4- Na, Osmolality, Fluid volume Flashcards
What is renin and what are its effects
Enzyme
Made and stored in JGA
Causes conversion of angiotensinogen to angiotensin 1
How is renin production activated
Increased sympathetic innervation (granular cells of JGA innervated by sympathetic system)
Wall tension in afferent arterioles falls
Decrease Na at macula densa leads to prostaglandins being release
What does angiotensin 2 do
Vasoconstricts efferent>afferent arterioles
Stimulates the zona glomerulosa to release aldosterone
What does aldosterone do
Increases Na reabsorb from PCT
Release ADH
Stimulates thirst
What factors affect Na reabsorb
Starlings force in PCT
Prostaglandins
ANP
What is Starlings force
Reabsorption depends on rate and amount of uptake from intercellular spaces into capillaries
Changes in body fluid volume alter plasma hydrostatic and oncotic pressure
If increase hydro and decreased oncotic in ECF it means NaCl reabsorbed by PCT decreases
Where are prostaglandins made
Cortex
Medullary interstitial cells
Collecting duct epithelial cells
What is the result of prostaglandins
Vasodilators- prevent excessive vasoconstriction
Renin release
Atrial natriuretic peptide produced from ? and work by ?
Produced by cardiac atrial cells in response to increased ECF
Inhibits Na/K atpase and closes ENAC of PCT
Reduced Na absorption and hence water
Vasodilation afferent arterioles = increase GFR
Inhibit aldosterone secretion
Inhibit ADH release
Decrease renin release
What cells do aldosterone target
Principal cells of DCT and CD
How does the descending limb of vasa recta reabsorb
Isosmotic blood enters hyperosmotic milieu of medulla
Na, Cl, urea diffuse into lumen
Why is the flow slow in the vasa recta
To allow it to equilibrate at each stratified level
To not compromise delivery of nutrients
Maintain medullary hypertonicity
How does the ascending limb of vasa recta reabsorb
Ascends towards cortex
Higher solute conc that interstitium
Water moves from descending limb of loop of Henle
Where are osmoreceptors located and what do they do if they sense change
Brain - hypothalamus.
Concentration of urine
Thirst
What is ADH and its effects
Peptide hormone
Name from supraoptic nucleus of hypothalamus
Stored in posterior pituitary
Increase osmolality = release
1. reduced water excretion
2. vasoconstriction
3. aquaporins fuse with luminal membrane - V2 receptor
In a state of reduced ECV does the set point for ADH get higher or lower
Lower
Relationship steeper
Volume trumps osmolarity
What is Diabetes insipidus
Inability to reabsorb water from distal part of nephron
Failure of secretion/ action of ADH
What causes Diabetes insipidus
Nephrogenic - failure to secrete ADH
Central - resistance to ADH
Central Diabetes insipidus
Impaired ADH secretion or synthesis
Damage to hypo or pituitary
Brain injury, sarcoidosis, aneurysm, tumour
How to treat Central DI
Desmopressin (ADH injection)
Nephrogenic DI
Acquired insensitivity of kidneys to ADH
ADH levels normal
How to manage nephrogenic DI
Low salt, low protein diet to reduce urine output
Causes of Nephrogenic DI
Chronic pyelonephritis, polycystic kidneys, lithium
What is SIADH
Excessive release of ADH from posterior pituitary
What are signs of SIADH
Dilutional hyponatremia
due to increase body fluid
Hyperosmotic urine
Inappropriate Na secretion despite decrease in plasma Na.
What causes SIADH
CNS disorder drugs lung disease metabolic disease malignancy
What is loss of large amount of hypo osmotic urine called
Diuresis
What will occur if osmolality increases by 10%
Thirst response
What is hypernatremia
> 140mmol/L
Increase solute:water ratio
Increased serum osmolality
Causes of hypernatremia
Osmotic diuresis- diabetes Fluid loss Diabetes insipidus IVI inappropriate Primary aldosteronism- too much = ENAC on
What is the main cause of hyponatremia
Too much fluid- dilutional
<130mmol/L
Symptoms of hyponatremia
Agitation
Focal neurology
Coma
Nausea
Causes of hyponatremia
Fluid reasons
True Na loss
FR: Diuretics Water overload or retention Increased ADH secretion - HF, kidney dx, liver dx, tumour, meds- anti epileptic Increases plasma osmolality (glucose)
TNL: Burns Peritonitis Diuretics/ renal failure D and V
Normal serum osmolality
275-295 mOsm/kg
How is osmolality calculated
2 Na + glucose + urea (mmol/L)
Treatment of Na imblance
Fluid restriction good
Hypertonic saline + furosemide in those symptomatic
What is Pontine demyelination
Rapid correction of hyponatremia
Leads to demyelination and neuron swelling
