1. Gas Exchange: Respiration

2. Gas exchange occurs across specialized respiratory surfaces
Supplies oxygen for cellular respiration and disposes of carbon dioxide
Figure 42.19
Organismal level
Cellular level
Circulatory system
Cellular respiration
ATP
Energy-rich molecules from food
Respiratory surface
Respiratory medium (air of water) O2
CO2

3. Animals require large, moist respiratory surfaces for the adequate diffusion of respiratory gases
Between their cells and the respiratory medium, either air or water

4. In mammals, air inhaled through the nostrils
Passes through the pharynx into the trachea, bronchi, bronchioles, and dead-end alveoli, where gas exchange occurs

5. Gas exchange: occurs in alveoli of lungs, diffusion of oxygen and carbon dioxide through capillaries
Ventilation: bringing in fresh air into the alveoli (breathing)
Cellular respiration: produces ATP for the cell, uses oxygen and produces carbon dioxide.

6. Mammalian Respiratory Systems: A Closer Look
A system of branching ducts
Conveys air to the lungs
Branch from the pulmonary vein (oxygen-rich blood)
Terminal bronchiole
Branch from the pulmonary artery (oxygen-poor blood)
Alveoli
Colorized SEM
SEM
50 µm
Heart
Left lung
Nasal cavity
Pharynx
Larynx
Diaphragm
Bronchiole
Bronchus
Right lung
Trachea
Esophagus
Figure 42.23

7. Alveoli
Very small but huge in numbers (large surface area for gas exchange)
Made up of a single layer of thin cells
Covered by a dense network of blood capillaries

8. Mammals ventilate their lungs by breathing
How a Mammal Breathes
Mammals ventilate their lungs by breathing
By negative pressure breathing, which pulls air into the lungs
Air inhaled
Air exhaled
INHALATION Diaphragm contracts (moves down)
EXHALATION Diaphragm relaxes (moves up)
Diaphragm
Lung
Rib cage expands as rib muscles contract
Rib cage gets smaller as rib muscles relax
Figure 42.24

9. Inhalation:
External intercostal muscles contract (moves rib cage up and out)
Diaphragm contracts
Increase in volume, drop in pressure (below atmospheric pressure)
Air flows into lungs until pressure inside lungs rises to atmospheric pressure.

10. Exhalation
Internal intercostal muscles contract (moves rib cage down and in)
Abdominal muscles contract, pushing up diaphragm
Decrease in volume, pressure rises above atmospheric pressure
Air flows out of lungs until the pressure in lungs falls back to atmospheric pressure.

11. Why do we need a ventilation system???
Maintain the concentration gradients of gases (oxygen/carbon dioxide) in the alveoli.
Carbon dioxide needs to be low in alveoli so it moves into the alveoli from capillaries.
Oxygen needs to be high in alveoli so it can move into capillaries.
Ventilation makes this possible by getting rid of carbon dioxide and bringing in oxygen

12. The Role of Partial Pressure Gradients
Gases diffuse down pressure gradients
In the lungs and other organs
Diffusion of a gas
Depends on differences in a quantity called partial pressure
A gas always diffuses from a region of higher partial pressure
To a region of lower partial pressure

13. In the lungs and in the tissues
O2 and CO2 diffuse from where their partial pressures are higher to where they are lower
RESPIRATION

14. Figure 42.27 Alveolar epithelial cells 2 1 Pulmonary arteries
Inhaled air
Exhaled air
160
0.2 O2
CO2
Alveolar epithelial cells
Pulmonary arteries
Blood entering alveolar capillaries
Blood leaving tissue capillaries
Blood entering tissue capillaries
Blood leaving alveolar capillaries
Tissue capillaries
Heart
Alveolar capillaries of lung
<40 >45
Tissue
cells
Pulmonary veins
Systemic arteries
Systemic veins
Alveolar spaces 2 1 3 4
Figure 42.27

15. Greatly increase the amount of oxygen that blood can carry
Respiratory Pigments
Respiratory pigments
Are proteins that transport oxygen
Greatly increase the amount of oxygen that blood can carry
The respiratory pigment of almost all vertebrates
Is the protein hemoglobin, contained in the erythrocytes

16. Like all respiratory pigments
Hemoglobin must reversibly bind O2, loading O2 in the lungs and unloading it in other parts of the body
Heme group
Iron atom
O2 loaded
in lungs
O2 unloaded
In tissues
Polypeptide chain O2
Figure 42.28