Gas Exchange and Breathing Regulation

Respiratory Quotient

• Indicates the ratio of carbon dioxide produced to oxygen consumed during metabolism.
• Helps determine metabolic pathways and nutritional status.

Oxygen Diffusion

• Oxygen diffuses from the blood in pulmonary capillaries to the tissues, primarily driven by differences in partial pressure.

Gas Exchange in Lungs

• Occurs in the alveoli where oxygen enters the bloodstream and carbon dioxide is expelled.
• Facilitated by diffusion across the alveolar-capillary membrane depending on concentration gradients.

Solubility of Gases

• Carbon dioxide is approximately 20 times more soluble than oxygen in water, impacting its transport and exchange.

Oxygen Transport in Blood

• Oxygen is primarily transported in the blood bound to hemoglobin.
• A small fraction is also dissolved directly in plasma but is negligible compared to hemoglobin binding.

Carbon Dioxide Transport

• Main form of carbon dioxide transported between tissues and lungs is as bicarbonate (HCO3-) in plasma.
• Carbon dioxide reacts with water to form carbonic acid, which dissociates into bicarbonate and protons.

Central Chemoreceptors

• Primary stimulus for central chemoreceptors is the increase in arterial carbon dioxide levels (hypercapnia) leading to a decrease in pH.

Oxygen Entry Rate

• Under steady-state conditions, the rate of oxygen entering pulmonary capillaries from alveolar air is equal to the rate of oxygen utilized by the tissues.

Hemoglobin in Systemic Arteries

• Under normal resting conditions, hemoglobin is approximately 95-98% saturated with oxygen in systemic arteries, reflecting efficient gas exchange.

pH and Hemoglobin-Oxygen Dissociation Curve

• The effect of pH on the hemoglobin-oxygen dissociation curve is known as the Bohr effect, where decreasing pH (increased acidity) shifts the curve to the right, reducing hemoglobin's affinity for oxygen.

Factors Affecting Alveolar PO2

• Factors that do not affect alveolar partial pressure of oxygen (PO2) include the rate of oxygen consumption and carbon dioxide production, assuming ventilation remains constant.