lecture 19

Question 1

what is the concentration of

n
o
co
and all

Answer 1

79
20
0.03

Question 2

at,mophiorc pressue at sea level is

Answer 2

760

Question 3

Dalton’s Law of Partial Pressures

Answer 3

otal pressure = sum of all gases
Pgas = fraction × total pressure
At sea level: total pressure ≈ 760 mmHg

Question 4

Two sites of gas exchange

Answer 4

• Lungs to blood
• Blood to tissues

Question 5

inspired air

po2

pco2

Answer 5

159

0.3

Question 6

Why does PO₂ drop from atmosphere to trachea?

Answer 6

Water vapor “takes up space,” so O₂ pressure drops from ~159 → 149 mmHg

Back:
Air gets humidified → adds water vapor
Water has pressure (PH₂O = 47 mmHg)

So:
PO₂ = fraction × (total pressure − PH₂O)

Example:
PO₂ = 0.2093 × (760 − 47) = 149 mmHg

Question 7

Why does PO₂ drop from atmosphere → trachea → alveoli?

Answer 7

Back:

Atmosphere: 159 mmHg
Trachea: 149 mmHg → air is humidified (−47 mmHg H₂O)
Alveoli: 103 mmHg → CO₂ enters from blood

Alveoli changes:

O₂ ↓ (20.93% → 14.5%)
CO₂ ↑ (0.03% → 5.5%)

Formula:
PO₂ = fraction × (total pressure − PH₂O)
= 0.145 × (760 − 47) = 103 mmHg

Question 8

Why does PO₂ drop from alveoli to arterial blood?

Answer 8

Back:
Alveoli: 103 mmHg → Arterial: ~100 mmHg

Drop is due to:

Shunting (mixing with deoxygenated blood)
Poorly ventilated alveoli

Question 9

Why is mean capillary PO₂ ~40 mmHg?

Answer 9

Blood enters capillaries at ~100 mmHg
Tissues use O₂ → O₂ diffuses out of blood

So blood leaving is low (~40 mmHg)

Mean capillary PO₂ reflects this drop

Question 10

what is p02 in the mitochondia

Answer 10

2-3mmgh

Question 11

What happens to PO₂ and PCO₂ during exercise?

Answer 11

Unchanged:

Atmospheric PO₂
Tracheal PO₂
Alveolar PO₂
Arterial PO₂
(ventilation increases to keep them stable)

Changes:

Venous PO₂ ↓ (~15 mmHg) → more O₂ used by muscles
Venous PCO₂ ↑ (~60 mmHg) → more CO₂ produced

Question 12

hat does “increased ventilation offsets increased V̇O₂” mean?

Answer 12

During exercise:

Body uses more O₂ (V̇O₂ ↑)
Breathing increases (V̇E ↑)

👉 This keeps alveolar & arterial PO₂ stable