Chapter 53

Summary		Questions		Media Resources
53.1 Respiration involves the diffusion of gases.
• The factors that influence the rate of diffusion, surface area, concentration gradient, and diffusion distance, are described by Fick's Law. • Animals have evolved to maximize the diffusion rate across respiratory membranes by increasing the respiratory surface area, increasing the concentration gradient across the membrane, or decreasing the diffusion distance.		1.  Approximately what percentage of dry air is oxygen, and what percentage is carbon dioxide? 2.  Why is it that only very small organisms can satisfy their respiratory requirements by direct diffusion to all cells from the body surface?		•Respiration •Gas Exchange Variations
53.2 Gills are used for respiration by aquatic vertebrates.
• As water flows past a gill's lamellae, it comes close to blood flowing in an opposite, or countercurrent, direction; this maximizes the concentration difference between the two fluids, thereby maximizing the diffusion of gases.		3.  What is countercurrent flow, and how does it help make the fish gill the most efficient respiratory organ?
53.3 Lungs are used for respiration by terrestrial vertebrates.
• Reptiles, birds, and mammals use negative pressure breathing; air is taken into the lungs when the lung volume is expanded to create a partial vacuum. • Mammals have lungs composed of millions of alveoli, where gas exchange occurs; this is very efficient, but because inspiration and expiration occur through the same airways, new air going into the lungs is mixed with some old air.		4.  How do amphibians get air into their lungs? How do other terrestrial vertebrates get air into their lungs? 5.  What two features in birds make theirs the most efficient of all terrestrial respiratory systems?		•Respiratory Tract A •Respiratory Tract B
53.4 Mammalian breathing is a dynamic process.
• The lungs are covered with a wet membrane that sticks to the wet membrane lining the thoracic cavity, so the lungs expand as the chest expands through muscular contractions. • Breathing is controlled by centers in the medulla oblongata of the brain; breathing is stimulated by a rise in blood CO2, and consequent fall in blood pH, as sensed by chemoreceptors located in the aorta and carotid artery.		6.  How are the lungs connected to and supported within the thoracic cavity? 7.  How does the brain control inspiration and expiration? How do peripheral and central chemoreceptors influence the brain's control of breathing?		•Boyle's Law •Breathing •Smoking Risks •Human Breathing • Disorders
53.5 Blood transports oxygen and carbon dioxide.
• Hemoglobin loads with oxygen in the lungs; this oxyhemoglobin then unloads oxygen as the blood goes through the systemic capillaries. • Carbon dioxide combines with water as the carbon dioxide is transported to the lungs for exhalation.		8.  In what form does most of the carbon dioxide travel in the blood? How and where is this molecule produced?		•Hemoglobin Module •Hemoglobin •Gas Exchange •Gas Exchange •Activity: Gas Exchange

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