Lecture 13: Acid base Flashcards Preview

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Flashcards in Lecture 13: Acid base Deck (42)
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1
Q

Fill in the blanks

A
2
Q

Why is maintained H+ within tight limits important?

A
  • Protein folding is effected by pH
  • Molecules are ionised- their state of ionisation depends on PH
3
Q

Name the 3 major components of acid-base regulation

A
  1. Ability to buffer
  2. Ability to ventilate
  3. Abilty of the kidneys to regulate the pH through secretion and rebasorption
4
Q

Which acid-base regulation component is able to defend against acidosis immediately?

A

Buffering system

5
Q

Which acid-base regulation component is able to defend against acidosis rapidly but not immediately?

A

Increase in ventilation

6
Q

Which acid-base regulation component is able to defend against acidosis slowly?

A

Renal adjustment

7
Q

How does the buffering system regulate acid-base homeostasis during acidotic states

A

CO2 + H20 <-> H+ + HCO3

Gain of H+ (during acidosis) leads to the equation being driven to the carbon dioxide end.

More CO2 and H20 formed to reduce the H+ levels

8
Q

How does the buffering system regulates acid-base homeostasis during alkoltic states

A

CO2 + H20 <-> H+ + HCO3

Loss of H+ leads to the equation being driven to the hydrogen end.

More H+ and HCO3 and less CO2 and H20 formed

9
Q

Name the buffers found in the body

A

Plasma proteins

Phosphate

Bicarbonate

Haemoglobin

Bone

PO4

10
Q

In which fluid compartment of the body does buffering occur?

A

Extracellular fluid and intracellular fluid

11
Q

Carbon dioxide is a?

A) Volatile acid

B) Fixed acid

A

A) Volatile acid

Meaning it can be eliminated from the body as a gas

12
Q

Give an example of a volatile acid

A

CO2

13
Q

Give an example of a fixed acid

A

Dietary acids and acid produced by anaerobic respiration are “fixed” – they cannot be “converted “ to CO2

14
Q

How are fixed and volatile acids excreted by the body?

A

Volatile acid: excreted from the body as gas

Fixed acids: buffered with HCO3

15
Q

The kidneys secrete ___ acids

A

Fixed

16
Q

What are the two main systems the kidneys use to secrete fixed acids

A
  1. Ammonia (NH4) system
  2. Bicarbonate (PO4)mechanism
17
Q

What are the 3 ways in which the kidneys regulate acid-base balance

A
  1. Reabsorb filtered HCO3
  2. Secrete fixed acid
    1. Ammonia system
    2. Bicarbonate system
18
Q

Reabsorption of HCO3 occurs where in the kidneys?

A

Largely in the proximal convoluting tubule

Small contributions from the distal convoluting tubule and the thick ascending loop of Henle

19
Q

What happens if there is an inability to reabsorb filtered HCO3

A

Metabolic acidosis

20
Q

Define GFR

A

Glomerular filtration rate

It is the amount of blood that is being presented to the glomerulus per minute

21
Q

How much HCO3 is reabsorbed by the kidneys?

A

(virtually) all filtered HCO3 is reabsorbed

22
Q

Describe the generic mechanism for reabsorbing bicarbonate

A

Filtered bicarbonate binds to secreted hydrogen ions and by the action of carbonic anhydrase causes the formation of water and carbon dioxide

The water and carbon dioxide enter the tubular cell and through the action of carbonic anhydrase forms hydrogen ion and bicarbonate.

The bicarbonate is transported into the interstitium back into the body.

Hydrogen ion is secreted back into the tubule lumen

23
Q

Which system is accounts for more acid excretion

A) Excretion of ammonium

B) Titration of phosphate

A

A) Excretion of ammonium -accounts for 50- 100 mmol H+/day

B) Titration of phosphate - only accounts for 40 mmol H+/day

24
Q

•Each H+ excreted is matched by what?

A

The generation of a new HCO3 which is absorbed

25
Q

What is the limits of the respiratory compensation

A

There is a limit to how hard patients can drive ventilation without tiring, and they can’t stop breathing

26
Q

Diagnosing acid-base disorders requires what?

A

Knowledge of H+, HCO3, CO2 (blood gases), electrolytes (Na, K, Cl) and a clinical history

27
Q

What are the mechansim of compensation with acid-base disorders

A
  1. Renal compensation
  2. Respiratory compensation- may not be complete
28
Q

What are the 3 most common cause of metabolic acidosis

A
  • Addition of extra acid
    • Generation of organic acid through metabolism – lactic acidosis, keto-acidosis
    • Ingestion of acid (e.g. methanol)
  • Failure to excrete acid
    • Renal tubular acidosis
  • Loss of HCO3
    • In stool (diarrhoea) or urine (“renal tubular acidosis”)
29
Q

What is the primary abnormality in metabolic acidosis

A

Fall in plasma HCO3

Loss of bicarbonate is like adding a hydrogen into the system.

30
Q

What are the systemic effects of metabolic acidosis

A
  • Cardiovascular system
    • Arrythmias, ↓cardiac contractility, vasodilation
  • Respiration
    • ↑ventilation (Kussmaul’s breathing)
  • Metabolic
    • Protein wasting, resorption of Ca from bone
  • Other
    • Neutrophilia
31
Q

Define anion gap

A

Represents the concentration of all the unmeasured anions in the plasma.

32
Q

Which anion makes up the majority of the unmeasured anion represented by the anion gap under normal circumstances.

A

The negatively charged proteins account for about 10% of plasma anions

33
Q

What is the equation for the anion gap

A

Anion gap = [Na+] - [Cl-] - [HCO3-]

34
Q

What must be adjusted for in the anion gap

A

Must adjust for low albumin

35
Q

Describe lactic acidosis

A
  • Lactic acid produced through glycolytic metabolism of pyruvate
  • Lactic acid is buffered by HCO3 to lactate and then metabolised in liver (and kidney to some extent)
  • Production of lactic acid is vastly greater than renal excretion of H+
  • Acidosis usually results from hypoperfusion and reduced hepatic clearance – major problem in sepsis
36
Q

What can cause lactic acidosis

A

Medications (metformin)

Liver failure

Poisoning (cynaide, aspirin)

37
Q

What is the primary abnormality in metabolic alkalosis

A

Primary abnormality is ¯ H+ and ­ HCO3

38
Q

High PCO2 is refers to as:

A) Hypoventilation

B) Hyperventilation

A

A) Hypoventilation

Reduced ventilation results in the high CO2 as less CO2 is getting blown off

39
Q

Low PCO2 is refers to as:

A) Hypoventilation

B) Hyperventilation

A

B) Hyperventilation

High ventilation results in the low CO2 as more CO2 is getting blown off

40
Q

What are the main causes of metabolic alkalosis

A

Vomiting- loss of gastric acid

Diuretics

aka volume depletion

41
Q

Bicarbonate reabsorption in distal convoluting tubule requires the section of which electrolyte

A

Chloride

42
Q

What is the treatment for acidosis and alkalosis

A

Main way to treat acidosis/alkaliosis- treat the cause removing the underlying tendency for acid/alkaline- the body will sort it out itself as it has a mechanisms to do so