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Renal system > Control, volume and composition of ECF > Flashcards

Control, volume and composition of ECF Flashcards

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1
Q

what is osmolarity?

A

when particles dissolve in solution they exert osmotic force that attracts water water

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2
Q

what determines osmotic pressure?

A

the number of active particles per unit of volume, not their size, all particles exert 1 unit of osmolarity

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3
Q

what is osmolality?

A

the number of particles of solute per kg of solvent

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4
Q

interstitial fluid

A

no protein
same as plasma otherwise
high sodium
low potassium

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5
Q

plasma

A

proteins - higher than interstitial but less than intracellular
otherwise same as interstitial fluid
high sodium
low potassium

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6
Q

intracellular fluid

A 
high potassium
low sodium 
no calcium 
lower carbonate
higher phosphate
highest protein
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7
Q

what do proteins contribute to?

A

oncotic pressure

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8
Q

osmolarity

A

starting osmotic pressure with all solutes

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9
Q

what is tonicity?

A

glucose taken up by cells and so this is the final osmotic pressure after any solute is removed

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10
Q

what is oncotic pressure?

A

the pressure generated by proteins, makes a major contribution to fluid movement between plasma and interstitial fluid, as it is the difference between the 2

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11
Q

IV fluids

A

usually approximately isosmolar but not all is isotonic

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12
Q

fluid distribution

A

2/3 body weight is liquid
1/3 is solid
of the 2/3 liquid 2/3 is intracellular and 1/3 extracellular
of the extracellular fluid 1/3 intravascular and 2/3 interstitial

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13
Q

composition of intravascular fluid

A

40% cells

60% plasma

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14
Q

water movement

A

moves between all compartments

movement sped by aquaporins

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15
Q

glucose movement

A

move into and out of cells through endothelium via glucose transporters
gaps in endothelium enhance movement

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16
Q

electrocyte movement

A

electrolytes pass through endothelial gaps easily but not through cell membranes as they need special channels/ pumps

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17
Q

protein movement

A

minimal movement of proteins between compartments as they are large and need movement by pinocytosis

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18
Q

osmoregulation

A

regulated by alterations in water content of urine or changing degree of thirst
ADH is the main regulating hormone

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19
Q

ADH

A

peptide
controlled by osmoreceptors
aka vasopressin

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20
Q

urine output

A

varies from 300mL/day to 10L/ day

very concentrated to very dilute

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21
Q

normal osmolality

A

290mosm/L

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22
Q

what happens if osmolality increases?

A

increased ECF osmolality
hypothalamic osmoreceptors stimulated
paraventricular and supra-optic nuclei make and control release of ADH
ADH release from posterior pituitary
ADH inserts aquaporins into collecting duct, increasing permeability
water retention by kidney
lateral preoptic area in hypothalamus causes thirst
drink water
osmolarity brought back to normal

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23
Q

what causes increased osmolality?

A

water deprivation
salt ingestion
diarrhoea

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24
Q

what happens if there is a decrease in osmolality?

A
  • decreased ECF osmolality
  • hypothalamic osmoreceptors are inhibited
  • lateral preoptic area supresses thirst
  • paraventricular and supra-optic nuclei cause ADH release to be suppressed
  • the collecting duct becomes more water impermeable
  • water excretion increased by kidney
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25
what causes decreased osmolality?
excessive fluid ingestion | decreased ECF osmolality
26
how is ADH made?
- made as pre-pro-hormone from 166 amino acid residues - successive cleavage during passage down neural transport system from hypothalamus to posterior pituitary - final form is a 9-peptide - stored in secretory granules
27
what stimulates ADH release?
osmoreceptors RAAS - part of shock response system sympathetic NS and angiotensin II
28
where are osmoreceptors?
vascular organ of lamina terminalis | outside BBB
29
how do osmoreceptors work?
contain aquaporins when plasma osmolarity rises water leaves the cells causing shrinkage triggers mechanically regulated ion channels to create an action potential causes ADH synthesis and release
30
how does ADH work?
loop of henle has created a hypertonic environment around medullary collecting ducts insertion of aquaporins allowing reabsorption of water via osmotic gradient ADH binds to ADH V2 receptors causing aquaporin insertion on luminal side due to activation of conversion of ATP to cAMP via GPCR extreme osmotic gradient between interstitial fluid and ECF so water pulled in
31
what else effects ADH release?
stimulated by nicotine inhibited by ANP inhibited by alcohol
32
damage to posterior pituitary
ADH production will cease causing diabetes insipidus (low ADH) large volumes of dilute urine excreted
33
volume regulation
osmolarity of ECF is tightly controlled volume of ECF is determined by total quantity of solute - mainly NaCl regulation of ECF volume is about sodium balance
34
what controls sodium balance?
aldosterone
35
aldosterone
main mineralocorticoid | steroid hormone
36
where is aldosterone made?
zona glomerulosa of adrenal cortex
37
what does aldosterone target?
principal cell - ENaC in | distal convoluted tubule
38
how does aldosterone work?
alters gene expression stimulates epithelial sodium channel - increases Na+ reabsorption and K+ secretion stimulates Na+/K+ pump to keep intracellular Na+ low
39
what stimulates release of aldosterone?
angiotensin II - RAAS increased plasma K+ - reabsorbing Na+ causes K+ loss, so if K+ increases it needs to be lost ACTH has some but little impact
40
what inhibits aldosterone release?
ANP
41
what causes ANP release?
elevated ECF volumes stretch receptors released from atrial wall
42
how does ANP work?
``` dilutes sodium increases GFR aldosterone secretion is inhibited renin and ADH release inhibited increases Na+ excretion in urine ```
43
how is osmolarity regulated?
altering water
44
how is volume regulated?
altering Na+
45
addison's disease
causes deficiency of aldosterone
46
Aldosterone drugs
``` agonist = fludrocortisone antagonist = spironolactone ```
47
ADH drugs
agonists = terlipressin/ desmopressin antagonist = tolvaptan vasopressors - raise low BP
48
ANP drugs
agonists = anartide | not in clinical use
49
spironolactone
given with loop diuretic diuretic on its own reduces effect of aldosterone causes loss of Na+
50
daily requirements
2.5-3L of water (drink just over 2L) | 1mmol/kg/day of Na+ and K+
51
what are the IV solution options?
0.9% saline Hartmann's saline 5% dextrose 4% dextrose and 0.18% saline
52
0.9% saline
physiological saline osmolarity close to plasma slightly higher conc of Na+ use being reduced due to concern over too much Cl-
53
Hartmann's solution
contains lactate and calcium as well as sodium, potassium, chloride and glucose closer to plasma
54
5% dextrose solution
close osmolarity to plasma gives water due to metabolism of glucose only contains dextrose
55
dextrose 4% and 0.18% saline
toxic as causes hyponatraemia | sick patients need more Na+ due to hormonal response to stress, surgery, illness which produces Na+ and water retention
56
24hr IV fluid plan
1L 0.9% saline or Hartmann's 2L 5% dextrose 60mmol K+
57
high K+ concentrations
cause death
58
hyponatraemia
<130mmol/L | caused by water retention which dilutes sodium or Na+ loss
59
what causes water retention?
heart failure inappropriate ADH - secretion excess intake - oral/ IV
60
what causes Na+ loss?
diuretics vomiting diarrhoea adrenal failure - Addison's disease
61
what is the danger of hyponatraemia?
water will move to equalise water into brain cells by osmosis causing cerebral oedema, coma and death greater risk in children
62
what is SIADH?
syndrome of inappropriate ADH secretion | oversecretion of ADH
63
causes of SIADH
tumours - small cell lung cancer infections - pneumonia drugs - SSRIs hypothyroidism
64
irrigation fluid for endoscopic resections
has to be non-conductive and heat stable (no glucose) due to diathermy so glycine (amino acid solution) used
65
problem with glycine
no sodium resection exposes open blood vessels and so irrigation fluid is absorbed straight into blood vessels causes hyponatraemia due to fluid overload
66
how to treat hyponatraemia?
water restriction/ no more IV saline can use hypertonic aline in a crisis over-rapid correction risks neuronal damage - demyelination
67
sweat
normal sodium content = 40mmol/L - lower than plasma concentration relative to ECF more water than sodium is lost in sweat hyperosmolar because sodium concentration rises with more loss of water increases thirst
68
rehydration after exercise
with just water restores volume but causes hyponatraemia as lowers ECF sodium concentration causes a fall in osmolarity inhibits ADH - excretion of water
69
what does alcohol do?
inhibits ADH water diuresis sodium concentration increases increased thirst

Renal system (17 decks)

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