Gas Transport (O2 & Co2)

Question 1

How many ATP produced from aerobic and anaerobic respiration?

Answer 1

38 ATP in O2 presence and 2 ATP from glycolysis

Question 2

Two ways O2 is transported into the bloodstream?

Answer 2

Dissolved in plasma and bound to Haemoglobin

Question 3

Explain the structure of Haemoglobin

Answer 3

Quaternary, tetramer protein composed of 4 haem groups
Haem is a porphyrin ring with ferrous Fe2+ in middle (red in colour when 4 O2 bound, purple when not)

Haemoglobin made of 4x Haem groups and 4x globin chains

Question 4

The two configurations of Hb and how this impacts O2 binding?

Answer 4

Tense = inhibits O2 binding
Relaxed = high O2 affinity, open and receptive structure

Question 5

Significance of Hb being in tense configuration? What causes this?

Answer 5

Acidity, high temperature, high Co2 and high DPG.

Inhibits O2 binding so that more O2 will be delivered to tissues in hypoxic conditions.

Question 6

Explain the dissociation curve

Answer 6

pO2 on x axis and saturation (O2Hb binding) on y axis.
Sigmoid shape, plateaus at maximal Hb binding (regardless of amount of RBCs)

Total O2 content = bound + dissolved

Question 7

What is the Bohr shift?

Answer 7

O2 binding inversely related to Co2 and affinity. Curve shifts to the right in low pH and high Co2

Question 8

What are long term physiological adaptations to chronic hypoxia?

Answer 8

Increased EPO to increase RBC production (from haematopoietic stem cells -> proerythroblasts)
Increased 2,3,-DPG
Increased capillary tissue density
Increased ventilation
= increase O2 delivery to tissues

Question 9

What are the 3 ways CO2 is transported?

Answer 9

Dissolved CO2 (reacts with H20 in plasma)
Carbamino-compounds
HCO3- (main way)

Question 10

Explain the CO2 + H20 equation

Answer 10

CO2 + H20 <> H2CO3 <> H+ + HCO3-
Carbonic anhydrase
Increase in CO2 pushes equation to the right to produce more H+
HCO3- buffers H+ and an increase pushes the equation to the left

Question 11

What’s the point of the Henderson-Hasselbalch equation?

Answer 11

Allows calculation of pH based on [HCO3-] and [CO2]

pH = pK + log10 (HCO3-/CO2)

Question 12

Explain the physiological buffering system

Answer 12

Respiratory: if body produces too much H+, it reacts with HCO3- to form CO2 which is breathed out

Renal: if pCO2 is too high the kidneys will excrete less HCO3- so concentration in plasma will increase to buffer excess H+ and restore pH

Question 13

Where is carbonic anhydrase found and how does it affect CO2 transport?

Answer 13

Found only in RBC so reaction between CO2 + H20 is more rapid there. HCO3- transported into plasma and H+ mopped up by Hb.
Slower reaction between CO2 + H20 in plasma as no enzyme there.

Question 14

How does HCO3- get into the plasma from RBC?

Answer 14

Hamburger shift: in exchange for Cl-

Question 15

How do the Bohr and Haldane effects effect one another?

Answer 15

Bohr effect at tissues: as O2 is given up to tissues in need, Hb affinity shifts from O2 to CO2 so that more O2 is deposited

Haldane effect in lungs: O2 reduces affinity for CO2 binding so CO2 offloaded in lungs to be exhaled
= facilitate gas exchange at tissues

Question 16

How is CO2 transported as a carbamino compound?

Answer 16

Reacts with protein amino groups, eg carbaminohaemoglobin which reduces affinity for O2 and shifts dissociation curve to the right

Question 17

What’s minute volume and if it’s increased in a healthy individual what parameter will increase?

Answer 17

Volume of gas inhaled/exhaled in 1 minute. If increased then pH will increase due to increased CO2 being blown off

Question 18

On what basis does O2 travel to tissues?

Answer 18

Down the ‘O2 cascade’ of differing partial pressures from atmosphere -> mitochondria in tissues

Question 19

How does Hb show cooperativity?

Answer 19

Binding of one O2 molecule to chain, the quaternary structure is modified and becomes more open making it easier for another O2 to bind
Binding becomes progressively easier as more O2 molecules bind

Question 20

What are some factors that decrease tissue oxygenation?

Answer 20

Hypovolaemia
Anaemia
Low Hb
Poor blood flow
Pulmonary disease

Question 21

What shifts O2 dissociation curve to the right and why?

Answer 21

Increased temp, pH and 2,3-DPG to reduce affinity so O2 is offloaded to tissues in need

Question 22

Where does CO2 dissolve and what does Henry’s law say?

Answer 22

Henry’s law: amount of CO2 dissolved will be proportionate to its tension

CO2 reacts with H20 in plasma and RBCs

Question 23

What’re the definitions of an acid and base

Answer 23

Acid = proton donator
Base = proton acceptor

Question 24

What’s the difference between strong and weak acids?

Answer 24

Strong acids completely dissociate in water

Weak acids only partially (reach equilibrium with conjugate base, forming a buffer pair)

Question 25

What’s the normal pH range of blood and the average pH?

Answer 25

7. 36-7.44

7. 4 average

Question 26

Why is the relationship between pH and H+ so important to regulate?

Answer 26

Because of pH scale being -log10 a 1 unit pH change is equivalent to 10 fold change in H+ ions

Question 27

What are sources of H+ in the body?

Answer 27

Volatile liquids - generated from aerobic metabolism and CO2 production in tissues, excreted via the lungs

Non-volatile liquids - generated from other metabolic processes (eg sulphuric acid) and excreted by the kidneys

Question 28

What’s the main role of CO2 in the blood?

Answer 28

Regulation of blood pH