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RBF > J de Zoysa: Renal Physiology; salt and water > Flashcards

J de Zoysa: Renal Physiology; salt and water Flashcards

1
Q

Body composition consisting of water?

Describe the two main components…

A

60% of our body. (42L)

This is divided in ICF and ECF

ECF:

  • many separate compartments
  • all external to the cell membrane
  • have similar composition

ICF

  • many separate compartments
  • all within the cell membrane
  • all have a similar composition
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2
Q

Normal fluid compartments

A
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3
Q

What is the interstitial fluid (ECF)

A
  • The fluid which lie in the interstices of all body tissues
  • The interstitial fluid bathes all the cells in the body and is the link between the ICF and the intravascular component
  • O2 , nutrients, wastes and chemical messengers all pass through the interstitial fluid
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4
Q

What is the transcellular fluid (ECF)?

A
  • small compartment (0.5-1L) that reps all body fluids which are formed from transport activities of cells
  • It is contained within epithelial lined spaces
  • includes
  • CSF, joint fluid, pericardial fluid, aqueous humour etc
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5
Q

Distribution of Na and K in ECF and ICF?

Why is this??

A

ECF: Na+ high and K+ low

ICF: Na+ low and K+ high

  • active pumping forces drive this in order to maintain electrical gradients
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6
Q

What is Molarity and what’s its constant.

What is Osmolarity?

A

Molarity:

  • Molarity: the number of moles per litre
  • 6.022 x 1023 Avogadro’s constant

Osmolarity:

  • Measure of solute concentration
  • It is the number of Osm of solute per litre of solution
  • Osmolarity is tightly regulated
  • Plasma osmolarity is 285-295 mOsm/L and is regulated using cations and water
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7
Q

Describe Tonicity

A
  • Tonicity of a solution refers to what happens to cells in a solution
  • If the cells take up water from a solution (ie; swell), then the solution is hypotonic
  • If the cells looses water to a solution (ie; shrink) then the solution is hypertonic
  • If no change is cell size is observed then the solution is isotonic
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8
Q

What filters water and by how much daily

A
  • In the nephron:
    • renal artery → arterioles → afferents → glomerulus → efferents​
    • Regulation of water in prox. tubule, LOH and distal tubule
  • Most of the filtration occurs at the glomerulus. free filtration of salt and water occurs here
  • GFR: 120ml/min
  • 120 x 60 x 24 hours = more than 170L/day
  • 200-300mg of protein filtered a day
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9
Q

Where does most of the salt and water reabsorbtion occur?

A

In the proximal tubules. 65-75% of sodium and water are reabsorbed here

Diuresis drugs are most effective here - carbonic anhydrase inhibitors

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10
Q

Describe the loop of Henle

A

The descending limb freely filters water

The ascending limb freely filter salt - reabsirbs (15-20%)

Diuretics such as frusemide and diurismide act on the LOH luminal surface

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11
Q

The distal convoluted tubule and the collecting tubules

A

DCT

  • Little bit of salt reabsorbed (5%)
  • Least effective diuretics act here - Thiazide diuretics

CT

  • Salt (5%) and water reabsorbed
  • controlled by ADH
    • prevents diuresis
  • K+ sparing diuretics such as spironolactone, aldosterone antagonsits
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12
Q

Describe ADH and what it does

A
  • Known as vasopressin
    • Binds to the vasopressin receptor and affects water in/output
  • Made in the hypothalamus, secreted from the p. pituitary
  • increased production in response to BP drop or osmolarity increase
  • Increases the reabsorption of water
  • Increases BP and reduces osmolarity
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13
Q

Describe aldosterone and what it does

A
  • A mineralocorticoid hormone
  • acts on the distal convoluted tubules and the collecting ducts
  • Increases sodium reabsorption and potassium excretion and angiotensin II
  • Binds to Aldosterone receptor and affects the Na/K ATPase pump
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14
Q

What is the RAAS

A

When the juxtaglomerular apparatus senses decreased renal perfusion and secretes renin

Renin increases production of angiotensin and angiotensin II

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15
Q

What does Angiotensin II do?

A
  • Potent vasoconstriction
  • ADH release stimulated
  • Sodium reabsorption in proximal tubule
  • Thirst
  • Lowers GFR by constriction of mesangial cells, thus reducing the area for glomerular filtration
  • Also increases GFR by constriction of efferent arteriole
  • Stimulates release of aldosterone
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16
Q

Disorders of sodium are

A

Abnormality of sodium or and abnormality of water (or both!)

  • Hypernatraemia Na > 145mmol/L
  • Normal Na 135-145 mmol/L
  • Hyponatraemia Na <135mmol/L
17
Q

Disorders of Sodium: Hypernatraemia

A
  • Impaired thirst/level of consciousness
  • no access
  • burns/diarrhoea/bloodloss
  • Solute diuresis (HONK/DKA)

Can be due occasionally to diabetes insipidus

18
Q

Disorders of sodium: diabetes insipidus

A

Huge amount of dilute urine and inc. thirst

  • Reduction in amount or efficacy of ADH
  • Polyuria and water loss
  • Dilute urine (<200mOsm/kg)
  • Patient can’t drink enough water to keep up with losses
  • Elevated plasma osmolality, hypernatraemia, dehydration

Can be central (50% from traumatic brain injury or pituitary hormone issues) or nephrogenic (problem with aquaporin channels in kidney, partial or complete resistance to ADH)

19
Q

Disorders of salt: Hyponatraemia

A

From either

  • Excessive sodium loss
  • excessive water retention

*pseudohyponatraemia: can be due to lab issues, check the serum osmolarity and only if normal do they have pseudohyponatraemia

20
Q

What do you do if the patient is hyponatraemic?

A
  1. Check urine osmolality
    • if low (<100mosm/kg), then they will be passing lots of very dilute urine
  2. Consistent with polydipsia/water intoxication
    • Ddx-psychotropic drugs
    • schizophrenia
    • beer potomania
21
Q

It is very important to check the patients fluid levels!!

Describe what you would see with a hypovolaemic patient

A
  • Check pulse,urinary losses BP, tissue turgor, JVP etc
  • Dehydrated. urine sodium <20mmol/L
  • Sodium loss but relatively less water loss
    • diarrhoea, vomiting
    • bowel obstruction
    • skin losses- burns
      • Diuretics
        • addisons disease
        • ketonuria osotic diuresis, RTA
22
Q

Describe Hypervolaemia

A
  • Fluid overloaded
  • Sodium retention BUT relatively more water retention
    • cirrhosis
    • nephrotic syndrome
    • HF
    • Renal failure
23
Q

How can you be hyponatraemic and euvolaemic?

A
  • SIADH (syndrome of inappropriate ADH)
  • endocrinopathies (hypothyroid/low cortisol)
    • check if they’re hyperthyroid or hyperadrenal
  • Diuretics
  • Fluid replacement
24
Q

Describe SIADH

A
  • Inappropriate ADH produced in absence of normal stimuli such as low BP
  • Body accumulates too much water (stored in cells so patient doesn’t appear to be fluid overloaded)
  • Urine osmol; not low- usually greater than 150mosmol/kg
  • Urine sodium; not low >20mmol/L
  • Plasma osmolality: low
25
Q

Cause of SIADH

A
  • Trauma (inc surgery)
  • Tumours (eg; lung)
  • Chronic lung disease
  • Head injury
  • Medications (eg; SSRIs)
26
Q

Symptoms of Hyponatraemia are…

A

Depends on how quickly it’s developed!

Common in the elderly

Slow: brain adaptation; confused, not quite self

Fast: cerebral oedema: confusion, seizures, coma

  • Water gain leads to cerebral oedema
  • Over time braincells adapt
  • Results in correction of cerebral oedema
27
Q

Treatment of Hyponatraemia

A

Also depends on speed of onset

THis requires constant check-ups, updates etc

28
Q

What can happen if you don’t treat hyponatraemia correctly?

A
  • Too rapid → brain doesn’t have time to adapt → brain dehydration = Central Pontine Myelinolysis
  • Compression of myelin sheaths; rapid demyelination (mainly in pons)
    • quadriparesis
    • pseudobulbar palsy
    • Locked in syndrome
    • Irreversible

RBF (32 decks)

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