Unit 5.4 - Transport of O2 and CO2 and Respiration Regulation

O₂ Transport

O₂ transport by blood can be accomplished in 2 stages: diffusion of O₂ through a blood-gas barrier, reaction with hemoglobin within the red blood cell.

Can be transported in 2 forms: by plasma as dissolved product, carried by red blood cells.

Oxygen-Hemoglobin Binding Factors

Flat Upper Portion: a substantial drop in P_O2 of the alveolar gas does not affect the saturation of the arterial blood.

Steep Middle Portion: rapid oxygen dissociation from hemoglobin with only a small decrease in partial pressure, therefore peripheral tissues can extract large amounts of oxygen with a small drop in capillary P_O2

CO₂ Transport

3 forms:

Dissolved - obey Henry’s Law, 20x more soluble than O₂, 8-10% of CO₂.

Bicarbonate Ions - 60% of CO₂.

Carbamino Compound - 30% of CO₂

Central Chemoreceptors

Located near the surface of the medulla.

Increase in P_CO2 stimulates ventilation

Decrease in P_CO2 inhibits ventilation

In both, increase the frequency and depth of respiration.

Peripheral Chemoreceptors

Located at the carotid bodies of the common carotid arteries.

Responds to decrease in arterial P_O2 and pH or increase in arterial P_CO2

In both, increase the frequency and depth of respiration.

Lung Receptors

Pulmonary Stretch Receptors - discharge in response to distention of lungs, prevent over-inflation of lungs.

Irritant Receptors - stimulated by noxious gases, inhaled dust, and cold air; can abnormally increase in depth and rate of respiration.

Juxta-Capillary Receptors - activated when there is engorgement of pulmonary capillaries or increase in interstitial fluid volume; induces rapid shallow breathing.

Joint and Muscle Receptors

Activated upon moving; helps increase ventilation during exercise.

Arterial Baroreceptors

Increased arterial blood pressure can cause hypoventilation.

Pain and Temperature

Pain often causes a period of apnea, followed by hyperventilation.

Heating of the skin may result in hyperventilation.