Lecture 4: Gas Exchange

Where does gas exchange happen in humans. State the order

Alveolar air → alveolar wall → capillary wall → blood plasma → red blood cells → O2 binds to hemoglobin 

What is the gas exchange surface in humans 

Alveolar-capillary membrane

How does gas travel across membranes

Diffusion. Gas diffuses from high → low concentration

What does high partial pressure mean

Area has a lot of gas 

What does low partial pressure mean

Area has little gas

Gas moves from high/low partial pressure area to high/low partial pressure area

high;low

There is the alveoli and body tissues. Which way does oxygen diffuse down the concentration gradient.

Alveoli → body tissues 

There is the alveoli and body tissues. Which way does carbon dioxide diffuse down the concentration gradient. 

Body tissues → alveoli

what is ficks law and what does each variable represent

Q: rate of diffusion 

A: area of membrane 

P1 - P2: partial pressure differential. Whats the partial pressure of the gas outside - (minus) inside

L: diffusion distance across the membrane. How far do gas molecules have to travel to get from outside to inside 

D: diffusion speed

how can animals take advantage of the variables of ficks law

1. Increasing A (area of membrane)

2. Increase P1 - P2 (partial pressure difference) 

3. Decreasing L (diffusion distance across membrane): animals will have a trait that placed their blood vessels close to gas exchanger surface 

4. Increasing D (diffusion speed): animal will obtain oxygen through air instead of water

   1. Oxygen is easier to obtain from air than water

5. Aquatic species cant obtain oxygen from air, so instead of increasing D, they need to increase  A (P1-P2)/L

Define ventilation

Active moving respiratory medium over surfaces 

Define perfusion

Actively moving blood over gas exchange surfaces 

what is active part of inhalation cycle?

what happens in the diaphragm? the lungs? pressure increases or decreases in lungs?

diaphragm contracts, lungs expands, pressure decreases

what is passive part of inhalation cycle?

diaphragm relaxes, lungs recoil, pressure increases

what are lamella and why is this beneficial for fish (aka which variables do they affect in fricks law?)

flat filaments that gills are made of.

Due to low oxygen in water (low D: diffusion speed bc its harder to obtain O2 in water), aquatic animals’ lamellae increase A (area of diffusion surface). decrease L (diffusion distance) by having capillaries close to lamellar surface

Fish ventilation is unidirectional. what does unidirectional mean

water flows in one continuous direction across the gills.

what is concurrent gas exchange in fish

water flows in one direction, blood flows in the opposite. Blood comes out the gills, across lamallae, and back to the body.

describe gas exchange in amphibians. What do the use for gas exhange, does it work better in air or water, which variable of fricks law does it take advatnage of, what is a risk of the organ they use for gas exchange?

Use cutaneous respiration: using skin as gas exchange membrane. If skin is thin enough, you can do gas exchange directly through skin. 

1. This increases rate of diffusion by decreasing L (capillaries are close to skin).

2. Cutaneous respiration works faster in air, but it works underwater. 

3. Negative of cutaneous respiration is losing water. We only really see animals with cutaneous respiration when they are from moist environments, like amphibians. 

what do insects use for gas exchange

Use tracheal system to allows individual cells to exchange gases with the environment. 

tracheal system is a tube system infiltrating the body, carrying oxygen directly to cells 

do humans use unidirectional or bidirectional flow

Use tidal ventilation (bidirectional flow) Air moves in and out through the same path. 

What is tidal volume, residual volume, dead space?

Tidal volume is the amount of air inhaled or exhaled during a single normal breath (typically about 500 mL).

Residual volume is the air remaining in the lungs after a maximal exhalation, which keeps the lungs from collapsing.

Dead space is the volume of air that does not participate in gas exchange, either because it stays in the conducting airways or reaches non-perfused alveoli

are humans lungs ever completely empty?

Lungs are never completely empty. There is stale air which is low in O2 that remains after exhaling. This stale low O2 air mixes with fresh air.

is oxygen non-polar or polar? does it dissolve in blood?

nonpolar; no

descrube sturcture of hemoglobin. which part holds iron

4 hemes with one iron in center, iron is responsible for holding oxygen

How tight iron holds oxygen molecules (affinity) is influenced by:

1. PO2  in blood, if its low, iron will let go 

2. pH of blood, if pH is low, iron will let go 

3. Concentration of glycolysis metabolites is high, iron will let go 

How blood transports Carbon dioxide

CO2 diffuses from the blood into the alveoli and is exhaled.