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A&P Fall 24' > Vanders Renal Ch5 > Flashcards

Vanders Renal Ch5 Flashcards

1
Q

What is the physiological utility of excreting or reabsorbing organic solutes?

A

To maintain homeostasis by discriminating between useful metabolites to retain and waste products to eliminate.

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2
Q

Where does active reabsorption or secretion of organic nutrients primarily occur in the kidneys?

A

In the proximal tubular systems.

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3
Q

What is glycosuria and under what conditions is it likely to occur?

A

Glycosuria is the presence of glucose in urine, likely occurring when plasma glucose exceeds the renal threshold (Tm).

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4
Q

How are proteins and small peptides handled by the kidneys?

A

They are filtered, endocytosed, degraded into amino acids, and reabsorbed into the bloodstream.

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5
Q

What is the role of para-aminohippurate in renal handling?

A

It is secreted by the kidneys as a model organic anion for studying renal clearance.

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6
Q

What is the process involved in the handling of urate?

A

It involves both reabsorption and secretion in the proximal tubule.

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7
Q

What are organic cations and how are they secreted in the kidneys?

A

Organic cations are positively charged molecules secreted via transporters in the proximal tubule, typically using antiporters.

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8
Q

How does tubular pH affect the excretion and reabsorption of weak acids and bases?

A

Changes in tubular pH can convert charged species to neutral forms, affecting their reabsorption and excretion.

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9
Q

What is the significance of urea in renal function?

A

Urea is a waste product that must be excreted to prevent accumulation but also helps regulate water balance.

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10
Q

What are the general properties of organic solute transport in the kidneys?

A

Transport proteins are promiscuous, and most organic solutes are handled in the proximal tubule.

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11
Q

What are the main transporters involved in glucose reabsorption?

A

Sodium-glucose symporters (SGLT-2 and SGLT-1) and glucose uniporters (GLUT).

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12
Q

What happens to glucose reabsorption when plasma glucose exceeds 200 mg/dL?

A

Filtered glucose begins to spill into urine as the transport maximum (Tm) is reached.

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13
Q

What is the typical Tm for glucose transport?

A

375 mg/min.

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14
Q

What occurs if the endocytic mechanism for protein uptake is saturated?

A

Increased filtered protein leads to significant protein excretion in urine.

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15
Q

True or False: The glomerular filtrate is completely free of proteins.

A

False.

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16
Q

What is the primary method for reabsorbing larger proteins in the kidneys?

A

Endocytosis followed by degradation in lysosomes.

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17
Q

How are organic anions secreted in the kidneys?

A

By using α-ketoglutarate (αKG) as a tool for active transport.

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18
Q

Fill in the blank: The kidneys perform a triage by reabsorbing _______, eliminating waste products, and partially reabsorbing a few special solutes.

A

metabolites.

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19
Q

What is the unique role of urea in the context of renal handling?

A

It is both a waste product and a regulator of water balance.

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20
Q

What is the consequence of glucose not being reabsorbed in the renal tubule?

A

It acts as an osmole, leading to osmotic diuresis.

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21
Q

What is the role of α-ketoglutarate (αKG) in the secretion of organic anions in the proximal tubule?

A

αKG is actively taken up from both the lumen and interstitium by a sodium-αKG symporter, raising cellular levels of αKG, which then effluxes across the basolateral membrane via an antiporter that imports an organic anion.

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22
Q

What is the function of the OAT family of transporters?

A

The OAT family facilitates the transport of organic anions across the cell membranes, playing a crucial role in the secretion of various organic anions in the kidney.

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23
Q

What happens if the plasma concentration of an organic anion is too high?

A

It will not be efficiently removed from the blood by the kidneys.

24
Q

What are some examples of organic anions actively secreted by the proximal tubule?

A
  • Uric acid
  • Glucuronate conjugates
  • Sulfate conjugates
25
Q

How is uric acid produced in the body?

A

Uric acid is continuously produced by the metabolic catabolism of purines.

26
Q

What is the pK of uric acid?

A

5.75.

27
Q

What clinical condition can arise from increased plasma urate concentration?

A

Gout, due to the deposition of sodium urate crystals in joints.

28
Q

What is the typical reabsorption rate of filtered urate in the kidneys?

A

About 90% of the filtered load is reabsorbed, and only 10% is excreted.

29
Q

What determines whether urate is secreted or reabsorbed in the kidneys?

A

The expression levels of relevant transporters in the apical or basolateral membranes.

30
Q

Fill in the blank: At low pH, weak acids are predominantly in their ______ form.

A

neutral

31
Q

Fill in the blank: At high pH, weak acids dissociate into an ______ and a proton.

A

anion

32
Q

True or False: Acidification of urine favors the passive reabsorption of weak bases.

A

False.

33
Q

What is the primary role of urea in the kidney?

A

Urea is an end product of protein metabolism and plays a crucial role in regulating water excretion.

34
Q

How does urea differ from other organic solutes in the proximal tubule?

A

Urea easily permeates tight junctions and is reabsorbed paracellularly, unlike other solutes that require specific transport mechanisms.

35
Q

What is the normal level of urea in the blood?

A

3–9 mmol/L.

36
Q

What is the net result of urea handling by the kidney?

A

About half of the filtered urea is reabsorbed and half is excreted.

37
Q

Fill in the blank: Urea is freely filtered and about half is reabsorbed passively in the ______ tubule.

A

proximal

38
Q

What happens to urea as it passes through the loop of Henle?

A

An amount equal to that reabsorbed in the proximal tubule is secreted back into the loop of Henle.

39
Q

What transporters handle urea beyond the proximal tubule?

A

Urea uniporters (UT family).

40
Q

How does dehydration affect urea concentration in the renal medulla?

A

It increases the urea concentration gradient favoring reabsorption.

41
Q

True or False: Urea is toxic to the body at normal levels.

A

False.

42
Q

What is the significance of tubular fluid pH on the reabsorption of weak organic acids and bases?

A

The pH affects the ionization state, influencing solubility and permeability.

43
Q

What is the relationship between tubular fluid concentration and urine flow rate?

A

Increasing urine flow increases the excretion of both weak acids and bases.

44
Q

What condition can result from a combination of excess plasma urate and low urinary pH?

A

Uric acid precipitation and the formation of uric acid kidney stones.

45
Q

What is the fate of important organic metabolites in renal reabsorption?

A

Reabsorbed almost completely (saved)

This indicates that the kidneys efficiently reclaim essential organic metabolites to maintain homeostasis.

46
Q

Where in the nephron are most organic solutes transported?

A

Proximal tubule

This region primarily utilizes multiporters for the transport of organic solutes.

47
Q

What happens to glucose reabsorption in pathological hyperglycemia?

A

Transport saturates, leading to glucose appearance in urine

This condition is known as glycosuria.

48
Q

How are peptides reabsorbed in the proximal tubule?

A

By endocytosis or as individual amino acids

Peptides undergo enzymatic degradation on the brush border before reabsorption.

49
Q

What can facilitate the passive reabsorption of some organic solutes?

A

Changes in tubular pH

Neutral forms of organic solutes can be reabsorbed passively in the distal nephron.

50
Q

What is the overall result of urea reabsorption and recycling in the nephron?

A

Net excretion of about half the filtered load

This process involves urea being reabsorbed and secreted multiple times.

51
Q

When does glucose appear in the urine?

A

When plasma glucose reaches high levels

This is a characteristic of conditions like diabetes mellitus.

52
Q

How are useful small organic metabolites generally handled by the kidneys?

A

Reabsorbed transcellularly

This means they are transported through the cells rather than between them.

53
Q

What is a key characteristic of organic anion secretion?

A

Involves a step of active influx across the basolateral membrane

This process differs from passive secretion mechanisms.

54
Q

A high urinary pH favors which of the following?

A

Low excretion of drugs that are weak acids

This is due to the increased ionization of weak acids at higher pH levels.

55
Q

Where does the tubular concentration of urea exceed plasma concentration?

A

At the hairpin turn of the loop of Henle

This indicates a critical point for urea concentration dynamics in the nephron.

56
Q

Where is urea secreted into the tubules?

A

At any of these sites depending on hydration status:
* Proximal tubules
* Thin descending limbs
* Medullary collecting ducts

Urea secretion is influenced by the body’s hydration needs.

57
Q

What is the normal range for blood urea nitrogen (BUN) levels?

A

8.4 to 25.2 mg/dL

This measurement reflects plasma urea concentration, which is critical for assessing kidney function.

A&P Fall 24' (27 decks)

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