TODAY: Structure & Function Part I
• Muscles & Movement
• Blood & Circulation
• Tracheal System & Gas Exchange
Muscles & Movement
IMPORTANT CONCEPTS:
• All striated (no smooth)
• Major Types:
1) Synchronous
2) Asynchronous
• Motion often driven by both muscles and
cuticular flexure + energy storage
Diagrammatic structure of a striated
muscle fibril, the basic muscle unit.
Z
X-sec
Z
A muscle unit comprised of several fibers
each made up of many fibrils
from Chapman
Typical ennervation of insect muscle; slow & fast axons in
parallel (vs. graded response of vertebrates).
from
Chapman
Muscle attachments to exoskeleton.
from Gullen & Cranston
the tentorium
an internal framework
for muscle attachment
in some insectsfrom Snodgrass 1935
Muscles of honey bee abdomen.
from Snodgrass
Caterpillar body wall
musculature; functions:
undulatory movement &
hydrostatic skeleton.
Caterpillar gut
musculature.
Types of Movement
Larvae
Sinuous motion, lateral muscular waves, some primitive fly larvae
e.g midges
Undulatory movement, anterior + posterior waves, typical of
moth & butterfly caterpillars
Whip-like, posterior + anterior waves, used with turgor muscles
some caterpillars such as inch worms
Adults
Walking, leg strokes
Jumping, aided by cuticular flexion
Swimming, aided by hairs, special appendages
Flying, aided by cuticular flexion at wing base & whole thorax
Typical “tripod gate” of an
insect, maximum center-ofgravity stability with simplest
mechanics and control.
Action:
Thoracic muscles pull on leg
bases; fine control by extension &
flexion of internal leg muscles
Rhythm: slight offset between legs:
1-2-3 & 1-2-3 … it’s a waltz!
Jumping
The main power
Resilin
source comes from
the release of energy in the cuticle,
which has been “cocked” by the
muscles. Super-flexible resilin
allows extreme bending of the joint.
distortion, cuticular
energy storage
Visible “chevrons” =
muscle attachments to
cuticle.
Swimming
Often assisted by paddlelike appendages &/or hairs
that fold backward on
protraction, reducing drag.
In aquatic beetles, the
different syncopation of
swimming legs is
characteristic of some
families.
Predaceous diving beetle swimming adult (top),
walking larva (bottom).
Thoracic musculature of honey bee.
from Snodgrass 1935
Indirect flight muscle
action within thorax
Circulatory System
Main Points:
• Blood = “haemolymph”
• Generally not pressurized
• Does not distribute oxygen
• Heart (“aorta”) is dorsal
Generalized insect circulatory system. (Gullen & Cranston, 2000, Fig. 3.9)
Haemolymph, insect blood
Body composition
Larvae 20-40%
Adults <20%
Constituents
H2O (~90%)
Plasma
amino acids
organic acids
phosphates
sugars,
trehalose (energy rich disaccharide characteristic of
insect blood)
Haemocytes, diverse cells with numerous functions
Haemolymph Functions
• Chemical exchange (e.g. ion exchange in excretory system)
• Nutrient distribution
• Waste removal
• Hormone transport
• Pressure changes
support: hydrostatic skeleton
molting turgor
ventilation
• Thermoregulation (heat distribution, protection against freezing)
• H2O reserve
• Defense
wound healing
toxins
haemocytic action
Haemocytes
Cell Type
Major Function(s)
Location
Plasmatocytes,
Granulocytes,
Prohaemocytes
Defense (e.g. phagothroughout hoemocoel
cytosis, encapsulation,
coagulation), storage &
distribution of nutrients
Cystocytes
coagulation
throughout hoemocoel
Nephrocyes
haemolymph filtering,
metabolize wastes for
excretion
localized: near dorsal
vessel
Oenocytes
lipid synthsis
(haemoglobin
synthesis, rare)
localized: fat body,
epidermis
Origin: embryonic mesoderm, singular generation (no bloodmaking organs in adult insects)
Defense Functions of Haemolymph
Coagulation
Phagocytosis
Antibacterial protein reactions
Immune response signaling
Noxious/toxic compound
reservoir & delivery:
Encapsulation:
from Chapman ca. 1970
from Gullen & Cranston 2000
from Gullen & Cranston 2000
Tracheal System
Main Points:
• Oxygenation of tissues is accomplished mostly by
passive diffusion
• Double diffusion gradients: O2 (in) & CO2 (out)
• Basic structure: spiracles =>tracheal system=>
ending in tracheoles
• Insect size partially determined by physical limits to
diffusion & tracheal system
Tracheal System
tracheole-tissue
interface
The end terminals of the tracheal system.
Spiracles
taenidia
• Interface with environment
• Beginning of O2 diffusion gradient
• Generally one pair per segment (up to 10 seg.)
but varies between species; position, shape,
number may be characteristic of taxon
Tracheoles
• Interface with O -demanding tissue
2
• Beginning of CO2 diffusion gradient
• Microscopic blind-end
• Liquid-filled
• May penetrate tissue
• Most numerous at highly active tissue
•
Can proliferate in response to long-term O2 deprivation
from Gullen & Cranston 2000
Physical Basis of Tracheal system: Diffusion
Amongst
tropical
slow-moving
• Limits: diffusion only works
over
thin layers
of tissue;
rhinocerous beetles are the
increased requirement formost
tracheation
with increase
massive modern
insect in size.
species. Surprizingly,
mostMost
can “large”
• Implication: Insect size limited
by air supply.
fly. or
Internally
they metabolism,
are filled
insects are long and slender,
have low
or
with a dense mass of tracheae.
display short durations of activity&/or are highly
tracheated.
Tinyknown
insects
have insect
reduced
tracheae because they
Longest
modern
(body):
Megaphasma
denticris
(PHASMATODEA)
can breathe
through their
outer
cuticle.
~ 30 cm long, native of SE Asian tropics. Long,
slender body => shorter diffusion distance
Modification & Control of the Tracheal System
Basic Division into sections:
spiracle => (trunk) => trachea => tracheole
Subdivision & specialization
trunks & air sacs
tracheole proliferation
gills
aeriferous tracheae
Control of flow
spiracular valves
water-conserving matrices, filters
atrial chambers
Movement-assisted air flow (“breathing”)
Thoracic/Abdominal pumping (trunks as “bellows”)
Tracheal contracting
Air Sacs
• Adaptations for more effective
air supply during flight, i.e. high
oxygen expendature.
• Expansion of lateral tracheal
trunks.
• Present in many flying insects.
• May take up large proportion of
body cavity.
• “Bellows” or quasi-lung
function.
• Depends on adaptation of
abdomen for “pumping” action.
from Snodgrass ca. 1935
Air sacs in the honey bee.
Open vs. Closed
Tracheal Systems
a)
cockroach, lateral trunks
b) honey bee, air sacs
c)
mosquito larva, siphon
d) small fly larva, cutaneous
gas exchange
e)
mayfly nymph, external
gills
f)
dragon fly nymph,
“internal” gills
Gullen & Cranston, 2000, Fig. 3.11
Gills
Closed system
Thin membrane allowing
diffusion of oxygen
CADDISFLY
abdominal
(TRICHOPTERA)
Configuration, extent,
location may be diagnostic
of taxon
Some types:
leaf-like abdominal lobes
(ODONATA: ZYGOPTERA)
from Gullen & Cranston 2000
internal gills
internal chamber
(ODONATA:
ANISOPTERA)
c.f. siphon (open, NOT gills)
from Borror & White
(HEMIPERA)
GIANT WATER BUG
The Physical or “Gas Bubble” Gill
• Underwater respiration with an open tracheal system
• A bubble of atmosphere is captured…
• …and serves as a gas-transfer chamber and water-stopper
Modifications of the Cuticle
for Aquatic Respiration
from Gullen & Cranston 2000
Subelytral space in a
predaceous diving
beetle; it physically
traps a temporary sir
supply.
from Chapman ca. 1970
The “plastron”, physical gill integrated into the
integument; channelized cuticle with hydrophobic
hairs; it holds a bubble by physical entrapment and
surface tension.
~ end ~