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