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Year 2 > Endocrine control of body fluid volume and composition > Flashcards

Endocrine control of body fluid volume and composition Flashcards

1
Q

How does the osmolarity of the tubular fluid leaving the loop of henle compare to that of the surrounding interstitial fluid?

A

Hypo-osmotic

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2
Q

Where does the distal tubule drain to?

A

Collecting duct (cortical)

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3
Q

How does the interstitial fluid change as the collecting duct progresses?

A

Increasing osmolarity (collecting duct drills down into medulla)

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4
Q

Where in the nephron is ion and water balance mainly regulated?

A

Distal tubule and collecting duct

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5
Q

Where does most reabsorption of ions occur?

A

Proximal tubule BUT the remaining ions are essential for salt balance

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6
Q

What is the main mechanism of salt and water regulation?

A

Hormonal

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7
Q

Where do the hormones acting on the kidney act?

A

Distal tubule and collecting duct

do NOT act on proximal tubule or loop of Henle

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8
Q

How permeable is the distal tubule to water and urea? What effect does this have?

A 
Not very (unless ADH levels are high)
Urea is concentrated in the tubular fluid which helps maintain the corticomedullary gradient
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9
Q

Describe what happens in the early and late parts of the distal tubule with regard to ion absorption

A 
Early
 - Sodium, chlorine and potassium triple co-transporter (i.e salt reabsorption)
Late
 - Calcium reabsorption
 - Hydrogen secretion
 - Sodium reabsorption
 - Potassium reabsorption
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10
Q

Is it the early or late distal tubule that is stimulated by hormones?

A

Late

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11
Q

Describe what happens in the early and late collecting duct with regard to ion absorption

A 
Early
 - Sodium reabsorption
 - Potassium reabsorption
 - Hydrogen secretion
 - Calcium reabsorption 
Late 
 - Low ion permeability 
 - Permeability to water varies with respect to ADH
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12
Q

Describe vasopressin secretion

A

Peptide hormone synthesised (supraoptic and paraventricular nuclei) in the hypothalamus >
Transported down nerves >
Stored in the posterior pituitary >
Released into blood in response to calcium dependent exocytosis (induced by action potentials)

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13
Q

Peptide hormones have a long half life. T/F

A

False - short half life

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14
Q

How does ADH increase the permeability of the collecting duct to water?

A

ADH binds to type 2 vasopressin receptors on the basolateral membranes of tubular cells >
Increase in intracellular cyclic AMP >
Increased expression of aquaporins (water channels) at the apical membrane >
Increased permeability to water

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15
Q

How is hypertonic urine formed?

A

In the presence of high ADH water moves from the collecting duct to the interstitial fluid along the osmotic gradient

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16
Q

How is hypotonic urine formed?

A

In the presence of low ADH water cannot leave the collecting duct and so is retained in the urine

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17
Q

Tubular fluid equilibrates with interstitial fluid via aquaporins under which condition?

A

High ADH

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18
Q

The collecting duct is impermeable to water so none is reabsorbed under which condition?

A

Low ADH

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19
Q

ADH affects salt and water reabsorption. T/F

A

False - ADH only has a direct effect on water reabsorption

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20
Q

Describe the ADH hormone axis

A

Increase in plasma osmolarity >
Hypothalamic osmoreceptors >
Increase in thirst and ADH secretion >
ADH causes vasoconstriction + increased distal tubular and collecting duct permeability to water >
Decreased urine output >
Increased plasma volume and decreased plasma osmolarity

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21
Q

When are left atrial volume receptors stimulated to produce ADH?

A

When there is a massive drop in ECF thus blood pressure and eventually decreased atrial stretch

22
Q

How can diabetes insipidus be classified?

A

Central

Nephrogenic

23
Q

Is diabetes insipidus hereditary?

A

Usually

24
Q

What are the symptoms of diabetes insipidus?

A

Large volumes of dilute urine

Constant thirst

25
Q

How is diabetes insipidus managed?

A

ADH replacement

26
Q

What medication (long term) induces diabetes insipidus?

A

Lithium as is used in bipolar disorder

27
Q

What controls feedforward ADH secretion?

A

Stretch receptors in the GI tract

28
Q

What effect do nicotine (i.e smoking) and alcohol have on ADH secretion?

A

Nicotine - increase ADH
Alcohol - decrease ADH

Nb - ecstasy also decreases ADH and thus poses a massive dehydration risk

29
Q

How does the tubular osmolarity change across the length of the nephron

A

Proximal tubule - low
Loop of Henle - high then low
Distal tubule - low (may rise if increased ADH)
Collecting duct - low (may rise if increased ADH)

30
Q

What type of hormone is aldosterone and where is it secreted form?

A

Steroid

Adrenal cortex

31
Q

What mnemonics can be used to remember the hormones secreted from the adrenal gland?

A

Get my = glomerulosa - mineralocorticoids (aldosterone)
Freaking gun = fasiculata - glucocorticoids (cortisol)
Right away = reticularis - androgens (sex hormones)
Magic = medulla - adrenaline, etc (magic rush)

32
Q

When is aldosterone secreted?

A

Directly in response to rising potassium
Indirectly in response to falling sodium
Indirectly as part of the renin-angiotensin-aldosterone system

33
Q

What effect does aldosterone have?

A

Increases sodium reabsorption
Increases potassium secretion

Nb - remember water follows salt so inc sodium helps to increased plasma volume

34
Q

What happens if a patient is not producing aldosterone?

A

Eventually leads to death due to low fluid volumes

35
Q

Where is potassium reabsorbed? How much potassium is excreted in the urine?

A

90% within the proximal tubule and 10% within the distal tubule. None

36
Q

How is potassium reabsorption affected by aldosterone?

A

Increase in potassium is detected by the adrenal cortex >
Aldosterone release >
Increased secretion of potassium

37
Q

Decreasing sodium indirectly stimulates aldosterone release how?

A

Lowered sodium levels detected within the juxtaglomerular apparatus stimulates the renin-angiotensin-aldosterone system

38
Q

Explain RAAS

A

Lowered ECF, sodium and BP >
Kidneys detect and secrete renin >
Renin acts on angiotensiogen (secreted by the liver) to covert it to angiotensin I >
Angiotensin I is converted to angiotensin II by angiotensin converting enzyme (ACE) in the lungs >
Angiotensin II acts on the adrenal cortex to stimulate aldosterone >
Aldosterone acts on the liver to decrease potassium and increase sodium reabsorption >
Increased salt causing increased water retention and thus fluid repletion

39
Q

What does angiotensin II do?

A

Increases thirst
Stimulates aldosterone release
Increases ADH
Causes arteriolar vasoconstriction

40
Q

How does the juxtaglomerular apparatus effect the RAAS?

A

Granular cells in the juxtaglomerular apparatus release renin in response to

  • decreased afferent blood pressure
  • decreased salt concentration
  • direct sympathetic stimulation
41
Q

How does aldosterone increase sodium reabsorption at the distal tubule and collecting duct?

A

Promotes increased expression of apical sodium channels

Increases number and activity of basolateral sodium potassium ATPases

42
Q

Abnormal activity of the RAAS causes what?

A

Hypertension

43
Q

What is the cause of fluid retention in congestive heart failure?

A

RAAS

44
Q

Where is atrial natriuretic peptide/hormone produced and stored?

A

Left atrium produces and atrial muscle cells store

45
Q

What is atrial natriuretic peptide released?

A

In response to mechanical stretch of the left atrium due to increased circulating plasma volume

46
Q

What does atrial natriuretic peptide do?

A

Increases excretion of sodium hence diuresis and thus reduction in circulating plasma volume
Decreases activity of RAAS
Arteriolar vasodilation
Decreases sympathetic stimulation

47
Q

Which two mechanisms control micturation?

A

Micturation reflex

Voluntary control

48
Q

What initiates the micturation reflex?

A

Stretch receptors in the bladder wall

49
Q

What is the micturation reflex?

A

Involuntary contraction of the detrusor and relaxation of the internal urethral sphincter

50
Q

How can micturation be stopped by voluntary control?

A

Central pathways cause the relaxation of the detrusor and contraction of internal
Voluntary contraction of external sphincter and levator ani

51
Q

What is the difference between water diuresis and osmotic diuresis?

A

Water - increased urine flow but no increased salt excretion
Osmotic - increase in urine flow is a result of primary increase in salt excretion

Year 2 (72 decks)

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