regulation of breathing and acid-base balance / oxygen and carbon dioxide transport

How is oxygen transported in the blood?

• Dissolved in plasma

• Bound to hemoglobin

Why is dissolved oxygen important if it carries so little oxygen?

It determines the partial pressure of oxygen (PO₂), which drives oxygen diffusion and helps regulate breathing.

Why is hemoglobin essential for oxygen transport?

Oxygen is poorly soluble in plasma, so hemoglobin greatly increases the blood’s oxygen-carrying capacity.

Why is hemoglobin located inside red blood cells?

Red blood cells allow large amounts of hemoglobin to be transported efficiently without greatly affecting blood osmolarity.

What is meant by hemoglobin saturation?

The percentage of oxygen-binding sites on hemoglobin that are occupied by oxygen.

What does the oxygen-hemoglobin dissociation curve show?

How readily hemoglobin binds or releases oxygen at different PO₂ values.

Why is the oxygen-hemoglobin dissociation curve S-shaped?

Binding of one oxygen molecule increases hemoglobin’s affinity for the next

Why is the plateau of the dissociation curve important?

It allows hemoglobin to remain highly saturated even if PO₂ falls slightly in the lungs.

Why is the steep part of the dissociation curve important?

A small decrease in PO₂ results in a large release of oxygen to tissues where it is needed

What is the Bohr effect?

Increased CO₂, increased acidity (lower pH), and increased temperature decrease hemoglobin’s affinity for oxygen, promoting oxygen release.

Why is the Bohr effect beneficial during exercise?

Active muscles produce more CO₂, heat, and acid, so hemoglobin releases more oxygen exactly where it is needed.

What drives oxygen movement throughout the body?

Differences in partial pressure

Describe the pathway of oxygen from the atmosphere to body cells.

Air → alveoli → blood → tissues → mitochondria.

What is the role of myoglobin?

Stores oxygen in muscle and releases it when oxygen demand increases.

Why does myoglobin bind oxygen more tightly than hemoglobin?

So it acts as an oxygen reserve within muscle rather than transporting oxygen in blood.

How is carbon dioxide transported in blood?

As bicarbonate, bound to hemoglobin, and dissolved in plasma.

What is the main way carbon dioxide is transported?

As bicarbonate ions.

Why is carbon dioxide converted into bicarbonate?

Bicarbonate is much more soluble than carbon dioxide, allowing much larger amounts to be transported.

What enzyme converts carbon dioxide into bicarbonate?

Carbonic anhydrase.

Why is carbonic anhydrase important?

It rapidly speeds up the conversion between carbon dioxide and bicarbonate

What is the chloride shift?

Bicarbonate leaves the red blood cell while chloride enters.

Why does the chloride shift occur?

To maintain electrical neutrality while bicarbonate is transported in plasma.

What is the Haldane effect?

Oxygen binding to hemoglobin promotes the release of carbon dioxide.

Why is the Haldane effect important?

It improves carbon dioxide removal in the lungs.

How do the Bohr and Haldane effects differ?

• Bohr effect: CO₂ and H⁺ influence oxygen unloading.

• Haldane effect: Oxygen influences carbon dioxide unloading.

Which part of the brain controls breathing?

The respiratory centres in the medulla

What is the role of the respiratory centre?

It integrates information from receptors and adjusts ventilation to maintain homeostasis.

What types of receptors regulate breathing?

Mechanical receptors and chemoreceptors.

What do stretch receptors do?

Detect lung inflation and help prevent over-expansion.

What do peripheral chemoreceptors detect?

Changes in oxygen, carbon dioxide, and blood pH.

What do central chemoreceptors primarily detect?

Changes in carbon dioxide (through changes in cerebrospinal fluid pH).

What is the main chemical stimulus controlling breathing at rest?

Carbon dioxide.

Why does carbon dioxide have a greater influence on breathing than oxygen?

Small increases in CO₂ quickly change blood pH, making ventilation highly sensitive to CO₂.

When does oxygen become a major driver of breathing?

When arterial oxygen falls to very low levels (below about 60 mmHg).

What happens during inspiration?

Inspiratory muscles contract, expanding the thoracic cavity and drawing air into the lungs.

Why is quiet expiration passive?

The diaphragm relaxes and the lungs recoil due to their elastic properties.

Why is maintaining blood pH important?

Enzymes and body cells function properly only within a narrow pH range.

What are the three lines of defence against changes in blood pH?

1. Chemical buffers

2. Respiratory system

3. Kidneys

Which defence against pH changes acts the fastest?

Chemical buffer systems.

Which defence provides long-term regulation?

The kidneys.

How does the bicarbonate buffer system help regulate pH?

It converts excess H⁺ into carbonic acid, which can then become CO₂ and water.

Why are the lungs important for acid-base balance?

They regulate how much CO₂ is removed from the body.

How does hyperventilation affect blood pH?

It removes more CO₂, decreasing H⁺ concentration and increasing pH.

How does hypoventilation affect blood pH?

It retains CO₂, increasing H⁺ concentration and decreasing pH.

Why is hemoglobin essential for life?

Without hemoglobin, blood could carry only a very small amount of oxygen dissolved in plasma.

Why are the Bohr and Haldane effects beneficial together?

They maximise oxygen delivery to active tissues while maximising carbon dioxide removal in the lungs.

How are the respiratory and cardiovascular systems linked?

The respiratory system loads oxygen and removes carbon dioxide, while the cardiovascular system transports these gases between the lungs and tissues.