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Renal > Lecture 2 - Renal Physiology > Flashcards

Lecture 2 - Renal Physiology Flashcards

1
Q

Where does all filtration happen?

A

through fenestrations in endothelial wall of glomerulus

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2
Q

How does blood enter the glomerulus?

A

Through the afferent artieriole

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3
Q

How does the afferent arteriole regulate blood flow through the glomerulus?

A

muscle tone

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4
Q

After plasma and small solutes escape thorugh fenestrations in the endothelial wall, where do the go?

A

through the basement membrane into Bowman’s Space

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5
Q

Bowman’s space is ______________ with the proximal tubule

A

continuous

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6
Q

What charge does the basement membrane hold?

A

negative charge

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7
Q

Why is the basement membrane negatively charged?

A

to repel other negatively charged proteins - preventing them from passing through it.

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8
Q

Along with the basement membrane holding a negative charge, what other mechanism does it have that prevents molecules from passing through it?

A

The basement membrane is also SIZE selective.

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9
Q

What is the size of molecules the basement membrane is impervious to?

A

molecules greater than 50-100 angstroms

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10
Q

What is the definition of GFR?

A

Total volume per unit in time (ml/min) which leaves the capillaries and enters Bowman’s space

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11
Q

How much fluid is filtered through the capillaries?

A

120ml/min which translates to 180L/day

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12
Q

How much of the 120ml/min becomes urine?

A

~ 1% (majority is reabsorbed)

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13
Q

What percentage of cardiac output goes to the kidneys? Does any other organ receive more than this?

A
  1. 20% of CO (1200 ml/min)

2. Only the liver gets more CO

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14
Q

what 4 factors determine GFR?

A
  1. Ultrafiltration coefficient
  2. Oncotic pressure
  3. Net hydraulic pressure
  4. Capillary plasma flow rate
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15
Q

How does the ultrafiltration coefficient affect GFR?

A

The ultratfiltration coefficient depends on capillary permeability and surface area available for filtration

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16
Q

How does oncotic pressure affect GFR?

A

Oncotic pressure opposes filtration. Since there should not be any free protein in Bowman’s space, the net direction of force should oppose filtration

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17
Q

How does Net hydraulic pressure affect GFR?

A

It will drive fluids from capillaries into Bowman’s space

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18
Q

How does capillary plasma flow rate affect GFR?

A

Higher flows = greater filtration

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19
Q

What is the typical Net Filtration Pressure?

A

10 mmHg

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20
Q

What two forces oppose osmosis in relation to GFR?

A

Bowman’s capsule pressure (18 mmHg)

Glomerular Oncotic pressure (32 mmHg)

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21
Q

What force drives fluid out of the capillaries into Bowman’s space in relation to GFR?

A

Glomerular hydrostatic pressure (net hydraulic pressure) (60 mmHg)

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22
Q

As plasma moves towards the end of the glomerular capillary, does filtration increase or decrease?

A

Decrease - because of an increased oncotic pressure. As fluid is removed, the protein concentration increases

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23
Q

Capillary hydrostatic pressure drops significantly at the level of the _______ ______ resulting in maximal reabsorbtion into the _____ _____ and ______ _______.

A
  1. efferent arteriole
  2. Vasa recta
    3 Peritubular plexi
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24
Q

What is the range of MAP that reflects the kidneys ability to regulate GFR over a range of conditions?

A

80 - 200 mmHg GFR and RBF remain contstant

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25
Q

What 2 mechanisms play a role in autoregulation of the kidneys?

A
  • Constriction and dilation of precapillary sphincters in the afferent and efferent arterioles
  • Increased Na delivery to the Macula Densa will decrease GFR
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26
Q

Where is the macula densa located?

A

It is part of the Distal Tubule

**increased Na in the MD will signal to decrease GFR

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27
Q

What are the 4 ways the kidneys handle fluids?

A
  1. Filtration
  2. Reabsorption
  3. Secretion
  4. Excretion
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28
Q

What is the definition of renal clearance?

A

Volume of plasma from which all of a given substance is removed per unit time in one pass through the kidney

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29
Q

If a substance is neither secreted nor reabsorbed then its clearance is__________ to GFR

A

EQUAL

** an example of this is insulin

30
Q

If a substance is completely reabsorbed then clearance is ________.

A

ZERO

**an example of this is glucose under normal conditions since you should not have glucose in your urine

31
Q

*If renal clearance is greater than GFR, then there must be net ___________

32
Q

*If renal clearance is less than GFR, then there must be net ___________

A

reabsorption

33
Q

*If renal clearance is equal to GFR, then there must be net ___________

A

No net - it will have neither net secretion or reabsorption

34
Q

What is used to estimate GFR?

A

renal clearance of creatinine (creatinine clearance)

35
Q

What is creatinine? What is the best way to evaluate creatinine clearance?

A

Creatinine is a byproduct of muscle protein

- 24 hr urine collection

36
Q

What is a normal GFR when you have 100% functioning nephrons?

A

120 ml/min

37
Q

What is a reduced GFR?

A

12-80 ml/min - 10-40% nephrons

38
Q

What is considered renal failure with regards to GFR?

A

< 12 ml/min - 0% nephrons functioning

39
Q

What are the 3 transport mechanisms used in reabsorption and secretion?

A
  1. Active transport
  2. Passive transport
  3. secondary active transport
40
Q

There are two kinds of passive transport - simple and facilitated. Which uses a protein channel? Which is diffusion of gasses or lipids?

A

Protein channel - Factilitated

Diffusion - simple

41
Q

In a Na/K ATPase pump, which direction does the pump take Na and K?

A

Na - out of cell

K - back into cell

42
Q

Briefly describe maximum transport (Tm) rate.

A

reabsorbtion and secreation of substances like glucose and amino acids are coupled with secondary active Na transport.
Until the transport mechanism is saturated the rate of secretion or absorption is proportional to the concentration of substrate and affinity of the carrier for the substrate.
**in other words the more substance you dump in, the more you secrete or absorb until you hit a limit and you can’t reabsorb any more and a bunch gets dumped.

43
Q
  • All reabsorbtion in the proximal tubule is ______
A

Iso-osmotic

44
Q

Where is the main reabsorptive area of the nephron?

A

Proximal tubule

45
Q

What kinds of things are reabsorbed from the proximal tubule?

A 
water
Na
vitamins
K
HCO3 (using carbonic anhydrase)
46
Q

What things are secreted in the proximal tubule?

A 
Organic acids (diuretics, antibiotics)
Ammonia (important for acid base fxn)
47
Q

In the remaining fluid in the proximal tubule, the chloride concentration is higher than plasma. Why is that?

A

More chloride remains inside the tubule to maintain electroneutrality because more HCO3- is reabsorbed (out).

48
Q

Which part of the thin Loop of Henle is permeable (ascending or descending)? What is it permeable to?

A

Descending Loop - Highly permeable to WATER and MOST SOLUTES

49
Q

Is water permeable in the ascending loop?

A

NO - but some ions like Calcium, Bicarb and Mag are permeable.

50
Q

Which part of the Loop of Henle is considered the MOST IMPORTANT?

A

Thick Ascending segment

51
Q

Why is the Thick Ascending Loop the most important?

A

This section is the “diluting’’ segment of the nephron

52
Q

Is the Thick ascending loop permeable or impermeable to water?

A

Impermeable to water while solute is pumped out of the tubular fluid

53
Q

The __________ membrane of the Thick ascending loop has a 1Na, 1K, 2Cl pump. This is the only nephron segment where ______ is actively transported

A

Luminal membrane

Chloride

54
Q

Where does Lasix work its magic?

A

Thick ascending loop –> Luminal Membrane –> Na/K/Cl pump

55
Q

Is the fluid in the thick ascending loop concentrated or diluted?

A

Dilute fluid but it is being set for concentration later

56
Q

What is the charge in the Thick Ascending Loop?

A

Positve charge - drives reabsorbtion of Mg++ and Ca++

57
Q

The first portion of the distal tubule or _____ ______, is responsible for what?

A

Macula Densa

Provides feedback control of GFR and blood flow in the same nephron

58
Q

Like the Thick ascending Loop, the early distal tubule is (permeable or impermeable) to water?

A

Impermeable

59
Q

Fluids in the early distal tubule are (dilute or concentrated)?

A

More dilute because more solutes are being removed

60
Q

What is reabsorbed in the early distal tubules?

A

Na, Cl, Ca, Mg

61
Q

The 2nd half of the distal tubule and cortical collecting tubules have similar functions of controlling the degree of dilution or concentration of urine. (T/F)

62
Q

Where does ADH work its magic?

A

Later distal tubule

63
Q

What is ADH affect on the later distal tubule?

A
  • High levels make it permeable to H2O (more reabsorbed)

- Low levels make it impermeable to H2O (less reabsorbed/more secreted)

64
Q

What hormone controls the reabsorbtion of Na or secretion of K in the Later Distal tubule?

A

Aldosterone

**Both Aldosterone and ADH work in the later distal tubule

65
Q

What cells in the distal tuble and early collecting ducts are responsible for reabsorbing Na and secreting K?

A

Principal Cells

66
Q

What cells in the distal tube and early collecting ducts are responsible for reabsorbing bicarb and K while secreting H?

A

Intercalated cells - important in acid-base regulation

67
Q

What is the final site for processing urine?

A

Medullary Collecting duct

68
Q

What is the medullary collecting duct permeable to?

69
Q

What controls the medullary collecting duct’s ability to reabsorb H2O?

A

ADH - Less than 10% of filtered H2O and Na are reabsorbed

70
Q

Hydrogen ions are secreted into the urine in what 2 places?

A

Later distal tubule

Collecting ducts

Renal (5 decks)

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