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Urinary system > Control of plasma osmolality > Flashcards

Control of plasma osmolality Flashcards

1
Q

What is normal body fluid osmolality? What is the exception to this?

A

285-295 mOsm/kg

Exception is urine

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2
Q

How is water taken into the body?

A

Drinking

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3
Q

How is water lost from the body?

A

Urine by the kidneys

Faeces from the GI tract

Expired air by the lungs

Sweat from the skin

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4
Q

How are water intake and water loss related to each other ideally?

A

Water intake = water loss

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5
Q

What happens to plasma osmolality when water intake = water loss? Why?

A

Remains the same

because have same amount of water per solute

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6
Q

What happens to plasma osmolality when water intake is more than water loss? Why?

A

Decreases

because have more water per solute

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7
Q

What happens to plasma osmolality when water intake is less than water loss? Why?

A

Increases

because have less water per solute

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8
Q

What is the relative size of the range of urine osmolality?

A

Large range

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9
Q

How is the osmolality of urine changed?

A

By changing the volume of urine

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10
Q

How does changing the volume of urine change its osmolality?

A

Different amounts of water to same amount of solute

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11
Q

What are the mechanisms that regulate plasma osmolality?

A

ADH

Thirst

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12
Q

What detects plasma osmolality?

A

Osmoreceptors

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13
Q

Where are osmoreceptors located?

A

OVLT in the hypothalamus

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14
Q

How do osmoreceptors in the OVLT in the hypothalamus get into contact with plasma?

A

The capillary endothelium supplying them is fenestrated

plasma leaks out of capillaries

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15
Q

What produces ADH?

A

Neurosecretory cells in the supraoptic and paraventricular nuclei of the hypothalamus

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16
Q

What happens to ADH after it is produced?

A

It is transported down the axon of the neurosecretory cell

stored in vesicles in its tip

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17
Q

Where is the tip of the neurosecretory cell located?

A

Posterior pituitary gland

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18
Q

What causes ADH to be released?

A

Osmoreceptors detect an increase in plasma osmolality

action potentials are fired down neurosecretory cells that produce ADH

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19
Q

How much does the plasma osmolality have to increase by for ADH to be released?

A

1%

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20
Q

How does the amount of ADH released change with plasma osmolality?

A

Below 285mOsm/kg
amount of ADH released is constant at above 0

As plasma osmolality increases above 285mOsm/kg
amount of ADH released increases proportionately

21
Q

How is ADH released?

A

Vesicles containing ADH in the tip of neurosecretory cells exocytose
release ADH into the blood

22
Q

Where does ADH travel to after it has been released?

23
Q

What does ADH do in the kidneys?

A

Increases the expression of aquaporin2 channels on the apical domain of epithelial cells in the later distal convoluted tubule and the collecting ducts

24
Q

What is the effect of increased expression of aquaporin 2 channels on the apical domain of epithelial cells in the later distal convoluted tubule and the collecting ducts?

A

More water molecules move through it from the tubular lumen into the epithelial cell
so more water is reabsorbed

Aquaporin3 and aquaporin4 channels on basolateral domain of epithelial cell
water molecules move through them from the epithelial cell into the interstitial fluid

25
Q

What is the effect of increased water reabsorption on the urine?

A

Smaller volume of more concentrated urine produced

26
Q

What is the effect of increased water reabsorption on plasma osmolality?

A

Plasma osmolality decreases

27
Q

What stimulates thirst?

A

Osmoreceptors detect an increase in plasma osmolality

action potentials are fired down neurones

28
Q

How much does the plasma osmolality have to increase by for thirst to be stimulated?

29
Q

When does the stimulation for thirst stop?

A

After a sufficient volume of water has been ingested

so before it has been absorbed into the blood

30
Q

What does thirst result in?

A

Increased water intake

31
Q

What is the importance of the stimulation for thirst stopping after water has been consumed, before it has been absorbed into the blood?

A

It takes a while for water to be absorbed into the blood
so prevent ingestion of water in the meantime
as this would lead to overhydration

32
Q

How do the ADH and thirst mechanisms regulating plasma osmolality compare to each other?

A

ADH mechanism occurs before thirst
so ADH mechanism is faster

ADH mechanism gives short-term solution
whereas thirst gives long-term solution

33
Q

What else can stimulate ADH release and increased thirst apart from increased plasma osmolality?

A

Decreased blood volume and blood pressure

34
Q

How does a decreased blood volume and pressure affect ADH release?

A

ADH released at lower plasma osmolalities than normal

More ADH released per unit increase in plasma osmolality

35
Q

What are ADH and the thirst mechanism more sensitive to: changes in plasma osmolarity or changes in blood volume and pressure? How is this shown?

A

More sensitive to changes in plasma osmolarity

Smaller changes in plasma osmolarity than blood volume and pressure can stimulate ADH and the thirst mechanism

36
Q

What is more important to control: plasma osmolality or blood volume and blood pressure? How is this shown?

A

Blood volume and blood pressure

Plasma osmolality will be compromised to maintain normal blood volume and blood pressure

37
Q

How does an increased blood volume and pressure affect ADH release?

A

ADH released at higher plasma osmolalities than normal

Less ADH released per unit increase in plasma osmolality

38
Q

How can ADH cause disease?

A

Deficiency of ADH

Excess of ADH

39
Q

What is the disease of ADH deficiency called?

A

Diabetes insipidus

40
Q

What are the types of diabetes insipidus?

A

Central

Nephrogenic

41
Q

What is central diabetes insipidus?

A

Low levels of ADH in the plasma

because the hypothalamus and posterior pituitary gland don’t produce and release enough

42
Q

What are the causes of central diabetes insipidus?

A

Damage to hypothalamus and posterior pituitary gland

  • tumours
  • trauma
  • infection
43
Q

What is nephrogenic diabetes insipidus?

A

Normal levels of ADH in the plasma

but the kidneys are insensitive to it

44
Q

What are the signs symptoms of diabetes insipidus?

A

Polyuria - large volume of dilute urine produced

Polydipsia

45
Q

How is diabetes insipidus treated?

A

Giving ADH

47
Q

How can ADH be given?

A

Injections

Nasal spray

47
Q

What is the disease of excess ADH called?

A

Syndrome of inappropriate ADH secretion (SIADH)

49
Q

What causes SIADH?

A

High levels of ADH in the blood

excessively produced by the hypothalamus, or other sources

49
Q

What are the signs and symptoms of SIADH?

A

Small volume of concentrated urine produced always

High total body fluid

Dilutional hyponatraemia

Urinary system (25 decks)

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