Transport of oxygen Flashcards
what is dalton’s law of partial pressure?
- each gas in a mixture of gases exerts a pressure that is proportional to its concentration and is independent of the other gases present
how is the partial pressure of oxygen calculated?
- PO2= Patm x Fo2
- where Fo2 is the fraction of oxygen in the atmosphere and patm is 760mmHg
- therefore PO2 = 760 x 021 = 159.6mmHg
why do we need to measure water vapour pressure?
- as when dry air is inhaled, the air gets in direct contact with water molcules in the respiratory tract
- the value is 47mmHg
what does the total amount of oxygen in solution depend on?
- the** solubility of oxygen** in solution
what is henry’s law?
- henrys law states that the amount of gas dissolved in a solution is directly proportional to the partial pressure of the gas in the solution
- ie conc of gas = S.P gas
How is oxygen transferred from alveoli to tissues?
- via passive diffusion
How is fick’s law related to oxygen transport?
- according to ficks law the rate of gas transfer across a tissue or plasma membrane is directly proportional to the** difference in partial pressure**s of the gas on the 2 sides of the membrane
- the rate of gas transfer is also proportional to the membranes diffusing capacity
- the membrane’s diffusing capacity is dependent on the solubility of the gas, membrane area and thickness & molecular weight
In what** 2 forms **is oxygen transported in the blood?
- dissolved in physical solution
- bound to haemoglobin
how much oxygen (in ml of O2) is transported in dissolved solution per 100ml of blood?
- 0.3ml of O2/100ml of blood
Describe the structure of haemoglobin
- a tetramer consisting of 4 polypeptide chains - 2 alpha and 2 beta chains
- there are 4 haem groups, each bound to an alpha or beta
what does each of the haem groups in haemoglobin contain?
- porphyrin ring and a ferrous atom (Fe++) which can bind reversibly with one oxygen
what are the** two types of confirmations** of haemoglobin?
-
tense confirmation (T)- when oxygen is not bound to haemoglobin - the globin chains are tighly bound and have a low affinity for oxygen
2. relaxed confirmation - the **binding of oxygen breaks these bonds **and exposes the remaining binding sites
what are the 3 types of haemoglobin?
-
haemoglobin A (Hb A) - normal adult
2. haemoglobin F (Hb F) - foetal - haemoglobin S - (Hb S) - sickle cell anaemia
what % of oxygen is transported via dissolved solution vs haemoglobin?
- dissolved solution - 3%
- haemoglobin - 97%
Describe the oxygen haemoglobin dissociation curve
- a curve that plots the proportion of haemoglobin that is bound to oxygen (oxyhaemoglobin) vs the partial pressure of oxygen
- sigmoidal shape
why does the oxygen dissociation curve have a sigmoidal shape?
- the curve is sigmoidal because of the co-operative binding of oxygen to the 4 polypeptide chains
- co operative binding means that haemoglobin has a greater affinity to bind oxygen after a subunit is already bound - ie Hb has the most affinity for oxygen when 3/4 of its chains are bound
what does a right vs left shift in the oxygen dissociation curve indicate?
- a right shift indicates decreased oxygen affinity of haemoglobin, allowing more oxygen to be available to the tissues
- a left shift indicates increased oxygen affinity of haemoglobin (ie Hb binds more tightly to O2), allowing less oxygen to be available for the tissues - as Hb is unable to unload oxygen
what** factors** can affect the oxygen dissociation curve?
- PH
- CO2
- temperature
- organic phosphates eg 2,3 DPG
Compare how each factor causes either a right or left shift
* decrease in PH shifts the curve to the right, while an** increase in PH shifts it the left
* a decrease in CO2 shifts the curve to the left while an increase in CO2 shifts the curve to the right
* a decrease in temp **shifts the curve to the left and an increase shifts curve to the right
* an increase in** 2,3 DPG** shifts the curve to the right while a decrease shifts the curve to the left
why does a decrease in PH cause the HB-O2 curve to shift to the right?
this occurs as a higher H+ ion concentration causes an alteration in amino acid residues that stabilises deoxyhaemoglobin in a state ( the T state) that has a lower affinity for oxygen - the BOHR effect
In what** 2 ways** does CO2 effect the curve?
- the accumulation of CO2 causes carbamino compounds to be generated - which bind to oxygen and form carbaminohaemoglobin
* carbaminohaemoglobin stabilises deoxyhaemoglobin in the T state - the accumulation of CO2** also causes an increase in the [H+] concentration** and therefore decreases the PH - which** shifts the curve to right**
Describe the effect that an increase in temperature has on the curve?
- increasing the temperature denatures the bonds between oxygen and haemoglobin, which increases the amount of oxygen and haemoglobin and **decreases the concentration of oxyhaemoglobin **
what promotes** tissue O2 unloading**?
- increased PO2
- increased H+
- increased temperature
these conditions are illustrated by exercising muscle
How does carbon monoxide interfere with O2 transport?
- carbon monoxide binds to haemoglobin to form carboxyhaemoglobin (COHb)
- CO has a 240x greater affinity to Hb than oxygen
* it prevents O2 binding to Hb
what is** oxygen capacity**?
- the max amount of oxygen that can be combined with Hb
- 20.8ml O2/ 100ml blood
what is oxygen saturation?
- percentage of available binding sites that have oxygen attached
what is the oxygen saturation calculation?
(O2 combined with Hb/ O2 capacity) x 100
what is moderate anaemia?
- reduced Hb concentration to 10g/100ml of blood
what is severe anaemia?
- Hb concentration of 5g/100ml of blood
