Gas Transport Flashcards
what is gas diffusion
movement of gas throughout the respiratory system occurs via diffusion
what are some anatomical and physiological properties that facilitate gas diffusion
- large surface area for gas exchange
- large partial pressure gradients
- gases with advantageous diffusion properties
- specialised mechanisms for transporting oxygen and carbon dioxide between lungs and tissues
what is total pressure
the sum of the partial pressures or tensions of a gas
what is the barometric pressure at sea level
760 mmHg
what is Pgas
partial pressure of a gas
what is Fgas
fraction of a gas
what does partial pressure equal
Fgas in gas mixture times by barometric pressure
what are the two forms of oxygen being carried in the blood
dissolved
bound to haemoglobin
describe how dissolved oxygen is measured
clinically in an arterial blood sample
how much of oxygen in the blood is dissolved
only a small percentage
what is the amount of oxygen dissoved in the blood proportional to
partial pressure
how many ml of oxygen per 100ml of blood for each mmHg of PO2
0.003
how many litres of oxygen in the blood when the arterial blood has a partial pressure of 100mmHg
3ml
is the transport of oxygen in the dissolved form adequate for the body’s requirements
no
what is the typical partial pressure of oxygen in the blood for healthy individuals
100mmHg
which artery is usually used to provide a sample for calculating partial pressure
radial
what does the amount of oxygen dissolved in the blood determine
the partial pressure of oxygen in the blood
what is the minimum tissue requirement of oxygen at rest
250ml of oxygen a minute
how many litres of blood per minute at rest cardiac output
5 litres
what are the tissue requirements for oxygen during strenuous exercise
3000 ml oxygen per minute
what is haemoglobin
major transport molecule for oxygen found in red blood cells
describe the structure of haemoglobin
four heme groups joined to globin proteins.
two alpha and two beta chains
what is heme
iron porphyrin compound
what is found in each heme group
iron in reduced ferrous form Fe+++
what is the site of oxygen binding in haemoglobin
each ferrous molecule in the heme groups
how many haemoglobin molecules per red blood cells
280 million
why is it necessary that the binding and dissociation of oxygen from haemoglobin happens in milliseconds
the red blood cells are only in capillaries for one second
what does the oxyhemoglobin dissociation curve show
the relationship between partial pressure of oxygen in the blood and the number of oxygen molecules bound to haemoglobin
describe what you see
the line is a sigmoid curve. big clinical significance of this shape.
flat portion - in a normal healthy individual when the partial pressure of oxygen is 100mmHg, almost up to 100% of haemoglobin molecules are saturated. this means the blood is well oxygenated.
steep portion - partial pressure is dropping, but the haemoglobin saturation is stable. this does not change until the gradient of 60mmHg. when the partial pressure drops below this, there is fast dissociation of oxygen from haemoglobin to get more oxygen into the blood to oxygenate the tissues.
how many oxygen molecules can bind to each haemoglobin molecules
four
what does oxygen saturation refer to
the amount of oxygen bound to haemoglobin relative to maximal amount that can be bound
how many ml of oxygen combines with a gram of haemglobin
1.39
how many grams of haemoglobin per litre of blood
150g
what is the average total oxygen capacity
211ml/s of oxygen per litre of blood
what are used to measure oxygen saturation
pulse oximeters
how do pulse oximeters work
they measure the ratio of absorption of red and infrared light by oxyHb and deoxyHb
how many molecules of carbon dioxide are expired for every 100 molecules of oxygen by the lungs of a healthy person
80
what is the respiratory exchange ratio
the ratio of expired carbon dioxide to oxygen uptake
what is the respiratory exchange ratio in normal conditions
0.8
what are the three forms that carbon dioxide travels the blood in
dissolved
bound to haemoglobin
converted to bicarbonate
how mcuh carbon dioxide in the blood is dissolved
7%
how much carbon dioxide in the blood is bound to haemoglobin
23%
how much carbon dioxide in the blood is converted to bicarbonate
70%
how much carbon dioxide is diffused into red blood cells
93%
describe the reaction of carbon dioxide converting to bicarbonate
H2Co3 - carbonic acid
HCO3- - bicarbonate
what determines the speed of bicarbonate production
concentration gradients
what happens to carbon dioxide in systemic capillaries
rightward reaction to form bicarbonate from carbon dioxide. the carbon dioxide is expelled into the blood
what happens to carbon dioxide in pulmonary capillaries
leftward reaction to form carbon dioxide from bicarbonate. the carbon dioxide is expelled into the alveoli
what does the carbon dioxide to bicarbonate pathway have a key role in
regulation of hydrogen ions and in maintaining acid base balance in the body
what can stabilise blood pH
changes in bicarbonate concentrations
what makes the buffering reaction strong in the blood
high bicarbonate concentration
what can regulate the acidity of the blood
ventilation to adjust the partial pressure of carbon dioxide OR using the kidneys to regulate the bicarbonate concentration
what is the shape of the oxygen dissociation curve
sigmoid curve
does partial pressure of oxygen have much of an impact on haemoglobin saturation
no
what is the enzyme that converts carbon dioxide to carbonic acid
carbonic anhydrase
what are some obstructive lung disease
emphysema
asthma
what are some restrictive lung diseases
pulmonary fibrosis
neuromuscular diseases
what is the percentage saturation of haemoglobin when PO2 is 10mmHg
10%
what is the percentage saturation of haemoglobin when PO2 is 20mmHg
35%
what is the percentage saturation of haemoglobin when PO2 is 30mmHg
60%
what is the percentage saturation of haemoglobin when PO2 is 40mmHg
75%
what is the percentage saturation of haemoglobin when PO2 is 50mmHg
80%
what is the percentage saturation of haemoglobin when PO2 is 60mmHg
90%
what is the percentage saturation of haemoglobin when PO2 is 70mmHg
90%
what is the percentage saturation of haemoglobin when PO2 is 80mmHg+
98%