BISC205 Topic 5 (in-person)

what is respiration? what is its purpose?

respiration: the entire sequence of events that results in the exchange of O2 and Co2 between external environment of an animal and the mitochondria within its cells

purpose: gas exchange. this involves receiving O2 from the environment and removing CO2 from the blood

what is partial pressure?

pressure that a single gas in the mixture would exert if it occupied the entire volume of the mixture by itself

ficks’ law of diffusion

how to increase rate of diffusion (based on ficks law)

increase diffusion constant of gas

increase SA of membrane

increase difference in partial pressure of gas

decrease diffusion distance across membrane

how to decrease rate of diffusion (based on Ficks law)

decrease diffusion constant of gas

decrease SA of membrane

decrease difference in partial pressure of gas

increase diffusion distance across membrane

equation of graham’s law

how to increase rate of diffusion based on graham’s law

increase solubility of a gas in medium

decrease the molecular weight of a gas

**liquid: solubility is more important than MW

**air: MW is more important than solubility

what is ventilation?

the active movement of respiratory medium (air or water) across respiratory surface

three types of ventilation with descriptions

1.) non-directional:

• medium flow past the respiratory surface in an unpredictable pattern

• found in animals that use cutaneous respiration or wave their external gills into the environmental medium

2.) unidirectional

• medium moves through respiratory system in one direction, passing over gas exchange surface before exiting through a separate pathway

• countercurrent vs crosscurrent

3.) tidal

• medium moves in and out of respiratory chamber in a back-and-forth movement

examples of animals that use each type of ventilation

1.) non-directional

• cutaneous respiration: earthworms, frogs, lungless salamanders,

• external gills: axolotl

2.) unidirectional

• seen in fish with internal gills (teleosts and elasmobranchs)

• avian lungs

3.) tidal

• lungs of mammals, insects, most reptilians (non-avian, except crocodiles), air breathing amphibians, and air-breathing fish

why is the non-directional graph shaped the way it is

medium moves across an organ’s respiratory surface in an unpredictable pattern, creating a well-blended pool of oxygenated or deoxygenated medium at the exchange surface

more mixing = more oxygenated medium rather than only stagnant unoxygenated medium, allowing for blood to pick up more oxygen

why is the tidal ventilation graph shaped the way it is

as the animal breathes in, incoming oxygenated medium mixes with stale deoxygenated medium left behind from the previous breath in the respiratory cavity. This means PO2 in the respiratory cavity is lower than that in the environment

two types of unidirectional ventilation

1.) countercurrent flow: blood flows in the opposite direction compared to medium along exchange surface

2.) crosscurrent flow: blood flows at a perpendicular direction compared to medium along exchange surface

why is the countercurrent exchange graph shaped the way it is

medium starts with high PO2 and decreases steadily as it gives up oxygen along the exchange surface. blood starts with low PO2 but increases as it picks up oxygen at exchange surface

why is crosscurrent exchange graph shaped the way it is

blood starts with low PO2 and steadily increases as it picks up oxygen from different parts of the medium. this causes the PO2 in blood to be higher than the PO2 in medium

examples of animals that use crosscurrent vs countercurrent exchange

still have to find

determine which is: unidirectional, tidal, crosscurrent, countercurrent

edit later

how does boyle’s law work

important to understand the mechanics of breathing. as volume decreases, pressure increases

4 steps in which elasmobranchs use buccal pump as a dual pumping mechanism for gill ventilation

1.) mouth opens and buccal cavity expands in volume, which decreases pressure inside the cavity

2.) suction phase: water rushes into buccal cavity through mouth and spiracles

3.) force phase: mouth and spiracles close, and muscles surrounding buccal cavity contract. this decreases volume of cavity and increases pressure inside, which forces water past gills and out through external gill slits

3 important structures of gills in bony (teleost) fish

1.) operculum

• flap-like structure that protects gills located in opercular cavity

• four gill arches in each opercular cavity

2.) gill arches

• provide structural support for two rows of gill filaments that project from each gill arch in a V-shape

3.) gill filaments or primary lamellae

4.) secondary lamellae

• main respiratory surface (thin walled and highly vascularized)

• rows of folds on each gill filament that are perpendicular to the filament

4 steps in which teleost fish use a buccal-opercular pump for ventilation

1.) draw water in

• mouth open

• opercular valve closed

• buccal cavity expands

• opercular cavity expands

2.) water moves from buccal cavity to gills

• mouth closed

• opercular valve closed

• buccal cavity compressed

• opercular cavity expanded

3.) water is forced over gills and out

• mouth closed

• opercular valve open

• buccal cavity compressed

• opercular cavity compressing

4.) return to step one, with some backflow of water

• mouth open

• opercular valve open

• buccal cavity expands

• opercular cavity compressed

how is gas exchange very effective at fish gills based on Fick’s Law

1.) lamellae have a very thin membrane (small diffusion distance)

2.) lamellae provide very large surface area for gills

3.) large partial pressure gradient of gas between water column and capillaries inside lamellae

how are fish gills an example of countercurrent exchange?

fish gills are an example of countercurrent exchange because blood flows through capillaries in the secondary lamellae in the opposite direction to water passing through gills

why is concurrent exchange not efficient with fish gills

if water passed through gills in the same direction as blood flow, the oxygen from the oxygen-rich water would quickly diffuse into the oxygen poor blood and reach an early equilibrium. Without the gradient, there is no more diffusion occurring and the fish will have insufficient oxygen.

what is ram ventilation?

when teleosts and elasmobranchs swim forward at higher rate of speed with mouth open to allow water to flow across gills without active pumping of the muscles surrounding buccal and opercular cavities

advantages of ram ventilation

1.) allows fish to dedicate more energy towards powerful swimming muscles instead of buccal/opercular muscles. this enhances speed

2.) increases flow rate of water over gills as fish swims faster. this increased oxygen uptake is needed to meet the higher metabolic needs of the fish

disadvantages of ram ventilation

1.) some fish (obligate ram ventilators) must swim continuously to breathe for survival

2.) opening mouth results in increased drag on fish and thus affects locomotion. this drag is minimized if they have a streamlined body shape

how do mudskippers perform air breathing? (focus on organs)

1.) absorb oxygen through their skin (cutaneous respiration)

2.) absorbs oxygen through the lining of their mouth and throat (both of which contain a high density of blood capillaries)

3.) they have modified gill chambers that help in trapping pockets of air and water while on land (this prevents gills from collapsing and allow for gas exchange)

how do electric eels perform air breathing?

they use extensive folds in mouth which are highly vascularized for substantial aerial gas exchange

how do armoured cat fish perform air breathing

they have a highly vascularized stomach that they use for gas exchange after gulping air. they can survive out of water for up to 30 hours if enough oxygen is stored in their bellies

how do bichirs perform air breathing

use paired lungs that are highly vascularized for gas exchange. they are facultative air breathers, accessing surface air to breathe when the water they inhabit is poorly oxygenated.

both of their lungs are unchambered sacs. the larger right lung reaches the whole length of the body cavity while the smaller left lung extends to the stomach

how do lungfish perform air breathing (most developed air breathing organs)

they have highly vascularized lungs that are complex and covered in folds and pockets that increase their surface area. most extant lungfish species have two symmetrical lungs (exception is Australian lungfish that has one lung)

how do insects use the tracheal system in respiration

1.) spiracles

• large trachea connect to spiracles (openings on surface along abdomen) where O2 enters and CO2 exits

• spiracles close using valves to reduce water loss, which lets the insect live in dry areas

• spiracles open with a rise in CO2 in the tracheal system

2.) air sacs

• reservoirs of air. they push air through the tracheal system when contracted

3.) tracheal tubes and tracheoles

• tubes that carry air throughout body directly to cells and tissues (like muscles)

how do amphibians and non-avian do respiration

it respires through its most skin (cutaneous respiration) and by using their lungs

why are frog lungs not as efficient as fish gills for respiration

1.) new air that is inhaled mixes with old air already in the lungs (since tidal ventilation is not as efficient as unidirectional)

2,) lungs have relatively smaller surface area

**this is okay because O2 levels are higher in air than in water

why can’t non-avian reptiles use cutaneous respiration like frogs/amphibians

they cannot perform cutaneous respiration because their dry scaly skin is watertight to avoid water loss

why do non-avian reptiles have more efficient lungs than amphibians/ frogs

the lungs of reptiles have a larger surface area than the lungs of amphibians