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Renal Physiology > The Regulation of Acid/Base balance > Flashcards

The Regulation of Acid/Base balance Flashcards

1
Q

What are acids?

A

substances that ‘give off’ hydrogen ions (H+) in solution

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2
Q

What are bases?

A

substances that bind H+

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3
Q

What is pH?

A

pH is the negative decadic logarithm of the molar H+ concentration (pH = -log10 [H+])
- The higher the [H+], the lower the pH

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4
Q

What is considered a normal arterial blood pH?

A 
7.4			
Normal range is 7.35 to 7.45
- pH > 7.45, alkalosis
- pH < 7.35, acidosis
Note: The lower limit at which a person can live for a few hours is 6.8 and the upper limit is 8.0
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5
Q

What are the dangers of acid/base imbalance?

A
  1. pH sensitive molecules including enzymes, receptors + their ligands, ion channels, transporters, structural proteins, etc
    e. g. The optimum activity of Na+/K+-pump falls by half when pH shifts ≈ 1 unit
  2. Activities of most cellular enzymes are pH dependant
    e. g. Activity of phosphofructokinase falls by 90% when pH decreases by 0.1
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6
Q

What is respiratory acidosis?

A

Decreased pulmonary ventilation results in increased PCO2 of ECF resulting in accumulation of H2CO3 leading to a fall in blood pH below normal i.e < 7.35
- Characterised by increased PCO2 and reduced pH

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7
Q

What are the causes of respiratory acidosis?

A
  1. pathological conditions that damage the respiratory centre in medulla oblongata or that decrease the lungs to eliminate CO2
  2. Obstruction of the passageways of the respiratory tracts
  3. pneumonia
  4. asthma
  5. decreased pulmonary membrane surface area, etc
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8
Q

What is respiratory alkalosis?

A 
Reduced PCO2 (hypocapnia), increased pH > 7.45
- rare
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9
Q

What is respiratory alkalosis caused by?

A
  1. hyperventilation by the lungs
  2. Drugs stimulating the respiratory centre
  3. brain disorder
  4. A physiological type of alkalosis occurs when a person ascends to high altitude
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10
Q

What is matabolic acidosis?

A

Low plasma in bicarbonate [HCO3-] and a decrease in pH

  • The most common type of acid base disorder
  • All other types of acidosis besides those caused by excess CO2 in the body fluids
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11
Q

What causes metabolic acidosis?

A
  1. Increased production of non-volatile acids such as lactic acids, ketone bodies or loss of blood HCO3-, leading to a fall in blood pH to below normal
  2. Failure of the kidney to excrete metabolic acids normally formed in the body
  3. addition of metabolic acids to the body by ingestion or infusion of acids
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12
Q

What is metabolic alkalosis?

A

A rise in pH as a result of loss of non-volatile acids or by excessive accumulation of bicarbonate in ECF

  • Characterised by elevated [HCO3-] and increased pH
  • Metabolic alkalosis is not nearly as common as metabolic acidosis
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13
Q

What causes metabolic acidosis?

A

vomiting of gastric contents alone without the lower GIT contents causes loss of HCl secreted by gastric mucosa
- The net result is a loss of acid from the ECF and development of metabolic alkalosis

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14
Q

What are the 3 primary systems that regulate pH in the body?

A
  1. The chemical acid buffer system of the body fluids
    - Bicarbonate
    - Phosphate
    - Protein
  2. The respiratory centre
    - Elimination of volatile acid(carbonic acid) by exhalation of CO2
  3. The kidneys
    - Excretion of non-volatile acids
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15
Q

What is a buffer?

A

any substance that can reversibly consume or release H+

  • Buffer (base) + H+ <> H Buffer (acid)
  • When the [H+] increases, the reaction shifts to the right
  • Buffers help to stabilise the pH
  • Buffers don’t prevent, but minimise pH changes
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16
Q

Describe the bicarbonate buffer system?

A

The most important buffer in the ECF

Bicarbonate salt occurs as NaHCO3 in ECF and ionises to Na+ and HCO3-

17
Q

Describe the phosphate buffer system?

A

Main elements are H2PO4- (dihydrogen phosphate = acid) and HPO42- (monohydrogen phosphate = base)
H2PO4- <> H+ + HPO42-
Much more effective in ICF than in ECF because [phosphate] is greater in ICF than ECF
Plays an important role in buffering renal tubular fluid because phosphates become greatly concentrated in the tubules due to reabsorption of water

18
Q

Describe the protein buffer system?

A

e.g albumin, haemoglobin
- most of this results from intracellular proteins
example:
In the red blood cells, haemoglobin is the important buffer:
H+ + HbO2 <> HHb + O2

19
Q

Describe the respiratory control of acid/base?

A
  1. pH fall during acidosis acts as a potent stimulus to increase the ventilation via activation of chemo-receptors within the brainstem (ventral medulla)
    - The blood PCO2 and pH are important regulators of ventilation
  2. This manifests as deep and rapid breathing (Kussmaul respiration)
  3. Within minutes to hours, this response drives CO2 below normal
20
Q

Kidneys regulate ECF [H+] through which 3 fundamental mechanisms?

A
  1. secretion of hydrogen ions
  2. reabsorption of bicarbonate
  3. production of new bicarbonate
21
Q

What is the renal mechanism of acid/base balance?

A

Secretion of hydrogen ions and reabsorption of bicarbonate

22
Q

Secretion of hydrogen ions and bicarbonate reabsorption occurs in which parts of the nephron?

A

occur in all parts of the tubules except the descending and ascending limb of Henle

23
Q

Where does most or the bicarbonate reabsorption and hydrogen secretion occur?

A

in the proximal tubules 80-90%

- small amount flows to the distal tubules and colleting ducts

23
Q

What is the principal physiological buffer in plasma?

A

HCO3-

- but note filtered HCO3- do not readily permeate the luminal membrane of tubular cells

23
Q

Describe the mechanism of proximal tubular bicarbonate reabsorption?

A
  1. Na+H+ antiport secretes H+
  2. H+ in filtrate combines with filtered HCO3- to form CO2 + H2O
  3. CO2 diffuses into cell and combines with water to form H+ and HCO3-
  4. H+ is secreted again and excreted
  5. HCO3- is reabsorbed
24
Q

Describe the mechanism of the secondary active secretion of H+?

A
  • is coupled with the transport of Na+ into the cell at the luminal membrane
  • the energy for H+ secretion against a concentration gradient is derived from the Na+ gradient favouring Na+ movement into the cell
  • this gradient is established by Na+/K+-ATPase pump in the basolateral membrane
25
Q

In chronic acidosis what is the dominant method with which acid is eliminated?

A

is NH4+ (ammonium anion) generation

  1. glutamine is metabolized to ammonium ion and HCO3-
  2. NH4+ is secreted and excreted
  3. HCO3- is reabsorbed
26
Q

What are the 2 types of intercalated cells of the distal nephron?

A

Types A and B

27
Q

Describe the function of type A cells of the distal nephron?

A

cells pump out H+ by H+-ATPase pump or by the H+/K+-ATPase pump and reabsorb HCO3- during acidosis

  • Acidosis is often associated with hyperkalaemia
  • HCO3- leaves cell by the HCO3- / Cl- antiporter
28
Q

Describe the function of Type B intercalated cells of the distal nephron?

A

reabsorb H+ and secrete HCO3- during alkalosis

29
Q

Describe the control of alkalosis by the kidneys?

A

When there is a decrease in [H+] in the ECF (alkalosis), kidneys fail to absorb all the filtered HCO3- leading to excretion of HCO3-
- This raises the [H+] in the ECF to normal

Renal Physiology (8 decks)

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