acid regulation Flashcards by Annna Oopp

what is the importance of ph on the body?

pH has an effect on the 3D structure of proteins
Controls the speed of enzyme activity
Controls the speed of electrical reactions – synaptic function depends on intra + extracellular pH gradients

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what is an acid?

proton donor

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what is a base?

proton acceptor

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what is the pH of gastric juice?

pH 2

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what is the pH of urine and saliva?

pH 6

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what is the pH of pure water, human blood, tears?

pH 7

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what is the pH of the small intestines?

pH 8

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what should the pH of normal blood be?

7.35 to 7.45

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what is the pH of venous blood and why?

Venous blood is slightly acidic bc it picks up the CO2 made by the tissues –> converted to carbonic acid

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when does acidemia occur?

when the pH is below 7.35

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when does alkalemia occur?

when the pH is above 7.45

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in what pH range can death occur?

below 6.8

above 8.0

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what diets produce more acids than bases?

diets high in proteins

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what processes form acid in the human body? what acids are formed?

o Produced from breakdown of foods (e.g. proteins)
 Oxidation of sulfur-containing amino acids  sulfuric acid
 Acid in diet produces about 60mmol/day
o CO2 + H2O  carbonic acid
 15 mol/day of CO2 leads to carbonic acid production
o Anaerobic respiration of glucose –> lactic acid
o Incomplete oxidation of fatty acids –> acidic ketone bodies
o Hydrolysis or phosphoproteins and nucleic acids –> phosphoric acids

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which diseases can produce more acid and what acid do they produce?

o Uncontrolled diabetes, starvation –> acetoacetate B-hydroxybutyrate
o Liver disease –> impaired lactate clearance –> lactic acid

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what mechanisms regulate concentrations of H+?

Chemical buffer systems in blood and ICF (immediate action)
Respiratory centre in the brainstem (acts within 1-3 mins)
Renal mechanisms (requires hours to days to affect pH changes)

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what is a buffer?

can resist changes in pH when small amounts of acid or base are added.
• Acts quickly (but temporarily) to bind/release H+
• Consists of a weak acid + salt of that acid (acts as a weak base)

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what are the 3 major chemical buffer systems in the body?

o Bicarbonate (HCO3-) buffer system (main)
o Proteins (hemoglobin &amp; albumin) buffer system 
o Phosphate (P043-) buffer system

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what effect does acidaemia have on potassium?

Acidemia leads to hyperkalemia (tissues release K+)

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what effect does alkalaemia have on potassium?

Alkalaemia leads to hypokalaemia (tissues take up K+)

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what are cations?

+ve ions

what are anions?

-ve ions

name unmeasured cations

calcium
magnesium
proteins

name unmeasured anions

phosphates
sulfate
proteins

what does the anion gap calculate?

measures how many ions aren’t accounted for – unmeasured ions are mainly anions (hence why it’s called the anion gap)

how do you calculate the anion gap? what should it normally be?

(Na+) – ([Cl-] + [HCO3-]) = 8 to 12 mEq/L

why is the anion gap measured without potassium?

so small it's irrelevant

how does normal gap metabolic acidosis occur?

- Big drop in HCO3- and an increase in Cl- --> anion gap doesn’t show a change - Cl- is exchanged for a HCO3- to maintain the electroneutrality of the body - HCO3- bc it's being used to buffer the acid

name causes of normal gap metabolic acidosis

severe diarrhoea, type 1 and 4 renal tubular acidosis and chronic laxative abuse Also; villous adenoma, external drainage of pancreatic/biliary secretions; losses via NG tubes; administration of acidifying salts; urinary diversions

what is normal gap metabolic acidosis seen in?

loss of bicarbonate | reduced kidney H+ excretion

how does elevated gap acidosis occur?

- drop in HCO3- - isnt compensated for by the surge of Cl- - isnt compensated for bc there's either a pathological amount of H+ or not enough HCO3-

why is there a high anion gap in elevated gap acidosis?

- no surge in Cl- to compensate for the decrease in HCO3- - low levels of Na+ and K+ - unmeasured anions increase

what causes elevated gap acidosis?

ketoacidosis, lactic acidosis, renal failure, toxic ingestions

what is the major unmeasured anion?

albumin

what is low gap acidosis linked to?

hypoalbuminaemia | causes a surge in HCO3- and Cl-

what are the causes of low gap acidosis?

haemorrhage, nephrotic syndrome, intestinal obstruction and liver cirrhosis

how does haemorrhage lead to low gap acidosis?

Haemorrhage leads to acidosis bc you lose blood --> less O2 --> anaerobic respiration --> lactic acid --> acidosis

what can cause metabolic acidosis?

vomiting or diuretic use

how does the serum anion gap change in metabolic acidosis?

small increase in the serum anion gap - approx 4-6 mEq/L

how does the serum anion gap change in respiratory alkalosis?

doesnt change notably

what are the 2 main roles of the kidneys in metabolic acidosis?

o Reabsorption of all filtered bicarbonate | o Excrete the daily acid load

how does the kidney get rid of metabolic acids?

o Hydrogen secretion o Bicarbonate reabsorption o Excretion of H+ ions with urinary buffers

where is bicarbonate reabsorbed and how?

reabsorbed by the PCT via carbonic anhydrase (converts CO2 and H2O to bicarbonate)

how is H+ excreted in the distal kidney?

o Via ATP pump (main way) o Swapped for Na+ o Proton-potassium pump – hence why hyer/hypokalaemia is linked to acidosis

what do a-intercalated cells do and how?

- Secretes acid as H+ ions (via an apical H+-ATPase and H+/K+ exchanger) - Reabsorbs bicarbonate (via band 3, a basolateral Cl-/HCO3- exchanger)

what do b-intercalated cells do and how?

- Secretes bicarbonate (via pendrin – specialised apical Cl-/HCO3-) - Reabsorbs acid (via a basal H+-ATPase)

how is bicarbonate produced?

* Glutamine is broken down in tubule cells to alpha-ketoglutarate * A-ketoglutarate --> NH4+ + glucose + HCO3-

in acidosis, how is acid removed?

* In acidosis, the kidney needs to reclaim the carbon to make bicarbonate * Releases bicarbonate back into the system * H+ can be exchanged for Na+ to pump it out * H+ needs to stay out, so it’s titrated either by an ammonium or phosphate buffer

in alkalosis, how is H+ retained?

* In alkalosis, tubular cells secrete HCO3- and reabsorb H+ to acidify the blood * Uses separate ATPases * K+ ions and swapped for H+ ions

what hormones are used in regulation of acid/base status and how do they work?

* Angiotensin 2 regulates the reabsorption of K+ which affects pH * Aldosterone puts Na+ back into the system - If Na+ is put back into the system then we have to swap it for H+ and K+ * Parathyroid hormone prevents the reabsorption of phosphate buffer (can’t leave the filtrate) – makes sure that H+ stays buffered.

what is the henderson hasselbach equation used for?

pH of a buffer solution | ratio of conjugate base to acid of the system