1 AP Biology March 2008 Respiration Chapter 42 Gas exchange occurs across specialized respiratory surfaces. 1) Gas exchange: Relies on the diffusion of gases down pressure gradients. At sea level, atmosphere exerts a total pressure of 760 mm Hg. i This is the downward force equal to that exerted by a column of mercury 750 mm high. ii Since the atmosphere is 21% O2 (by volume) Then the partial pressure of oxygen is 2) Gases will diffuse down a pressure gradient across a respiratory surface if it is: permeable i moist Factors Influencing Gas Exchange 1) Surface-to-volume ratio: 2) Ventilation
2 3) Transportation pigments Aids in the movement of gases throughout the body, increasing the quantity of molecules the blood can carry. c) It consists of four subunits, each of which is a heme group with an embedded iron atom. i The iron atom binds O2, thus one hemoglobin can carry 4 oxygen molecules. Contains copper, the oxygen-binding component. i Common in arthropods and many mollusks. ii Dissolved in hemolymph rather than being confined to cells. Invertebrate Respiration 1) Respiratory medium: the source off the oxygen. 2) Respiratory surface: the part of an animal where oxygen from the environment diffuses into living cells and carbon dioxide diffuses out. Always moist 3) Used by small invertebrates, such as flatworms and earthworms. c) Earthworms have a mucus coating on their surface that helps keep the surface moist to allow the O2 to diffuse inward through the epidermis. 4) Gills Used by invertebrates in aquatic environments. A gill has a thin, moist, vascularized epidermis.
3 c) Gill walls are highly folded to increase surface area. 5) Tracheal respiration Consists of internal tubes that branch repeatedly and deliver air directly to body cells. c) Air enters the tracheae through openings called spiracles on the body surface and passes into smaller tubes called tracheoles. d) In most cases no participation by the circulatory system is needed, neither is any respiratory pigments needed. Vertebrate Exchange 1) Gills of Fishes and Amphibians Gills: variously shaped outfoldings of the body surface specialized for gas exchange. The total surface are of the gills is often much greater than that of the rest of the body. c) Water flows over the gills and blood circulates through them in OPPOSITE DIRECTIONS. Countercurrent Exchange: d) This mechanism is highly efficient in extracting O2 from water whose oxygen content is lower than air. 2) Lungs Lungs provide a membrane for gaseous exchange with blood. i Gases diffuse across the inner respiratory surfaces of the lungs. ii
4 iv) In body tissues, O2 diffuses from CO2 travels the route in reverse. c) Lungs also participate in sound production by forcing air to pass through the glottis opening causing the vocal cords on either side to vibrate. d) Amphibians have small lungs or no lungs, and they rely heavily on the diffusion of gases across other body surfaces. Frogs: the skin supplements gas exchange. e) Turtles are another vertebrate exception. Rigid shell restricts breathing movements. i Supplement with gas exchange across moist epithelial surfaces in their mouth and anus. Human Respiratory System 1) Anatomy of respiratory system Located in the thoracic (chest) cavity. c) Then filtered by hairs, warmed, humidified, and sampled for odors as it flows through a maze of spaces in the nasal cavity. d) Nasal cavity leads to the pharynx. i When food is swallowed, the larynx (the upper part of the respiratory tract) moves upward and tips the epiglottis over the glottis (the opening of the wind pipe). ii This allows food to go down the esophagus to the stomach. iv) The rest of the time the glottis is open and we can breath. e) From the larynx, air passes into the trachea, or windpipe. f) One leading to each lung. g) Within the lung, the bronchus branches repeatedly into finer and finer tubes called bronchioles.
5 h) The thin epithelium of the millions of alveoli in the lung serves as the respiratory surface. O2 in the air conveyed to he alveoli dissolves in the moist film and diffuses across the epithelium and into a web of capillaries that surrounds the alveolus. i Breathing Cyclic Reversals in Air Pressure Gradients 1) The Respiratory Cycle Negative pressure breathing: works like a suction pump, pulling air, instead of pushing it, down into the lungs. i Results from changes in the volume of the lungs. ii Diaphragm: In exhalation, the actions listed above are reversed; the elastic lung tissue recoils passively. i ii 2) Lung Volumes Vital capacity: the maximum volume that can be moved in or out. Lungs cannot be completely emptied. c) Tidal volume: the amount of air that enters and leaves with each breath -- about 500 ml. Gas Exchange and Transport 1) Gas Exchange The partial pressure gradients are sufficient to move O2 in and CO2 out of the blood passively.
6 2) Oxygen transport Hemoglobin is a protein with four heme groups that bind oxygen. c) O2 diffuses down a pressure gradient into the blood plasma, then into the red blood cells, where it binds reversibly to hemoglobin Each hemoglobin molecule can bind 4 O2 molecules. i ii Consists of four subunits, each with a cofactor called a heme group that has an iron atom at its center. iv) Iron actually binds the oxygen. d) Hemoglobin gives up its O2 in tissues where: i ii iv) 3) Carbon Dioxide Transport Because the concentration of CO2 is higher in body tissues, it diffuses into the blood. c) d) 4) Matching Air Flow with Blood Flow Gas exchange in the alveoli is most efficient when airflow equals the rate of blood flow. c) The brain monitors input from CO2 sensors in the bloodstream and from receptors sensitive to decreases in O2 partial pressures (carotid bodies and aortic bodies) i ii iv)