Gas Exchange: Respiration

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

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

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

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.

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

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

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

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.

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.

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

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

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

Figure 42.27 Alveolar epithelial cells 2 1 Pulmonary arteries Inhaled air Exhaled air 160 0.2 O2 CO2 40 45 100 40 104 40 120 27 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

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

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