Exam 3 Acid Base Balance Flashcards
pH is an indirect measure of:
[H+]
pH is the ____ of the hydrogen ion concentration
Negative log
What is arterial blood pH?
~7.40
What is venous blood pH?
7.35 (slightly lower than arterial)
What does pH stand for?
Potential of hydrogen
If arterial blood pH=7.4, what is the pCO2?
40 mmHg
If venous blood pH is 7.35, what is the pCO2?
45 mmHg
Name 4 disorders in the blood
- Acidemia
- Alkalemia
- Hypocapnia
- Hypercapnia
What is acidemia?
Low pH < 7.35
What is alkalemia?
High pH > 7.35
What is hypocapnia?
Low PCO2 (< 36 mmHg)
What is hypercapnia?
High PCO2 (> 44 mmHg)
An acid releases ____ in solution. Therefore it is a H+ ____
H+; donor
Name some examples of acids
- Hydrochloric acid
- Carbonic acid
- Carboxyl groups
What is a base?
An ion or molecule that combines with protons
What are some examples of a base?
- Hydroxyl ions
- Ammonia
- Bicarbonate
- Amino groups
True or false: Maintaining a pH between 7.37 and 7.42 is essential for the human body
True
What pH range is compatible with human life?
6.8-7.8
Normal pH is essential for normal ____ function
Metabolic (such as enzyme activity, blood clotting, muscle contraction)
Metabolism produces acid which threatens to disturb ____
Body pH
What are the two types of acids in the body?
- Volatile acids
- Non-volatile acids (fixed acids)
What are examples of volatile acids?
- Carbonic acid formed from CO2
- Cellular metabolism of carbs and fats produces CO2
What are some examples of non-volatile acids (fixed acids)?
- Sulfuric acid
- Hydrochloric acid
- Phosphoric acid
Sulfuric acid is made from:
Metabolism of methionine and cysteine
Hydrochloric acid is made from:
Lysine, arginine, histidine
Phosphoric acid is made from:
Phospholipids, nucleic acids, etc.
What is acid-base balance concerned with?
Maintaining a normal H+ ion concentration in body fluids
Acid-base balance is achieved by what 3 processes?
- Buffer systems in ECF and ICF
- Respiratory mechanisms that excrete CO2
- Renal mechanisms that reabsorb HCO3- and secrete H+
True or false: the processes by which acid-base balance is achieved can correct the cause of the imbalance
False - they only compensate for an imbalance and attempt to restore blood pH to normal
Chemical buffers are on the scene in ____
Seconds
____ are always present in tissue and will handle major changes in the acid base balance
Chemical buffers
Respiratory compensation mechanism is by way of:
Retention or elimination of CO2 via lungs
The respiratory compensation mechanism works within ____
Minutes
Renal compensation mechanism regulates:
HCO3- to combat H+ losses and gains
How quick does the renal compensation mechanism work?
Slow to start and requires up to 5 hours to complete
Acids must be:
- Buffered
- Transported away from cells
- Eliminated from the body
What is a buffer?
Any substance that reversibly consumes or releases H+
A buffer is something that acts like a:
Protective cushion or shield
A ____ helps to minimize changes in pH that occurs when acid or base is added to a system
Physiological buffer
True or false: a buffer can prevent changes in pH
FALSE - they just minimize the change
What do buffers consist of?
- Weak acid with its conjugate base OR
- Weak base with its conjugate acid
When does maximum buffering occur?
When pH = pKa (means that there are equal concentrations of HA and A-)
What are 4 important physiological buffers?
- Bicarbonate
- Ammonia
- Phosphate
- Proteins
Where does bicarbonate act as a buffer?
In ECF and renal tubular filtrate
Ammonia is an important buffer for _____
Renal tubular filtrate
Where is phosphate an important buffer?
ECF and renal tubular filtrate
___ are important ICF and plasma buffers
Proteins
Why are proteins important ICF and plasma buffers?
Amino acids contain positively charged amino groups (R-NH2) and negatively charged carboxyl groups (R-COOH)
What are some examples of important protein buffers?
Hemoglobin and albumin
What are the two most important intracellular buffers?
Proteins and phosphates
The ____ is the 1st line of defense when H+ is gained or lost from the body
Bicarbonate buffering system
In the bicarbonate buffering system, the buffer is the ____ and its conjugate base is _____
Carbonic acid (H2CO3); Bicarbonate ion (HCO3-)
True or false: since carbonic acid is a weak acid, H2CO3 easily dissociates into H+ ions and HCO3- ions
True
The bicarbonate buffering system reaction is catalyzed by what enzyme?
Carbonic anhydrase (CA) enzyme
What is the bicarbonate buffering system reaction?
____ provides information regarding acid base imbalances
The dissociation equation for carbonic acid
The concentration of H2CO3 is a direct function of:
PCO2
At what concentration is [HCO3-] maintained at by renal tubular reabsorption?
~24 mM
[PCO2] and thus ____ are regulated by ____
[carbonic acid]; Alveolar ventilation
Increased Va will ____ [PCO2] and ____ [carbonic acid] in the plasma
Decrease; increase
PCO2 is maintained at _____ by alveolar ventilation
40 mmHg
What does the HH equation state?
The pH in blood is equal to a constant (pKa) plus the log ratio of HCO3- to PCO2
Bicarbonate ions and carbonic acid are present in blood in what ratio?
20:1
As long as the 20:1 ratio of HCO3- to ___ PCO2, the pH remains at ____
0.03; 7.4
Changes in [HCO3-] are termed ____
Metabolic
Changes in PCO2 are termed ____
Respiratory
True or false: nearly all proteins function as buffers
True
What is H+ buffered in RBC’s by?
Hemoglobin (H+ + Hb –> HHb)
Phosphate is present in what ionic forms?
HPO42-, H2PO4-, H3PO4
What is the most common form of phosphate?
HPO42-
Bone and teeth bind up ____ of the body’s phosphate as part of calcium phosphate salts
85%
Where else is phosphate found?
Phospholipids, ATP, nucleotides, buffers
What are the three buffering systems?
- Intracellular and extracellular buffering system
- Respiratory buffering system
- Renal buffering system
The intracellular and extracellular buffering system uses:
Bicarbonate, phosphate, protein
The respiratory buffering system uses:
Bicarbonate
The renal buffering system uses:
Bicarbonate, phosphate, ammonia
____ is the main input regulating ventilation under normal conditions
PCO2 of arterial blood
Increased PCO2 is sensed by ____. Where are they found?
Chemoreceptors; Centrally (medulla) and peripherally (carotid and aortic bodies)
Increased PCO2 triggers ____
Ventilation
What is hypoventilation?
Holding your breath
What happens during hypoventilation?
Lowers blood pH; acidosis
What does hyperventilation cause?
Lowers PCO2, increases blood pH, alkalosis
How is alkalosis remedied?
By re-breathing air from a paper bag
True or false: minor adjustments in breathing are usually sufficient to adjust the pH of the blood by changing how much CO2 is exhaled
True
Most of the HCO3- filtered by the kidneys is ____
Reabsorbed
What happens during the renal mechanism?
- the kidney generates new HCO3- to replenich HCO3- lost in buffering
- Also excretes acid equivalent to the amount of fixed acid produced each day
- this is excreted as titratable acid and ammonium
What does the kidney do if the body is too alkaline?
Kidneys can also secrete HCO3- by stimulating a-intercalated cells in the collecting ducts
Urine is typically acid because of the need to:
Eliminate acidic metabolites and retain HCO3
Since HCO3- is a very powerful and fast-acting buffer ____ is vital for the maintenance of acid-base balance
Recovery of HCO3-
What is the major site for HCO3- reabsorption?
Proximal tubule (80%)
___% of filtered HCO3- is reabsorbed
99.9%
True or false: virtually no HCO3- remains in urine
True
