Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

💦 Essays > pH Control > Flashcards

pH Control Flashcards

1
Q

Explain step 1 and step 2

A
  • Metabolic acidosis followed by respiratory compensation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Explain step 1 and 2

A
  • Respiratory alkalosis followed by renal compensation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Explain step 1 and 2

A
  • Metabolic alkalosis followed by respiratory acidosis
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Explain step 1 & 2

A
  • Respiratory acidosis followed by renal compensation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What drug or condition could cause step 1? Explain your answer

A
  • Metabolic acidosis
  • Acetalozamide
    • Inhibits carbonic acid anhydrase
    • Reduces H+ and HCO3- generation within the renal tubular cells resulting in metabolic acidosis
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What drug or condition could cause step 1?

A
  • Respiratory alkalosis
  • Anxiety (hyperventillation)
    • Excessive respiratory removal of CO2
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What drug or condition could cause step 1?

A
  • Metabolic alkalosis
  • Loop diuretics & thiazides
    • Furosemide inhibits Na+-K+-Cl- co-transporter on apical side
    • Bendoflumethiazide inhibits Na+Cl- symporter on apical side
  • Increased distal tubular sodium concentration results in reuptake of Na+ by apical epithelial Na+ channels which increases Na+ influx via the Na+-H+ exchanger resulting in greater HCO3- reabsorption and more H+ secretion into the tubular lumen.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What drug or condition could cause step 1?

A
  • Respiratory acidosis
  • Opioids
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is pH?

A

A measure of [H+] defined by the equation pH = -log10[H+]

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is an acid?

A

H+ donor

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is a base?

A

H+ acceptor

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is an alkali?

A
  • Soluble base
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is an acid-base disturbance?

A

A primary abnormality of acid-base balance that has the potential to shift plasma pH outside of the normal range (7.35 – 7.45) if there were no compensation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is compensation?

A
  • A secondary response of the pH regulatory system to a primary acid-base balance disutrbance that maintains plasma pH within the normal range
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is acidosis?

A

An abnormal condition/process in which plasma pH could be lowered if there were no compensation (can lead to acidaemia)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is alkalosis?

A

An abnormal condition/process in which plasma pH could be raised if there were no compensation. (can lead to alkalaemia)

17
Q

What is acidaemia?

A

Plasma pH < 7.35

18
Q

What is alkalaemia?

A

Plasma pH > 7.45

19
Q

Why is pH maintained?

A
  • pH homeostasis is important because changes in [H+] alter the valence of proteins, promoting alterations in bonding patterns that lead to conformational changes, disrupting normal function such as enzyme activity
  • Phosphofructokinase activity falls by 90% with a 0.1 unit change in pH
  • Cell mitogenic activity can fall by 85% when the pH falls by only 0.4
20
Q

Describe the systems which control pH?

A
  • The physiological systems that control of influence pH are:
    • They act to reduce pH disturbances by physiological activity
  • Buffer system
    • Sequesters or releases free H+
  • Respiratory & renal system
    • Eliminates acids or bases from the body fluids
21
Q

Name physiological activities that can change pH

A
  • Exercise
  • Ketogenesis
    • Diet
22
Q

Explain the traditional model

A
  • The traditional model of acid-base balance emphasises the matching of H+ input to and output from the body fluids.
  • It relies on the HCO3- buffer system and the Henderson-Hasselbalch equation (HHE).

HCO3- buffer system

  • The HCO3- buffer equilibrium is depicted in the equation below:

Carbonic anhydrase

CO2 + H2O

H+ + HCO3-

Henderson-Hasselbalch equation

  • The HHE can be derived by the modification of the equilibrium constant equation of this reaction.

pH = 7.4

pK = -logK = 6.1

[HCO3-] = 24 mM (normal)

a: Solubility coefficient of CO2 = 0.03 mM/kPa

PCO2 : Partial pressure of CO2 in blood = 5.3 kPa (normal)

  • The HHE states that pH is dictated by the [HCO3-]/PCO2 ratio.
  • An increase in the ratio results in an increase in pH, while a decrease lowers pH.

Increase in ratio

Increase in pH – alkalosis

Decrease in ratio

Decrease in pH - acidosis

  • The two independent variables that control pH are:
    (1) PCO2
    (2) [HCO3-]

HCO3-

Regulated by the kidneys

PCO2

Regulated by the lungs

23
Q

Evaluate the traditional model

A
  • Advantages
    • The advantage of the traditional model is that it is simple to understand
  • Disadvantages
    • Does not take other factors into account
    • Does not include buffers other than HCO3-
    • [HCO3-] is not a true independent variable
24
Q
  • Under normal conditions with a Western diet, how much is the net addition to the body fluids?
A
  • 70mEq/day
25
Q

Describe voltatile acids

A
  • In aerobic conditions, carbohydrates and fatty acids are metabolised to CO2, which diffuses into the ECF and promotes a decrease in pH (via HCO3- equilibrium)
  • CO2 is described as volatile acid because it generates H+ after reaction with H2O.
  • PCO2 is regulated by the lungs because CO2 can be exchanged with the alveolar air.
26
Q

Describe non-volatile acids

A
  • Non-volatile acids (NVAs) are those not derived from CO2 hydration.
  • These include H2SO4, HCl, and certain organic acids, which are produced by the metabolism of:
    • (1) sulfur-containing amino acids
      • e.g. cysteine and methionine
    • (2) cationic amino acids
      • e.g. lysine
  • Plasma [NVA] is controlled by the kidney.
  • Some is offset by HCO3- production from amino acid metabolism
27
Q

Explain the buffer system

A
  • Buffers are substances that reversibly bind free H+ in equilibrium reactions.
  • Buffers mediate short term regulation of pH on the timescale of seconds.
    • Rise in [H+] promotes rapid H+ sequestration
    • Fall in [H+] promotes H+ release

Buffers in compartments

  • Plasma buffers
    • The most quantitatively important plasma buffers are HCO3- and haemoglobin (Hb) in red blood cells.
    • Other plasma buffers include phosphate species (HPO42-, H2PO4-) and plasma proteins.
    • Proteins and Hb
      • Proteins have negatively charged groups that can accept H+ such as carboxyl, phosphate, and imidazole groups.
      • Deoxygenated Hb has a greater buffering capacity than other plasma proteins because (1) of its large quantity and (2) each molecule has a large number of imidazole groups.
      • RBC also mediate Cl- shift (exchange HCO3- in the cell for Cl-)
  • Bone
    • Bone matrix can also act as a buffer.
    • Short term buffering is mediated by the displacement of Ca2+ from CaCO3 by H+.
      • In long term acidosis, osteoclasts degrade bone matrix and release HCO3- which is why chronic acidosis can lead to osteoporosis
  • Cells
    • Cells can also buffer H+ by transcellular shifts with K+
    • In acidosis, H+ can be exchanged for K+, leading to hyperkalemia
      • In alkalosis, the reverse reaction occurs (k+ into cells) leading to hypokalemia
  • Intracellular buffers
    • Within cells, phosphate and proteins bind to H+ and HCO3- that is exchanged over the cell membrane from the ECF
28
Q

What are the limitations of the buffer system?

A

Closed system

  • Buffers do not contribute to long term pH regulation because they do not exchange H+ with the external environment, constituting a closed system.

Finite

  • Although the buffering capacity is large, eventual depletion of buffers would lead to an extreme shift in pH.
  • Open systems of pH regulation are therefore required (respiratory and renal).
29
Q

Explain respiratory control

A
  • Respiratory control of plasma pH is driven by changes in pulmonary ventilation (PV), which alter the rate of CO2 removal from the plasma and thus affect PCO2.
  • CO2 expiration removes the CO2 (volatile acid) generated by aerobic cellular metabolism.
  • Importance of an open system
    • The lungs have infinite ability to excrete CO2, thus pull the equilibrium of the HH equation towards CO2 production
    • This is important as the normal pKa of the blood does not favour CO2 production (instead HCO3- production), but as it is an open system, the concentration gradient maintains the activity.
  • Ventilation provides rapid adjustment of pH, acting on the timescale of minutes.

Chemoreceptors

  • Changes in plasma PCO2 and pH independently control ventilation by stimulating chemoreceptors, which deliver signals to respiratory muscles via the medullary respiratory centre.
  • Low pH
    • In low pH conditions, the central chemoreceptors detect a rise in brain extracellular [H+] due to a rise in PaCO2
      • Central chemoreceptors = medullary neurones
    • Peripheral chemoreceptors in the carotid bodies are stimulated by high PaCO2and low pH
    • Increase in pulmonary ventilation
      • thus increasing CO2 removal from the blood, lowering PaCO2, increasing [HCO3-]/PCO2 and raising pH
    • Altitude
      • Peripheral chemoreceptors are important at altitude to stimulate an increase in PV in phase 1 and 2 of acclimatisation
      • This is because unlike central chemoreceptors, they are sensitive to low PO2 (in phase 1)
      • Hyperventilation results in respiratory alkalosis that inhibits the central chemoreceptors during phase 2 of acclimatisation
  • High pH
    • Has opposite effect
    • Promotes decreased pulmonary ventilation and increasing PaCO2, lowering [HCO3-]/PCO2, and lowering pH.
30
Q

Explain kidney control

A
  • The kidney is the most powerful pH regulatory system but is slow, acting on a timescale of days.

Acid Load

  • The kidney mediates the neutralisation of non-volatile acids (NVAs) that cannot be expired by the lungs such as H2SO4, HCl, and certain organic acids.
  • NVAs are produced by the metabolism of:
    1. Sulfur-containing amino acids
  • E.g. cysteine and methionine
    1. Cationic amino acids
  • E.g. lysine

Acid-base models

Traditional

  • The function of the kidney in the traditional model is the replenishment of plasma HCO3- by:
    1. HCO3- reabsorption
    2. HCO3- regeneration
  • The HCO3- then buffers acid in the extracellular fluids.

Stewart model

  • In the Stewart model, the kidney regulates pH by modulation of the strong ion difference (SID) – this involves adjustments to the absorption and secretion of strong ions such as Na+, K+ and Cl-

The renal control of pH can be seen in clinical and experimental evidence.

31
Q

Explain HCO3- reabsorption

A
  • HCO3- reabsorption is important because a large amount of HCO3- is filtered by the kidneys each day, which would lead to a large decrease in the buffering capacity of the plasma if excreted in urine.
    • 5 mMol HCO3- filtered daily

Diagram

  • Of the filtered HCO3-, the proximal tubule (PT) reabsorbs 80% and the thick ascending limb of the loop of Henle (TALH) reabsorbs 15% by the mechanism depicted in the diagram below:

Steps

  1. Firstly, carbonic anhydrase in the proximal tubule cell catalyses the reaction: CO2 + H2O à H+ + HCO3
  2. The HCO3- is moved across the basolateral membrane into the interstitial fluid and plasma by the Na+/3HCO3- cotransporter and the HCO3-/Cl- cotransporter (the anion exchanger)
  3. The H+ is moved across the apical membrane into the tubule fluid by the Na+/H+ exchanger isoform 3 (most important) and H+ ATPase
  4. In the lumen, H+ reacts with filtered HCO3- in the following reaction: H+ + HCO3- à H2O + CO2, which is catalysed by carbonic anhydrase in the apical membrane.
  5. The CO2 produced diffuses into the PT cell and participates in the reaction of step (1).
  • The overall effect is a net movement of one HCO3- from the tubule fluid to the plasma.
  • In the distal nephron, HCO3- is regenerated
  • In acidosis, the upregulation of the NH3 to increase the reabsorption of bicarbonate
    • This is unusual as the PCT is not usually regulated and is the site of bulk reabsorption
  • However, the increased reabsorption is important for regeneration

Mechanism

NH3 is upregulated (absolute transport capacity) in acidosis

This is thought to be due to phosphorylation by PKC

  1. In acidosis the PCT cell is acidified
  2. Leads to intracellular calcium displacement
  3. PKC activation

NHE3 phosphorylation

Importance

Reabsorption of all the filtered HCO3- decreases the extent to which HCO3- needs to be regenerated in the distal nephron and allows HCO3- to be regenerated earlier

The upregulation of NH3 is important HCO3- reabsorption is limited by H+ availability

💦 Essays (7 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions