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