1. Internal Morphology
Lecture 2

2. Circulatory Systems
• For larger or more active animals, some form
of more efficient circulatory system is
necessary for internal transport.
• Two types of circulatory system are found:
Open Circulatory Systems
Closed Circulatory Systems

3. Open Circulatory System
• Hemolymph leaves the heart
in short, branched arteries
that open up into large
spaces called sinuses.
• Hemolymph percolates
around organs, directly
bathing the cells.
• Hemolymph then returns to
the heart directly or through
short veins.

4. Insect Circulatory System
Heart Portion of
Aorta Portion of
Dorsal Vessel
Dorsal vessel Ostia

5. Insect circulatory system
• Only one vessel-------- dorsal vessel
• Posteriorly (Abdominal Region) it act as heart
pumping blood forward to anterior parts
(Head and Thorax)
• In head and thorax region dorsal vessel act as
aorta which dump the blood into head region
• Blood return to the heart posteriorly via ostia
• Ostia is a small slits in the heart regions of
dorsal vessel for hemolymph uptake

6. Open Circulatory System
• Advantage - Exchange of materials is direct
between the hemolymph and tissues. There is
no diffusion barrier.
• Disadvantage - Little fine control over
distribution of the hemolymph to body
regions. No mechanism for reducing flow to a
specific part of an organ.

7. Composition of hemolymph
• Insect Blood Called Hemolymph
• Watery fluid, clear but sometime yellowish
or greenish in colour
• Hemolymph= 90% plasma+10% hemocytes
• Lack hemoglobin unlike humans
• Oxygen is delivered by respiratory system

8. Why Circulatory system
• Responsible for movements of
nutrients, salts, hormones and metabolic wastes
• Insects defense system
– Seals off wounds through a clotting reaction
– Encapsulates and destroy internal parasites
– Produce distasteful compounds that protect them
against predators
• Hydraulic properties of blood create pressure
inside egg shell and help hatching, molting in
instars, expansion of body and wings, physical
movements, reproduction e.g. oviposition

9. Why circulation is important
• Help in thermoregulation;
– it can help cool the body by conducting excess
heat away from active flight muscles
– It can help warm the body by collecting and
circulating heat absorbed while relaxing in the sun
•