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Physiology Flashcards

1
Q

What is the definition of osmolarity?

A

Concentration of osmotically active particles present in a solution

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2
Q

Why is the unit of osmolarity usually mosmol/l for body fluids?

A

They are weak salt solutions

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3
Q

How is osmolarity calcluated?

A

molar concentration of the solution X no. of osmotically active particles present

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4
Q

What is the normal osmolarity of body fluids?

A

300 mosmol/L

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5
Q

What is the difference between osmolarity and osmolality?

A

OsmolaLity has units of osmol/kg water

OsmolaRity has units of osmol/l

virtually they are interchangeable

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6
Q

What is tonicity?

A

the effect a solution has on cell volume

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7
Q

What is meant by an isotonic solution?

A

Has no effect on cell volume

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8
Q

What effect does a hypotonic solution have on cell volume?

A

Increases cell volume

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9
Q

What effect does a hypertonic solution have on cell volume?

A

Decreases cell volume

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10
Q

What can occur in red blood cells if they are placed in a hypotonic solution?

A

Cell lysis

they burst

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11
Q

How do urea and sucrose have the same osmolarity, yet urea is a hypotonic solution?

A

red blood cell membrane is more permeable to urea than sucrose

tonicity takes membrane permeability to substances into account

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12
Q

What is the difference in total body water between males and females?

A

Males ~60% body weight = water

Females ~50% body weight = water (due to increased fat)

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13
Q

More of the total body water is stored in the extracellular fluid compartment. TRUE/FALSE?

A 
FALSE
Intracellular fluid (ICF)	67% of TBW
Extracellular fluid (ECF)	33% of TBW
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14
Q

What are the different types of extracellular fluid (ECF)?

A

Plasma 20%
Interstitial fluid 80%
Lymph
Transcellular fluid (pleural/cerebrospinal)

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15
Q

How do we measure the volume of fluid contained in a body fluid compartment?

A

We use a tracer and measure the distribution volume

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16
Q

What tracers can be used to measure TBW, ECF and Plasma ?

A

TBW: 3H2O
ECF: Inulin
Plasma: labelled albumin

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17
Q

Body fluid osmolarity changes when there is a water imbalance (AKA input =/ output). TRUE/FALSE?

A

TRUE

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18
Q

In what situations would you require extra intake of water due to increased output through sweat and other mechanisms?

A

In hot weather

During exercise

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19
Q

What ions are plentiful in the ECF?

A

Na+

Cl-

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20
Q

What ion is mainly foind in the ICF and plays a role in setting a membrane potential?

A

K+

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21
Q

What is the fluid shift?

A

Movement of water between ICF and ECF in response to an osmotic gradient.

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22
Q

If the fluid osmolarity is changed, both ICF and ECF volumes will change. TRUE/FALSE?

A

TRUE

whereas if an isotonic solution is added (e.g. 0.9% saline), only ECF volume will change

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23
Q

Why is low salt intake important in maintaining a healthy blood pressure?

A

NaCl is isotonic and therefore doesnt change fluid osmolarity
=> only changes the ECF volume (e.g. plasma) => more blood to pump round and heart needs to work harder

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24
Q

Why can minor fluctuations in plasma [K+] have detrimental consequences?

A

If K+ leaks out of cell and changes the membrane potential this can cause issues in excitable cells

=> Muscle weakness/paralysis
=> cardiac irregularities/arrest

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25
Q

How much salt is excreted in the urine per day (on average)?

A

10g

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26
Q

What is meant by a functional unit, and what is the functional unit of the kidney?

A

Smallest structural unit which can perform the function of the organ
=> Nephron

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27
Q

Describe the blood supply to and from the nephron

A

Artery -> afferent arteriole -> glomerular capillary -> efferent arteriole -> peritubular capillaries -> venule -> Renal Vein

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28
Q

What blood vessels surrounding the nephron are responsible for secretion/ reabsoprtion?

A

Peritubular capillaries

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29
Q

What is meant by the juxtaglomerular apparatus?

A

Fork created by the afferent and efferent arteriole

distal convoluted tubule passes through the middle

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30
Q

Tubular fluid changes to what name once it has left collecting duct?

A

Urine

as it undergoes no further change

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31
Q

What are the two main types of nephron in the kidney?

A

Cortical (more common)

Juxtamedullary

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32
Q

What differences do juxtamedullary nephrons have compared to cortical nephrons?

A

Longer loop of henle
NO peritubular capillaries, Instead = vasa rectae
Produce more concentrated urine

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33
Q

Granular cells on the outer membrane of the afferent arteriole produce and secrete what substance?

A

Renin

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34
Q

What cells are salt sensitive and where are they found?

A

Macula densa

found in distal convoluted tubule at the juxtaglomerular apparatus

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35
Q

The diameter of the AFFERENT arteriole is larger than that of the EFFERENT arteriole. TRUE/FALSE?

A

TRUE

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36
Q

Basement membrane is interchangeable with what other term?

A

Basal lamina

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37
Q

A single layer of capillary endothelial cells and podocytes forms what?

A

Glomerular Membrane

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38
Q

How much of the plasms which enters the glomerulus from the afferent arteriole is filtered to become tubular fluid?

A

20%

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39
Q

What are the two calculations which can calculate the rate of excretion?

A

1) concentration of substance in plasma X GFR

2) concentration of substance in urine X urine production rate (Vu)

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40
Q

If rate of filtration > rate of excretion, has net reabsorption occured?

A

Yes

If rate of filtration < rate of excretion, then net secretion has occurred

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41
Q

The basement membrane is acellular. TRUE/FALSE?

A

TRUE

only contains collagen and glycoproteins

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42
Q

A negative basement membrane prevents what?

A

Large plasma proteins moving from capillary to Bowmans capsule

=> no RBCs in tubular fuid as they cant get through basement membrane

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43
Q

What pressures favour net diffusion into the glomerulus?

A

glomerular capillary blood pressure

Bowman’s capsule oncotic pressure

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44
Q

What pressures decrease net diffusion into the glomerulus?

A

Bowman’s capsule hydrostatic pressure

Capillary Oncotic pressure

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45
Q

What is meant by oncotic pressure?

A

Presence of plasma proteins

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46
Q

How does the glomerular capillary blood pressure remain constant throughout?

A

Afferent arteriole diameter is larger than efferent arteriole diameter

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47
Q

How is GFR extrinsically regulated?

A

Sympathetic control via baroreceptor reflex

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48
Q

How is GFR regulated intrinsically?

A

Myogenic

Tubulogomerular feedback

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49
Q

What is a normal GFR?

A

around 125 ml/min

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50
Q

Why is Bowmans oncotic pressure normally 0mmHg?

A

NO plasma proteins can diffuse into the tubular fluid as they are too large

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51
Q

Vasoconstriction decreases GFR. TRUE/FALSE?

A

TRUE

=> Vasodilation increases GFR

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52
Q

Where are the baroreceptors located?

A

Arch of Aorta

Carotid sinus

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53
Q

What does Autoregulation prevent?

A

Small changes in Mean Arterial Blood Pressure changing the GFR

=> helps to maintain unintentional shifts of fluid/salt

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54
Q

Why should the GFR remain constant even at a low BP?

A

To make sure waste products are still being excreted and not remaining in the body

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55
Q

Describe the process of myogenic autoregulation

A

vascular smooth muscle is stretched
=>(i.e. arterial pressure is increased
Myogenic makes it contract thus constricting the arteriole to compensate

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56
Q

Describe the process of tubuloglomerular feedback

A 
GFR rises
more NaCl flows through tubule 
Macula densa releases vasoactive chemicals
Causes smooth muscle to contract
Decreases blood flow to glomerulus
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57
Q

Kidney stones increase what pressure affecting net filtration and GFR?

A

Bowmans capsule hydrostatic pressure

Due to fluid back up

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58
Q

What can increase capillary oncotic pressure and therefore decrease GFR?

A

Diarrhoea due to dehydration (loss of water but no loss of plasma proteins)

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59
Q

How is capillary oncotic pressure reduced in patients with severe burns?

A

The site of the burn loses/leaks plasma proteins
=> decreases Capillary oncotic pressure
=> favours net filtration
=> increases GFR

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60
Q

What is meant by plasma clearance?

A

volume of plasma completely cleared of a particular substance per minute

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61
Q

What is a normal glucose clearance?

A

0
(all glucose that is filtered is reabsorbed in the proximal tubule)
=> glucose in the urine is abnormal

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62
Q

How much of the urea that is filtered at the glomerulus is reabsorbed vs excreted in the urine?

A

50% reabsorbed

50% excreted in the urine

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63
Q

What substance is used to calculate renal plasma flow?

A

para-amino hippuric acid

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64
Q

What is renal plasma flow?

A

how much plasma enters the kidneys per minute

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65
Q

What blood vessels secrete PAH into the tubular fluid if it is not filtered at the glomerulus?

A

secreted from the peritubular capillaries

66
Q

Where does most reabsorption occur in the nephron?

A

The proximal tubule

although all parts can reabsorb

67
Q

What substances are reabsorbed by the kidneys?

A

99% Fluid and Water
100% Glucose and amino acids
50% Urea
0% Creatinine

68
Q

How much fluid is reabsorbed into the proximal tubule per minute?

A

80ml/min

=> if a normal GFR is 125ml/min, then the loop of henle only receives 45ml/min of fluid

69
Q

What substances are secreted into the proximal tubule?

A 
H+ (maintains acid-base balance)
Neurotransmitters (Noradrenaline, Adrenaline, ACh)
Drugs (Atropine/Morphine/Penicillin)
Bile pigments
Uric acid
Toxins
70
Q

What are the 2 ways in which reabsorption can occur?

A

Transcellular

Paracellular

71
Q

What membrane of the tubular epithelial cell faces the lumen and which faces the interstitial fluid?

A
  • Apical/luminal membrane faces the Tubular Lumen

- Basolateral membrane faces interstitial fluid

72
Q

Give an example of Primary active transport and how this works

A

Na/K Pump
Energy required for this (ATP)
For every ATP = 3 Na+ OUT 2 K+ IN

73
Q

Describe Secondary Active Transport

A

The molecule is transported coupled to the concentration gradient of an ion (usually Na+)

Either moves in SAME direction as Na (Symport)
OR in the OPPOSITE direction from Na (Antiport)

74
Q

What is facilitated diffusion?

A

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

75
Q

How are Na and Cl reabsorbed from the proximal tubule?

A 
Na = transcellular
Cl = paracellular
76
Q

How are salt and water reabsorbed in equal proportion?

A

Removing 20% of the plasma fluid in the glomerulus conentrates the plasma proteins in the efferent arteriole/peritubular capillary

This sets up oncotic pressure which drags fluid into the capillary

77
Q

What transport mechanisms does glucose use at each membrane in order to be reabsorbed into the capillary?

A

Secondary Active Symport at APICAL membrane

Facilitated Diffusion at Basolateral Membrane

78
Q

Describe the relationship between plasma glucose level and reabsorption?

A

Plasma glucose levels can rise until they reach the Transport Maximum

At this level, reabsorption occurs at a steady rate, and glucose which cannot be reabsorbed in time is excreted.

79
Q

Secreted substances also have a transport maximum (much like reasorbed substances) TRUE/FALSE?

A

TRUE

e.g. PAH

80
Q

What is the main function of the Loop of Henle?

A

Creates a cortico-medullary solute concentration gradient

=>allows formation of hypertonic urine

81
Q

Describe the difference in water and salt permeability between the descending and ascending limbs of the Loop of Henle?

A

Descending Limb = impermeable to salt but permeable to water

Ascending Limb = Permeable to NaCl at all points but effectively impermeable to water

82
Q

How is NaCl reabsorbed in the thick ascending limb?

A

Into Epithelial cell via triple transporter which also includes K+

Exits epithelial cell via either K/Cl symporter OR Na/K Pump

83
Q

How does the Loop of Henle change the osmolarity in the tubules and the interstitial fluid?

A

Solute OUT of ascending limb
=> Osmolarity DOWN

=> Tubular fluid is diluted and
=> OSMOLARITY of interstitial fluid is RAISED

Water leaves the descending limb by osmosis

=> Fluid in the descending limb is concentrated
=> Osmolarity RAISED

84
Q

What two environments are created when countercurrent multiplication reaches a steady state in the Loop of Henle?

A

Iso-osmotic going IN

Hypo-Osmotic coming out

85
Q

What substance passively diffuses into the loop of henle and contributes to the higher osmolarity in the medulla?

A

Urea

  • diffuses into loop
  • also adds MORE solute to interstitium
86
Q

What is the purpose of countercurrent multiplication?

A

Allows kidney to produce different amounts and concentrations of urine in response to different levels of ADH

87
Q

What is the normal volume of urine produced with a normal fluid intake?

A

~1 ml/min

88
Q

If someone has consumed far more fluid than normal, what can their fluid output rise to?

A

25 ml/min

89
Q

What is the countercurrent exchanger in Juxtamedullary nephrons?

A

Vasa recta

90
Q

Why are the vasa rectae arranged in hairpin loops?

A

To counteract the change in osmolarity as they descend into medulla

=> but coming back up the blood that enters the vein has the same osmolarity as blood at start of hairpin

91
Q

Most filtered ions are reabsorbed before reaching the distal tubule. TRUE/FALSE?

A

TRUE

92
Q

What hormones are important in regulating salt and water?

A 
Antidiuretic hormone (ADH)
Aldosterone
Atrial natriuretic hormone
93
Q

What is the early distal tubule responsible for reabsorbing?

A

NaCl

via triple co-transporter (Na/K/2Cl)

94
Q

What does the late distal tubule reabsorb?

A

Ca2+
Na+
K+

95
Q

What is secreted into the late distal tubule?

A

H+

96
Q

What type of hormone is ADH and how long is its half life?

A

OctaPEPTIDE

peptide hormones have relatively short half lives - e.g. 10-15 mins

97
Q

How is ADH transported from the hypothalamus to the posterior pituitary?

A

passes down nerve axons

98
Q

What is the main function of ADH?

A

Increases permeability of luminal membrane to H2O

by inserting new water channels (aquaporins)

99
Q

How does ADH let more water into the cells surrounding the lumen?

A

ADH binds to receptor
Increases intracellular cAMP
Allows aquaporins to set up in apical membrane
Let H2O flow through from tubule/duct

100
Q

Where are the aquaporins stored when ADH levels are low?

A

In vesicles in the cell cytoplasm

101
Q

Describe how more water is reabsorbed when you are dehydrated.

A

Dehydration = raised plasma osmolarity
Dehydration stimulates MORE ADH
Plasma osmolarity =/ duct osmolarity
=> H2O leaves the duct via aquaporins set up by the ADH

102
Q

Describe the urine produced when you are dehydrated

A

Small volume of concentrated urine

as lots of water is reabsorbed

103
Q

Describe the urine produced when you are over-hydrated and explain why this occurs.

A

Overhydrated = less ADH release
=> No aquaporins are put into apical membrane for water to move out of the duct and into the cell
=> Large volume of unconcentrated urine

104
Q

Solute excretion remains the same regardless of ADH. TRUE/FALSE?

A

TRUE

ADH has no influence over salt excretion

105
Q

What is the difference between central and nephrogenic Diabetes Insipidus?

A

Central = can’t make or secrete ADH

Nephrogenic = Can produce/secrete ADH normally, but ADH is not acting on the target cell receptors

106
Q

What are the main two symptoms of diabetes insipidus?

A
  • Large volumes of dilute urine (up to 20 litres per day)

- Constant thirst

107
Q

When is aldosterone secreted?

A
  • rising [K+] or falling [Na+] in the blood

- activation of the RAAS system

108
Q

What is the main function of aldosterone?

A

Stimulates Na+ reabsorption and K+ secretion

Na+ reabsorption increases BP

109
Q

Where is most K+ reabsorbed in the kidney?

A

Proximal Tubule

110
Q

How are the granular cells stimulated to produce renin?

A

When the afferent arteriole puts less pressure on the granular cells this produces renin and starts the RAAS pathway

111
Q

What senses low plasma NaCl levels and encourages the body to reabsorb Na?

A

Macula densa cells

112
Q

Aldosterone increases the expression of what ion channels?

A

Na channels on APICAL membrane

Na/K pump on basolateral membrane

113
Q

What transporter do loop diuretics inhibit?

A

Triple cotransporter

114
Q

Why are heart failure patients treated with diuretics?

A

Low Cardiac output and BP stimulates fluid retention

BUT this just makes it more difficult for the heart to pump

115
Q

What is the function of Atrial Naturetic Peptide (ANP)?

A

Released when heart muscle cells are stretched
DUE TO: increase in the circulating plasma vol.

Promotes excretion of Na+ and diuresis
=> decreasing plasma volume

116
Q

After what volume has entered the bladder does the micturation reflex occur?

A

250-400 ml

117
Q

What is the difference between Water Diuresis and Osmotic Diuresis?

A

Water diuresis:

  • increased urine flow
  • NO increased solute excretion

Osmotic diuresis:
- the increased urine flow
DUE TO primary increase in salt excretion

118
Q

What is the normal blood pH, and is arterial or venous blood usually more acidic?

A

7.35-7.45

venous blood is usually more acidic due to CO2 forming carbonic acid

119
Q

Describe the effect acidosis and alkalosis have on the CNS?

A 
Acidosis = depression of the CNS.
Alkalosis = overexcitability of the PNS then CNS.
120
Q

What 3 metabolic actions add H+ to the body fluid?

A
  • Carbonic acid formation
  • Inorganic acids produced during breakdown of nutrients
  • Organic acids resulting from metabolism
121
Q

What is the pK of an acid?

A

The pH it is at when the reaction is at equilibrium

122
Q

How do the kidneys control HCO3 concentration?

A

They are able to vary how much is reabsorbed and create more when required

123
Q

The HCO3 found in the tubule is NOT transported directly to the surrounding tubule cell. TRUE/FALSE?

A

TRUE

indirectly transported across the membrane via formation and dissociation of carbonic acid

124
Q

When HCO3 is low in the tubular fluid as it is being reabsorbed, what does the H+ combine with to be buffered?

A

Phosphate PO4

125
Q

What transporter does HCO3 use to get from the tubular epithelial cell to the interstitial fluid?

A

Na/HCO3 co-transporter

126
Q

When H+ and Phosphate combine this is excreted in the urine. TRUE/FALSE?

A

TRUE

127
Q

If all HCO3 and PO4 have been used to buffer H+ yet we are still producing it, what else can be used as the buffer?

A

Glutamine is broken down to ammonia which can pass into the tubular fluid

This then combines with the secreted H+ to form ammonium ion

This is excreted in the urine

128
Q

What 3 factors contribute to a normal acid-base balance

A 
Plasma pH   (7.4)
[HCO3-]p   (25 mmol/l)
Arterial PCO2   (40 mmHg)
129
Q

What is meant by compensation of acid base disturbance?

A

Restore pH to 7.4 as soon as possible

irrespective of what happens to [HCO3-]p and PCO2

130
Q

What is meant by correction of acid base balance?

A

Restoring the pH, HCO3- and PCO2 back to normal

131
Q

What are the 4 main types of acid base disturbance?

A

Respiratory Acidosis
Respiratory Alkalosis
Metabolic Acidosis
Metabolic Alkalosis

132
Q

What is meant by “buffering” of a pH change?

A

Immediate dilution of the acid or base in ECF

133
Q

Give examples of buffers found in the blood?

A

Hb

HCO3

134
Q

What is the disadvantage of buffering?

A

buffer stores are quickly depleted

=> kidney has to rectify stores

135
Q

What biochemical abnormality causes respiratory acidosis?

A

Retention of CO2

136
Q

What specific conditions can cause respiratory acidosis?

A 
chronic bronchitis
chronic emphysema
Airway restriction (e.g. asthma/tumour)
Chest injuries
Respiratory depression (e.g. from morphine)
137
Q

CO2 + H2O => H2CO3 => H+ + HCO3-

What way does the equilibrium of this reaction shift if a patient is in CO2 retention?

A

To the right

=> more H+ and HCO3 is made

138
Q

Describe the appearance of the pH and PCO2 in an uncompensated respiratory acidosis?

A

pH < 7.35

PCO2 > 45 mmHg

139
Q

Describe the shift of respiratory acidosis compared to normal on a Davenport diagram?

A 
pH lowers (shifts left)
HCO3 conc goes up (shifts up)
140
Q

There is virtually NO extracellular buffering in respiratory disorders. TRUE/FALSE?

A

TRUE

141
Q

How does the renal system compensate for a respiratory acidosis?

A

high blood PCO2 makes kidney secrete H+ into filtrate
=> H+ is excreted in the urine

All filtered HCO3- is reabsorbed (i.e. no HCO3- excretion)

142
Q

How is a respiratory acidosis corrected?

A

Correction requires lowering PCO2 by restoring normal ventilation

143
Q

What is meant by a respiratory alkalosis?

A

Excessive removal of CO2 by the body

144
Q

What actions can cause a respiratory alkalosis?

A

Low inspired PO2 at altitude
Hyperventilation
Hysterical overbreathing

145
Q

CO2 + H2O => H2CO3 => H+ + HCO3-

In what direction does respiratory alkalosis cause the equilibrium to move?

A

To the left due to reduced CO2

This causes a fall in H+ and HCO3- concentration

146
Q

Describe the appearance of the pH and PCO2 in a respiratory alkalosis?

A

pH > 7.45

PCO2 < 35 mmHg

147
Q

Describe the shift of respiratory alkalosis compared to normal on a Davenport diagram?

A 
pH increases (shifts right)
HCO3 decreases (shifts down)
148
Q

How does the kidney compensate a respiratory alkalosis?

A

Excessive removal of CO2 reduces H+ secretion into the tubule
=> less H+ in the urine

Less HCO3- is reabsorbed => excreted in urine

149
Q

What causes a metabolic acidosis?

A

Excess H+ from any source other than CO2

150
Q

What can cause a metabolic acidosis?

A

Ingestion of acids or acid-producing foodstuffs

Excessive metabolic production of H+

  • lactic acid during exercise
  • ketoacidosis in T2DM

Excessive loss of base from the body
- diarrhoea – loss of HCO3-

151
Q

What happens to the pH and HCO3- in uncompensated metabolic acidosis?

A

Uncompensated metabolic acidosis indicated by:
pH < 7.35
[HCO3-]p is low

152
Q

Describe the shift of metabolic acidosis compared to normal on a Davenport diagram?

A 
pH decreases (shifts left)
HCO3- decreases (shifts down)
153
Q

How does the respiratory system compensate in a metabolic acidosis?

A

Ventilation is quickly increased and more CO2 is blown off

154
Q

How is metabolic acidosis corrected?

A

Filtered HCO3- = reabsorbed

H+ secretion produces TA & NH4+
=> generates new HCO3- into blood

Acid excreted in urine

Ventilation can then be normalised

155
Q

What is a metabolic alkalosis?

A

Excessive loss of H+ from the body

156
Q

What actions can cause a metabolic alklalosis?

A
  • Loss of HCl from the stomach (vomiting)
  • Ingestion of alkali or alkali-producing foods
  • Aldosterone hypersecretion
157
Q

What indicates an uncompensated metabolic alkalosis?

A

pH > 7.45

[HCO3-]p is high

158
Q

Describe the position of a metabolic alkalosis in comparison to normla on a Davenport diagram?

A 
pH increases (shifts right)
HCO3 ncreases (shifts up)
159
Q

How does the respiratory system compensate in a metabolic alkalosis?

A

Increased pH slows ventilation (peripheral chemoreceptors)

CO2 retained, PCO2 rises

160
Q

How is metabolic alkalosis corrected?

A

Not all filtered HCO3- is reabsorbed (due to large vol)

No TA or NH4+ is generated

HCO3- is excreted (urine is alkaline)

[HCO3-]p falls back towards normal

RENAL (24 decks)

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