Circulation and Gas Exchange

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The pons regulates the tempo.

Slide 81

Sensors in the aorta and carotid arteries monitor O2 and CO2 concentrations in the blood.

These sensors exert secondary control over breathing.

Slide 82

Automatic control of breathing

Breathing

control

centers

Cerebrospinal

fluid

Pons

Medulla

oblongata

Carotid arteries

Aorta

Diaphragm

Rib muscles

Slide 83

Adaptations for gas exchange include pigments that bind and transport gases

The metabolic demands of many organisms require that the blood transport large quantities of O2 and CO2

Blood arriving in the lungs has a low partial pressure of O2 and a high partial pressure of CO2 relative to air in the alveoli.

In the alveoli, O2 diffuses into the blood and CO2 diffuses into the air.

In tissue capillaries, partial pressure gradients favor diffusion of O2 into the interstitial fluids and CO2 into the blood.

Slide 84

Loading and unloading of respiratory gases

Alveolus

PO2 = 100 mm Hg

PO2 = 40

PO2 = 100

PO2 = 100

PO2 = 40

Circulatory

system

Body tissue

PO2 ≤ 40 mm Hg

PCO2 ≥ 46 mm Hg

Body tissue

PCO2 = 46

PCO2 = 40

PCO2 = 40

PCO2 = 46

Circulatory

system

PCO2 = 40 mm Hg

Alveolus

(b) Carbon dioxide

(a) Oxygen

Slide 85

Respiratory Pigments

Respiratory pigments = proteins that transport oxygen, greatly increase the amount of oxygen that blood can carry.

Arthropods and many molluscs have hemocyanin with copper as the oxygen-binding component.

Most vertebrates and some invertebrates use hemoglobin with iron = oxygen-binding component contained within erythrocytes.

Slide 86

Hemoglobin

A single hemoglobin molecule can carry four molecules of O2

The hemoglobin dissociation curve shows that a small change in the partial pressure of oxygen can result in a large change in delivery of O2

CO2 produced during cellular respiration lowers blood pH and decreases the affinity of hemoglobin for O2

This is called the Bohr shift.

Slide 87

 Chains

Iron

Heme

 Chains

Hemoglobin

Slide 88

Dissociation curves for hemoglobin at 37ºC