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Respiratory physiology > Transport of oxygen > Flashcards

Transport of oxygen Flashcards

1
Q

what is dalton’s law of partial pressure?

A
  • each gas in a mixture of gases exerts a pressure that is proportional to its concentration and is independent of the other gases present
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2
Q

how is the partial pressure of oxygen calculated?

A
  • 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
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3
Q

why do we need to measure water vapour pressure?

A
  • as when dry air is inhaled, the air gets in direct contact with water molcules in the respiratory tract
  • the value is 47mmHg
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4
Q

what does the total amount of oxygen in solution depend on?

A
  • the** solubility of oxygen** in solution
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5
Q

what is henry’s law?

A
  • 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
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6
Q

How is oxygen transferred from alveoli to tissues?

A
  • via passive diffusion
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7
Q

How is fick’s law related to oxygen transport?

A
  • 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
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8
Q

In what** 2 forms **is oxygen transported in the blood?

A
  1. dissolved in physical solution
  2. bound to haemoglobin
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9
Q

how much oxygen (in ml of O2) is transported in dissolved solution per 100ml of blood?

A
  • 0.3ml of O2/100ml of blood
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10
Q

Describe the structure of haemoglobin

A
  • 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
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11
Q

what does each of the haem groups in haemoglobin contain?

A
  • porphyrin ring and a ferrous atom (Fe++) which can bind reversibly with one oxygen
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12
Q

what are the** two types of confirmations** of haemoglobin?

A
  1. 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
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13
Q

what are the 3 types of haemoglobin?

A
  1. haemoglobin A (Hb A) - normal adult
    2. haemoglobin F (Hb F) - foetal
  2. haemoglobin S - (Hb S) - sickle cell anaemia
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14
Q

what % of oxygen is transported via dissolved solution vs haemoglobin?

A
  • dissolved solution - 3%
  • haemoglobin - 97%
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15
Q

Describe the oxygen haemoglobin dissociation curve

A
  • a curve that plots the proportion of haemoglobin that is bound to oxygen (oxyhaemoglobin) vs the partial pressure of oxygen
  • sigmoidal shape
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16
Q

why does the oxygen dissociation curve have a sigmoidal shape?

A
  • 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
17
Q

what does a right vs left shift in the oxygen dissociation curve indicate?

A
  • 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
18
Q

what** factors** can affect the oxygen dissociation curve?

A
  • PH
  • CO2
  • temperature
  • organic phosphates eg 2,3 DPG
19
Q

Compare how each factor causes either a right or left shift

A

* 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

20
Q

why does a decrease in PH cause the HB-O2 curve to shift to the right?

A

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

21
Q

In what** 2 ways** does CO2 effect the curve?

A
  1. the accumulation of CO2 causes carbamino compounds to be generated - which bind to oxygen and form carbaminohaemoglobin
    * carbaminohaemoglobin stabilises deoxyhaemoglobin in the T state
  2. the accumulation of CO2** also causes an increase in the [H+] concentration** and therefore decreases the PH - which** shifts the curve to right**
22
Q

Describe the effect that an increase in temperature has on the curve?

A
  • increasing the temperature denatures the bonds between oxygen and haemoglobin, which increases the amount of oxygen and haemoglobin and **decreases the concentration of oxyhaemoglobin **
23
Q

what promotes** tissue O2 unloading**?

A
  • increased PO2
  • increased H+
  • increased temperature

these conditions are illustrated by exercising muscle

24
Q

How does carbon monoxide interfere with O2 transport?

A
  • 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
25
Q

what is** oxygen capacity**?

A
  • the max amount of oxygen that can be combined with Hb
  • 20.8ml O2/ 100ml blood
26
Q

what is oxygen saturation?

A
  • percentage of available binding sites that have oxygen attached
27
Q

what is the oxygen saturation calculation?

A

(O2 combined with Hb/ O2 capacity) x 100

28
Q

what is moderate anaemia?

A
  • reduced Hb concentration to 10g/100ml of blood
29
Q

what is severe anaemia?

A
  • Hb concentration of 5g/100ml of blood

Respiratory physiology (17 decks)

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