Gas Transport (O2 & Co2) Flashcards
How many ATP produced from aerobic and anaerobic respiration?
38 ATP in O2 presence and 2 ATP from glycolysis
Two ways O2 is transported into the bloodstream?
Dissolved in plasma and bound to Haemoglobin
Explain the structure of Haemoglobin
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
The two configurations of Hb and how this impacts O2 binding?
Tense = inhibits O2 binding Relaxed = high O2 affinity, open and receptive structure
Significance of Hb being in tense configuration? What causes this?
Acidity, high temperature, high Co2 and high DPG.
Inhibits O2 binding so that more O2 will be delivered to tissues in hypoxic conditions.
Explain the dissociation curve
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
What is the Bohr shift?
O2 binding inversely related to Co2 and affinity. Curve shifts to the right in low pH and high Co2
What are long term physiological adaptations to chronic hypoxia?
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
What are the 3 ways CO2 is transported?
Dissolved CO2 (reacts with H20 in plasma)
Carbamino-compounds
HCO3- (main way)
Explain the CO2 + H20 equation
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
What’s the point of the Henderson-Hasselbalch equation?
Allows calculation of pH based on [HCO3-] and [CO2]
pH = pK + log10 (HCO3-/CO2)
Explain the physiological buffering system
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
Where is carbonic anhydrase found and how does it affect CO2 transport?
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.
How does HCO3- get into the plasma from RBC?
Hamburger shift: in exchange for Cl-
How do the Bohr and Haldane effects effect one another?
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
How is CO2 transported as a carbamino compound?
Reacts with protein amino groups, eg carbaminohaemoglobin which reduces affinity for O2 and shifts dissociation curve to the right
What’s minute volume and if it’s increased in a healthy individual what parameter will increase?
Volume of gas inhaled/exhaled in 1 minute. If increased then pH will increase due to increased CO2 being blown off
On what basis does O2 travel to tissues?
Down the ‘O2 cascade’ of differing partial pressures from atmosphere -> mitochondria in tissues
How does Hb show cooperativity?
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
What are some factors that decrease tissue oxygenation?
Hypovolaemia Anaemia Low Hb Poor blood flow Pulmonary disease
What shifts O2 dissociation curve to the right and why?
Increased temp, pH and 2,3-DPG to reduce affinity so O2 is offloaded to tissues in need
Where does CO2 dissolve and what does Henry’s law say?
Henry’s law: amount of CO2 dissolved will be proportionate to its tension
CO2 reacts with H20 in plasma and RBCs
What’re the definitions of an acid and base
Acid = proton donator Base = proton acceptor
What’s the difference between strong and weak acids?
Strong acids completely dissociate in water
Weak acids only partially (reach equilibrium with conjugate base, forming a buffer pair)
What’s the normal pH range of blood and the average pH?
- 36-7.44
7. 4 average
Why is the relationship between pH and H+ so important to regulate?
Because of pH scale being -log10 a 1 unit pH change is equivalent to 10 fold change in H+ ions
What are sources of H+ in the body?
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
What’s the main role of CO2 in the blood?
Regulation of blood pH
