Chapter 22 Gas Exchange

Surviving in Thin Air The high mountains of the Himalayas Surviving in Thin Air The high mountains of the Himalayas Have claimed the lives of even the world’s top mountain climbers The air at the height of the world’s highest peak, Mt. Everest is so low in oxygen that most people would pass out instantly if exposed to it Your body will not increase in the affinity of hemoglobin for oxygen.  

Twice a year, flocks of geese migrate over the Himalayas Twice a year, flocks of geese migrate over the Himalayas They are able to fly at such a high altitude because of the efficiency of their lungs These birds have blood with hemoglobin with a very high affinity for oxygen This adaptation allows them to carry large amounts of oxygen to their tissues to exchange with carbon dioxide Birds do not have mitochondria that are more efficient than those of other vertebrates.  

The process of gas exchange, often called respiration Is the interchange of O2 and CO2 between an organism and its environment Animals need oxygen because without it, animals cannot obtain enough energy from their food.

MECHANISMS OF GAS EXCHANGE 22.1 Overview: Gas exchange involves breathing, transport of gases, and exchange of gases with tissue cells The three phases of gas exchange O2 1 Breathing CO2 Lung Circulatory system 2 Transport of gases by the circulatory system Mitochondria 3 Exchange of gases with body cells O2 CO2 Capillary Figure 22.1 Cell

Gas exchange provides O2 for cellular respiration and removes its waste product, CO2 The process of moving air in and out of the lungs is called breathing. When blood passes by body cells, the body cells take up oxygen and release carbon dioxide to the blood.

22.2 Animals exchange O2 and CO2 across moist body surfaces 22.2 Animals exchange O2 and CO2 across moist body surfaces Respiratory surfaces must be thin and moist for diffusion of O2 and CO2 to occur The part of an animal where gas exchange occurs is called the respiratory surface.   Animals that use their body surface for gas exchange must have a high ratio of body surface area to volume.

Some animals, like the earthworm Some animals, like the earthworm Use their entire skin as a gas-exchange organ Cut Cross section of respiratory surface (the skin covering the body) CO2 Capillaries O2 Figure 22.2A

In most animals Specialized body parts provide large respiratory surfaces for gas exchange Body surface Body surface Respiratory surface (air tubes) Respiratory surface (gill) Body cells (no capillaries) O2 CO2 Figure 22.2C CO2 Capillary O2 Body surface Figure 22.2B Respiratory surface (within lung) CO2 O2 CO2 O2 Figure 22.2D Capillary

22.3 Gills are adapted for gas exchange in aquatic environments 22.3 Gills are adapted for gas exchange in aquatic environments Gills are extensions of the body that absorb O2 dissolved in water Gills are generally unsuitable for animals living on land because the animals would lose too much water.   The chief advantage of exchanging gases in water is that no energy need be expended to keep the exchange surface wet.

In a fish, gas exchange is enhanced by ventilation and the countercurrent flow of water and blood In the countercurrent exchange systems of fish gills the blood and water flow in opposite directions. Gill arch Oxygen-poor blood Lamella Direction of water flow Oxygen-rich blood Gill arch 15% 40% 70% 30% 5% 100% 60% Blood vessels 80% % O2 in water flowing over lamellae % O2 in blood flowing through capillaries in lamellae Gill filaments Figure 22.3 Countercurrent exchange

22.4 The tracheal system of insects provides direct exchange between the air and body cells Land animals Exchange gases by breathing air

Tracheal systems in insects Tracheal systems in insects Transport O2 directly to body cells through a network of finely branched tubes Air sacs Tracheae Opening for air Body cell Air sac Tracheole LM 250 Trachea O2 CO2 Body wall Figure 22.4A, B

22.5 Terrestrial vertebrates have lungs 22.5 Terrestrial vertebrates have lungs In mammals, air inhaled through the nostrils Passes through the pharynx and larynx into the trachea, bronchi, and bronchioles Nasal cavity Pharynx (Esophagus) Left lung Larynx Trachea Right lung Bronchus Bronchiole Diaphragm Figure 22.5A (Heart)

The nasal cavities in humans is used for: humidification of inhaled air   warming of inhaled air   filtering of inhaled air   sampling of inhaled air for odors  

The bronchioles end in clusters of tiny sacs called alveoli The bronchioles end in clusters of tiny sacs called alveoli Where gas exchange occurs Oxygen-rich blood Oxygen-poor blood Bronchiole Alveoli Colorized SEM 6,200 Blood capillaries Figure 22.5B, C

22.6 Smoking is a deadly assaults on our respiratory system CONNECTION 22.6 Smoking is a deadly assaults on our respiratory system Mucus and cilia in the respiratory passages Protect the lungs Can be destroyed by smoking causing coughing.

Smoking causes lung cancer, heart disease, and emphysema & reduces the lungs’ capacity for gas exchange. Lung Heart Figure 22.6

22.7 Breathing ventilates the lungs 22.7 Breathing ventilates the lungs Breathing is the alternation of inhalation and exhalation Inhalation in humans is achieved by  contraction of the diaphragm and chest muscles.   Exhalation results mainly from the relaxation of the chest muscles and diaphragm.  

The contraction of rib muscles and the diaphragm The contraction of rib muscles and the diaphragm Expands the chest cavity and reduces air pressure in the alveoli (negative pressure breathing) Rib cage expands as rib muscles contract Rib cage gets smaller as rib muscles relax Air inhaled Air exhaled Lung Diaphragm Diaphragm contracts (moves down) Diaphragm relaxes (moves up) Figure 22.7A Inhalation Exhalation

Vital capacity is the maximum volume of air we can inhale and exhale But our lungs still hold a residual volume

Air sacs empty; lungs fill Air flows in one direction through the more efficient lungs of birds The function of air sacs in birds is to permit one-way ventilation of the lungs. Anterior air sacs Air Air Posterior air sacs Trachea Lungs Air tubes in lung Inhalation: Air sacs fill Exhalation: Air sacs empty; lungs fill 1 mm Figure 22.7B

22.8 Breathing is automatically controlled 22.8 Breathing is automatically controlled Breathing control centers in the brain Keep breathing in tune with body needs, sensing and responding to the CO2 level in the blood Brain Cerebrospinal fluid Pons Medulla Breathing control centers stimulated by: Nerve signals trigger contraction of muscles CO2 increase / pH decrease in blood Nerve signals indicating CO2 and O2 levels CO2 and O2 sensors in aorta Diaphragm Figure 22.8 Rib muscles

A drop in blood pH Triggers an increase in the rate and depth of breathing

TRANSPORT OF GASES IN THE BODY 22.9 Blood transports respiratory gases The heart pumps oxygen-poor blood to the lungs Where it picks up O2 and drops off CO2 Then the heart pumps the oxygen-rich blood to body cells Where it drops off O2 and picks up CO2

Gas transport and exchange in the body Gas transport and exchange in the body Exhaled air Inhaled air Alveolar epithelial cells Air spaces CO2 O2 CO2 O2 Alveolar capillaries of lung CO2-rich, O2-poor blood O2-rich, CO2-poor blood Heart Tissue capillaries CO2 O2 CO2 Interstitial fluid O2 Figure 22.9 Tissue cells throughout body

Gases diffuse down partial-pressure gradients In the lungs and the tissues

22.10 Hemoglobin carries O2 and helps transport CO2 and buffer the blood Hemoglobin in red blood cells Transports oxygen, helps buffer the blood, and carries some CO2 Iron atom O2 loaded in lungs O2 unloaded in tissues Heme group Figure 22.10 Polypeptide chain

Most CO2 in the blood Is transported as bicarbonate ions in the plasma Most CO2 in the blood Is transported as bicarbonate ions in the plasma CO2 + H2O H2CO3 H+ + HCO3– Carbon dioxide Water Carbonic acid Hydrogen ions Bicarbonate

CONNECTION 22.11 The human fetus exchanges gases with the mother’s bloodstream A human fetus Exchanges gases with maternal blood in the placenta Placenta, containing maternal blood vessels and fetal capillaries Umbilical cord, containing fetal blood vessels Amniotic fluid Uterus Figure 22.11

Fetal hemoglobin Enhances oxygen transfer from maternal blood At birth, increasing CO2 in the fetal blood causes the baby to start breathing.