Gas Exchange/RespirationShivani Barot

Caroline KapcioKathryn 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