Topic 6: Gas Exchange

physiological respiration

process by which animals exchange gases with their surroundings

how they take in O2 from the environment and deliver it to body cells

how they remove CO2 from body cells and deliver it to the environment

cellular respiration

includes all the oxidative reactions that lead to the production of ATP in the mitochondria of animal cells

the way gas exchange occurs depends on what?

respiratory medium and the nature of its respiratory surface

respiratory medium

water for aquatic animals, air of terrestrial animals, both for amphibians

breathing

the exchange of gases with the respiratory medium; whether the medium is air or water

respiratory surface

formed by a layer of epithelial cells; the interface between the body and the respiratory medium 

how does exchange of O2 and CO2 across the respiratory surface occur?

by simple diffusion

what two structural properties of respiratory surfaces favor a high rate of diffusion?

• they’re thin

• they have large surface areas

the rate of diffusions is inversely proportional to…

the square of the distance over which diffusion occurs 

the rate of diffusion is directly proportional to…

the surface area across which diffusion occurs

How does the rate of diffusion increase?

with a larger concentration gradient and with increased temperature

the respiratory surface in some small animals (sponges, ctenophores, flatworms, roundworm) is

their entire body surface 

in large animals, the respiratory surface…

is made up of specialized structures (lungs and gills) 

what respiratory system do insects have?

tracheal system

tracheal system

a system of branching tubes; channels air from the outside to the internal organs and most indiividual cells

Why must the respiratory surface always be wet?

because gases must dissolve in water to enter and leave epithelial cells

what can respiratory surfaces be wetted by?

• thin film of water

• respiratory medium

evaginations 

extend outward from the body into the respiratory medium (gills)

invaginations

deep within the body’s interior where they’re less susceptible to drying out (lungs) 

what is system is responsible for gas exchange?

respiratory system 

What are the two adaptations that help animals maintain the different concentrations between gases inside and outside the respiratory surface? What does it lead to?

1) ventilation

2) perfusion  

leads to the max rate of gas exchange 

ventilation

the flow of the respiratory medium over the external side of the respiratory surface 

perfusion

the flow of blood or other body fluids to the internal side of the respiratory surface 

What adaptations do animals have if their skin is the respiratory surface?

body is elongated or flattened

What adaptations do animals have if they use gills as a respiratory surface?

respiratory surface has highly branched structures with many small projections

What adaptations do animals have if they use lungs or trachea as a respiratory medium?

respiratory surface has many branched structures with many small projections

How does water act as a respiratory medium?

• holds less oxygen than air

• oxygen content is affected by temperature and solute concentration 

• take significantly more energy to move water than air over a respiratory surface 

How does air act as a respiratory medium?

• relaytively higher oxygen content 

• low density, viscosity, low energy needs for ventilation 

• gas molecules diffuse faster in air than water 

• con: animals lose water during breathing 

countercurrent exchange

uses one-way flow of water over the gulls to maximize the oxygen and carbon dioxide exchange with water

Which direction does water flowing over gills move?

in the opposite direction of the flow of blood under the respiratory surface 

How much oxygen is removed from water during countercurrent exchange?

80-90%

How do insects breathe air?

through trachea (conducting tubes) 

what is an insect’s exoskeleton made up of?

invaginations of the outer epidermis of the animal reinforced with rings of chitin

spiracles

openings in the chitinous exoskeleton where air enters and leaves the tracheal system, open and close in coordination with body movements 

What pumps air through the tracheal system?

alternating compression and expansion of the body 

tracheoles

finest branches: dead-end tubes with very small fluid-filled tips that are in contact with cells of the body, forming the respiratory surface

at place within the body the tracheae expand into…

internal air sacs that act as air reserviors

what are one of the primary adaptations that allowed animals to live in terrestrial environments

lungs 

positive pressure breathing

a gulping motion that forces air into the lungs (lungfishes, amphibians, frogs)

negative pressure breathing

muscular contractions that expand the lungs, lowering the pressure, and causing air to be pulled inward 

what is the sequence of the human respiratory system?

• air enters through nostrils and mouth

• air moves through the throat (pharynx) and “voice box” (larynx) into the windpipe (trachea)

• the trachea branches into two airways (bronchi) leading to the two lungs

• inside the lungs, the bronchi narrow and branch, becoming progressively narrower and more numerous

• terminal airways (bronchioles) lead into cup-shaped pockets (alveoli), where gas exchange occurs

larynx, trachea, and the larger bronchi are….

non-muscular tubes encircled by rings of cartilage

the walls of smaller bronchi and bronchioles have…

smooth muscle cells that contract or relax to control the amount of air flowing to and from the alveoli

What does the epithelium of the bronchi contain and what does it do?

contains cilia and mucus-secreting cells that trap bacteria and airborne particles, moving them upward into the throat

what paralyzes the cilia in the bronchi?

tobacco smoke

diaphragm

dome-shaped sheet of skeletal muscle that separates the chest cavity containing the lungs from the abdominal cavity 

pleura 

double layer of the epithelial tissue that covers the lungs, a slippery fluid between the inner and outer layer allows the lungs to move freely within the chest cavity 

What brings air to the lungs?

contraction of the diaphragm and external intercostal muscles by negative pressure mechanisms 

why do the lungs resist stretching?

because they’re elastic and fluid 

What happens when oxygen demand is high?

air is expelled forcefully by contraction of abdominal wall muscles and internal intercoastal muscles; reduces the volume of the chest cavity

How is partial pressure determined?

by its proportion in the mixture

partial pressure

the pressure of each individual gas in a mixture

What is the partial pressure of oxygen in dry air at sea level?

160 mmHg (21% of total atmospheric pressure: 760 mmHg)

What is the partial pressure of carbon dioxide in dry air at sea level?

0.3 mmHg (4% of total atmospheric pressure)

What do oxygen and carbon dioxide diffuse to and from?

partial pressure gradients between alveolar air and plasma in pulmonary capillaries

Where is most of the oxygen in blood stored?

in the hemoglobin (98.5%)

hemoglobin-O2 dissociation curve

the pattern by which the reversible combination of hemoglobin with oxygen is related to the partial pressure of oxygen 

in the hemoglobin-O2 dissociation curve, what does the plateau of the S-shaped curve represent?

above 60 mmHg, the partial pressure of oxygen range found in the pulmonary capillaries, blood remain highly saturated 

in the hemoglobin-O2 dissociation curve, what does the steep part between 0 and 60 mmHg represent?

the partial pressure of oxygen range found in body capillaries, small changes in the partial pressure of oxygen result in a large change in oxygen bound to hemoglobin

Is the acidity in active tissues higher or lower? What does this create?

higher, oxidative reactions release CO2 which mixes with water to create carbonic acid (H2CO3) 

Bohr effect

how a lower pH affects hemoglobin’s conformation and its affinity to oxygen, causing it to release O2 and have it used in cellular respiration

Where does CO2 produced by cellular oxidations diffuse from active cells to?

to interstitial fluid (partial pressure of carbon dioxide - 46 mmHg), then into capillary networks (40 mmHg) 

Where does some CO2 remain 

stays in solution in the plasma; most (70%) combines with water to make carbonic acid

Where does CO2 + H2O ← → H2CO3 happen?

both the plasma and erythrocytes

carbonic anhydrase

enzyme that facilitates CO2 and water to become carbonic acid

Where do most H+ from carbonic acid go?

combine with hemoglobin or proteins in the plasma, acting as a buffer for the pH of blood, maintaining 7.4

Why is pH homeostasis important?

because many enzymes are sensitive to minor changes in pH

What happens as blood goes through capillary networks surrounding the alveoli?

the process of CO2 uptake is reversed; CO2 diffuses from the blood into the air