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Y2 Renal > Physiology > Flashcards

Physiology Flashcards

1
Q

What is osmolarity

A

Concentration of osmotically active particles present in a solution

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2
Q

How do you calculate osmolarity

A

Molar concentration of the solution x number of osmotically active particles

E.g. 150mM NaCl
150 x 2 = 300 mosmol/l

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3
Q

What is tonicity

A

Effect a solution has on cell volume

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4
Q

3 types of tonicity

A

Isotonic
Hypotonic
Hypertonic

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5
Q

Hypotonic solution effect on cell

A

Water moves into cell

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6
Q

Hypertonic solution effect on cell

A

Water moves out of cell

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7
Q

Isotonic solution effect on cell

A

No change in cell volume

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8
Q

Tonicity is dependent on

A

Osmolarity
Ability of solutions to cross the cell membrane

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9
Q

Total body water is made of what compartments

A

Intracellular fluid + Extracellular fluid

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10
Q

Extracellular fluid includes

A

Mostly interstitial fluid
plasma
Lymph
Transcellular fluid

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11
Q

How do you measure the body fluid compartments

A

Use tracers

For TBW = 3H20
For ECF = Inulin
For plasma = labelled albumin

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12
Q

Water loss occurs at

A

Skin
Lungs
Sweat
Faeces
Urine

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13
Q

Hot weather causes increase / decrease in water loss from lungs

A

Decrease

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14
Q

Hot weather causes increase / decrease in water loss from urine

A

Decrease (since more is lost in sweat; decreased excretion of urine is a compensatory mechanism)

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15
Q

How is water balance achieved when there is extra water loss due to exercise / hot weather / cold weather

A

Increased water ingestion
Decreased excretion of water by kidneys to a certain extent, not sufficient alone

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16
Q

Describe the characteristics of ionic composition of ICF and ECF

A

There is always more Na+, Cl-, HCO3- in ECF than ICF
There is always more K+ in ICF than ECF

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17
Q

Why is regulation of ECF volume essential

A

Because it contain plasma so regulation of ECF is required for regulation of blood pressure

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18
Q

Gain in NaCl in ECF causes

A

Osmolarity of ECF to increase
Causes fluid to move from ICF into ECF
ICF decreases
= fluid homeostasis

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19
Q

Na+ is mainly present in which body fluid compartment
What does this imply for the compartment

A

ECF
So it is a major determinant of ECF volume

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20
Q

K+ plays a key role in

A

Establishing membrane potential

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21
Q

K+ is mainly in which body fluid compartment

A

ICF

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22
Q

Functions of the kidney

A

Regulate volume, osmolarity, composition of body fluids
Excretion of waste produces and exogenous foreign compounds (drugs / additives)
Secretion of renin
Secretion of erythropoietin
Conversion of vitamin D into active form

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23
Q

Functional unit of kidneys

A

Nephron

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24
Q

General function of nephron

A

Filter out tubular fluid
Reabsorb substances from the fluid or secrete substances into the tubular fluid

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25
Q

Vessels in nephron

A

Afferent arteriole -> Glomerulus -> efferent arteriole -> peritubular capillaries -> venule -> vein

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26
Q

What is Glomerulus

A

Cluster of blood vessels located in bowman’s capsule where filtering of the blood occurs

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27
Q

What is the bowman’s capsule

A

where waste in blood is filtered out of glomerular capillaries and enters the lumen of bowman’s capsule which then enter the Proximal tubule

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28
Q

Bowman’s capsule is made of what cells

A

Podocytes

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29
Q

Which are the 3 filtration barriers

A

Capillary endothelium
Basal lamina
Podocytes

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30
Q

Why can’t proteins enter the glomerular filtrate

A

Net negative charge of basal lamina repel the proteins
Too big to go through the pores of endothelium

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31
Q

Except from capillary endothelial cells, the glomerulus also contains

A

Mesangial cells

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32
Q

Function of mesangial cells

A

control glomerular filtration
provide structural support

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33
Q

How do mesangial cells control glomerular filtration

A

Mesangial cells can contract which narrows the capillary lumen hence less flow of blood = less filtration

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34
Q

Location of mesangial cells

A

intercapillary space
Between the afferent and efferent arterioles

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35
Q

2 types of nephron

A

Juxtamedullary
Cortical

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36
Q

Which type of nephron is predominant in humans

A

Cortical nephron (80%)

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37
Q

Differences between juxtamedullary and cortical nephron

A

Juxtamedullary nephron has longer loop of Henle
Juxtamedullary nephron does not have peritubular capillaries, it has 1 capillary called vasa recta

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38
Q

Route of vasa recta

A

Follows the loop of Henle

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39
Q

The diameter of afferent arteriole is larger / smaller than efferent arteriole

A

Larger

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40
Q

Renin is secreted by

A

Granular cells

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41
Q

4 parts of the nephron

A

Renal corpuscle
Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule

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42
Q

Renal corpuscle consists of

A

Glomerulus and Bowman’s capsule

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43
Q

Function of Renal corpuscle

A

Production and collection of glomerular filtrate

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44
Q

Function of proximal convoluted tubule

A

Reabsorption of water, amino acids, glucose

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45
Q

Function of loop of Henle

A

Creation of hyper osmotic environment in medulla

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46
Q

Function of distal convoluted tubule

A

Absorption of water, Na+, bicarbonate, K+ and H+
for acid-base and water balance

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47
Q

What proportion of sodium is reabsorbed in proximal tubule and through which mechanism

A

70% by active transport

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48
Q

What proportion of glucose and amino acids is reabsorbed in proximal tubule and through which mechanism

A

All glucose and amino acids; by co-transport

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49
Q

What feature do the lining of proximal convoluted tubule have to increase reabsorption

A

Microvilli

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50
Q

Histological differences between proximal and distal convoluted tubules

A

PCT larger
PCT less well defined lumen margin due to microvilli

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51
Q

How does the thickness of loop of henle vary

A

Descending limb - first thick then thin limbs
Ascending limb - thick limb

52
Q

Type of epithelial cell that lines the loop of Henley

A

thick limbs (ascending and descending limbs) - simple cuboidal
thin limbs (descending limb) - simple squamous

53
Q

Is there microvilli in distal convoluted tubule

A

No, very sparse apical microvilli

54
Q

Reabsorption of Na+ hence water in DCT is controlled by which hormone

A

Aldosterone

55
Q

Reabsorption of water in collecting duct is controlled by which hormone

A

ADH

56
Q

How does ADH increase water reabsorption in collecting duct

A

Increase aquaporin channels

57
Q

The epithelium of minor, major calyxes, ureter, bladder and urethra

A

Urothelium

58
Q

Urothelium type of epithelium

A

transitional epithelium

59
Q

What is transitional epithelium

A

= properties lie between stratified squamous and simple non-stratified

60
Q

What are the cells of urothelium that is facing the lumen called

A

Umbrella cells

61
Q

Special properties of umbrella cells and why

A

thickened and inflexible membrane, to provide a highly impermeable barrier

62
Q

Layers below the urothelium (from inner to outer)

A

Connective tissue
Smooth muscle
Adventitia
Serosa

63
Q

The smooth muscle in urinary bladder is called

A

Detrusor muscle

64
Q

Function of detrusor muscle

A

Contract to
- push urine out of bladder
- prevent back flow of semen during ejaculation
- prevent back flow of urine into ureter

65
Q

Pressures that are included in the net filtration pressure for glomerular filtration

A

Bowman’s capsule fluid pressure
Glomerular capillary blood pressure
Capillary oncotic pressure
Bowman’s capsule oncotic pressure

66
Q

Which pressure is the key driver of glomerular filtration

A

Glomerular capillary blood pressure

67
Q

Pressures that pushes plasma through the filtration barriers

A

Glomerular capillary blood pressure
Bowman’s capsule oncotic pressure ( but 0 mmHg)

68
Q

Pressures that draws fluid away from bowman’s capsule

A

Bowman’s capsule hydrostatic pressure
Capillary oncotic pressure

69
Q

What is capillary oncotic pressure

A

Due to presence of plasma proteins = higher osmolarity than filtration fluid hence wants to draw fluid back into vessel

70
Q

Why is bowman’s capsule oncotic pressure 0 mmHg

A

because there is no plasma proteins in filtration fluid hence no oncotic pressure that will try to draw water in

71
Q

Normal net filtration pressure

A

10 mmHg

72
Q

GFR =

A

filtration coefficient x net filtration pressure

73
Q

Filtration coefficient can change depending on

A

how permeable the glomerular membrane is

74
Q

Why is glomerular capillary blood pressure constant throughout

A

Because the afferent arteriole has a wider diameter than efferent arteriole

75
Q

What happens to GFR when there is an increase in arterial BP

A

Increase in arteriole BP -> increase in BP in afferent arteriole -> increase in Glomerular capillary BP -> increase in net filtration pressure -> increase in GFR

76
Q

What happens to urine volume when there is an increase in GFR

A

Increases

77
Q

Changes in systemic arterial BP does not necessarily result in changes in GFR. Why is that

A

Due to auto regulation, compensatory mechanisms ; but only to a certain extent

78
Q

what are the 2 mechanisms of auto regulation to prevent changes in GFR

A

Myogenic
Tubuloglomerular feedback

79
Q

What is the myogenic auto regulation of GFR

A

Increase in BP causes vascular smooth muscle to stretch -> causes constricting of arteriole -> less blood flowing through to glomerulus

80
Q

What is the tubuloglomerular autoregulation of GFR

A
  1. Rise in GFR
  2. more NaCl flow through the tubule
  3. constriction of afferent arterioles
81
Q

Tubuloglomerular auto regulation involves which type of nephron

A

Juxtaglomerular

82
Q

Effect of kidney stones in GFR

A

Stone blocking fluid causing fluid to accumulate -> Increases bowman’s capsule fluid pressure -> lower net filtration pressure -> GFR decrease

83
Q

Effect of diarrhoea in GFR

A

diarrhoea causes dehydration causing higher osmolarity in blood
so increase in capillary oncotic pressure
hence draws more fluid out
reduces net filtration pressure
= decrease in GFR

84
Q

What is plasma clearance

A

measures how effectively kidneys can clean the blood of a substance
each substance will have their own specific plasma clearance

85
Q

What is plasma clearance

A

measures how effectively kidneys can clean the blood of a substance
each substance will have their own specific plasma clearance

86
Q

Plasma clearance =

A

rate of excretion of X / plasma concentration of X

87
Q

Rate of excretion of X =

A

[X in urine] x Urine production rate

88
Q

What is used to measure the GFR

A

Inulin clearance = GFR

89
Q

Why is inulin used to measure GFR

A

Because it is freely filtered at glomerulus but it is not absorbed / metabolised hence can be measured in urine

90
Q

If clearance < GFR

A

Substance is reabsorbed into the tubule

91
Q

If clearance = GFR

A

Neither reabsorbed nor secreted

92
Q

If clearance > GFR

A

Substance is secreted into tubule

93
Q

If clearance > GFR

A

Substance is secreted into tubule

94
Q

What is reabsorption

A

water and solutes within the tubule are transported into the bloodstream

95
Q

Around how much plasma entering the glomerulus is being filtered

A

20%; 80% of the plasma is not filtered and leaves via efferent arteriole

96
Q

Kidneys reabsorb what % of fluid and salt

A

99%

97
Q

Kidneys reabsorb what % of glucose and amino acids

A

100%

98
Q

Kidneys reabsorb what % of creatinine

A

0%

99
Q

What is reabsorbed in the proximal tubule

A

67% of all salt and water
100% of glucose and amino acids
Phosphate
Sulphate
Lactate

100
Q

What is secreted in the proximal tubule

A

H+
Neurotransmitters
Bile pigements
Uric acid
Drugs
Toxins

101
Q

2 routes reabsorption takes place

A

transcellular ( through cells)
paracellular ( between cells)

102
Q

How does transcellular reabsorption occur

A

Primary active transport
Secondary active transport
Facilitated diffusion

103
Q

How is Na+ reabsorbed back into capillary

A
  1. Basolateral sodium potassium ATPase transports K+ into the tubular cell in exchange for sodium out of the cell = reabsorbed
  2. This creates a concentration gradient for Na+ between the filtrate and tubular cell
  3. So sodium in the filtrate enters the tubular cell via facilitated diffusion (and this sodium will later be transported out via sodium potassium ATPase)
  4. Reabsorption of Na+ sets up an electrochemical gradient that drives the passive movement of Cl- via the paracellular route
104
Q

Describe the paracellular route of Cl-

A
  1. Cl- moves passively into the interstitial fluid (between tubular cell and capillary) via paracellular route due to electrochemical gradient set up by Na+
  2. forms NaCl
  3. NaCl reabsorbed
  4. Sets up a osmotic gradient that drives passive movement of water via the paracellular route
  5. Because the water movement is dependent on NaCl, their reabsorption are equal
  6. so no change in osmolarity in filtrate fluid
105
Q

Why is the filtrate in proximal tubule isosmotic

A

Because the reabsorption of NaCl and water is equal

106
Q

Na+ is reabsorbed everywhere in the nephron except

A

descending limb of loop of henle

107
Q

What is transport maximum

A

maximum rate at which we can reabsorb a particular substance

108
Q

What determines the limit for transport maximum

A

saturation of the specific transport systems of substance = i.e. if more substances come in, they cannot be reabsorbed

109
Q

Why is transport maximum important in relation with glucose

A

Glucose transport maximum is 375mg/min; exceeding this = glucose in urine

110
Q

What is renal threshold

A

the concentration of a substance dissolved in the blood above which the kidneys begin to remove it into the urine. - this can be reabsorbed depending on the transport maximum

111
Q

Renal threshold and transport maximum varies between substances. Why is it beneficial for renal threshold to be lower than transport maximum for certain substances - glucose / amino acids

A

This means that some glucose/ amino acids will be in the urine but because transport maximum is higher, all of those substances can be reabsorbed up to a certain extent

112
Q

Function of loop of Henle

A

Generates a cortico-medullary solute concentration gradient
in order to form hypertonic urine

113
Q

Describe the flow of fluid in loop of Henle

A

Countercurrent flow - the flow of fluid in both limbs are opposing each other

114
Q

Why is there an osmotic gradient in the medulla

A

Due to difference in permeability of water and salt for descending and ascending limbs

115
Q

Describe the permeability to water and NaCl for descending and ascending loops of henle

A

Descending - permeable to water, not to NaCl
Ascending - impermeable to water, NaCl can be reabsorbed

116
Q

Mechanism of sodium reabsorption in ascending loop of Henle

A

via Na K Cl transporter (triple transporter)

117
Q

The reabsorption of water in descending limb of loop of Henle uses

A

Countercurrent flow mechanism

118
Q

Describe the countercurrent flow mechanism

A
  1. Na+ and Cl− are actively pumped out of the filtrate in ascending limb
  2. Water does not follow because it is impermeable to water
  3. This causes the osmolarity of the interstitial fluid to be raised
  4. Water moves out of the descending limb by osmosis
  5. But Solute cannot enter the descending limb
  6. Because water is moving out of DL, osmolarity of fluid in DL is raised while the interstitial fluid is lowered
  7. concentrated fluid in DL then moves into AL, process begins again
119
Q

What drugs blocks the triple transporter in ascending limb and why

A

Loop diuretics
So less Na+ reabsorbed = increased excretion of water (less water reabsorbed from descending loop) = decreased blood pressure

120
Q

Osmolarity of fluid leaving the ascending loop of Henle

A

Hypotonic (low osmolarity)

121
Q

What structure is involved in countercurrent exchange

A

Vasa recta

122
Q

Describe the countercurrent exchange mechanism

A

As the concentrated fluid flows next to the vasa recta, the electrolytes and water that have been reabsorbed from the filtrate diffuse out of the fluid and into the blood vessels

123
Q

What property of vasa recta allows countercurrent exchange mechanism to work

A

It is freely permeable to water and NaCl
Blood flow to vasa recta is slow

124
Q

Describe the change in blood osmolarity in vasa recta

A

Rises as it goes down into the medulla - because solute is reabsorbed from the concentrated interstitial fluid
Decreases as it rises back up into the cortex - because water in interstitial fluid is reabsorbed

125
Q

Slow blood flow in vasa recta allows

A

maintains the solute concentration gradient in the medulla
because solute that is reabsorbed into blood can go back out into the interstitial fluid

126
Q

Effect of low ADH

A
  1. collecting ducts in the kidney remain relatively impermeable to water
  2. This means that water cannot be effectively reabsorbed
  3. Since the urine is not concentrated in the collecting ducts, there is no significant driving force to draw water out of the descending limb
  4. = weak concentration gradient in medulla
  5. = large amount of diluted urine

Y2 Renal (12 decks)

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