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Renal - Rao > Reabsorption/Secretion in the Proximal Tubule > Flashcards

Reabsorption/Secretion in the Proximal Tubule Flashcards

1
Q

What are the main waste products excreted by the kidney?

• How much is REABSORBED?

A
  • Urea
  • Creatinine
  • Uric Acid

***Filtering this out ~60 times a day keeps things clean

2/3 of glomerular Filtrate is Reabsorbed in the Proximal Tubule*** this includes water and solutes

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2
Q

How many times per day is the entire body fluid turned over?
• why is this necessary?

A

5 times daily

• Essential to Maintain ECFV, Electrolytes, and Solutes in Glomerular Filtrate

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3
Q

What major process takes place in the proximal tubule?

A
  • Filtration = Glomerulus
  • Reabsorption = Proximal Tubule
  • Secretion = Distal Tubule
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4
Q

What formula is used to determine rate of flow into the loop on henle?

A

V = (GFR x Ps) / TFs

V = rate of flow into Loop of Henle
Ps = Plasma Concentration of Substance
TFs = Tubule Fluid Concentration of Substance
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5
Q

How do you use the rate of flow of fluid into the loop of henle to determine the amount of Resorption occurring?

A

Resorption = Starting Flow. - V

V = rate of flow into L.O.H.

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6
Q

What processes allow for isotonic reabsorption in the proximal tubule?

A

Reabsorption:
• Sodium
• Chloride
• Bicarbonate

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7
Q

How can reabsorption of solutes in the proximal tubule like Na+, HCO3-, Cl- occur without a change in filtrate osmolarity?
• how is this different from inulin?

A
  • Water Follows these 3 major solutes that are reabsorbed so overall concentration is not reduced but FLUID AMT. IS reduced
  • Inulin is NOT reabsorbed so as you move down its concentration just stays the same
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8
Q 
Sodium Transport in Proximal Tubule: 
• Active or Passive? 
• Driving Forces?
• How do these arise? 
• Describe Luminal and Apical transport
A

ACTIVE TRANSPORT:
• Drives sodium movement

DRIVING FORCES:
• Depends on DECREASED [Na+] and…
• INCREASED membrane (-) membrane potential

Creation of Gradient:
BASOLATERAL Na+/K+ = Key driving forces:
• is ATP dependent

REABSORPTION OF Na+:
LUMINAL channels are responsible for getting Na+ into tubular cells

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9
Q

What are some of the molecules that get co-transported with Na+/ what are the transporters called?

A
  • Na+ - H+ exchanger
  • Na+ - Glucose co-transport
  • Na+ Amino Acid co-transport
  • Na+ - Phosphate co-tranporter
  • Claudin-2 in Tight juntions = another transporter
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10
Q

What is sodium Reabsorption always accompanied by?

• how is this accomplished?

A
  • ANION reabsorption - specifically Cl- and HCO3-

* Na+ movement to interstitium generates -5mV gradient and LEAKY EPITHELIUM of proximal tubule and potassium follows

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11
Q

How does Chloride move across the proximal tubule?

A

• Claudin 4 (Cldn 4) IN TIGHT JUNCTIONS allows Cl- to pass PARACELLULARLY

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12
Q

How does the rate Chloride reabsorption compare to Bicarbonate reabsorption in the proximal tubule?
• why is this the case?

A
  • Chloride Reabsorption occurs more slowly because it just uses the -5mV gradient and Claudin-4 to move Paracellularly
  • HCO3- uses ACTIVE transport to move across lumen so its MORE RAPIDLY absorbed in Proximal tubule
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13
Q

T or F: bicarbonate just neutralized so that it can move across luminal cells.

A

FALSE, this is ACTIVE transport, not just neutralization

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14
Q

**Describe the Method by which bicarbonate is reabsorbed.

A
  1. H2O and CO2 come together to make H2CO3 via Intracellular Carbonic Anhydrase
  2. H2CO3 dissociates into H+ and HCO3-

Following HCO3- => INTERSTIUM
a. 3 HCO3- can be transferred to INTERSTITIUM via HCO3-/Na+ exchanger

Following Hydrogen => LUMEN
a. H+ is exported via hydrogen channel? or Na+/H+ exchanger

b. This lumenal H+ combines with HCO3- in the LUMEN to make H2CO3
c. H2CO3 dissociates into H2O and CO2

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15
Q

How is water Reabsorbed?

A

LEAKY Epithelium with Lots of AQUAPORINS = HIGH Kf (high hydraulic conductivity)

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16
Q

What are the aquaporins that are responsible for absorption of H2O in the proximal tubule?
• what about elsewhere in the nephron?

A

PROXIMAL TUBULE:
•AQP-1 - Apical side of cell
• AQP-4/5 Basolateral membrane

DISTAL TUBULE:
• AQP - 2 - regulated by vasopressin

17
Q

What Factors drive H2O uptake INTO CAPILLARIES from interstitial Fluid?

A
  1. POSITIVE PRESSURE of INTERSITIAL FLUID
  2. LOW hydrostatic pressure in the capillary
    • because of pressure drop across afferent and efferent arterioles
  3. HIGH ONCOTIC pressure in peritubular capillary
    • because of glomerular filtration and retention of proteins
18
Q

Why does inulin increase to 3 times the concentration in the glomerular capillaries by the time it gets to the Loop of Henle?

A

because it is not reabsorbed so Amt. stays the same but the water volume is decreased to 1/3 of the orginal vol.

***This means concentration is increased by 3.

19
Q

How is glucose transported across the proximal tubule?
• what is Threshold?
• what is Tm?

A

Sodium-Glucose co-transporter (SGLT1 and 2)
• couple glucose transport to the Na+ gradient

Threshold:
• at 200-220 mg/dL some nephrons become saturated with glucose and you START TO SEE GLUCOSE IN THE URINE

Tm:
• ALL nephrons are maxed out and GLUCOSE INCREASES IN THE URINE ARE PROPORTIONAL TO PLASMA GLUCOSE

20
Q

What are some physiologic and pathologic causes of Glucosuria?

A

Physiologic:
• Pregnancy

Pathologic:
• DIABETES MELLITUS
• FAMILIAL RENAL GLUCOSURIA MUTATION IN SGLT1/2

21
Q

Describe the absorption of amino acids and organic acids in the proximal tubule of the kidney?
• where do most organic acids come from?

A

Amino Acids:
• Co-transport with Na+
• only 0.5-2% excreted

Organic Acids:
• Co-transport with Na+
• Most organic acids come from Krebs Cycle intermediates

22
Q

What are some diseases where ORGANIC acid secretion is hight?

A

Organic Acids:

• High in DIABETIC KETOACIDOSIS

23
Q

T or F: there are many transporters to reabsob peptides.

A

True, very little peptide should ever be excreted in the urine

24
Q

What are some diseases that cause Proteinuria?

A
  • Multiple Sclerosis
  • Hemoglobinemia
  • Myoglobinemia
25
Q

T or F: like glucose, phosphates have a fixed transport maximum.

A

FALSE, PTH controls the transport maximum for phosphate

26
Q

Why is phosphate often excreted rather than reabsorbed?
• what causes changes in this?
• Transport mechanism when resorption is used?

A

Phosphate:
• Important buffer in the blood so we need to keep it at a constant concentration

Changes:
• PTH secreted by the pituitary controls this

Mechanism:
• Na+ cotransport is used when reabsorption is done

27
Q

While 66% of fluid is reabsorbed in the proximal tubule, only 60% of Cl- is reabsorbed. why?

A

Cl- must compete with ACTIVELY transported HCO3-

28
Q

How is urea reabsorbed?

*what would be an easy way to increase urea excretion?

A

Urea is PASSIVELY reabsorbed in the PT
• this is SLOW so a greater URINARY FLOW would DECREASE urea absorption

**Typically only 50% reabsorbed

29
Q

What is the use of substances that are FREELY FILTERED but not rapidly reabsorbed?
• example?

A

DIURESIS:
• MANNITOL - will increase osmolarity of filtrate so less H2O leaves tubule and more gets excreted

CLINICAL USE:
• Reduction of Intracranial Pressure, Intraocular Pressure, promotes excretion of toxins and edema

Renal - Rao (13 decks)

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