Homeostasis
-Acid - base balance by Respiratory
and Circulatory system
Vibuntita Chankitisakul, D.V.M., Ph.D.
Endocrine
hormones
H20 & electrolytes (Na+, K+, Cl-)
Biochemical reaction
A-------------- -> B
CO2
NH3
enzyme
pH
Temperature
oxygen
Glucose & others
nutrients
In case of pH imbalance..
• proteins are denatured and digested,
• enzymes lose their ability to function,
• death may occur.
What is acid-base balance?
• Refers to the difference in quantity between
input and output of acids and bases
• Balance depends on regulate of free hydrogen
ions (H+)
• Acidosis
– Caused by accumulation of acids or by loss of
bases
– Release H+ into solution
• Alkalosis
– Occurs when bases accumulate or acids are lost
– Remove H+ from solution
Sources of acid in the body
• Consumer or Metabolism
1) Volatile acids: CO2 -> removed by Lungs
2) Nonvolatile acids: derived from sources other than
CO2
• Metabolic products of sulfur & phosphorus containing
compounds (H2SO4, HCl, HPO42-) -> complete metabolize of
– Lactic acid -> incomplete metabolize of CHO
– Keto acids -> incomplete metabolize of lipid
• Removed by Kidneys
protein
Metabolism of food
1.
VFA
Non-VFA
2.
Regulation of acid-base balance
1. Respiratory system
2. Renal excretion
3. Body fluid buffers; Chemical systems
1. Buffer system
• A solution containing substances that have the
ability to minimize changes in the pH when an acid
or base is added to it.
• HCO3Most important!!
• Phosphate
• Proteins
• Hemoglobin
1. Buffer system
H2SO4 + 2NaHCO3
Na2SO4 + 2CO2 + H2O
HCl + NaHCO3
NaCl + CO2 + H2O
Kidney
Hb –
buffer in
plasma
2. Respiratory system
1. Respiratory system = controlled by central chemoreceptors
in the medulla (brain)
pH, pCO2
1. Respiratory system = controlled by central chemoreceptors
in the medulla (brain)
In case of pCO2
pH = base
= hypoventilation
to increase the pCO2,
carbon dioxide is retained.
conversely, to decrease the pCO2, ventilation is increased
= hyperventilation
3. Renal excretion = (1) bicarbonate reabsorption & (2)H+
excretion
(1) bicarbonate reabsorption
Segmental HCO3reabsorption by
each segment of
the nephron
rapidly
Cellular
mechanism for
proximal tubule
H and HCO3
transport. CA,
carbonic
anhydrase.
• Metabolic disturbance
• Respiratory disturbance
– Metabolic acidosis
– Metabolic alkalosis
– Respiratory acidosis
– Respiratory alkalosis
pH changed by HCO3
pH changed by pCO2
Metc acidosis = diarrhea, renal failure Resp acidosis = pulmonary edema, brain center is
inhibited
Met alkalosis = vomit
Resp alkalosis = hyperventilation
Compensatory response
• Metabolic disturbance
• Respiratory disturbance
• Respiratory
compensation and
buffer system
• Renal compensation
and buffer system