Week 10 - Flashcards
Daltons law
The pressure of gas mixture is equal to the sum of the pressures of the individual gases
How to work out partial pressure of atmospheric gases
Atmospheric pressure x composition of air in atmosphere
Sum of these values would equal the atmospheric pressure
What is different about the partial pressure of gases in the respiratory system?
You have to take water vapour into account
Air in the lungs is fully saturates with water vapour. It is 46mmHg at 37 degrees
If the total pressure is 760mmHg, water vapour is 46mmHg and the presence of nitrogen is 78.1%, oxygen is 20.9% and co2 is 0.033%, work out the partial pressure for each compartment
N2: (760 - 46) x 78.1% = 558mmHg
O2: (760 - 46) x 20.9% = 149 mmHg
co2: (760 - 46) x 0.033% = 0.24 mmHg
Ficks law of diffusion
Rate of diffusion is proportional to the Area/thickness x (P1 x P2) x D
Area is usually very large and thickness is small
D = a constant
Gas molecules move between air and liquid in order to achieve equilibrium of partial pressures. Movements of molecules depend on:
Temperature
Pressure difference
Solubility
At equilibrium, what happens to the pressure and concentration of oxygen and carbon dioxide
At equilibrium, po2 in air and water is equal. However, low o2 solubility means that concentrations are not equal
Co2 is more soluble, so the conc of co2 would be greater in o2 in solution
What affects the rate of diffusion
Impairment of diffusion due to blood/gas barrier thickening or lower partial pressure of inspired oxygen (altitude, disease) can affect arterial content of oxygen and limit functional capacity
Emphysema
Destroys structure of alveolar sacs
Causes limited surface area and poor elastic recoil
Fibrotic lung disease
Causes stiff lungs and hard to inflate
Pulmonary oedema
Causes by pressure changes in capillaries
Asthma
Poor ventilation of alveoli due to constricton of airways
Calculating metabolic rate requires knowledge of
how much oxygen the body consumes and how much carbon dioxide it produces at any given time
The ability to measure oxygen consumption and carbon dioxide production requires the knowledge of
the inspired and expired volumes of these gase
How to work out oxygen consumption
volume of inspired o2 - volume of expired o2
How to work out the volume of inspired/expired o2
volume of inspired/expired air x percentage of inspired/expired o2
How to work out carbon dioxide production
Expired co2 - inspired co2(usually very small as there is little co2 in atmosphere) = co2 production
How to work out volume of expired/inspired co2
volume of expired/inspired air x percentage of expired/inspired co2
What does the law of mass action state
When a reaction is at equilibrium, the ratio of the substrates and products will remain constant
Hb + o2 –> Hbo2 (formation of oxyhaemoglobin)
What happens if you add more oxygen
Reaction shifts to the right
More oxyhaemoglobin forms
What is haemoglobin
It is an oxygen binding protein contained within the red blood cells
Each molecule contains 4 globins and 4 haem groups. In the centre of each haem group is a ferrous atom (fe2+) that binds oxygen
How is o2 transported from the lungs
O2 arrives at the alveoli and diffuses down the partial pressure gradient into the plasma
Greater o2 content in plasma promotes greater diffusion of in rbc, which combines with haemoglobin to produce oxyhaemoglobin.
Hbo2 transported to cells, oxyhaemoglobin dissociates into Hb and O2. O2 is then dissolved in plasma, meaning it can be used in cellular respiration.
Anaemia
A condition where you lack enough healthy red blood cells to carry adequate oxygen to your body’s tissues
There are less binding sites for oxygen to bind to haemoglobin
How much oxygen gives 50% saturation of haemoglobin
28 mmHg
When the oxyhaemoglobin dissociation curve shifts to the left, what happens
Increased affinity for oxygen
Haemoglobin more readily accepts oxygen
What is the bohr shift
Curve shifts to the right
Haemoglobin has decreased affinity for oxygen
What causes a rightward shift of the oxyhaemoglobin curve
Increased acidity (decreased pH)
Increased blood co2
Increased DPG
Increased temperature
______ of all co2 is carried in the form of bicarbonate ions (hco3-)
70%
Formation of hco3 - equation
co2 + h2o –> h2co3 –> H+ + hco3-
_____ of all co2 that is carried binds to haemoglobin
23%
Formation of carbaminohaemoglobin equation
Hb + co2 –> Hbco2
What else does haemoglobin do?
They bind the hydrogen ions that are released from the reaction of co2 and h20 to form hco3-
What part of the respiratory group is associated with inspiration
The dorsal respiratory group
What part of the respiratory group is associated with inspiration
The dorsal respiratory group
Breathing can be altered voluntarily
Hyperventilation
Breath holding
Speaking, swallowing
Stretch receptors and the hering breuer reflex
Stretch receptors are activated when tidal volume approaches the physical limitations of the lung tissue for expansion.
This mechanism, called the hering breur reflex, protects the lungs from over inflating
What do peripheral chemoreceptors do
Where are they located
They detect changes in arterial blood oxygen
Located in the carotid and aortic bodies
What do central chemoreceptors do
They detect changes in carbon dioxide through changes in concentration of Hydrogen ions and changes in the pH of the cerebrospinal fluid
What stimulates peripheral chemoreceptors
The partial pressure of oxygen not the content of oxygen
