Lecture 3: Acid Base Physiology

Question 0

Why is regulation of pH pivotal ?

Answer 0

To maintain adequate cellular function

Question 1

What must there be a balance between to achieve homeostasis? Acid base physiology

Answer 1

Intake or production of H+/HCO3- and net removal of H+/HCO3- from the body

Question 2

How is the H+ concentration kept in the composition of body fluids, compared to other ions?

Answer 2

At a low level

The concentration of sodium in ecf is 3.5million times as great as the concentration of H+

Question 3

What is the concentration of H+ in ecf?

Answer 3

Averages 0.00004mEq/L

Question 4

What is a hydrogen ion?

Answer 4

Single free proton released from a hydrogen atom

Question 5

What are acids referred as ?

Answer 5

Molecules containing hydrogen ions that can release hydrogen ions in solutions

Question 6

What is a base?

Answer 6

An ion or molecule that can accept H+

Question 7

Why can proteins in the body also function as bases?

Answer 7

Because some of the amino acids that make up proteins have negative charges and can readily accept H+

Question 8

What is a strong acid?

Answer 8

Rapidly dissociates and releases especially large amounts of H+ in solution

Question 9

What is a weak base?

Answer 9

Ones that are less likely to dissociate their ions and therefore release H+ with less vigour

Question 10

What is the difference between alkali and base?

Answer 10

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-

Question 11

What is alkalosis?

Answer 11

Excess removal of H+ from body fluids

Question 12

What is acidosis?

Answer 12

Excess addition of H+ to bodily fluids

Question 13

What is the normal pH of arterial blood?

Answer 13

7.4

Question 14

What is the normal pH of venous blood and interstitial fluids? Why is this different?

Answer 14

7.35, because extra amounts of CO2 have been released to form H2CO3 in these fluids

Question 15

What are the three primary systems which regulate H+ concentration in the body to prevent acidosis and alkalosis?

Answer 15

1. Chemical acid base buffer systems of body fluids
2. Respiratory centre
3. The kidneys

Question 16

How do the chemical acid base buffer systems regulate pH?

Answer 16

They immediately combine with acid or be to prevent excessive changes in H+ concentraaitons

Question 17

How does the respiratory centre regulate pH?

Answer 17

The respiratory centre regulates the removal of CO2, and therefore H2CO3 from the ECF

Question 18

How do the kidneys regulate pH?

Answer 18

They excrete either acid or alkaline urine, thereby readjusting the ECF fluid H+ concentration

Question 19

Which system is the first to react?

Answer 19

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

Question 20

What is the second defence? What does it do?

Answer 20

Respiratory system acts within a few minutes to eliminate Co2 and therefo H2CO3 from the body

Question 21

What is the third line of defence?

Answer 21

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

Question 22

What are the three different buffer systems

Answer 22

Bicarbonate buffer system

Phosphate buffer system

Proteins as important intracellular buffers

Question 23

Describe the bicarbonate buffer system

Answer 23

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.

Question 24

Describe the phosphate buffer system

Answer 24

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

Question 25

Describe the role of proteins as buffers

Answer 25

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

Question 26

Describe how the respiratory control regulates acid balance

Answer 26

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

Question 27

What are the three mechanisms kidneys use to regulate acid base balance

Answer 27

1) secretion of H+
2) reabosorption of HCO3-
3) production of new HCO3-

Question 28

How is H+ secreted?

Answer 28

By secondary active transport in the early tubular segments

Question 29

Why is the kidney regulation of acid base complicated?

Answer 29

Kidneys need to ensure H+ in the body is balanced without excreting bicarbonates as that would alter the buffer system concentrations

Question 30

Describe the kidney regulation

Answer 30

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