Lecture 6a: Acid Base Balance I Flashcards
Why is Acid-Base Balance
in the Body Important? (4 points)
- Our diets contain many acids and bases; cellular catabolism of foodstuffs produces the majority of acids and bases in our bodies.
- Bases normally lost in feces; the net effect of accumulation of acid in body fluids.
- Cellular functions are sensitive to pH.
- Acid must be excreted for the normal physiological function of cells and organs.
Acids ____ H+ ions. Bases ____ H+ ions
donate, receive
____ dissociate completely or almost completely into H+ and their conjugate base.
Strong acids
____ are only slightly ionized in aqueous solution
Weak acids
What is a buffer?
A mixture of substances in an aqueous solution that can resist changes in H+ ion concentration when strong acids or bases are added.
Buffers are usually a combination of a weak acid and its conjugate base
Acidity is determined by what?
The activity of H+ ions in a solution
What is the pH scale?
A convenient way to express a wide range of acidities
pH=
-log(H+ activity)
In the body, H+ activity is equal to _________. Therfore pH= _________
- H+ concentration
- pH=-log[H+]
pH of arterial blood is normally close to?
7.40
[ ]=40 nM
What is the normal range for pH of arterial blood?
7.35 to 7.45
Under pathologic conditions, the arterial blood pH can range from ____________.
6.9 to 7.8
What is the arterial blood pH w/ Acidemia?
pH<7.35
What is the arterial blood pH w/ Alkalemia?
pH>7.45
What are the sources of Acid in the body?
- Cellular metabolism (main source)
- Accidentally Ingested Fixed Acids
- Abnormally High Fixed Acid Production (e.g. Diabetic Ketoacidosis)
What are the 5 types of cellular metabolism occuring in our body that serves as a source of acid?
1. Oxidation of glucose and fatty acids (major)
2. Oxidation of sulfur-containing amino acids
3. Oxidation of phosopholipids/phosphoprotein
4. Conversion of NH4Cl to Urea
5. Anaerobic metabolism of glucose
Cellular Metabolism
Oxidation of glucose and fatty acids (major)
- Produces?
- Removed by lungs or kidneys?
- Volatile or Fixed acid?
- Produces CO2
- CO2 removed by lungs
- Volatile Acid
Cellular Metabolism
Oxidation of sulfur-containing amino acids
- Produces?
- Removed by lungs or kidneys?
- Volatile or Fixed acid?
- Produces sulfuric acid (H2SO4)
- Removed by kidneys
- Fixed Acid
Cellular Metabolism
Oxidation of phosopholipids/phosphoproteins
- Produces?
- Removed by lungs or kidneys?
- Volatile or Fixed acid?
- Produces phosphoric acid (H3PO4)
- Removed by kidneys
- Fixed Acid
Cellular Metabolism
Conversion of NH4Cl to Urea
- Produces?
- Removed by lungs or kidneys?
- Volatile or Fixed acid?
- Produces HCl
- Removed by kidney
- Fixed Acid
Urea comes from liver
Cellular Metabolism
Anaerobic metabolism of glucose
- Produces?
- Conversion?
- Volatile or Fixed acid?
- Produces Lactic Acid
- May be converted to CO2
- Can be Volatile or Fixed
Which two organs use alot of bicarbonate?
Liver and Kidney
Liver uses bicarb + aluminum chloride to create urea
Regulation of body pH is acheives by what 3 mechanisms?
Acid-Base Balance
- Chemical Buffering (immediate)
Respiratory Compensation (fastest)
Renal Compensation (Long-term)
What does the graph below show?
- Distilled water has no buffer system and you see the pH decrease very fast wehn around 25mEq H+ were added.
- In vivo there is a buffering system so it can maintain pH and resist change in acidity
What is the Henderson-Hasselbalch
Equation?
List the 3 main important buffer system pairs and their location
- HCO3-/CO2: Plasma, Interstitial, Cells (mainly ECF)
- Protein^n-/HnProteins: RBCs, Plasma, Cell; Hemoglobin & others (ECF + ICF)
- Phosphate^n-/HnPhosphate (HPO42-/H2PO4): Intracellular (mainly ICF)
What is the first line of defense to resist change in acidity?
Fast Chemical Buffering in plasma
- Strong acid + Buffer salt -> Neutral salt + Weak acid
Review Slide 11
Explain the Isohydric Princple
- Each of the 3 major buffering systems all have different pK values each system changes concentration
- All buffer to the same pH (7.4)
What are 3 special characteristics of the
bicarbonate buffer system?
- High [HCO3-]
- [HCO3-]/CO2 = 20 : 1
- Open System: Controlled pCO2
Review Slide 13, 14 &15
What does this graph represent?
Titration Curves for the Bicarbonate
and Phosphate Buffer Systems.
- By the time you lose all the acid or base the buffer system is gone.
- That is why you see a significant pH jump on the left and most right of the graph.
- The buffer system is in the middle area and you see a gradual change in pH
What is essential for optimal physiological function of cells and organ?
Maintenance of an optimal plasma and ECF pH
What accounts for most acid production in the body?
Catabolism of dietary foodstuffs
Volatile acids result from what?
Aerobic carboyhdrate and lipid metabolism, and can be converted to gas and removed by the lungs
Fixed acids result from what?
Other metabolic processes or direct intake, cannot be removed by the lungs, and are typically removed by the kidney
____ prevents drastic changes in body fluid acidity.
Chemical Buffering
True or false: A weak acid dissociates less in solution than a strong acid
TRUE
Which is produced and excreted in greater quantity?
A. Volatile Acid
B. Fixed Acid
A. Volatile Acid
What is the normal [HCO3-]/[CO2] ratio in arterial blood?
20:1
