Diagram 1: The three phases of gas exchange

Size: px

Start display at page:

Download "Diagram 1: The three phases of gas exchange"

Amie Young
5 years ago
Views:

1 1

2 Diagram 1: The three phases of gas exchange 1. Breathing When an animal breathes, a large, moist internal surface is exposed to air. O 2 diffuses across the cells lining the lungs and into surrounding blood vessels. At the same time, CO 2 diffuses out of the blood and into the lungs. As the animal exhales, CO 2 is removed from the body 2. Transport of gases by the circulatory system The O 2 that diffused into the blood attaches to hemoglobin in red blood cells. The red vessels in the diagram are transporting O 2 -rich blood from the lungs to capillaries in the body s tissues. CO 2 is also transported in blood from the tissues back to the lungs, shown here by the blue vessels 3. Body cells take up O 2 from the blood and release CO 2 to the blood O 2 functions in cellular respiration in the mitochondria as the final electron acceptor in the stepwise break down of fuel molecules. H 2 O and CO 2 are waste product, and ATP is produces to power cellular work 2

3 The partof an animal where gases exchange are exchanged with the environment is called the respiratory surface. Respiratory surfaces are made up of living cells whose plasma membranes must be wet to function properly. Gas Exchange takes place by diffusion. The surface area of the respiratory surface must be extensive enough to take up sufficient O 2 for every cell in the body and to dispose of waste CO 2. Figure 1:The earthworm is an example of gas exchange through the use of the entire outer skin. Oxygen diffuses into a dense net of thin-walled capillaries lying just beneath the skin. Earthworm's and other skin breathers must live in damp places or in water because their whole body surface has to stay moist. Small size or flatness provides a high ratio of respiratory surface to body volume, allowing for sufficient gas exchange for the entire body Figure 2: Gills have evolved in most aquatic animals. Gills are extensions, or outfoldings, of the body surface specialized for gas exchange. A fish has a set of feather-like gills on each side of its head. O 2 diffuses across the gill surfaces into capillaries, and CO 2 diffuses into the opposite direction, out of the capillaries and into the external environment. 3

4 Figure 3:The tracheal system of an insect is an extensive system of branching internal tubes with the respiratory surface found at their tips. The smallest branches exchange gases directly with body cells and therefore gas exchange in insects requires no assistance form the circulatory system. Figure 4: Most terrestrial vertebrates have lungs which are internal sac lined with moist epithelium. As the diagram indicates, the inner surfaces of the lungs branch extensively, forming a large respiratory surface. Gases are carried between the lungs and the body cells by the circulatory system. 4

5 Diagram 2: Structure of Fish Gills There are four supporting gills arches on each side of the body. Two rows of gill filaments project from each gill arch. Each filament bears many platelike structures called lamellae (singular, lamella) which are the actual respiratory surfaces. A lamella is full of tiny capillaries that are separated from the outside by only one of or a few layers of cells. Ventilation refers to any mechanism that increases the flow of the surrounding water or air over the respiratory surface (gills, tracheae, or lungs). Increasing this flow ensures a fresh supply of O 2 and the removal of CO 2. Swimming fish simply open their mouths and let water flow over the gills while pumping water across the gills by the coordinated opening and closing of the mouth and operculum, the stiff flap that covers and protects the gills. Countercurrent Exchange The arrangement of capillaries in a fish gill enhances gas exchange. Blood flows opposite the movement of water past the gills. This makes it possible to transfer oxygen to the blood by an efficient process called countercurrent. Countercurrent exchange is the transfer of a substance from a fluid moving in one direction to another fluid moving in the opposite direction. 5

6 Aircontains a much more higher concentration of O 2, the air is much lighter and easier to move than water. Thus, a terrestrial animal expends much less energy than an aquatic animal ventilating its reparatory surface. The main problem facing any air breathing animal is the loss of water to the air by evaporation. Figure 5: Illustrates the tracheal system in a grasshopper. The largest tubes, called tracheae, open to the outside and are reinforced by rings of chitin, as shown in the blowup on the bottom right of the figure Figure 6: An insect in flight has a very high metabolic rate and consumes times more O 2 than it does at rest. In many insects, alternating contraction and relaxation of the flight muscles rapidly pumps air through the tracheal system. 6

7 It now seems clearthat tetrapods first evolved in shallow water from what some researchers jokingly call fishapods. These ancient forms had both gills and lungs. The adaptations for air-breathing evident in their fossils include a stronger and elongated snout and a muscular neck that enabled the animal to life the head clear of water into the unsupportive air. Strengthening of the lower jaw may have facilitated the pumping motion presumed to be used by early air-breathing tetrapods and still employed by frogs to inflate their lungs. The recently discovered 375 million year old fossil of Tiktaalikillustrates some of these air-breathing adaptations. 7

8 Mammalianlungs are located in the chest or thoracic cavity and protected by the supportive rib cage. The thoracic cavity is separated from the abdominal cavity by a sheet of muscle called the diaphragm. Diagram 4 shows the human respiratory. Air enters our respiratory system through the nostrils. It is filtered by hairs and warmed, humidified, and sampled for orders as it flows through a maze of space in the nasal cavity. We can also draw in air through the mouth, but mouth breathing does not allow the air to be processed by the nasal cavity. From the nasal cavity or mouth, air passes to the pharynx, where the paths for air and food cross. From the pharynx, air is inhaled into the larynx (voice box). When we exhale, the outgoing air rushes by a pair of vocal cords in the larynx, and we can produce sounds by voluntarily tensing muscles in the voice box. From the larynx, or windpipe. Rings of cartilage reinforce the walls of the larynx and trachea, keeping this party of the airway open. The trachea forks into two bronchi, one leading to each lung. Within the lung, the bronchus branches repeatedly into finer and finer tubes called bronchioles. Respiratory Problems Alveoli are so small that specialized secretions called surfactants are required to keep them from sticking shut due to the surface tension of their moist surface. A lack of lung surfactant is a major problem for babies born very prematurely. 8

9 One of theworst sources of lung-damaging air pollutants is tobacco smoke, which is mainly microscopic particles of carbon coated with toxic chemicals. Tobacco smoke irrigates the cells that line the respiratory tract, inhibiting or destroying their cilia. Smoke s toxins also kill the macrophages that reside in the respiratory tract and engulf fine particles and microorganisms. Figure 8: Illustrates a cutaway view of a pair of healthy human lungs (left) and the lungs of a cancer victim (right), whose lungs are black form the long-term buildup of smoke particles. 9

10 Breathing is the alternateinhalation of air. This ventilation of our lungs maintains high O 2 and low CO 2 concentrations at the respiratory surface. Diagram 5: Shows the changes that occur in our rib cage, chest cavity, and lungs during breathing. Inhalation -During inhalation, the rib cage expands as muscles between the ribs contract. At the same time, the diaphragm contracts, moving downward and expanding the chest cavity, The volume of the lungs increases with the expanding chest cavity during inhalation, which lowers the air pressure in the alveoli to less than atmospheric pressure. Flowing from a region of higher pressure to one of lower pressure, air rushes through the nostrils and down the breathing tubes to the alveoli. This type of ventilation is called negative pressure breathing. Exhalation The rib muscles and diaphragm both relax, decreasing the volume of the rib cage and chest cavity, which increases the air pressure inside the lungs, forcing air out. Notice that the diaphragm curves upward into the chest cavity when relaxed. 10

11 Althoughwe can voluntarily hold our breathe faster and deeper, most of the time our breathing is under automatic control. Breathing control centers are located in parts of the brain called the pons and medulla oblongata. The control center in the pons smoothsout the basic rhythm of breathings set by the medulla. Diagram 6: 1. Nerves from the medulla s control center signal the diaphragm and rib muscles to contract, making us inhale. When we are at rest, these nerve signals result in about 10 to 14 inhalations per minute. Between inhalations, the muscles relax, and we exhale 2. The control center regulates breathings rate in response to changes in the CO 2 level of the blood. When we exercise vigorously, for instance, our metabolism speeds up and our body cells generate more CO 2 as a waste product. The CO 2 goes into the blood, where it reacts with water to form carbonic acid. The acid slightly lowers the ph of the blood and the cerebrospinal fluid. When the medulla senses this ph drop, its breathing control center increases the breathing rate and depth. As a result, more CO 2 is eliminated in the exhaled air, and the ph returns to normal 3. Secondary control over breathing is exerted by sensors in the aorta and carotid arteries that monitor concentrations of O 2 as well as CO 2. When the O 2 level in the blood is severely depressed, these sensors signal the control center via nerves to increase the rate and depth of breathing. This response may occur, for example, at high altitudes, where the air is so thin that we cannot get enough O 2 by breathing normally. 11

12 Diagram7: Illustrates the main components of our circulatory system and their role in gas exchange. One side of the heart handles oxygen-poor blood (colored blue). The other side handles oxygen-rich blood (red). As indicated in the lower left of the diagram, oxygen poor blood returns to the heart from capillaries in body tissues. The heart pumps this blood to the alveolar capillaries in the lungs. Gases are exchanged between air in the alveolar spaces and blood in the capillaries (top of diagram). Blood leaves the alveolar capillaries, having lost CO 2 and gained O 2. This oxygen-rich blood returns to the heart and is pumped out to body tissues. 12

13 Oxygen is not very soluble in water, and most animals transport O 2 bound to proteins called respiratory pigments. Most of these molecules have distinctive colors, hence the name pigment. Many mollusks and arthropods use a blue, copper-containing pigment. Almost all vertebrates and many invertebrates use hemoglobin, an iron-containing pigment that turns red when bound with O 2. A hemoglobin molecule consists of four polypeptide chains of two different types, depicted with two shades of purple in the above figure. Attached to each polypeptides is a chemical group called a heme(colored green in the figure), at the center of which is a iron atom (black). Each iron atom can carry one O 2 molecule. Thus, every hemoglobin molecule can carry up to four oxygen molecules. Hemoglobin loads up with O 2 in the lungs and transports it to the body s tissues. There, hemoglobin unloads some or all of its cargo, depending on the O 2 needs of the cells. 13

14 Figure 9shows the human fetus inside the mother s uterus. The fetus literally swims in a protective watery bath, the amniotic fluid. Its lungs are full of fluid and are nonfunctional. A composite organ that includes tissues from both the fetus and the mother. A large net of capillaries fans out into the placenta from blood vessels in the umbilical cord of the fetus. These fetal capillaries exchange gases with the maternal blood that circulates in the placenta, and the maternal circulatory system carries the gases to and from the mother s lungs. Aiding O 2 uptake by the fetus is fetal hemoglobin, a special type that attracts O 2 more strongly than does adult hemoglobin. 14

Chapter 22 Gas Exchange

Chapter 22 Gas Exchange PowerPoint Lectures for Biology: Concepts & Connections, Sixth Edition Campbell, Reece, Taylor, Simon, and Dickey Lecture by Edward J. Zalisko Introduction: Surviving in Thin Air