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Physiology - Guyton & Hall > chapter 29 renal lecture 3 > Flashcards

chapter 29 renal lecture 3 Flashcards

1
Q

to excrete excess water consumed..

A

it is necessary to dilute filtrate as it passes along tubule

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2
Q

after ingestion of excess water, the kidney does what

A

excretes excess water, but relative solute excretion concentration stays the same

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3
Q

Does osmolality in PCT change?

A

as fluid goes through PCT, solutes and water are reabsorbed in equal proportions=PCT filtrate isosmotic to plasma

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4
Q

in descending loop of henle, what happens to filtrate

A

water is reabsorbed and filtrate becomes hyper osmotic and becomes hypertonic (in equilibrium with interstitium)

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5
Q

what happens to tubular fluid in ascending LOH

A

tubular fluid is diluted in thick segment with Na, K and Cl reabsorbed. this part of LOH is impermeable to water (even with ADH) so tubular fluid becomes more dilute as it flows up ascending LOH into the early DCT, about 100 mOmos

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6
Q

What is the osmolality of filtrate entering the early DCT

A

hypo osmotic, about 1/3 of normal osmolarity so 100 mOsmos

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7
Q

In the absence of ADH, what happens to tubular fluid in DCT and collecting duct

A

tubular fluid is further diluted, additional reabsorption of Na Cl, and osmolarity further decreases to about 50 mOsmos

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8
Q

what is mechanism for forming dilute urine

A

continue to reabsorb solutes from DCT and no additional reabsorption of water, resulting in excretion of dilute urine

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9
Q

How is water lost in the body

A

breathing, feces, skin evaporation and perspiration, and kidney elimination

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10
Q

how do the kidneys form concentrated urine during times of decreased intake

A

kidneys continue to excrete solutes while increasing water reabsorption and decreasing the volume of urine formed

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11
Q

what is maximum urine concentrating ability in humans

A

1200 to 1400 mOsmos

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12
Q

What is maximum concentrating ability of kidneys?

A

600 mOsm/L of solute each day

If maximum concentrating ability of urine is 1200, than the minimal volume of urine 0.5L/day

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13
Q

urine specific gravity

A

measures osmolarity of urine is about 1.002 to 1.028 rising .001 for every 35 to 40 mOsmo increase

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14
Q

what are some requirements for excreting a concentrated urine

A

high ADH levels and hyper osmotic renal medulla

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15
Q

what does high ADH do

A

increases the permeability of the DCTand collecting ducts to water thereby allowing tubular reabsorption of water

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16
Q

what does a high osmolarity of the renal interstitial fluid do

A

provides osmotic gradient necessary for water reabsorption to occur in the presence of high levels of ADH involves countercurrent multiplier mechanism

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17
Q

what does counter current multiplication involve

A

arrangement of LOH and vasa rectae, specialized peritubular capillaries of nephron

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18
Q

what percentage of renal medulla contains juxtamedullary nephrons

A

25% that have LOH and vasae rectae that go deep in the medulla before returning to cortex with some LOH dipping to the tips of renal papillae that project from medulla to renal pelvis, and vase rectae parallel loops of henle

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19
Q

what is the osmolarity of interstitial fluid in the medulla of the kidney

A

1200 to 1400 in pelvic tip of medulla, due to large accumulate of solutes

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20
Q

what contributes to buildup of solutes in renal medulla

A

1) active transport of na and co transport of K, CL, and other ions out of the TAL into medullary interstitium
2) active transport of ions from the CD into medullary interstitial
3) facilitated diffusion of urea from the inner medullary collecting ducts to medullary interstitial
4) diffusion of only small amounts of water from medullary tubules into interstitium

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21
Q

what happens to osmolarity of tubular fluid as it diffuses from descending LOH to ascending

A

water diffuses out of descending limb into interstitial and the tubular fluid osmolarity gradually increases as it flows towards tip of LOH

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22
Q

In the presence of ADH, which parts of kidney that are not normally permeable to water become permeable

A

DCT, cortical collecting tubule, and inner medullary collecting duct

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23
Q

which areas of kidney participate in active transport of NACL

A

PCT, thick ascending LOH, DCT, CT, medullary CD

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24
Q

which areas of kidney are normally permeable to water

A

PCT, thin descending limb of LOH

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25
Q

is the ascending LOH permeable to water

A

no

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26
Q

in the presence of ADH, which part of the kidney that is not normally permeable to urea becomes permeable to urea

A

medullary collecting duct

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27
Q

what areas of kidney are normally permeable to urea

A

PCT, thin descending and ascending LOH

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28
Q

which areas of kidney are impermeable to urea

A

TAL, DCT, CD

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29
Q

counter current multiplication creation of hyper osmotic renal medullary interstitial steps

A

repeated reabsorption of NACL by thick ascending limb and continued inflow of new NACL from PCT into LOH multiplies solute concentration in medullary interstitium

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30
Q

What is role of DCT and CD in excreting concentrated urine

A

hypo osmolar urine from ascending LOH enters DCT, and Na is actively transported from tubular fluid to interstitium and tubular fluid becomes more dilute as it enters collecting duct. in absence of ADH the DCT and CD are impermeable to water, and solutes are continually reabsorbed from filtrate.

In presence of ADH, Collecting tubule becomes permeable to water and water is reabsorbed into cortex interstitium - where it is sequestered back into blood by peritubular capillaries

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31
Q

How is renal medulla interstium fluid hyperosmolarity preserved

A

large amounts of water reabsorption in presence of ADH in the cortex interstitum rather than medullary interstitium

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32
Q

what happens to collecting ducts in presence of ADH

A

collecting ducts become permeable to water so fluid at end of collecting ducts are essentially the same osmolarity as the interstitial fluid of the renal medulla, about 1200 mOsmos. By reabsorbing as much water as possible and excreting the same amount of solutes making concentrated urine

33
Q

What happens to urea in the presence of ADH and water shortage in body

A

large amounts of urea passively reabsorbed from inner medullary collecting ducts into interstitium

34
Q

what is mechanism for reabsorption of urea

A

water flows up ascending LOH into DCT and cortical collecting tubules, in the presence of ADH, water is reabsorbed and urea concentration increases in tubule as it is not permeable in this area. upon arriving to medullary collecting duct and water is continually reabsorbed, and urea transporters take urine from medullary collecting ducts to renal interstitial fluid, but results in high urea levels in tubular fluid. Malnutrition people lack ability to concentrate urine, high protein diets people have a higher concentrating ability of urine

35
Q

3 determining factors of urea excretion

A

1)urea concentration in plasma
2)GFR
3)renal tubular reabsorption of urea
urea is recirculated in kidney several times before it is excreted. urea concentration in tubular fluid increases incrementally as it moves through tubular fluid

36
Q

In the presence of reduced GFR how is urea excretion effected

A

it is still excreted normally

37
Q

what happens to urea when there is excess water in body

A

urine flow rate increased, reduced levels of urea in medullary collecting ducts and medullary interstitium. because there is low ADH, there is decreased permeability of inner medullary collecting ducts to water and urea, and more urea is excreted in urine

38
Q

what does counter current exchange in vasa rectae do

A

preserves hyperosmolarity of renal medulla by providing sluggish blood flow resulting in less solute loss (counter current exchanger)and sufficient blood flow to meet metabolic needs of medulla (as medullary BF metabolic needs are low)

39
Q

how does blood enter and leave medulla

A

vasa rectae at boundary of cortex and medulla

40
Q

blood concentration in vasa rectae arrives as hyper osmolar or hypoosmolar

A

hyperosmolar, 1200 in equilibrium with medullary interstitium, but as it travels back from medulla to cortex it becomes less concentrated as water moves from interstitial to vasa rectae

41
Q

What does U shape of vasa rectae provide

A

minimizes loss of solute from interstitim carries away only water and solutes that is absorbed from medullary tubules, preserving high concentration of solutes established by counter current mechanism

42
Q

what does increased medullary blood flow do to urine concentrating ability

A

reduces urine concentration ability, such as large increases in arterial BP, washing out hyper osmotic interstitium

43
Q

what are two crucial components of urine concentrating ability

A

ADH and hyper osmolarity of renal medullary interstitial fluid

44
Q

where is renin produced

A

Juxtaglomerular apparatus

45
Q

what are 4 components of Juxtaglomerular apparatus

A

1) modified smooth muscle cells in afferent arteriole
2) modified smooth muscle cells in efferent arteriole
3) extraglomerular mesangial cells
4) macula dense cells in DCT

46
Q

where are macula densa located

A

DCT, sense salt concentrations

47
Q

what are 3 triggers for RAAS

A

low BP, SNS stimulation, macula dense sense low salt concentrations

48
Q

Describe RAAS in presence of low BP

A

renin secreted from JXA
renin cleaves angiotensinogen from liver to angiotensin I
angiotensin I converted to angiotensin II in lungs
angiotensin II is most potent vasoconstrictor

49
Q

what are 5 actions of angiotensin II

A

1) vasoconstriction and increased BP
2) increased aldosterone synthesis and release
3) increased ADH
4) increased thirst
5) feedback inhibition of renin release

50
Q

Where does Angio II act upon

A

constricts afferent and efferent arterioles, releases PGE to maintain GFR

51
Q

Where is aldosterone synthesized

A

steroid hormone in zona glomerulosa of adrenal cortex

52
Q

what causes release of aldosterone name 3

A

increased K levels in ECF
Angio II
Decreased Na levels

53
Q

what are actions of aldosterone

A

acts on distal tubule and collecting ducts to cause K secretion and H in exchange for NA
*get rid of K and H

54
Q

describe Conn’s Syndrome

A

Aldosterone secreting tumors tha cause HTN, hypernatremia, hypokalemia. The increased NA concentration exceeds ability of DCT and CD to reabsorb NA, but K excretion=hypokalemia

55
Q

Where is ADH stored and released

A

ADH is synthesized in hypothalamus, stored and released in posterior pituitary, plays a role in conserving water by concentrating urine

56
Q

what is stimuli for ADH release

A
  • osmoreceptors in hypothalamus sense increased osmolality
  • mechanoreceptors in atria and aorta detect decreases in volume
  • angio II, SNS, nausea, hypoxia, pain
  • decreased blood volume, BP
  • morphine, nicotine, cyclophosphamide
57
Q

what causes decreased ADH

A
  • decreased plasma osmolality
  • increased blood volume
  • increased blood pressure
  • alcohol
  • clonadine, haloperidol
58
Q

where does ADH act on

A

distal tubule, medullary collecting ducts, cortical collecting tubule

59
Q

what does ADH do to permeability of collecting system to water

A

increases permeability

60
Q

what happens when ADH is absent

A

collecting system is impermeable to water leading to dilute urine

61
Q

what effect does ADH have on urea permeability

A

ADH increases urea permeability in medullary collecting ducts

62
Q

what causes ADH to work

A

driving force to move water out of tubules to the interstitium-hypertonic salty interstitium

63
Q

what does the countercurrent multiplier U shape in LOH provide

A

U shape of LOH allows flow in opposite directions

64
Q

what does differences in permeability of certain nephron segments provide in counter current multiplication

A

allows for flow in opposite directions

65
Q

where does energy for counter current multiplier come from

A

ATP NA/K ATPase

66
Q

urea is a byproduct of what

A

amino acid metabolism

67
Q

what is the thick ascending loop of hence impermeable to

A

water and urea

68
Q

when is inner medulla permeable to urea

A

only in presence of ADH, urea diffuses into inner medulla and is trapped here

69
Q

is the thin ascending limb permeable to urea

A

yes, urea diffuses into the tubule and is recycled

70
Q

what is the role of urea in max concentration urine

A

40% of osmolarity of renal medulla gradient during maximum urine concentration

71
Q

in low water states, what happens with urea in medullary collecting duct

A

urea passively diffuses from medullary collecting duct during water deficits when ADH present, and urea is recirculated from medulla interstitial to LOH and returned to tubular fluid

72
Q

urea moves back and forth between?

A

outer and inner medulla

73
Q

what are two functions of vasa rectae

A

1) remove reabsorbed fluid from interstitium to circulation

2) minimize solute uptake from medulla-maintains medullary hypertonicity

74
Q

how does medullary blood flow contribute to solute concentration during countercurrent exchange in vasa rectae

A

1) low blood flow-sluggish flow minimizes solute loss
2) U shape act as countercurrent exchangers to minimize solute washout, with little net diffusion of interstitial by U shaped vessels

75
Q

what happens in descending vasa rectae

A

more fluid leaves than solute enters because of the rapid flow

76
Q

what happens in ascending vasa rectae

A

decreasing hydrostatic pressure and increased osmolarity of blood

77
Q

in the vasa rectae is more fluid reabsorbed or lost

A

more fluid is reabsorbed than lost

78
Q

what does aldosterone stimulation cause

A

K secretion, Na reabsorption in exchange for H excretion

Physiology - Guyton & Hall (21 decks)

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