Cockroach Circulatory System
Imagine you're a cockroach. You don't have a network of tubes like our blood vessels. Instead, your entire body cavity is a single open space — the haemocoel — filled with a fluid called haemolymph. This fluid sloshes around freely, bathing all your organs directly. That's the core idea: an open circulatory system.
In a closed system (like ours), blood stays inside vessels. In an open system, the fluid leaves the vessels and floods the tissues. The cockroach doesn't need high pressure or fast delivery because its tissues get oxygen through a separate tracheal system (air tubes). The circulatory system's main job here is transport of nutrients, wastes, and hormones — not oxygen.
The Pump: A Dorsal Heart
The heart of a cockroach is a long, tubular structure running along the dorsal (back) side of the body, just under the exoskeleton. It's not a single chamber like ours — it's segmented, with a series of chambers called chambers (usually 13 in the cockroach). Each chamber has a pair of slit-like openings called ostia (singular: ostium).
The heart pumps haemolymph forward (toward the head). The ostia allow haemolymph to enter the heart from the body cavity, but prevent backflow when the heart contracts.
How It Works: The Flow
- Heart Relaxes (Diastole): The heart chambers expand. Haemolymph from the haemocoel rushes in through the open ostia.
- Heart Contracts (Systole): The heart walls squeeze. The ostia close (like one-way valves). Haemolymph is forced forward through the heart, chamber by chamber, toward the head.
- Into the Head: At the front, the heart opens into a space called the aorta (a short vessel). Haemolymph spills out into the head region.
- Backward Flow: From the head, the haemolymph percolates backward through the body cavity, bathing all organs — the gut, the nerve cord, the muscles, the reproductive organs.
- Return to Heart: Eventually, the haemolymph reaches the posterior end of the body cavity, where it re-enters the heart through the ostia of the last chambers. The cycle repeats.
There are no capillaries. The haemolymph simply flows through the spaces between organs. The movement is driven by the heart's pumping and by body movements (like walking or flying) that squeeze the haemocoel.
Key Components at a Glance
| Component | Location | Function |
|---|
| Heart | Dorsal, tubular, segmented | Pumps haemolymph forward |
| Ostia | Slits on each heart chamber | One-way entry valves for haemolymph |
| Aorta | Anterior end of heart | Short vessel that releases haemolymph into head |
| Haemocoel | Entire body cavity | Open space where haemolymph bathes organs |
| Haemolymph | Fluid in haemocoel | Transports nutrients, wastes, hormones (not oxygen) |
Why This System Works for a Cockroach …