Circulatory system + gas exchange

Hemocoel 

Open organized zone/cavity that encloses hemolymph fluid. 

Hemolyph

“blood“. It does not directly touch the cells.

It:

• NO O2 TRANSPORT

• Transport nutrients, water, hormones, chemicals, heat, etc…

• Chemical defense, ex, reflex bleeding in ladybugs

• Acts as a hydrostatic skeleton used to push and inflate prolegs, wing enlargement, caterpillars, hatching and moulting, etc

composed of plasma and hemocytes

Median basement membrane

Ensures that the hemolymph does not directly touch cells. It covers the cells and mediates transactions.

Plasma

The fluid of the hemolymph. 

• Water

• Inorganic Ions, of different concentrations depending on the diet of insects. 

• Waste, uric acid, urea, ammonia

• Organic acids

• Sugars specifically Trehalose but also others such as glycerol.

• Lipids (free)

• Amino acids, é source for flight 

• proteins:

• Hexamerins -> store proteins created from the fat body, important for pupation.

• Lipophorin -> transports lipids

• JH-binding proteins

Hexamerins

A store proteins created from the fat body. It is important for pupation. 

Lipophorin

Protein in the plasma that transports lipids.

Hemocytes

Blood cells of the hemocytes.

• A lot of different types of nucleated blood cells.

• Phagocytosis: ingestion of small particles and substances. 

• Encapsulation of parasites: foreign material, using melanin

• Coagulation of the hemolymph:  used for wound closing

• Store and distribute nutrients. 

Septa

a wall, dividing a cavity or structure into smaller ones. Go through the appendages so the hemolymph doesn’t mix. 

Sinus

  a channel for venous blood/a dilatation in a bodily canal or vessel

dorsal vessel

 It is a simple tube of myocardial cells. It lies in the pericardial sinus above the dorsal diaphragm. It uses peristaltic motions to push hemolymph around the body with contractile motions. It has ostia.

Aorta

The anterior dorsal vessel 

Dorsal diaphragm

Found within the pericardinal sinus. It is a diaphragm found on the dorsal side. It is a separating membrane. It is a fibromuscular septum of connective tissue and alary muscles used to support dorsal vessels. 

Ostia

They help fluid get into the dorsal vessel. They are segmented 1 way valves so no back flow is possible.

Ventral diaphragm

a fibromuscular septum that lies on the ventral floor. It is associated with the ventral nerve cord and aids in circulation. It pumps parasitically, pumping hemolymph backwards and laterally towards the appendages

Accessory pulsatile organ

pumps to appendages. It is found at the base of cerci, wings, legs and septas. They are little pumps that separate flow, 1 way.

Spiracles

 small external openings on the side where air enters the insect body. They branch off into the tracheal system in the body and become thinner and thinner. Sometimes they are even 1 cell thick . 

• There can be up to 10 pairs however simplification is not uncommon. 

• 2 thoracic spiracles and 8 abdominal spiracles. 

• Spiracles can open and close due to both a lack of O2 and too much CO2. 

Simple

• the spiracle entrance is at the surface.

Atriate

: filtered spiracles, the entrance is covered by lips

Filtering

It stops particles from entering with their fuzzy lips. This is more common in subterranean insects to prevent dirt from getting into their spiracles

Trachea

• the large pathways

• Paired invasignations of epidermis (ectodermal origin) meaning it is shed during moulting. 

• The taenida are sclerotized for support

Tracheoles

• Fine tubules for gas exchange. 

• Really tiny

  • Not always shed at moulting

Taemidia

• Spiral structural support made up of thickenings of the trachea. 

• They are heavily sclerotized for support, flexibility and to stop internal collapsing

Intima

• Ectodermally derived internal cuticle

• Forms the inner lining of the trachea, foregut and hindgut. It is a chitinous layer to slow down O2 absorption so that not all the O2 is absorbed at once. 

Lateral trachea trunk

This is the main “train track” but it branches off into the rest of the body.

Visceral trachea

Trachea that is found in the gut.

Closed spiracle phase

The body has sufficient oxygen = closed spiracles, the body consumes the O2 within itself and the O2 levels drop.

Flutter phase

The spiracles open and close in a flutter like motion that lets more O2 in the body but continues to build up CO2 levels. THe rising CO2 levels start to become a problem.

Open spiracle phase

The spiracles open up and CO2 is lost, the body is able to take in more O2. This comes at the cost of more water loss.

passive diffusion/ventilation

Ventilation requires the compression of the body to reduce the amount of diffusion needed. It is assisted by air sacs, ventilation movement (compression by the thorax and abdomen), strategic opening/closing of the spiracle and hemolymph movement

Air sacs

evolved solely as reservoirs of O2. They have now been co-opted for,

• Tracheal dilation

• Increase tidal air flow, increases the amount of tidal air that can be changed. 

• More buoyancy during flight. 

• Decrease mass of insect when flying

• Distribution of air to manage overheating. 

• Space for moulting, inflation of the body.

• Tympanic structure, noise making structure

• Escaping pupal casing/opens caps, very niche

open system

spiracles present

closed system

 no spiracles this is especially common in cutaneous exchange insects and aquatic insects. The trachea divides peripherally.

Terminal spiracle

“the snorkel”, an adaptation in aquatic insects where the terminal spiracle siphons O2 from the atmosphere. This is possible because of an appendage (often covered in water repellent hairs) piercing the surface tension. The snorkel can be constantly up or it can come back down. Ex, mosquito larvae

Piercing siphon

 a terminal spiracle pierces the aerenchyma of aquatic plants

Hydrofuge hairs

The hair is closed over spiracles to protect it. It then separates by expanding and the tension exposes the spiracles.

Air bubbles

the air bubble is found under the wing cover. The trachea opens into air space. The O2 from the water around it will naturally diffuse into the bubble as well. The challenge with this strategy is that you are constantly fighting buoyancy. Therefore these insects are strong swimmers. Use sub-elytra for a super fast collection.

Compressable gills

These insects trap lots of air including CO2 which is lost because it is dissolvable in water. As they breathe the proportion of Nitrogen increases, then the nitrogen diffuses/leaves and the bubble will get smaller and smaller. 

Plastrons

incompressible gills. It has many, many, many permanent hairs that trap air. The bubble never shrinks or goes away. They are sedimentary insects that need to live in fast moving water so that the water is highly oxygenated.

Tracheal gills

There are no spiracles, they need to get O2 from the water, and use trachea for gas exchange. This strategy increases the surface area. Usually found abdomenally. Ex, Dragon fly larvae have them in their rectum

Respiratory pigment

 Ex, hemoglobin in the hemolymph helps pull O2 out of the water. These insects can live in highly anoxic environments.