This document discusses circulatory systems, comparing open and closed systems. It focuses on the insect circulatory system, which is an open system. The insect system has a single dorsal vessel that acts as both the heart and aorta. Blood called hemolymph is pumped forward and returns via small slits in the dorsal vessel. Hemolymph directly bathes tissues. Advantages include direct exchange, while disadvantages include less control over distribution. Hemolymph is mostly water and plasma, lacking hemoglobin. Circulation is important for nutrient/waste transport, defense, development, reproduction, and thermoregulation.

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
•