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Renal > 1.8: Physiology 4 > Flashcards

1.8: Physiology 4 Flashcards

1
Q

Name the parts of the nephron?

A

Glomerulus

Bowman’s Capsule

Proximal Convoluted Tubule

Loop of Henle (Descending and Ascending Limbs)

Distal Convoluted Tubule

Collecting Duct

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2
Q

Where does the majority of reabsoption occur?

A

Mainly in the proximal conovluted tubule

Although it occurs along the length of the nephron

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3
Q

Why do we need reabsorption?

A

The entire plasma volume is filtered about 65 times a day

Reabsorption is vital to retain important fluids and electrolytes while also removing waste products and toxins

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4
Q

How much of each substance do the kidneys reabsorb:

  • Fluid?
  • Salt?
  • Glucose?
  • Amino Acids
  • Urea
  • Creatinine (Explain this one)
A

Fluid = 99%

Salt = 99%

Glucose = 100%

Amino Acids = 100%

Urea = 50%

Creatinie = 0% (It is all filtered hence why it can be used as a measure of GFR)

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5
Q

Match the mechanism to the description:

  • Reabsorption
  • Filtration

A) Very specific

B) Non specific

  1. Active
  2. Passive
A

Reabsorption = Very specific and active

Filtration = Non specific and passive

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6
Q

Describe the glomerular filtrate?

A

This is just a modified filtrate of blood

Contains fluid and salts in relatively the same concentration as plasma

Contains no RBC or plasma proteins

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7
Q

What is the glomerular filtration rate?

(The figure, not a description)

A

125ml/min

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8
Q

Approxiamtely, what is the rate of fluid reabsorption in the proximal tubule?

What is the rate of filtrate entering the loop of Henle?

A

Reabsorption = 80ml/min

Entering loop of henle = 45ml/min

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9
Q

Describe the osmolarity of the fluid reabsorbed from the proximal tubule?

A

It is iso-osmotic with the filtrate

Water and salts are re-absorbed in equal properties

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10
Q

List some substances that are:

  • Re-absorbed in the proximal tubule?
  • Secreted in the proximal tubule?
A

Re-absorbed: Glucose, amino acids, phosphate, sulphate, lactate

Secreted: Acetylcholine and noradrenaline (neurotransmitters), drugs, H+, uric acid, toxins

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11
Q

What are the two types of reabsorption?

A

Transcellular

Paracellular

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12
Q

Describe the barriers to transcellular reabsorption?

A

Apical Membrane

Cytoplasm

Basolateral Membrane

Interstital Fluid

Capillary Wall (Endothelium)

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13
Q

Describe paracellular reabsorption?

A

Ajacent epithelial cells have ‘tight junctions’

These can be ‘leaky’ - this determines how much paracellular reabsorption occurs

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14
Q

Describe the types of carrier-mediated membrane transport?

A
  • Primary Active Transport

(Hydrolyses of ATP required for energy, moves a solute against its concentration gradient)

  • Secondary Active Transport

(Molecule is transported coupled to an ion which moves along its concentration gradient)

Faciliated Diffusion

  • Membrane transport proteins help move a substance down an already existing concentration gradient
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15
Q

Name all the ways molecules can move transcellularly

A
  • Diffusion through channels
  • Diffusion across membrane
  • Faciliated Diffusion
  • Primary Active Transport
  • Secondary Active Transport
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16
Q

Where is the sodium/potassium pump found?

A

At the basolateral membrane of epithelial cells

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17
Q

What kind of transporter is the sodium potassium pump?

Describe how it works?

A

This is a primary active transporter

This means it requires energy to work

For every molecule of ATP that is hydrolysed, it exports 3 sodium ions and imports 2 potassium ions (2-K-IN)

Moves ions against their concentration gradient

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18
Q

Sodium leaves the tubular epithelial cells via the basolateral sodium/potassium pump. How does it cross the apical membrane?

A
  1. Sodium dependent glucose transporter
  2. Sodium/Hydrogen antiporter
  3. Sodium Dependent Amino Acid Transporter
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19
Q

Give a summary of sodium reabsorption?

A

Crosses the apical membrane via 3 transporters (Sodium dependent glucose transporter, sodium/H+ antiporter, sodium dependent amino acid transporter
Leaves the basolateral membrane in the sodium/potassium pump

This is an example of the TRANSCELLULAR ROUTE

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20
Q

Describe the effect of sodium reabsorption on chloride and water?

A

When sodium is reabsorbed, it sets up an electrochemical gradient (Na+)

This causes Chloride to move across the epithelial cells by the PARACELLULAR route

Sodium and chloride set up an osmotic gradient

Water moves down the gradient

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21
Q

Explain why water and sodium chloride reabsorption at the proximal tubule is in the same amounts?

A

Sodium is uptaken actively

Chloride follows due to electrochemical gradient

Water then follows the sodium and chloride down the osmotic gradient

Salt reabsorption drives water reabsorption

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22
Q

Describe glucose reabsorption in the proximal tubule?

A

100% of glucose that has been filtered is reabsorbed here

Crosses the apical membrane at the sodium dependent glucose transporter

Leaves the basolateral membrane by faciliated diffusion (down the gradient)

Glucose reabsorption sets up an osmotic gradient and causes water reabsorption

23
Q

Describe how glucose is moved across the epithelial cells?

Why is there a limit to how much glucose can be moved in unit time?

A

It is moved by membrane transport proteins

For these proteins to transport and release glucose, they must undergo conformational changes

This means only so much glucose can be moved in unit time - as the conformational changes take time to occur

24
Q

Describe the relationship between rate of filtration and concentration of glucose?

Describe the relationship between concentration and rate of reabsorption?

A

As the concentration increases, the rate of filtration increases

As the concentration increases, the rate of reabsorption increases until a point. After this point, there is a plateau in the amount of glucose being re-absorbed

This is because the transport proteins have been saturated.

This is called the transport maximum

25
Q

Describe the transport maximum?

Give a value?

A

As concentration of glucose increases, rate of reabsorption also increases until a point. After this, glucose reabsorption plateaus.

This is because the transport mechanisms are saturated and no more glucose can be physically moved

This point is called the ‘transport maximum’

The transport maximum is at about 2mmol/min

26
Q

Describe the transport maximum in relation to diabetes?

A

In uncontrolled diabetics, the blood glucose is very high

This is above the renal threshold

The kidneys are unable to re-absorb anymore glucose as the transport mechanisms are saturated

The transport maximum has been reached

The rest of the glucose is therefore excreted in the urine

27
Q

Fill in the blanks:

  • About 2/3rds of all salt and water reabsorption occurs in the…?
A

About 2/3rds of all salt and water reabsorption occurs in the proximal convoluted tubule

28
Q

Fill in the blanks:

  • All sugar and amino acid re-absorption takes place in the…?
  • Sodium reabsoprtion is driven by the sodium-potassium pump in the….?
A

All sugar and amino acid re-absorption takes place in the proximal convoluted tubule

Sodium reabsorption is driven by the sodium potassium pump in the basolateral membrane

29
Q

Fill in the blanks:

Sodium reabsoprtion, by the …. pathway, also drives chloride reabsorption by the …. pathway.

Water is re-absorbed by osmosis in the … pathway.

A

Sodium reabsorption, by the transcellular pathway, also drives chloride reabsorption by the paracellular pathway

Water is reabsorbed by osmosis in the paracellular pathway

30
Q

The reabsorption mechanisms (eg: For glucose) can become saturated.

The secretory mechanisms (Eg; for PAH) can ALSO become saturated.

True or false?

A

TRUE

It isn’t just the mechanisms for reabsorption that can become saturated - the secretory mechanisms can also become saturated.

31
Q

When tubular fluid leaves the proximal tubule it is:

A) Hypo-osmotic

B) Hyper-osmotic

C) Iso-osmotic

?

A

When tubular fluid leaves the proximal tubule it is

ISO-OSMOTIC

(Approx. 300mosmol/l)

32
Q

What is the function of the loop of Henle?

A

To create a cortico-medullary solute concentration gradient

This refers to the interstitial fluid

This allows for the formation of hypertonic urine (very concentrate)

33
Q

Which nephron is used to produce concentrate urine?

A

Juxtamedullary Nephron

34
Q

What is the osmolarity of the filtrate in the proximal convoluted tubule?

What is the osmolarity of the intersitital fluid surronding the proximal convoluted tubule?

This means the filtrate is …. with it’s surrondings.

A

The filtrate of proximal convoluted tubbule = 300mosmol/l

The intersitial fluid around proximal convoluted tubule = 300mosmol/l

This means the filtrate is ISO-OSMOTIC with its surrondings

35
Q

What is the difference in osmolarity between the filtrate and the interstitial fluid around the ascending limb of the loop of henle?

What is the difference in osmolarity between the filtrate and interstitial fluid around the descending limb of the loop of henle?

A

Difference of 200mosmol/l

Difference of 0 mosmol/l

36
Q

Describe salt and water in the descending limb of the loop of Henle?

Describe salt and water in the ascending limb of the loop of Henle?

A

Descending:

  • Does not reabsorb salt
  • Highly permeable to water

Ascending:

  • Does reabsorb salt
  • Highly impermeable to water
37
Q

Describe sodium and chloride reabsoption in the ascending limb?

A

Passive in thin ascending limb (posh)

Active in thick ascending limb (becks)

38
Q

What is countercurrent flow?

A

This is opposing flow in the two limbs of the loop of Henle

39
Q

How is sodium and chloride reabsorbed in the thick ascending limb of the loop of Henle?

An osmotic gradient is set up but water does not enter. Why?

A

This is done by the potassium, sodium, chloride co-transporter (triple transporter)

Active transport

The tight junctions in this region are very tight and the membrane is impermeable to water

40
Q

Describe the net movement of:

  • Sodium
  • Chloride
  • Potassium
  • Water

At the thick ascending limb of the loop of Henle?

A

Sodium moves from tubular fluid to interstitial fluid

Chloride moves from tubular fluid to interstitial fluid

Potassium is recycled back into the tubular fluid

Water does not enter the epithelium (impermeable membrane) so not net movement

41
Q

Describe the action of loop diuretics?

A

These inhibit the action of the triple co-transporter at the apical membrane of the ascending limb

42
Q

In the steady state, there is a concentration gradient in the Loop of Henle. Describe the concentration gradient?

A

Concentration gradient from the cortex to the medulla

(Most concentrated filtrate at the bottom of the loop)

43
Q

Describe the osmolarity of the fluid entering the loop of henle?

Describe the osmolarity of the fluid leaving the loop of henle?

A

Iso-osmotic enters (300mosmol/l)

Hypo-osmotic leaves (100mosmol/l)

44
Q

Describe how the concentration gradient of the loop of henle is set up?

A

Solute is pumped out of the tubular filtrate of the ascending through the triple co-transporter

This leaves diluted tubular fluid and concentrated interstitial fluid

Water moves from the tubular fluid of descending limb into interstitial fluid to dilute it

Tubular fluid moves round loop of henle - water removed from descending, salt removed from ascending

45
Q

Describe how the fluid entering the loop of Henle is modified (give the osmolarities) all the way until it leaves the loop of Henle?

A

Enters from proximal tubule

  • 300mosmol/l

Moves down the descending tubule where water is removed into the interstital fluid

  • Osmolarity increases from 300mosmol/l up to 1,200 mosmol/l at the very bottom of the top

Moves into the ascending tube where salt is removed into interstitial fluid

  • Osmolarity decreases from 1,000mosmol/l to 100mosmol/l

100mosmol/l tubular fluid enters distal tubule

46
Q

Urea contributes to approximately half of the ……. gradient?

A

Urea contributes to approx half of the corticomedullary concentration gradient

47
Q

Describe the movement of urea?

A

Urea comes out of the end of the distal tubule

Some passively moves into Loop of Henle

None moves passively into distal tubule as it is not permeable

Collecting duct absorbs about 50% of urea (controlled by ADH)

48
Q

Describe countercurrent flow?

A

The opposing limbs of the loop of henle (ascending and descending) are flowing in opposite directions

This is countercurret flow

49
Q

What is countercurrent multiplication?

Why do we have this?

A

Sets up a concentration gradient

There is active transport of ions from ascending limb to medulllary interstitial fluid

This concentrates the medullary interstitial fluid

This causes passive movement of water from descending into medullary interstital fluid

This allows different volumes and concentrations of urine to be produced depending on amount of antidiuretic hormone (ADH)

50
Q

What’s the normal amount of urine produced per minute?

What are the extremes?

A

1ml/min

0.3ml-25ml/min

51
Q

What type of Nephrons is the vasa recta found in?
Describe its interaction with the interstital fluid as it:

  • Dips into medulla?
  • Comes back into cortexz?
A

Juxtamedullary

The blood of the vasa recta equilibrates with the interstitial fluid

  • Increased osmolarity as it dips (Water loss, salt gain)
  • Decreased osmoalrity as it rises (Water gain, salt loss)
52
Q

Blood flow through the medulla tends to wash away….?

How is this corrected?

A

Blood flow through the medulla tends to wash away salt and urea (they are taken into the blood)

Corrected by:

  • Hairpin loops (allows time for NaCl and Urea to be excreted into interstitium)
  • Capillaries freely permeable to NaCl and Urea (it can get back into intersitium)
  • Blood flow to vasa recta is low (only a few juxtamedullary nephrons)
53
Q

To maintain the medullary gradient, there is ACTIVE or PASSIVE movement across the endotheilum?

A

Passive Movement

Renal (34 decks)

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