Acid-Base Balance

indicator of the acidity or basicity of a solution. Measure of the hydrogen ion concentration.
pH ranges
0-14. pH<7.0 is acidic, pH>7.0 is basic, pH=7.0 is neutral.
Normal Blood pH
7.35-7.45 values slightly above or below this range may be compatible with life, but can lead to serious acidosis or alkalosis.
Effects of Altered pH in the blood
Enzymes can become destructive or not function properly, oxygen delivery can be severely compromised, organ systems can become compromised, food digestion and absorbtion can be affected.
(academia) high hydrogen ion concentration. Blood pH <7.35.
(alkalemia) low hydrogen ion concentration. Blood pH >7.45.
Plasma Total CO2 (TCO2)
estimate of the sum of bicarbonate (HCO3), carbonic acid (H2CO3), and dissolved CO2.  Venous blood can be used, performed with urea and electrolytes tests.
Oxygen (PO2)
measures the partial pressure of oxygen in the blood and how well oxygen is able to move from the lungs into the blood.
Carbon Dioxide (PCO2)
MEasures gaseous carbon dioxide in the blood, and how well carbon dioxide can exit the body.  Indicates whether a respiratory problem exists.  Low PCO2 indicates hyperventilation.  High PCO2 indicates hypoventilation.
OXygen Saturation Point (SO2)
measure of the capacity of oxygen transport.  percentage of hemoglobing binding sites in the bloodstream occupied by oxygen (oxyhemoglobin)
Henderson-Hasselbach Equation
pH=pKa + log[HCO3]/[H2CO3]
represents the contribution of pH from the kidneys.
represents the contribution of pH from the lungs.
What is the ratio of (HCO3)/(H2CO3) in healthy individuals?
Ka & pKa

Ka represents the concentrations of ions that dissociate when an acid is placed in solution. It is known as the “dissociation constant.”

pKa is the negative log of the “dissociation constant”

Solutions of weak acids or bases and their associated salts.  Resists changes in pH by reacting with an acid or base.
Weak Acid
substance that separates less readily into ions.  gives up H+ ions with difficulty.  forms conjugated bases with the loss of hydrogen ions.
Weak Base
Substance that has the slight affinity to gain hydrogen ions.  form conjugate acids with the additon of hydrogen ions.
How does a buffer work with a STRONG acid?
hydrogen ions of the strong acid will react with the conjugate base of the buffer system, reducing the concentration of hydrogen ions by making a weak acid.
How does a buffer work with a STRONG base?
hydroxide (OH-) ions of the base react with the weak acid of the buffer system, reducing OH ions by making water and the conjugate base of the weak acid.
Acid-Base Balance
amount of acid or base produced and absorbed equals the amount of acid or base excreted and expired.
What are the 4 acid-base balance systems?

Intracellular Buffers (inside all cells)

Extracellular Buffers (Blood, urine, CSF)

Respiratory MEchanisms (Lungs)

REnal Mechanisms (Kidneys)

Extracellular Buffers
React very rapidly (Within seconds) with the lungs.  Include; Bicarbonate-Carbonic Acid, Proteins, Phosphate.
Intracellular Buffers
Found in all cells of body.  Bicarbonate-Carbonic Acid, Hemoglobin, Proteins, Phosphate.
Bicarbonate-Carbonic Acid (HCO3/H2CO3)
main buffer of plasma.  Regualted by the lungs (changes with ventalation and CO2 excretion). Regulated by the kidneys (reabsorbtion of Bicarb, and excretion of hydrogen ions). Works by using hydrogen ions to react with bicarb to from carbonic acid.
Main buffer systems inside the RBC. Hb binds either Carbon dioxide or hydrogen ions produced from cell metabolism to minimize pH changes in the body.
CO2 + Hb <---> HbCO2 (Carboxyhemogobin)
one of the main bufers inside the cells and plasma.  Made up of a series of amino acids that have side groups, which are either positive or negative charge.  NEgative amino acids can bind hydroen ions to minimize pH change.
Phosphate (HPO42-/H2PO4) Buffer
Buufer of extracellular fluid, Intracellular fluid and the kidneys.  Composed of Monohydrogen Phosphate (weak base, H+ acceptor) and Dihydrogenphosphate (Conjugate acid, H+ donor.).
Internal Respiration
cells/tissues.  production of faseous CO2 from the metabolism and the diffusion of this CO2 into plasma and RBCS for transport to the lungs.
External Respiration
lungs.  Diffusion of gaseous CO2 from plasma and the RBCs to the alveoli for excretion.
the rate of the air exhcange between the lungs, O2 inhaled and CO2 exhaled.
PArtial Pressure
the force exerted by a single gas that is present in a mixture of several gases.
How do respiratory mechanisms aid in acid-base balance?
chemosensitive areas of the brain stem detect changes in PCO2 or Hydrogen ion concentration, these changes become a potent stimulator of respiration.  The respiratory center responds by either increasing or decreasing ventilation.
increased ventilation, faster and deeper breathing, decreases CO2 and H+ in the extracellular fluid.
decreased ventilation, slower and shallow breathing, increases CO2 and H+ in extracellular fluid.

Explain Internal Respiration

(only until the CO2 diffuses into the RBC)

1) O2 is consumed, CO2 is produced in the cell, this increases PC02 in cells.

2) This increase in PCO2 in the cells causes the diffusion of gaseous CO2 out of the cells into the interstitial fluid, raising the PCO2 of the interstitial fluid.

3) The increase in interestitial PCO2 causes the diffusion of CO2 into the plasma.

4) As plasma PCO2 increases 89% of CO2 diffuses into the red blood cell, the other 11% remains as 1% bound to amino groups, 5% converted to Bicarb, 5% converted to carbonic acid.

After CO2 is diffused into the RBCs what happens?

of the 89%:

5% is dissolved gaseous CO2.

21% of gaseous CO2 is bound to the globin portion of Hb

63% reacts with water to form Carbonic acid.

Most of the Carbon Dioxide is transported to the lungs in plasma as bicarbonate ions.

Describe External Respiration

The 89% of CO2 in the red blood cell travel to the alveoli. 

5% of this is exhaled, 21% comes from carbinohemoglobinm and 63% comes from plasma bicarbonate, and when in the lungs, the chloride shift causes the diffusion of bicarb back into the RBC, Bicarb reacts with H+ to form carbonic acid which dissociates to water and CO2, which is hten exhaled.

Chloride Shift
the simulataneous exchange of chloride ions into the RBC for bicarbonate ions out of the red blood cell.
What percent of O2 is dissolved in plasma?  What happens to it?
1.5%.  IT diffuses out of the capillaries and into the cells/tissues.
What percent of blood oxygen is bound to Hb, and how?
98.5% There are four iron-heme sites in each Hb molecule and each iron atom can bind one oxygen molecule.
What is the total amount of oxygen in 1L of arterial blood?  How is it dispersed?
200mL.  Approximately 3 mL is dissolved in plasma (this is the form that is measured for PCO2), 197 mL is bound to Hb inside the RBC.
What is the primary from of O2 transport?
What is the PO2 in the lungs, what happens when it reaches this?
105 mm Hg, more oxyhemoglobin is formed.
PO2 in blood vessels?  Corresponds with?
95 mm Hg, with a 97% oxygen saturation in a normal healthy person.
PO2 of interstitual flyid?  What happens?
40mm Hg, faciliates diffusion of O2 from plasma into cells, O2 will be released from Hb to meet cellular needs.
PO2 of the cells?  What happened?
5-40mm Hg, cells consume about 25-35% of the normal oxygen in blood.
What affects PO2?
Increased blood flow to the tissue.
What factors affect oxygen binding to Hb?
Bohr effect, Temperature, 2,3 DPG
Properties of the Renal Mechanisms in Acid-Base Balance
reacts slowly to changes in pH, and lasts longer than other mechanism. helps maintain the pH of urine between 4.5 to 8.0. Exrete acids as Hydrogen ions, and base as bicarb.
Hydrogen ion excretion in urine
Hydrogen ions are neutralized by other buffer systesm found in urine: Bicarb-carbonic acid, ammonia-ammonium, phosphate, urate, and citrate.
Reabsorbtion of Bicarb back into the blood
Gaseous CO2 diffueses from blood and urine into the renal tubular cells and forms carbonic acid. Bicarb is formed from the dissociation of Carbonic acid and reabsorbed into the plasma along with Na+ ions.
Ammonia-Ammonium Buffer
Accounts for 60% excretion of hydrogen from acids in the from of Ammonium ion. Bicarb is formed from the degradation of glutamine along with ammoniums. Bicarm is reabsorbed into the plasma, and the ammonium is buffered in the urine.
SErum Electrolytes
Routine test, used to screen or monitor electrolyte or acid-base imbalaces (ordered along with ABG). Measures key electrolytes (Na, Cl, K, HCO3) Bicarb is reported as tCO2
Anion Gap
direct measure of the concetration of unmeasured acid anions. difference between the measure cations and the measured anions. Increase indicates metabolic acidosis.
Arterial Blood Gases
measures acid-base balance and oxygenation status in the blood. Evaluates gas exchange in the lungs by measure pH, PCO2, PO2, SO2. Should be analyzed immediately or stored on ice water and analyzed within 1 hour.
Why are ABGs not performed frequently?
Painful procedure, preanalytical erros.
Base Excess (base deficit)
Measures all buffers in the blood. the deviation of all blood buffers in a patient sample. calculates the amount of acid or base that would have to be addd to the blood to bring it to normal pH. Negative or Positive. NEgative indicates acidosis, positive value indicates alkalosis. Affected by blood lactate and organic acids.
Clinical Significance of Acidosis
Increased acid production from metabolism, decreased acid excretion, increased excretion of base. Occurs when pH<7.35
Alkalosis causes
Decreased excretion of base, excess excretion of acids. Occurs when pH>7.35
Respiratory Acidosis Findings
Excess carbon dioxide retention. pH<7.35, PCO2>40mm HG, HCO3->24mEq/L
Respiratory Acidosis Causes
CNS depression from drugs, injury or disease, Asphyxia, Hypoventilation.
REspiratory Alkalosis Findings
Excess CO2 excretion. pH>7.45, PCO2<40mm Hg, HCO3-<24mEg/L.
Respiratory Alkalosis Causes
Hyperventilation, Respiratory stumylation, gram-negative bacterial infections.
Metabolic Acidosis Findings
Kidneys increase excretion of bicarbonate.<24mEq/L
CAsues retention of acids in the blood pH<7.35 and PCO2 <40mm Hg
MEtabolic Acidosis Causes
Bicarbonate depleteion due to renal disease, excessive production of organic acids, endocrine disorders.
Metabolic Alkalosis Findings
Kidneys decrease excretion of bicarbonate>25mEq/L.
CAuses excretion of acids from the blood. pH>7.45 and PCO2 >40mm Hg
MEtabolic Alkalosis Causes
Excessive excreiton of acids due to renal disease, loss of gastric hydrochloric acid, Loss of potassium, excessive alkali ingestions.
Lactic Acidosis
Most common type of metabolic acidosis. Excess production or diminish removal of lactic acid.
Type A Lactic Acidosis
caused by inadequate Oxygen delivery, caused by shock, cardiac arrest, severe anemia, carbon monoxide, and hypoxia.
Type B Lactic acidosis
adequate O2 delivery, caused by epileptic seizures, cyanide poisoning, strokes, uncontroleed diabetes mellitus and liver failure.

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