Download Entomology: March 29, 2000

Entomology: May 15, 2006
Circulatory, Excretory and Tracheal Systems
I.
Circulatory system
A.
Functions
1.
Movement of nutrients, salts, hormones and metabolic wastes
2.
Defense
a)
wound clotting
b)
encapsulation/destruction of internal parasites and other invaders
c)
sequestering of distasteful compounds
3.
Hydrostatic pressure (muscles push against fluid-filled spaces)
a)
facilitates hatching, molting, expansion of body and wings after
molting, physical movement (esp. in soft-bodied larvae)
b)
evagination of some eversible exocrine glands (examples?)
4.
Thermoregulation (some insects)
B.
Key features
1.
Open circulatory system. What does this mean?
2.
Main vessel: Dorsal vessel
a)
Heart: posterior portion of the dorsal vessel usually expanded into
a segmented heart (“dead end” posteriorly)

Note the alary muscles: Location and function

Circular muscles surround the main vessels (function?)
b)
Aorta: anterior portion of the dorsal vessel
3.
Hemocoel: main body cavity containing the hemolymph
a)
Usually divided by diaphragms into three distinct spaces. The
diaphragms are perforated to allow some movement of hemolymph

Pericardial, perivisceral and perineural sinuses

**Possibly additional, vertically-positioned diaphragms
b)
Not a true coelom
4.
Accessory pulsatile structures (Location and functions?)
C.
Movement of hemolymph through the heart and body
1.
Movement through the heart
a)
Circular muscles contract in peristaltic waves. What does this
accomplish?
b)
Intrinsic, non-neurally controlled rhythm
2.
Hemolymph is pumped through the aorta (which is itself muscular, so the
peristaltic wave is continued) and into the hemocoel.
a)
Be able to describe the directionality of flow through the body!
3.
Movement of hemolymph through the hemocoel is accomplished by
movement of dorsal and ventral diaphragms, as well as contraction of
body muscles.
4.
Role of the accessory pulsatile structures?
5.
Hemolymph re-enters the heart through the incurrent ostia when the heart
is expands
a)
The expansion of the heart is facilitated by contraction of the
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II.
__________ muscles.
b)
What keeps hemolymph from flowing out of the incurrent ostia?
6.
Heartbeat: 30-200 beats/min, depending upon the insect.
a)
Relationship of heart rate and temperature?
D.
Composition of hemolymph
1.
90% plasma: watery fluid with relatively high concentrations of amino
acids, proteins, sugars and organic ions compared to vertebrate blood
a)
Amino acids (List at least 4 functions…)
b)
Other organic acids

Several produced during breakdown of glucose

Balance inorganic cations?
c)
Proteins

Numerous functions similar to those in vertebrates

List at least five functions of hemolymph-associated
proteins.
d)
Carbohydrates (List at least three major functions.)
e)
Lipids

In which form are they found, and why does this matter?

Do they have any function in the hemolymph? Why else
are they there?
f)
Nitrogenous wastes
g)
Inorganic ions (sodium, potassium, calcium, trace metals, etc…)
h)
Gases

Why are they usually present in such low concentrations
compared to vertebrate blood?

Exceptions: A few insects do have hemoglobin

Example: the horse bot fly
2.
10% hemocytes (cells): much lower than the cell concentration of human
blood.
a)
Major function(s) of hemocytes?
Excretory system
A.
Anatomy of Malpighian tubules (named for Marcello Malpighi)
1.
Location of distal vs. proximal ends. Know...
2.
Blind at the distal (hemocoel) end
3.
Usually in pairs, from 1 pair to over 100 pairs.
4.
Have associated muscles allowing for movement.
5.
Large numbers of mitochondria within the cytoplasm of the MT cells.
B.
Dietary diversity and excretion
1.
The major types of ions and other substances conserved vs. excreted
depends upon the type of food.
a)
Example 1: Vertebrate blood-suckers

What does vertebrate blood lack?
b)
Example 2: Plant-feeding (phytophagous) insects

What is important for these insects to excrete?
2.
Salt and water balance
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a)
b)
III.
Terrestrial insects vs. freshwater insects.
Location of water intake into the Malpighian tubules?

By what mechanisms do the substances enter the tubules?
c)
Location of water/ion resorption?

Resorption in terrestrial vs. freshwater insects?
3.
Nitrogenous wastes
a)
Absorbed by Malpighian tubules; excreted with other wastes
b)
Most nitrogenous wastes of insects are excreted in what form?
c)
What is unique about cockroaches in terms of nitrogenous wastes?
What is the potential adaptive value of this difference? What
would they need beside the nitrogenous waste to take advantage of
this potential benefit?
Tracheal system
A.
Functions
1.
Gas exchange: Delivery of oxygen and removal of carbon dioxide
2.
Role in hearing in some insects (i.e. crickets)
3.
See also “air sacs” below for additional functions....
B.
Structure
1.
Network of tubes: air enters relatively large tracheal tubes through the
spiracles
2.
Large tubes are further subdivided into smaller diameter tubes.
a)
All tracheal tubes are reinforced with rings of cuticle inside to
prevent collapse (shed with each molt)
3.
Each tracheal tube ends in a special cell, the tracheal end cell which have
several tracheoles, thin tubes with moist surfaces for gas exchange.
a)
No cuticle
C.
Gas exchange
1.
Major mechanism of oxygen and carbon dioxide movement from/to
tracheoles?
2.
Where in the tissues are tracheoles located?
D.
Movement of air through the system
1.
Diffusion.
a)
How can this possibly be effective?
2.
Creation of flow through the system (how?)
3.
How is the functioning of the tracheal system related to insect size?
E.
Air sacs
1.
Specialized portions of tracheal tubes which lack cuticular rings
a)
What is the adaptive value of this lack of cuticle?
2.
Functions
a)
Increase of tidal volume (amount of air inspired and expired)
b)
Decrease specific gravity to aid in flight
c)
Expand body cavity to provide room for organ growth (Example?)
d)
Aid in heat conservation: higher temperatures facilitate flight
e)
form tympanic cavity for some insects with acoustic organs
f)
form sound-producing cavity of cicadas (Homoptera)
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Study questions:
1.
What are major roles of the insect circulatory system? Provide specific examples of each
major role.
2.
Describe several ways in which insects utilize hydrostatic pressure (created when muscles
push against the fluid filled spaces of the circulatory system.)
3.
Does an insect have an open or closed circulatory system? What is the difference between
these two types of systems?
4.
What is a hemocoel? Name the major sinuses into which the hemocoel is divided. Where
are the diaphragms located within the hemocoel and what do they do?
5.
List the major parts of the insect circulatory system, as well as the pathway that blood
follows. Be sure to include flow into the wings and legs, naming the structures that
facilitate this flow. You should be able to sketch a simple diagram of the parts and blood
flow, or label a diagram given to you (similar to Figures. 4.9 and 4.10, to level presented
in lecture.)
6.
Compare the location and roles of the circular muscle surrounding the dorsal vessel (both
in the heart and the aorta) with the alary muscles.
7.
How, through which structures, and when in the heart’s cycle, does blood re-enter the
heart? What keeps blood from flowing out of the (incurrent) ostia during the contraction
of the heart?
8.
How is heart rate related to temperature?
9.
Name the major categories of solutes dissolved in the hemolymph, as well the major roles
of these solutes (to the level provided in lecture).
10.
What are the cells within the hemolymph called? What are their major functions?
11.
What function of most circulatory systems is not carried out by the insect circulatory
system? Which system plays this role instead?
12.
What are the major excretory structures of insects? Describe what they look like,
approximately how many there are, and whether they have associated muscles.
13.
Where is the distal portion of a Malpighian tubule found, and by what mechanism do
water and dissolved substances enter it?
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14.
Where is the proximal portion of a Malpighian tubule found? What is the adaptive
advantage of this location compared to, say, having a separate opening directly out of the
body?
15.
How might diet affect which substances are ultimately secreted by the insect? Provide
examples.
16.
How does water balance differ for terrestrial vs. freshwater insects?
17.
What is the most common type of nitrogenous waste in insects? What is the consistency
of this substance when excreted, and how is this of adaptive value to terrestrial insects?
18.
Cockroaches store uric acid in special “spherules” in the fat body. What is the potential
adaptive value of this practice? In addition to the uric acid itself, what would be required
in order for cockroaches to benefit from these stores of uric acid?
19.
What are the two key functions of the tracheal system in insects?
20.
Describe the basic appearance of the tracheal system. What are the openings of the
tracheal system to the outside called?
21.
In a basic diagram of the tracheal system, be able to identify the trachea (or “tracheal
tubes”), tracheal end cell (or “tracheole cell”) and the tracheoles themselves.
22.
Which parts of the tracheal system are lined with cuticle, and what is the function of the
cuticle there? Which parts of the tracheal system are not lined with cuticle, and why is
this important in terms of their functions?
23.
Where do the tracheoles end? Describe for different tissues. In which case is the oxygen
delivery and carbon dioxide removal particularly efficient?
24.
Where in the tracheal system does gas exchange occur? By what mechanism does it
occur?
25.
How does air move through the tracheal system? Describe both passive and active
mechanisms.
26.
Describe six functions of air sacs in insects. In what basic way do air sacs differ
structurally from the tracheal tubes? (HINT: You should’ve already answered this in a
previous question…)
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