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Physiology Flashcards

1
Q

What is osmolarity

A

Concentration of osmotically active particles present in a solution

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2
Q

What 2 factors do you need to calculate osmolarity

A

Molar concentration

Number of osmotically active particles

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3
Q

What is the difference between osmolarity and osmolality

A

The units - osmolality is osmol/kg of water
osmolarity is osmol/l

In weak salt solution the 2 are interchangeable

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4
Q

What is tonicity

A

The effect a solution has on cell volume

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5
Q

What effect will a isotonic solution have on cell volume

A

There will be no change to cell volume

Concentrations equal in and out of cell so no gradient

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6
Q

What effect will a hypotonic solution have on cell volume

A

Will lead to an increase in cell volume
Due to movement of water into the cell - down gradient
Cell may burst

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7
Q

What effect will a hypertonic solution have on cell volume

A

Decrease in cell volume as there is less water outside the cell
Water moves out of cell down the gradient

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8
Q

RBC are permeable to urea - true or false

A

TRUE
They have specific transporters for it
This is why it draws water into the cells

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9
Q

Why do women’s total body water make up less of their body weight compared to men

A

Females have higher % body fat which contain less water

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10
Q

List sources of insensible water loss

A

This is water loss we have no control over
Through skin by diffusion
Lungs - we breathe out small volumes

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11
Q

List sources of sensible water loss

A

Sweat
Faeces
Urine
Determined by a variety of regulatory mechanisms

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12
Q

What are the main ions in the ECF

A

Na+, Cl- and HCO3-

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13
Q

What are the main ions in the ICF

A

K+, Mg2+ and negatively charged proteins

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14
Q

The ECF has a higher osmotic concentration than the ICF - true or false

A

False

They are identical

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15
Q

What factors can alter fluid homeostasis

A

Gain or loss of water
Gain or loss of NaCl
Gain or loss of isotonic fluid

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16
Q

Regulation of ECF volume is important for what

A

Long term regulation of blood pressure

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17
Q

Why is electrolyte balance important

A

Total conc can directly affect water balance

The conc of individual electrolytes can affect cell function

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18
Q

Which electrolytes are the biggest contributors to osmotic concentration of ECF and ICF

A

Na+ for ECF

K+ for ICF

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19
Q

What affect can altered K+ lead to

A

Muscle weakness then paralysis

Cardiac irregularities that can lead to arrest

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20
Q

What are the functions of the kidneys

A

Water and salt balance
Maintaining plasma volume and osmolarity
Acid-base balance
Excretion of metabolic waste products and exogenous foreign compounds
Secretion of renin and erythropoietin
Conversion of Vit D to its active form

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21
Q

Describe the lining of the ureter

A

Lined by smooth muscle – peristaltic movement helps propel urine towards the bladder

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22
Q

At what point is there no more modification of urine

A

Once it enters the ureter

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23
Q

Describe the progression of blood vessels through the kidneys

A

Artery > afferent arteriole > glomerular capillary > efferent arteriole > peritubular capillary > venule > vein

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24
Q

What are the peritubular capillaries

A

They form a network that is closely related to the nephron

They collect anything that is reabsorbed from the nephron tubules

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25
Q

What is the substance found in the nephron called

A

Tubular fluid

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26
Q

At what point does tubular fluid become urine

A

As it leaves the collecting duct to the renal pelvis

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27
Q

What are the differences between the cortical and juxtamedullary nephrons

A

Juxtamedullary has a much longer loop of henle

Cortical has the peritubular capillary network whilst the juxtamedullary has a single vasa recta

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28
Q

What is the juxtaglomerular apparatus

A

Area of nephron where arterioles form a fork around part of the distal tubule

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29
Q

Afferent arteriole is narrower than the efferent one - true or false

A

False

It is greater in diameter

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30
Q

What makes up the glomerular membrane

A

Endothelial cells, basement membrane + podocytes

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31
Q

Where are the macula densa found

A

In the distal tubule

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32
Q

What is the function of the macula densa

A

Salt sensitive cells that monitor salt content of tubular fluid
If too salty it releases vasoactive chemicals that cause constriction of the afferent arteriole

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33
Q

What are the 3 processes that contribute to urine production

A

Glomerular filtration
Tubular reabsorption
Tubular secretion

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34
Q

GFR in a healthy adult is usually kept constant - true or false

A

True

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35
Q

How do you calculate rate of filtration of substance X

A

Xplasma x GFR

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36
Q

How do you calculate rate of excretion of substance X

A

Xurine x urine production rate

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37
Q

How do you calculate rate of reabsorption of substance X

A

Rate of filtration - rate of excretion

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38
Q

How do you calculate rate of secretion of substance X

A

rate of excretion of X – rate of filtration of X

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39
Q

Describe the charge of the basement membrane

A

Basement membrane is negatively charged

Plasma proteins are also negatively charged so should be repelled and remain in the plasma

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40
Q

RBC can normally enter the nephrons and then the urine

A

RBC are too big to filter through so if blood is present in the urine it means there is damage to the system

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41
Q

Which forces make up net filtration pressure

A

Glomerular capillary blood pressure - for filtration
Bowman’s capsule hydrostatic pressure - opposes filtration
Capillary oncotic pressure - opposes filtration
Bowman’s oncotic pressure - for filtration

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42
Q

Oncotic pressure refers to what

A

Gradients created by plasma proteins

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43
Q

Which of the 4 net filtration forces should be 0

A

Bowman’s capsule oncotic pressure

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44
Q

Glomerular filtration is a passive process - true or false

A

True

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45
Q

What is GFR

A

rate at which protein-free plasma is filtered from the glomeruli into the Bowman’s capsule per unit time.

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46
Q

What is the normal GFR in a healthy adult

A

125ml/min

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47
Q

What extrinsic mechanism regulates GFR

A

Sympathetic control via baroreceptor reflex

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48
Q

What intrinsic mechanisms regulate GFR

A

Myogenic - affects vascular smooth muscle

Tubuloglomerular feedback

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49
Q

GFR is relatively unaffected by MAP - true or false

A

True
This avoids unintentional fluid shifts
If BP drops you still produce enough urine to get rid of waste

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50
Q

What can increase pressure in Bowman’s capsule

A

Kidney stone causing a blockage that leads to increase in hydrostatic pressure
Will lead to decreased GFR

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51
Q

What increases capillary oncotic pressure

A

Dehydration (e.g. diarrhoea) means there is higher conc of plasma proteins so increases oncotic pressure
There will be more opposition to filtration

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52
Q

What is plasma clearance

A

A measure of how effectively the kidneys can ‘clean’ the blood of a substance
Equal to the volume cleared per minute

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53
Q

Clearance of what exogenous substance is equal to GFR

A

Inulin

Has to be infused so not very practical

54
Q

Which body substance is used to estimate GFR

A

Creatinine

55
Q

Name a substance that is completely reabsorbed by the kidney

A

Glucose

Should be none in the urine

56
Q

If clearance of a substance is less than GFR what does it tell us

A

At least some of it is being reabsorbed

e.g. urea

57
Q

If clearance of a substance is more than GFR what does it tell us

A

More of the substance is being secreted into the nephrons and not reabsorbed
e.g. H+

58
Q

How do you measure renal plasma flow

A

PAH clearance test

All of it will be excreted

59
Q

What properties should a clearance marker have

A

non-toxic
inert
easy to measure

60
Q

Where in the nephron does the majority of reabsorption occur

A

Proximal tubule

61
Q

Which substances are 100% reabsorbed in the kidney

A

Glucose - exception is poorly controlled diabetes

Amino acids

62
Q

Is reabsorption specific or non-specific

A

Specific - relies on specific transport proteins or channels for each substance

63
Q

Kidneys reabsorbed the majority of salt and fluid that is filtered - true or false

A

True

99% is reabsorbed

64
Q

How does the glomerular filtrate differ from blood

A

It contains the same concentration of ions and solutes but lacks RBC and large proteins

65
Q

Which substances are reabsorbed in the proximal tubule

A 
Sugars
Amino acids
Phosphate
Sulphate
Lactate
66
Q

which substances are secreted in the proximal tubule

A

H+
Uric acid
Bile pigments
Drugs and toxins

67
Q

Describe the steps in transcellular tubular reabsorption

A

Must cross the apical/luminal membrane of the epithelial cell, cross the cytoplasm, leave via the basal membrane, cross the interstitial membrane and then into the capillary

68
Q

Describe the process of paracellular reabsorption

A

Substances pass between the cells - across junctions

Varies depending on how tight the junction is

69
Q

What is primary active transport

A

When energy is required to move the substance against its concentration gradient
e.g. Na/K pump

70
Q

What is secondary active transport

A

A substance is transported alongside an ion that is moving down its gradient - coupled

71
Q

What is facilitated diffusion

A

Passive carrier-mediated transport of a substance down its concentration gradient

72
Q

Where is the Na/K pump found

A

Basolateral membrane of tubular cells

Drives reabsorption of salt

73
Q

Describe how salt is absorbed in the proximal tubule

A

Sodium enters the epithelial cells down its concentration gradient and then leave the cells via the Na+/K+ pump
This sets up an electrical gradient that causes Cl- to follow
Also creates a osmotic gradient so water follows

74
Q

How is glucose reabsorbed in the proximal tubule

A

By secondary active transport

Coupled to the movement of Na+ - co-transport

75
Q

Why do you get glucosuria in diabetes

A

Glucose transporters become saturated at a certain level - cannot reabsorb any more
High blood sugar seen in diabetes exceeds the limit and so some is excreted

76
Q

What is meant by counter current flow in the loop of Henle

A

There is opposing flow in the two limbs (ascending and descending)
Generates a concentration gradient between the cortex and medulla

77
Q

What is reabsorbed in the ascending loop of Henle

A

Na+ and Cl-

Impermeable to water

78
Q

What is reabsorbed in the descending loop of Henle

A

Water

Impermeable to salt

79
Q

Describe the osmolarity of the tubular fluid, and interstitial fluid as they leave the loop of Henle

A

Tubular fluid has low osmolarity - lower than plasma

Interstitial fluid in the cortex is 300

80
Q

Describe the changes in interstitial fluid osmolarity as the collecting duct passes down through the medulla

A

Progressively increases

81
Q

Hormones affect which parts of the nephron

A

Hormones only affect the distal tubule and collecting duct – only have influence in the later parts

82
Q

List the hormones that affect ion and water balance in the kidneys

A

ADH - water reabsorption
Aldosterone - increases Na reabsorption and H/K secretion
Atrial natriuretic hormone - decreases Na+ reabsorption
parathyroid hormone - increased Ca reabsorption and decreased phosphate

83
Q

Describe water reabsorption in the distal tubule

A

It isn’t permeable to water

However, ADH release can change this by recruiting water channels

84
Q

Where is ADH released from

A

It is synthesised by nerve cells in the hypothalamus

Stored as granules in the posterior pituitary

85
Q

How does ADH work

A

Hormone binds to receptor that triggers an intracellular increase in cAMP (secondary messenger)
This stimulates insertion of aquaporin channels into the tubular cells – allows more water to move

86
Q

ADH has a long half life - true or false

A

False

Very short = 10/15 mins

87
Q

What stimulates ADH release

A

Dehydration
By releasing ADH you reabsorb more water

Also stimulated by nicotine

88
Q

What happens in the distal tubule when there is little or no ADH

A

Low ADH = fewer aquaporin channels so little or no water reabsorption

89
Q

Does ADH have any influence on salt reabsorption

A

NO

solute conc remains constant regardless of ADH level

90
Q

What are the 2 types of diabetes insipidus

A

Central – unable to produce or secrete ADH

Nephrogenic – ADH is secreted but it cannot act on the target cells (e.g. defective receptor)

91
Q

What are the symptoms of diabetes insipidus

A

Constant thirst

Producing large volumes of dilute urine

92
Q

What inhibits ADH release

A

Alcohol

93
Q

Where is aldosterone secreted from

A

Adrenal cortex

94
Q

When is aldosterone secreted

A

In response to rising [K+] or falling [Na+] in the blood

Or activation of the renin-angiotensin system

95
Q

What does aldosterone do

A

Stimulates Na+ reabsorption and K+ secretion

96
Q

What triggers renin release form the juxtaglomerular apparatus

A

Reduced pressure in afferent arterioles
Reduced NaCl - detected by the macula densa cells
Increased sympathetic activity

97
Q

Defects in the RAAS can lead to what

A

|Hypertension

Fluid retention - congestive heart failure

98
Q

When is ANP released

A

Released from the walls of the atria when they are mechanically stretched
- e.g. when blood volume is higher

99
Q

What is the function of ANP

A

Promotes excretion of Na+ and diuresis so will decrease plasma volume

100
Q

What controls emptying of the bladder

A

Micturition reflex - stretch receptor

Voluntary control of the external sphincter

101
Q

Venous blood is more alkaline than arterial - true or false

A

False

More acidic due to higher CO2 content

102
Q

What is defined as acidosis

A

pH below 7.35

103
Q

What is defined as alkalosis

A

pH above 7.45

104
Q

What can acidosis lead to

A

Depression of the CNS

This can lead on to coma and death in severe cases

105
Q

What can alkalosis cause

A

Over-excitability of the nervous system and later the CNS
Get pins and needles and muscle spasms
Severe cases include spasms of the respiratory muscles

106
Q

How is H+ added to the blood

A

Continually due to metabolic reactions such as:
Carbonic acid formation
Inorganic acids from breakdown of nutrients
Organic acids from metabolism

107
Q

Which type of acids dissociate completely in solution

A

Strong acids

Weak acids only dissociate partly

108
Q

What happens if acid is added to the acid dissociation equation

A

The free A- mops up the excess protons to form more HA

This stops the pH falling

109
Q

What happens if base is added to the acid dissociation equation

A

The excess base is taken up with combining with H+ so more HA dissociates
Prevents rise in pH

110
Q

Which organ controls HCO3 levels

A

Kidney

111
Q

Which organ controls CO2 levels

A

Lungs

112
Q

How does the kidney affect HCO3 levels

A

They regulate reabsorption by varying how much is reabsorbed
They can add new HCO3 to the blood

All dependent on H+ secretion

113
Q

Describe how HCO3 is reabsorbed in the proximal tubule

A

Carbonic anhydrase forms carbonic acid in the epithelial cell
H+ is released from this and enters the tubular fluid in exchange for Na
Filtered bicarbonate combines with the secreted H+ to form carbonic acid again
This is broken down into CO2 and water by carbonic anhydrase
The products can enter the epithelial cell where it is reabsorbed as bicarb by sodium co-transport

114
Q

How does the kidney form new HCO3

A

When HCO3 is low, the secreted H+ combines with phosphate instead
As the H+ leaves the epithelial cell, it allows Na to move in
This Na is used to pump HCO3 created in the cell back into the blood

115
Q

What is the titratable acid

A

The measure of the amount of H+ excreted as H2PO4

Max is 40mmol/day

116
Q

How do you measure titratable acid

A

Record the amount of NaOH needed to get urine pH back to 7.4

Doesn’t determine amount of ammonium

117
Q

High ammonium in the urine is caused by what

A

Acidosis
If the maximum amount of titratable acid has been produced but you are still acidotic, the excess H+ combined with ammonia from broken down glutamine to form ammonium which is then excreted

118
Q

What range of HCO3 and PCO2 is considered normal

A

HCO3 - 23-27 mmol/l

Arterial PCO2 - 35-45mmHG

119
Q

What is the difference between compensation and correction

A

Compenstaion comes first and is the restoration of pH, regardless of levels of CO2 or HCO3

Correction occurs after and is when pH is restored and HCO3 and CO2 return to normal

120
Q

What buffers exist in the blood

A

Hb
HCO3
First line of defence in acid-base balance

121
Q

What causes of respiratory acidosis

A

Retention of CO2

E.g. chronic bronchitis or emphysema, airway restriction, chest injury

122
Q

How do we compensate for respiratory acidosis

A

H+ secretion in the urine via the renal system
It increases excretion of titratable acid and ammonium (gets rid of H+)
Generates more HCO3 to balance pH

123
Q

How do we correct respiratory acidosis

A

After renal system compensates you need to correct by lowering CO2 by restoring normal ventilation

124
Q

What causes respiratory alkalosis

A

Excessive CO2 removal
Low inspired PO2 - altitude
Hyperventilation

125
Q

How do you compensate for respiratory alkalosis

A

Renal system
The H+ secretion isn’t enough to reabsorb all the HCO3 (even though bicarb is normal)
So some HCO3 is excreted in the urine
Also no TA or ammonium is formed so no new HCO3 is made

126
Q

How do we correct respiratory alkalosis

A

Need to restore normal ventilation

127
Q

What causes metabolic acidosis

A

Excess H+ from any source other than CO2
Excessive metabolic production - exercise or DKA
Excessive loss of base - diarrhoea

128
Q

How do we compensate for metabolic acidosis

A

Respiratory system compensates by increasing ventilation and more CO2 is blown off

129
Q

How do we correct after metabolic acidosis

A

Renal system kicks in later to increase H+ secretion and generate more HCO3
Ventilation can then return to normal

130
Q

What causes metabolic alkalosis

A

Excessive loss of H+

Vomiting, alkali ingestion, aldosterone hypersecretion

131
Q

How do we compensate for metabolic alkalosis

A

respiratory system compensates - slows ventilation

CO2 is retained so pH lowers

132
Q

How is metabolic alkalosis corrected

A

H+ cannot drive the reabsorption as HCO3 conc is too high so HCO3 is excreted in the urine

No new HCO3 is generated either

Renal (18 decks)

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