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Physiology III - Freedman > Unit 4: Renal Physiology: PART TWO: Reabsorption and Secretion > Flashcards

Unit 4: Renal Physiology: PART TWO: Reabsorption and Secretion Flashcards

1
Q

What is the Glomerular Filtration rate?

A

180 L/ day = 125 mL/min

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2
Q

What are the two ways to get ride of stuff through the kidney?

A
  1. Filtration–> and do NOT reabsorb it

2. Secretion (from blood in peritubular capillaries into where filtered stuff went too)

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3
Q

What is the amount of a substance filtered across the glomerular called?

A

the filtered load

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4
Q

What is occurring during filtration?

A

an interstitial like fluid is filtered across the glomerular cap into Bowman’s space

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5
Q

What does the Filtered Load equal?

A

= GFR x plamsa conc. of substance X x % unbound in plasma

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6
Q

What does the Filtration Fraction equal?

A

= GFR / RPF

the fraction of renal plasma flow that is filtered across the glomerular capillaries
- normally is 20% (.2)

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7
Q

What is the fraction of renal plasma flow that is filtered across the glomerular capillaries? What is it normally?

A

Filtered Fraction

normally is .2 (20%)

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8
Q

What does the excretion rate equal?

A

urine flow x conc. of substance X in urine

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9
Q

What does Reabsorption or secretion rate = ?

A

= Filtered Load - excretion rate

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10
Q

What is the fluid in Bowman’s Space and lumen of a nephron called?

A

tubular fluid

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11
Q

What sort of things are reabsorbed?

A
  • water
  • Na+
  • Cl-
  • HCO3-
  • glucose
  • AAs
  • urea
  • Ca++
  • Mg++
  • phosphate
  • lactate
  • citrate
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12
Q

What is the mechanism for reabsorption?

A

transporters in membrane of tubular epithelial cells

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13
Q

What is the MOST important function of the kidney? Why?

A

reabsorption of Na+–> b/c it is linked to ALL other reabsorption and virtually drives all resabsorption in the kidney!!!!*

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14
Q

What is the major cation in the ECF?

A

Na+ (plasma and interstitial fluid)

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15
Q

What does the amount of Na+ in ECF influence?

A

influences ECF volume–> influencing plasma volume, blood volume, and BP

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16
Q

How much of sodium is reabsorped?

A

output = intake

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17
Q

What happens if we increase the intake of Na+?

A

volume expansion

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18
Q

What substances are SECRETED from peritubular blood into the tubular fluid via the tubular epithelium?

A

organic acids, organic bases, K+

Secretion–> is an additional mechanism fro excreting substance into the urine

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19
Q

What refers to the amount of substance excreted per unit of time?

A

Excretion

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20
Q

What is excretion the net result of?

A

Excretion = filtration - reabsorption + secretion

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21
Q

What can we compare excretion rate to in order to determine if a substance has been reabsorbed or secreted?

A

compare to Filtrated Load

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22
Q

What is the equation for Excretion Rate? What is it for Filtered Load?

A

Excretion rate = urine flow x urine conc. of substance X

Filtered Load = GFR x plasma conc. of substance X

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23
Q

What if the filtered load is greater than the excretion rate? What substance is this an example of?

A

= net reabsorption

Ex: Na+

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24
Q

What if the filtered load is less than the excretion rate? What substance is this an example of?

A

= net secretion

Ex: PAH

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25
What are the two ways needed to get glucose reabsorbed and then transported into peritubular blood?
in early Proximal Tubule by Carrier-Mediated mechanisms (along with Na+) 1. "SGLT"--> Secondary Active Transport (from tubular fluid into cell) 2. GLUT 1 and GLUT 2--> Facilitate Diffusion (from cell into peritubular blood)
26
What type of transporter is used for glucose absorption, to get it from the tubular fluid into the tubular cell? What is moving uphill vs downhill? What other pump is necessary for this to occur?
Na+ glucose cotransporter (symporter) called "SGLT" (Sodium Glucose linked Transporter) 2 Na+ and 1 glucose - glucose moves uphill - Na+ moves downhill Secondary Active Transport-->Uses: Na+/K+ pump on peritubular capillary side keeps Na+ low in ECF
27
How is glucose transported from the tubular cell into the peritubular capillary?
via Facilitated Diffusion - moving DOWN conc. gradient - no energy needed - GLUT 1 and GLUT 2 (= insulin independent)
28
What is the filtered load for Glucose? What happens as plasma conc. of glucose increases?
glucose is freely filtered Filtered Load = GFR x Plasma conc. of glucose filtered load increases linearly
29
At what plasma concentration is all glucose reabsorbed?
less than 200 mg/dl all glucose can be reabsorbed
30
At what plasma concentration does "splay" occur with glucose reabsorption? What is "splay"?
greater than 200 mg/dl, but less than 350 mg/dl splay = bending of reabsorption curve--> a threshold where not all glucose is reabsorbed reabsorption is approaching saturation
31
What are two reasons for "splay" to occur for glucose titration curve?
1. Low affinity of Na+ glucose cotransporter (glucose detaches and is excreted; few remaining binding sites near Tm) 2. Heterogeneity of nephrons (some have higher Tm, some have lower; some glucose excreted before average Tm is reached)
32
At what plasma glucose concentration is Tm reached? What occurs here on the titration curve?
greater than 350 mg/dl glucose carries fully saturated and reabsorption of glucose flattens out
33
At what plasma glucose conc. does excretion of glucose occur? When does excretion follow a linear increase as there is an increase in filtered load?
beings when it is greater than 200 mg/dl (hit threshold) greater than 350 mg/dl
34
What is the term for glucose in the urine? What three things could this be due to?
Glucosuria; Due to: 1. High plasma glucose (>200mg/dl); diabetes 2. Pregnancy (increased GFR which increases filtered load--> may spill some glucose into urine) 3. Congenital abnormalities of Na+-glucose cotransporter
35
Is urea freely filtered across the glomerular capillaries? How is it secreted or reabsorbed?
yes; and it is transported in most segments of the nephron secreted or reabsorbed by diffusion (simple or facilitated)
36
How is the secretion or reabsorption rate of Urea determined?
concentration gradient and permeability
37
What happens to urea concentration in the tubular fluid as water is reabsorbed from the tubule? What does this create?
urea conc. increases--> creates a conc. gradient driving reabsorption of Urea
38
T/F. Urea does not follow water reabsorption
False--- urea does follow water reabsorption
39
Where is 50% of Urea reabsorbed? And by what type of transport?
50% reabsorbed in Proximal Tubule via simple diffusion
40
Where is urea secreted in the nephron? Is more or less of urea secreted than what was previous reabsorbed in the Proximal Tubule?
in the thin descending limb--> due to high conc. in interstitial fluid in inner medulla MORE secreted than previously reabsorbed in Proximal tubule
41
What parts of the nephron are impermeable to urea? What occurs here under the influence of ADH?
- Thick ascending limb - distal tubule - cortical collecting duct - outer medullary collecting duct ADH--> will stimulate water reabsorption here and therefore Urea is left behind (increase urea conc. in tubule fluid)
42
What is the total filtered load for Urea? Of that, what is reabsorbed? What is excreted?
110% filtered load - 70% reabsorbed - 40% excreted
43
After urea has traveled through the Loop of Henle, where is is reabsorbed? By what transporter?
Inner Medullary collecting duct--> by Urea Transporter 1
44
What activates the Urea Transporter 1? Where is this located? And what is it doing?
ADH activates it; in inner medullary collecting ducts | Facilitated diffusion from tubular lumen--> ISF 70% of filtered load reabsorbed --the other 40% is excreted
45
Can urea to toxic?
yes, at high levels
46
What does the Urea recycling that occurs in the nephron cause? And therefore what does it help with?
causes buildup of high urea concentration in inner medulla--> creating osmotic gradient at Loop of Henle so water can be reabsorbed
47
What substance is an example of secretion and is used to measure renal plasma flow?
PAH (para-aminohippuric acid) RPF = to clearance of PAH
48
Of the filtered load for PAH, what percentage is filterable and what isn't and why?
10% filterable 90% not filterable b/c bound to plasma proteins
49
Where is PAH secreted in the nephron? What happens when Tm is reached?
Proximal Tubules in peritubular membranes by transporters Tm is reach and secretion is maxed out
50
What happens to excretion of PAH as unbound plasma conc. of PAH increases?
excretion rises sharply and BOTH filtration and secretion are increased
51
Once Tm is reached for PAH, what happens to excretion and filtered load?
rise in excretion parallels an increase in filtered load
52
What does excretion equal for PAH?
= sum of filtration + secretion (as non is reabsorbed)
53
What inhibits the secretion of PAH by transporters in peritubular membranes of Proximal Tubular cells?
probenecid
54
What happens once the PAH transporters have hit maximum secretion? What then occurs with an increase in filtration?
filtration and excretion are parallel and increase filtration results in an increase excretion
55
What are the two forms that many substances secreted by the Proximal Tubule exist in?
(many substances are weak acids and weak bases) 1. charged and uncharged 2. relative amounts depend on pH
56
What are examples of weak acids? What are examples of weak bases?
PAH and salicylic acid (aspirin) quinine, morphine
57
When it comes to charges, what is the acid form of a weak acid? What is the conjugate base form? How does the charge effect reabsorption?
acid form = HA (uncharged) - can be pulled back conjugate base form = A- (charged) - can NOT be pulled back and is secreted
58
At a low pH, what form of a weak acid will predominate?
the HA (acid form) predominates--> therefore can reabsorb easier
59
At a high pH, what form of a weak acid will predominate?
the A- (conjugate base) form predominates--> can excrete more readily
60
If we want to excrete an acid, will we want to increase or decrease the pH?
increase the pH or urine --> therefore it will be in the A- form and cannot be reabsorbed
61
What is the base form and the conjugate acid form for a weak base?
base form = B (uncharged) - pull back easier conjugate acid form = BH+ (charged) - cannot be pulled back and is excreted
62
At a high pH, what form of a weak base predominates?
the B form (base form) --> can reabsorb easier
63
At a low pH, what form of a weak base predominates?
BH+ form (conjugate acid)--> therefore can excrete
64
If we want to excrete a base, what do we want to pH of urine to be, high or low?
want pH to be low--> therefore will be in conjugate acid form (BH+)--> making it charged and therefore cannot be reabsorbed and will be secreted
65
What substances can diffuse across the tubular cells and therefore can be reabsorbed?*
the UNcharged substances | charged forms are excreted
66
At a high pH what are we excreting, weak acid or weak base? What about at a low pH?
high pH--> excretion of weak acid low pH--> excretion of weak base
67
What are the two forms of Aspirin and which has a charge? Which can be reabsorbed and which cannot?
salicylic acid = HA form - can be reabsorbed salicylate = A- form - cannot be reabsorbed
68
If someone has an aspirin overdose, what do we want to do to maximize the loss of it?
put it in charged form--> so want to put it at a high pH, therefore it would be in the A- form (salicylate)

Physiology III - Freedman (18 decks)

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