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Flashcards in Physiology Deck (154):
1

What is osmolarity?

Concentration of osmotically active particles in a solution

2

What are the units of osmolarity?

mosmol/L

3

How is osmolarity calculated?

Molar concentration of a solution (e.g. 150mM)
and
number of osmotically active particles present (Na+, Cl- = 2 particles)
150 *2= 300

4

What is the osmolarity of plasma?

300mosmol/L

5

What is tonicity?

The effect on the cell that a solution has on it

6

What is an isotonic solution?

Causes no change to cell volume. Water balance is the same

7

What is a hypotonic solution?

Water moves from solution to cell since less water in cell.
Causes lysis.

8

What is a hypertonic solution?

Water concentration is higher inside cell than outside so cell loses water.

9

What makes up Total Body Water?

Intracellular fluid (66%)
Extracellular fluid

10

What separates ICF and ECF?

Plasma membrane

11

What is included in ECF?

Lymph
Plasma
Interstitial fluid (80%)

12

What tracer is used to measure total body water?

3H20

13

What tracer is used to measure ECF ?

Inulin

14

What tracer is used to measure plasma?

Labelled albumin

15

What is included in insensible losses?

Loss of water from skin by passive diffusion and lungs by expiration

16

In relation to Na+ and Cl- where is most of it found?

Extracellular fluid, bathing the cells

17

Where is most K+ found?

Intracellular fluid

18

What is fluid shift?

The movement of water between ICF and ECF in response to an osmotic gradient

19

What three factors affect fluid homeostasis?

Change in [water]
Change in [NaCl]
Gain or loss of isotonic fluid

20

Why can small K+ changes cause such big differences?

It is ICF so has bigger impact

21

What is glomerular filtration?

Bloods enters in afferent arteriole and is filtered through the glomerulus to the Bowman's capsule

22

What is tubular reabsorption?

While filtrate is in proximal convoluted tubule it has the opportunity to be reabsorbed back into the efferent arteriole

23

What is tubular secretion?

While in the efferent arteriole, material may be transferred to PCT

24

What is rate of filtration?

Mass of a substance filtered into the Bowman's capsule per unit time

25

What is the equation for rate of filtration?

Concentration of substance in plasma X GFR

26

What is GFR?

Glomerular filtration rate

27

What is the equation of rate of excretion?

Concentration of X in urine X urine flow rate

28

If the total amount filtered is significantly more than the amount excreted what has happened?

Significant reabsorption has occurred.

29

What are the 3 barriers to filtration in the glomerulus?

Glomerular capillary endothelium
Basement membrane
Podocytes

30

What is the basement membrane made of?

Glycoproteins and collagen

31

How does the basement membrane act as a barrier to filtration?

Has a net negative charge so repels negatively charged plasma proteins

32

What are the forces called that balance hydrostatic and oncotic pressures?

Starling Forces

33

In the kidney, what are the 4 forces which contribute to the net filtration pressure?

Glomerular BP
Bowman's capsule hydrostatic pressure
Capillary oncotic pressure
Bowman's capsule oncotic pressure

34

What is oncotic pressure?

Pressure exerted by plasma proteins

35

Which forces favour filtration?

Glomerular BP
Bowman's capsule oncotic pressure

36

Which forces disfavour filtration?

Bowman's capsule hydrostatic pressure
Capillary oncotic pressure

37

What is the equation for net filtration?

Forces favouring - forces against

38

Why is the glomerular capillary blood pressure constant throughout the glomerulus?

Efferent is smaller than afferent so creates pressure in itself

39

What is the normal GFR?

125

40

What is the major determinant for GFR?

Glomerular BP

41

How is GFR regulated? (2)

Extrinsically by sympathetic control by baroreceptors
Intrinsic autoregulation

42

What effect does vasoconstriction of the afferent arteriole have on the GFR?

Decreased GFR

43

What is the consequence of a decreased GFR?

Lower urine volume

44

What is the equation for MAP?

1/3 (systolic-diastolic) +diastolic

45

What are the two mechanisms of autoregulation of glomerular BP?

Myogenic
Tubuloglomerular feedback - more NaCl leads to constriction

46

Which cells in the juxtaglomerular apparatus sense NaCl?

Macula densa

47

What is plasma clearance?

Measures how effectively the kidneys can clean the blood of a particular substance per minute

48

What is the equation for plasma clearance?

Clearance = rate of excretion / plasma concentration

49

How does inulin excretion give an exact measurement of GFR?

It is freely filtered at the glomerulus and is neither reabsorbed nor secreted at PCT

50

Give an example of a substance which is completely reabsorbed

Glucose
Its clearance is 0.

51

When would clearance be 0?

If a substance is not filtered and not secreted e.g. RBC

52

Give an example of a substance which is partly reabsorbed and not secreted

Urea

53

Give an example of a substance which is filtered, secreted and not re-absorbed

H+ ions

54

What is renal plasma flow?

The amount of plasma that runs through the glomerulus in 1 minute

55

What is the value for RPF?

650

56

Which substance is used to measure RPF?

Para-amino hippuric acid (PAH)

57

Why is PAH used to measure RPF?

Freely filtered at the glomerulus, secreted into tubule and not reabsorbed. It is completely cleared.

58

Why is inulin not commonly used to measure GFR?

Exogenous so needs to be measured.
Creatinine is used instead

59

What is the filtration fraction?

Fraction of plasma in glomeruli which is filtered into the tubules

60

How is filtration fraction worked out?

GFR / renal plasma flow

61

What is glomerular filtrate?

Blood without RBC and plasma proteins
It is therefore iso-osmotic with plasma

62

What is reabsorbed in the PT to the capillaries?

Sugars
Amino acids
Phosphate
Lactate

63

What is secreted to the PT from the capillaries?

H+
PAH
Uric acid
Drugs
Toxins

64

Name the 5 layers the filtrate must pass through from the PT to the capillaries

Apical membrane
Cytoplasm
Basolateral membrane
Interstital fluid
Endothelium of capillary

65

What two ways can the filtrate leave the PT?

Transcellularly
Paracellularly

66

Name 3 types of carrier-mediated membrane transport than occurs in the PT

Primary active transport
Secondary active transport
Facilitated diffusion

67

How does primary active transport work?

Energy required to move substrate against concentration gradient

68

How does secondary active transport work?

Carrier molecule is coupled with another ion movement

69

What is facilitated diffusion?

Passive carrier-mediated transport down the concentration gradient

70

Where is a secondary active transporter used at the PCT?

To transport Na out of the tubular cell and into the interstitium. Uses K. Uses ATP

71

At a Na/K pump, what is the ratio used?

3 Na in
2 K out

72

Describe Na reabsorption at the PCT

Uses Co-transporters
Uses anteporters

73

When Na leaves the tubular cells, what is the consequence?

Water follows into the interstitium

74

How much glucose is reabsorbed into the capillary?

Almost all

75

How is glucose reabsorption faciltated?

Co-transporters
Facilitated diffusion

76

At what point will glucose no longer be fully excreted?

10-12 mmol/L

77

What is glucose in urine called?

Glucosuria

78

What does the loop of Henle do?

Creates a solute concentration gradient and forms hypertonic urine
Countercurrent multiplier

79

What does the descending limb of the loop of Henle do?

Absorbs water but no effect on salts

80

What does the ascending limb do?

Reabsorption of Na and Cl
No water absorption

81

What is the difference in the thick upper part of the ascending limb and the thinner lower part?

Thick upper part reabsorbs by active transport
Thin lower part is passive reabsorption

82

Where is the loop of Henle?

In the medulla

83

Why is there no water absorption in the upper limb?

Tight junctions so no water can be reabsorbed

84

What transport system for sodium is facilitated in the upper part of the ascending limb?

Triple co-transporter

85

What happens to the K+ in the co-transporter?

K is recycled and put back to the ascending limb

86

How does the fluid leaving the ascending limb become concentrated?

Solute is removed from ascending limb and water cannot follow.
Water leaves in the descending limb though so the fluid is concentrated

87

What happens to the osmolarity as the fluid leaves the DL?

Osmolarity increases

88

Why does water move passively from the DL?

Because solute is pumped into the interstitial fluid, which increases the osmolality of the interstitial fluid

89

What is the purpose of countercurrent multiplication?

To concentrate the medullary interstitial fluid

90

Which hormone is responsible for producing urine of various concentrations and volumes?

Anti-diuretic hormone (ADH)

91

What role does the vasa recta play?

Equilibrates with the interstitial fluid alongside the loop of Henle

92

What are the vasa recta permeable to?

NaCl and water

93

On leaving the loop of Henle and entering the distal tubule, how is the fluid described?

Hypo-osmotic at 100mosmol/L

94

What does an increased amount of ADH cause?

Increased water reabsorption to blood

95

If there is more water reabsorption to the blood by ADH what is then urine like?

Small amounts of concentrated urine.
ANTI- diuretic.

96

What is the distal convoluted tubule divided into?

Early and late

97

What does the early part of the distal convoluted tubule do?

Reabsorbs NaCl

98

What does the late part of the distal convoluted tubule do?

Reabsorbs Ca++, Na+ and K+

99

How is the collecting duct divided?

Early
Late

100

What part of the collecting duct is particularly influenced by ADH?

Late

101

Where does ADH come from?

Neurohormone produced by supraoptic and paraventricular nuclei in hypothalamus

102

Where is ADH stored?

Posterior pituitary

103

What receptor on the basolateral membrane of the collecting tube is sensitive to ADH?

Type 2 vasopressin receptor

104

What kind of receptor is the type 2 vasopressin receptor?

G protein coupled

105

What does the activation of the type 2 vasopressin receptor do?

Causes ATP to release cAMP which causes increased expression of aquaporins at the apical membrane

106

What is the result of more aquaporins at the apical membrane?

Increased permeability for water to move from the collecting tube to the interstitial fluid and then to the capillary.

107

If ADH is low then what is the urine like?

High volume of dilute urine

108

True or False
More ADH causes more salt to be excreted

False.
Salt excretion is constant, regardless of ADH

109

What hormone causes arterial vasoconstriction?

ADH

110

If blood pressure is low, what happens to ADH secretion?

Increases to reduce water lost in urine to maintain blood volume

111

Which substance inhibits ADH release?

Alcohol.
Low ADH --> more urine

112

If ADH is low, how does this affect glomerular flow?

Increases flow to 20ml/min

113

If ADH secretion is maximal, how does this affect glomerular flow rate?

Reduces flow to 0.2ml/min

114

Why does osmolarity increase in the collecting duct if ADH secretion is high?

High ADH means less water in tubule so a higher proportion of salt, raising the osmolarity

115

Where is aldosterone secreted from?

Adrenal cortex

116

What does aldosterone do?

Activates RAAS to stimulate Na+ reabsorption and secrete K+

117

If there was no aldosterone what effect would this have on sodium?

Sodium would be excreted

118

What does an increase in plasma potassium cause?

Stimulation of adrenal cortex to make aldosterone

119

Which organs makes angiotensinogen?

Liver

120

Which organ makes renin?

Kidney

121

Which organ makes angiotensin converting enzyme?

Lungs

122

What does ACE do?

Converts angiotensin 1 to angiotensin 2

123

What does angiotensin 2 do?

Stimulates adrenal gland to make more aldosterone
Increases thirst
Increase ADH

124

Which cells in the juxtaglomerular apparatus sense a difference in Na?

Macula densa

125

What is the relationship between renin and Na?

More renin means more sodium will be reabsorbed

126

How does aldosterone cause Na reabsorption?

Acts on sodium channels to open them

127

What is ANP?

Atrial natiuretic peptide

128

What does ANP do?

Released from atrial muscle cells when they are stretched due to increased plasma volume.
Promotes Na excretion to reduce BP

129

What is the micturition reflex?

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

130

What is the equation for pH?

pH = log 1/ H+

131

What is the pH of arterial blood?

7.45

132

What is the pH of venous blood?

7.35

133

What effect does an increase in H+ ions have on pH?

Reduces pH

134

What effect does an acidic environment have on the body?

Denatures enzymes
Depresses CNS
Changes K+ levels

135

What is the dissociation constant?

K = [H+] [A-} / [HA]

136

What is the Henderson Hasselbach equation?

pH = pK + log [A-] / [HA]

137

What systems controls bicarbonate levels?

Kidneys
Lungs

138

What enzyme is needed to balance carbon dioxide and water?

Carbonic anhydrase

139

Where is HCO3- reabsorbed?

Proximal tubule

140

How does kidney make new HCO3-?

CO2 in interstitial fluid forms with water.

141

What substance produced in the liver forms ammonia?

Glutamine

142

What should HCO3 in plasma be?

25

143

What is respiratory acidosis?

Retention of CO2, reduces pH

144

How does kidney compensate for respiratory acidosis?

H+ secretion is stimulated, raising pH

145

What is respiratory alkalosis?

Removal of CO2 from body
High pH

146

What causes respiratory alkalosis?

Hyperventilation
Low pO2

147

How does kidney compensate for respiratory alkalosis?

No new HCO3 is produced.
Maintains/lowers pH

148

What is metabolic acidosis?

Excess H+ not from CO2
pH low

149

What causes metabolic acidosis?

Loss of base e.g. diarrhoea
Ingestion of acids
Lactic acid production

150

How is metabolic acidosis compensated?

Ventilation increased to blow off CO2 to reduce acid

151

Why does metabolic acidosis compensated by kidney?

Acid load is excreted.
Takes a long time

152

What is metabolic alkalosis?

Excessive loss of H+ from body
pH high

153

What causes metabolic alkalosis?

Loss of HCl from vomiting
Ingestion of alkali
Aldosterone hypersecretion

154

How does the respiratory system compensate for metabolic alkalosis?

CO2 retention