Lecture 9: O2 transport, Hb saturation curves, Co2 transport, Co2 relationship with pH, control of ventilation, peripheral chemoreceptors, central chemoreceptors)

most of O2 in the blood is….

98.5% of O2 in the blood is bound to hemoglobin (Hb) in red blood cells

what is the major determinant of Hb saturation

Po2

Hb saturation

% of heme sites that have O2 bound (if Hb is 100% saturated, every single heme binding site has O2 bound)

O2 binds where on hemoglobin

binds to heme. there are 4 hemes per hemoglobin.

what happens during oxygen diffusion in lungs

1. alveolar Po2 > cap Po2

2. O2 diffuses into blood and binds Hb

what happens during oxygen diffusion in tissues

1. cap Po2 > ISF Po2

2. Hb releases O2 and O2 diffuses into ISF and cells

right shift factors in Hb saturation curve

• increase Pco2

• increase temperature

• increase 2,3 DPG

• increase H+ (decrease pH)

difference between blood Po2, Hb saturation, total blood oxygen content

• blood Po2: amount of O2 dissolved in blood

• Hb saturation: percentage of hemoglobin binding sites occupied by oxygen.

• total blood oxygen content: total amount of oxygen carried in the blood.

write out the relationship between Co2, H+, HCo3-. what enzymes catalyzes the reaction

how is Co2 transported in the tissues

• PCo2 in tissues > PCo2 in capillaries , so Co2 diffuses into capillaries

• Co2 + H2O → H2Co3 by carbonic anhydrase

• H2CO3 → HCO3- + H+

what is the effect of CO2 in blood on O2

increase Co2 in blood will cause more O2 to be unloaded

how is Co2 transported in the lungs

PCo2 in lung capillaries > PCo2 alveolus → co2 diffuses and is exhaled

why is arterial vs. venous pH values different

increased PCo2 in venous blood → increase H+ (decreased pH) in venous blood, so venous pH (7.36) < arterial pH (7.4)

dead space value

150 mL

breathing rate (frequency) value

12 breaths/min

TV value

500 ml/breath

arterial Po2 value

100 mmHg

arterial PCo2 value

40 mmHG

arterial pH value

pH = 7.4

venous Po2 value

40 mmHg

venous PCo2 value

45-46 mmHg

venous pH value

pH = 7.36

pre-botzinger complex

central pacemaker neurons

explain how AP in motor neurons controls inspiration and expiration

• inspiration is initiated by burst of APs in the motor neurons to inspiratory muscles

• expiration occurs when the APs cease

increasing the # of AP bursts/min will

increase frequency of breaths

increasing the # of APs within a burst will

increase depth of breaths

where are peripheral chemoreceptors located and what changes in variables do they detect

• located in aortic arch and each of the carotid arteries

• detect changes in Po2 (direct), pH (direct), and PCo2 (indirect through H+ change)

where are central chemoreceptors located and what changes in variables do they detect

• located in medulla oblongata

• detect changes in Pco2 (indirectly)

explain mechanistic steps of how elevated Co2 in blood is detected by central chemoreceptors

elevated Co2 in blood → elevated Co2 in brain → elevated H+ in brain (cannot cross blood-brain barrier) → central chemoreceptors sense the increase brain H+ from CO2

effect of H+ on ventilation

• increase in H+ → increase in minute ventilation

• response mediated by peripheral chemoreceptors

effect of PCo2 on ventilation

• increase PCo2 → increase ventilation

• response mediated by peripheral AND central chemoreceptors

  

explain what happens when you breathing normally and then hold your breath

• Po2

• PCo2

• chemoreceptors

• breaking point

• Po2 decreases

• PCo2 increases

• peripheral and central chemoreceptors both respond

• breaking point will be caused by Co2

if you hyperventilate first, then hold your breath…

• after hyperventilating, Po2 + Pco2

• during breathing holding, Po2 + Pco2

• chemoreceptors

• breaking point

• after hyperventilating, Po2 increases and Pco2 decreases a lot

• during breathing holding, Po2 decreases and Pco2 increases

• peripheral chemoreceptor respond

• breaking point will be caused by o2

effect of Po2 on ventilation