Last week I gave a presentation on pulsatory organs and hemolymph, which pretty much turned into a presentation about the insect circulatory system. Insects have an open circulatory system. Their hemolymph (insect blood) is not channeled through veins and is instead free-flowing through the body cavity. Because they lack the veins and arteries needed to get hemolymph to their extremities they have pulsatory organs instead that pump the hemolymph to where it is needed. They are also known as accessory hearts because they pump hemolymph independent of the dorsal vessel (insect heart and aorta).
The insect circulatory system is very interesting and after I put together my presentation I wanted to know more. So this weeks discussion was done differently. Instead of the usual “paper report” format, I asked each of the pundits to elaborate on one of the broad topics covered in my mini-lecture. What they came up with was pretty awesome!
Steve gave a micro-lecture about cercal vessels. The cercal vessels are pulsatory organs that are unique to insects that have long cerci at the base of their abdomen. The kind of pulsatory organs an insect has is customized to what the insect needs. If the insect has no cerci than it lacks the cercal vessel and if is have very short cerci it may have a membrane that helps channel hemolymph into the cerci but it will lack any pumping ability.
After last weeks mini-lecture, Colin was curious if there were any pulsatory organs in insects that are synchronized with the dorsal vessel. After combing the literature, it appears that most pulsatory organs are not in sync with the dorsal vessel or with one another. In fact, cockroaches have six leg hearts and they are never in perfect phase with one another. This is like due to the fact that the pulses are neural but myogenic in origin. Another point Colin made that I thought was really interesting is that there is no link between the heart beat and the squeezing of the abdomen and the insect abdomen is more effective at circulating the hemolymph than the dorsal vessel. Insects have developed so many way to get hemolymph to where it needs to be! It is quite impressive.
Ann talked about some of the immune functions of the hemolymph. We learned that the coagulation of insect hemolymph occurs by two different processes working together; clotting and inflammation. This is unique because in most other animal these two processes occur as one system. She also brought us delicious treats! A flan to represent coagulation and a roll cake to represent a muscle fiber (relevant to the presentation she would be giving that day). They were delicious!!
Trish shed some light on how insects tolerate cold and escape death by freezing. Insects mostly fall into two categories; freeze tolerant insects that can survive when the hemolymph freezes and freeze avoiding insects that prevent the hemolymph from freezing. The freeze tolerant insects use protein ice nucleators to limit supercooling and induce freezing at high subzero temperatures which inhibits lethal intracellular freezing. Antifreeze proteins (AFPs) are used by both freeze tolerant and freeze avoidance insects to protect from damage. The mechanism for this type of cryoprotection is not known but it may prevent re-crystallization of the hemolymph and stabilization of the membrane. Think about a frozen blueberry. When it is frozen it looks like a fresh blueberry but as it thaws it begins to collapse in on itself and its juices ooze out. The juices ooze out of holes that were created by crystallized shards that punctured the membrane. A similar thing can happen to cells when they are frozen and the damage that is caused is irreversible in most animals with the exception of the unsinkable Nematode!!