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MD3002 Physiology > Obligatory Reabsorption and Secretion in the Proximal Convoluted Tubule > Flashcards

Obligatory Reabsorption and Secretion in the Proximal Convoluted Tubule Flashcards

1
Q

What is the hydrostatic pressure of the tubule?

A

-15 mmHg

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2
Q

What is the Blood Hydrostatic pressure?

A

+55 mmHg

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3
Q

What is the Blood Oncotic Pressure?

A

-30 mmHg

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4
Q

What is the net filtration pressure?

A

+10 mmHg

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5
Q

What are the factors that lead to the blood hydrostatic pressure in the capillaries of renal corpusles not changing much?

A

Autoregulation of Glomerular Filtration

  • Myogenic mechanism
  • Tubuloglomerular feedback (nephrogenic)
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6
Q

Between what arterial blood pressures does the renal blood flow not really change?

A

~ 80 - 150 mmHg

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7
Q

What does constriction of the efferent arteriole cause within the capillary?

A

Increased Filtration pressure and increased flow rate

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8
Q

What does constriction of the affereant arteriole cause within the capillary?

A
  • Reduced filtration pressure and decreased GFR
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9
Q

What is the main controller of GFR the afferent or efferent arteriole?

A

The afferent (both usually work together at the same time)

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10
Q

What is the renal blood flow? per min?

A

1 - 1.2 L/min

RBF essentially constant over wide range of BP

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11
Q

What causes vasoconstriction in response to decreased afferent blood flow?

A
  • Sympathetic nerves releasing NE
  • Circulating epinephrine
  • Angiotensin II
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12
Q

What causes vasodilation in response to increased afferent blood flow?

A
  • Renal prostaglandins

- Atrial natriuretic peptide

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13
Q

What are the 5 steps in the kidney nephron?

A
  1. Filtration by glomerulus
  2. Obligatory absorption and secretion by proximal tubule
  3. Generation of osmotic gradient by loop of Henle
  4. Regulated absorption and secretion by distal tubule
  5. Regulation of water uptake by collecting ducts
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14
Q

What are the functions of the proximal tubule?

A
  • Most of the recovery of ions, sugars, amino acids, peptides and a considerable amount of the total water is achieved in the first part of the PT
  • In addition the PT actively secretes a number of compounds for excretion with urine, and metabolises some of the amino acids
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15
Q

What are the 2 pathways molecules and ions can cross the tubule epithelium?

A
  • Transcellular route (through the cell body)

- Paracellular route (through the leaky ‘tight’ junctions between cell bodies)

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16
Q

What are the forces involved in the obligatory reabsorption from the proximal tubule?

A
  • Ion gradients across the basolateral membrane
  • Sets up an electrochemical gradient of about -3mV (tubule lumen negative; causes paracellular efflux of cations)
  • Osmotic gradient set up by pumping Na out of the cell into the interstitial space
  • Water moving along the paracellular path due to osmotic pressure drags solutes along with it. Known as sovent drag
  • Chemical concentration of solutes left behind when water leaves the tubule facilitates a chemical gradient
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17
Q

What is co-transport in the PCT?

A

Sodium moves substances into the cell

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18
Q

What is counter transport (exchange) in the PCT?

A

Sodium moves a substance out

19
Q

What percentage of bicarbonate is reabsorbed?

A

Proximal Tubule

- Through the action of carbonic anhydrase

20
Q

Where is the majority of Mg2+ absorbed?

A

Thick ascending limb

21
Q

What passes through tight junctions in the proximal tubule?

A
  • H2O
  • K+
  • Na+
  • Ca2+
22
Q

What is solvent drag (‘bulk transport’)?

A

Movement of solutes in the ultrafiltrate that are transported back from the renal tubule by the flow of water rather than specifically by ion pumps or other membrane transport proteins by the paracellular route

23
Q

What is the tubular potential in the proximal tubule?

A

-4 (causes absorption of anions)

24
Q

What is transport maximum

A
  • Limit as to how muvch can be moved
  • Often discussed in terms of glucose and the PAH
  • Measured in mg/min or mmol/min (rate)
  • If blood conc. is high, Tmax can be exceeded
25
Q

How is the amount filtered calculated?

A

Plasma conc. x GFR

26
Q

When does a substance appear in urine?

A

When it is above threshold (when normally 100% reabsorbed)

27
Q

What is the threshold of a substance?

A

Point at which the amount filtered is equivalent to Tmax

28
Q

When is the concentration of glucose in urine proportional to plasma concentration?

A

Above threshold

29
Q

How much glucose can the Na-glucose transporter reclaim?

A

~ 375 mg/min of glucose

30
Q

What is Para-amino hippurate for?

A

Measuring secretion through the kidneys can be infused into patient to measuring secretion

31
Q

Where is PAH secreted?

A

Distal parts of proximal tubule

32
Q

How much of a substance appears in urine that is excreted by the kidneys?

A

Amount filtered plus amount secreted

33
Q

When does the secretion line level off?

A

Once maximum secretion level is reached

34
Q

How much urea is reabsorbed in the proximal tubule?

A

~ 50% through simple diffusion

35
Q

What is the obligatory reabsorption of glucose, amino acids and lactate?

A

100%

36
Q

What is the obligatory reabsorption of bicarbonate?

A

90%

37
Q

What is the obligatory reabsorption of water and sodium?

A

65%

38
Q

What is the obligatory reabsorption of potassium?

A

55%

39
Q

What is the obligatory reabsorption of chloride?

A

50%

40
Q

What is clearence?

A
  • Volume of plasma which is cleared of the substance per unit time (theoretical as in reality no substance is completely cleared)
41
Q

What are the 3 renal processes that determine and modify composition of urine?

A
  • Glomerular filtration
  • Tubular reabsorption
  • Tubular secretion
42
Q

What are the requirments of a substance in order to measure GFR?

A
  • Freely filtered at the glomerulus
  • Neither secreted or reabsorbed
  • Not metabolised
  • Not toxic
43
Q

What can clearence be used to determine?

A
  • Renal transport mechanism
  • Net reabsorption
  • Net secretion

MD3002 Physiology (24 decks)

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