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02.05 Circulation and Gas Exchange

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Bugs 101: Insect-Human Interactions

University of Alberta

4.8 (16 ratings) | 5.3K Students Enrolled

Of all the animals on earth, which are the strongest for their size? What about the fastest? Who were the first animals to evolve flight? Insects take all of these titles and more! As the most abundant animals on the planet, insects and other arthropods affect our lives in so many ways. From beneficial interactions like pollination and biological pest control, to the transmission of life threatening diseases; this course will teach you about the big ways that these little arthropods impact our lives. In Bugs 101: Insect-Human Interactions, you will be plunged into the diverse (and sometimes alien) world of arthropods to learn how they work, what they do, and how insects and humans interact every day. After completing this course, you will be able to: Describe the evolutionary relationships between insects and their arthropod relatives Inventory major groups of insects and their diversity Demonstrate evolutionary adaptations that make insects successful Discuss insect biology and human-insect interactions Evaluate positive and negative interactions between insects and humans Propose practical and symbolic roles insects play in human societies

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Skills You'll Learn

Biology, Entomology, Science, Ecology

Bewertungen

4.8 (16 ratings)

5 stars
15 ratings
2 stars
1 ratings

VI

Aug 13, 2019

A study which is highly enjoyable and useful for professionals

CS

Aug 15, 2019

Overall a great course. Would, and have, recommend to others.

Aus der Unterrichtseinheit

Module 02: The Business of Being an Insect Part 1

What makes an insect an insect? How do these strange creatures operate? This module begins to uncover the inner workings of insects, starting with the digestive and circulatory systems.

02.05 Circulation and Gas Exchange11:04

Unterrichtet von

Dr. Maya Evenden
Professor of Entomology

Skript

Let's take a look at the insect circulatory system.

As we've previously learned,

insects and other arthropods have

an open circulatory system.

This means that the insect equivalent of blood,

the haemolymph is contained within

the insect body cavity known as the hemocoel,

and not restricted to blood vessels like in humans.

The haemolymph however, does not come

into direct contact with cells or tissues,

instead basement membranes line

the internal organs and the inside of the exoskeleton,

which creates a selective barrier

between the haemolymph and the tissues.

The haemolymph is a watery fluid that

contains cells, inorganic ions,

and organic molecules such as lipids,

sugars, amino acids, and proteins.

It is typically colorless

unlike the blood of vertebrates,

though in some cases,

pigments provide colors such as yellow,

blue, and rarely even red.

The haemolymph is a major component of an insect's mass.

In soft body larvae,

this fluid can make up 20 to 40 percent

of the insects body weight,

and usually makes up about 20 percent

of the body weight in nymphs and adults.

Haemolymph has two main components,

the liquid plasma, and the

cells referred to as haemocytes.

Plasma is the main constituent of the haemolymph,

and mediates all chemical exchanges including hormones,

nutrients, and wastes between insect tissues.

For example, plasma distributes

nutrients such as trehalose,

the main blood sugar in many insects.

Insect hormones including those

that regulate growth and development,

are also distributed by the plasma.

Maybe surprisingly haemolymph does

not transport oxygen to insect tissues.

This is because it lacks oxygen carrying pigments,

like hemoglobin used by vertebrates such as ourselves.

However, some insects that live

in low oxygen environments,

such as stone flies,

and some Kiran amid midge larvae,

have specialized proteins that help store

oxygen to allow them to

survive in these difficult conditions.

These proteins can even include hemoglobin,

although in these insects it is primarily used for

oxygen storage rather than transportation.

For the most part,

the circulatory and respiratory systems

in insects are separate.

Hemocytes are nucleated cells that serve many functions,

and are the main component of the insects immune system.

Some hemocytes ingest foreign particles, microorganisms,

or dead and dying cells,

while others work together to encapsulate parasites.

Hemocytes are also involved in

haemolymph coagulation in the event

of a wound to the integument.

The coagulation helps to heal the injury,

and inhibit the entry of harmful pathogens,

and foreign substances into the insects body.

In many insects, distasteful chemicals are

incorporated into the haemolymph

to deter hungry predators.

The insect circulatory system has

a single tubular muscular vessel,

the dorsal vessel which is

supported by the muscular dorsal diaphragm.

Haemolymph moves into the dorsal vessel through

one-way valves located along

the length of the Oregon known as Ostia.

Waves of muscular contractions along

the dorsal vessel push haemolymph anteriorly,

and out of the vessel into the insect's head.

Haemolymph is then gradually directed

back to the rear end of the body by

the rhythmic contractions of

a muscular structure known as the ventral diaphragm.

Haemolymph movement into major appendages,

such as the antennae, wings,

and legs is managed by

additional pulsatile pumps located

at the base of each appendage.

There's a regular pattern of

haemolymph flow between body segments and appendages,

thanks to impressive coordination

between the dorsal vessel,

accessory pumps, and diaphragms.

The insect nervous system helps

to mediate such coordination,

and we'll learn more about

the nervous system in the next module.

Gas exchange refers to the intake of oxygen,

and release of carbon dioxide

between organic tissues and the environment.

As we have discussed previously,

gas exchange in insects,

is achieved by a network of tubes lined

with cuticle known as trachea,

located throughout the body.

The cuticular lining is reinforced along

most areas by spiral thickenings

that prevent it from collapsing,

while still retaining flexibility,

because they are cuticular in nature,

these linings are shared with

the rest of the exoskeleton,

and replaced every time the insect molts.

To transport oxygen to the tissues that need it,

the trachea branch into smaller tubes called tracheoles,

that measure less than one micrometer in diameter.

Tracheoles are in close contact with tissues,

or even embedded into organs.

Tracheoles generally occur in higher numbers

in tissues that have high demand for oxygen,

such as the muscles that power flight.

The trachea connect to the outside environment,

through openings in the insect body wall

called spiracles.

Spiracles are generally found laterally

along an insect's thorax, and abdomen.

They can have filters or valves,

that open only when gas exchange is taking place.

This helps prevent entry of

harmful particles and microorganisms,

and reduces water loss from evaporation.

If the spiracles are held closed,

insects can quite literally hold their breath,

and minimize exposure to

parasites or airborne insecticides.

In highly active insects,

the tracheal system may make up

as much as 50 percent of the insect's body volume,

while in relatively inactive insects,

it can take up as little as 5 percent

of the insects body volume.

One fascinating thing about tracheal cells,

is that they are particularly sensitive to oxygen levels.

If areas with low oxygen levels are

detected within the insects body,

additional tracheal tissues will grow to

supply these oxygen deprived tissues.

In some insects, parts of

the tracheal network maybe enlarged to form air sacs,

which are flexible structures with multiple functions.

For instance, the air sacs act as a reservoir,

and their expansion and contraction,

can help increase the volume of

air flowing through the tracheal,

and allow more efficient distribution of oxygen.

Air sacs are also involved in

sound production by some insects, such as cicadas.

Finally, they may be compressed to provide room for

the growth of internal tissues

before the insects next molds.

While the insects gas exchange system is

relatively consistent across species,

like most things we've discussed so far,

it can be adopted for

specific functions by insects in different habitats.

Let's compare the gas exchange system

between terrestrial and aquatic insects.

Most terrestrial insects have what is

called an open tracheal system,

whereby spiracles connect the tracheal system

to the external environment.

In most aquatic insects and some parasitic larvae,

the spherical are absent,

which produces a closed tracheal system.

In these insects, a network of

tracheal is formed near the insects integument.

This allows gas exchange to occur through the cuticle,

which may be thinner in these areas.

Some aquatic insects have

special respiratory structures such as gills,

leaf-like extensions of the body

covered by a thin layer of

cuticle with a network of

tracheal located immediately underneath.

So how does the tracheal system work?

Airflow in the tracheal system is driven by the diffusion

of gases from high to low concentration,

which is often supplemented by active ventilation.

Oxygen enters through the spiracles and

diffuses through the trachea to the tracheoles,

and into tissues and cells.

This produces a net movement of

oxygen inwards into the insects body.

At the same time,

carbon dioxide moves outward

through the tracheal network,

and is released from the spiracles.

Another way in which carbon dioxide

may travel through an insect's body,

is diffusion from the tissues through

the haemolymph into trachea near the spiracles,

where it is released to the external environment.

This is because carbon dioxide

tends to be more soluble than oxygen,

and so it's movement is not

limited only to the tracheal network.

Other than carbon dioxide,

water vapor is also released

from an insect during gas exchange.

In terrestrial insects, the loss of water from

gas exchange can be costly especially in arid habitats.

Therefore, gas exchange in terrestrial insects,

is a delicate balance between

oxygen intake and water loss.

Depending on the insect and its habitat,

the spiracles may be left open

continuously, cyclically, or discontinuously.

Discontinuous gas exchange is often practiced by

insects during periods of inactivity or diapass.

The spiracles are kept closed

and opened only periodically.

In insects without air sacs,

gas exchange is achieved through diffusion,

although some insects may facilitate

airflow by pumping the thorax and abdomen.

Some insects also coordinate

the opening and closing of the spiracles,

to help create unidirectional airflow

in the main trachea.

Specifically, anterior spiracles are

open during air intake,

and posterior ones are opened when the air is expelled.

The rate of gas exchange is typically

dependent on two factors.

The first is the diameter of the trachea,

which can be enlarged in some species in

low oxygen environments to allow greater airflow.

The second factor, the distance of

diffusion is typically more important.

Generally, the shorter the distance of diffusion,

the greater the rate of airflow.

As such, the diffusion based nature of gas exchange in

insects is a limiting factor on insect body size,

as oxygen diffusion can only occur

effectively over short distances.

Typically, the larger the insect,

the greater the proportion of body mass

dedicated to a tracheal network,

because diffusion is not efficient over large distances.

To compensate for this,

many large insects have

long thin body plans like we see in dragonflies,

that result in short distances between

the spiracles and the body tissues.

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