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X Physiology 1B > Renal System > Flashcards

Renal System Flashcards

1
Q

What are the 7 main roles of the kidneys?

A

excretion of metabolic products and foreign substances
retrieval and retention of useful substances
regulation of body fluid osmolarity and volume
regulation of electrolyte balance
regulation of acid-base balance
production and secretion of hormones
the storage and voiding of urine

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2
Q

Why is maintenance of plasma fluid volume important?

A

maintains the equilibrium of other fluid areas in the body

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3
Q

what are the main sections of the urinary tract?

A

kidney, ureter, bladder and urethra

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4
Q

what section of the nervous system innervates the kidneys?

A

sympathetic branch of ANS

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5
Q

What sections is the medullary layer of the kidney split into?

A

renal pyramids and papillae

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6
Q

what does the renal papillae drain into?

A

minor and major calyxes and then the pelvis of the kidney

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7
Q

What is the basic functional unit of the kidney?

A

nephron

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8
Q

what are the two types of nephron?

A

cortical nephrons and juxtamedullary nephrons

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9
Q

where are cortical nephrons found?

A

in the cortex

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10
Q

where are juxtamedullary nephrons found?

A

deep into medulla

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11
Q

What is the role of juxtamedullary nephrons?

A

urine concentration due to their long loops of Henle

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12
Q

what is the main role of cortical nephrons?

A

absorption and secretion

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13
Q

where is fluid filtered from into the nephron?

A

the blood stream

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14
Q

what is ultrafiltrate similar to?

A

plasma

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15
Q

how does ultrafiltrate differ from plasma?

A

doesn’t contain proteins but is otherwise the same

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16
Q

what happens to most of the filtrate?

A

it is reabsorbed after modification

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17
Q

what happens to the excess ultrafiltrate that is not reabsorbed?

A

voided as urine

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18
Q

what type of capillaries are found in the glomerulus?

A

fenestrated

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19
Q

what can fit through fenestrated capillaries?

A

plasma proteins, water, nutrients, waste and electrolytes

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20
Q

what is the glomerulus?

A

the capillary network in the kidneys where ultrafiltration occurs

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21
Q

what will not fit through fenestrated capillaries?

A

formed elements of blood (e.g. RBC)

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22
Q

where is the only place in the body where capillary bed is fed and drained by arterioles?

A

glomerulus in kidneys

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23
Q

what is the Bowman’s capsule?

A

contains glomerulus

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24
Q

what occurs within the Bowman’s capsule?

A

filtration to create ultrafiltrate

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25
Q

Describe the path from Bowman’s capsule to collecting duct

A

proximal convoluted tubule - loop of Henle - distal convoluted tubule - collecting duct

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26
Q

what happens in the proximal tubule?

A

most of the fluid is reabsorbed along with vital nutrients

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27
Q

what happens in the loop of Henle?

A

urine concentration is controlled

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28
Q

what happens in the distal convoluted tubule?

A

fine tuning of electrolyte concentrations

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29
Q

What does the blood supply of the kidney consist of?

A

two capillary beds in series (one after the other)

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30
Q

what are the glomerular capillaries the site of?

A

filtration

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31
Q

is blood leaving the glomerulus oxygenated?

A

yes

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32
Q

what is the name of the vessels that supply and leave the glomerulus?

A

afferent and efferent arterioles

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33
Q

what is the name of the second capillary bed in the kidney?

A

vasa recta

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34
Q

what does the vasa recta surround?

A

the nephron

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35
Q

what happens at the vasa recta?

A

site of gaseous exchange and collection of solutes and water reabsorbed by nephron

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36
Q

how is the juxtaglomerular apparatus (JGA) formed?

A

the distal convoluted tubule loops back and makes physical contact with the glomerulus which forms the JGA

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37
Q

what is the importance of the JGA?

A

secretes important hormones

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38
Q

what remains the same in the kidney despite changes in the arterial blood pressure?

A

glomerular filtration rate

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39
Q

what does autoregulation of renal blood flow mean?

A

blood flow remains constant despite changes in arterial blood pressure

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40
Q

between what pressures is renal blood flow autoregulated?

A

60 to 160 mmHg

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41
Q

if renal blood flow is autoregulated what does this mean for glomerular filtration rate

A

will also be relatively constant despite changes in arterial blood pressure

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42
Q

what is a proposed explanation for autoregulation?

A

if blood pressure increases the initial increased flow will stretch the muscle in the arteriole wall and cause it to contract. If GFR were to increase this is sensed by cells in the JGA which release a constrictor

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43
Q

why must RBF and so GFR remain so constant?

A

kidney requires a constant supply of glomerular filtrate

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44
Q

what is the endothelium of the glomerulus formed of?

A

3 layers including a basement membrane

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45
Q

what is the function of podocytes?

A

envelop the fenestrated capillary and prevent large molecules from leaving the capillary (e.g. albumin). Are a barrier to leakage of protein into ultrafiltrate

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46
Q

what are the two processes found on popcytes?

A

primary and secondary

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47
Q

what is the gap between secondary processes of podocytes called?

A

filtration slit

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48
Q

what forms the major filtration barrier to macro molecules?

A

the podocyte

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49
Q

what do the capillary fenestrations allow?

A

movement of water, smaller molecules and ions

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50
Q

why does fluid cross the glomerular capillaries into the nephron?

A

due to physical forces across the capillary wall

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51
Q

what are the forces which act on fluid to move it from glomerular capillaries to the nephron?

A

hydrostatic pressure in the capillary from blood pressure

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52
Q

what are the forces which act on fluid to move it from nephron to the glomerular capillaries?

A

osmotic forces across the capillary due to plasma proteins

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53
Q

how is the net hydrostatic force calculated

A

hydrostatic pressure of capillary - hydrostatic pressure in Bowman’s capsule

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54
Q

how is the net reabsorption force calculated?

A

osmotic (oncotic) pressure of capillaries - osmotic (oncotic) pressure of Bowman’s capsule

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55
Q

in a healthy person what will the net filtration force create?

A

net force out of the capillary

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56
Q

what is the result of glomerular filtration forces?

A

a large volume of filtrate per unit time which is cell and protein free
the concentration of small solutes is the same as in plasma

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57
Q

what is creatinine a product of?

A

waste product of natural muscle breakdown

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58
Q

why is the amount of creatinine in urine due to glomerular filtration only?

A

it is freely filtered, not reabsorbed from tubule, not secreted into tubule and inert

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59
Q

what is a common blood borne biomarker of GFR?

A

creatinine

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60
Q

how can creatinine indicate kidney issues?

A

amount will decline if GFR declines which indicates state of kidney. There is an expected amount in urine in a healthy person

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61
Q

what is urinary excretion of creatinine proportional to?

A

it’s delivery by the renal artery

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62
Q

what is the proportionality of urinary excretion of creatinine and it’s delivery by the renal artery called?

A

creatinine clearence

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63
Q

how can creatinine clearance be calculated?

A

clearance = urine production rate/plasma creatinine concentration

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64
Q

what is the estimate of rate of filtration an important measurement of?

A

the ability of the kidneys to function properly

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65
Q

what is the preferred reference for the blood flow in the kidneys?

A

renal plasma flow

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66
Q

what is renal plasma flow usually?

A

750 ml/min

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67
Q

how much of the renal plasma flow is used as glomerular filtrate?

A

15-20%

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68
Q

how much urine is usually produced per minute?

A

1 ml

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69
Q

what percentage of filtrate is reabsorbed along the nephron?

A

99%

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70
Q

if renal plasma flow isn’t used as glomerular filtrate what happens to it?

A

leaves the glomerulus through the efferent arteriole

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71
Q

how much of total tubular reabsorption does proximal tubule reabsorption make up?

A

70%

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72
Q

what happens in the proximal tubule?

A

reabsorption of several vital solutes as wel as the bulk of the filtered fluid. It is the site of secretion from the blood to tubular fluid

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73
Q

what state does fluid in the proximal tubule remain in throughout passage through the tubule?

A

isotonic (isosmotic)

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74
Q

what is the average glomerular filtration rate in a healthy young adult?

A

120 ml/min or 175 ltres per day

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75
Q

what happens to glomerular filtrate/

A

reabsorbed either in the proximal tubule, loop of Henle or collecting duct. alternatively it is voided as urine

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76
Q

what are the two surface of the proximal tubule cells?

A

apical surface facing the tubular lumen and baso-lateral surface on the inner layer close to the blood vessels

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77
Q

what are the two main features of the apical cell surface of the epithelial cells?

A

microvilli and many mitochondria

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78
Q

what is the function of the microvilli on the apical surface of epithelial cells?

A

greatly increases surface area which enhances transport capacity

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79
Q

what is the significance of many mitochondria in the epithelial cells?

A

shows lots of metabolic activity

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80
Q

what are the 4 vital functions of the proximal tubule?

A

reabsorption of the bulk of filtered NaCl and isotonic NaCl
reabsorption of essential solutes
contribution ot the regulation of body fluid pH
secretion of some orgainic molecules

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81
Q

where does secondary active transport occur in the epithelial cell of the proximal tubule?

A

apical side of the epithelium

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82
Q

what is the movement of Na+ indirectly coupled to when it moves with it’s concentration gradient across the apical layer?

A

ATP hydrolysis to maintain the Na+ gradient across the cell membrane

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83
Q

what does the position o fth secondary and primary active transporters do to transport?

A

gives directionality

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84
Q

what is the primary active transport pump on the baso lateral layer?

A

Na+/K+ ATPase

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85
Q

what is happening when substances move from apical to basolateral layers?

A

reabsorption

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86
Q

what is happening when substances move from basolateral to apical layers?

A

secretion

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87
Q

what is Na+ transport across the apical membrane enabled by?

A

cotransport with another essential solute (e.g. glucose)

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88
Q

what will happen to the solute that is co transported alongside Na+?

A

it will diffuse out across the basolateral membrane

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89
Q

How is the membrane potential created in the proximal tubule?

A

by the transport of Na+ ions out of the tubule by secondary active transport

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90
Q

what is the effect of the membrane potential in the proximal tubule created by transport of Na+ ions?

A

anions can now flow into blood vessels down concentration gradient

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91
Q

what must the number of Na+/glucose transporters ensure?

A

all glucose is reabsorbed under normal circumstances

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92
Q

what are some other Na+ coupled transporters?

A

those for bases, neutral or amino acids

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93
Q

what ions flow down their electrochemical gradient out of the proximal tubule?

A

Cl-

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94
Q

how is isotonic NaCl transported?

A

Cl- following on electrochemical gradient created by co transport of Na+

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95
Q

how is there no concentration of tubular fluid?

A

movement of water by osmosis and NaCl by transport and creation of electrochemical gradient

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96
Q

what is glucose reabsorption mediated by?

A

carriers

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97
Q

what is a consequence of carrier mediated glucose reabsorption?

A

it has a maximum transport rate

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98
Q

what is the maximum transport rate of glucose known as?

A

tubular transport maximum or Tmax

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99
Q

at what concentration can the kidney completely reabsorb the filtered glucose load?

A

normal plasma (and filtrate) concentrations (4-6mM)

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100
Q

where may blood glucose levels rise to shortly after eating?

A

8mM

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101
Q

is the short term rise of glucose after eating enough to exceed Tmax?

A

no

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102
Q

what is Na+ across the membrane also enabled by?

A

counter transport with H+ ions

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103
Q

how is Na+ transported across the basolateral membrane after counter transport with H+ across the apical membrane?

A

primary active transport with sodium/potassium ATPase

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104
Q

how does the cell regulate intracellular pH?

A

extruding excess H+

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105
Q

what is H+ produced in the cell by?

A

metabolism exchange for Na+

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106
Q

how does Cl- and water move when Na+ is counter transported with H+?

A

Cl- moves along electrochemical gradient and water by osmosis

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107
Q

what element of body fluids does the kidney play a vital role in maintaining?

A

the correct pH

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108
Q

what is the normal pH of plasma?

A

7.35-7.45

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109
Q

what is the intracellular pH of most cells?

A

7.0-7.1

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110
Q

what is the activity of most enzymes dependent on?

A

pH

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111
Q

under what circumstances is the activity of pH dependent enzymes be greatest?

A

at their optimum pH

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112
Q

where can an excess of CO2 come from in the tubular fluid?

A

the blood

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113
Q

can Co2 enter the cell easily?

A

yes

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114
Q

what does CO2 react with H2O to form?

A

H+ and HCO3-

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115
Q

what is the creation of H+ and HCO3- from CO2 and H2O catalysed by?

A

carbonic anhydrase

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116
Q

where does HCO3- leave the cell?

A

across the basolateral membrane by a number of co and counter transporters

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117
Q

where does H+ leave the cell?

A

across the apical membrane via Na+/H+ counter transporter

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118
Q

what happens to some of the H+ in the tubule?

A

bound by buffers and excreted in urine

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119
Q

what happens to other H+ molecules which are not bound to buffers and lost in urine?

A

react with HCO3- catalysed by carbonic anhydrase to restart the cycle

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120
Q

what is a key feature of proximal tubule secretion?

A

able to rid the body of certain substances

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121
Q

what is the proximal tubule able to excrete?

A

a number of organic ions and cations

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122
Q

what are the organic ions and cations secreted by the proximal tubule the products of?

A

end products of metabolism

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123
Q

what effect can proximal tubule secretion have on therapeutic drugs?

A

may limit the time that they are in circulation and so reduce their efficacy

124
Q

what proportion of resting cardiac output do the kidneys receive?

A

25%

125
Q

define osmolality

A

concentration of impermeable solutes per kg of solute

126
Q

what happens if a cell is placed in a hypotonic solution?

A

water moves into the cell and it swells

127
Q

what happens if a cell is placed in a hypertonic solution?

A

water leaves the cell and it shrinks

128
Q

what is the kidneys’ response to dehydration?

A

to retain water and produce a small volume of concentrated urine

129
Q

what is the risk of overhydration?

A

dilatation of plasma

130
Q

how do the kidneys respond to overhydration?

A

produce a large volume of dilute urine

131
Q

why is plasma osmolality regulated?

A

to prevent cell swelling or shrinkage

132
Q

how is plasma osmolality regulated?

A

by controlling water influx and efflux from the body

133
Q

what methods of intake and output of water from the body are physiologically controlled?

A

intake of water through drinking and output via urine production

134
Q

why is the control of drinking and urination so importnat?

A

their values are similar

135
Q

what is an important mode of control in regulation of plasma osmolality?

A

generation of urine of different concentrations

136
Q

under what circumstances is urine concentrated?

A

if the body must conserve water to replace excessive loss

137
Q

when is urine dilute?

A

if the body needs to lose excessive water

138
Q

what is normal plasma osmolality?

A

290 mosmol.kg-1 H2O

139
Q

how much variation in plasma osmolality will activate compensation mechanisms?

A

1% - tightly controlled

140
Q

what is a change in plasma osmolality detected by?

A

osmoreceptors in the hypothalamus

141
Q

when a change is detected by the osmoreceptors in the hypothalamus what is initiated?

A

release of ADH from the pituitary gland

a change in the perception of thirst from the thirst centre

142
Q

what is the effect of ADH?

A

influences urine concentration

143
Q

what is the effect of the thirst response?

A

water intake is altered

144
Q

what sort of feedback process is plasma osmolality regulation?

A

negative feedback process

145
Q

what is ADH?

A

Anti-diuretic hormone

146
Q

what type of hormone is ADH?

A

peptide

147
Q

where is ADH secreted from?

A

the posterior pituitary gland

148
Q

what are the 3 actions of ADH on the kidney?

A

it increases water permeability of the collecting duct
increases NaCl reabsorption in the thick ascending limb
increases urea permeability in the inner medullary region of the collecting duct

149
Q

what is the net effect of ADH?

A

to aid reabsorption by the kidney

150
Q

what neurones is ADH produced in?

A

supraoptic and paraventricular

151
Q

Where is ADH transported to once it is produced?

A

axon terminals in the posterior pituitary

152
Q

what causes ADH to be released into the blood?

A

a rise of plasma osmolality a small as 1% which activates hypothalamic neurons

153
Q

when is ADH release reduced?

A

when osmolality falls

154
Q

what does the plasma concentration of ADH between 0.5 and 5 pg.ml-1 account for?

A

100-1250mosmol.kg H2O-1 urine osmolality

155
Q

what effect does an increase in ADH have on urine output?

A

a small volume of concentrated urine

156
Q

what effect does a decrease in ADH have on urine output?

A

a large volume of dilute urine

157
Q

in what osmotic state is the tubular and interstitial fluid when it leaves the proximal tubule?

A

isosmotic

158
Q

where is sodium chloride and potassium chloride absorbed from in the nephron?

A

ascending limb of the loop of Henle

159
Q

what portion of the nephron is impermeable to water?

A

ascending limb of the loop of Henle

160
Q

which part of the loop of Henle is permeable to water?

A

the descending loop of Henle

161
Q

due to the properties of the ascending and descending loops of Henle what happens to the fluid within it?

A

becomes hyper osmotic

162
Q

what is the net result of the counter current mechanism in the loop of Henle?

A

an osmolality gradient is generated in the medullary interstitium

163
Q

where is there hypo-osmotic fluid in the nephron?

A

in the distal tubule and collecting duct

164
Q

how is the concentrating mechanism set up?

A

by ion transport in the ascending limb of the loop of Henle which is impermeable to water

165
Q

what pump is used in transport of ions to create concentrated urine ?

A

Na+/K+/2Cl- co-transporter and a baso-lateral Na-pump

166
Q

how much of the filtered Na+, K+ and Cl- is reabsorbed?

A

about 20%

167
Q

what can the Na+/K+/2Cl- co-transporter be blocked by?

A

loop diuretics

168
Q

summerise the the counter-current mechanism

A

an osmolarity gradient is generated in the medullary interstitium.
fluid entering the distal tubule and collecting duct is hypo-osmotic

169
Q

how does ADH increase the water permeability of the distal tubule and collecting duct cells?

A

binds to the membrane of the distal tubule and collecting duct

170
Q

why does water leave the hypotonic nephron fluid?

A

equilibrate with with hypertonic medullary interstitium fluid

171
Q

tubular fluid becoming more concentrated leads to?

A

concentrated urine

172
Q

what is the name of the receptor ADH binds to on the basolateral surface of the tubule cell?

A

a V2 receptor

173
Q

what does the binding of ADH to V2 receptors on the basolateral surface of the tubule cell do?

A

stimulates adenylate cyclase to generate cAMP and activate protein kinases

174
Q

what does the generation of cAMP and activation of protein kinases do?

A

increases the insertion of water channels into the apical surface of the cell and so increase water permeability

175
Q

what is the name of water channels in the basolateral surface?

A

aquaporins

176
Q

what does the increase in aquaporins in the descending loop of Henle lead to?

A

water flowing from the more dilute tubular fluid to the hyperosmotic medullary interstitium which concentrates the tubular fluid

177
Q

describe the thirst mechanism

A

increased ECF (plasma) osmolarity is associated with reduced saliva and dry mouth. This increases activity of osmoreceptors in hypothalamus leading to stimulation of hypothalamic thirst centre. This increases the sensation of thirst so the person needs to drink. Water moistens the mouth and throat and stretches stomach and intestine. Water is then absorbed from the GI tract returning plasma osmolarity to normal.

178
Q

what is control of blood volume also sometimes referred to as?

A

control of effective circulating volume

179
Q

what do the kidneys control?

A

plasma constituents

180
Q

why does plasma volume affect blood volume?

A

the cellular component of blood is usually fixed so and volume changes will be caused by changes in plasma

181
Q

as all fluid compartments of the body are linked, how does this affect volume control?

A

if volume of one is altered it will affect the volume of the others

182
Q

how does the kidney indirectly control plasma volume?

A

by regulating Na+ excretion

183
Q

what is blood pressure determined by?

A

the rate of blood returning to the heart and therefore the preload on the ventricles

184
Q

if blood volume is controlled what else may be controlled?

A

arterial blood pressure

185
Q

what does decreased venous return lead to according to Starlings Law?

A

reduced preload and so reduced SV

186
Q

how might the kidneys respond to hypovolaemia?

A

sensing reduced blood pressure and flow, reducing Na+ loss in the urine and so reducing water loss in the urine

187
Q

how can blood volume be restored?

A

increase Na+ retention which will cause water to be drawn into the blood by osmosis, this increases blood volume

188
Q

what do the kidneys regulate in order to maintain blood volume?

A

sodium loss into urine

189
Q

where are the high pressure sensors of blood volume found?

A

systemic arterial

190
Q

where are the low pressure sensors of blood volume found?

A

systemic venous and pulmonary

191
Q

what do high pressure sensors respond to?

A

variations in arterial blood pressure

192
Q

where are arterial barorecptors located?

A

carotid sinus and aortic arch

193
Q

how do the arterial baroreceptors respond to hypovolaemia?

A

increases sympathetic activity to the kidneys due to a fall in pressure and reduced baroreceptor signalling

194
Q

what does the juxtaglomerular apparatus of the kidney respond to?

A

reduced blood pressure

195
Q

how does the juxtaglomerular apparatus respond to hypovolaemia?

A

hormonal response leads to reduced Na+ loss and so reduced water loss in response to reduced blood pressure/renal flow

196
Q

what are low pressure sensors used for?

A

excretion of retained plasma fluid

197
Q

where are the low pressure sensors found within systemic venous and pulmonary areas?

A

cardiac atria and pulmonary vasculature

198
Q

during hypovolaemia what do sympathetic nerves innervate?

A

afferent arterioles

199
Q

why is sympathetic activity increased during hypovolaemia?

A

part of the baroreceptor reflex

200
Q

describe the baroreceptor response to reduced blood pressure

A

baroreceptor signalling reduces leading to increased sympathetic activity and constriction of afferent arterioles. This leads to reduced glomerular filtration and reduced filtered load of Na+ which in turn reduces water loss. Blood volume is restored

201
Q

what is the juxtaglomerular apparatus involved with?

A

replacement of lost volume

202
Q

what is the juxtaglomerular apparatus?

A

structure in the nephron where the distal tubule makes close contact with the glomerulus and it’s vasculature

203
Q

what do juxtaglomerular cells secrete in response to low blood flow or increased sympathetic activity?

A

the hormone renin

204
Q

what is the effect of renin?

A

directly involved with Na+ and so water reabsorption at the distal tubule

205
Q

describe the response of juxtaglomerular apparatus to reduced blood pressure

A

reduced blood flow/pressure triggers renin secretion from the kidney this reduces Na+ secretion and so water loss so blood volume is restored

206
Q

what is the renin-angiotensin-aldosterone system (RAAS) key in?

A

regulation of blood volume by controlling NaCl and so water reabsorption by nephron

207
Q

what type of enzyme is renin?

A

proteolytic enzyme

208
Q

what is the substrate of renin?

A

circulating angiotensinogen

209
Q

what is angiotensinogen produced by?

A

the liver

210
Q

when is angiotensinogen is hydrolysed by renin what is the product?

A

decapeptide known as angiotensin I

211
Q

what is angiotensin 1 converted into?

A

octapeptide angiotensin 2

212
Q

what is angiotensin 1 converted into angiotensin 2 by?

A

an angiotensin converting enzyme (ACE) in the lung

213
Q

what are the 3 roles of angiotensin 2?

A

exerts vasoconstrictor response
stimulates ADH release and so water retention by kidney
stimulates aldosterone release from adrenal cortex and so increases Na+ retention by kidney (and thereofre reduces water loss)

214
Q

what type of hormone is aldosterone?

A

steroid

215
Q

where is aldosterone secreted from?

A

zona glomerulosa of the adrenal glands

216
Q

what is aldosterone secreted by?

A

angiotensin 2 stimulating its release from adrenal cortex

217
Q

what does circulating aldosterone bind to?

A

it binds to a receptor on the nephron basolateral membrane

218
Q

what does the receptor - aldosterone complex stimulate?

A

transcription (nucleus) of apical membrane Na+ channels (ENaC)

219
Q

what effect does the increased number of ENaC channels on the apical membrane of the nephron have?

A

increases NaCl reabsorption via principal cells in the distal tubule/collecting duct

220
Q

what substances will follow Na+ across the apical membrane when it is moved through ENaC channels and into the blood stream?

A

Cl and water

221
Q

Summarise the RAAS control of plasma volume

A

reduced blood volume/pressure
reduced renal blood flow
increased renin secretion
increased angiotensin 2
increased aldosterone secretion from adrenal glands
increased sodium, and so water, reabsorption by kidneys

222
Q

what will an increase in blood volume or venous return cause in the atria?

A

excessive stretch of atria and release of ANP

223
Q

where is ANP stored?

A

atrial myocytes

224
Q

what does ANP stand for?

A

atrial natiuretic peptide

225
Q

what does ANP cause?

A

natriurisis

226
Q

what is natriurisis?

A

excretion of Na+ (as NaCl) and so water

227
Q

what are the 5 effects of ANP release?

A

inhibition of aldosterone secretion
inhibition of renin secretion
vasodilation of afferent arteriole leading to increased glomerular filtration rate
reduced Na+ absorption in convoluted tubules
inhibition of ADH release leading to increased water excretion

228
Q

what ions does the kidney regulate?

A

K+ and Ca+

229
Q

where is the bulk of body K+ found?

A

in the intracellular space

230
Q

how does regulation of K+ occur?

A

by keeping the extracellular concentration of K+ within very narrow margins

231
Q

what is the normal value of K+ within the body?

A

3.5 to 5.5 mmol/l

232
Q

what is hyperkalaemia?

A

increase of K+ to greater than 5.5 mmol/l

233
Q

what does hyperkalaemia cause?

A

membrane depolarisation of excitable cells and increases excitability

234
Q

what is hypokalaemia?

A

a decrease of K+ to less than 3.5 mmol/l

235
Q

what does hypokalaemia cause?

A

hyperpolorization of cells and decrease in excitability

236
Q

what happens to an excitable cell during hyperkalaemia?

A

cell potential is closer to threshold meaning it is easier to excite/propagate action potential

237
Q

what is a key danger during hyperkalaemia?

A

cardiac electrophysiological problems such as arrhythmias due to the cell being more excitable

238
Q

what happens to an excitable cell during hypokalaemia?

A

the cell is much harder to excite and so normal AP will not be propagated as quickly as normal

239
Q

what are the symptoms of hyperkalaemia?

A

non-specific - palputations, muscle weakness and breathlessness

240
Q

what are the characteristic ECG changes shown in a hyperkalaemic patient?

A

tall T waves, prolonged QRS complex in severe cases

241
Q

what are the symptoms of hypokalaemia?

A

arrhythmia, fatigue, muscle damage and constipation

242
Q

where is 90% of the filtered load of K+ reabsorbed in the kidneys?

A

proximal tubule

243
Q

where does most of the K+ secretion into urine take place?

A

the distal tubule

244
Q

what are the 2 main regulators of K+ secretion?

A

plasma K+ and plasma aldosterone

245
Q

what does an increase in plasma K+ cause?

A

enhances secretion of aldosterone and depolarizes cells of the zona glomerulosa in the adrenal cortex

246
Q

what does an increase in plasma aldosterone cause?

A

enhances secretion of potassium through activation of apical K+ channels

247
Q

what stimulates the release of aldosterone from the adrenal cortex?

A

Ca2+ influx into the cell

248
Q

how does hyperkalaemia increase K+ secretion?

A

stimulates the adrenal cortex to release aldosterone

249
Q

what does aldosterone do to increase K+ secretion?

A

increase sodium/potassium ATPase sites at the basolateral membrane and so stimulate their activity
increase presence of Na+ and K+ channels at the apical membrane

250
Q

What effect does hypokalaemia have on aldosterone?

A

opposite to hyperkalaemia

251
Q

where is the bulk of body Ca stored?

A

in the bones and teeth

252
Q

how much of total Ca in the body is exchangeable with ECF?

A

1%

253
Q

what are the short term effects of hypocalcaemia?

A

increase the excitability of nerves and muscles

254
Q

what are the long term effects of hypocalcaemia?

A

demineralisation of bones

255
Q

what are the different states of Ca?

A

bound and ionised

256
Q

what is the normal value of Ca2+ in plasma?

A

2.2-2.6 mmol/l

257
Q

what does Ca2+ tend to bind to in the blood?

A

plasma proteins (e.g. albumin and anions such as HCO3)

258
Q

How much does the ionised form of Ca2+ make up of the whole?

A

50% of the total

259
Q

what are Ca2+ sites competitively bound by?

A

H+

260
Q

as Ca2+ sites are competitively bound by H+ what does alkalaemia cause?

A

more Ca2+ can be bound and the ionised fraction is reduced

261
Q

what is alkalaemia?

A

increased plasma pH

262
Q

what is the precursor of activated vitamin D?

A

cholecalciferol

263
Q

what is cholecalciferol obtained from?

A

the diet and action of UV light on the skin

264
Q

is cholecalciferol active?

A

no - functionally inactive and must be converted to active form

265
Q

what is the active form of cholecalciferol (vitamin D)?

A

1,25 (OH) vitamin D3

266
Q

what happens to cholecalciferol in the liver?

A

hydroxylation to 25 (OH) vitamin D3

267
Q

what happens to 25 (OH) vitamin D3 in the kidneys?

A

hydroxylated to 1,25 (OH) vitamin D3

268
Q

what can 25 (OH) vitamin D3 also be hydroxylised to in the kidney?

A

24,25 (OH) vitamin D3

269
Q

what is the purpose of 24,25 (OH) vitamin D3?

A

means to prevent the excessive generation of 1,25 (OH) vitamin D3

270
Q

what causes hypoxia of a tissue?

A

too little O2 delivered

271
Q

what are the 3 factors which determine the amount of CO2 delivered to tissues?

A

% saturation of haemoglobin with O2
the amount of haemoglobin in any volume of blood (e.g haematocrit or individual cells)
the flow of blood (CO)

272
Q

what is the effect of reduced RBC number?

A

reduced O2 delivery to tissues and the tissue becomes hypoxic

273
Q

what is blood cell development called?

A

erythropoiesis

274
Q

what is erythropoietin?

A

hormone which is synthesised by the kidneys that activates production of RBC

275
Q

what does tissue hypoxia produce?

A

hypoxia inducible factor-2 alpha (HIF-2a)

276
Q

what organs is hypoxia inducible factor-2 alpha produced by?

A

in foetuses and neonates - liver

in adults - kidneys

277
Q

what does hypoxia inducible factor-2 alpha stimulate?

A

interstitial fibroblast-like cells to release erythropoietin

278
Q

what does erythropoietin do one released from near the kidney tubules?

A

goes to bone marrow to encourage production of erythrocytes. Erythropoiesis restores O2 delivery to tissues

279
Q

what is the role of the urinary tract?

A

carries urine from the kidneys to be stored in the bladder and then voided

280
Q

what happens in the upper urinary tract?

A

urine is collected in the renal pelvises and conveyed by the ureters to the bladder

281
Q

why can’t urine empty from the bladder during storage?

A

because the urethra (outflow tract) presents a high resistance to fluid flow

282
Q

what must happen to allow urine to be voided?

A

bladder contracts and outflow tract relaxes

283
Q

where does the wave of peristalsis in the ureter originate?

A

pacemaker cells in the renal pelvis

284
Q

what smooth muscle is the bladder lined by?

A

detrusor

285
Q

what sort of muscle is the urethra formed from?

A

smooth muscle

286
Q

what is the external urethral sphincter formed of?

A

a ring of skeletal muscle which surrounds the urethra

287
Q

what is the detrusor muscle supplied by?

A

post-ganglionic parasympathetic nerve fibres which release acetylcholine to contract the muscle

288
Q

what is the innermost layer of the bladder formed of?

A

urothelium

289
Q

what is a key function of urothelium?

A

provides a protective layer by forming a tight barrier to prevent urine leaking to the underlying tissues

290
Q

what does urothelium release when stretched?

A

agents which excite afferent nerves

291
Q

describe what happens during bladder filling without leakage

A

volume increase by up to 500ml with little rise in pressure due to bladder compliance, there is no leakage due to the contracted state of the urethra and external urethral sphincter. The subject senses bladder filling due to sensory nerve signalling but he brain suppresses voiding

292
Q

where do afferent nerves from the bladder synapse within the brain?

A

peri-aqueductal grey (PAG) neurons in the midbrain

293
Q

where are the signals from the afferent nerves of the bladder sent once they reach the peri-aqueductal grey (PAG) neurons in the midbrain?

A

sent to anterior cingulate gyrus insula and pre frontal cortex via the thalamus

294
Q

what does the process of transmission of afferent bladder signals do to the type of signal?

A

changes it to sensation of bladder filling

295
Q

where is the decision not to void the bladder made?

A

medial pre-frontal cortex

296
Q

how is storage of urine maintained?

A

by chronic inhibition of the PAG and so the mictruition centre

297
Q

what 3 nerves are involved in urine storage?

A

pelvic nerve, pudendal nerve and hypogastric nerve

298
Q

which nerve activity is suppressed in order to store urine?

A

the parasympathetic (pelvic) nerve so the bladder is relaxed

299
Q

what nerves are activated to ensure bladder storage?

A

sympathetic (hypogastric) and somatic (pudendal) cause urethra and external sphincter to contract

300
Q

how does the brainstem cause the bladder to store urine?

A

suppresses pelvic nerve and so bladder relaxes

activates pudendal nerve and hypogastric nerve to cause external sphincter and urethra to contract

301
Q

describe what happens during voiding of the bladder

A

brain makes the decision to void (is is socially acceptable). The bladder wall contracts and pressure in the urethra lumen increases soon after the flow starts due to rising pressure and relaxation of outflow tract muscles. The sensation of bladder fullness is reduced and the bladder completely empties

302
Q

how is the decision to void made in the brain?

A

once afferent input is sufficient the decision to void is made

303
Q

what happens within the brain once the decision to void urine is made?

A

the medial pre-frontal cortex relaxis it’s inhibition of PAG. The hypothalamus also provides a signal

304
Q

what is the effect of ending inhibition of the PAG when the decision to void urine is made?

A

PAG excites PMC to send descending motor output to the sacral spinal cord to relax the urethral sphincter and contract the detrusor so that voiding occurs

305
Q

how does the brainstem cause voiding of the bladder?

A

pelvic nerve is activated causing contraction of bladder. Pudendal nerve and hypogastric nerve is suppressed to cause relaxation of external sphincter and urethra

X Physiology 1B (5 decks)

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