Physiology (6-8) Flashcards Preview

Year 2 - Renal (DP) > Physiology (6-8) > Flashcards

Flashcards in Physiology (6-8) Deck (96):
1

What is the tonicity of the tubular fluid entering the DCT compared to blood?

hypo-osmotic (~100mosmol/L)

2

What is the collecting duct bathed in?

Progressively increasing [ISF]:
- 300 -> 1200mosmol/L

3

What percentage of filtered ions are reabsorbed before the DCT?

>95%

4

What is the residual load of NaCl that reaches the DCT?

~700-1000nmol/day

5

Why is the residual load of NaCl in the DCT important?

Salt balance

6

What effect does ADH have on the regulation of water and ion balance?

Increases water reabsorption

7

What effect does Aldosterone have on the regulation of water and ion balance?

Increases Na+ reabsorption
Increases H+ and K+ excretion

8

What effect does Atrial Natriuretic hormone have on the regulation of water and ion balance?

Reduces Na+ reabsorption

9

What effect does PTH have on the regulation of water and ion balance?

Increases calcium reabsorption
Decreases phosphate reabsorption

10

What does the DCT have a low permeability to?

Water
Urea

11

What happens in the early segment of the DCT?

NaCl reabsorption via the Triple-transporter

12

Which of the following does not happen in the late segment of the DCT:
- Calcium reabsorption
- H+ secretion
- Na+ reabsorption
- K+ reabsorption
- Phosphate secretion

Phsophate secretion

13

What is the early collecting duct similar to?

Late DCT

14

What is the permeability of the late collecting duct?

Low ion permeability
High water permeability

15

Where is ADH (an octopeptide) synthesised and from what?

Supraoptic nuclei and Paraventricular nuclei in the hypothalamus

16

Where is ADH stored?

In granules in the posterior pituitary

17

What is the approximate half life of ADH in the plasma?

10-15 minutes

18

How does ADH increase water reabsorption?

1. Binds to an Arginine Vasopressin Receptor 2 (V2)
2. ATP -> cAMP
3. cAMP causes increased transcription and insertion of aquaporins in the lumenal/apical membrane

19

In high [ADH]p, what is urine like?

Hypertonic (Up to 1400mosmol/L)
Low volume

20

In low [ADH]p, what is urine like?

Hypotonic urine (

21

What is the dominant factor controling thirst and ADH secretion?

Increased osmolarity activating hypothalamic osmoreceptors

22

When are left atrial volume receptors important in water balance?

In large plasma volume or BP changes

23

What causes left atrial volume receptors to encourage ADH release?

Very low plasma volume
OR
Hugh drop in BP

24

Apart from increasing water reabsorption, how else does ADH increase BP?

Causes peripheral vasoconstriction -> BP rises

25

Where is aldosterone secreted from?

Adrenal cortex

26

When is aldosterone secreted?

In response to:
- Increased [K+]p
- Decreased [Na+]p
Activation of RAAS

27

If aldosterone is absent, how much K+ is present in the urine?

None

28

How does decreased [Na+]p result in aldosterone secretion?

Indirectly via the juxtaglomerular apparatus

29

Where is renin produced and what does it do?

Kidneys:
- Converts Angiotensinogen -> Angiotensin I

30

Where is ACE produced and what does it do?

Lungs:
- Converts Angiotensin I -> Angiotensin II

31

What effects does Angiotensin II have?

Increases adrenal cortex secretion of Aldosterone
Increases thirst

32

What can the juxtaglomerular granular cells release and when do they secrete it?

Renin:
- When afferent arteriole BP drops
- When macula dense senses decreases [Na+]DCT
- Increased SNS activity due to reduced BP

33

How does fluid retention arise in CHF?

1. Failing heart
2. Decreased CO and SV
3. Decreased BP
4. Activation of RAAS
5. Increased Na+ and water retention
6. Fluid overload
7. Further heart failure

34

Where is ANP produced and stored?

Produced by heart
Stored in atrial muscle cells

35

When is ANP released?

When atrial muscle cells are stretched due to increased plasma volume

36

What effects does ANP have?

Increases Na+ excretion
Diuresis
Reduces BP via CVS affects
(All reduce plasma volume and hence BP)

37

How does ANP reduced BP via the SNS?

Inhibits SNS:
- Reduces CO
- Reduces peripheral resistance

38

What effect does ANP have on afferent arterioles in the kidney?

1. Smooth muscle contraction inhibited
2. Vasodilation
3. Increased GFR
4. More Na+ and water filtered
5. Increased excretion of Na+ and water

39

How can micturition be voluntarily controlled?

Tightening of:
- External urethral sphincter
- Pelvic diaphragm

40

What happens when bladder stretch receptors are activated?

Bladder contracts
Urethral sphincters open

41

How much urine can the bladder hold before the stretch receptors are activated?

250-400ml of urine

42

What part of the brain controls the voluntary inhibition of the micturition reflex?

Cerebral cortex

43

What branch of the ANS controls the micturition reflex?

PNS

44

What causes the maximum ADH secretion?

Increased ECF osmolarity AND decreased ECF volume

45

What is the pH of arterial blood?

7.45

46

What is the pH of venous blood?

7.35

47

How can pH be calculated?

pH = log(1/[H+])

48

How can acidosis arise via the CNS?

CNS depression

49

How can alkalosis arise via the CNS?

Overexcitability of peripheral nervous sytem and the CNS later

50

What are the three sources of H+ in the body?

Carbonic acid formation
Inorganic acid formation during nutrient breakdown
Organic acids from metabolism

51

What do buffer systems consist of?

One substance to yield H+ if [H+] decreases -> HA
One substance to bind H+ if [H+] increases -> A-

52

What happens to HA H+ + A- if H+ is added to the system?

Equilibrium shifts left:
- A- mops up excess H+ -> Increased [HA]
Results in increased [HA] and decreased [A-]

53

What happens to HA H+ + A- if a base is added to the system?

Equilibrium shifts right:
- Base has added OH-
-> H+ mops up OH- to form water
- [H+] decreases -> Increased HA dissociation
Results in decreased [HA] and increased [A-]

54

What is Ka?

The dissociation constant for acids

55

How can Ka be calculated?

Ka = ([H+] x [A-]) / [HA]

56

How is pKa calculated?

pKa = -log(Ka)

57

How can [H+] be calculated from the equation from Ka?

[H+] = (Ka x [HA]) / [A-]

58

How can pH be calculated from pKa? What is the name for his equation?

pH = pKa + log([A-] / [HA])
Henderson-Hasselbach equation

59

What is the most important physiological buffer equation?

CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻
^
Carbonic Anhydrase

60

How can the pH of a solution of H₂CO₃ be calculated?

pH = pKa + log([HCO₃⁻] / [H₂CO₃)

61

Given the pKa of a solution of H₂CO₃ is 6.1 and H₂CO₃ is a function of Pco₂ (with the arterial Pco₂ = 40mmHg and the solubility constant of CO₂ = 0.03mmol/mmHg/L) calculate the pH of a solution of H₂CO₃ when [HCO₃⁻] = 24mmol/L (normal [HCO₃⁻]p)

pH = 6.1 + log([HCO₃⁻] / Pco₂ x solubility constant of CO₂)
Therefore
pH = 6.1 + log(24mmol/L / 40 x 0.03) = 7.4

62

What effect do the kidneys have on [bicarbonate]?

1. Variable reabsorption of filtered bicarbonate
2. Kidneys can add 'new' bicarbonate to the blood:
- [HCO₃⁻]renal vein > [HCO₃⁻]renal artery

63

If no bicarbonate was reabsorbed, how much HCl would this be equivalent to adding to the body?

4L

64

Describe the unorthodox reabsorption of HCO₃⁻

1. HCO₃⁻ disappears in tubule to make H₂CO₃
2. Reappears in ISF from H₂CO₃

65

What happens if [HCO₃⁻]tubular fluid is low?

H+ combines with the next most powerful buffer -> PO₄³⁻

66

What is the process by which more HCO₃⁻ is made if [HCO₃⁻]tubular fluid decreases?

1. [HCO₃⁻] falls
2. More H+ secreted
3. [H+]i falls
4. H₂CO₃ ⇌ H⁺ + HCO₃⁻ shifts right to replace lost H+
5. HCO₃⁻ also made
6. [HCO₃⁻]i rises

67

How does PO₄³⁻ aid in increasing [HCO₃⁻]i?

1. HPO₄²⁻ ⇌ PO₄³⁻ + H+ moves right
2. H+ secreted into lumen
3. [H+]i falls
4. H₂CO₃ ⇌ H⁺ + HCO₃⁻ shifts right to replace lost H+
5. HCO₃⁻ also made
6. [HCO₃⁻]i rises

68

How can we measure the amount if titratable acid?

Measure amount of strong base (NaOH) that needs added to urine to get the pH = 7.4

69

What is the max amount of titratable acid that can be made every day and what implication does this have?

~40mmol/L
This means the max amount of 'new' HCO₃⁻ that can be made is ~40mmol/L

70

What is the normal ammonium excretion?

~20mmol/day

71

During acidosis, what can the ammonium excretion rise to?

500-600mmol/day

72

Approximately 4300mmol/day of bicarbonate is reabsorbed every day, what implication does this have?

~4300mmol/day H+ must be secreted

73

How much phosphoric acid is produced per day and what implication on H+ does this have?

20mmol of phosphoric acid produced per day so 20mmol of H+ must be secreted

74

How much ammonium is produced per day and what implication on H+ does this have?

40mmol of ammonium produced per day so 40mmol of H+ must be secreted

75

How can the total H+ secretion be calculated?

Bicarbonate reabsorption (4300mmol/day)
TA (Phosphoric acid) excretion (20mmol.day)
Ammonium excretion (40mmol/day)

Total = 4360mmol/day H+ secreted

76

How can the total H+ excretion be calculated?

TA (Phosphoric acid) excretion (20mmol.day)
Ammonium excretion (40mmol/day)

Total = 60mmol/day H+ excreted = 60mmol/day 'new' bicarbonate made per day

77

What three conditions need met for a person to be of normal acid-base status?

1. Plasma pH close to 7.4 (7.35 - 7.45)
2. [HCO₃⁻]p close to 25mmol/L (23 - 27)
3. Paco₂ close to 40mmHg (35-45) (4.5 - 6.0 kPa)

78

What is the primary priority is the normal acid-base balance is disrupted?

Restore pH to 7.4
- This is compensation
- Restored irrespective of what happens to
-> [HCO₃⁻]p
-> Paco₂

79

What conditions must be met for an acid-base disturbance to be corrected?

Restoration (to normal) of:
- pH
- [HCO₃⁻]p
- Paco₂

80

What is the name of the diagram that an ABG can be plotted on?

Davenport diagram

81

What is respiratory acidosis?

Carbon dioxide retention

82

What can cause respiratory acidosis?

COPD
Airway restriction (Asthma or Tumour)
Chest injuries
Respiratory depression

83

What criteria need to be met for uncompensated respiratory acidosis?

pH 45mmHg

84

What is the main way that respiratory acidosis can be compensated?

Via increased H+ excretion in the kidneys

85

What causes respiratory alkalosis?

Reduction in inspired PO2 at altitude:
1. Hypoxia stimulates peripheral chemoceptors
2. Hyperventilation -> Reduces Paco₂

86

What else can cause hyperventilation and therefore result in respiratory alkalosis?

Fever
Brainstem damage
Hysteria

87

What criteria need to be met for uncompensated respiratory alkalosis?

pH >7.45
Paco₂

88

How do the kidneys compensate for respiratory alkalosis?

Reduces H+ secretion which increases HCO₃⁻ excretion

89

What can cause a metabolic acidosis?

Ingestion of:
- Acids
- Acid producing food
Excessive H+ production:
- Lactic acid during exercise
- DKA
Excessive loss of base:
- Diarrhoea -> HCO₃⁻ lost

90

What criteria need to be met for uncompensated metabolic acidosis?

pH

91

What causes a reduced [HCO₃⁻]p in metabolic acidosis?

Buffers excess H+
HCO₃⁻ loss

92

How does respiratory compensation aim to fix metabolic acidosis?

Reduced pH -> Peripheral chemoceptors -> Carbon dioxide blown off

93

How is metabolic acidosis corrected?

Reduced filtered HCO₃⁻ therefore it is all readily reabsorbed
Increased H+ secretion:
- Increases TA + ammonium production
-> Increases production of 'new' HCO₃⁻

94

What can cause metabolic alkalosis?

Vomiting -> HCl loss
Ingestion of:
- Alkali (eg NaHCO₃ in antacids)
- Alkali producing food
Aldosterone hypersecretion:
- Increased Na+/H+ exchange -> Acid secretion

95

How is metabolic alkalosis compensated?

Increased pH -> Reduced ventilation -> Increased Paco₂
Increased [H+]p -> Decreased pH
[HCO₃⁻]p rises more

96

How is metabolic alkalosis corrected?

Increases filtration of HCO₃⁻ -> Reduced HCO₃⁻ reabsorption -> Increased HCO₃⁻ excretion (alkaline urine)
No TA or ammonium generated