Respiratory 4

Question 1

Proportions of CO2 in the blood:

Answer 1

10% is dissolved
30% bound to hemoglobin
60% HCO3 through carbonic anhydrase working in RBC

(H20 + CO2 <> H2CO3 <> H+ + HCO3-)

Question 2

Pathway of CO2:

Answer 2

Metabolic cells produce CO2 -> dissolved CO2 goes into tissue capillary (10% stays in plasma) -> in the RBC: hemoglobin just had
let go of O2 and now binds to CO2 > HbCO2

carbonic anhydrase: CO2+H20 -> H2CO3 dissolves to H+ + HCO3-

Question 3

How does bicarbonate (HCO3-) get into the plasma?

Answer 3

Through Cl(-) shift: carbonic acid (H2CO3) dissociates to HCO3- and H+ and HCO3- is transported from RBC to the plasma

Question 4

What would happen without Cl(-) shift?

Answer 4

Depolarization, membrane potential would become more positive

Question 5

How does CO2 get from blood/pulmonary capillaries to the lungs (alveoli)?

CO2 —» to lungs to breathe out

Answer 5

1. dissolved CO2 in plasma of pulmonary capillary goes to alveoli
2. in RBC: CO2 bound to Hb (HbCO2) dissolves to Hb (can now bind O2) and CO2 -> CO2 walks from RBC to alveoli
3. HCO3- is transported into RBC with reverse Cl(-) shift -> HCO3- fuses with H+ and forms H2CO3 ->
   carbonic anhydrase converts H2CO3 to H2O and CO2 -> CO2 walks from RBC to alveoli

Question 6

What happens with H+ produced in the intermediate steps?

Answer 6

Build: H2CO3 dissociates in H+ and HCO3-

H+ binds to Hb, Hb had just let go O2

Question 7

How does O2 move from blood to the tissue?

Answer 7

1. dissolved O2 just walks through to the capillary wall into the tissue
2. in RBC: HbO2 dissolves in Hb and O2 -> O2 walks from RBC to tissue

Question 8

What nerve is stimulated while breathing?

Answer 8

Action potential in phrenic nerve to the diaphragm

taking a deep breath (higher tidal volume) will increase the frequency during inspiration

increase the rate of breathing there will be a shorter gap between action potentials

Question 9

Where is the respiratory center?

Answer 9

in the CNS -> brainstem (many involuntary functions)
Medulla and Pons

Question 10

How is the respiratory center regulated?

Answer 10

By central chemoreceptors (in CNS)
and peripheral chemoreceptors carotid and aortic bodies

-> they control breathing through inspiratory muscles: external intercostals and diaphragm

Question 11

How are chemoreceptors in the respiratory center stimulated?

Answer 11

By H+ concentration coming from H2CO3

CO2 (gas) is small enough to cross the blood-brain barrier -> reacts with O2 to H2CO3 (carbonic acid) !!! catalyzed by carbonic anhydrase

H2CO3 dissolves in H+ and HCO3- -> H+ is detected by chemoreceptors, which are sending signals to the medullary respiratory center -> controlling pulmonary ventilation

They cant respond to metabolic acids, because of the blood-brain barrier

Question 12

What is the consequence of high amounts of CO2 and subsequently more H+ in the respiratory center?

Answer 12

It increases ventilation, which will increase elimination of CO2

Question 13

How are peripheral chemoreceptors stimulated?

Answer 13

By partial pressure of oxygen (O2) and H+ (coming from: H+ - HCO3-)

O2 bound to Hemoglobin does not contribute to partial pressure P(O2), so anemia doesn’t affect peripheral chemoreceptors

stimulation leads to an increase in pulmonary ventilation

Question 14

What kind of partial pressure of O2 do peripheral chemoreceptors respond to? (they stimulate ventilation)

Answer 14

As they stimulate ventilation, they must respond to low P(O2) to increase O2

Question 15

What kind of H+ concentration would stimulate the peripheral chemoreceptors?

Answer 15

High CO2 will shift the reaction towards H+
(CO2 + H20 -> H2CO3<> H+ HCO3-)

this leads to increased ventilation to blow out CO2

Question 16

How do we calculate the minute ventilation (L/min)
similar to alveolar ventilation!

Answer 16

Amount of air we breathe in and out in a minute:
Tidal volume (ml/breathe) * respiration rate (breaths/min) -> ml/min

Question 17

Again:
A: What happens if p (CO2) increases?

B: What happens if p (O2) goes down?

C: What happens if H+ increases?

Answer 17

A: Increase of ventilation to blow out the CO2

B: Increase of ventilation to breathe in more O2

C: means more CO2 -> increase of ventilation, to blow out CO2

Question 18

How strong must p(O2) drop before we see an increase in ventilation?

Answer 18

drop from normal 100 mmHg to 60 mmHg

Question 19

can H+ coming from metabolic acid (f.e. lactic acid) affect ventilation?

Answer 19

Yes, it can increase ventilation even if CO2 is not the problem

Question 20

Describe the pathway of how the ventilation increases IN CASE of low p (O2)

Answer 20

inspired p(O2) drops, alveolar p(O2) drops -> arterial p(O2) drops ->

Peripheral chemoreceptor fires and activate the contraction of inspiratory muscles (diaphragm and external intercostals) -> increase of ventilation until normal level of p(O2)

Question 21

Describe the pathway of how the ventilation increases IN CASE of low p (O2)

Answer 21

alveolar p(CO2) high -> arterial p(CO2) high -> arterial(H+) high -> peripheral chemoreceptor fires -> stimulation of respiratory muscle -> more ventilation until normal level of CO2 -> shift in the reaction causing H+ to drop

Brain pathway: high p(CO2) -> high(H+) -> firing of central chemoreceptors -> stimulatio nof respiratory muscles -> …

Question 22

How does metabolic acidosis affect peripheral chemoreceptors?

Answer 22

Basically the same as with H+ from pulmonary origin: -> stimulation through medullary respiratory neurons -> stimulation of inspiratory muscles -> increase of ventilation -> CO2 blown out until normal level of H+

Question 23

What happens if H+ is low: alkalosis?

Answer 23

chemoreceptors are not going to fire -> decrease of ventilation -> increase of CO2 -> increase of H+