Biology 1107; Topic 6: Gas Exchange

what are different strategies animals use for ventilation all based on?

use of simple passive diffusion, favorable gradients

ventilation

the use of a muscle action to induce a flow of a respiratory medium over the external side of the respiratory surface

respiratory medium

the environment animals use as a source of oxygen, typically either air or water (or both for amphibians)

respiratory surface

formed by a layer of epithelial cells; the special area developed to be the site of gaseous exchange (usually in larger and more complex organisms); interface between respiratory medium and body (inside and outside); typically have two structural properties that favor high diffusion - thin, and have high surface area

how do small animals (sponges, roundworms, flatworms, etc.) typically perform gas exchange?

maximize body cell surface area (expose skin to water or air); those epithelial cells perform gas exchange (entire body surface serves as respiratory surface)

how do insects and arachnids perform gas exchange?

have evolved a tracheal system to bring oxygen to individual body cells

tracheal system

important evolutionary development in the history of terrestrial animals; the most direct and efficient respiratory system in animals; consists of a network of small tubes (called tracheae, which branch into tracheoles) that lead from openings (called spiracles, which carry air); however, they are strictly diffusive - why insects cannot get so big

evolutionary advantage and disadvantage of gill

gills have direct access to the respiratory medium (water), but are exposed to the environment

evolutionary advantage and disadvantage of lungs

lungs are protected from the environment (internal) but the animal must have a mechanism to get the oxygen down (which requires energy) - lungs are also the best system in terms of getting bigger (have the best capacity to get oxygen to the biggest bodies)

what are the two structural properties respiratory surfaces typically have?

they are thin, and they have large surface areas (to optimize gas exchange)

Fick’s law

the rate of diffusion across a membrane is directly proportional to the concentration gradient of the substance on the two sides of the membrane and inversely related to the thickness of the membrane

transitional groups between lungs and gills

mudskippers, lungfish; have modified swim bladders (also called air bladders) that usually operate as a buoyancy organ but can also function as a primitive lung or respiratory aid - allowed them to explore terrestrial environments

countercurrent gas exchange system

how fish solved the problem of gas exchange; contains an oral cavity that funnels water over a respiratory surface (the gill) and then back out into the environment; water is pushed over the gill’s epithelium which contains less O2 and more CO2 (*water and blood flow in opposite directions), passive diffusion occurs; very efficient and optimal strategy for diffusion (removes ~80-90% of water’s O2 content)

positive pressure breathing

the forcing of air into the lungs, notably done by amphibians (and humans can do it for medical reasons but we don’t do it naturally)

pressured breathing in amphibians vs. humans

amphibians can gulp air in to create positive pressure, we have intercostal muscles and a diaphragm that allows us to create an internal vacuum

negative pressure breathing

muscular contractions that expand the lungs, lowering the pressure and causing air to be pulled inward (done by reptiles and mammals)

trachea (in humans)

articulated from our oral cavity; the singular tube that connects our oral cavity with our lungs

bronchi (humans)

branches from the trachea into our two lungs; the epithelium of this contains cilia and mucus-secreting cells that trap bacteria and airborne particles and move them upward into the throat (but tobacco smoke paralyzes the cilia)

bronchioles

smaller tubes branching from a bronchus in one lung, lead to the alveoli

alveloi

the small high SA low volume area that is covered with capillary beds; allows for / is the site of gas exchange

partial pressure

the relative concentration of a gas; principle is applied in living organisms in biological processes involving gases

hemoglobin

a protein in our RBCs that is structured to have a varied affinity for O2 (has four active sites that each have an iron/heme group) - rate of saturation is sigmoidal because of cooperative binding - more O2 that binds, easier it is to bind even more O2 - resulting from Hb’s conformational folding as molecule becomes more saturated

Bohr effect

a term that describes how we get our body’s Hb to release O2; the process by which Hb’s conformational shape is changed using pH and ppCO2 alterations

carbonic anhydrase

as CO2 product moves out of tissues and into the blood plasma and then RBCs, this enzyme combines CO2 with water to form carbonic acid (H2CO3) which dissociates into the bicarbonate ion (which is moved out into the blood plasma) and hydrogen protons; free H+ unite w/ Hb molecules, causing Hb to unload O2 into the cytosol; enzyme operates FAST

physiological respiration

the process by which animals exchange gases with their surroundings - includes taking in O2 and delivering it to body cells, and removing CO2 from body cells and delivering it to the environment

cellular respiration

all of the oxidative reactions that lead to the production of ATP in the mitochondria of animal cells - where O2 is used, and CO2 is released

breathing

the exchange of gases with the respiratory medium (can be air or water)

evagination

a part of the body (in this case the respiratory system) that extends outwards into the respiratory medium - e.g. gills

invagination

a part of the body (in this case the respiratory system) that is deep in the body interior (where they are less susceptible to drying out) - e.g. lungs

respiratory system

responsible for gas exchange, consists of all parts of the body involved in exchanging air between external environment and blood

perfusion

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

ventilation vs. perfusion

ventilation - over EXTERNAL side of resp. surface; perfusion - over INTERNAL side of resp. surface

comparing air vs. water respiratory mediums

water - holds less O2, content affected by temp and solutes, takes much more energy to move water over respiratory surface

air - holds more O2, low viscosity of air reduces energy required for ventilation, gas molecules diffuse faster in air than water, HOWEVER animals LOSE WATER during gas exchange (breathing)

tracheoles

dead-end tubes with very small fluid-filled tips that are in contact with the cells of the insect’s body (forms the respiratory surface); at places within the body they expand into internal air sacs that act as air reservoirs

pleura

the double layer of epithelial tissue that covers the lungs; there is a slippery layer between the inner and outer layers that allows the lungs to move freely within the chest cavity