Download Role of buffers in hydrogen ion homeostasis &amp

Role of buffers in hydrogen ion homeostasis &
Respiratory control of acid base balance
ACID BASE HOMEOSTASIS
• Acid-Base homeostasis involves chemical and
physiologic processes responsible for the maintenance
of the acidity of body fluids at levels that allow optimal
function of the whole individual
• The chemical processes represent the first line of defense to an acid
or base load and include the extracellular and intracellular buffers
• The physiologic processes modulate acid-base composition by
changes in cellular metabolism and by adaptive responses in the
excretion of volatile acids by the lungs and fixed acids by the kidneys
ACID BASE HOMEOSTASIS
• The need for the existence of multiple mechanisms involved in AcidBase regulation stems from the critical importance of the hydrogen
ion (H+) concentration on the operation of many cellular enzymes and
function of vital organs, most prominently the brain and the heart
ACID BASE HOMEOSTASIS
• The task imposed on the mechanisms that maintain Acid-Base
homeostasis is large
– Metabolic pathways are continuously consuming or producing H+
– The daily load of waste products for excretion in the form of
volatile and fixed acids is substantial
EFFECTS OF pH
• The most general effect of pH changes are on enzyme function
– Also affect excitability of nerve and muscle cells
ACID-BASE BALANCE
• Acid - Base balance is primarily concerned with two ions:
– Hydrogen (H+)
– Bicarbonate (HCO3- )
• Derangements of hydrogen and bicarbonate concentrations in body
fluids are common in disease processes
H+ ion has special significance because of the
narrow ranges that it must be maintained in order
to be compatible with living systems
• Primarily controlled by regulation of H+ ions in the body fluids
– Especially extracellular fluids
ACID-BASE REGULATION
ACID-BASE REGULATION
• Maintenance of an acceptable pH range in the extracellular fluids is
accomplished by three mechanisms:
– 1) Chemical Buffers
• React very rapidly
(less than a second)
– 2) Respiratory Regulation
• Reacts rapidly (seconds to minutes)
– 3) Renal Regulation
• Reacts slowly (minutes to hours)
• Chemical Buffers
– The body uses pH buffers in the blood to guard against sudden changes in
acidity
– A pH buffer works chemically to minimize changes in the pH of a solution
• Respiratory Regulation
– Carbon dioxide is an important by-product of metabolism and is constantly
produced by cells
– The blood carries carbon dioxide to the lungs where it is exhaled
• Respiratory Regulation
– When breathing is increased,
the blood carbon dioxide level
decreases and the blood
becomes more Base
– When breathing is decreased,
the blood carbon dioxide level
increases and the blood becomes more Acidic
– By adjusting the speed and depth of breathing, the respiratory control
centers and lungs are able to regulate the blood pH minute by minute
• Kidney Regulation
– Excess acid is excreted by the kidneys, largely in the form of ammonia
– The kidneys have some ability to alter the amount of acid or base that is
excreted, but this generally takes several days
ACID-BASE REGULATION
• Enzymes, hormones and ion distribution are all affected by Hydrogen
ion concentrations
ACIDS
• Acids can be defined as a proton (H+) donor
•
Hydrogen containing substances which dissociate in solution to
release H+
• Acids can be defined as a proton (H+) donor
•
Hydrogen containing substances which dissociate in solution to
release H+
ACIDS
• Acids can be defined as a proton (H+) donor
•
Hydrogen containing substances which dissociate in solution to
release H+
•
Many other substance (carbohydrates) also contain hydrogen but
they are not classified as acids because the hydrogen is tightly bound
within their molecular structure and it is never liberated as free H+
• Physiologically important acids include:
– Carbonic acid (H2CO3)
– Phosphoric acid (H3PO4)
– Pyruvic acid (C3H4O3)
– Lactic acid (C3H6O3)
• These acids are dissolved in body fluids
BASES
• Bases can be defined as:
– A proton (H+) acceptor
– Molecules capable of accepting a hydrogen ion (OH-)
• Bases can be defined as:
– A proton (H+) acceptor
– Molecules capable of accepting a hydrogen ion (OH-)
• Bases can be defined as:
– A proton (H+) acceptor
– Molecules capable of accepting a hydrogen ion (OH-)
• Physiologically important bases include:
– Bicarbonate (HCO3- )
– Biphosphate (HPO4-2 )
pH SCALE
• pH refers to Potential Hydrogen
• Expresses hydrogen ion concentration in water solutions
• Water ionizes to a limited extent to form equal amounts of H+ ions
and OH- ions
–
H2O
H+ + OH-
• H+ ion is an acid
• OH- ion is a base
•
•
•
•
H+ ion is an acid
OH- ion is a base
H+ ion is an acid
OH- ion is a base
• Pure water is Neutral
– ( H+ = OH- )
• pH = 7
• A c id
– ( H+ > OH- )
• pH < 7
• Base
– ( H+ < OH- )
• pH > 7
• Normal blood pH is 7.35 - 7.45
• pH range compatible with life is 6.8 - 8.0
• pH equals the logarithm (log) to the base 10 of the reciprocal of the
hydrogen ion (H+) concentration
• H+ concentration in extracellular fluid (ECF)
• Low pH values = high H+ concentrations
– H+ concentration in denominator of formula
• Unit changes in pH represent a tenfold change in H+ concentrations
– Nature of logarithms
• pH = 4 is more acidic than pH = 6
• pH = 4 has 10 times more free H+ concentration than pH = 5 and 100
times more free H+ concentration than pH = 6
pH SCALE
pH SCALE
ACIDOSIS / ALKALOSIS
References
• Acid Base Balance, Advanced Physiology By Terry Wiseth,
Instructor, Northland College
• Harpers Biochemistry, water & pH: Chapter 2. pp 6-13
THANKS