Acid Base Balance and pH

Pregunta	Respuesta
What is pH?	a measure of Hydrogen ion concentration in solution
In pure water, what is the ratio of Hydrogen ions to Hydroxide ions?	1:1
What is involved in protein denaturation?	adding or removing hydrogen ions from proteins, causing conformational change and denaturing the protein
What effect can a low pH have on the central nervous system?	a low pH has a depressive effect on the CNS
What is the usual range of pH for extracellular fluid?	7.36-7.44
What is the usual range of pH for intracellular fluid?	7.10-7.20
Is the pH of body fluids always closely associated with the pH of plasma?	no, can largely deviate from each other like in gastric juice and pancreatic juice
What kind of scale is the pH scale and what does this mean about small pH changes?	logarithmic scale, so a small increase in pH can equal a large change in ionic concentrations
What is the first line of defense against H+ concentration changes and how quickly does it react?	body's buffer systems, reacting almost immediately
What is the second line of defence against H+ concentration changes and how quickly does it react?	the lungs, reacting rapidly but not as immediately as buffer systems
What is the third line of defence against H+ concentration changes and how quickly does it react?	the kidneys, reaction time can take up to several hours
What are the lungs unable to do regarding H+ changes that the buffers and kidneys can do?	remove excess acids or bases
What does the Law of Mass action state?	the rate of a reaction is proportional to the product of the concentrations of the reactants
What is a weak acid or alkali?	one that only partially dissociates in solution
What is formed when an alkali accepts a proton?	a conjugate acid
In what blood vessels is H+ concentration highest?	in venous blood
H+ concentration rises as blood flows through which vessels?	peripheral capillaries
What is the relationship between pH and H+?	negative logarithm: pH = -log10[H+]
What are volatile acids?	an acid that can be easily removed when an animal breathes
How are volatile acids derived?	from CO2, as H+ can be made from H2CO3 (potential acid)
What are non-volatile acids?	acids that cannot be eliminated by the lungs
In an animals, where do non-volatile acids derive from?	produced during metabolism (lactic acid) and are then rapidly metabolised to H20 and CO2
Problems with which system can affect CO2 levels in the body?	respiratory system
The influence of dietary feed on acid-base balance depends on what ratio?	the ratio between the content of dietary bases and the components that metabolise into non-volatile acids
In carnivores, is there a net acid or net base production?	net acid (net acid producers)
When organic anions are metabolised, what is produced?	HCO3-
What happens to excess HC03- that is produced from anion metabolism?	excess bicarbonate is excreted in the kidneys
Why do some herbivores/omnivores have alkaline urine?	the dietary bases are higher than the production of non-volatile acids and so they produce more excess HCO3-, which is excreted in the urine
Why do carnivores have the highest acid production?	there is a higher concentration of dietary proteins and as these are oxidised, they produce non-volatile acids
What does a a buffer do?	a buffer minimises the change in pH when an acid or base is added
What is a base?	a proton acceptor
What is an acid?	a proton donor
What are amphoteric buffers?	a buffer with both basic and acidic characteristics and can accept or donate protons
What equation can be used to predict changes in pH?	Henderson-Hasselbalch equation : pH= pK + log[base] [acid]
Buffers work best when there is what kind of difference between pH and pK?	small difference, pH and pK should ideally be close together
When pH=pK, how does H+ changes affect pH?	any H+ changes will have a minimal effect on pH
Out of all the body buffering systems, which one maintains around half the body's buffering capacity?	intracellular buffers inc. proteins and inorganic/organic phosphates
Which buffering systems are involved in long term acidosis?	Carbonate in bone and Ion exchange in bone
What is meant by a closed buffer system?	a system where the sum of the two components of the buffer pair is constant
What is meant by an open buffer system?	a system where the concentrations of both components of the buffer pair are subject to regulation
Why is the bicarbonate buffer system so important in the body?	two elements of the system can be regulated, as changes work across a 3 part equilibrium at both ends of the equations, making it flexible for acidosis and alkalosis
How do kidneys control the H+ concentration in ECF?	can produce acidic or alkaline urine to compensate for H+ balance changes, by varying H+ secretion and bicarbonate reabsorption)
How do the lungs control Carbon Dioxide levels in the body?	can vary respiratory rate to increase or decrease the pCO2
What does the amount of HCO3- absorbed depend on?	the composition of the diet, with herbivores reabsorbing around 99%
Why do carnivores continuously produce HCO3-?	H+ is produced for metabolism and so bicarbonate is needed to buffer the acidic metabolism process
What percentage of bicarbonate is reabsorbed in the proximal tubule?	85%
What percentage of bicarbonate is reabsorbed in the LoH?	10%
As HCO3- can't cross the apical membrane in the tubules, how is is reabsorbed into the capillary lumen?	CO2 freely diffuses from the tubular lumen into the tubular cell, where it reacts to make bicarbonate which can then diffuse across the interstitium into the capillary
What is the ionic movement within bicarbonate secreting cells?	bicarbonate ions are secreted into the tubular lumen whilst Cl- is transported into the cell H+ moves into the capillary from the tubular cell
What ionic movement takes place in H+ secreting cells?	H+ is secreted into the tubular lumen in exchange for K+ ions bicarbonate and Cl- are transported into the capillary lumen
What are the two types of urinary buffers?	inorganic phosphate and ammonia/ammonium
Which is the most important urinary buffer?	ammonia/ammonium buffer as it can cope with large acid increases
Why is the phosphate buffer only useful with small changes in H+?	the concentration of phosphate in renal tubules is always low and so only limited H+ can be excreted in urine as bound to phosphate
How does the inorganic phosphate buffer exist in solution?	equilibrium between a weak base and a weak acid : Na2HPO4 (alkaline) and NaH2PO4 (acid)
How does NH3 produce NH4+?	crosses the membrane to 'mop up' H+ to convert into NH4+
How does the ammonia/ammonium system also influence Na+ levels in the body?	contributes to Na+ levels in the body by allowing Na+/NH4+ exchange
What is acidosis?	acidosis occurs when the arterial pH falls below 7.35
What is alkalosis?	alkalosis occurs when the pH of arterial blood rises above 7.45
In acid-base disturbances, what is involved in Compensation?	rapid, short term pH regulation using buffers and the respiratory system
In acid-base disturbances, what is involved in Correction?	longer term effect to return bicarbonate and carbon dioxide levels to normal
How can respiratory acidosis/alkalosis occur?	when the lungs remove CO2 at a lower or higher rate
With respiratory acid-base disturbances, in what way do H+ and HCO3- concentrations change?	both H+ and bicarbonate concentrations are changed in the same direction - in acidosis, both ion concentrations increase
What system is involved in compensation of respiratory acid-base disturbances?	The kidneys are used to regulate ECF pH back to normal levels in compensation
In respiratory acidosis, what happens to kidney function?	as the pCO2 increases and pH decreases, there's an increased stimulation of urinary H+ excretion and increased bicarbonate production
How are metabolic acid-base disturbances defined?	metabolic acid-base disturbances arise when the H+ comes from another source other than CO2, like lactic acid
In metabolic acid-base disturbances, H+ and bicarbonate changes occur in which direction?	H+ and bicarbonate change in opposite directions
In metabolic acid-base disturbances, what system is involved in compensation and what type of compensation is it?	the lungs compensate by altering pCO2, however this is only partial or incomplete compensation
In metabolic acid-base disturbances, what system is needed for complete correction?	kidneys
What is the primary determinant of intracellular pH?	arterial pH
Do respiratory or metabolic changes have a greater effect on H+ secretion?	changes in arterial pH due to respiratory changes more readily affect H+ secretion
Why do respiratory changes have a more rapid effect on pH changes than metabolic changes?	CO2 crosses cell membranes more easily than H+ and bicarbonate ions and so can more quickly change the pH levels
In acid-base balance, what are the two main functions of H+ excretion?	- facilitates bicarbonate reabsorption - facilitates bicarbonate formation
Following arterial H changes, what is the most important determinant of H+ renal excretion?	changes in K+ plasma concentration
Why does K+ plasma concentration have a large effect on H+ excretion rates?	K+ influences how H+ is transported across cell membranes, as they are often involved in carrier proteins or exchange mechanisms
Hyperkalemia will cause what type of acid-base disturbance?	metabolic acidosis - more K+ efflux will lead to a greater rate of H+ influx, so more H+ will be excreted into the urine
Hypokalemia causes what type of acid-base disturbance?	metabolic alkalosis

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