Lecture 12 - Gas Exchange and Transport within Blood

Question 1

what is responsible for the exchange of O2 and CO2?

Answer 1

• partial pressure (high to low pressure)

Question 2

where does CO2 and O2 gas exchange occur?

Answer 2

• alveoli and pulmonary capillaries (alveolar-arterial interface)
• tissue and tissue capillaries (arterial-myocyte interface)

Question 3

what is the range of PO2 concentration in venous blood?

Answer 3

• 40-50 mmHg

Question 4

what is the range of PCO2 concentration in venous blood?

Answer 4

• 45-50 mmHg

Question 5

what is the range of PO2 concentration in arterial blood?

Answer 5

• 90-105 mmHg

Question 6

what is the range of PCO2 concentration in arterial blood?

Answer 6

• 38-42 mmHg

Question 7

what is ‘external’ gas exchange?

Answer 7

• 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

Question 8

what is ‘internal’ gas exchange?

Answer 8

• 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)

Question 9

what is the oxygen transport cascade?

Answer 9

• how the partial pressure of oxygen changes throughout the body

Question 10

where is oxygen partial pressure the highest?

Answer 10

• in the air

Question 11

where is oxygen partial pressure the lowest?

Answer 11

• in the mitochondria

Question 12

how is O2 transported in the blood?

Answer 12

• in red blood cells (erythrocytes) and in hemoglobin

Question 13

what are the characteristics of red blood cells?

Answer 13

• no nucleus
• unable to reproduce
• replaced regularly (~4 months)
• produced and destroyed at equal rates
• contain hemoglobin

Question 14

what are the characteristics of hemoglobin?

Answer 14

• 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)

Question 15

what are the components of blood (and their respective percentages)?

Answer 15

• 55% plasma (water, plasma proteins
• 45% formed elements (red and white blood cells and platelets)

Question 16

what is hematocrit?

Answer 16

• formed elements / total blood volume
• will be low in people with leukemia

Question 17

what is the difference between red blood cell transportation in capillaries vs thick venules and arterioles?

Answer 17

• 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

Question 18

how does blood transport O2?

Answer 18

• dissolved in the fluid portion of blood (2%) - aka plasma
• combined with hemoglobin in red blood cells (98%)

Question 19

how does PO2 of blood change from the pulmonary artery to the pulmonary vein? (alveoli to blood)

Answer 19

• pulmonary artery = 40
• middle between = 85
• pulmonary vein = 95

Question 20

what is the equation to calculate arterial O2 content?

Answer 20

• 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%

Question 21

how does the PO2 of blood change from the artery to vein? (blood to muscle)

Answer 21

• artery = 95
• middle = 50
• vein = 45

Question 22

what is the equation for a-vO2difference?

Answer 22

• 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

Question 23

why does venous oxygen content fall during exercise?

Answer 23

• we are using more oxygen
• difference gets wider despite arterial content staying the same

Question 24

what is the oxyhemoglobin dissociation curve?

Answer 24

• 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

Question 25

what happens when you drop below the shoulder of the dissociation curve?

Answer 25

• PO2 falls drastically and quickly (slowly at first until hits the shoulder, than quick)

Question 26

what is left shifting on the oxyhemoglobin dissociation curve?

Answer 26

• 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

Question 27

what is right shifting on the oxyhemoglobin dissociation curve?

Answer 27

• 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

Question 28

what is the Bohr shift?

Answer 28

• no change in PO2 despite oxygen intake being increased
• oxygen is less tightly bound so released more readily during exercise

Question 29

how does PCO2 of blood change from the artery to the vein? (muscle to blood)

Answer 29

• high in the muscle (krebs cycle production)
• low in the blood (heart)
• artery = 40
• vein = 46

Question 30

what are the 3 ways blood transports CO2?

Answer 30

1. dissolved in fluid portion of blood (10%)
2. combined with hemoglobin in red blood cells (20%)
3. combined with water as bicarbonate (70%)

Question 31

how does PCO2 of blood change from the pulmonary artery to the pulmonary vein? (blood to alveoli)

Answer 31

• from blood to alveoli to be exhaled
• CO2 at high pressure (in heart/blood) to low (alveoli)
• pulmonary artery = 46
• pulmonary vein = 40

Question 32

what is the haldane effect?

Answer 32

• 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