Physiology (1-5) Flashcards Preview

Year 2 - Renal (DP) > Physiology (1-5) > Flashcards

Flashcards in Physiology (1-5) Deck (126):
1

What is osmolarity?

Concentration of osmotically active particles in a solution

2

What is the approximate osmolarity of the body's fluids?

~300mosmol/L

3

How can the osmolarity of a solution be calculated?

If the following are known:
- Molar concentration
- Number of particles present

4

What is the osmolarity of a 100mM solution of magnesium chloride?

Molar concentration = 100mM
Number of particles present = 3
Osmorality = 100 x 3 = 300mosmol/L

5

What are the units of osmolality?

osmol/kg of water

6

When are osmolarity and osmolality bascially interchangeable?

Weak solutions
Body fluids

7

What is tonicity?

Effect a solution has on cell volume

8

What effect does a hypotonic solution have on cells?

Cell lysis

9

What effect does a hypertonic solution have on cells?

Cell shrinkage

10

What does tonicity take into account?

Solute's ability to cross cell membranes

11

How much of the total body water is made up of ICF?

67%

12

How much of the total body water is made up of ECF?

33%

13

What forms the ECF?

Plasma (20%)
ISF (80%)
Lympha and transcellular fliud (Negligible)

14

What tracer can we use to calculate total body water?

³H₂O

15

What tracer can we use to calculate ECF?

Inulin

16

What tracer can we use to calculate plasma volume?

Labelled albumin

17

How can we calculate ICF?

TBW = ECF + ICF
(We know TBW and ECF from ³H₂O and Inulin respectively)

18

How can we calculate the volume of distribution?

1. Add a does of tracer (D) to an unknown volume of water (V)
2. Allow tracer to mix evenly
3. Take a small sample and measure [Tracer] (C)
4. Calculate V as follows:
V(litres) = Does (D)/[Sample](C)
Where [Sample] = Mass/Volume in mg/L

19

Calculate the volume of distribution for the following values:
- Dose given = 42mg
- Sample volume is 5ml
- Sample tracer mass is 0.01mg

[Tracer] in sample = 0.01/0.005 = 2mg/L
V = 42/2 = 21L

20

Which of the following are sensible water losses and which are insensible:
- Sweat
- Faeces
- Skin
- Urine
- Lungs

Sensible:
- Sweat
- Faeces
- Urine
Insensible:
- Skin
- Lungs

21

What sources of water loss are increased and decreased in hot weather?

Increased:
- Sweat
Decreased:
- Lungs
- Urine

22

What sources of water loss are increased and decreased during prolonged heavy exercise?

Increased:
- Lungs
- Sweat
Decreased:
- Urine

23

What is the main method of maintaining water balance?

Increasing water intake

24

What is the ionic composition of ICF in regards to the following ions:
- Na+
- K+
- Cl-
- Bicarbonate

Sodium -> 10mM
Potassium -> 140mM
Cloride -> 7mM
Bicarbonate -> 10mM

25

What is the ionic composition of ECF in regards to the following ions:
- Na+
- K+
- Cl-
- Bicarbonate

Sodium -> 140mM
Potassium -> 4.5mM
Cloride -> 115mM
Bicarbonate -> 28mM

26

What are the main ions in the ICF?

Na+
Cl-
Bicarbonate

27

What are the main ions in the ICF?

K+
Mg²⁺
Negatively charged proteins

28

What causes water movement between the ICF and ECF?

Osmotic gradient

29

What results when there is a gain or loss of H₂O in regards to fluid osmolarity and ICF/ECF volumes?

Change in fluid osmolarity
Similar change in ICF and ECF volumes

30

What results when there is a gain or loss of NaCl in regards to fluid osmolarity and ICF/ECF volumes?

Change in fluid osmolarity
Increased ECF NaCl:
- Increased ECF volume
- Decreased ICF volume
Decreased ECF NaCl:
- Decreased ECF volume
- Increased ICF volume

31

What results when there is a gain or loss of isotonic fluid in regards to fluid osmolarity and ICF/ECF volumes?

No change in osmolarity
Change in ECF volume

32

What does the kidney alter in terms of the ECF and what is this vital for?

Composition
Volume:
- Both aid in BP control

33

What affect can small leaks or increased cell uptake of K⁺ have?

Severe changes in [K⁺]p:
- Muscle weakness -> Paralysis
- Arrhythmias -> Cardiac arrest

34

What does the rate of excretion of any substance equal?

Filtration rate + Secretion rate - Reabsorption rate

35

What does the rate of filtration of a substance X equal?

[X]plasma x GFR

36

What does the rate of excretion of a substance X equal?

[X]urine x Vu (urine flow rate)

37

What does the rate of reabsorption of a substance X equal?

Rate of Filtration of X - Rate of Excretion of X

38

What does the rate of secretion of a substance X equal?

Rate of Excretion of X - Rate of Filtration of X

39

If there is net reabsorption of a substance, what must be true?

Rate of Filtration > Rate of Excretion

40

If there is net secretion of a substance, what must be true?

Rate of Filtration

41

What acts as a barrier to RBC filtration into the glomerulus?

Glomerular capillary endothelial cells

42

What acts as a barrier to plasma protein filtration into the glomerulus?

Basement membrane
Slit processes of podocytes in glomerular epithelium

43

What is the approximate glomerular capillary BP/hydrostatic pressure (BPgc)?

55mmHg

44

What is the approximate Bowman's capsule hydrostatic pressure (Hpbc)?

15mmHg

45

What is the approximate capillary oncotic pressure (COPgc)?

30mmHg

46

What is the approximate Bowman's capsule oncotic pressure (COPbc)?

0mmHg

47

How can the net filtration pressure be calculated?

(BPgc + COPbc) - ( Hpbc + COPgc)
(55 + 0) - (15 + 30) = 10mmHg

48

What is the balance of hydrostatic pressure and osmotic forces known as?

Starling forces

49

How can GFR be calculated?

Filtration coefficient (Kf) x Net filtration pressure

50

What is the filtration coefficient?

How 'hole-y' the glomerular membrane is

51

What is a normal GFR?

Approximately 125ml/min

52

What is the main determinate of the GFR?

Glomerular afferent capillary BP/hydrostatic pressure

53

How are renal blood flow and GFR maintained extrinsically?

Sympathetic control -> The baroreceptor reflex

54

How are renal blood flow and GFR maintained intrinsically?

Myogenic mechanism
Tubuloglomerular feedback

55

What happens to BPgc if the afferent arteriole is:
- Constricted
- Dilated

Constricted -> Falls
Dilated -> Rises

56

What does autoregulation of renal blood flow do?

Prevents short-term BP changes affecting the GFR

57

How does the myogenic mechanism aid autoregulation of renal blood flow?

If vascular smooth muscle is stretched (due to increased BP) it contracts -> Afferent arteriole constriction -> GFR reduced

58

How does Tubuloglomerular feedback aid autoregulation of renal blood flow?

Involves the justaglomerular apparatus:
- If GFR rises -> Tubular NaCl flow increases
-> Afferent arteriole constriction -> GFR reduced

59

What can cause an increased Bowman's capsule hydrostatic pressure and what effect does this have on GFR?

Kidney stone
Reduces GFR

60

What can cause an increased glomerular capillary oncotic pressure and what effect does this have on GFR?

Diarrhoea
Reduces GCR

61

What can cause a decreased glomerular capillary oncotic pressure and what effect does this have on GFR?

Severe burns
Increased GFR

62

If the filtration coefficient is reduced, what happens to GFR?

Decreases

63

What is plasma clearance?

Volume of plasma completely cleared of a substance per minute (ml/min)

64

How can we calculate the clearance of substance X?

Clearance of X = Rate of Excretion of X / [X]p
Clearance of X = [X]u x Vu / [X]p

65

What is the clearance of a substance which is filtered, completely reabsorbed and not secreted? Give an example?

Zero
Glucose

66

When else is the clearance of a substance 0?

If substance is not filtered and not secreted

67

What is the clearance of a substance which is filtered, partly reabsorbed and not secreted? Give an example?

Clearance

68

What is the clearance of a substance which is filtered, secreted and not reabsorbed? Give an example?

Clearance > GFR
All of filtered plasma cleared
Peritubular plasma also cleared
H+

69

If clearance

Substance is reabsorbed

70

If clearance = GFR?

Substance neither reabsorbed or secreted

71

If clearance

Substance secreted

72

What can Para-amino Hippuric Acid (PAH) be used to calculate?

Renal plasma flow

73

What is a normal renal plasma flow?

650ml/min

74

WHich of the following is not a feature of PAH:
- Freely filtered at glomerulus
- Produced in small (but quantifiable) amounts by the body
- Secreted into tubule
- Not reabsorbed at all
- Completely cleared from plasma

Produced in small (but quantifiable) amounts by the body

75

True or False; All PAH which escapes filtration is secreted from peritubular capillaries?

True

76

What is the filtration fraction?

Fraction of plasma flowing through glomeruli which is filtered into tubules

77

What properties should a clearance marker have?

Non-toxic
Inert (not metabolised)
Easy to measure

78

What additional features should a GFR marker have?

Freely filtered
Not:
- Secreted
- Reabsorbed

79

What additional features should a RPF marker have?

Freely filtered
AND
Completely secreted

80

Why is inulin not a convenient substance to use to estimate GFR?

Requires a constant infusion to maintain [Inulin]p

81

How is the filtration fraction calculated?

GFR/Renal Plasma Flow

82

What is the normal filtration fraction?

~20%

83

How is renal blood flow calculated?

RPF x 1/1-HCT (Where HCT is the Haematocrit):
- HCT is the % of blood which is RBCs
-> ~45% in males
-> ~40% in females
RBF = 650/1-0.45 = 650 x 1.85 = 1200ml/min

84

What rate is the filtrate absorbed in the PCT?

~80ml/min

85

What rate is the filtrate absorbed in the Loop of Henle?

~45ml/min

86

Is reabsorbed fluid hypotonic, isotonic or hypertonic to the glomerular filtrate?

Isotonic

87

Which of the following is not reabsorbed in the PCT:
- Sugars
- Amino acids
- Na⁺
- PO₄³⁻
- SO₄²⁻
- Lactate

Na⁺

88

Which of the following is not secreted into the PCT:
- H⁺
- Hippurates
- Neurotransmitters
- Bile pigments
- K⁺
- Uric acid
- Drugs
- Toxins

K⁺

89

What are the two routes by which a substance can be reabsorbed from the tubule?

Transcellular (mainly)
Paracellular

90

How does primary active transport work?

Energy required to operate carrier
Substance moved AGAINST its concentration gradient

91

How does secondary active transport work?

Carrier molecule transported coupled to the concentration gradient of an ion -> Usually Na⁺

92

How does facilitated diffusion work?

Passive carrier-mediated transport
DOWN its concentration gradient

93

What chemicals can diffuse through the lipid bilayer?

Oxygen and Carbon dioxide

94

Give an example of a compound that is carried through a membrane by facilitated diffusion?

Glucose

95

Give an example of a primary active transport

Na+/K+ ATPase:
- Na+ reabsorbed
- K+ secreted

96

Give an example of secondary active transport

Na+/Glucose co-transporter:
- Glucose carried coupled to Na+

97

What is the approximate renal threshold for glucose?

[Glucose]p 10-12mmol/L

98

What is the transport maximum for glucose?

~2.0mmol/min

99

What happens once glucose filtered > glucose reabsorbed?

Excretion = Filtration = Reabsorption

100

What happens to the clearance of a substance that is reabsorbed or secreted once Tm (Transport maximum) is reached?

It is not constant

101

How is Cl- reabsorption driven in the PCT?

Na+ reabsorption drives Cl- reabsorption via the paracellular pathway

102

How is water reabsorbed in the PCT?

Osmosis

103

What is the osmolality of the tubular fluid when it leaves the PCT?

~300mosmol/L (ie isotonic to plasma)

104

What are the main functions of the Loop of Henle?

Generates a corticomedullary solute concentration gradient
Helps form hypertonic urine

105

What sort of flow does the Loop of Henle have?

Countercurrent

106

What runs alongside the Loop of Henle that helps establish a hyperosmotic medullary ISF?

Vasa recta

107

What is reabrosbed in the ascending limb of the Loop of Henle?

Na+ and Cl-

108

How does reabsorption occur in the thick upper part of the ascending limb of the Loop of Henle?

Active transport

109

How does reabsorption occur in the thin lower part of the ascending limb of the Loop of Henle?

Passive transport

110

How permeable is the ascending limb of the Loop of Henle to water?

Very impermeable (little/no water follows Na+)

111

What processes do and don't occur in the descending limb of the Loop of Henle?

Highly permeable to water -> Reabsorbed
NaCl is NOT reabsorbed

112

What transporter is present on the apical/lumenal membrane of the PCT?

Na+/K+/2Cl- co-transporter

113

What transporters are present on the basolateral membrane of the PCT?

K+/Cl- co-transported
Na+/K+ exchanger

114

What does K+ recycling in the PCT do?

Allows NaCl to be absorbed into the ISF

115

The following steps are the first part in setting up the corticomedullary solute concentration gradient via the triple co-transporter, put them in order:
- ISF can't enter DL of Loop of Henle
- Fluid in DL is concentraed
- Tubular fluid diluted and ISF osmolarity rised
- NaCl removed from AL (and water can't follow)
- Water leaves DL by osmosis

1. NaCl removed from AL (and water can't follow)
2. Tubular fluid diluted and ISF osmolarity rised
3. ISF can't enter DL of Loop of Henle
4. Water leaves DL by osmosis
5. Fluid in DL is concentraed

116

After the initial corticomedullary solute concentration gradient via the triple co-transporter is set up, what happens next?

1. Fluid enters descending limb of Loop of Henle
2. Fluid moves into ascending limb
3. Hypotonic fluid enters DCT

117

What is the third step in setting up the corticomedullary solute concentration gradient?

1. Solute pumped out of ascending limb
2. ISF osmolarity rises
3. Passive water efflux from descending limb
4. Flow occurs

118

How does countercurrent multiplication finish the set-up of the corticomedullary solute concentration gradient?

1. Iso-osmotic fluid leaves the PCT and enters the descending limb of the Loop of Henle
2. Hypo-osmotic fluid enters the DCT
3. Horizontal gradient multiplied into a large vertical gradient

119

What are the steps in the urea cycle throughout the nephron?

1. PCT and Loop of Henle relatively impermeable to urea -> Concentration in tubule rises
2. DCT is totally impermeable to urea -> [Urea]t rises
3. ~50% of urea absorbed into ISF at the collecting duct
4. Urea diffuses passively into Loop of Henle

120

Why is a corticomedullary solute concentration gradient set up?

Enables the kidnesy to produce urine of varying volumes and concentrations

121

What is the Vurine on normal fluid intake?

~1ml/min

122

Which nephrons does the vasa recta run alongside?

Juxtamedullary nephrons

123

What happens to the blood in the vasa recta?

Equilibrates with ISF due to the 'leaky' endothelium

124

What happens to the blood osmolarity as the vasa recta enters the medulla?

It increases:
- Water leaves
- Solute enters

125

What happens to the blood osmolarity as the vasa recta rises back into the cortex?

It decreases:
- Water enters
- Solute leaves

126

The vasa recta blood flow tends to wash away the concentration gradient set up in the medulla, how is this reduced?

1. Vasa recta follows hairpin turns
2. It is freely permeable to NaCl, water and urea
3. Vasa recta blood flow is low