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Physiology > Tubular processing of glomerular filtrate > Flashcards

Tubular processing of glomerular filtrate Flashcards

1
Q

What are the 3 basic renal processes that represent all the substances in the urine?

A
  • glomerular filtration
  • tubular reabsorption
  • tubular secretion
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2
Q

Is tubular reabsorption passive or selective?

A

Highly selective!!

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3
Q

The glomerular filtrate that is presented to the tubules is basically ______

A

Plasma, without the protein or anything bound to protein

- need to consider when administering drugs that are bound to protein

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4
Q

Calcium is bound to ____

A

Albumin

- filtrate should contain half the concentration of total calcium or the same amount as ionized/unbound calcium

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5
Q

Carrier mediated reabsorption process

A

Too many solutes presented to be reabsorbed will cause carrier proteins to become saturated and any more solute will pass on and fail to be reabsorbed

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6
Q

What are 4 main substances that are usually reabsorbed 100%?

A
  • glucose
  • amino acids
  • protein
  • bicarb (>99.9%)
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7
Q

What is 1 substance that is never reabsorbed?

A

Creatinine

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8
Q

Why is urea reabsorbed 50% of the time if it is a waste product?

A

To increase tonicity of the medulla to allow for reabsorption of water

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9
Q

Route of transport for tubular reabsorption

A
  • across tubular epithelial membranes
  • into renal interstitial fluid
  • through the peritubular capillary membrane back into the blood
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10
Q

How are water and solutes transported?

A
  • transcellular: thought the cell membrane

- paracellular: through spaces between the cell junctions

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11
Q

Substances are diffused through the peritubular capillary walls into the blood by what 3 forces?

A
  • hydrostatic
  • colloidal
  • osmotic
  • Starlings forces*
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12
Q

Active transport

A

Moves a solute against an electrochemical gradient and requires energy derived from metabolism

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13
Q

Primary active transport

A

Transport that is coupled directly to an energy source

- ex: sodium-potassium ATPase pump

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14
Q

Secondary active transport

A

Transport that is coupled indirectly to an energy source

- ex: reabsorption of glucose due to an ion gradient

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15
Q

Osmosis

A

Reabsorption of water by a passive physical mechanism, from a region of low solute concentration to high solute concentration

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16
Q

In the proximal tubules, water passage is relatively ______

A

Unobstructed

- compare to controlled passage in the distal tubules and collecting ducts

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17
Q

What are the 4 primary known active pumps?

A
  • Na K ATPase (provides electrochemical gradient for secondary active facilitated uptake of other substances)
  • Ca ATPase
  • H ATPase
  • H K ATPase
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18
Q

Ultrafiltration

A

Bulk flow

  • passive method of transporting solutes thru the peritubular capillary walls into the blood
  • mediated by hydrostatic and colloid osmotic forces
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19
Q

Is reabsorption of sodium primary or secondary active transport?

A

Primary

- utilizes an electrochemical gradient (Na-K ATPase)

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20
Q

Where is the Na-K ATPase pump located within the cell?

A

On the basolateral side

- uses released energy from hydrolysis of ATP to transport sodium ions out of the cell and into the interstitum

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21
Q

Where does sodium diffuse to once it is in the interstitium?

A

Could go into the peritubular capillary and into the blood, or it could diffuse back into the tubular lumen

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22
Q

Why would sodium move back into the tubular lumen?

A

Ensures that there is always sodium available to provide substrate for the cotransport of molecules and prevents excessive sodium resorption in times of excessive sodium consumption

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23
Q

There is a ____ concentration of sodium and a ____ concentration of potassium inside the cell

A

Low; high

- creates a negative charge of -70 millivolts

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24
Q

What is located on the apical side of the proximal tubular epithelial cells to facilitate diffusion?

A
  • brush border
  • channels
  • molecules/ligands to bind both sodium and another solute (glucose, amino acids, etc)
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25
Q

What are the 3 steps of sodium transport from the tubular lumen into the blood?

A
  • Na diffuses across apical membrane into cell DOWN an electrochemical gradient
  • Na is transported across basolateral membrane AGAINST an electrochemical gradient
  • Na, water, etc are reabsorbed from intestinal fluid into peritubular capillaries by ultrafiltration
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26
Q

How are proteins reabsorbed due to their large size?

A

Attach to specific receptor molecules on tubular epithelial cell membrane and are invaginated internally into the cell
–> pinocytosis

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27
Q

What are the requirements of pinocytosis?

A
  • tubulin polymerization
  • small changes in cytoskeleton
  • both require energy, so pinocytosis is another form of active transport!!*
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28
Q

In secondary active transport _____ interacts with _____ and are transported together across the membrane

A

2 (or more) substances; specific membrane protein (carrier)

  • requires a specialized carrier molecule designed to fit both transported molecules
  • BOTH molecules need to be present and bound to carrier for it to work
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29
Q

Does secondary active transport require energy directly from ATP?

A

No, utilizes electrochemical gradient created by simultaneous facilitated diffusion of another transported substance (usually sodium)

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30
Q

Glucose and amino acids are transported into the cell ______ the electrochemical gradient and are diffused across the basolateral membrane by _______

A

Against; facilitated diffusion due to concentration gradient inside the cell

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31
Q

Sodium glucose co-transporters

A

Located on brush border of apical membrane, carry glucose into cell against concentration gradient
- SGLT2, SGLT1

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32
Q

Glucose transporters

A

Located on the basolateral membrane, diffuses glucose out of the cell into the interstitial spaces (expends no energy)
- GLUT2, GLUT1

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33
Q

A substance is said to undergo “active” transport when ______

A

At least one of the steps in reabsorption involves primary or secondary active transport, even though other steps in the reabsorption process may be passive

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34
Q

Counter-transport

A

Electrochemical gradient created by Na-K ATPase pump provides energy needed to eliminate unwanted substances (hydrogen) from the cell, into the tubular lumen

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35
Q

Transport maximum

A

Limit to the rate at which the solute can be transported

  • glucose
  • amino acids
  • protein
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36
Q

Why doesn’t sodium exhibit a maximum transport rate?

A

There are so many avenues through which sodium can move

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37
Q

When does glucosuria occur?

A

When all of the transport proteins are occupied and there is still glucose in the lumen —> glucose will be lost in urine

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38
Q

Excess protein loss could be due to

A

Glomerulonephritis
- more proteins leak across the glomerulus than the tubules can handle
Tubular disease
- tubules are too injured to handle even a normal protein load

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39
Q

Glucosuria could be the result of what 2 processes?

A
  • hyperglycemia: increased glucose in the blood, causing more glucose to be filtered and presented to the tubules than there are transport molecules for reabsorption
  • normoglycemic glucosuria: sick, injured tubular epithelium where there are a diminished number of transport molecules that can’t handle even a normal glucose load
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40
Q

Why does osmotic diuresis occur?

A

When glucose is left in the tubule, it provides an osmotic effect of holding water in the tubule
= increased urine output, followed by compensatory polydipsia

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41
Q

Different tubules have different _______

A

Transport maximums

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42
Q

What is another factor that can affect reabsorption?

A

Time
- if the flow rate of filtrate is so fast that there is insufficient time for reabsorption to occur, then spillage into the urine might occur

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43
Q

Unique features of the proximal tubule

A
  • high cell surface area (brush border)
  • high metabolic rate due to high mitochondria amount, leading to high oxygen consumption
  • loaded with protein carrier molecules
44
Q

____of the filtered load of sodium and water is reabsorbed in the proximal tubules

A

65%

- reabsorbs essentially all glucose and amino acids

45
Q

Why is the secretion of hydrogen ions into the tubular lumen important?

A

Is an important step in reabsorption of bicarb from tubule

- combines H with HCO3 to form H2CO3, which dissociates into H2O and CO2

46
Q

In the first half of the proximal tubule, sodium is reabsorbed by co-transport with ______

A

Glucose, amino acids, other solutes

- preferred

47
Q

In the second half of the proximal tubule, sodium is reabsorbed by co-transport with_____

A

Chloride
- higher chloride concentration favors diffusion from lumen through intercellular junctions into the renal interstitial fluid

48
Q

Why does the total solute concentration remain the same all along the proximal tubule?

A

Due to extremely high permeability of the proximal tubule to water

49
Q

Proximal tubule is an important site for secretion of _____

A

Organic acids and bases, and drugs/toxins

50
Q

As solutes are absorbed, the filtrate becomes more _____, while the solutes in the interstitum become more _____

A

Dilute; concentrated

flow of solutes always favors movement into the capillary

51
Q

Solvent drag

A

As water flow, some of the things dissolved in water flow with it

52
Q

Concentration of solutes that are not absorbed _____ as water flows

A

Increases

  • if the tubule is permeable, they will move down their own concentration gradient back into circulation
  • if tubule is impermeable, then the concentration will continue to increase
53
Q

In the proximal tubule, passive reabsorption of chloride occurs due to

A
  • changes in electrical and concentration gradient

- secondary active reabsorption via Na-Cl cotransport molecule

54
Q

How is urea passively reabsorbed?

A

Urea is a non-polar, lipid soluble compound so as water is reabsorbed, the urea concentration increases in the tubule lumen and some will be passively reabsorbed

55
Q

Does the concentration of sodium change throughout the proximal tubule?

A

No, the total amount of Na decreases but the concentration does not due to water moving with Na

56
Q

While the total solute concentration does not change, the relative ______ does change

A

Proportion that each solute contributes

57
Q

Loop of Henle

A
  • no brush border
  • thin epithelial membranes
  • minimal metabolic activity, with few mitochondria
58
Q

Thin descending segment

A

Passive, highly permeable to water

- 20% of water absorption

59
Q

Why is water absorbed in the thin descending segment at a rate that increases the osmolarity of the urine, when the osmolarity did not increase in the proximal tubule?

A

Because the interstitial fluid of the renal medulla becomes more hypertonic as it descends
- water moves passively out of the tubule lumen following concentration gradients

60
Q

The ascending limb (both thin and thick segments) is virtually impermeable to _____

A

Water

  • important for concentrating urine
  • all the water that had been reabsorbed from the filtrate in the thin descending limb, causing the filtrate to become more concentrated would move back into the lumen as the tubule exited the hypertonic area of the medulla
61
Q

The thin ascending loop is moderately permeable to ____

A

Urea, due to presence of transport molecule facilitating movement of urea into the lumen
- may be slightly permeable to Na

62
Q

Thick ascending loop

A
  • increased surface area
  • increased mitochondria = high metabolic activity
  • impermeable to water (even in presence of ADH)
  • impermeable to urea
63
Q

Thick ascending segment accounts for _____ of reabsorption of Na, Cl, and K

A

25%

  • facilitated co-transport system that depends on sodium gradient generated by Na-K ATPase pump on basolateral membrane
  • water does not follow!!
64
Q

Na-K ATPase pump in the thick ascending loop also creates a _____

A

Negative K ion gradient, allowing K to diffuse across cell membranes back into the tubule lumen
- back diffusion of K creates a slight positive charge pushing other cations to be reabsorbed

65
Q

Urine becomes more ____ in the thick ascending segment as solutes are absorbed

A

Dilute

66
Q

Furosemide blocks the _______, PGE2 down regulates its activity

A

Sodium - 2 Chloride - Potassium co-transporter on the apical membrane of the thick ascending limb

67
Q

Prostaglandin E2

A

Decreases sodium reabsorption at the thick ascending limb of the loop of Henle
- only occurs during dehydration

68
Q

Administration of NSAIDs ____ sodium reabsorption

A

Increases, by blocking action of PGE2

- eliminates ability to promote vasodilation to maintain blood flow and delivery of oxygen to renal medulla

69
Q

Early distal tubule

A
  • goes back into the cortex
  • impermeable to water (further dilution)
  • impermeable to urea
  • active reabsorption of Na, Cl, etc
  • functionally similar to thick ascending loop
70
Q

The early distal tubule contains the _____

A

Macula densa
- group of closely packed epithelial cells that is a part of the juxtaglomerular complex and provides feedback control of GFR and blood flow to the same nephron

71
Q

Regulated reabsorption and/or secretion begins in the

A

Late distal tubule and cortical collecting duct

- everything up until this point has been unregulated

72
Q

The late distal tubule and collecting duct are impermeable to ___

A

Urea

73
Q

Ability of LDT and CT to reabsorb sodium ions and the rate of reabsorption is controlled by _____ and _____

A

Aldosterone and angiotensin (upregulates Na K pumps)

74
Q

Principle cells

A

Secrete potassium from peritubular capillary blood into the tubular lumen

  • controlled by aldosterone and concentration of potassium ions in the body fluids
  • reabsorb sodium and water from the lumen
75
Q

Intercalated cells

A

Type A secrete hydrogen ions by active hydrogen-ATPase

  • different from H secretion that occurs in the proximal tubule
  • is capable of secreting H ions against a large concentration gradient
  • plays a key role in acid-base regulation
76
Q

Permeability of LDT and CT to water is controlled by

A

Concentration of ADH

  • high levels of ADH cause tubular segments to be permeable to water (dehydration)
  • absence of ADH, they are impermeable to water
77
Q

Principle cells contain ____ on the basolateral membrane and ______ in the apical membrane

A

Na-K ATPase pumps; Na and K channels
- both are under control of aldosterone, which stimulates activation of operon coding for nuclear transcription of mRNA for production of proteins and enzymes

78
Q

Diuretics that block action of aldosterone

A

Decrease activity of Na K ATPase pump and decrease insertion of Na channels into the apical cell membrane
- K sparing

79
Q

Process of principal cells secreting potassium

A
  • K enters cell due to Na-K ATPase pump, which maintains a high intracellular K concentration
  • once inside the cell, K diffuses DOWN its concentration gradient across apical membrane into tubular lumen
80
Q

Intercalated cells are important for _____

A

pH control

81
Q

Intercalated cells utilize ____ and ______

A
  • Na concentration gradient, created by Na K ATPase pump to move H out
  • K excreted by principle cells to enable an energy dependent K/H counter transport to pump H out against a larger conc gradient
82
Q

By exchanging ___ for ___, the intercalated cells are helping prevent the K loss that would have occurred during acidosis

A

H for K

- also eliminates the H that was the cause of the acidosis

83
Q

ADH

A

Causes proteins in the cell to cluster together and fuse into a water channel that is inserted into the cell membrane, making the lipid bilayer of the cell membrane permeable to water

84
Q

Medullary collecting duct

A
  • H2O permeability controlled by ADH
  • permeability to Na and K controlled by aldosterone
  • H secretion against a large concentration gradient
85
Q

Medullary collecting duct is permeable to urea due to

A

Urea transport molecules that facilitate uptake of urea out of the lumen and into the interstitium (down the concentration gradient)

  • helps to raise osmolaltiy
  • ADH induces an increase in the number of urea transport molecules
86
Q

Na reabsorption throughout the tubules

A
  • 65% in the proximal tubule
  • 25% in the thick ascending loop of Henle
  • 5-7% in the distal tubule
  • 5-10% in the collecting tubule
87
Q

Hormones affecting tubular resorption regulation

A
  • angtiotensin 2
  • aldosterone
  • ADH
  • atrial natiruetic factor
88
Q

How does angiotensin 2 affect tubular resorption?

A
  • increase efferent arteriole constriction
  • increase tubular Na resorption directly
  • increase tubular Na resorption via increased aldosterone secretion
89
Q

Glomerulotubular balance

A

Ability of certain segments of the nephron (proximal tubule and thick ascending limb) to increase the amount of water and solutes reabsorbed as filtrate flow increase or decreases within physiologic range

90
Q

Glomerulotubular balance helps prevent _____

A

Overloading of distal tubular segments when GFR increases

- buffers the effects of spontaneous changes in GFR on urine output

91
Q

Peritubular physical forces

A

Balance between hydrostatic and colloidal pressure and concentration gradients across the peritubular capillaries

92
Q

An increase in resistance of the arterioles _____ peritubular capillary hydrostatic pressure and _____ reabsorption rate

A

Reduces; increases

93
Q

Raising the colloid osmotic pressure _____ peritubular capillary reabsorption

A

Increases

- colloid osmotic pressure is determined by systemic plasma colloid osmotic pressure and filtration fraction

94
Q

If arterial pressure and/or blood volume increases without any other opposing force ____ increases as well

A

Renal capillary pressure

95
Q

Pressure diuresis

A

More fluid is filtered, less of the filtered fluid is reabsorbed = increases in urinary excretion of sodium and water

96
Q

Natriuresis occurs due to

A

Increase in pressure resulting in a down regulation of angiotensin 2 and its effect on sodium resorption directly and mediated thru aldosterone secondarily

97
Q

A decrease in systemic blood pressure, or CO, or an increase in afferent arteriolar sphincter tone will lead to a ____ in both glomerular and peritubular capillary hydrostatic pressure

A

Decrease
- decrease in peritubular capillary hydrostatic pressure leads to an increase in absorption = greater absorption of what was filtered

98
Q

What causes the precursor for angiotensin to be released?

A

Decreased RBF leads to decreased GFR –> results in slower flow thru the tubule —> allows more time for more Na reabsorption —> stimulates macula densa to produce and release renin

99
Q

Angiotensin 2 increases ______ and ______

A

Sodium and water reabsorption

  • mediated by increasing multiple cAMP controlled mechanisms of transmembrane Na transport
  • stimulates aldosterone secretion
  • constricts efferent arteriole
100
Q

Aldosterone increases _____ and _____

A

Sodium reabsorption and potassium secretion

- stimulates Na K ATPase pump and increase Na permeability on the apical membrane

101
Q

What is the primary site of action for aldosterone?

A

Principle cells of the cortical collecting tubule

102
Q

ADH increases _____

A

Water reabsorption

103
Q

Inappropriate secretion of ADH results in _____

A

Hyponatremia

104
Q

Atrial natriuretic hormone decreases ____ and _____

A

Sodium and water reabsorption

105
Q

Atrial natriuretic peptide is secreted when

A

Atria become distended due to increases water absorption, leading to blood volume expansion
- ANF blocks Na resorption in the collecting ducts

Physiology (33 decks)

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