Lecture 3: Acid Base Physiology Flashcards
Why is regulation of pH pivotal ?
To maintain adequate cellular function
What must there be a balance between to achieve homeostasis? Acid base physiology
Intake or production of H+/HCO3- and net removal of H+/HCO3- from the body
How is the H+ concentration kept in the composition of body fluids, compared to other ions?
At a low level
The concentration of sodium in ecf is 3.5million times as great as the concentration of H+
What is the concentration of H+ in ecf?
Averages 0.00004mEq/L
What is a hydrogen ion?
Single free proton released from a hydrogen atom
What are acids referred as ?
Molecules containing hydrogen ions that can release hydrogen ions in solutions
What is a base?
An ion or molecule that can accept H+
Why can proteins in the body also function as bases?
Because some of the amino acids that make up proteins have negative charges and can readily accept H+
What is a strong acid?
Rapidly dissociates and releases especially large amounts of H+ in solution
What is a weak base?
Ones that are less likely to dissociate their ions and therefore release H+ with less vigour
What is the difference between alkali and base?
They are often used synonymously.
Alkali is a molecule formed by the combination of one or more of the alkaline metals, Na, K, Li etc
They have a highly basic ion OH-
What is alkalosis?
Excess removal of H+ from body fluids
What is acidosis?
Excess addition of H+ to bodily fluids
What is the normal pH of arterial blood?
7.4
What is the normal pH of venous blood and interstitial fluids? Why is this different?
7.35, because extra amounts of CO2 have been released to form H2CO3 in these fluids
What are the three primary systems which regulate H+ concentration in the body to prevent acidosis and alkalosis?
- Chemical acid base buffer systems of body fluids
- Respiratory centre
- The kidneys
How do the chemical acid base buffer systems regulate pH?
They immediately combine with acid or be to prevent excessive changes in H+ concentraaitons
How does the respiratory centre regulate pH?
The respiratory centre regulates the removal of CO2, and therefore H2CO3 from the ECF
How do the kidneys regulate pH?
They excrete either acid or alkaline urine, thereby readjusting the ECF fluid H+ concentration
Which system is the first to react?
The buffer systems react within seconds to minimise changes in H+ concentrations.
Buffer systems don’t eliminate H+ from or add them to the body’s but keeps them tied up until balance can be reestablished
What is the second defence? What does it do?
Respiratory system acts within a few minutes to eliminate Co2 and therefo H2CO3 from the body
What is the third line of defence?
The kidneys can eliminate excess acid or be reform the body.
Kidneys are relatively slow to respond over a period of hours to several days, however they are the most powerful
What are the three different buffer systems
Bicarbonate buffer system
Phosphate buffer system
Proteins as important intracellular buffers
Describe the bicarbonate buffer system
HCO3- and CO2
Not a Powerful buffer system as ECF pH is about 7.4 and pK of buffer is 6.1 allowing 20x as much bicarbonate buffer system in the form of HCO3- as in the form of CO2 - not equal concentrations?
System operates on the portion of the buffering curve where slope is low and buffering power is poor.
Concentrations of the two elements of the bicarbonate system are not great.
Describe the phosphate buffer system
H2PO4- and HPO42-
An especially important system in the tubular fluids of kidneys as
1) phosphate usually greatly concentrated in these tubules, increasing buffering power of the system
2) tubular fluid usually considerably lower pH than ECF, bringing operating range of buffer closer to pK of 6.8
Describe the role of proteins as buffers
Approx 60-70% of total chemical buffering of body fluids is inside cells. Most of this from intracellular proteins.
Except RBC, the slow movement of H+ and HCO3- into cell membranes delays several hours the max ability of intracellular rote ins to buffer extracellular acid base abnormalities
Describe how the respiratory control regulates acid balance
Increasing ventilation eliminates CO2 from ECF and reduces H+ concentration - hyperventilation as a result of acidosis
Hypo ventilation will occur if alkalosis occurs and body needs to increase H+ levels, slower breathing will restore CO2 levels, and thus, H+ levels
What are the three mechanisms kidneys use to regulate acid base balance
1) secretion of H+
2) reabosorption of HCO3-
3) production of new HCO3-
How is H+ secreted?
By secondary active transport in the early tubular segments
Why is the kidney regulation of acid base complicated?
Kidneys need to ensure H+ in the body is balanced without excreting bicarbonates as that would alter the buffer system concentrations
Describe the kidney regulation
Kidneys have a different environment so the H+ separates from the H2CO3 to form H+ + HCO3-
In alkalosis there is a low H+
Kidneys will not reabsorb all filtered HCO3-
This increases excretion of bicarbonate which raises H+ as bicarbonate is a buffer for H+
In acidosis
Kidneys don’t excrete HCO3- in urine, but reabsorbs HCO3- but it first combines with H+ to form H2CO3
This is added to ECF and H+ concentration will decrease as it is secreted out.
For each bicarbonate reabsorbed an H+ is secreted
