Transportation in Cockroach

Haemocoel: The Blood-filled Body Cavity

The haemocoel is a unique feature of cockroaches, where the body cavity is filled with blood. It is divided into two distinct cavities by a transverse pericardial membrane. The dorsal cavity is referred to as the pericardial cavity (sinus), while the ventral cavity is known as the perivisceral cavity (which surrounds the viscera). Notably, the pericardial membrane contains perforations.

 

Open Circulatory System: Blood Flowing Freely

Unlike closed circulatory systems found in some animals, cockroaches possess an open circulatory system. This means that the blood is not always enclosed in tubes, but instead flows freely among the tissues in the body, without the presence of capillaries.

 

Haemolymph: The Colorless Fluid

The blood of cockroaches, known as haemolymph, is a colorless fluid that serves multiple functions. It contains white blood cells that act as phagocytes, playing a role in the cockroach's immune response.

 

Function of Blood

Nutrient Transport, Not Respiration

The primary function of cockroach blood is to transport absorbed nutrients throughout the body. Unlike respiratory systems, blood in cockroaches does not play a role in respiration, which is instead carried out by the tracheal system.

 

The Blood Vessel: Heart and Aorta

Cockroaches have a single, long tubular mid-dorsal blood vessel below the targa, which constitutes the blood vessel. Each segment of the thorax and abdomen is composed of a dorsal plate called the tergum (plural terga), a ventral plate known as the sternum, and soft cuticle, the pleuron, joining them at the sides. The dorsal vessel is further differentiated into the heart and aorta.

 

Heart: Pumping Blood in Eight Chambers

The heart, located in the abdomen, is a complex organ divided into eight chambers. Each chamber features a pair of lateral ostia, which are openings that allow blood to enter. Valves are present at the ostia to prevent backflow of blood. Additionally, the heart is equipped with alary muscles that aid in the blood flow.

 

Aorta: Extending to Thoracic and Head Regions

The aorta is a section of the dorsal vessel that extends into the thoracic and head regions of the cockroach. Unlike the heart, it lacks chambers and opens anteriorly with a funnel-shaped opening into the haemocoel.

 

Transportation in Cockroach

Circulation: Coordinated Blood Flow

Blood circulation in cockroaches is coordinated through the rhythmic contraction of the alary muscles. When the alary muscles contract, the heart chambers relax, allowing blood from the perivisceral cavity to enter the pericardial cavity through the ostia. The heart then contracts, closing the ostia with valves, and propelling blood along the dorsal aorta. The contraction wave begins at the posterior end and progresses towards the anterior end. From the heart, blood flows into the aorta, reaching the perivisceral cavity in the head region and then circulating backward, bathing all the organs, appendages, and wings. Blood re-enters the pericardial cavity through the perforations in the pericardial membrane and returns to the heart through the ostia, completing the circulation cycle.