GAS TRANSPORT IN BLOOD OXYGEN TRANSPORT

• Oxygen transport is facilitated by (Hb)

▪ Hemoglobin is a protein found in erythrocytes

▪ Hemoglobin binds and releases oxygen by two reactions: loading and unloading

o loading, oxygen from alveoli binds to hemoglobin in pulmonary capillaries; converts deoxyhemoglobin (HHb) to

oxyhemoglobin (HbO2) ▪ Hemoglobin saturation depends on two factors:

1. Partial pressure of oxygen 2. Affinity OXYGEN TRANSPORT

Figure 21.22 Transport of oxygen: loading and unloading of oxygen.

© 2016 Pearson Education, Inc. OXYGEN TRANSPORT

▪ One of main determinants of percent saturation of Hb is

PO2 of blood and tissues

o Higher blood PO2; loading reaction is favored as more O2 molecules are available to bind to Hb

o Lower blood PO2; unloading reaction is favored as fewer O2 molecules are available to bind to Hb OXYGEN TRANSPORT

Figure 21.23 The oxygen-hemoglobin dissociation curve.

© 2016 Pearson Education, Inc. OXYGEN TRANSPORT

▪ Effect of affinity on hemoglobin saturation

1. Increasing temperature __?___ Hb’s affinity for oxygen; facilitates unloading reaction of oxygen into tissues

2. BPG (2,3-bisphosphoglycerate) – made by erythrocytes as a side reaction of glycolysis :BPG binds with Hb, reducing its affinity for oxygen which __?___ unloading reaction of oxygen to tissues OXYGEN TRANSPORT

Figure 21.24 Effect of temperature, pH, and PCO2 on oxygen unloading.

© 2016 Pearson Education, Inc. TRANSPORT

▪ CO2 quickly diffuses into erythrocytes where it encounters (CA) (Figure 21.25a), an enzyme; rapidly catalyzes following reversible reaction:

– + CO2 + H2O ↔ H2CO3 ↔ HCO3 + H

▪ Carbonic acid (H2CO3) is quickly converted to – + ion (HCO3 ) and hydrogen ion (H ) CARBON DIOXIDE TRANSPORT

– ▪ HCO3 carries a negative charge; counteracted by chloride shift; chloride ions move into erythrocytes as bicarbonate ions move out to balance charges

Figure 21.25a Transport of carbon dioxide. CARBON DIOXIDE TRANSPORT

▪ Carbonic acid-bicarbonate buffer system

1. When pH decreases (becomes more acidic), H+ binds with buffers like bicarbonate making carbonic acid (weak acid with little affect on pH

2. When pH increases (becomes more basic), same reaction generates H+ that decreases pH CARBON DIOXIDE TRANSPORT

Figure 21.26 Effect of pattern of ventilation on blood pH.

© 2016 Pearson Education, Inc. NEURAL • usually occurs without conscious thought or control

▪ Dyspnea

▪ Eupnea CONTROL OF THE BASIC PATTERN OF VENTILATION • Brainstem (particularly medulla oblongata) – region of brain that controls ventilation; neurons in pons influence respiratory rhythm but are not responsible for maintaining eupnea

▪ Respiratory rhythm generator (RRG)

▪ Neurons found in medullary reticular formation: ventral and dorsal respiratory groups CONTROL OF THE RATE AND DEPTH OF VENTILATION

Figure 21.28 Neural control of the basic pattern of ventilation.

© 2016 Pearson Education, Inc. CONTROL OF THE RATE AND DEPTH OF VENTILATION 1. Central relay information to DRG which alerts VRG

2. VRG responds by changing rate and depth of ventilation to match conditions detected, either stimulating or inhibiting inspiratory or expiratory

muscles leading to loss or retention of CO2 and normalization of blood pH