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Physiology > Specific Tubule Functions Along the Nephron > Flashcards

Specific Tubule Functions Along the Nephron Flashcards

1
Q

What does the proximal tubule mainly absorb?

A

It absorbs around 2/3 of the water, sodium, potassium and chloride ions. It also absorbs nearly all of the glucose and amino acids that are filtered.

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2
Q

What is the main mechanism for the proximal tubule absorption?

A

Na-K ATPase in the membrane as every substance has its reabsorption linked to this pump.

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3
Q

Describe sodium reabsorption in the first half of the proximal tubule.

A

Na uptake is coupled with either H+ or organic solutes using the Na-H+ anti porter

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4
Q

What does the Na-H+ anti porter secrete and reabsorb?

A

It secretes H+ and absorbs NaHCO3

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5
Q

What are the two mechanisms for Na reabsorption in the first half of the proximal tubule?

A
  • Na-H Antiporter

- Na-Glucose Symporter

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6
Q

What type of transport occurs with Na in the first half of the proximal tubule?

A

Transcellular

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7
Q

How is the Na transported out of the basolateral membrane after its uptake via a Na-Glucose Symporter?

A

Passive Transport Mechanisms

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8
Q

How is Na transported out after its uptake with the Na-H+ Antiporter?

A

Uses the Na-K ATPase

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9
Q

How is Na reabsorption related to that of water?

A

It creates an osmotic gradient that provides the driving force for the passive reabsorption of water

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10
Q

Describe Na reabsorption in the second half of the proximal tubule.

A

It is reabsorbed coupled with Cl- in the second half primarily, rather than HCO3- or other solutes like it was in the first half of the tubule

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11
Q

What type of transport occurs with Na in the second half of the proximal tubule?

A

Both paracellular and transcellular

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12
Q

What is the mechanism for Na transport in the second half of the proximal tubule?

A

It is transported via the parallel operation of Na-H and Cl-Anion anti porters. Na is transported in and H+ and Cl is transported in and an anion is transported out.

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13
Q

How does Na leave the cell in the second half of the proximal tubule?

A

Na leaves via the Na-K ATPase

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14
Q

How does Cl leave the cell in the second half of the proximal tubule?

A

Cl leaves via a K-Cl symporter that transports both ions out from the cell

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15
Q

How is water reabsorption occurring in the proximal tubule?

A

It is a passive process that is driven by the osmotic gradient that is generated from the active solute reabsorption (mainly Na)

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16
Q

What is the meaning of isosmotic absorption?

A

It means that water reabsorption occurs in equal proportion with that of the reabsorbed solutes.

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17
Q

What type of transport occurs with water in the proximal tubule?

A

Both transcellular and paracellular

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18
Q

What is the importance of solvent drag in water reabsorption?

A

Solutes that are trapped in the water are also reabsorbed as a result and this is most important for K and Ca

19
Q

How much of filtered protein is reabsorbed by the proximal tubule?

A

100% ideally

20
Q

What happens to reabsorbed proteins that makes it different form other reabsorbed substances?

A

They are degraded into amino acids rather than taken up in their original forms.

21
Q

What happens when the protein reabsorption process is saturated?

A

Proteinuria - that is protein begins to appear in the urine

22
Q

What happens with organic ions in the proximal tubule?

A

The ones that are necessary are reabsorbed with the rest of them being actively secreted into the proximal tubule.

23
Q

What is a possible danger of organics that share the same carrier?

A

The can elevate the plasma concentration of the other and lead to drug toxicity

24
Q

What happens to urine with a low osmolality ratio ( <1.0 )?

A

Low [ADH] and urine is pale and dilute

25
Q

What happens to urine with a high osmolality ratio ( >1.0 )?

A

High [ADH] and urine is dark and concentrated

26
Q

What is absorbed in the thick ascending loop of Henle?

A

25% of Na and other solutes are absorbed, with no water absorbed as it is H2O impermeable

27
Q

What is the main transporter in the loop of Henle?

A

Na-K ATPase

28
Q

What is absorbed in the thin descending loop of Henle?

A

H2O is absorbed passively and it is impermeable to ions like Na and Cl

29
Q

What is absorbed in the thin ascending loop of Henle?

A

Na and Cl are reabsorbed and it is impermeable to H2O

30
Q

What is the transporter into the cell for the thick ascending loop of Henle?

A

1 Na - 2 Cl - 1 K Symporter

31
Q

What transports Na out of the cell in the thick ascending loop of Henle?

A

Na-K ATPase

32
Q

What transports K and Cl out of the cell in the thick ascending loop of Henle?

A

K - Cl Symporter

33
Q

What is reabsorbed in the distal tubule?

A

Remaining 8% of Na in the urine

34
Q

How much of Na is reabsorbed by the time it reaches the distal tubule?

A

99.9%

35
Q

What is the role of principal cells?

A

Absorbs NaCl and secretes K+

36
Q

What is the role of intercalated cells?

A

Secrete H+ and HCO3-

37
Q

What happens with a decrease in the extracellular fluid volume in regards to the RAA system?

A

The Renin-Angiotensin-Aldosterone system is activated and angiotensin-II is increased leading to increased reabsorption of Na/Cl/H2O in the proximal tubule.

38
Q

What happens with an increase in the extracellular fluid volume in regards to atrial natriuretic peptide?

A

It will lead to atrial stretch which increases atrial natriuretic peptide and leads to increased natriuresis and the decrease in total peripheral resistance and decreased reabsorption of Na/Cl in the proximal tubule. There is a decrease in ADH.

39
Q

What happens with a decrease in the extracellular fluid volume in regards to sympathetics?

A

Sympathetic activity will increase and release NE and E leading to increased reabsorption of Na/Cl in the proximal tubule.

40
Q

What happens with an increase in the ECFV in regards to dopamine?

A

It will increase dopaminergic activity and lead to the decreased reabsorption of Na/Cl in the proximal tubule.

41
Q

What is the effect of ADH?

A

With a decrease in the ECFV, ADH will increase and lead to increased H2O reabsorption in the collecting duct with little effect on the Na and Cl excretion.

42
Q

What is glomerulotubular balance?

A

Despite variations in GFR it is the fact that a constant fraction of Na and H2O are still reabsorbed from the proximal tubule.

43
Q

How does increased GFR affect reabsorption?

A

It will increase the amount of H2O and Na reabsorbed

Physiology (81 decks)

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