lecture 20

Question 1

What is the arteriovenous oxygen difference (a-v̄O₂ difference)?

Answer 1

The difference between arterial O₂ content (CaO₂) and mixed venous O₂ content (Cv̄O₂)
Formula:
a-v̄O₂ difference = CaO₂ − Cv̄O₂
Represents how much oxygen is extracted by tissues
Typical value at rest: ~40–50 mL O₂/L blood
Example:
191.3 − 151.1 = 40.2 mL O₂/L blood

Question 2

How does arteriovenous oxygen difference (a-v̄O₂) change from rest to intense exercise?

Answer 2

Arterial blood (leaving lungs):
O₂ content: 16–24 mL O₂ / 100 mL blood
O₂ saturation: ~95–98%
At rest:
a-v̄O₂ difference: ~4–5 mL O₂ / 100 mL blood
≈ 25% O₂ extraction
During intense aerobic exercise:
a-v̄O₂ difference: ~15–20 mL O₂ / 100 mL blood
≈ 75–100% O₂ extraction
Key idea:
Oxygen extraction increases with exercise due to greater tissue demand
Values depend on hemoglobin (Hb) content

Question 3

How is carbon dioxide (CO₂) transported in the blood?

3 ways what prcentage

Answer 3

Back:

CO₂ produced in tissues diffuses into blood → transported to lungs for exhalation

Three forms of transport:

Dissolved in plasma & RBCs
~10% total
(5% plasma, 5% red blood cells)

Bicarbonate (HCO₃⁻)
~65% total
Main form of transport

Carbamino compounds (bound to hemoglobin)
~25% total
(5% plasma, 20% red blood cells)

Question 4

Carbamino compounds (bound to hemoglobin) when does it happen

Answer 4

CO₂ binds to hemoglobin (Hb) → forms carbaminohemoglobin
Happens more easily when hemoglobin is deoxygenated

👉 Key idea:

Deoxy-Hb carries more CO₂ (important during exercise)

Accounts for ~25% of CO₂ transpor

Question 5

3. Bicarbonate (HCO₃⁻) — THE BIG ONE (~65%) what are the stepps for how its transferd

Answer 5

This is the one you really need to understand.

Step-by-step (in tissues):
CO₂ diffuses into red blood cells (RBCs)
(because tissues are producing CO₂)

Inside RBCs, CO₂ reacts with water:

CO₂ + H₂O → H₂CO₃ (carbonic acid)

Carbonic acid quickly breaks down:

H₂CO₃ → H⁺ + HCO₃⁻

Bicarbonate (HCO₃⁻) leaves the RBC and goes into plasma
This is how most CO₂ is carried in the blood
H⁺ is buffered by hemoglobin
Prevents blood from becoming too acidic

Question 6

What role do plasma proteins play in CO₂ transport and pH regulation?

Answer 6

Do not directly transport CO₂
Act as secondary buffers
Can bind or release H⁺
Example: albumin
Support overall pH homeostasis

Question 7

Law of mass action

Answer 7

“More CO₂ = more bicarbonate formed.”

Question 8

What is the function of buffers in the body?

Answer 8

Resist changes in pH (H⁺ concentration)
Maintain stable internal environment
Prevent large swings in acidity

Question 9

How do buffers respond to changes in pH?

Answer 9

↓ pH (↑ H⁺) → buffers absorb H⁺
↑ pH (↓ H⁺) → buffers release H⁺

Question 10

What are the main chemical and physiological buffer systems?

Answer 10

Chemical buffers:

Bicarbonate (primary)
Hemoglobin (protein)
Phosphate

Physiological buffers:

Ventilation (controls CO₂ levels)

Question 11

Front:
How does increasing ventilation affect pH?

Answer 11

Back:

↑ Ventilation → ↓ CO₂ (↓ PₐCO₂)
Shifts reaction left → ↓ H⁺
pH increases (less acidic)
More CO₂ is exhaled