lecture 27

Question 1

the amount of gas in solution depends on solubility and partial pressures

Answer 1

• at equilibrium partial pressure in solution will be equal but concentrations are unlikely to be equal
• CO2 is 20x more soluble than O2 because it converted to and transported as HCO3-

Question 2

O2 transport in the blood

Answer 2

• transported with hemoglobin which is found in the RBCs
• it has 4 subunits and each with contain a porphyrin ring and at the center of this ring is an iron atom which binds the oxygen molecule
• Hb has ability to bind 4 O2 molecules

Question 3

total O2 in blood =

Answer 3

amount dissolved in plasma + amount bound to hemoglobin

Question 4

red blood cells with hemoglobin are carrying ______ of their maximum load of oxygen

Answer 4

98%

Question 5

what is the plateau portion of the O2-Hb dissociation curve

Answer 5

60-100 mm Hg

Question 6

what propert of Hb leads to this sigmoidisity

Answer 6

• because of it is cooperative, the binding of O2 molecules increases binding affinity of remaining sites

Question 7

if O2 binding lacked cooperativity what kind of graph would it be

Answer 7

hyperbolic

Question 8

in the steep region

Answer 8

a small change in PO2 can result in a large change in % Hb saturation

Question 9

what is P50

Answer 9

• P50 is the partial pressure of oxygen at which it hemoglobin is 50% saturated with O2
• 27 mm Hg

Question 10

as p50 increases, hemoglobin’s affinity for oxygen _______

Answer 10

decreases

Question 11

when PO2 levels are low the saturation of Hb with O2 ______ because ________

Answer 11

decreases because the affinity for O2 decreases

Question 12

oxygen binding by Hb - effect of changing pH

Answer 12

1. normal physiological pH = 7.4
2. decrease in pH = 7.2
3. increase in pH = 7.6

Question 13

when pH decreases what happens

Answer 13

• it decreases hemoglobin affinity for oxygen therefore P50 increases
• Hb saturation curve shifts to the right and facilitates offloading of oxygen for working skeletal muscles that are producing lactate and need more oxygen

Question 14

where in the body do we see a decrease in pH

Answer 14

we see a decrease in pH in skeletal muscle that are respiring and maybe building up things like lactate and protons that decrease pH

Question 15

what happens to affinity of Hb for oxygen when we increase pH

Answer 15

• increasing pH will shifts Hb saturation curve to the left
• increasing pH will increase affinity of hemoglobin for oxygen and reduce offloading

Question 16

oxygen binding by Hb - effect of changing PCO2

Answer 16

decreased PCO2: 20 mm Hg, shift Hb saturation curve to the left
Normal PCO2: 40 mm Hg
Increased: 80 mm Hg, shift Hb saturation curve to the right, O2 dissociates more readily at tissues where PCO2 is higher

Question 17

what happens when there is an increase in PCO2

Answer 17

an increase in PCO2 leads to a decrease in affinity of hemoglobin for oxygen (the opposite is also true)

Question 18

O2 transport in the blood

Answer 18

• oxygen from alveolus diffuses into plasma (diffusion 1: alveolus to plasma) because PO2 is high in lungs
• Then little bit of oxygen dissolved in plasma (2%)
• The oxygen dissolved in plasma will diffuse across another plasma membrane into RBC (diffusion 2: plasma into RBC)
• Once in RBC we bind to hemoglobin we’ll see our deoxyhemoglobin to oxyhemoglobin reaction
• This is about 98% of the oxygen transported in the blood in form of oxyhemoglobin (were in the lungs loading up)
• Off we go through systemic circulation
• Then we are in the tissues and PO2 in tissues will be lower than PO2 in arterial blood and opposite reaction is going to occur
• So the little bit of oxygen that is dissolved in plasma will diffuse rapidly into tissues
• Then O2 that is bound to hemoglobin will unbind and that will facilitate cooperativity (unloading of oxygen at tissues)
• Reaction will favour deoxyhemoglobin and oxygen which diffuses into tissues and used for cellular respiration

Question 19

CO2 transport in the blood (%)

Answer 19

• 7% transported as dissolved gas in plasma
• 23% is transported as HbCO2 (hitches a ride with Hb)
• 70% transported as HCO3- dissolved in plasma

Question 20

what is carbonic anhydrase

Answer 20

an enzyme that can facilitate conversion to carbonic acid

Question 21

CO2 transport in the blood

Answer 21

1. Well start at where CO2 is produced at the tissues
2. CO2 will diffuse from respiring tissues into plasma, and some of it will be dissolved in plasma about 7%
3. Some will diffuse in and hitch a ride on hemoglobin bound to amine groups which is 23%. This compound is called carbaminohemoglobin
4. Carbonic anhydride lives inside RBC and this reaction happens once CO2 diffuses in
5. When CO2 diffuses in it will combine with water and carbonic anhydrase will facilitate conversion to carbonic acid which will dissociate into bicarbonate and H+
6. Bicarbonate is what is transporting CO2 and H+ is buffered by hemoglobin
7. Bicarbonate we will kick out and it will be transported/dissolved in plasma
8. So it is converted inside red blood cell and kicked out of red blood cell through a process called ion exchange (bicarbonate out, chloride in) to maintain resting membrane potential
9. NET RESULT: bicarbonate in plasma
10. Now all of this will now move through systemic circulation into pulmonary system and back into the lungs where we need to offload
11. Now the dissolved CO2 in plasma is just gonna go and CO2 that hitched a ride on Hb will unbind and defuse out of RBC and go
12. Last thing is we will run this reaction in reverse because CO2 that is diffusing out of RBC and out of plasma into lungs will create a pressure gradient that will shift this reaction to the right
13. The carbonic anydrasebwill catalyze the reverse reaction and it will create a gradient that will drive bicarbonate in and kick chloride out

Question 22

CO2, pH and O2 are sensed by ______

Answer 22

chemoreceptors

Question 23

where are central chemoreceptors located

Answer 23

medulla

Question 24

where are peripheral chemoreceptors located

Answer 24

• same place we saw baroreceptors
• carotid and aortic arteries

Question 25

peripheral chemoreceptors respond too

Answer 25

elevated PCO2 and H+ or decreased PO2

Question 26

central chemoreceptors respond to

Answer 26

to elevated PCO2