respitory 3

Question 1

: How is oxygen and carbon dioxide transported in blood?

Answer 1

1.5% dissolved, 98.5% bound to Hb. CO₂ – 7% dissolved, 23% bound to Hb, 70% as bicarbonate.

Question 2

What part of hemoglobin binds oxygen, and how many O₂ molecules can each Hb carry?

Answer 2

The heme group (iron) binds O₂, with 4 O₂ per hemoglobin molecule.
Extra Note: Iron deficiency → less O₂ binding → anemia.

Question 3

What type of protein structure does hemoglobin have and what is formed when O₂ binds?

Answer 3

Quaternary structure; binding O₂ forms oxyhemoglobin

Question 4

What is cooperative binding in hemoglobin?

Answer 4

he first O₂ binding changes Hb shape, increasing affinity for the next O₂ molecules.

Question 5

ow does hemoglobin unload O₂ at tissues efficiently?

Answer 5

: At tissues: First O₂ released makes next O₂ molecules release more easily. Facilitates delivery

First O₂ release lowers Hb affinity, making subsequent O₂ release easier.

Question 6

What does hemoglobin saturation mean?

Answer 6

% of heme sites occupied by O₂. 100% = all four sites filled.

Question 7

What graph shows the relationship between PO₂ and Hb saturation?

Answer 7

The oxygen–hemoglobin dissociation curve.

Question 8

Why is the O₂–Hb dissociation curve sigmoidal (S-shaped)?

Answer 8

: Because Hb’s affinity for O₂ increases as more O₂ binds, and decreases as O₂ is released (cooperative binding/unloading).

Diffusion rule: gases move from high partial pressure → low partial pressure.

Affinity rule: hemoglobin’s affinity for O₂ increases as more O₂ binds.
Result:

At high PO₂ (lungs), Hb binds O₂ strongly (saturation near 100%).

At low PO₂ (tissues), Hb releases O₂.

Question 9

Different tissues have different PO₂ levels:

Answer 9

Arteries: ~100 mmHg → Hb ~98% saturated.

Veins (resting tissues): ~40 mmHg → Hb ~75% saturated.

Active muscle (exercise): ~20 mmHg → Hb saturation drops more → more O₂ released.
This allows Hb to automatically adjust how much O₂ it delivers.

Question 10

How does temperature affect the O₂–Hb dissociation curve?

Answer 10

High temperature → Hb releases O₂ more easily (curve shifts right).

Low temperature → Hb holds onto O₂ more tightly (curve shifts left).
In the body, temp is usually stable, but exercising muscles get hotter → O₂ release improves.

Question 11

Hormones & DPG Effect

Answer 11

Some hormones (androgens, epinephrine, thyroid, growth hormone) ↑ red blood cell production of 2,3-DPG (diphosphoglycerate).

DPG binds Hb and reduces its affinity for O₂ → promotes O₂ release.

This ensures Hb gives up O₂ more easily to tissues.

Question 12

Q: What is the Bohr effect?

Answer 12

Blood pH affects Hb’s affinity for O₂.

Low pH (acidic, more H⁺/CO₂) → Hb releases O₂ more easily (curve shifts right).

High pH (basic, less H⁺/CO₂) → Hb holds onto O₂ more tightly (curve shifts left).
This is called the Bohr effect. It ensures active, acidic tissues (like muscles during exercise) get more

Question 13

How do CO₂ levels affect the O₂–Hb dissociation curve?

Answer 13

The Bohr effect also ties directly to PCO₂:

High CO₂ → low pH → more O₂ released.

Low CO₂ → higher pH → Hb binds O₂ more tightly.
This double link (CO₂ + pH) makes Hb very responsive to tissue needs.

Question 14

CO₂ transport occurs via 3 pathways:

Answer 14

icarbonate (HCO₃⁻): ~70% → major pathway.

Dissolved in plasma: ~7% → small contribution.

Bound to hemoglobin (Hb–CO₂, carbaminohemoglobin): ~23%

Question 15

Bicarbonate Formation

Answer 15

Inside RBCs, CO₂ enters and reacts with H₂O, catalyzed by carbonic anhydrase:

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This reaction produces bicarbonate (HCO₃⁻) and a free proton (H⁺).

Bicarbonate then leaves RBCs into plasma for transport.

Question 16

Chloride Shift

Answer 16

As HCO₃⁻ leaves the RBC, chloride ions (Cl⁻) enter to maintain electrical neutrality.

This exchange is called the chloride shift.

It prevents charge imbalance while allowing efficient CO₂ transport.

Question 17

Reverse Reaction at Lungs

Answer 17

The reaction reverses: H⁺ + HCO₃⁻ → H₂CO₃ → CO₂ + H₂O.

CO₂ diffuses from RBC → plasma → alveoli → exhaled.

The reverse chloride shift occurs (Cl⁻ leaves, HCO₃⁻ re-enters RBC).

Question 18

Dissolved CO₂ in Plasma

Answer 18

Although CO₂ is not very soluble, about 7% dissolves directly into plasma.

This dissolved CO₂ is the form that directly diffuses into alveoli across the respiratory membrane for exhalation.

It also contributes to blood pH regulation.

Question 19

CO₂ Bound to Hemoglobin

Answer 19

About 23% of CO₂ binds directly to hemoglobin.

Unlike O₂, which binds to the heme (iron), CO₂ binds to the amino groups of the globin portion → forming carbaminohemoglobin (Hb–CO₂).

This only occurs when Hb is not fully saturated with O₂.

Question 20

: How does the partial pressure gradient drive CO₂ movement at tissues and lungs?

Answer 20

At tissues: PCO₂ in tissues (~45 mmHg) > PCO₂ in blood (~40 mmHg) → CO₂ diffuses into blood.

At lungs: PCO₂ in blood (~45 mmHg) > PCO₂ in alveoli (~40 mmHg) → CO₂ diffuses into alveoli and is exhaled.
Extra Note: Despite smaller pressure differences than O₂, CO₂ diffuses efficiently due to its high solubility.

Question 21

The Haldane effect

Answer 21

the relationship between O₂ and Hb’s ability to carry CO₂.

High O₂ (in lungs): Hb is saturated with O₂ → releases CO₂.

Low O₂ (in tissues): Hb not saturated → binds CO₂ more readily.
This complements the Bohr effect.

Question 22

Step 1: Breathing (Pulmonary Ventilation)

Inhalation: Diaphragm contracts, rib cage expands, thoracic volume ↑ → pressure in lungs ↓ → air flows in.

Exhalation: Diaphragm relaxes, rib cage falls, thoracic volume ↓ → pressure in lungs ↑ → air flows out.

Step 2: External Respiration (Lungs ↔ Blood)

O₂: Alveoli PO₂ ~105 mmHg, venous blood PO₂ ~40 → O₂ diffuses into blood.

CO₂: Blood PCO₂ ~45 mmHg, alveoli PCO₂ ~40 → CO₂ diffuses into alveoli and is exhaled.

Step 3: Gas Transport in Blood
Oxygen (O₂):

~98.5% carried bound to Hb (Hb–O₂).

~1.5% dissolved in plasma.

Carbon Dioxide (CO₂):

~70% as bicarbonate (HCO₃⁻, via carbonic anhydrase inside RBCs).

~23% bound to hemoglobin (Hb–CO₂, carbaminohemoglobin).

~7% dissolved in plasma.

Step 4: Internal Respiration (Blood ↔ Tissues)

O₂: Blood PO₂ ~100 mmHg, tissues PO₂ ~40 → O₂ diffuses into tissues.

CO₂: Tissues PCO₂ ~45 mmHg, blood PCO₂ ~40 → CO₂ diffuses into blood.
👉 O₂ fuels cellular respiration, CO₂ is the waste.

Answer 22

Step 5: Haldane Effect

Here’s where the “smart exchange system” comes in:

In tissues (low O₂):

Hb is not fully saturated with O₂.

Hb’s affinity for CO₂ ↑ → more CO₂ binds (Hb–CO₂).

This helps carry CO₂ away from tissues.

In lungs (high O₂):

Hb binds O₂ strongly.

Hb’s affinity for CO₂ ↓ → CO₂ is released.

CO₂ diffuses into alveoli and is exhaled.

👉 Summary:

The Bohr effect = CO₂/pH controls O₂ release.

The Haldane effect = O₂ controls CO₂ release.

Question 23

Hyperpnea:

Answer 23

increased breathing depth/rate that matches O₂ demand (normal in exercise).

Question 24

Hyperventilation

Answer 24

increased breathing depth/rate beyond O₂ needs, causing ↓ CO₂ in blood (respiratory alkalosis).

Question 25

Steady-State Exercise (Phase 1)

Answer 25

There is a small anticipatory rise (psychological) → then a steep increase in ventilation due to feedback from working muscles.

Question 26

Steady-State Exercise (Phase 2–3)

Answer 26

After the steep rise, ventilation gradually fine-tunes to meet O₂ demand, then levels off into a steady state (hyperpnea).

Question 27

Maximal Exercise

Answer 27

Near exhaustion, ventilation increases sharply as the body pushes to get maximum O₂ and expel CO₂.