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Physiology - Guyton & Hall > Chapter 27 - Guyton > Flashcards

Chapter 27 - Guyton Flashcards

1
Q

Pathway of glomerular filtrate.

A

proximal tubule–>loop of Henle–>distal tubule–>collecting tubule–>collecting duct

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2
Q

Which substances are almost entirely reabsorbed, so that they should not be present in urine?

A

glucose and amino acids

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3
Q

What two processes must occur in order for a substance to be reabsorbed?

A

transported across the tubular epithelial membranes into the renal interstitial fluid and through the peritubular capillary membrane back into the blood

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4
Q

Two pathways for water and solutes to travel across the tubular epithelium into the interstitial fluid?

A

transcellular route - through
the cell membranes themselves; paracellular route - through the junctional spaces between the cells (can be passive or active transport)

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5
Q

After absorption across the tubular epithelial cells into the interstitial fluid, water and solutes are transported the rest of the way through the peritubular capillary walls into the blood by ___________ that is mediated by hydrostatic and colloid osmotic forces.

A

ultrafiltration (bulk flow)

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6
Q

The sodium-potassium ATPase pump is what kind of transport?

A

primary active transport

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7
Q

Reabsorption of glucose in the renal tubule is an example of what type of transport?

A

secondary active transport (transport is coupled indirectly to an energy source such as ion gradient)

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8
Q

In renal tubular cells, most of the sodium is transported via the (transcellular/paracellular) pathway.

A

transcellular

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9
Q

What is the special importance of primary active transport?

A

it can move solutes against an electrochemical gradient

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10
Q

Explain why sodium will tend to be reabsorbed from the tubular lumen back into the blood (3 main reasons).

A
  1. Sodium diffuses across the luminal membrane
    (apical membrane) into the cell down an electrochemical gradient established by the sodium-potassium ATPase pump on the basolateral side of the membrane.
  2. Sodium is transported across the basolateral
    membrane against an electrochemical gradient
    by the sodium-potassium ATPase pump.
  3. Sodium, water, and other substances are reabsorbed from the interstitial fluid into the peritubular capillaries by ultrafiltration, a passive process driven by the hydrostatic and colloid osmotic pressure gradients.
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11
Q

Means of transport for glucose and amino acids across the apical side of the tubular epithelial cells.

A

secondary active transport (co-transport with sodium)

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12
Q

Means of transport for glucose and amino acids through the basolateral membranes.

A

facilitated diffusion (driven by the high glucose and amino acid concentrations in the cell)

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13
Q

How does hydrogen exit the tubular epithelial cells and enter the tubular lumen?

A

counter-transport with sodium (secondary active transport), sodium into the cell and hydrogen out to be excreted; sodium wants to come in because of the concentration gradient established by the sodium-potassium ATPase pump on the basolateral membrane

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14
Q

Pinocytosis is used to reabsorb proteins. What type of transport is pinocytosis?

A

active transport (requires energy)

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15
Q

Why do substances that are actively reabsorbed have a transport maximum?

A

saturation of the specific transport systems involved when the amount of solute delivered to the tubule (referred to as tubular load) exceeds the capacity of the carrier proteins and specific enzymes involved in the transport process

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16
Q

Why might glucose be found in the urine of a person with uncontrolled diabetes mellitus?

A

plasma glucose levels rise to levels high enough to exceed transport maximum, diseased nephrons lowers the glucose reabsorption ability

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17
Q

Substances that are passively reabsorbed do not have a transport maximum because?

A

1) electrochemical gradient for diffusion of the substance across the membrane; 2) permeability of the membrane for the substance; 3) time that the fluid containing the substance remains within the tubule

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18
Q

What is the difference between water osmosis in the proximal tubule, loop of Henle, and distal tubules/collecting ducts?

A

proximal tubule - water reabsorption high; ascending loop of Henle - always low; distal tubules/collecting tubules/collecting ducts - high or low depending on presence of ADH

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19
Q

The active reabsorption of sodium is closely coupled to the passive reabsorption of _______ by way of an electrical potential and a ________
concentration gradient.

A

chloride

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20
Q

The _______ tubules reabsorb about 65% of the filtered Na, Cl, bicarbonate, and K and essentially all the filtered glucose and amino acids.

A

proximal

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21
Q

How is chloride transported through secondary active transport across the luminal membrane?

A

co-tranport with sodium

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22
Q

Water reabsorption through osmosis is coupled to reabsorption of which ion?

A

sodium

23
Q

What specific cellular characteristics of the proximal tubule contribute to its high capacity for reabsorption?

A

large number of mitochondria, extensive brush border on the luminal (apical) side of the membrane, extensive labyrinth of intercellular and basal channels, extensive membrane surface of the epithelial brush border is also loaded with protein carrier molecules (co-transport, counter-transport)

24
Q

Provides the major force for reabsorption of sodium, chloride, and water throughout the proximal tubule.

A

sodium-potassium ATPase pump

25
Q

Explain the differences in the mechanisms by which sodium and chloride are transported through the luminal side of the early vs. late portions of the
proximal tubular membrane.

A

first half of the proximal tubule - sodium is reabsorbed by co-transport along with glucose, amino acids, and other solutes; second half of the
proximal tubule - little glucose and amino acids remain, sodium is now reabsorbed mainly with chloride ions

26
Q

Why would sodium concentration remain relatively the same throughout the length of the proximal tubule (even though a large quantity is being reabsorbed)?

A

concentration of sodium (and the total osmolarity) remains relatively constant because water permeability of the proximal tubules is so great that water reabsorption keeps pace with sodium reabsorption

27
Q

About 20% of the filtered water is reabsorbed in the loop of Henle, and almost all of this occurs in the thin __________ limb.

A

descending

28
Q

The ascending limb, including both the thin and thick portions, is virtually impermeable to water, a characteristic that is important for what?

A

concentrating the urine

29
Q

About 25% of the filtered loads of sodium, chloride, and potassium are reabsorbed in the loop of Henle, mostly where? Considerable amounts of other ions, such as calcium, bicarbonate, and magnesium, are also reabsorbed here.

A

thick ascending limb

30
Q

So called “loop” diuretics such as furosemide inhibit the sodium 2-chloride, potassium co-transporter to promote diuresis. Where is the site of action?

A

thick ascending limb of the loop of Henle

31
Q

The thiazide diuretics, which are widely used to treat disorders such as hypertension and heart failure, inhibit what?

A

sodium-chloride co-transporter (early distal tubule - diluting tubule)

32
Q

What are the functional differences between the principal and intercalated cells in the late distal tubule?

A

principal cells - reabsorb sodium and water from the lumen and secrete potassium ions into the lumen; intercalated cells - reabsorb potassium ions and secrete hydrogen ions into the tubular lumen

33
Q

The _______ _____ are the primary sites of action of the potassium-sparing diuretics (sodium channel
blockers as well as the aldosterone antagonists).

A

principal cells (late distal tubule)

34
Q

Summarize functional characteristics of the late distal tubule and cortical collecting tubule.

A
  1. urea excretion (relatively impermeable to urea)
  2. principal cells reabsorb sodium and secrete potassium (aldosterone)
  3. intercalated cells secrete hydrogen ions by an active hydrogen-ATPase mechanism
  4. permeability of the late distal tubule and
    cortical collecting duct to water is controlled by
    the concentration of ADH, which is also called
    vasopressin (degree of dilution or concentration of the urine)
35
Q

Medullary collecting duct

A
  1. The permeability of the medullary collecting duct
    to water is controlled by the level of ADH.
  2. Unlike the cortical collecting tubule, the
    medullary collecting duct is permeable to urea.
  3. The medullary collecting duct is capable of
    secreting hydrogen ions against a large
    concentration gradient, as also occurs in the
    cortical collecting tubule (acid-base balance).
36
Q

The rate of _____ clearance can be used to estimate the renal plasma flow.

A

PAH; average person can clear about 90% of the PAH from the plasma flowing through the kidneys and excrete it in the urine

37
Q

Because it is neither reabsorbed or secreted by the renal tubules, this substance is used to estimate water reabsorption (also GFR).

A

inulin

38
Q

Glomerulotubular Balance

A

total rate of reabsorption increases as the filtered load increases, even though the percentage of GFR reabsorbed in the proximal tubule remains relatively constant at about 65% (this also occurs in the loop of Henle)

39
Q

Which two factors primarily prevent large changes in fluid flow in the distal tubules when the arterial pressure changes or when there are other disturbances?

A

renal autoregulatory mechanisms, especially tubuloglomerular feedback, which help prevent changes in GFR and golmerulotubular balance to maintain reabsorption according to flow

40
Q

What governs the rate of reabsorption across the peritubular capillaries, just as these physical forces control filtration in the glomerular capillaries.

A

hydrostatic and colloid osmotic forces

41
Q

Which forces favor reabsorption?

A

hydrostatic pressure in the renal interstitium outside the capillaries, colloid osmotic pressure of the peritubular capillary plasma proteins

42
Q

Which forces oppose reabsorption?

A

hydrostatic pressure inside the peritubular capillaries (peritubular hydrostatic pressure), colloid osmotic pressure of the proteins in the renal
interstitium

43
Q

Reabsorption =

A

Kf x Net reabsorptive force

44
Q

What is the effect of increased arterial pressure on urine output?

A

pressure natriuresis and pressure diuresis (increased output), due to slight increase in GFR (more if kidney diseased), decreased sodium and water reabsorption in the tubules (increased hydrostatic pressures), reduced angiotensin II formation

45
Q

The primary site of aldosterone action is on the _______ cells of the cortical collecting tubule.

A

principal (increase action of sodium-potassium ATPase pump on the basolateral membrane to increase sodium reabsorption)

46
Q

perhaps the body’s most powerful sodium-retaining hormone

A

Angiotensin II

47
Q

The increased formation of angiotensin II helps to return blood pressure and extracellular volume toward normal by increasing sodium and water reabsorption from the renal tubules through three main effects:

A
  1. stimulates aldosterone secretion
  2. constricts the efferent arterioles (reduces peritubular capillary hydrostatic pressure and raises filtration fraction in the glomerulus and increases the concentration of proteins and the colloid osmotic pressure in the peritubular capillaries)
  3. stimulates sodium reabsorption in the proximal tubules, the loops of Henle, the distal tubules, and the collecting tubules (stimulates sodium transport across both the luminal and the basolateral surfaces of the epithelial cell membrane in the tubules)
48
Q

The most important renal action of _____ is to increase the water permeability of the distal tubule, collecting tubule, and collecting duct epithelia.

A

ADH (anti-diuretic hormone)

49
Q

What is the function of atrial natriuretic peptide?

A

when the atrial pressure rises (increased blood volume), this peptide is released and acts on the collecting ducts to decrease the reabsorption of sodium and water by the renal tubules, especially collecting ducts to increase urinary excretion

50
Q

__________ hormone is one of the most important
calcium-regulating hormones in the body. Its principal action in the kidneys is to increase tubular reabsorption of calcium, especially in the distal tubules and perhaps also in the loops of Henle.

A

Parathyroid

51
Q

Sympathetic nervous system action is to increase/decrease sodium reabsorption.

A

increase

52
Q

What is renal clearance?

A

calculated from the urinary excretion rate of that substance divided by its plasma concentration; mathematically C = (U x V) / P where [C=clearance, U x V=urinary excretion rate, P=plasma concentration]

53
Q

If the clearance rate of a substance is greater than that of inulin, what does this mean?

A

the substance must be secreted by the nephron tubules because inulin is neither absorbed or secreted in the tubules

Physiology - Guyton & Hall (21 decks)

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