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body systems 2 > concentrating mechanisms > Flashcards

concentrating mechanisms Flashcards

1
Q

urine appearance

A

almost colourless to deep amber, yellow colour due to urochrome, from the breakdown of haemoglobin
- drugs, food stuffs can change this

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2
Q

urine odour

A

urine starts to smell when the urea in urine is broken down by bacteria broken down to ammonia

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3
Q

pH of urine

A

range: 4.5 - 8.2 , usually 6.0
Urine tends to be acidic because it is the main mechanism for excretion of protons

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4
Q

chemical composition

A

95% water water, 5% solutes
- urea, Na+, K+, Cl-, creatinine

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5
Q

osmolality of urine

A

ranges from 50 mOsm/kg-1 to 1200 mOsmkg-1

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6
Q

osmolality of plasma

A

despite changes in water intake, the osmolality of plasma appears to stay relatively constant (290-300 mOsm kg-1)
- tells us that the kidney must be able to regulate water loss in urine by: producing large amounts of dilute urine when water is in abundance
- and by concentrating urine when water is limited

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7
Q

what can the kidneys do to regulate water loss

A
  • produce a hypo-osmotic urine - low con dilute
  • produce a hyper-osmotic urine - high conc
  • maximum conc. 1400mOsmol
  • 5 x more concentrated than plasma
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8
Q

how does the kidney regulate this

A
  • water reabsorption as fluid flows through the medullary collecting ducts
  • interstitial fluid surrounding these collecting ducts in the medulla is extremely hyper osmotic and varies dramatically
  • urea transport
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9
Q

increase of medullary osmolality in the renal system

A

cortex - 300mOsmol
corticomedullar - 300-600 mOsmol
medulla - 600-900 mOsmol
inner medulla - 900mOsmol
papillar/ pelvis - 1200 mOsmol

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10
Q

where is this increase of medullary osmolality created within the renal system

A

the loop of Henle

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11
Q

LOH

A
  • descending limb
  • thin ascending limb
  • thick ascending limb
  • osmolality similar to plasma - 300mOsmol
    filtrate in LOH: no glucose, Na+, K+, and H20, Cl-, AA
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12
Q

method of transport in LOH

A

in descending limb:
- passive reabsorption water - aquaporin 1
- UREA= passive secretion in the thin descending limb
- secretion via UT- facilitated diffusion
- no movement of Na+/Cl-
-tubular fluid (filtrate) becomes more concentrated (less volume) as descend into the medulla

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13
Q

what happens in the descending limb of the loop of Henle

A
  • urea transport is by passive diffusion. freely permeable across apical membrane via UT-A2 in thin descending limb
  • water moves by osmosis out of the loop into interstital fluid
  • increased concentration in the filtrate
  • urea accumulates in the filtrate then it returns to the interstitial fluid in the renal medulla by reabsorption in the collecting duct
  • this is critical in the kidney being able to concentrate urine
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14
Q

ascending limb

A

impermeable to water
- no movement of water
- no aquaporins
- active reabsorption of Na+/k+/Cl-

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15
Q

why does osmolality increase as descend into the medulla

A

ion transport in the LOH determines the rise in osmolality
COUNTERCURRENT MULTIPLIER
- active reabsorption of NaCl in ascending limb with no parallel movement of water

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16
Q

ion transport in the LOH

A

reabsorption of Na+/K+/Cl- ascending limb

  • no parallel reabsorb of water

fluid of the medulla hyperosmotic to the fluid in the ascending limb

17
Q

counter current multiplier

A

active transport of NaCl with no passive release of water
- passive secretion of urea

18
Q

vasa recta

A

a parallel countercurrent multiplier exists in the vasa recta
- due to increased osmolality of ECF water in plasma leaves descending limb of vasa recta
- re enters ascending limb of the vasa recta
- solutes leave ascending limb and re - enters descending limb of vasa recta

maintain osmotic gradient

19
Q

loop of Henle function

A

reabsorbs: water (descending limb)
urea secretion
Na+ and Cl- and K+ (ascending limb)

20
Q

distal tubule function

A

reabsorbs: Na+, Cl-, bicarbonate, K+. h20
secretes: H+, k+

21
Q

COLLECTING DUCT FUNCTION

A

reabsorbs: Na+, Cl-, H20, urea (K+)
secretes: H+NH4+(K+)

22
Q

factors that would increase the effectiveness of the LOH to concentrate urine

A
  • an increase in the length of the loop of Henle
  • a reduction in the flow rate of filtrate through the loop
  • alter protein in diet? increase UT transport
  • increase in the number or capacity of the pumps (Na+/K+/2Cl-) - increase conc gradient
23
Q

consequences of the counter current multiplier

A

the fluid leaving the ascending limb is hypo-osmotic compared to that entering it
- there is a continuous gradient of tissue fluid from 300m Osmol to 1200 mOsmol
- this gradient allows water reabsorption in the collecting ducts where permeability is high under the influence of hormones

24
Q

what alters water permeability in the collecting duct

A

anti diuretic hormone alters water permeability in the collecting duct

25
Q

antidiuretic hormone

A
  • also known as arginine vasopressin
  • 9 amino acid peptide
  • released from the posterior pituitary gland
  • rapid-acting with a short t1/2
  • released in response to a rise in plasma osmolality
26
Q

what is an antidiuretic hormone receptor released in response to

A

released in response to plasma osmolality
- primarily detected by osmoreceptors
- volume and pressure sensors detect a fall in blood volume (5-10%)
- stimulated by angiotensin 2

27
Q

ADH

A

ADH present at very low concentrations when plasma osmolality less than 280 mOsmol
- threshold 280mOsmol - normal plasmal small amount circulating - 2 pg/ml
- osmolality above 290 mOsmol kg sharp increase in ADH secretion

  • decreased blood volume -> increased ADH -> increased permeability of DCT and CD (aquaporins
28
Q

what is ADH release stimulated by

A
  • osmolality ECF detected by osmoreceptors in hypothalamus
  • circulating blood volume detected by cardiovascular volume receptors
  • arterial BP detected by cardiovascular baroreceptors
29
Q

what can ADH also be stimulated by

A

pain
stress
nausea

30
Q

what is ADH inhibited by

A

alcohol

31
Q

over hydration

A

increased blood volume - dilute tubular fluid
- decreased body fluid osmolality
- decreased firing hypothalamic osmoreceptors (which detect increasing and decreasing osmolality)
- posterior pituitary decrease ADH secretion
- decreased plasma ADH
- decreased permeability of CD to water
- increased water excretion (large amount of dilute urine)

32
Q

factors affecting medullary osmolality

A
  • ADH secretion
  • dietary protein (increased urea)
  • increased medullary blood flow (increase BP)
    Wash out NaCl + urea
    decrease osmotic gradient
    less conc urine
33
Q

aging and dehydration

A
  • associated with an inability to conc urine so risk of dehydration
  • thought to be decreased function of nephrons
  • shown to be associated with reduced AQP-2 expression in IMCD under ADH control

body systems 2 (19 decks)

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