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Renal > Endocrine Control of Body Fluid Volume and Composition > Flashcards

Endocrine Control of Body Fluid Volume and Composition Flashcards

1
Q

What property does the tubular fluid leaving the loop of Henle have in relation to the plasma?

A

It is hypo-osmotic to the plasma = 100 msomol/l

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2
Q

What is the osmolarity of the interstitial fluid surrounding the renal cortex?

A

300 mosmol/l

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3
Q

Where does the distal tubule empty into?

A

The collecting ducts

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4
Q

What are the collecting ducts bathed in as they descend though the medulla?

A

Progressively increasing concentrations of surrounding interstitial fluid (300-1200 mosmol/l)

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5
Q

What are the major sites for the regulation of ion and water balance?

A

The distal tubule and collecting duct

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6
Q

Where do all the tubules of the kidney empty into?

A

The cortical collecting ducts

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7
Q

What happens to filtered ion loads before they reach the distal tubule?

A

> 95% are reabsorbed before the filtrate reaches the distal tubule = residual load is very important for salt balance

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8
Q

What mainly affects the fluid and NaCl regulation?

A

Hormones

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9
Q

What are the effects of some hormones on the kidneys?

A 
ADH = increases water reabsorption
Aldosterone = increases Na+ reabsorption and H+/K+ secretion
ANP = decreases Na+ reabsorption
PTH = increases Ca2+ reabsorption and decreases PO4- reabsorption
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10
Q

What does the distal tubule have low permeability to?

A

Urea and water = urea is concentrated in the tubular fluid

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11
Q

What does the concentration of urea in the distal tubule help to establish?

A

Osmotic gradient within the medulla

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12
Q

What are the two segments of the distal tubule?

A

Early = Na+-K+-2Cl- transporter (NaCl reabsorption)

Late

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13
Q

What are the functions of the late segment of the distal tubule?

A

Ca2+, Na+ and K+ reabsorption, and H+ secretion in the basal state
K+ secretion when K+ secretory cells are activated by aldosterone

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14
Q

What are the two segments of the collecting duct?

A 
Early = similar function to late distal tubule
Late = low ion permeability, permeability to water and urea influenced by ADH
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15
Q

What is the first step in ADH secretion?

A

Octapeptide synthesised by the supraoptic and paraventricular nuclei in the hypothalamus

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16
Q

Where is ADH transported from once it leaves the hypothalamus?

A

Transported down nerves to terminals where it is stored in the granules in the posterior pituitary

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17
Q

How is ADH released?

A

Released into blood when action potentials down the nerves lead to Ca2+ dependent exocytosis

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18
Q

What is the plasma half life of ADH?

A

10-15 minutes

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19
Q

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

A

By inserting new aquaporins

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20
Q

What happens in the presence of maximal plasma ADH concentration?

A

Water moves from the collecting duct lumen along the osmotic gradient into the medullary interstitial fluid = enables hypertonic urine formation

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21
Q

What happens if there is high ADH concentration?

A

High water permeability in the collecting duct = hypertonic urine (up to 1400 mosmol/l)

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22
Q

What happens if there is low ADH concentration?

A

Low water permeability in the collecting duct = hypotonic urine (<50 mosmol/l)

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23
Q

What happens to urine production in the presence of maximal ADH plasma concentration?

A

Small volumes of concentrated urine = tubular fluid equilibrates with interstitium via aquaporins

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24
Q

What happens to urine production in the presence of minimal ADH plasma concentration?

A

Large volumes of dilute urine = collecting duct is impermeant to water so no water reabsorption

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25
Q

What is the most important stimulus for ADH release?

A

Hypothalamic osmoreceptors

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26
Q

What is the accessory pathway for ADH release?

A

Activation of left atrial stretch receptors

27
Q

What does decreased atrial pressure cause?

A

Increased ADH release = need large changes in plasma volume

28
Q

What effect does nicotine have on ADH?

A

Stimulates its release

29
Q

What effects does alcohol have on ADH?

A

Inhibits its release

30
Q

What effect does stimulation of stretch receptors in the upper GI tract have on ADH?

A

Exerts a feed-forward inhibition

31
Q

How is diabetes insipidus classed?

A

Central or nephrogenic (usually hereditary)

32
Q

What are the symptoms of diabetes insipidus?

A

Large volumes of dilute urine (up to 20l per day)

Constant thirst

33
Q

How is diabetes insipidus treated?

A

ADH replacement

34
Q

What is aldosterone?

A

Steroid hormone secreted by the adrenal cortex

35
Q

What is aldosterone secreted in response to?

A

Rising K+ concentration or falling Na+ concentration in the blood, or activation of the renin-angiotensin system

36
Q

What does aldosterone stimulate?

A

Na+ reabsorption and K+ secretion = causes Na+ retention which increases blood volume and pressure

37
Q

What normally happens to K+ in the nephron?

A

Normally 90% is reabsorbed in the early regions of the nephron (mainly the proximal tubule)

38
Q

What happens to the K+ not reabsorbed in the nephron when aldosterone is absent?

A

Reabsorbed in the distal tubule = no K+ is excreted in the urine

39
Q

What effect does an increase in plasma K+ concentration have?

A

Directly stimulates the adrenal cortex = aldosterone stimulates the secretion of K+

40
Q

What effect does a decrease in plasma Na+ concentration have?

A

Promotes indirect stimulation of aldosterone by means of the juxtaglomerular apparatus = aldosterone increases Na+ reabsorption in the distal and collecting tubules

41
Q

Where is renin released from?

A

Granular cells in the juxtaglomerular apparatus

42
Q

What does reduced pressure in the afferent arteriole cause?

A

More renin is released = more Na+ reabsorbed so blood volume increased and blood pressure restored

43
Q

What cells sense with amount of NaCl in the distal tubule?

A

Macula densa cells = if NaCl reduced more renin is released and more Na+ is reabsorbed

44
Q

What effect does increased sympathetic activity as a result of reduced arterial BP have?

A

Granular cells are directly innervated by the sympathetic nervous system so release more renin

45
Q

What are some conditions linked with abnormal RAA system?

A

Hypertension = abnormal increase in RAA system

Congestive heart failure = fluid retention due to low BP caused by reduced cardiac output

46
Q

How is congestive heart failure treated?

A

Low salt diet and loop diuretics

47
Q

What are the actions of ACE inhibitors?

A

Stop fluid and salt retention

Stop arteriolar constriction

48
Q

Where is atrial natriuretic peptide (ANP) produced?

A

Produced by heart and stored in atrial muscle cells

49
Q

When is ANP released?

A

When atrial muscle cells are stretched due to an increase in the circulating plasma volume

50
Q

What does ANP promote?

A

Excretion of Na+ and diuresis = reduces plasma volume

Also exerts effect on CV system to lower blood pressure

51
Q

Where is urine temporary stored?

A

In the bladder = emptied by micturition

52
Q

What happens to urine once it has been formed by the kidneys?

A

It is propelled by peristaltic contractions through the ureters to the bladder for temporary storage

53
Q

What controls micturition?

A

Micturition reflex and voluntary control

54
Q

How much urine can the bladder hold before stretch receptors in its walls starts the micturition reflex?

A

250-400ml

55
Q

What occurs in the micturition reflex?

A

Involuntary emptying of the bladder by simultaneous bladder contraction and opening of the internal and external urethral sphincters

56
Q

How can micturition be voluntarily prevented?

A

By deliberate tightening of the external sphincter and surrounding pelvic diaphragm

57
Q

What is water excess/deficit a response to?

A

Changes in ECF osmolarity

58
Q

How is ECF osmolarity monitored?

A

Hypothalamic osmoreceptors detect and initiate the priority mechanism for regulation of ECF osmolarity = signal to ADH and thirst

59
Q

How able are renal mechanisms to cope with water excess/deficit?

A

Renal mechanisms suffice during water excess, but during deficit it is necessary to increase intake

60
Q

What is salt excess/deficit a response to?

A

Changes in ECF volume (e.g salt deficit due to haemorrhage)

61
Q

What occurs in water diuresis?

A

Increased urine flow but not an increased solute excretion

62
Q

What occurs in osmotic diuresis?

A

Increased urine flow is as a result of a primary increase in salt excretion

63
Q

What are the rules around diuresis?

A

Any loss of solute in the urine must be accompanied by water loss (osmotic diuresis), but the reverse isn’t true (water diuresis isn’t necessarily accompanied by equivalent solute loss)

Renal (36 decks)

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