Water and Electrolytes Flashcards

1
Q

what gains water in the body

A

water ingested and water formed in metabolism

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2
Q

what loses water

A

urine, faeces
sweat and expired air

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3
Q

do we gain or lose more water every day

A

even

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4
Q

what part of water balance is under homeostatic control

A

urination

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5
Q

what are the features of the kidney

A

glomerulus
proximal convoluted tubule
loop of henle
distal convoluted tubule
collecting ducts

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6
Q

label this

A
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7
Q

what does the glomerulus do

A

involved in renal blood flow and filtration of plasma

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8
Q

what is the renal blood flow rate

A

1200ml per minute

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9
Q

what is ithe glomerular filtration rate

A

120ml per minute

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10
Q

what are the filtration pressures

A

pressures that vary along the length of glomerular capillary form afferent arterioles

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11
Q

what is the capillary hydrostatic pressure

A

45-50mmHg

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12
Q

what is the plasma protein oncotic pressure

A

25-35mmHg

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13
Q

what is the capsular pressure

A

10mmHg

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14
Q

what is the net filtration pressure

A

10-15mmHg

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15
Q

what does the proximal convoluted tubule absorb

A

60-70% of the glomerular filtrate

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16
Q

what is absorbed in the proximal convoluted tubular

A

ions and small organic molecules

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17
Q

what is secreted in the proximal convoluted tubule

A

hydrogen ions

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18
Q

how are things absorbed in the proximal convoluted tubule

A

active transport and facilitated diffusion

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19
Q

is there any control of reabsorption in the proximal convoluted tubular

A

very little

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20
Q

what occurs in the loop of henle

A

this is important for concentration of urine
length of the loop correlates with the ability to concentrate urine

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21
Q

what is the countercurrent exchange mechanism

A

this is how urine is concentrated in the loop of henle, and the concentration depends on active transport pumps in the thick ascending limb of the loop of henle

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22
Q

what is the net reabsorption of liquid in the loop of henle

A

10%

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23
Q

what is absorbed in the distal convoluted tubule

A

sodium
chloride
calcium

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24
Q

what is secreted in the distal convoluted tubule

A

hydrogen
potassium

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25
Q

what hormones control the activity of the distal convoluted tubular

A

aldosterone
atrial natriuretic hormone
ADH
parathyroid hormone

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26
Q

what happens in the collecting ducts of the kidney

A

water reabsorpiton, under the influence of ADH, and there are membrane channels for water reabsorption

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27
Q

how does water move along the collecting ducts

A

along osmotic gradients created by the counter current exchange mechanism

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28
Q

which hormones regulate water and electrolytes

A

antidiuretic hormone
renin angiotension aldosterone system
atrial natriuretic hormone

29
Q

what is vasopressin

A

ADH, produced in the hypothalamus and released from the posterior pituitary gland

30
Q

what does vasopressin act on

A

the distal convoluted tubule and collecting ducts to increase water and permeability by insertion of aquaporin channels
water moves passively between the tubule lumen and the interstitial fluid

31
Q

what leads to an increase in ADH release in the posterior pituitary

A

decreased plasma volume
decreased baroreceptor
increased plasma osmorality
increased osmoreceptor activation

32
Q

what is ADH secretion increased by

A

decreased extracellular fluid
increased extraecllular fluid osmorality
ADH also causes constriction of blood vessels

33
Q

how is a decreased in extracellular fluid detected

A

low pressure receptors in the atria and great veins

34
Q

how is an increase in extracellular fluid osmorality detected

A

osmoreceptors in the hypothalamus

35
Q

what are electrolytes

A

ions present in intracellualr and extracellular fluid

36
Q

what are electrolytes subject to the control of

A

homeostasis

37
Q

what are some important electrolytes

A

sodium
potassium
hydrogen
calcium

38
Q

what does much of the homeostatic control of electrolytes involve

A

determining how much is excreted through the kidneys

39
Q

how is sodium controlled

A

RAAS and ANH

40
Q

describe how RAAS controls sodium levels

A

promotes reabsorption of sodium and water in distal convoluted tubule in exchange for potassium and hydrogen ions
angiotensin is a potent vasoconstrictor

41
Q

describe how the atrial natriuretic hormone controls sodium

A

increases excretion of sodium and water, and has the opposite effects of aldosterone

42
Q

what stimulates atrial natriuretic hormone release

A

an increase in plasma volume which causes an increase in atrial distension

43
Q

why do cell membrane potentials rely on extracellular fluid

A

due to the presence of potassium

44
Q

what can small changes in potassium ions lead to

A

nerve and muscle function

45
Q

what regulates potassium levels

A

aldosterone

46
Q

what are the two disorders of ADH secretion

A

hyposecretion and hypersecretion

47
Q

describe hyposecretion of ADH

A

happens in diabetes inspidus, where there are large volumes of inspid, tasteless urine

48
Q

describe hypersecretion of ADH

A

syndrome of inappropriate ADH, which leads to excess ADH and water retention

49
Q

what are the effects of potassium electrolytes on nerve function

A

increasing extracellular fluid leads to depolarisation
depolarisation causes axons to fire action potential
membrane potential does not return to resting levels, the result is that the axon is in refractory period

50
Q

why are there potassium salts in toothpaste

A

to desensitise hypersensitive dentine

51
Q

what is the manufacturers claim in regard to potassium salts in toothpaste

A

potassium ions will diffuse from paste along the dentinal tubules and raise the potassium ion concentration at the end of the tubules. this leads to depolarised nerves, and inactivated sodium channels, causing a prolonged refractory period
the issue is that potassium ion build up does not persist

52
Q

what causes an increase in renin secretion

A
  • decreased plasma volume
  • increased sympathetic nerve activity
  • decreased renal blood flow, leading to a decrease in glomerular blood flow, leading to stretch of J-G baroreceptors and decreased sodium concentrations in tubular fluid
  • this affects the juxta glomerulosa apparatus, increasing renin secretion
53
Q

what are the two factors that increase renin secretion

A

increased sympathetic nervous activity and the macula densa

54
Q

what is the macula densa

A

lining of specialised cells in the kidney

55
Q

is there much control over the glomerular filtration rate

A

no because of the flow

56
Q

are there any hormonal impacts in the proximal convoluted tubule

A

no it happens despite any hormonal action

57
Q

describe the counter current exchange

A

flow is generated into the loop of henle, which works to concentrate the urine.
the concentration depends on the active transport in the thick limb of the loop of henle, so there are working pumps

58
Q

what is the sodium ion involved in

A

depolarisation of nerves

59
Q

what are calcium ions involved in

A

cardiac conducting system, or as second messenger

60
Q

what are the chlorine ions involved in

A

saliva secretion, as they produce a concentration gadient with chloride in the lumen, to allow water flow into the lumen

61
Q

why do we excrete hydrogen ions

A

to prevent metabolic acidosis

62
Q

what does ADH do to allow water absorption

A

provides channels

63
Q

which hormone is involved in water absorption

A

ADH

64
Q

which hormone is involved in electrolyte reabsorption

A

RAAS and ANH

65
Q

what is octopressin

A

vasoconstrictor used in local anaesthetic

66
Q

how long after dirnking does fluid get lost through urine

A

half an hour

67
Q

which ions are exchanged when absorbing water and sodium

A

potassium and hydrogen

68
Q

what does sensitive toothpaste cause the production of

A

tertiary dentine by odontoblasts