pH homeostasis: acid base balance Flashcards
acids are proton (H+) ____
donors
substances containing hydrogen which dissociate in a solution releasing H+
acids
some physiologically important acids that are dissolved in body fluids
- Carbonic acid (H2CO3)
- Phosphoric acid (H3PO4)
- Pyruvic acid (C3H4O3)
- Lactic acid (C3H6O3)
basses are proton (H+) ____
acceptors
molecules of capable of accepting a hydrogen ion are
bases
physiologically important bases
- Bicarbonate (HCO3- )
- Biphosphate (HPO4^2- )
acid base balance within the body is primarily concerned w what 2 ions
- Hydrogen (H+)
- Bicarbonate (HCO3-)
pH
Specifies the acidity of a solution – the “power of hydrogen”
* Logarithmic scale
* Inversely expresses hydrogen ion concentration in solutions
Water ionizes to a limited extent to form equal amounts
of H+ ions and OH- ions
* H+ ion is an acid
* OH- ion is a base
pure water
always equal numbers of hydrogen ions and OH- ions
neutral solutions pH
7
acidic pH
less than 7
basic pH
higher than 7
solution with a pH of 4 has ____ times more free protons floating around than a
solution with a pH of 5 and ____ times more free protons than a solution w pH of 6
10
100
pH range compatible w life
6.8-8.0
normal blood pH
7.35-7.45
what is more acidic: venous blood or arterial blood
venous
The overall process of aerobic respiration can be summarized as
glucose plus oxygen gives carbon dioxide, water and energy
where does acid come from
- cellular respiration: glucose + oxygen –> carbon dioxide + water + energy
- carbon dioxide diffuses out of cells into blood as bicarb
- carbonic anhydrase causes CO2 and water to from carbonic acid, which dissociates into 2 ions: hydrogen and bicarb
- acid produced as result of presence of CO2 is called volatile acid
Three mechanisms maintain the pH of extracellular fluid in an acceptable range:
- Chemical Buffers (in blood)
- React very rapidly (seconds) - Respiratory Regulation
- Reacts rapidly (minutes) - Renal Regulation
- Reacts slowly (hours)
CO2 is constantly produced and Combines with H2O in RBCs to form carbonic acid which dissociates into
H+ and HCO3-
more CO2 means
body becomes more acidic
if breathing increases
more CO2 removed, blood becomes less acidic, pH increases
if breathing decreases
less CO2 removed, blood becomes more acidic, pH decreases
how can we alter ventilation with breathing
- speed; resp rate
- depth of breathing; tidal volume
The control of breathing has to be automatic, and is part of the autonomic nervous system, why
The need to maintain levels of oxygen and
carbon dioxide, as well as keep the amount of acid in the blood within a narrow range
is constant, even during sleep.
_____ in the _____ of brain sense pH changes and Vary the rate and depth of breathing to compensate
Chemoreceptors
medulla
Excess acid is excreted by the
kidneys
Excess acid is excreted by the kidneys Mostly as
ammonia
Base (HCO3-) can be reabsorbed (indirectly) by the
kidneys
Kidneys can alter the amount of acid or base that is excreted, how long does this take
Generally takes several days (slowest way body regulates acid-base balance)
pH buffers in the blood guard against sudden changes in
acidity
pH buffers Works to minimise changes in the pH of a solution by
binding free acid or base
chloride shift
Most of the carbon dioxide molecules that diffuse into the blood from the peripheral tissues are transported to the lungs as bicarbonate. Most bicarb is produced in red blood cells, after CO2 diffuses in. Carbonic anhydrase (CA) causes carbon dioxide and water to form carbonic acid, which then dissociates into hydrogen and bicarb ions. Bicarb builds up
in the red blood cells, so there’s a greater concentration inside, than outside in the
surrounding blood plasma. So the bicarb moves down it’s concentration gradient, and
gets exchanged for another negative ion, chloride.
The chloride shift is the exchange of chloride ions for bicarb, as the bicarb moves down it’s concentration gradient. It ensures electrical neutrality.
The hydrogen ions that are produced are buffered by
haemoglobin
how does haemoglobin buffer H+
Haemoglobin can bind protons and carbon dioxide, which causes a change in shape of the protein. This facilitates the release of oxygen.
This decrease in haemoglobin’s affinity for oxygen by the binding of carbon dioxide
and acid is known as the Bohr effect – it shifts the oxygen saturation curve to the right
Bohr effect
decrease in haemoglobin’s affinity for oxygen by the binding of carbon dioxide and acid
What happens when the blood gets to the lungs?
When the blood gets to the lungs, the concentration of carbon dioxide levels in the blood decrease, as it diffuses into
the alveolus.
Carbon dioxide and protons are released from haemoglobin, increasing the oxygen affinity of the protein. Bicarb ions diffuse back into the red blood cells, reacting with hydrogen ions to form carbon dioxide and water.
Two major disturbances possible in Acid-Base balance
- Acidosis (Acidaemia)
- Alkalosis (Alkalaemia)
pH changes have dramatic effects on normal cell function such as (3)
- Changes in excitability of nerve and muscle cells
- Influences enzyme activity
- Influences K+ levels
cell excitability: Decrease in pH
- More acidic
- Depresses the central nervous system
- Can lead to loss of consciousness
cell excitability: increase in pH
- More basic
- Can cause over-excitability
- Tingling sensations, nervousness, muscle twitches
pH on enzyme activity
- Alter the shape of the enzyme
- Can make it non-functional
- Can result in accelerated or depressed metabolic actions within the cell
Acidosis and Alkalosis can arise in two fundamentally different ways:
Respiratory acidosis or alkalosis: Acidosis or alkalosis caused by faulty breathing
Metabolic acidosis or alkalosis: Acidosis or alkalosis caused by vomiting, diarrhoea, ineffective bicarbonate buffering, kidney disorders, or ingestion of acid/base
parietal cells secretion
Parietal cells secrete H+ into the lumen of the stomach. Bicarbonate ions diffuse from the parietal cells into the bloodstream, to maintain electrical neutrality in the parietal cell.
In pancreatic cells the direction of ion
movement is reversed:
H+ ions are secreted into the blood
Bicarb ions diffuse into pancreatic juice
severe diarrhea effects
- Fluids rich in HCO3 - are released and reabsorbed during
the digestive process - During diarrhoea this HCO3 - is lost from the body rather than reabsorbed
- Loss of HCO3- without corresponding loss of H+ lowers pH
- Less HCO3- is available for buffering H+
- results in metabolic acidosis
other than diarrhea, what can also result in metabolic acidosis
prolonged deep vomiting from the duodenum can also result in a metabolic acidosis.
metabolic alkalosis from vomiting
- vomitting results in Excessive loss of H+ ( as HCl)
- Bicarbonate not neutralised in the plasma
- Loss of HCl increases the plasma bicarbonate
- Results in an increase in pH of the blood
- results in metabolic alkalosis
Reaction of the body to alkalosis is to lower pH by:
- Retain CO2 by decreasing breathing rate
- Kidneys increase the retention of H+
Primary acid-base disorder
- Initial changes in PCO2 or HCO3-
Compensatory or secondary acid-base disorder
- Subsequent response
- Not strong enough to keep the pH constant
- Do not correct the acid-base derangement
- Only act to limit the change in pH that results from a primary change in PCO2 or HCO3-
normal pH in presence of an acid-base disorder always signifies
Mixed respiratory and metabolic acid base disorder
PCO2
partial pressure of CO2 in blood
High PCO2
respiratory acidosis
low PCO2
respiratory alkalosis
respiratory component of arterial blood gas
metabolic component of arterial blood gas
PCO2
bicarb
low bicarb
metabolic acidosis
high bicarb
metabolic alkalosis
What are the 2 variables that can be controlled in respiration, to regulate the pH of the blood?
Respiratory frequency; Tidal Volume
Which of the following is NOT a mechanism which contributes to maintaining the pH of extracellular fluid within an acceptable range?
A.
Renal regulation
B.
Cardiac regulation
C.
Respiratory regulation
D.
Chemical buffers in blood
B. Cardiac regulation
Which ion is exchanged for bicarbonate ions, to maintain the electrical neutrality of red blood cells?
Cl−
Which of the following statements regarding acid-base balance in the body is INCORRECT?
A.
Aerobic respiration in cells produces carbon dioxide, which diffuses out of the cell, into the blood, and into red blood cells. In the presence of carbonic anhydrase, it reacts with water to form carbonic acid, which dissociates into hydrogen ions and bicarbonate. This increases the amount of acid in the venous blood, decreasing the pH.
B.
In the lungs, carbon dioxide is removed from the body via respiration. This increases the amount of acid in the blood, decreasing the pH.
C.
Venous blood is more acidic than arterial blood
D.
The normal pH of blood is 7.35–7.45
In the lungs, carbon dioxide is removed from the body via respiration. This increases the amount of acid in the blood, decreasing the pH.
A blood gas sample is taken from a vomiting dog. Results show that the patient has a blood pH of 7.65 (normal is 7.35–7.45), and a bicarbonate concentration of 30 meq/L (normal is 24 meq/L). What type of acid-base disorder does this dog have?
Metabolic alkalosis
(recall bicarb is metabolic, PCO2 is resp, and then just use logic, high bicarb means more base means alkalosis)
