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Gas Exchange/Respiration. Shivani Barot Caroline Kapcio Kathryn Routier. Chapter 42.5 (Introduction) Gas Exchange (respiration)- the uptake of O2 from the environment and the release of CO2 into the environment * supports the production of ATP IN cellular respiration
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Gas Exchange/Respiration Shivani Barot Caroline Kapcio Kathryn Routier
Chapter 42.5 (Introduction) • Gas Exchange (respiration)- the uptake of O2 from the environment and the release of CO2 into the environment * supports the production of ATP IN cellular respiration * involves the respiratory and circulatory system
Gas exchange and cellular respiration are distinct processes * Cellular respiration (the metabolic process in which an organism obtains energy) occurs in individual cells of the organism * Gas exchange supports cellular respiration by constantly supplying oxygen and removing carbon dioxide
Respiratory Medium- the source of O2 * air for terrestrial animals * water for most aquatic animals • Earth's atmosphere is composed of much more oxygen than water (by a given volume) * Bodies of water contain dissolved oxygen - the warmer and saltier the water, the less DO - air is less viscous than water - acquiring oxygen from air requires 1/10 the energy than from water
Respiratory Surface- part of the animal's body where gases are exchanged with the surrounding environment * Movement of O2 and CO2 across the surface occurs by diffusion - the rate of diffusion is proportional to the surface area on which diffusion occurs - inversely proportional to the square of the distance molecules move
Respiratory Surfaces cont'd • Diffusion cont'd * All living cells must be bathed in water to maintain their plasma membrane - Respiratory surfaces of all animals are moist - O2 and CO2 must dissolve in water before diffusing across these surfaces
Problem: The respiratory surface must supply O2 and expel CO2 for the entire body • Solutions which have evolved over time: - the size of the organism - whether it lives in water or on land - metabolic demands for gas exchange
Respiratory surfaces tend to be thin and have a large surface area - maximizes rate of gas exchange • Gas exchange in simple animals (i.e. sponges, cnidarians, worms, unicellular organisms, etc.) - use their entire outer skin as a respiratory organ Example: earthworms and some amphibians have moist skin, and gas exchange occurs by diffusion across the general body surface * These types of animals are usually small, long and thin or flat, and with a high ratio of surface area to volume
Large animals lack surface area to exchange gases for the whole body • They have a respiratory organ that is excessively folded or branched - increases surface area • Three most common respiratory organs: - Gills - Tracheae - Lungs
Gills in Aquatic Animals • Gills- outfoldings of the body surface that are suspended in the water
The total surface area of the gills is often much greater than that of the rest of the body • Water has advantages - The aqueous environment keeps the plasma membranes of the respiratory surfaces moist • Water has disadvantages * O2 concentrations in water are low
Ventilation • Ventilation- increasing the flow of the respiratory medium over the respiratory surface * helps aquatic animals obtain enough O2 from water * without ventilation: - low O2, and high CO2 levels * Ventilation in fish: - water enters through the mouth - passes through slits of pharynx - flows over gills - exits the body
Countercurrent exchange- blood flows in the direction opposite to the movement of water past the gills - makes it possible to transfer O2 to the blood * Along the entire capillary, there is a diffusion gradient favoring the transfer of O2 from water to blood • This exchange mechanism - allows the gills to remove more than 80%of the dissolved O2 passing over the respiratory surface - affects temperature regulation
Advantages of air over water * contains more oxygen (about 210 mL O2 per liter of air) * O2 and CO2 diffuse faster in air - less vigorous ventilation * less energy is required - air is lighter - easier to pump - less volume of air needs to be inhaled • Disadvantages of air over water * respiratory surface (must be large and moist) loses water to air by evaporation Solution: A respiratory surface folded into the body
Tracheal Systems in Insects • Tracheal system- made up of air tubes that branch throughout the body * tracheae- the largest tubes - open to the outside - finest branches extend to the surface of nearly every cell ~ gas exchange occurs at the terminal ends of the system * there is a very short distance between the respiratory medium and all body cells - the circulatory system is not involved in gas exchange
Types of insects * Small insects - process of gas gas exchange if fulfilled by diffusion through the trachea * Larger insects - higher energy demands - ventilate tracheal systems with rhythmic body movements that compress and expand the air tubes * Insects in flight - very high metabolic rate - alternating contraction and relaxation of flight muscles compress and expand the body * Flight muscle cells are packed with mitochondria - tracheal tubes supply these ATP generating organisms with ample O2
Lungs • Lungs are restricted to one location * circulatory system fills gap between the respiratory surface and all other parts of the body - transports gases between lungs and the rest of the body • Lungs have a dense net of capillaries under epithelium that forms the respiratory surface • Lungs have evolved in animals such as: -spiders, terrestrial snails, and vertebrates
Some vertebrates (i.e. amphibians) have small lungs * rely heavily on diffusion across other body surfaces for gas exchange Example: turtles perform gas exchange across moist epithelial surfaces in their mouth and anus • Most reptiles, all birds, and mammals * rely entirely on lungs for gas exchange • Evolutionary aspect * Lungs and air breathing have evolved in a few aquatic vertebrates - adaptation to living in O2-poor water - adaptation to spending part of their time exposed to air
Mammalian Respiratory System: A Closer Look • Ventilation- supply of air to the lungs * a ventilation is needed to maintain high concentration gradients in the alveoli • Located in the thoracic cavity • Spongy texture * honeycombed with moist epithelium - functions as respiratory surface • A system of branching ducts conveys air to the lungs
Process of Gas Exchange in Mammals • Nasal Cavity * air is filtered by hairs - warmed, humidified, and sampled for odors • Pharynx- an intersection where the paths for air and food cross • Larynx- when food is swallowed, the larynx moves upward and tips the epiglottis over the glottis (the opening of the windpipe) - allows food to go down the esophagus to the stomach - opening of the epiglottis enables breathing
Larynx * adapted as a voice box - sounds are produced when voluntary muscles in the voice box are tensed - stretching of vocal cords causes muscles to vibrate • Trachea- windpipe * C-shaped rings of cartilage maintain shape • Bronchi- trachea forks into two bronchi, each leading to a lung • Bronchioles- finer tubes within the lung which the bronchus branches in to • Branches are covered by cilia and a thin film of mucus - mucus traps particulate contaminants - moving cilia move the mucus upward to the esophagus, cleansing the respiratory system
Alveoli- a cluster of air sacs at the ends of the tiniest bronchioles • Gas exchange occurs across the thin epithelia of the lung's millions of alveoli - sufficient to carry out gas exchange for the entire body * O2 entering the alveoli dissolves in the moist film - diffuses across epithelium - enters a web of capillaries surrounding each alveolus * CO2 diffuses in the opposite direction - from the capillaries - across the epithelium of alveolus - into air space