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P1: Ren > Acid-base Balance > Flashcards

Acid-base Balance Flashcards

1
Q

Why is it important to keep the pH in a narrow range?

A

→ The body has a lot of enzymes which only function at a particular pH

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2
Q

What is the normal pH of body fluids?

A

→ 7.35-7.45

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3
Q

What are the sources of acid in the body?

A

→Metabolism of carbohydrates and fats produces CO2
→ CO2 + H2O → H2CO3 → H+ + HCO3-
→ can be removed by the lungs

→ Metabolism of proteins

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4
Q

What does metabolism of proteins generate?

A

→ Non-volatile (fixed acids)
→ S- containing amino acids → H2SO4
→ Lysine,arginine,histidine → HCl

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5
Q

How do we know that we can control our pH?

A

→ 156 ml of HCl infused IV into a dog
→ 156 ml of HCl added to 11.4 l of water ( same as body water of dog)

→ Dogs arterial plasma decreased gradually from 7.44 to 7.14 (severe acidosis but survival is possible)
→ pH of water dropped to 1.84 (fatal if in vivo)

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6
Q

What is it about plasma that controls pH?

A

→ Presence of buffers that are effective in vivo

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7
Q

What is the first line of defense when there is a change in pH?

A

→ Buffer system in the blood (ICF and ECF)

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8
Q

What is disturbance in H+ compensated for?

A

→ ICF & ECF buffering systems
→ Respiratory systems
→ Kidney

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9
Q

What is the equation for the bicarbonate system?

A

→ H+ + HCO3- ⇌ H2CO3 ⇌ CO2 + H2O

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10
Q

What is the equation for the phosphate system?

A

→ H+ + HPO4 2- ⇌ H2PO4-

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11
Q

What is the equation for protein buffers?

A

→H+ + Pr - ⇌ HPr

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12
Q

What is pK?

A

→ The equilibrium point of a buffer
→ Where it most strongly resists changes in pH
→ Near where [acid and base] are equal

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13
Q

What is the range over which a buffer is effective?

A

→ 1 pH on either side of the PK

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14
Q

If the pK of the phosphate buffer is 6.8 what are the pH ranges over which it is effective?

A

→ 5.8

→ 7.8

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15
Q

Which buffer is theoretically better and why?

A

→ Phosphate
→because the PK lies within the body pH ranges
→each molecule of phosphate can buffer more H+ than an equal amount of bicarbonate.

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16
Q

Which buffer is biologically better and why?

A

→ Bicarbonate
→lungs control PCO2
→ Kidneys control HCO3-
→ Independent controlled regulation of both variables

plays a much more important role as an extracellular buffer than does phosphate

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17
Q

What is the henderson hasselbach equation used for?

A

→ Measuring the pH of a buffer system

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18
Q

What is the ratio of [HCO3-]: [CO2]?

A

→ 24 : 1.2

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19
Q

How do you calculate the concentration of CO2 in the blood if it is a gas?

A

→ Plasma CO2 is proportional to the partial pressure of CO2

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20
Q

How do kidneys control acid base levels?

A

→ Excrete acidic or basic urine

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21
Q

What are the primary mechanisms involved in excretion of urine?

A

→ Reabsorption and secretion of HCO3-
→ Formation of new HCO3-
→ Secretion of [H+] into tubular fluid
→ Buffer systems within the tubule that react with secreted [H+]

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22
Q

What happens to proteins at the glomerulus?

A

They are not filtered and remain in the plasma

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23
Q

What happens to bicarbonate at the glomerulus?

A

→ Freely filtered
→bicarbonate is reabsorbed from the tubule
→ Kidney generates new HCO3-
→ Released into plasma at a controlled rate

24
Q

What happens to phosphate at the glomerulus?

A

→ freely filtered

→ Reabsorbed from the tubule

25
Q

What does the kidney produce that contributes to buffering other than bicarbonate?

A

→ HCO3-

26
Q

What do kidney tubule cells form?

A

→ carbonic acid from CO2 and water

→ via carbonic anhydrase

27
Q

What happens to the carbonic acid produced by kidney tubule cells ?

A

dissociates into H+ and HCO3-
→ Na+ moves into the cell down the concentration gradient into the cell
→ provides the energy for active secretion of H+ into lumen

28
Q

How does H+ get into tubular fluid?

A

→ Na+ moves into the cell down the concentration gradient
→ provides the energy for active secretion of H+ into lumen
→With each H+ that is secreted, one HCO3- enters blood accompanied by Na+

29
Q

What are the 2 ways H+ gets into urine?

A

→ H+ ATPase

→ while Na+ moves in H+ moves out

30
Q

What happens to the HCO3- in tubular cells?

A

→ diffuses out and goes back into blood

→ Via a symporter with Na+ ions

31
Q

What can carbonic anhydrase be inhibited by?

A

→ acetazolamide and other thiazide diuretics

32
Q

Where is most HCO3- reabsorbed?

A

→ 85-90% at the proximal tubule

→ Secrete H+

33
Q

What is the balance of bicarbonate?

A

→for every 1 bicarbonate ion that is filtered

→1 is returned back into plasma

34
Q

Where is carbonic anhydrase present in the kidney?

A

→ ONLY in the luminal brush border of the PCT

35
Q

Flowchart of fate of bicarbonate in PCT

A

Bicarbonate is freely filtered
↓
Filtered HCO3- combines with H+ to form carbonic acid
↓
Carbonic acid dissociates to form CO2 and H2O this is catalyzed by carbonic anhydrase
↓
CO2 crosses into the tubular cell down a gradient
↓
CO2 recombines with H2O (carbonic anhydrase) to form carbonic acid
↓
Dissociates into H+ and HCO3-
↓
HCO3- passes into the blood stream while H+ is exchanged for Na+

36
Q

What can the bicarbonate reabsorption also be stimulated by?

A

→ angiotensin II

37
Q

What is the pH like in the DCT and why?

A

→H+ ATPase pumps out the H+
→ DCT has a lower pH
→ HCO3- is low because it has been reabsorbed and H+ needs to react with other buffers

38
Q

what does HPO4 2- buffer and why is it effective?

A

→ further H+ secreted into the lumen

→ PK is close to pH of filtrate

39
Q

Flowchart for fate of H+ with phosphate in intercalated cells

A

Carbonic acid dissociates into H+ and HCO3-
↓
H+ is secreted via ATPase (aldosterone sensitive)
↓
reacts with phosphate
↓
becomes H2PO4-
↓
excreted into urine because it has a charge
↓
HCO3- reabsorbed with a HCO3- / Cl antiporter

40
Q

Flowchart for fate of H+ in tubular epithelium, Creation of new Bicarbonate:

A

Ammonia + a ketoglutarate is produced from glutamine metabolism p
↓
a ketoglutarate is metabolized to form two H2CO3
↓
dissociates to form 2x H+ and 2x HCO3-
↓
H+ combined with ammonia to form ammonium
↓
ammonium is exchanged for Na+ in an antiporter and ammonium is excreted in the blood
↓
HCO3- is reabsorbed into blood

41
Q

What does the tubular epithelium produce?

A

→ NH3 from glutamine with glutaminase

42
Q

Describe the summary of the ion flow through the tubules?

A

1) reabsorption of bicarbonate
2) formation of titratable acid phosphate
3) ammonia secretion which creates new bicarbonate

43
Q

What are changes in acid base balance called and what are the two types?

A

→ acidosis or alkalosis

→ respiratory or metabolic

44
Q

What are the correction mechanisms for changes in pH?

A

1) intra and extra cellular buffering
2) respiratory adjustment of ECF PCO2
3) renal adjustment of ECF [HCO3-]

45
Q

What area regulates respiration in the brain and how?

A

→ chemosensitive area in medulla
→ monitors H+ of plasma via CSF indirectly
→ charged ions cannot cross blood brain barrier but CO2 does

46
Q

What happens if plasma pH decreases?

A

→ Plasma PCO2 increases
→ CSF pH decreases
→ Respiratory ventilation increases to remove CO2

47
Q

How is the change in plasma pH monitored?

A

→ peripheral chemoreceptors in aortic arch and carotid body

48
Q

What is metabolic acidosis characterized by?

A

→ low pH
→ High ECF H+
→ Low ECF HCO3-

49
Q

What is metabolic acidosis caused by?

A

→ sepsis or shock - lactic acid increases
→ Uncontrolled diabetes - overproduction of 3OHbutyric acid or ketoacids
→ diarrhoea - loss of HCO3- from GI tract

50
Q

What happens if there is an increase in H+?

A

1) ICF and ECF buffers bind to H+ to try and get rid of it
2) if H+ is still high the lungs increase ventilation to remove CO2
3) this compensates for decreased ECF pH
4) kidney increases H+ secretion
5) NH4+ secretion increases - forms new HCO3- ions

51
Q

What is metabolic alkalosis characterized by?

A

→ Increase in ECF HCO3-

→ Decrease in ECF H+

52
Q

What is metabolic alkalosis caused by?

A 
→ Excessive diuretic use
→ Chronic loss of Cl-, Na+, K+, increase of H+
→ Vomiting - loss of H+
→ Antacids
→ Hypokalemia
53
Q

What happens if there is an increase in HCO3-?

A

1) ICF and ECF bind to HCO3- to get rid of it
2) if HCO3- is still high the lungs decrease ventilation to increase CO2
3) compensates for increased ECF pH
4) Kidneys decreases H+ secretion
5) decreased HCO3- formation and reabsorption
6) Increased HCO3- excretion

54
Q

What is the excretion and retention of CO2 controlled by?

A

the lung

55
Q

What is regeneration of HCO3 controlled by?

A

the kidney

56
Q

What is effect on pH because of reabsorption of HCO3?

A

a slight fall in tubular fluid pH (from 7.4 to 7.0), and no change in the PCO2 of tubular fluid.

P1: Ren (13 decks)

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