Physiology of Acid-Base Balance Flashcards
What organs are the main contributors to acid-base balance?
Kidney, lungs, natural/biological buffers
come back to 1st slide
What is acid-base balance?
The maintenance of the constancy of the physiologic range of acid-base status of the body
the regulation of the pH of the body fluids towards maintaining a normal range of acid-base status for a given animal species
The physiologic adjustments of the hydrogen ionh concentration of the extracellular fluids towards its physiologic limits for optimum physiological activities
What is pH?
The level of hydrogen ions (H+) available in a solution
What is the smallest ionic particle in biological systems?
a hydrogen ion
(single, very reactive, proton)
(shows severe effects on the physiological activities of the body even in low concentrations)
An increase in H+ concentration means:
a decrease in pH and the condition is said to be acidic
A decrease in H+ concentration means:
an increase in pH and the condition is said to be basic
What are the normal pH levels in dogs?
7.35-7.45 (same as cat)
What are the normal pH levels in cats?
7.35-7.45 (same as dog)
What are the normal pH levels in horses?
7.32-7.44
What is the normal pH of mammalian arterial blood?
7.36-7.44
What is the average mammalian arterial blood pH?
7.4
What does a pH lower than normal cause?
acidosis
What does a pH higher than normal cause?
alkalosis
What is caused by low O2 partial pressure levels?
hypoxemia
blood oxygen levels are lower than normal, which can leading to hypoxia
What is caused by high O2 partial pressure levels?
oxygen toxicity
What is caused by low bicarbonate (HCO3) levels?
metabolic acidosis
What is caused by high bicarbonate (HCO3) levels?
metabolic alkalosis
What are normal bicarbonate levels in dogs?
18-24 mEq/L
What are normal bicarbonate levels in cats?
18-24 mEq/L
What are normal partial pressure of CO2 levels in dogs?
30-40 mmHg (millimeters of mercury)
What are normal partial pressure of CO2 levels in cats?
30-40 mmHg
What are normal partial pressure of O2 levels in dogs?
85-110 mmHg
What are normal partial pressure of O2 levels in cats?
90-110 mmHg
The pH of body fluids is easily disturbed by an addition of small amounts of:
A strong acid or base
What is caused by CO2 partial pressure levels above normal?
respiratory acidosis
What is caused by CO2 partial pressure levels below normal?
respiratory alkalosis
What are normal partial pressure of CO2 levels in cats and dogs?
30-40 mmHg
Respiratory changes are defined by _______.
changes of arterial PCO2 (partial pressure of carbon dioxide)
What are metabolic changes?
changes of arterial bicarbonate ions that are not attributed to a change in PCO2 (partial pressure of carbon dioxide)
slide 7
What are acids?
substances that donate hydrogen ions (protons) to a solution
What are bases?
substances that accept and bind hydrogen ions (protons) from a solution
When is acid-base balance in ECF disrupted?
When acids or bases are added to or removed from the body fluids
What is acidemia?
A depression of blood pH to a value below the normal range
What is alkalemia?
An increase in blood pH to a value above the normal range
The addition of excess acid or removal of base from the ECF causes:
acidosis
The addition of excess base or removal of acid from the ECF causes?
alkalosis
What are the main sources of body acids and bases?
- ingestion in food (Protein diet= more acid, plant diet= more bases)
- cellular metabolism
- gain or loss of acids and bases during disease conditions (insufficient respiratory ventilation, vomiting, diarrhea, renal insufficiency)
During the metabolism of feeds of plant origin, what forms in the bloodstream?
large amounts of base, in the form of bicarbonate
Where is bicarbonate usually excreted?
in urine (this explains why the urine of herbivores is usually alkaline)
Which type(s) of animal excrete alkaline urine?
Ruminants, equids, and other herbivores
Which type(s) of animal excrete acidic urine?
Dogs, cats, and other carnivores
What are the 3 main mechanisms the body uses for the regulation of acid-base status?
- Acid-base buffer system (compounds)
- Respiratory mechanism (Lungs)
- renal mechanism (Kidney)
What is a buffer?
A compound that has the capacity to regulate the availability of reactive hydrogen in a system
(can react with hydrogen or release hydrogen)
What is an acid-base buffer system?
The combination of a weak acid (protonated compound) and a weak base- the salt (unprotonated compound)
When a strong acid is added, it reacts with the ______.
weak base
When a strong base is added, it reacts with the _____.
weak acid
In an acid-base buffer system, either the weak acid or base helps prevent pH changes by reacting when either a _______ or _____ is present.
strong acid; strong base
What are the 3 important types of buffer systems?
- Bicarbonate buffer system (main buffering system in ECF)
- Phosphate buffer system (intracellular)
- Protein buffer system (plasma and Hemoglobin)
What is the weak acid component in the bicarbonate buffer system?
(Carbonic acid) H2CO3
What is the weak base component in the bicarbonate buffer system?
(bicarbonate) HCO3-
What is the weak acid component in the phosphate buffer system?
dihydrogen phosphate (H2PO4), in the form of sodium dihydrogen phosphate (NaH2PO4)
What is the weak base component in the phosphate buffer system?
hydrogen phosphate (HPO4), in the form of disodium hydrogen phosphate (Na2HPO4)
The weak acid component of a buffer easily ___ hydrogen, while the weak base component easily ___ hydrogen.
releases; accepts
If the pH is low, HCO3 can ____ H+.
Pick up -> H2CO3
If the pH is high, HCO3 can ____ H+.
Release -> H+ + HCO3
What are the elements of proteins that form the 3 weak (amino) acids in plasma?
- C-terminal carboxyl group, N-terminal amino group, and side chain amino group of glutamic acid
- Side chain amino group of lysine
- Imidazole group of histidine
What is the second most important blood buffer and most important and effective protein buffer?
Hemoglobin
Why does hemoglobin have about 6x more buffering capacity than the plasma proteins?
It is in higher concentration than plasma proteins (?)
How is excess CO2 removed from the body?
hyperventilation
What makes a buffer poor?
The pKa of the buffer is far away from the desired pH to establish. The pKa of the buffer should be very close to the intended pH to restore
The bicarbonate buffer system plays the most important role in maintaining the pH of ________. Why?
body fluids
- all the components of the system (HCO3 and H2CO3) are well separately regulated by the renal and respiratory systems respectively.
How do the lungs contribute to the buffer mechanism?
CO2 builds up hypoventilation- respiratory acidosis
the extent to which ventilation maintains normal CO2 partial pressure
The kidney manages the concentrations of ____ & _____ in the blood.
H+ and HCO3
How does the kidney maintain the acid-base balance of the body?
By the secretion of H+ ions and the retention of HCO3. This is accompanied by sodium reabsorption
Acidemia and hypercapnia (high CO2) result in what in the kidney?
increased H+ secretion
Alkalemia and hypocapnia (low CO2) result in what in the kidney?
decresead H+ secretion
What does a high pH (alkalosis) do in the kidney?
It depresses hydrogen ion secretion into the tubular lumen.
What does a low pH (acidosis) do in the kidney?
It increases the rate of hydrogen ion secretion into the tubular lumen.
comeback to slide 27 with table
How does Acidosis affect potassium?
H+ secretion is increased and goes into the urine while K is moved out of the cells (potassium is retained in plasma)
potassium shifts from inside the cell to outside
can lead to hyperkalemia
How does Alkalosis affect potassium?
H+ secretion is decreased in cells and retained, leading to lower K levels (hypokalemia)
increased potassium excretion
