Gas Exchange

What is internal respiration?

In mitochondria, oxygen is used as the final electron acceptor in aerobic respiration

What is external respiration?

Animals obtain O2 from the environment, which then follows a pathway to the mitochondria

What happens to CO2 is aerobic respiration?

It is a waste product, so it must be efficiently removed because it acidifies body fluids

How does partial pressure work?

Partial pressure of a gas equilibrates between air and liquid

At the same partial pressure, there is a much lower concentration of the gas in liquid than in air

What is the pathway for oxygen?

Air fills the lungs

Oxygen diffuses across the alveolar epithelium and capillary epithelium

O2 diffuses down the partial pressure (PP) gradient (higher in lungs, lower in blood)

O2 binds to hemoglobin on red blood cells

O2 diffuses from blood into body cells (down PP gradient)

O2 and CO2 are transported by diffusion and bulk flow (no active transport)

O2 is carried in the bulk flow of air into the lungs and alveoli

O2 is also carried by the bulk flow of blood from capillaries to interstitial fluid

What is bulk flow?

Passive flow of matter (material carried within media) from one place to another

What is a good example of bulk flow?

Movement of CO2 and O2 with blood circulation

What are gas exchange membranes?

Thin layers of tissue where respiratory gases move between the environment and the internal tissues

What is breathing?

aka external respiration

Process by which O2 and CO2 are transported between environment and gas exchange membrane

What is a special feature of breathing organs?

They have a large surface area of gas exchange membrane, achieved by folding and branching

How do lungs achieve a large surface area?

Lungs are invaginated (folded inward) into the body and contain the environmental medium

How do gills achieve a large surface area?

Gills are evaginated (folded outward) from the body and are surrounded by the environmental medium

What is ventilation?

Bulk flow of air or water between the gas exchange membrane and the outside world

What is tidal ventilation?

Air moves in and then out the same passageways

Some fresh (O2-rich) and O2-depleted air mix

What is unidirectional ventilation?

aka flow-through ventilation

In animals with gills, water moves in a one-way stream across the gills

No mixing of fresh and O2-depleted air

More efficient at gas exchange

What is perfusion?

Blood flow through capillaries or other small blood vessels of a tissue

What speed does perfusion need?

Perfusion must be fast enough for O2 to be efficiently picked up from breathing

Blood must then circulate fast enough to efficiently deliver O2 and remove CO2 to body cells

How do the respiratory environments of air and water compare?

Diffusion is much faster through air than water

O2 solubility in water is low and decreases with increasing temperature, resulting in low PO2 in water compared to air

How do sea turtles demonstrate diffusion concepts?

Sea turtles lay eggs in the sand

Eggs get plenty of O2 if the sand is moist, but not wet

If the nest is flooded, PO2 is much lower and the eggs die

How are fish gills structured?

Fish gills have an enormous surface area for gas exchange

Each gill arch has two rows of gill filaments, each with numerous secondary lamellae on its upper and lower surfaces

How do fish pump water?

Unidirectionally

Through mouth cavity and gill slits, over the gills, and out from under the opercular flaps

Blood flows through each lamella in the opposite direction, a countercurrent system

How do terrestrial vertebrates exhibit tidal ventilation?

Dead-end sacs of gas exchange membrane

Inner surfaces of vertebrate lungs are coated with a lung surfactant that reduces surface tension and prevents the gas exchange tissue from sticking together

How do birds exhibit unidirectional air flow

Bird lungs unidirectional air flow to supply O2 to tissues at high rates

Air sacs expand and contract, acting like bellows to push air past gas exchange surfaces in the lungs

What is the tracheal breathing system?

In insects and spiders

Spiracles (openings) in the abdomen open into tubules called tracheae

The tubules branch in such a way that a gas-filled tubule comes close to every cell

Gases are exchanged directly with the atmosphere, so the circulatory system plays little role in O2 and CO2 transport

How are lung passages branched in mammals?

The trachea branches into two primary bronchi, then into secondary bronchi, then into bronchioles, which end in alveolar sacs of epithelial tissues

How are alveolar sacs structured?

The walls of each alveolar sac consists of pocket-like structures called alveoli, where gas exchange occurs

What is the most efficient system at transferring O2 from the environment into the blood?

Flow-through ventilation with countercurrent exchange

What is tidal volume?

Amount of air that moves in and out of the lungs per breath

What is respiratory minute volume?

Total volume of air inhaled and exhaled per minute

What happens to tidal volume during exercise?

People increase tidal volume and breaths per minute and thus increase respiratory minute volume

What is residual volume?

Lungs and airways are never completely empty

Some stale air is left behind

Each inhalation brings in a mixture of fresh air and stale air