

Which of the following would be best used for measuring GFR

Radiolabelled albumin
Inulin.
Deuterium oxide
Tritium oxide
Mannitol

Answer

A

Inulin.

Gold standard

Question 10

Q

given the following values, calculate the GFR: urine PAH 90, plasma PAH 0.3, urine inulin 35, plasma inulin 0.25, urine flow 1mL/min, Hct 40%

120
150
180
240
400

Answer

A

150

RPF = 90 / 0.3 = ~300ml/min

GFR = 35/0.25 = 140ml/min

(do not need the haematocrit as this is just used to work out the total renal blood flow - TRBF = RPF x 1 / 1-hct)

Question 11

Q

What is the clearance of a substance when its concentration in plasma is 1mg/mL, its concentration in urine is 10mg/mL and urine flow is 2mL/min

2mL/min
10mL/min
20mL/min
200mL/min
clearance cannot be determined from the information given

Answer

A

= (10 / 1) x 2

=20ml/min

Question 12

Q

Regarding filtration in the nephron which is false

Contraction of mesangial cells decreases GFR
Particles less than approx 4nm are freely filtered
Angiotensin II and vasopressin causes mesangial cell contraction
Exchange across the glomerular capillaries is diffusion not flow limited.
Albuminuria in nephritis occurs without an increase in filtration size

Answer

A

Exchange across the glomerular capillaries is flow limited.

There is little in the way to stop small particles crossing.*
Ang II and vasopressin do cause contraction - if hypotensive, want to reduce GFR to preserve BP*

Question 13

Q

regarding tubuloglomerular feedback, which is true

tends to maintain renal blood flow.
the sensor is JG cell.
operates via contraction of the mesangial cells.
acts to reduce GFR if the flow rate in the ascending loop of Henle falls
GFR is modulated via contraction or dilation of the afferent arteriole

Answer

A

GFR is modulated via contraction or dilation of the afferent arteriole

tends to maintain the salt load to the distal tubule
the sensor is Macula densa
operates via relaxation of the mesangial cells.
acts to increase GFR if the flow rate in the ascending loop of Henle falls

Question 14

Q

The juxtaglomacular apparatus

Contains macular densa cells in afferent and efferent arterioles.
Contains juxtaglomerular cells in the afferent arterioles only.
Responds to a fall in arterial pressure by increasing renin secretion
Responds to an increase in Na concentration by increasing GFR.
Releases renin which is activated by angiotensin I.

Answer

A

Responds to a fall in arterial pressure by increasing renin secretion

Contains macular densa cells in the DCT.
Contains juxtaglomerular cells in the afferent, and to a lesser extent efferant arterioles
Responds to an increase in Na concentration by d**ecreasing GFR
Releases renin which activates angiotensin

Question 15

Q

renal autoregulation

the macula densa cells sense change in afferent arteriolar pressure.
falling GFR results in feedback to decrease efferent arteriolar pressure.
falling GFR results in an increase in renin secretion from the macula densa cells.
decreased macula densa concentration of NaCl results in dilation of the afferent arteriole
decreased GFR decreases NaCl reabsorption in the ascending loop of Henle.

Answer

A

decreased macula densa concentration of NaCl results in dilation of the afferent arteriole

Hypotonic fluid -> increase filtration as likely volume overloaded

Juxtaglomerula cells sense change in afferent arteriolar pressure.
falling GFR results in feedback to increase efferent arteriolar pressure/resistence (via Ang II)
falling GFR results in an increase in renin secretion from the JG cells
decreased GFR decreases NaCl reabsorption in the PCT

Question 16

Q

With regard to tubuloglomerular feedback

The GFR increases when flow through the distal tubule increases.
The macula densa on the afferent arteriole is the sensor.
The afferent arteriole is constricted by TXA2.
It is designed to maintain Na re-absorption.
It does not operate in individual nephrons.

Answer

A

It is designed to maintain Na re-absorption.

The GFR decreases when flow through the distal tubule increases.
The macula densa in the DCT is the sensor.
The afferent arteriole is constricted by adenosine
- Increasing Na/Cl flow-> increased Na-K-ATPase activity in macula densa -> increased adenosine (due to increased ATP hydrolysis) -> Ca release from macula densa to smooth muscle -> vasoconstriction (and also reduced renin release by JG cells)
It does operate in individual nephrons - alters flow nephon to nephron (much like alveoli vary their flow depending on individual O2 concentration)

Question 17

Q

All of the following effect GFR except

Changes in renal blood flow
Urethral obstruction
Dehydration.
Oedema outside of the renal capsule
Glomerular capillary pressure

Answer

A

Oedema inside of the renal capsule

Dehydration increases plasma oncotic pressure*
Urethral obstruction increases hydrostatic pressure in bowmans capsule*

Question 18

Q

With regard to the kidney

Has optimum autoregulation over a range of 60-100mmHg.
Medullary blood flow is greater than cortical blood flow.
PGs decrease medullary blood flow
PGs increase cortical blood flow

Answer

A

PGs decrease medullary blood flow

PGs increase cortical blood flow

As per Ganongs both of these are correct

Has optimum autoregulation over a range of 90-220mmHg
Medullary blood flow is less than cortical blood flow.
- Cortical blood flow needs to be high to have enough to filter the glomeruli
- Medullary flow can be low as its actions are active (with the vasa recta etc)
- Medullary O2 consumption is higher than cortical for these reasons too.

Question 19

Q

concerning the glomerular filtration rate (GFR), it:

a. is approximately 250ml/min in an average sized normal man.
b. exceeds the clearance of a substance if there is net tubular reabsorption
c. is independent of the size of the renal capillary bed.
d. is greater for anionic than for cationic molecules of equal size.
e. is maintained despite a fall in systemic pressure below 90mmHg.

Answer

A

b. exceeds the clearance of a substance if there is net tubular reabsorption

a. is approximately 125**ml/min in an average sized normal man.
c. is dependent on the size of the renal capillary bed.
d. is less for anionic than for cationic molecules of equal size. due to the negative charge of podocytes
e. is maintained until a fall in systemic pressure below 90mmHg.

Question 20

Q

GFR:

a. Is higher per body surface area in women
b. Increases with a decrease in MAP
c. Normally 80% of filtrate is reabsorbed
d. Is accurately estimated by serum creatinine
e. Decreases with ureteral obstruction

Answer

A

e. Decreases with ureteral obstruction

a. Is higher per body surface area in men
b. decreases with a decrease in MAP
c. Normally >**99% of filtrate is reabsorbed
d. Is roughly estimated by serum creatinine as this varies based on muscle mass, age, gender etc

Question 21

Q

In the loop of Henle

Descending limb is impermeable to water
Thin ascending limb is permeable to water
Thick ascending limb is permeable to water
Fluid in the descending limb becomes hypotonic
Fluid at the top of the ascending limb is hypotonic cf plasma

Answer

A

Fluid at the top of the ascending limb is hypotonic cf plasma

Question 22

Q

With respect to tubular function

Creatinine resorption is dependent on tubular flow rates
Creatinine is secreted by the tubules
Sodium is actively transported out of the thin portion of the loop of Henle.
glucose resorption occurs by passive diffusion mainly in proximal tubules.
urine acidification does not occur in the collecting tubules

Answer

A

Creatinine is secreted by the tubules

Creatinine resorption is independent of tubular flow rates
Sodium is actively transported out of the thick portion of the loop of Henle.
glucose resorption occurs by secondary active transport mainly in proximal tubules.
urine acidification ???? occur in the collecting tubules

Question 23

Q

Regarding renal tubular function

The clearance is less than the GFR if there is tubular secretion.
The active transport of Na occurs in all portion of the tubule.
Proximal tubular reabsorptate is slightly hypotonic.
Water can leak across tight junctions back into the tubule lumen
30% of the filtered water enters the DCT.

Answer

A

Water can leak across tight junctions back into the tubule lumen

The clearance is more than the GFR if there is tubular secretion.
The active transport of Na occurs in most portions of the tubule, except the thin LoH
distal tubular reabsorptate is slightly hypotonic. Proximal tubule is isotonic
15% of the filtered water enters the DCT - the reabsorption of this remainder determines urine conc/volume

Question 24

Q

Which is false about the loop of Henle

Descending loop is permeable to water
Ascending loop is impermeable to water
Chloride is transported out of the thick part of the ascending limb
At the top of the ascending loop the tubular fluid is hypotonic
Tubular fluid is hypertonic as it enters the descending limb

Answer

A

Tubular fluid is isotonic as it enters the descending limb

Question 25

Q

With respect to the counter current system

The loops of Henle act as counter current exchangers.
Solutes diffuse out of vessels conducting blood towards the cortex
Water diffuses out of the ascending vessels.
Water diffuses into the collecting ducts.
Counter current exchange is passive and can operate even if counter current multiplication ceases.

Answer

A

Solutes diffuse out of vessels conducting blood towards the cortex

ie the ascending LoH

The loops of Henle act as counter current multipliers.
- LOH = CC multipliers. Vasa recta = CC exchangers
Water does not diffuses out of the ascending vessels, as they are Impermeable to water
Water diffuses out of the collecting ducts, assuming ADH is present
Counter current exchange is passive, but relies on CCM to set up its gradients or it ceases to function.

Question 26

Q

regarding the osmolality of renal tubular fluid it is

hypotonic in the loop of Henle.
isotonic in the PCT
hypertonic in the DCT.
hypotonic in the collecting duct. Hypotonic when it enters but then can vary
hypotonic in the PCT

Answer

A

isotonic in the PCT

hypertonic in the descending loop of Henle.
hypotonic in the DCT.
hypotonic early in the collecting duct, but if ADH is present can be very hypertonic by the end

Question 27

Q

regarding the PCT which is false

Na is co-transported out with glucose
Na is actively transported into the intracellular spaces by Na/K ATPase
The cells are characterized by a brush border and tight junctions
ADH increases the permeability of water by causing the rapid insertion of water channels into the luminal membrane.
Water moves out passively along osmotic gradients

Answer

A

ADH increases the permeability of water by causing the rapid insertion of water channels into the luminal membrane.

This occurs in the CD. PCT has aquaporin 1 in basolateral and apical membrane, and is not triggered by ADH

Question 28

Q

the thin ascending loop of Henle is

relatively permeable to water
relatively impermeable to Na
permeable to both Na and water
relatively impermeable to water
relatively impermeable to both Na and water

Answer

A

relatively impermeable to water

Reabsorbs solutes but less than thick asceding LoH i think

Question 29

Q

The thick ascending loop of Henle

Is impermeable to water
Has maximal permeability to NaCl.
Is relatively permeable to water.
Is impermeable to NaCl.
Is a site where there is no active transport of Na

Answer

A

Is impermeable to water

Thin ascending LoH has maximal permeability to NaCl
Is relatively impermeable to water.
Is somewhat permeable to NaCl.
Is a site where there is active transport of Na.

Question 30

Q

What is the osmolality of the interstitium of the tip of the papilla

200
800
1200
2000
3000

Question 31

Q

with regard to osmotic diuresis

urine flows are much less than in water diuresis.
ADH secretion is almost zero
The concentration of the urine is less than plasma.
Increased urine flow is due to decreased water resorption in the proximal tubule and loop of Henle
Osmotic diuresis can only be produced by sugars such as mannitol.

Answer

A

Increased urine flow is due to decreased water resorption in the proximal tubule and loop of Henle

urine flows are much more than in water diuresis.
ADH secretion Can approach maximal
The concentration of the urine is more than plasma
Osmotic diuresis can be produced by sugars such as mannitol, and a**ny solute that is filtered but not absorbed

Question 32

Q

During an osmotic diuresis, which is true

The concentration of sodium delivered to the loop of Henle falls
The sodium concentration in the interstitium of the PCT falls.
Increased fluid load but decreased sodium load to the DCT.
The concentration gradient in the medullary pyramid rises.
Volumes of urine are less than a pure water diuresis.

Answer

A

The concentration of sodium delivered to the loop of Henle falls

The sodium concentration in the interstitium of the PCT rises as less water is absorbed
- cf LoH and CD where the interstitial osmo falls as less Na is reabsorbed -> less osmotic gradients -> lower interstitial Na load
Increased fluid load but increased sodium load to the DCT (but reduced sodium concentration)
The concentration gradient in the medullary pyramid f**alls
Volumes of urine are more than a pure water diuresis.

Question 33

Q

Osmotic diuresis

Increased urine flow is due to decreased water reabsorption in the PCT and loops
In osmotic diuresis the amount of water reabsorbed in PCT is normal.
Na reabsorption from the proximal tubules is unaffected by osmotic load.
Medullary hypertonicity is increased.
ADH prevents the concentration of urine approaching that of plasma.

Answer

A

Increased urine flow is due to decreased water reabsorption in the PCT and loops

In osmotic diuresis the amount of water reabsorbed in PCT is reduced
Na reabsorption from the proximal tubules is impaired by high osmotic load
Medullary hypertonicity is decreased
ADH allows the concentration of urine to approach that of plasma.

Question 34

Q

regarding the bladder, which is false

there is no somatic innervation to the detrusor muscle
the reflex contraction of the detrusor usually begins at approximately 300-400mL
long term lesions of the cauda equine produce a dilated thin walled bladder
micturition is fundamentally spinal cord reflex

Answer

A

long term lesions of the cauda equine produce a dilated thin walled bladder

Initially thin walled and overfilled, but with time reflex contactions return resulting in a small hypertrophied bladder that causes dribbling of urine.*
Afferent nerve damage causes a dilated thin-walled bladder*

Question 35

Q

In micturition

Contraction of the trigone is mainly responsible for emptying of the bladder.
The relationship between bladder volume and intravesical pressure has a linear relationship.
The first urge to urinate is produced at 250mL.
Urine in the female urethra empties by contraction of the periurethral smooth muscle.
Sympathetic nerves play no role in micturition

Answer

A

Sympathetic nerves play no role in micturition

Contraction of the detrusor (circular muscle) is mainly responsible for emptying of the bladder.
The relationship between bladder volume and intravesical pressure has a linear relationship only at part Ib, which is a partially filled bladder
The first urge to urinate is produced at 350mL
Urine in the female urethra empties by gravity. In males a few contractions of bulbocavernosus is needed to empty the urethra.

Question 36

Q

In the normal bladder, micturition is

Initiated by the pelvic nerves
Co-ordinated in the lumbar portion of the spinal cord.
Initiated at a volume of 600mL.
Significantly affected by sympathetic nerves.
not facilitated at the level of the brain stem.

Answer

A

Initiated by the pelvic nerves

Co-ordinated in the sacral portion of the spinal cord.
Initiated at a volume of 350mL
Not at all affected by sympathetic nerves
Inherently a spinal reflex, but can be facilitated or inhibited at the level of the brain stem

Question 37

Q

The reabsorption of Na in the proximal tubules

Reabsorbs 80% of the filtered sodium load.
Causes increased hypertonicity.
Is powered by N/H ATPase.
Shares a common carrier with glucose.
All of the above

Answer

A

Shares a common carrier with glucose.

SGLT - secondary active reabsorption of glucose

Reabsorbs 60% of the filtered sodium load
Na reabsorption in the PCT carries water with it, so fluid remains isotonic
Na/H is a passive exchanger, utilising the conc gradient set up by Na-K-ATPase in the basolateral membranes

Question 38

Q

Which of the following is most permeable to water

Thin ascending limb of the loop of Henle
Distal convoluted tubule
Thin descending limb of the loop of Henle
Cortical portion of the collecting tubule
Thick ascending loop of Henle

Answer

A

Thin descending limb of the loop of Henle

Question 39

Q

with regard to urea

it moves actively out of the proximal tubule
it plays no part in the establishment of an osmotic gradient in the medullary pyramids.
all of the tubular epithelium is impermeable to urea except for the inner medullary portion of the collecting duct.
a high protein diet reduces the ability of the kidneys to concentrate urine.
ADH has no effect on the movement of urea across tubular epithelium.

Answer

A

Does not appear to be a correct answer

it moves passively out of the proximal tubule, by facilitated diffusion through channels
- An amount equal to that reabsorbed is secreted back into the LoH (~50% total)
it plays a large part (50%) in the establishment of an osmotic gradient in the medullary pyramids.
Urea is reabsorbed in the PCT, DCT, and primarily the CD
a high protein diet increases the ability of the kidneys to concentrate urine, as there is more urea
ADH causes increased urea reabsoprtion (increasing the concentrating ability of the kidney) by increasing the number of transporters in the CD

Question 40

Q

regarding water excretion in the kidney, which one is false

a minimum of 87% of filtered water is reabsorbed
aquaporin 2 is inserted into the luminal membrane of the collecting duct under the control of vasopressin
the DCT removes approximately 5% total filtered fluid
the thin part of the ascending loop of Henle is permeable to water
the PCT removes 60 – 70% of the filtered load

Answer

A

the thin part of the ascending loop of Henle is impermeable to water

Question 41

Q

calculate the free water clearance based on the following values. Urine flow 200mL/h, plasma osmolality 300mOsm/kg and urine osmolality 450 mOsm/kg

100 mL/h
77 mL/h
300mL/h
-77 mL/h
-100mL/h

Answer

A

Free water clearance = flow - ((urine osm x flow) / Plasma osm)

=200 - (450 x 200)/300

= 200 - (90000 / 300)

= -100ml/hr

Question 42

Q

regarding Na handling by the kidney, which is false

aldosterone acts via synthesis of new sodium channels
ANP produces a diuresis through the inhibition of Na/K ATPase
Angiotensin II acts to increase Na absorption in the PCT
PGE2 causes a natriuresis
Daily output can range from 1 – 400mEq/d

Answer

A

ANP produces a diuresis through downregulation of ENaC in the CD

Ang II increases Na-H exchanger in PCT*
Aldosterone upregulates ENaC in CD (counteracts ANP)*

Question 43

Q

Regarding the regulation of K excretion, which of the following is true

The rate of K excretion is inversely proportional to the rate of flow of tubular fluid.
K secretion is increased in conditions of alkalosis.
Hypoaldosteronism produces elevated urinary K levels.
Carbonic anhydrase inhibitors decrease the excretion of K.
Increased Na delivery to the collecting ducts leads to increased K reabsorption.

Answer

A

K secretion is increased in conditions of alkalosis.

As K is reabsorbed in the CD in exchange for H (H-K-ATPase), so in alkalosis, H+ will be reabsorbed, increasing K excretion.

The rate of K excretion is proportional to the rate of flow of tubular fluid, as rapid flow does not allow [K] to reach a value that stops secretion
Hypoaldosteronism produces decreased urinary K levels, as there is less Na-K-ATPase activty, hence less K excretion
Carbonic anhydrase inhibitors increase the excretion of K.
- CA inhibitors result in reduced H+ secretion (create an alkalotic urine/serum acidosis), with resultant increase in Na+ and K+ secretion
Increased Na delivery to the collecting ducts leads to increased K secretion.
- Potassium is secreted in CD, and increased Na delivery will likely enhance secretion as urine tubular flow will be increased

Question 44

Q

In the kidney

K is actively reabsorbed in the DCT.
K excretion is decreased when H secretion is decreased.
K does not compete with H in tubular fluid
The rate of K secretion is proportionate to the rate of flow of tubular fluid in the distal nephron
K is reabsorbed and Na secreted in DCT

Answer

A

The rate of K secretion is proportionate to the rate of flow of tubular fluid in the distal nephron

K is actively secreted in the DCT.
K excretion is increased when H secretion is decreased.
- K-H-ATPase exchanges K for H, so if the excretion of one is increased, the other will decrease
K does compete with H in tubular fluid
K is secreted and Na reabsorbed in DCT.
- Na is never excreted in the kidneys. Potassium is first absorbed along with Na, then excreted in DCT

Question 45

Q

In regards to the renal handling of Na

Na is actively transported out of all parts of the renal tubule.
Na is pumped out of the thin portion of the loop of Henle by Na/K ATPase.
The N/K ATPase extrudes 1 Na in for 1 K out of the tubular cell.
Most of the Na is actively transported out of the tubular cell into the lateral intercellular spaces
Around 60% of Na is reabsorbed back into the circulation.

Answer

A

Most of the Na is actively transported out of the tubular cell into the lateral intercellular spaces

Na is actively transported out of most parts of the renal tubule, except the thin loops
Na is not pumped out of the thin portion of the loop of Henle by Na/K ATPase, as it is not transported out of the thin loop, but also is not ‘pumped’ out, it follows a concentration gradient set up by basal Na-K-ATPase.
The N/K ATPase extrudes 3 Na out for 2K in of the tubular cell.
Around 99% (97-100% depending on aldosterone) of Na is reabsorbed back into the circulation

Question 46

Q

In the kidney

K secretion in DCT and collecting ducts mainly occur through Na dependent transport mechanism.
pH of 4.5 in the urine is the limiting pH for H secretion
for each H secreted, 2 Na ions are reabsorbed.
the H secretion in the PCT is mainly dependent on ATP driven proton pump.
the carbonic anhydrase inhibitors increase H secretion.

Answer

A

pH of 4.5 in the urine is the limiting pH for H secretion

K secretion in DCT and collecting ducts mainly occur through H+ dependent transport mechanism.
for each H secreted, 1 Na ions is reabsorbed
the H secretion in the PCT is mainly dependent on 2’ active transport (Na-H exchanger)
the carbonic anhydrase inhibitors decresases H secretion (alkaline urine, acid plasma)

Question 47

Q

In the kidney

Glucose is secreted by the collecting duct.
The renal threshold refers to glucose resorption from the urine.
Glucose is reabsorbed by 2ndary active transport
Glucose is reabsorbed in the loop of Henle
There is no glucose carrier in the kidney

Answer

A

Glucose is reabsorbed by 2ndary active transport

Glucose is absorbed by 2’ active transport in PCT (Na-glucose co-transporter)
The renal threshold refers to glucose loss from the urine
- Nick questions why this was wrong - techinically it is the threshold at which glucose cannot by reabsorped any longer. Unclear why it is wrong but I have taken a guess above.
- “RT for glucose is the plasma level at which glucose first appears in the urine in more than normal minute amounts”
Glucose is reabsorbed in the PCT
The glucose carrier in the kidney is SGLT from tubule to cell, and GLUT from cell to interstitium

Question 48

Q

With respect to filtered water by the nephron

At the end of the PCT 15% of filtered water is resorbed.
5% of filtered water is removed by the DCT
<87% of filtered water is reabsorbed when the urine volume is 23L in 24hours.
30% of filtered water is removed by the loop of Henle.
total solute excretion over 24 hours depends on the urine volume

Answer

A

5% of filtered water is removed by the DCT

At the end of the PCT 60% of filtered water is resorbed.
At least 87% of filtered water is reabsorbed when the urine volume is 23L in 24hours
15% of filtered water is removed by the loop of Henle.
total solute excretion over 24 hours is generally fairly stable, and dependent on solute load.

Question 49

Q

In the kidney

Glucose is removed from the urine by secondary active transport
100% glucose is absorbed in the DCT.
the calculated renal threshold for glucose is lower than its actual value.
phlorizin enhances glucose binding to the sodium – glucose symport
levo isoform of glucose is more efficiently transported by the sodium – glucose symport

Answer

A

Glucose is removed from the urine by secondary active transport

100% glucose is absorbed in the PCT
the calculated renal threshold for glucose is higher than its actual value.

Question 50

Q

Regarding the renal handling of sodium

80% of the total filtered sodium load is reabsorbed.
Na is actively transported out of all parts of the renal tubule except for the thin portion of the loop of Henle.
Only a minority of Na is actively transported via the lateral intercellular spaces.
Na transport is coupled to the movement of H and glucose but not to amino acids and phosphates.
The Na/H exchanges in the proximal tubule extrudes one Na for every H reabsorbed

Answer

A

Na is actively transported out of all parts of the renal tubule except for the thin descending limb of LoH

In all other places it is actively absorbed by basolateral Na-K-ATPase setting up concentration gradients that allows it to use channels (ENaCs), cotransporters (Na-K-2CL, SGLT etc), or exchangers (Na-H)

96-99% of the total filtered sodium load is reabsorbed.
a majority of Na is actively transported via the lateral intercellular spaces.
Na transport is coupled to the movement of H, glucose, amino acids, and phosphates.
The Na/H exchanges in the proximal tubule absorbs one Na for every H extruded

Question 51

Q

with respect to how sodium is handled by the kidney

is actively transported out of all parts of the renal tubule except the thick portion of the LOH.
changes in aldosterone concentration takes ~ 6 hours before an appreciable change to sodium reabsorption is noted.
increasing intracellular Ca concentration inhibits sodium reabsorption
most of the Na/H exchange by active transport is performed in the DCT.
tubuloglomerular feedback ensures a constant proportion of Na is reabsorbed for any change in the GFR

Answer

A

tubuloglomerular feedback ensures a constant proportion of Na is reabsorbed for any change in the GFR

is actively transported out of all parts of the renal tubule except the descending LoH and CD
changes in aldosterone concentration takes 30min before an appreciable change to sodium reabsorption is noted, due to non-genomic action (stimulation of Na-K-ATPase)
increasing intracellular Ca concentration inhibits sodium reabsorption
most of the Na/H exchange by active transport is performed in the PCT

Question 52

Q

Water excretion

At least 95% is reabsorbed.
50% of the filtered water is reabsorbed by the end of the PCT.
the first part of the DCT is impermeable to water
water tends to recirculate in the medullary pyramids.
decreasing the tonicity in the medulla has no effect on water excretion.

Answer

A

the first part of the DCT is impermeable to water

At least 87% is reabsorbed
65% of the filtered water is reabsorbed by the end of the PCT.
solutes tends to recirculate in the medullary pyramids, water is absorbed back into the systemic circulation
decreasing the tonicity in the medulla impairs the ability to produce concentrated urine, as concentration gradients arent as large

Question 53

Q

In the kidney Na is mostly absorbed with

HCO3
Glucose
K
Ca
Cl

Answer

A

Cl

HCO3 was given as correct but I think is wrong*
60% of Na reabsorption occurs in the PCT, as a result of Na-H exchange*
Chloride almost always follows Na shifts in order to preserve electroneutrality - this is the answer on another question which does not include HCO3 as an option*
Indirecly HCO3 is taken up, as H2O and CO2 (products of carbonic anhydrase)*

Question 54

Q

With regards to the regulation of K excretion, K is

Passively reabsorbed in the DCT.
secretion does not undergo adaptation
excretion is increased when H ion secretion is increased.
is actively reabsorbed in the PCT
excretion is independent of Na concentration in the distal tubular fluid

Answer

A

is actively reabsorbed in the PCT

Passively secreted in the DCT.
secretion does undergo adaptation, and generally matches K intake
excretion is decreased when H ion secretion is increased.
excretion is dependent on Na concentration in the distal tubular fluid - low Na reaching the distal tubule causes a reduction in K excretion.

Question 55

Q

The greatest permeability to urea is found in

Inner medullary portion of the collecting tubule
DCT
Thin descending limb of loop of Henle
Thick ascending limb of loop of Henle
Thin ascending limb of loop of Henle

Answer

A

Inner medullary portion of the collecting tubule

Absorbed by urea-channels by facilitated diffusion.*
When ADH is high, more urea is reabsorbed, creating a larger diffusion gradient to allow more absorption of water*

Question 56

Q

Regulation of potassium excretion in the kidney involves:

a. Secretion by proximal tubule cells
b. Exchange with Na+ on the tubular side via an active pump
c. Passive reabsorption in the ascending limb of the loop of Henle
d. Active reabsorption in the proximal tubules
e. Active exchange with Ca2+ via a K+/Ca2+ exchange

Answer

A

d. Active reabsorption in the proximal tubules

a. Secretion by distal tubule cells
b. Exchange with Na+ on the interstitial side via an active pump
c. active reabsorption in the proximal tubules
e. ???Active exchange with Ca2+ via a K+/Ca2+ exchange

Question 57

Q

Sodium reabsorption in the kidney is:

a. Actively transported in the thin portions of the loop of Henle
b. Coupled to the movement of glucose and amino acids in the distal tubule
c. Decreased by atrial natriuretic peptide
d. Reabsorbed against its concentration gradient
e. Independent of chloride absorption

Answer

A

c. Decreased by atrial natriuretic peptide

a. Actively transported in the thin portions of the loop of Henle
b. Coupled to the movement of glucose and amino acids in the proximal tubule
d. Reabsorbed down its concentration gradient
e. Dependent on chloride absorption - Na-2Cl-K cotransporter in Thick ascending limb, and Na-Cl CT in the DCT

Question 58

Q

In the distal tubular cells:

a. K+ secretion is mainly by active transport mechanisms
b. K+ secretion is decreased in acidosis
c. K+ secretion is increased when Na+ delivery to the tubule is decreased
d. Loop diuretics will cause decreased K+ secretion
e. K+ is reabsorbed by the Na+/K+/2Cl- transporter

Answer

A

b. K+ secretion is decreased in acidosis

As K is reabsorbed in the CD in exchange for H via the K-H-ATPase

a. K+ secretion is mainly by passive transport mechanisms (though this seems to happen more in the CD than DCT)
c. K+ secretion is reduced when Na+ delivery to the tubule is decreased
????d. Loop diuretics will cause ??? K+ secretion as they inhibit the Na-K-2Cl cotransporter, leading to more K+ in the urine, and this can lead to a hypokalaemia (and H+ retention)
e. K+ is reabsorbed by the Na+/K+/2Cl- transporter - this occurs in the Thick ascending LoH

Question 59

Q

With regard to osmotic diuresis

a. Urine flows are much less than in a water diuresis.
b. Vasopressin secretion is almost zero.
c. The concentration of the urine is less than plasma.
d. Increased urine flow is due to decreased water reabsorption in the proximal tubule and loop of Henle
e. Osmotic diuresis can only be produced by sugars such as mannitol.

Answer

A

d. Increased urine flow is due to decreased water reabsorption in the proximal tubule and loop of Henle

a. Urine flows are much more than in a water diuresis.
b. Vasopressin secretion is Normal / elevated (cf water diuresis, where it is almost zero)
- Body is trying to retain water but unable to overcome the osmotic gradient produced by the osmotic agent
c. The concentration of the urine is the same as plasma.
- Water diuresis the urine concentration is lower (osmotic diuresis is due to osmotically active agent in the urine)
e. Osmotic diuresis can be produced by sugars such as mannitol, as well as by NaCl, glucose

Question 60

Q

With regard to the effects of hormones on the renal tubules, which is correct

Aldosterone increases K reabsorption from the distal tubule.
Angiotensin II increases H secretion from the proximal tubule
ADH increases water reabsorption in the PCT.
ANP decreases Na reabsorption from the PCT.
PTH increases PO4 reabsorption.

Answer

A

Angiotensin II increases H secretion from the proximal tubule

By upregulating Na-H exchanger

Aldosterone increases K secretion from the distal tubule.
- Stimulates Na-K-ATPase
ADH increases water reabsorption in the CD
ANP decreases Na reabsorption from the CD
- ANP / ADH have opposing actions in the CD
PTH increases PO4 Excretion

Question 61

Q

What factor decreases renin secretion

Hypovolaemia
Supine position
Cardiac failure
Na depletion

Answer

A

Supine position

The others all create a low BP or low Na state, where not enough Na is getting to the macula densa

Question 62

Q

With regard to the renin-angiotensin system

Prorenin has 50% the activity of renin
Renin secretion will be increased by propranolol.
Angiotensinogen is synthesised by the liver
Angiotensin I in a potent vasodilator
Angiotensin II acts at receptors in the nucleus

Answer

A

Angiotensinogen is synthesised by the liver

Prorenin has essentially no biologic activity
Renin secretion will be decreased by propranolol, as it blocks symp nerves
Angiotensin I is essentially inert
Angiotensin II acts at GPCR receptors

Question 63

Q

ANP

Stimulates the secretion of vasopressin.
Secretion will be decreased by scuba diving
Is a typical dual chain helix structure
Stimulates EPO production
Has generally the opposite action to angiotensin II

Answer

A

Has generally the opposite action to angiotensin II

Inhibits the secretion of vasopressin.
- Vasopressin wants to conserve fluid, ANP lose it
Secretion will be increased by scuba diving, as increased pressure outside the body causes an increase in venous pressure -> increased atrial stretch -> ANP
Pretty sure its mainly hypoxia that Stimulates EPO production

Question 64

Q

Renin secretion is increased by

High Na and Cl reabsorption across the macula densa
Increased afferent arteriole pressure
Prostaglandins
ADH
Angiotensin II

Answer

A

Prostaglandins

(as well as sympathetic nerve activity and catecholamines)

Others all reduce it

Answer 64

A

Carbamazepine

ADH promote water retention.*
Increase: Standing, Angiotensin II, exercise/stress/pain, decreased ECF volume, N+V, increased plasma oncotic pressure*
Decrease: Alcohol, increased ECF volume, decreased plasma osmo*

Answer 65

A

Production is inhibited by Theophylline

Produced in the kidney*
Increases RBC by increasing the number of stem cells*
Causes RBC increase in 2-3 days*
Inactivated in the liver.*

Answer 66

A

Inhibits the secretion of ADH

Aims to reduce systolic BP
Increases the responsiveness of vascular smooth muscle to dopamine??

Answer 67

A

Prostaglandins increase the secretion of renin

As do sym nerve activity and catecholamines

Renin causes (via Ang I) Ang II to releases aldo
Angiotensinogen is converted to angiotensin I by renin in the circulation.
- Ang I -> Ang II via ACE in the lungs
Increased Na reabsorption at the macula densa causes decreased renin
Oestrogens ?increase production of angiotensinogen

Answer 68

A

ANP has the greatest affinity for the ANPR-_A_ receptor on the glomerulus

Answer 69

A

Ammonia

“In chronic acidosis, glutamine synthesis in the liver is increased, using some NH4 which is usually converted into urea, and the glutamine provides the kidneys with another source of NH4”

Acutely, the major buffer systems in the urine (and CSF) are bicarbonate and phosphate.

In respiratory acidosis, the renal compensation is through HCO3 (increasing intracellular PCO2 -> increased H+ secretion due to increased intracellular CA activity, which then combines with HCO3 in the tubule to H2CO3 -> H20 + CO2 via tubular CA)

In metabolic acidosis the buffer systems of HCO3-, NH3-, and HPO4- are used for compensation (otherwise the urine pH would quickly reach 4.5 and no further H+ could be secreted)

Answer 70

A

Partly compensated metabolic acidosis

Slightly acidotic so not completely compensated, but CO2 is reduced in an acidosis so is attempting compensation.

Answer 71

A

Ca

pCO2 - increases due to increased intracellular CA activity -> more H+ to secrete
K - Hypokalameia -> intracellular acidosis (H+ moves intracellularly to compensate for reduced K+), which leads to more H+ excretion
Carbonic anhydrase - inhibition reduces secretion, as less H+ can be produced intracellularly (also increases HCO3 excretion)
Aldosterone - increases activity of H+-ATPase in the DCT to increase excretion.

Answer 72

A

High pH, low HCO3 and PaCO2

Uncompensated respiratory alkalosis = pH >7.45, pCO2 low, bicarb normal/low

Low CO2 -> low intracellular levels -> less CA activity to convert H20 and CO2 into H+ + HCO3, so there is less H+ excretion and hence less HCO3 reabsorption, further lowering the already low biarb. This helps to reduce the pH towards normal.

Answer 73

A

For each H+ secreted in the PCT, one Na and one HCO3 enters the interstitium

H+ is secreted in the PCT via Na/H exchange
- In the DCT it is an ATPase
I cells in the collecting duct actively excrete acid
The limiting urine pH is approximately 4.5
Carbonic anhydrase in thePCT luminal membrane facilitates H+ buffering and the formation of H2CO3
- Then H2CO3 -> H20 + CO2 which diffuse into cells

Answer 74

A

Carbonic anhydrase inhibitors

Reduces H+ excretion, and creates a metabolic acidosis

Answer 75

A

ADH

Hypokalaemia -> increased H+ excretion*
Increased CO2 -> increased excretion*
CA inhibiton -> Decreased excretion*
Aldosterone -> increased excretion (increased ATPase in DCT)*

Answer 76

A

the most effective buffers have pK values close to the pH of the environment they operate in

The closer to the pK, the more they can buffer without a change in pH

RBC, kidneys, and lungs are rich in carbonic anhydrase
Deoxyhaemoglobin is better buffer than oxyhaemoglobin.
- Thus once Hb has offloaded O2 into the tissues, it is better able to buffer products of metabolism etc on the way back to the lungs
Phosphate is an important buffer in intracellular fluid, along with protein.
- Blood buffers are bicarb, protein and Hb. Bicarb is an interstitial buffer
Metabolic acidosis buffering load is 20% in ECF, 80% ICF.
- For metabolic alkalosis, the ratio is closer to 1:2 (ECF:ICF)

Answer 77

A

Base excess is positive

Because there is more base than acid (hence the alkalosis)

the ingestion of aspirin causes a metabolic ACIDOSIS - (Fixed acid)
Respiratory compensation cant restore pH to normal
- There is only so much hypoventilation possible before hypoxia stimulates respiratory drive.
Treatment with NaHCO3 will make this worse, as it is a weak base itself
There is less renal excretion of H ions, as the body wants to conserve acid

Answer 78

A

Reduction in the pCO2 of alveolar gas

Fall in pH is not compensatory, it is the thing.*
There will be increased CO2 production likely (increased H+ + HCO3-) to try and remove H+*
Minute volume will increase to remove CO2*
Urine will be acidic as the body excretes acid*

Answer 79

A

Dibasic phosphate plays a role in buffering in the distal tubule and the collecting ducts

Adds H+ to become monobasic phosphate

Carbonic anydrase in the PCT increases the buffering capacity.
The conversion of glutamine to glutmate in the renal tubular cells provide NH3 for buffering.
The largest pH difference between the tubular cells and the lumen occurs across the DCT or CD
The HCO3- content of the urine increases with serum HCO3 concentrations above 28mmol

Answer 80

A

In a few days time they would compensate by lowering HCO3 concentrations

Acute uncompensated respiratory alkalosis, will be compesated with a metabolic acidosis

Answer 81

A

Diphosphate

As well as protein*
ECF = bicarbonate*
Blood = bicarb, protein, Hb*

Answer 82

A

Respiratory compensation in metabolic alkalosis is limited by carotid and aortic chemoreceptor response.

Hypoventilation to compensate for alkalosis can not go so far as to cause hypoxia

HCO3 concentration will increase in compensated respiratory acidosis, as HCO3 is absorbed in exchange for H+ secretion
The rate of renal H secretion increases due to increasing pCO2 in respiratory acidosis.
Cl excretion is increased in respiratory acidosis
Hepatic glutamine synthesis is increased in chronic metabolic acidosis, t**o produce more NH4+ and HCO3- to act as buffers

Answer 83

A

HCO3 reabsorption depends upon the rate of H secretion by the renal tubular cells

The rate of HCO3 reabsorption is proportional to the arterial pCO2 - increased pCO2 -> increased HCO3 reabsorption/H+ excretion
In respiratory acidosis, HCO3 reabsorption is Increased (see above)
Changes in plasma Cl concentration are ?inversely proportional to HCO3 concentrations
In respiratory alkalosis, renal H secretion is Decreased

Answer 84

A

HCO3

ICF = protein + phosphate*
Plasma = protein, bicarb, Hb*

Answer 85

A

It consists mostly of HPO42-, SO42- and organic acids.

Increases with increasing negative charge (eg proteins), decreasing positive charge (eg Ca/Mg), or organic anions such as lactate are present (eg lactic acidosis, ketoacidosis)

It is the difference between cations other than Na and anions other than Cl and HCO3
It is normal in hyperchloraemic acidosis secondary to ingestion of NH4Cl, as the Cl is measured in the AG
It is increased when Ca/Mg is decreased
It is increased when the albumin is increased

Answer 86

A

10

pKa of HCO3 is 6.1. At this level HCO3 = carbonic acid. An increase of 1 equates to a 10-fold increase in HCO3 (more basic = more bicarb)

Answer 87

A

carbonic anhydrase inhibitors

Inhibit CA in the cells -> less H+ secretion, so there is less exchange with K+ so it is excreted*
diuretics cause a hypokalaemic metabolic alkalosis (this happens because there is increased Na delivery to the DCT, increasing aldosterone stimulation of the Na-K-ATPase, which acts to increase Na reabsorption in exhange for K and H secretion)*

Answer 88

A

Fruit.

Mainly alkali load

CRF causes an acid load by ????

Answer 89

A

0.00004meq/L

4 zeroes and then a 4

Answer 90

A

Diuretic use

Carbonic anhydrase inhibition -> Hypokalaemic metabolic acidosis (due to incresased HCO3 loss in urin, and reduced H+ secretion -> increased K+ excretion )

Chronic diarrhea -> Hypokalaemic acidosis due to K and HCO3 loss in the stools

Answer 91

A

e. Secondary active transport mechanism operates in distal tubule

DCT H+ loss is due to an ATPase (stimulated by aldosterone)

a. Acetazolamide decreases tubular secretion (by reducing the formation of H2CO3 in the lumen -> increased HCO3 loss)
b. Aldosterone increases distal tubular secretion (see above)
c. Much more acid secretion occurs in proximal than distal tubule (due to Na-H exchanger)
d. Lowest tubular fluid pH achievable is 4.5 (hence buffering needed)

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Renal Physiology ( 15% ) Flashcards

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