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P1: Ren > Control Abnormalities Body Water > Flashcards

Control Abnormalities Body Water Flashcards

1
Q

What happens if you add more water to a Na+ solution?

A

→ Hyponatremia

→ Concentration decreases

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2
Q

What happens if you remove water from a Na+ solution?

A

→ Hypernatremia

→ Concentration increases

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3
Q

What does osmolarity relate to?

A

→ Number of particles per unit volume of fluid

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4
Q

What does osmolality relate to?

A

→ Number of particles per unit weight of fluid

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5
Q

What is the equation for estimating plasma osmolarity?

A

→ 2[Na+] + 2[K+] + [glucose] + [urea]

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6
Q

What is normal plasma osmolality?

A

→ 275-295 mOsm kg-1

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7
Q

What does hypernatremia mean?

A

→ hyper osmolality

→ too little water

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8
Q

What does hyponatremia mean?

A

→ hypo-osmolality

→ too much water

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9
Q

What happens during diabetes mellitus?

A

→ Diabetes mellitus the glucose concentration rises
→ It contributes to the osmolality
→ high glucose concentration is filtered into the kidney tubule

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10
Q

What are osmoreceptors?

A

→ Sensory receptors located in the hypothalamus sense changes in osmolality of ECFV

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11
Q

What does an increase in osmolality stimulate?

A

→ Thirst

→ Secretion of vasopressin

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12
Q

How does ADH regulate plasma osmolality?

A

→Controlling water excretion and reabsorption

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13
Q

What does concentrated urine tell you about ADH levels?

A

→ ADH relatively high

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14
Q

Describe the loop of henle

A

→ Tubular fluid is iso-osmotic in the PCT
→ along the descending limb there is active reabsorption of Na+
→ Water moves out passively
→The loop has very concentrated interstitial fluid
→ in the ascending loop there is dilution of the tubular fluid as there is reabsorption of NaCl
→ at the DCT the tubular fluid is the most dilute

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15
Q

What is the effect of ADH on the collecting duct?

A

→ ADH binds to basolateral receptors

→ more water channels inserted in the luminal membrane

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16
Q

What is the mechanism ADH uses?

A

1) ADH binds to the receptor V2 on principal cells
2) Receptor activates cAMP
3) inserts AQP2 into apical membrane
4) V1 receptors on vascular smooth muscle - vasoconstriction but only significant with very high ADH levels- increases systemic BP

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17
Q

What is the function of ADH under normal conditions?

A

→ Osmoregulation

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18
Q

What does a large drop in arterial pressure cause?

A

→ release of ADH

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19
Q

Why is ADH secreted during hypovolaemia?

A

→ retention of water to increase blood volume

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20
Q

What happens to plasma osmolality during severe haemorrhage?

A

→ Loss of BP is sufficient to stimulate ADH
→ decrease in plasma osmolality
→ ADH effect is always dilutional (adds pure water)

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21
Q

What are the two systems activated during hypovolaemia?

A

→ RAAS occurs first

→ ADH secretion happens later

22
Q

What is the first line of defense against dehydration?

A

→ Thirst

23
Q

What kind of thirsts are there?

A

→ hyperosmotic

→ hypovolemic

24
Q

What is hyperosmotic thirst?

A

→ after eating a lot of salt

25
Q

What is hypovolemic thirst?

A

→ After losing a lot of blood

26
Q

What is the metabolic waste product in the kidney excreted as?

A

→ in a solute form

→ called the solute load

27
Q

How do you estimate the solute load?

A

→ body weight x 10

28
Q

How do you work out how much water is needed to excrete the solute load?

A

→ divide the urine concentration by the solute load

29
Q

What is water excess (hyponatremia)?

A

→ excessive water intake

→ impairment in renal water excretion

30
Q

What is water depletion (hypernatremia) ?

A

→ Insufficient water intake

→ Impairment in renal water reabsorption

31
Q

What are situations where water intake is continued but ADH is suppressed?

A 
→ vomiting , diarrhoea
→ Ecstasy
→ Ectopic secretion of ADH (SIADH)
→ Hypocortisolism
→ Primary adrenal insufficiency ( Addisons)
32
Q

What is missing in people with Addisons?

A

→ Loss of cortisol

→ Loss of aldosterone

33
Q

What is the effect of Addisons?

A

→ Lack of sodium retention
→ Water is lost with it
→ hyponatremia due to water intake

34
Q

What are the major causes of SIADH(syndrome of inappropriate antidiuretic hormone secretion )?

A

→ TUMOR - ectopic production of ADH
→ CNS disturbance - trauma, stroke, infection
→ DRUGS - carbamazepine, prozac

35
Q

What are signs of SIADH?

A

Low plasma sodium
→ Low plasma osmolality
→ High urine osmolality

36
Q

How can water depletion from decreased intake of water occur?

A

→ Infants
→ Elderly
→ Individuals in a coma
→ Individuals with no access to water

37
Q

How can water depletion from increased loss of water through the kidney occur?

A

→ Diabetes mellitus

→ Impairment in ADH release

38
Q

What are nephrogenic causes of diabetes insipidus?

A

→ Mutation of ADH receptor
→ Mutation of ADH dependent H2O channels
→ Renal disease
→ Lithium

39
Q

What are central causes of diabetes insipidus?

A

→ genetic mutations
→ head trauma
→ disease of the hypothalamus /pituitary region

40
Q

What is the ECF divided into?

A

the interstitial compartment and the plasma compartment.

Movement between the two is controlled by starling’s forces

41
Q

What happens when pure water was added to ECF?

A

initially the concentration in ECF will be diluted but then this creates osmotic gradient between ICF and ECF resulting in movement of water into ICF.

42
Q

How is the osmolarity of the ECF adjusted?

A

adding or removing water, not solute

43
Q

What happens as a defence against dehydration with ADH?

A

→Net water loss increases ECF osmolarity

→Changes detected by osmoreceptors in anterior hypothalamus
→Project to magnocellular neurons of paraventricular and supraoptic nuclei of hypothalamus
→PVN and SON neurons release ADH from their axon terminals in posterior pituitary

44
Q

What is the normal range for ADH?

A

Normal range 285-295 mOsm/kg

Above this range small changes in osmolality produce large changes in ADH secretion

45
Q

What happens to stimulate thirst in defence against dehydration?

A

Changes detected by osmoreceptors in anterior hypothalamus

→Strong desire to drink when plasma osmolality ≥295 mOsm/kg
→Large (10-15%) drops in blood volume/pressure
→Angiotensin 2 acting on hypothalamus in significant drop of blood volume

46
Q

What other receptors reduce thirst?

A

Oropharyngeal and upper gastrointestinal receptors reduce thirst on drinking- unless osmolarity is brought back within controlled range, thirst sensation returns

47
Q

What does principle of electroneutrality dictate?

A

dictates that a molar equivalent number of anions must be present
→Mainly Cl-, significant amount HCO3-, small contribution from other inorganic and organic anions

48
Q

Causes of hypernatremia in gain of sodium…

A

→Iatrogenic- mistakes in i.v
→Excess ingestion (rare)
→Excess mineralocorticoid activity

49
Q

What is diabetes insipidus?

A

a condition characterized by large amounts of dilute urine and increased thirst.

50
Q

What happens in severe volume depletion?

A

the retention of water will lead to hyponatraemia

51
Q

Why is ADH less effective to retain water than RAAS?

A

ADH promotes retention of pure water which will distribute between ICF and ECF so effect is weaker

52
Q

What happens in hypervolemic hyponatremia?

A

→Can occur when total sodium is increased, but total water increased more
→Example: congestive heart failure
→RAAS ‘thinks’ body is hypovolemic
→Na/water retention (volume expansion)
Volume expansion is ineffective because perturbed Starling forces (excess capillary filtration): oedema
→If low volume signals activate ADH hyponatremia will ensue
→If continued intake of water then hyponatremia

P1: Ren (13 decks)

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