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Renal and urology > Renal physiology > Flashcards

Renal physiology Flashcards

1
Q

What is the plasma clearance?

A

The volume of plasma completely cleared of a particular substance per minute

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2
Q

How can the plasma clearance of a substance be calculated?

A

Clearance of substance X = rate of excretion of X/plasma concentration of X

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3
Q

What is the clearance of inulin and what implications does this have clinically?

A

Inulin clearance = GFR

Therefore, inulin clearance can be used to calculate GFR

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4
Q

What is the plasma clearance of glucose and why?

A

Clearance = 0

It is filtered in the glomerulus, completely reabsorped and not secreted from plasma or excreted in urine

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5
Q

What will the clearance of a substance that is filtered, partly reabsorped and not secreted be and give an example?

A

Clearance < GFR

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6
Q

What will the clearance of a substance that is filtered, secreted and not reabsorped be, and give an example?

A

Clearance > GFR

H+

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7
Q

What is para-amino hippuric acid?

A

An exogenous organic anion used clinically to calculate renal plasma flow

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8
Q

What is the clearance of para-amino hippuric acid?

A

Complete - it is filterd, secreted, but not reabsorped

All the PAH in the plasma that escapes filtration is secreted from the peritubular capillaries

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9
Q

What is the filtration fraction?

A

The fraction of plasma flowing through the glomeruli that is filtered into the tubules

i.e. ~20% of the plasma that enters the glomeruli is filtered - the remaining 80% moves on to the peritubular capillaries

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10
Q

Which substances are reabsorped in the proximal tubule?

A

Sugars

Amino acids

Phosphate

Sulphate

Lactate

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11
Q

Which substances are secreted in the proximal tubule?

A

H+

Hippurates

Neurotransmitters

Bile pigments

Uric acid

Drugs

Toxins

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12
Q

What are the five steps in tubular reabsorption?

A
  1. Absorption into epithelial cell
  2. Movement across epithelial cell
  3. Transport out of epithelial cell
  4. Diffusion across interstitial fluid
  5. Diffusion across capillary wall
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13
Q

What does paracellular transport in the proximal tubule depend on?

A

Tightness of junction between tubular epithelial cells

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14
Q

Which kind of transport mechanism is essential at th basolateral membrane for sodium reabsorption, and how does this occur?

A

The energy-dependent Na+-K+ ATPase transport mechanism at the basolateral membrane pumps sodium out of the epithelial cell, creating a concentration gradiant that draws sodium out of the proximal tubule by diffusion

Sodium pumped into interstitial fluid is then taken into blood by diffusion

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15
Q

How can the concentration gradient of sodium from proximal tubule to epithelial cell, created by the active transport pump at the basolateral membrane, be used for reabsorption of other substances?

A

The sodium gradient can be used to drive glucose and amino acid uptake, using secondary active transport and co-transporters
It can also be used to secrete H+ into the filtrate

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16
Q

What percentage of the filtered glucose is reabsorbed in the proximal tubule?

A

Normally 100%

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17
Q

What is the definition of the transport maximum e.g. of glucose?

A

The greatest quantity of glucose filtered from the plasma that can successfully be reabsorped in the proximal tubule

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18
Q

Explain why the blue line for ‘excreted’ only occurs later in the graph?

A

Glucose only begins to be excreted once the transport maximum has been reached

Excretion is the difference between filtration and reabsorption

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19
Q

What percentage of salt and water is reabsorbed in the proximal tubule?

A

~67%

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20
Q

How is Cl- reabsorption in the proximal tubule driven?

A

Driven by the paracellular pathway to Na+ reabsorption

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21
Q

What is the function of the loop of henle?

A

To create a cortico-medullary solute concentration gradient

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22
Q

What is reabsorped in the ascending limb of the loop of henle?

A

Na+

Cl-

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23
Q

Is the ascending limb of the loop of henle permeable or impermeable to water?

A

Relatively impermeable

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24
Q

Is the reabsorption of salt active or passive in the ascending limb of the loop of henle?

A

Active in the upper/thick part

Passive in the lower/narrow part

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25
What is reabsorped in the descending limb of the loop of henle?
Water It does not reabsorb salt
26
Through which transport mechanism is salt reabsorped in the thick ascending limb of the loop of henle?
Na+ K+ Cl- triple co-transporter
27
How is potassium from the triple co-transporter in the thick ascending limb of the loop of henle used in salt reabsorption?
It is recycled: a cotransporter uses potassium to pump Cl- into the interstitial fluid and then the K+ is used in a countertransporter to pump Na+ from the cell
28
What is the purpose of countercurrent multiplication?
To concentrate the medullary interstitial fluid, enabling the kidney to respond to ADH to produce urine of different volume and concentration
29
What effect does ADH have on the collecting duct?
ADH changes the permeability of the collecting duct from water impermeable to water permeable, to allow reabsorption
30
What is vasa recta?
A group of straight capillaries in the medulla that lie alongside the loop of henle and act as a countercurrent exchanger
31
How does the vasa recta ensure NaCl and urea aren't washed away by essential medullary blood flow, as illustrated in this diagram?
Vasa recta capillaries follow hairpin loops and are freely permeable to NaCl and water Blood flow to vasa recta is low
32
Which two receptors control ADH release?
Hypothalamic osmoreceptors Atrial stretch receptors
33
What is ADH release stimulated by?
Increased osmolarity (detected by hypothalamic osmoreceptors) Decreased blood pressure/fluid volume (detected by atrial stretch receptors)
34
Does nicotine inhibit or stimulate ADH release?
Stimulates
35
Does alcohol inhibit or stimulate ADH release?
Inhibit
36
How does salt imbalance manifest in the body?
As changes in extracellular volume
37
When is aldosterone secreted?
In response to the RAAS In response to rising K+ or falling Na+ in the blood
38
What does aldosterone do?
Stimulates Na+ reabsorption and K+ secretion
39
What effect does a change in body pH have on the nervous system?
Acidosis can lead to depression of the CNS Alkalosis can lead to overexcitability of the peripheral NS and later the CNS
40
From what three sources is H+ continually added to the body from?
Carbonic acid formation Inorganic acids produced during breakdown of nutrients Organic acids resulting from metabolism
41
What is pKa?
The pH at which an acid is 50% dissociated = -logK
42
What is the normal plasma pH?
7.4
43
What is the most important physiological buffer system?
The CO2-HCO3 buffer system
44
How is bicarobonate reabsorbed in the proximal tubule?
CO2 and H2O are taken into the epithelial cell and carbonic anhydrase converts these into carbonic acid, H2CO3 This then dissociates into H+ and bicarbonate, HCO3 Bicarbonate is then taken into the extracellular fluid by co-transportation out of the epithelial cell with Na+
45
What happens to H+ ions that have dissociated from carbonic acid in the epithelial cell?
It can be transported actively back into the tubule and can either combine with phosphate to be excreted or may be recycled and taken back into the epithelial cell
46
How is 'new' bicarbonate generated in the kidney?
In the epithelial cell, carbonic acid dissociated into H+ and bicarbonate The H+ is pumped actively into the tubule and binds with phosphate to form an acid, which is then excreted It can also bind to NH3 in the filtrate to form ammonia which is then excreted The corresponding bicarbonate is then reabsorped, and there is a net gain of bicarbonate
47
What is titratable acid and how is it measured?
The amount of H+ excreted as (largely) H2PO4- Measured as the amount of strong base needed to titrate the solution back to pH 7.4
48
What is the maximum amount of titratable acid the kidneys can produce daily?
~40mmol/day
49
What is the normal bicarbonate concentration in plasma?
Close to 25mmol | (23-27)
50
What is the normal arterial pCO2?
40mmHg | (35-45)
51
What is the difference between compensation and correction?
Compensation is the fixing of pH irrespective of what happens to pCO2 and [HCO3-] Correction restores pH, pCO2 and [HCO3-] to normal
52
How does CO2 retention generate acidosis?
Increased [CO2] increases [H+] as the equilibrium of the CO2-HCO3 buffer system is shifted to the right This also increases [HCO3] but pH is only a measure of [H+] concentration so only this is reflected
53
When is uncompensated respiratory acidosis indicated?
pH \< 7.35 and PCO2 \> 45 mmHg
54
Where would respiratory acidosis lie on a Davenport diagram?
Low pH, high [HCO3-]
55
How is respiratory acidosis compensated for?
Virtually no cellular buffering High pCO2 stimulates H+ secretion into the filtrate This generates 'new' HCO3 and plasma [HCO3] concentration rises
56
How does compensated respiratory acidosis look on a Davenport diagram?
57
What are some of the causes for respiratory alkalosis?
Low inspired PO2 at altitude (hypoxia stimulates peripheral chemoreceptors, hyperventilation lowers PCO2) Hyperventilation (causes include fever, brainstem damage) Hysterical overbreathing
58
How does excessive removal of CO2 due to ventilation disorders cause alkalosis?
59
When is uncompensated respiratory alkalosis indicated?
pH \> 7.45 and PCO2 \< 35 mmHg
60
What does uncompensated respiratory alkalosis look like on a Davenport diagram?
61
How is respiratory alkalosis compensated for?
Reduced pCO2 reduces secretion of H+ from the kidney This reduces the reabsorption of HCO3- and it is excreted in the urine, making the urine slightly alkaline Plasma [HCO3-] is lowered
62
What does compensated respiratory alkalosis look like on a davenport diagram?
63
What are [H+] and [HCO3-] in metabolic acidosis and why?
Raised [H+] = lowered pH Depleted [HCO3] due to excess buffering of H+, or due to loss from the body e.g. diarrhoea
64
How is metabolic acidosis indicated?
pH \< 7.35 and [HCO3-]p is low
65
What does uncompensated metabolic acidosis look like on a davenport diagram?
66
How is metabolic acidosis compensated for?
Excess CO2 is blown off, shifting equilibrium to the right and decreasing [H+] and [HCO3-] Because [HCO3-] is very low, filtered HCO3- is also low and very readily reabsorbed This stimulates H+ secretion into the tubule to 1) allow more excretion of acid in the urine in the form of NH4 and titratable acid 2) generate 'new' bicarbonate
67
What does compensated metabolic acidosis look like on a davenport diagram?
68
How is metabolic alkalosis indicated?
pH \> 7.45 and [HCO3-]p is high
69
What does metabolic alkalosis look like on a davenport diagram?
70
How is metabolic alkalosis compensated for?
Hypoventilation Retention of CO2 shifts equilibrium to the right [H+] and [HCO3-} increases Filtered HCO3- load is so large compared to normal that not all of the filtered HCO3- is reabsorbed, so much of the HCO3- is excreted in the urine
71
What does compensated metabolic alkalosis look like on a davenport diagram?

Renal and urology (11 decks)

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