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KP222 > Quiz #7 > Flashcards

Quiz #7 Flashcards

1
Q

What are some of the kidneys functions?

A 
regulate plasma ion concentrations
regulate BV and BP
regulate blood osmolarity
stabilize blood pH
removal of waste
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2
Q

What are the 3 distinct regions of the kidney?

A

renal cortex
renal medulla
renal pelvis

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3
Q

What is the renal cortex?

A

granular-appearing superficial region

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4
Q

What is the renal medulla?

A

deep to cortex
composed of cone-shaped medullary pyramids
- broad base of pyramid faces cortex, papilla (tip) faces inwards
- separated by renal columns (inwards extensions of cortical tissue)
- form lobes

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5
Q

What is a lobe?

A

medullary pyramid and its surrounding cortical tissue

about 8 per kidney

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6
Q

What is the renal pelvis?

A

funnel-shaped tube continuous with ureter

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7
Q

What are the minor and major calyces?

A

minor = cup shaped areas that collect urine draining from pyramidal papillae

major = areas that collect urine from minor calyces and empty into renal pelvis

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8
Q

Describe urine flow starting in the renal pyramid.

A

renal pyramid - minor calyx - major calyx - renal pelvis - ureter

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9
Q

What are nephrons?

A

the structural and functional units that form urine

2 main parts

  • renal corpuscle
  • renal tubule
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10
Q

What is the renal corpuscle?

A

made of the Bowmans capsule and glomerulus

Bowmans capsule
- hollow structure that contains the glomerulus

glomerulus
- ball of specialized capillaries

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11
Q

What is the renal tubule?

A

proximal tubule

  • where most reabsorption occurs
  • have microvilli to increase surface area

loop of Henle

  • creates dilute urine
  • regulates concentration gradient to concentrate urine
  • osmotic gradient generated since descending end only permeable to water, ascending end only permeable to salt

distal tubule
- fine regulation of salt and water balance

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12
Q

What are the collecting ducts?

A

collect filtrate from many nephrons

fine regulation of salt and water balance

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13
Q

What are the 2 types of nephrons?

A

cortical

  • 85%
  • almost entirely in cortex

juxtamedullary

  • originate near junction between cortex and medulla
  • important for production of concentrated urine
  • have very long nephron loops
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14
Q

What is filtration?

A

anything that exits the capillary

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15
Q

What is reabsorption?

A

anything that goes back in the capillary

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16
Q

How does blood flow enter the kidney?

A

afferent arteriole brings blood into the glomerulus, efferent arteriole brings blood away from the glomerulus

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17
Q

What capillary bed are cortical nephrons associated with?

A

peritubular capillaries

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18
Q

What is the vasa recta associated with?

A

juxtamedullary nephrons

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19
Q

What is the role of the glomerulus?

A

capillaries specialized for filtration
fed and drained by arteriole
- afferent arteriole enters glomerulus, efferent arteriole leaves and feeds into either peritubular capillaries or vasa recta

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20
Q

Why is blood pressure in the glomerulus high?

A

afferent arteriole is larger in diameter than efferent, restricting the blood that can leave

arterioles are high resistance vessels

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21
Q

What are peritubular capllaries?

A

low pressure, porous capillaries adapted for absorption of water and solutes

where reabsorption occurs

arise from efferent arterioles, empty into venules

cling to adjacent renal tubules in cortex

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22
Q

What is the vasa recta?

A

long, thin-walled vessels parallel to long nephron loops of juxtamedullary nephrons

arise from efferent arterioles

function in formation of concentrated urine

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23
Q

What is a juxtaglomerular complex?

A

each nephron has one

involves modified portion of :
ascending limb of loop of Henle
afferent (sometimes efferent) arteriole

important in regulating the rate of filtrate formation and blood pressure

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24
Q

What are the 3 cell populations seen in juxtaglomerular complexs?

A

macula densa
granular cells
extraglomerular mesangial cells

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25
Q

What are macula dense?

A

tall, closely packed cells of the ascending limb

contain chemoreceptors that sense salt content of filtrate (too much mean glomerular filtration rate is too high, vice versa)

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26
Q

What are granular cells?

A

enlarged, smooth muscle cells of afferent arteriole

act as mechanoreceptors to sense blood pressure in arteriole

contain secretory granules containing renin

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27
Q

What are extraglomerular mesangial cells?

A

located between arteriole and tubule cells

interconnected with gap junctions

may pass signals between macula densa and granular cells

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28
Q

What are the 3 processes involved in urine formation and adjustment of blood composition?

A

glomerular filtration
tubular reabsorption
tubular secretion

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29
Q

What is glomerular filtration?

A

produces cell and protein free filtrate
movement of blood into the lumen of the nephron (takes place only at renal corpuscle)
walls of glomerular capillaries and Bowmans capsule are modified to allow bulk flow

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30
Q

What is tubular reabsorption?

A

selectively returning 99% of substances from filtrate to blood in renal tubule and collecting ducts

31
Q

What is tubular secretion?

A

selectively move substances from blood to filtrate in renal tubules and collecting ducts

32
Q

What are the 4 main processes occurring at the kidneys?

A

filtration - blood to lumen
secretion - blood to lumen
reabsorption - lumen to blood
excretion - lumen to external environment

33
Q

What is excretion?

A

excretion = filtration + secretion - reabsorption

100% volume enters afferent arteriole
20% of volume is filtered
over 19% of fluid is reabsorbed
less than 1% of volume is excreted to external environment

34
Q

Describe step 1 of urine formation.

A

glomerular filtration

passive/no energy required

hydrostatic pressure forces fluids and solutes through filtration membrane into glomerular capsule

35
Q

What is the filtration membrane?

A

porous membrane between the blood and the interior of the glomerular capsule

allows water and solutes smaller than plasma proteins to pass

3 layers

macromolecules stuck in membrane are engulfed by glomerular mesangial cells

36
Q

What do plasma proteins do?

A

remain in blood to maintain colloid osmotic pressure

prevents loss of all water into capsular space

proteins in filtrate indicate membrane issue

37
Q

What Starling forces in glomerular filtration favour filtration?

A

glomerular capillary hydrostatic pressure
- 60 mmHg (high due to resistance of efferent arteriole)

Bowmans capsule osmotic pressure
- 0 mmHg (low due to lack of protein in filtrate)

38
Q

What Starling forces in glomerular filtration oppose filtration?

A

Bowmans capsule hydrostatic pressure
- 15 mmHg (relatively high due to large volume of filtrate in closed space)

glomerular oncotic pressure
- 29 mmHg (higher than in systemic capillaries due to plasma proteins in smaller volume of plasma)

39
Q

What is the net filtration pressure?

A

outward pressure - inwards pressure
Pgc - (Pbc - Pgo)
60 - (15 + 29)
16 mmHg

40
Q

What is glomerular filtration rate?

A

volume of filtrate formed per minute by both kidnets

directly proportional to net filtration pressure, surface area available for filtration, and filtration membrane permeability

41
Q

How can resistance at the efferent or afferent side alter hydrostatic pressure and flow?

A

afferent side - decreases hydrostatic pressure, decreases GFR

efferent side - increases hydrostatic pressure, increases GFR

42
Q

How are GFR and systemic blood pressure related?

A

increased GFR causes increased urine output which lowers blood pressure, vice versa

43
Q

What things regulate glomerular filtration?

A

local intrinsic controls try to maintain GFR in kidney

  • renal autoregulation
  • when MAP is in range of 80-180 mmHg

extrinsic controls try to maintain systemic blood pressure
- nervous system and endocrine mechanisms

44
Q

What are the 2 types of renal autoregulation?

A

myogenic mechanism

tubuloglomerular feedback mechanism

45
Q

What is the myogenic mechanism?

A

local smooth muscle contracts when stretched

high BP causes muscle to stretch, leading to constriction of afferent arterioles

restricts blood flow entering glomerulus

protects glomeruli from damaging in high BP (decreased BP causes dilation of afferent arterioles)

46
Q

What is the tubuloglomerular feedback mechanism?

A

flow-dependent mechanism directed by macula densa cells (responding to filtrates salt concentration)

if GFR increases, filtrate flow rate increases, leads to decreased reabsorption time causing high salt levels in filtrate

feedback mechanism causes constriction of afferent arteriole to lower GFR and allow more time for salt reabsorption (reverse for when GFR is decreased)

47
Q

How does the SNS act to control GFR?

A

under normal rest conditions, renal blood vessels are dilated and renal autoregulation mechanisms prevail

under abnormal conditions (low ECF volume/low BP):
- NE released by SNS and E released by adrenal medulla causing systemic vasoconstriction (increasing BP) and constriction of afferent arterioles (decreasing GFR)

48
Q

What is the renin-angiotensin-aldosterone mechanism?

A

main mechanism for increasing BP

3 pathways to renin release by granular cells:

  • direct stimulation of granular cells by SNS
  • stimulation activated by macula densa cells when filtrate salt concentration is low
  • reduced stretch of granular cells
49
Q

Describe the 2nd step of urine formation.

A

tubular reabsorption

quickly reclaims most tubular contents and returns them to blood (99%+)

almost all organic nutrients reabsorbed, water/ion reabsorption is hormonally regulated

includes active and passive reabsorption

substances can follow 2 routes

50
Q

Where does most solute reabsorption occur>

A

proximal convoluted tubule

some in distal convoluted tubule

51
Q

What are the 2 routes substances can follow in tubular reabsorption?

A

transcellular route

paracellular route

52
Q

What is the transcellular route?

A

soulte enters apical membrane of tubule cells
travels through cytosol
exits basolateral membrane of tubule cells
enters blood through endothelium of peritubular capillaries

53
Q

What is the paracellular route?

A

between tubule cells
limited by tight junctions, but these are leaky in the proximal nephron
- water, Ca2+, K+, and some Na+ in proximal convoluted tubule move through this route
move through interstitial fluid and into capillary

54
Q

What is transport maximum?

A

rate of transport when carriers are saturated

when carriers are saturated, extra is excreted into urine

55
Q

What is renal threshold?

A

if solute in filtrate saturates carrier, some solute is excreted in urine

solute in plasma that causes solute in filtrate to saturate carriers and spill over into urine

transport max/GFR

56
Q

Describe the 3rd step of urine formation.

A

tubular secretion

reabsorption in reverse, almost completely in proximal convoluted tubule

selected substances moved from peritubular capillaries through tubule cells and out into filtrate

57
Q

What is tubular secretion important for?

A

disposing of substances that are bound to plasma proteins

eliminating undesirable substances that were passively reabsorbed (ex. urea)

ridding the body of excess K+

controlling blood pH by altering levels of H+ or HCO3-

58
Q

What is micturition?

A

urination
urine formed in renal tubules drains into renal pelvis and into ureter, which leads to bladder

bladder stores urine until it is excreted

59
Q

Describe the role of sphincters in micturition.

A

internal sphincter relaxes under PNS control
external sphincter relaxes under motor/conscious control, but not until after age 2
- before this urination is simply reflexive

60
Q

Describe the process of micturition.

A

increased volume of fluid in bladder expands bladder walls and activates stretch receptors

signal travels to spinal cord

decreases SNS and increases PNS to open internal urethral sphincter

decreases somatic motor neuron activity to open external urethral sphincter

micturition

61
Q

What cells regulate solute and water balance?

A

cells in late distal tubule and collecting duct

principal cells - water and electrolytes

intercalated cells - acid-base balance

62
Q

Where does water reabsorption occur?

A

proximal tubules

  • 70% of filtered water is reabsorbed
  • not regulated

distal tubules and collecting ducts

  • most remaining water is reabsorbed
  • regulated by ADH
63
Q

Describe how water reabsorption follows solute reabsorption.

A

in proximal tubules

primary solute = sodium

solutes are actively reabsorbed, increasing osmolarity of peritubular fluid and plasma, creating osmotic gradient

water reabsorbed by osmosis

64
Q

Describe how the medullary osmotic gradient is established.

A

by countercurrent multiplier dependent on loop of Henle

ascending limb

  • impermeable to water
  • active transport of Na+, Cl-. K+
  • fluid osmolarity decreasesas it ascends

descending loop

  • permeable to water
  • no transport of Na+, Cl-, K+
  • fluids osmolarity increases as it decends
65
Q

What are countercurrent mechanisms?

A

fluid flows in opposite directions in 2 adjacent segments of the same tube

multiplier
- interaction of filtrate flow in ascending/descending limbs of nephron loops of juxtamedullary nephrons

exchanger
- blood flow in ascending/descending limbs of vasa recta

66
Q

What is the role of urea in the medullary osmotic gradient?

A

nitrogen elimination

generated by liver, extremely water soluble, requires urea transporters (UTA, UTB, UTC)

transport through UTA from filtrate to peritubular fluid contributes approximately 40% of osmolarity of gradient

67
Q

What is the role of the vasa recta in the medullary osmotic gradient?

A

anatomical arrangement prevents the diffusion of water and solutes from dissipating the osmotic gradient

descending limb
- water leaves capillaries via osmosis and solutes enter by diffusion

ascending limb
- water moves into plasma and solutes move into interstitial fluid

68
Q

Where in the nephron does water reabsorption occur?

A

70% in proximal tubule
- unregulated

20% in distal tubule
- ADH regulated

10% in collecting ducts
- ADH regulated

69
Q

What does water permeability depend on?

A

presence of aquaporins

70
Q

How does ADH relate to aquaporin2?

A

ADH stimulates insertion of aquaporin2 into the apical membrane

71
Q

What determines the maximum amount of water reabsorbed?

A

length of the loop of Henle

72
Q

What would the GFR response be if BP dropped below 80mmHg?

A

decrease in GFR
decrease in water filtered
decrease in water excreted

73
Q

What would the GFR response be if BP moved to over 180mmHg?

A

increase in GFR
increase in water filtered
increase in water excretion

KP222 (7 decks)

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