acid based disturbance (W3)

Question 1

how is CO2 produced

Answer 1

metabolism of carbohydrates, fat and proteins give rise to CO2

Question 2

what does CO2 create

Answer 2

CO2 dissolves in the plasma and forms carbonic acid

Question 3

what is the other cause of hydrogen ion disturbance

Answer 3

protein metabolites are broken down to amino acids, some of these contain sulphur which is then metabolised to sulphuric acid which is a much stronger acid
nucleic acids contain phosphates which go on to form phosphoric acid

Question 4

what is acidaemia? how does it affect proteins?

Answer 4

build up of acid in the plasma
causes proteins to change their solubility enzymes to change their activity
ion pumps across membranes don’t function as well

Question 5

what are the responses to changes in plasma H+

Answer 5

buffering - instantaneous, take up or release of ions in response to changes in concentrations, most powerful buffer is bicarbonate, phosphate and proteins are buffered themselves at lower concentrations
ventilation of CO2 by the lungs - rapid
elimination of non-volatile acids - slow, excretion of H+, regeneration of bicarb, this is done by the kidneys

Question 6

how does the CO2 - bicarb buffer system work

Answer 6

CO2 is generated by all cells, it dissolves in the plasma to form carbonic acid
this quickly forms bicarbonate and H+
bicarbonate can be further ionised to form a carbonate and another proton (but this is significant as it rarely occurs)

Question 7

what is the total CO2

Answer 7

concentration of CO2 and carbonic acid
due to carbonic anhydrase they are always in the same ratio
usually it is expressed as a partial pressure in kilopascals

Question 8

what is the dissociation equilibrium

Answer 8

H+ concentration is proportional to the total dissolved CO2, and inversely proportional to the bicarb concentration

Question 9

what are the life threatening H+ concentrations

Answer 9

less then 20nmol/L or more than 120nmol/L

Question 10

what are the types of acidaemia

Answer 10

acidaemia is when the H+ concentration is higher then 44nmol/L
respiratory acidaemia - too much CO2
metabolic acidaemia - too little bicarbonate

Question 11

what are the types of alkalaemia

Answer 11

when H+ concentration is lower then 36nmol/L
respiratory - too little CO2
metabolic - too much bicarb

Question 12

what is acidosis

Answer 12

general term of when something is happening in your body that may cause acidaemia

Question 13

what is the physiological response to disturbances

Answer 13

rate of respiration is controlled by H+ concentration in the plasma
rate of filtration by the kidneys and absorption of of bicarb is controlled in the same way

Question 14

how does compensation occur

Answer 14

respiratory acidaemia has metabolic compensation
metabolic acidaemia has respiratory compensation
respiratory alkalaemia has metabolic compensation
metabolic alkalaemia has respiratory compensation

Question 15

rules of thumb for compensation

Answer 15

compensatory response changes the parameter that was not affected by the primary disturbance
the change is always in the same direction as the parameter that cause the primary disturbance (CO2 falls, bicarb falls)
respiratory comp is quick while metabolic is slow

Question 16

how to classify acid base disturbances

Answer 16

look at H+ conc, if lower than 36 its alkalaemia, if its higher than 44 its acidaemia
if CO2 has changed there is respiratory disturbance, then would the change cuase the change in H+ or would it oppose it
if bicarb is abnormal then metabolic disturbance has occurred, again look to see if the change in bicarb would’ve caused the change in in H+ or oppose it
if the change would oppose it then it means compensation has occurred

Question 17

what also occurs when plasma H+ falls

Answer 17

as plasma H+ falls, H+ dissociate from the side chains of plasma proteins
proteins now have a greater negative charge, so bind more Ca2+
total plasma Ca2+ is unchanged but since more Ca2+ is protein bound, the free Ca2+ concentration falls

Question 18

when might reparatory acidaemia without compensation occur

Answer 18

often in crush injuries muscle injury causes a release of myoglobin, this can travel through the blood and end up at the kidneys, this can precipitate at low pH and then block renal function
this means that metabolic compensation does not occur

Question 19

why does pyloric stenosis cause metabolic alkalaemia

Answer 19

pyloric stenosis is when the exit from the stomach is blocked resulting in projectile vomiting
loss of gastric fluid stimulates gastric acidification (production of HCL by parietal cells) , at the same time these cells export bicarb out into the plasma

Question 20

what is cheyne-stokes breathing

Answer 20

sometimes after a heart attack or stroke, where a disturbance in the respiratory rate is overcompensated, respiratory centres that have been damaged by the stroke or heart attack don’t recognise this immediately and then stop respiration as they sense a massive lack in CO2
the person oscilates between not breathing and hyperventilating