Transport Of Gases Flashcards
What is blood plasma?
Contains digested food products like glucose, amino acids, hormones , antibodies as well as distributing heat around the body
Summarise leucocytes (white blood cells)
Divided into two groups of immune cells
1) granulocytes - have granular cytoplasm and lobed nuclei . Their function is to engulf pathogens by phagocytosis.
2) Agranulocytes - produce antibodies and antitoxins , have a clear cytoplasm and spherical nucleus
What are thrombocytes (platelets)
Involved in blood clotting
Summarise erythrocytes
Filled with haemoglobin and have three important features to allow effective transport of gas
1) bioncave disc - large surface area so more o2 can diffuse across the membrane
2) no nucleus - more room for haemoglobin so more o2 can be transported
3) flexible- so they can fit through very narrow lumen of capillary
Summarise haemoglobin
-Complex globular protein
-Quaternary structure with four polypeptide chains
- centre of each polypeptide chain is a haem group (contains fe2+) each haem is a binding site for one oxygen
- one molecule of haemoglobin is able to bind to four molecules of o2 to form oxyhaemoglobin
- held by ionic , hydrogen bonds disulphide bridges and hydrophobic interactions
Reaction between o2 and haemoglobin
Haemoglobin + O2 ——> oxyhaemoglobin
Hb + 4O2——> Hb4 (o2)
What is affinity?
The degree to which one molecule (Hb) is chemically attracted to another molecule
(O2)
What is saturation ?
Percentage of o2 bound to Hb
What is association / loading
The uptake of o2 by Hb to form oxyhaemoglobin at lungs
What is dissociation? Unloading
Release of o2 at the respiring tissues to form Hb
Summarise the transport of O2
O2 conc is measured using partial pressure
When O2 partial pressure = high (lungs) Hb has a high affinity for O2 so O2 dissociates with Hb to form oxyhaemoglobin
Higher percent saturation
When O2 partial pressure = low (respiring tissues) Hb has low affinity for O2 so O2 dissociates from oxyhaemoglobin , forming haemoglobin
Lower percent saturation
Summarise the O2 dissociation curve
Shows the uptake of O2 by Hb at different partial pressures of O2
Haemoglobin line is sigmoidal
Describe the general trend in a o2 dissociation curve
At a very low ppoz, it is difficult for haemoglobin to load oxygen. In respiring tissues, the ppo, is low because oxygen is being used up in aerobic respiration. The oxygen then unloads from oxyhemoglobin (dissociates).
Oxygen affinity decreases as the ppo, decreases.
This means that it is readily released to meet respiratory demands.
As seen on the graph, la very small reduction in the ppOz leads to oxygen unloading (dissociating) from oxyhaemoglobin rapidly.
Haemoglobin’s affinity for oxygen is high at high partial pressures of oxygen Haemoglobin loads oxygen (associates) in the lungs, where the oxygen partia pressure (ppOz) is high.
The haemoglobin becomes saturated with oxygen, and forms oxyhemoglobin.
Oxygen is transported in this form to respiring tissues, such as muscles.
What is a pulse oximeter used for?
Estimates the oxygen saturation in your blood
By sending infrared light into capillaries in your finger
Why is the o2 saturation of Hb only 98/99% and not 100%?
Some o2 doesn’t collide and so associates with the fourth iron ion of Hb
Rate of blood flow through pulmonary capillaries still too fast for all oxygen to diffuse into blood
Some o2 is used by the respiring cells of the alveoli
Summarise the foetal haemoglobin curve
Foetal haemoglobin has an oxygen dissociation curve shifted to the left of the adult curve.
This means it has a higher affinity for oxygen and therefore can load oxygen from the mother’s blood at all partial pressures of oxygen.
Why doesn’t a baby retain its foetal haemoglobin once its born
Foetal Hb has higher O2 affinity and so not enough O2 would be unloaded to respiring tissues of a baby
If female when having own children, the adult needs its haemoglobin to have lower affinity than foetal Hb
Summarise llama and lugworm Hb
Llamas live at high altitude. With an increase in altitude, there is a drop in atmospheric pressure and therefore a reduction in the partial pressure of oxygen (kPa).
To compensate for this, a llama’s haemoglobin has a higher affinity for oxygen and therefore picks up oxygen more readily at the lungs. The curve is shifted to the left.
They have a lot of red blood cells to make more Hb so more O2 can be loaded and transported
Lugworms
live in burrows in the sand on the seashore. They absorb oxygen from the seawater they pump through their burrows.
In order to cope with the low oxygen concentration of seawater they have a dissociation curve shifted to the left - higher affinity for oxygen - so the haemoglobin more readily takes up oxygen.
Summarise the o2 dissociation curve for myoglobin
Myoglobin is a tertiary structured protein and is more stable than Hb
Acts as o2 store in muscle tissues and prevents the onset of anaerobic respiration .
Curve shifts far to left - has a much higher affinity for O2 so can unload O2 at very low partial pressures
At every partial pressure of O2 myoglobin has a higher % O2 saturation than Hb
Why at low partial pressures do we have low saturation of O2
Cooperative binding
One O2 binds to iron ion of the first polypeptide which changes its tertiary structure of second sub unit
This makes it more accessible to the next O2 and so on
Summarise the Bohr effect
When the partial pressure of carbon dioxide is high (due to carbon dioxide production in respiring tissues, e.g. contracting muscle) the conditions inside the red blood cells become more acidic.
This causes haemoglobin to change shape slightly and so haemoglobin now has a lower affinity for oxygen, unloading this oxygen to the respiring tissues more readily.
S shaped curve shifted to RIGHT
The higher the CO2 conc the lower the affinity of Hb for O2 at all partial pressures
The lower the % saturation becomes the more O2 is being loaded to respiring tissues
Summarise the chloride shift
CO2 from respiring cells diffuses into plasma and then red blood cells
CO2 reacts with water to produce carbonic acid (H2Co3) - the enzyme used to catalyse this is carbonic anhydrase
Carbonic anhydrase dissociates into H+ and HCo3- (hydrogen carbonate) ions .
The HCo3- ions diffuse into plasma
They combine with Na+ ions to form sodium hydrogen carbonate
In red blood cells there is an accumulation of H+ ions which causes a fall in PH so cytoplasm becomes more acidic
Alters haemoglobin and reduced affinity for O2 .
H+ combine with Hb to form Haemoglobinic acid this releases oxygen
The released O2 diffuses out of red blood cells and into respiring tissues
Movement of negatively charged HCO3- ions out of red blood cell is balanced by movement of chloride ions into red blood cells by facilitated diffusion . This maintains electrochemical neutrality and is known as the chloride shift
10% of CO2 binds to haemoglobin and is transported as carbamino haemoglobin
5% of co2 dissolves in blood plasma
85% of co2 is carried in blood and converted into hydrogen carbonate ions and transported in plasma.
What is the link between transport of CO2 and Bohr effect
The formation of carbonic acid and subsequent fall in pH inside the red blood cells explains the Bohr effect.
The high concentration of CO2 produced by actively respiring tissues reduces the affinity of haemoglobin for oxygen and therefore enables cells requiring more oxygen to obtain it by promoting the dissociation of oxygen from oxyhaemoglobin in the red blood cells.
The more carbon dioxide produced, the more acidic the conditions will be and so more oxygen will dissociate from the oxyhemoglobin.
High co2= ph drops = lower affinity at same ppto2 value
Exchange of materials in capillaries
Capillaries are
Thin and have permeable walls
Large surface area for exchange of materials
Blood flows slowly through capillaries allowing time for exchange of materials
Fluid is forced out of the fenestrations in endothelium which becomes tissue fluid
Venous end of capillary network has low oxygen partial pressures but high carbon dioxide partial pressures
Arteriole end of capillary has high oxygen partial pressure but low carbon dioxide partial pressure
