Lecture 12 - Gas Exchange and Transport within Blood Flashcards
what is responsible for the exchange of O2 and CO2?
- partial pressure (high to low pressure)
where does CO2 and O2 gas exchange occur?
- alveoli and pulmonary capillaries (alveolar-arterial interface)
- tissue and tissue capillaries (arterial-myocyte interface)
what is the range of PO2 concentration in venous blood?
- 40-50 mmHg
what is the range of PCO2 concentration in venous blood?
- 45-50 mmHg
what is the range of PO2 concentration in arterial blood?
- 90-105 mmHg
what is the range of PCO2 concentration in arterial blood?
- 38-42 mmHg
what is ‘external’ gas exchange?
- gas exchange between the alveoli and arteries
- high to low gradient (for both O2 and CO2)
- PO2 is lower on the arterial side because some capillaries don’t interact with the alveoli
- O2 diffuses into arterial ends of capillaries
- CO2 diffuses into the alveoli
what is ‘internal’ gas exchange?
- return to the left side of the heart
- oxygen is high in the blood and low in the tissue –> flows down gradient (opposite for CO2)
what is the oxygen transport cascade?
- how the partial pressure of oxygen changes throughout the body
where is oxygen partial pressure the highest?
- in the air
where is oxygen partial pressure the lowest?
- in the mitochondria
how is O2 transported in the blood?
- in red blood cells (erythrocytes) and in hemoglobin
what are the characteristics of red blood cells?
- no nucleus
- unable to reproduce
- replaced regularly (~4 months)
- produced and destroyed at equal rates
- contain hemoglobin
what are the characteristics of hemoglobin?
- a protein
- transports O2
- contains heme = pigment, iron and o2
- contains globin = protein
- 250 million per red blood cell
- o2 binding increases affinity for second o2 to bind (so red blood cells do not leave without carrying the maximal amount of oxygen)
what are the components of blood (and their respective percentages)?
- 55% plasma (water, plasma proteins
- 45% formed elements (red and white blood cells and platelets)
what is hematocrit?
- formed elements / total blood volume
- will be low in people with leukemia
what is the difference between red blood cell transportation in capillaries vs thick venules and arterioles?
- capillaries are thin and can only transport one red blood cell at a time (important that they know where to go)
- thick venules and arterioles can contain more than one red blood cell and therefore have faster transportation
how does blood transport O2?
- dissolved in the fluid portion of blood (2%) - aka plasma
- combined with hemoglobin in red blood cells (98%)
how does PO2 of blood change from the pulmonary artery to the pulmonary vein? (alveoli to blood)
- pulmonary artery = 40
- middle between = 85
- pulmonary vein = 95
what is the equation to calculate arterial O2 content?
- CaO2 = (Hb x 1.34 x SaO) + (Pa2 x 0.003)
- where 1.34 is a constant (how much oxygen hemoglobin is able to carry)
- normal saturation = ~96-99%
how does the PO2 of blood change from the artery to vein? (blood to muscle)
- artery = 95
- middle = 50
- vein = 45
what is the equation for a-vO2difference?
- a-vO2 = CaO2 - CvO2
- calculating how much oxygen is arriving at the muscle vs. how much is leaving
- lower percentage of oxygen left in the veins when working at VO2 max than at rest
- higher intensity = more oxygen required
why does venous oxygen content fall during exercise?
- we are using more oxygen
- difference gets wider despite arterial content staying the same
what is the oxyhemoglobin dissociation curve?
- how does hemoglobin know to release oxygen
- this is the relationship between oxyhemoglobin and the partial pressure of oxygen
- partial pressure is the independent variable
- high PO2 = high saturation
- shoulder of the curve allows for a greater room for error –> changes in the atmosphere don’t affect us as much because we never really drop below the shoulder
what happens when you drop below the shoulder of the dissociation curve?
- PO2 falls drastically and quickly (slowly at first until hits the shoulder, than quick)
what is left shifting on the oxyhemoglobin dissociation curve?
- decreased unloading of O2 (increased affinity)
- relevant to hypothermia, hyperventilation, etc.
- hemoglobin holds on to oxygen more
- alkalosis (increased pH)
- decreased PCO2
- decreased temp
- decreased 2,3-diphosphoglycerate
what is right shifting on the oxyhemoglobin dissociation curve?
- increased unloading of O2 (decreased affinity)
- relevant to exercise (Bohr shift) –> increased metabolic heat and acidity in active tissue = increased O2 released
- acidosis (decreased pH)
- increased PCO2
- increased temp
- increased 2,3-diphosphoglycerate
what is the Bohr shift?
- no change in PO2 despite oxygen intake being increased
- oxygen is less tightly bound so released more readily during exercise
how does PCO2 of blood change from the artery to the vein? (muscle to blood)
- high in the muscle (krebs cycle production)
- low in the blood (heart)
- artery = 40
- vein = 46
what are the 3 ways blood transports CO2?
- dissolved in fluid portion of blood (10%)
- combined with hemoglobin in red blood cells (20%)
- combined with water as bicarbonate (70%)
how does PCO2 of blood change from the pulmonary artery to the pulmonary vein? (blood to alveoli)
- from blood to alveoli to be exhaled
- CO2 at high pressure (in heart/blood) to low (alveoli)
- pulmonary artery = 46
- pulmonary vein = 40
what is the haldane effect?
- promotes CO2 transport
- when O2 binds with hemoglobin in the lung, CO2 is released
- when O2 offloads from hemoglobin (tissue), CO2 binds to increase CO2 transport
