Lecture 25 Respiratory 2

Question 1

Gas exchange

Answer 1

gas exchange in the lungs occurs by diffusion across the respiratory membrane

Question 2

Partial pressure

Answer 2

(PO2, PCO2) is the driving force for diffusion of gases

gases diffuse down a partial pressure gradient (from high to low partial pressure)

Question 3

Dalton’s Law

Answer 3

total pressure = sum of partial pressure of gases in a mixture
Ptotal = PN2+PO2 + PCO2+PH2O

Question 4

Ptotal

Answer 4

is atmospheric pressure = 760 mm Hg at sea level (lower at high altitude)
PO2= Ptotal X (%O2/100) = 760 X.021 = 160 mm Hg

Question 5

Partial pressure

Answer 5

+ total pressure X fractional concentration of gas (%100)

Question 6

How does O2 diffuse

Answer 6

O2 diffuses from air in alveoli to blood in pulmonary capillaries

Question 7

How does CO2 diffuse

Answer 7

CO2 diffuses from pulmonary capillaries into alveoli

Question 8

High diffusion efficiency due to

Answer 8

1. high surface area of alveoli

2. thin respiratory membrane

Question 9

Inspired air PO2 and PCO2

Answer 9

PO2 = 160
PCO2 = 0.3

Question 10

Alveolar air PO2 and PCO2

Answer 10

PO2 = 100 
PCO2 = 40

Question 11

Pulmonary veins and systemic arteries PO2 and PCO2 and saturation

Answer 11

PO2 = 100
PCO2 = 40
O2 saturation = 98% (arterial blood)

Question 12

Vena Cava and Pulmonary arteries PO2 and PCO2 and O2 saturation

Answer 12

PO2= 40
PCO2= 46
saturation = 75% (mixed venous blood)

Question 13

Pulmonary gases and diffusion

Answer 13

blood PO2 and PCO2 in pulmonary capillaries normally reach equilibrium with alveolar air
ventilation and pulmonary blood flow maintain PO2 and PCO2 gradients between air and blood

Question 14

Respiratory centers control breathing

Answer 14

primary respiratory control regions located in brainstem
controls inspiratory neurons and expiratory (E) neurons
medulla oblongata
pons

Question 15

Medulla oblongata

Answer 15

central pattern generator generates breathing rhythm
dorsal respiratory group (mostly I neurons)
ventral respiratory group (E and I neurons)

Question 16

Pons

Answer 16

pontine respiratory group, functions to smooth out breathing rhythm

Question 17

Chemoreceptors

Answer 17

central chemoreceptor in medulla oblongata

peripheral chemoreceptors in carotid bodies

Question 18

Central chemoreceptors

Answer 18

sensitive to PCO2 via increase [H+] (decrease pH) of cerebrospinal fluid (CSF)
increase arterial PCO2 -> increase PCO2 of CSF
CO2 + H20 -> H2CO3 -> H+ + HCO3-
increase [H+] in CSF -> stimulates increase ventilation

*central chemoreceptor has the dominant role in regulating breathing at rest

Question 19

Peripheral chemoreceptors

Answer 19

sensitive to low PO2 also PCO2 and pH of arterial blood
stimulate ventilation directly at very low PO2 (<60 mm Hg)
increase sensitivity of central response to CO2
contribute to increase in ventilation during exercise

Question 20

Ventilation

Answer 20

is normally regulated to maintain constant arterial PCO2 (normal = 40 mm Hg)

Question 21

Hypoventilation

Answer 21

increase PCO2 (>45 mm Hg)

Question 22

Hyperventilation

Answer 22

decrease PCO2 (<35 mm Hg)