Setrics Tracker

Pages

Acid-Base Homeostasis – outline notes

By at October 11, 2011 | 7:53 am | Print

Acid – Base imbalance will affect all systems inclusing cardiovascular system (heart) and nervous system.

I. Acids and Bases

A. Acids – release H+ (proton donors)
-Strong acids – completely dissociate in water
HCl —-> H+ + Cl-
-Weak acids – do not completely dissociate in water
H2CO3 <—-> H+ + HCO3-

B. Bases – accept H+ (proton acceptors)
– HCO3- (bicarbonate ion) acts as a base because it accepts H+

C. Buffers – resist changes in pH by releasing H+ when solution is challenged by
a base and binds H+ when solution is challenged by an acid

Example:       Carbonic Acid – Bicarbonate buffer system
CO2 + H2O <—-> H2CO3 <—-> H+ + HCO3-

D. pH = -log [H+]  or  pH = log 1 / [H+]
– increase [H+] —–increase acidity —- decrease pH
– increase PCO2 —decrease pH
– increase HCO3- — increase pH

E. pH scale
– ranges 0 to 14
– pH = 7 is neutral
– >7 is basic
– <7 is acidic

II. Physiological Abnormalities of Acid-Base Balance
-Normal pH range = 7.35 – 7.45
Acidosis – pH < 7.35
Alkalosis – pH > 7.45
-absolute limits –
-low of 7.0 (depresses CNS; coma and death)
-high of 7.8 (overexites CNS; muscle tetany, extreme nervousness,
convulsions, respiratory arrest)

III. Classes of Acidosis and Alkalosis

A. Respiratory – pH imbalance due to failure of respiratory system to
perform its normal pH balancing role.
*Normal range — Pco2 = 35 – 45 mm Hg

B. Metabolic – pH imbalance due to all abnormalities of acid-base
imbalance except those caused by CO2 in blood.(Kidneys / Renal)
*Normal range — HCO3- = 22 – 26 mEq/L

Four Major Classes

1. Respiratory acidosis
-Possible causes
-anything impairing gas exchange or lung ventilation (emphysema,
cystic fibrosis)
-depress respiratory center (overdose of barbiturate)
-shallow breathing
-pH < 7.35
-PCO2 > 45 mm Hg

2. Respiratory alkalosis
-Possible causes
-hyperventilation in asthma, pneumonia, anxiety
-pH > 7.45
-PCO2 < 35 mm Hg

3. Metabolic acidosis
-Possible causes
-severe diarrhea – loss of bicarbonates
-renal disease – failure of kidneys to rid body of metabolic acids
-diabetes mellitus – ketoacidosis
-starvation – acidic metabolites are formed as body proteins and fat
reserves are used for energy
-excess alcohol ingestion – results in excess acids in blood
-high ECF [K+] – K+ is secreted at kidneys instead of H+
-pH < 7.35
-HCO3- < 22 mEq/L

4. Metabolic alkalosis
-Possible causes
-vomiting – loss of HCl
-diuretics – cause low K+ – stimulates tubule cells of kidneys to
secrete H+
-ingestion excess antacids (NaHCO3 )  –increases HCO3- in ECF
-constipation – prolonged retention of feces results in increased
amounts of HCO3- to be reabsorbed
-pH > 7.45
-HCO3- > 26 mEq/L

 

IV. Respiratory and Renal Compensations
-when one system (respiratory or kidneys) is failing the other will attempt
compensation

V. Rules to determine acidosis/alkalosis, respiratory/metabolic, compensation

A. Note the pH
-greater than 7.45 = alkalosis
-less than 7.35 = acidosis

B. Check the PCO2
-Example
—-If the pH indicates acidosis and
1. the PCO2 is over 45 mm Hg = Respiratory acidosis
2. the PCO2 is below 35 mm Hg = Metabolic acidosis with
respiratory compensation
3. the PCO2 is 35-45 mm Hg = Metabolic acidosis with no
respiratory compensation

C. Check HCO3-
-In the example above (2 and 3), since the respiratory system is not the
cause of the acidosis, the cause must be metabolic; reflecting a decreased HCO3- level (below 22 mEq/L)

 

Physiology outline notes

Related Posts

Trackbacks For This Post

  1. […] electrolytes are electronically charged particles. They conduct electric current, help keep our pH in balance, and are involved with how fluids pass in and out of cells. They help regulate the neuromuscular, […]

One Comment


Post Your Comments