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The Hemocoele/Mixocoele:• Not a true coelom, which

is lined with mesoderm (small remnants only)

• Instead, it’s lined with ectoderm & endoderm

• Hemolymph is thus separated from organs by basement membrane (amorphous muco-polysaccharide + collagen – very complex)

An open system• small size, short diffusion

distances

• no blood gasses to distribute

The insect circulatory systemDorsal vessel

HeartAorta

Dorsal vessel

OstiumPERICARDIALSINUS

PERIVISCERAL

SINUS

PERINEURAL

SINUS

PERINEURAL SINUS

PERICARDIAL SINUS

PERIVISCERAL SINUS

Ostium

(dorsal septum)

(ventral septum)

Alarymuscle

Not:

heartPERICARDIAL SINUS

PERIVISCERALSINUS

pleuro-sternalboundary

PERINEURALSINUS

ventral nerve cord

ventralseptum

dorsalseptum

alarymuscle

septum (diaphragm)

fenestra

X

The insect circulatory system: some details

os = ostium; v = valve (Diptera)

gut

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Pattern of circulation

wing heart

excurrent ostium incurrentostium

nervecordheart

ganglionleg

extension ofventral septum

legdorsal vessel

(aorta)

leg ampulla

antenna

antennalampulla

wingampulla

one-wayvalve of

incurrentostium

dorsal & ventral septa with fenestrae at edges

ampulla

ampulla

aorta (dorsal vessel)

brain

Accessory pulsatile organs (APO)in a cockroach

distal vessel

proximal vessel

dilator muscleof ampulla accessory

dilatormuscle

esophagus

aortal dilation

eye

corpus cardiacum& corpus alatum

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Circulation in the wing venation of three beetles

Cupedidae

Carabidae

Scarabaeidae

Lateral segmental vessels

heart septum

vessel

Some roaches & mantids(Dictyoptera)

2 thoracic, 4 abdominal

4 abdominal

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alary (aliform)muscle

aorta ordorsal vessel

dorsaldiaphragm

tergo-sternalmuscle

heart

segmental orlateral vessel

incurrentostium

segmental orlateral vessel

Segmental vesselsin Blaberus(2 pairs thoracic,

4 pairs abdominal)

Thermoregulation and the “rete mirabile”

heartaorta

convolutions (rete mirabile)

Bees & wasps(Hymenoptera)

rete mirabile

(116.6° F)

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Bumble bee circulation& thermoregulation

rete mirabile

(radiator)(tidal air)

Centralization(shortening) of the heart

heart

aorta

3 pairs of ostia

certain Diptera & mayflies(Ephemeroptera)

Number of pairs of ostia:• 3 to 9 in mayflies & roaches• 3 in higher Diptera• 1 in a highly specialized mayfly

Drosophila melanogaster

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alary (aliform)muscle

aorta ordorsal vessel

dorsaldiaphragm

tergo-sternalmuscle

heart

segmental orlateral vessel

incurrentostium

segmental orlateral vessel

Number &

placement of ostia;

nature of alary muscles

Ex. = ancestral condition

Heartbeat:• Heartbeat and alary

contraction synchronous

• Heartbeat and alary contraction asynchronous

• 14–150 beats/minute (stag beetle vs. house fly)

• Varies with O2, temperature, diet, life stage (or instar)

• myogenic not neurogenic

• also from neurosecretions of corpora cardiaca, etc.

Hemopoietic organ (“lymph glands”)

Prohemocyte

Prohemocyte

Hemolymph (“blood”):• Clear & colorless or yellowish

or greenish

• pH 6–7.5

• Na+, Cl-, Ca++, K-

• 5–40% of body weight **

• Filled with fats, organic acids, amino acids, carbs, proteins, & pigments

• 1k–275k cells/mm3

** 7–8% of a person’s weight is blood

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Cells in the hemolymph (hemocytes)

ProhemocytePlasmatocytes

Granularhemocytes

Cystocytes(coagulocytes)Spherule cell

Adipohemocyte

Oenocytoid

vermiform cell

BASOPHILIC(hematoxylin)

ACIDOPHILIC(eosin)

Yeager (1945) described 10 classes with 32 types of blood cells

neg– pos+

epithelium

basementmembrane

cuticle

oenocyte

cytoplasmicstrand

Pericardial cells(can be in phagocytic organs)

Oenocytes(epicuticle, wax & cement, enzymes)

(170-180µ)

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Blood Function:

Chrysomelidae (leaf beetle)

Coccinellidae (lady beetle)

Hemolymph functions:• Water storage

• Osmoregulation (organics)

• Transport (e.g. hormones)

• Food storage (e.g. trehalose, a disaccharide)

• Respiration (at the cellular level of diffusion)

• Protection

• reflex bleeding

• clotting

• phagocytosis

• encapsulization

• immune response (innate not “learned”)

• antifreeze (glycols)

• Mechanical (hydrostatic)

• Thermoregulation

Wound-healing and clotting

nematode parasite

entrance wound

Diptera larva

a blood clot

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Immune function of blood: Encapsulization

Hydrostatic functions of blood

Eversible male genitalia Molting & wing expansion

Hydrostatic skeleton

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Fat body3 masses

on each sideof body

fat body cells (= trophocytes,urocytes, and mycetoctyes)

(may also surround gut)

GUT

Fat body functions:• Food storage (trophocytes)

• Secretion, synthesis, & catabolism (metabolic)

• Waste storage (urocytes) –storage excretion as uric acid

• “Real” excretion

• Nutritional endosymbiosis (mycetocytes)

• Bioluminescence

Coleoptera: Lampyridae

Muscles: categories

Labium of a cricket

Metathoracic leg of a grasshopper

levator (extensor)

depressor

extrinsicmuscle

intrinsicmuscle

intrinsicmuscles

extrinsicmuscle

Muscle contraction:1. Nerve impulse

2. Secretion of acetylcholine

3. voltage change across muscle membrane

4. chemical changes in muscle:

a. flooding in of Ca++

b. changes bonding of actin & myosin

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Muscle

Ultrastructure

sarcolemma mitochondria

fibrils (myofibrils)

basementmembrane

nucleus

nerve/musclejunction

neurallamella

glialsheath

nerveaxon T-tubule

I -band

A-band

H-band

A-band

I -band

Z-disc

muscle fiber(or muscle cell)

actin filament

myosin filament

actinmolecule(filament)

myosinfilament

headsforming

cross-bridges

Flightmuscle

Visceralmuscle

I -band

Z-disc

Sar

com

ere

Muscle

Ultrastructure II

(the sarcomere isthe contractile element)

Muscle fiber (or muscle cell)

Fibril (myofibril)Sarcomere

X-sec. Myofilaments