Circulatory System of Cockroach

Circulatory System of Cockroach

Blood vascular system is open and lacunar type. Body cavity contains blood, which bathes viscera in it therefore known as Haemocoel.

Blood vascular system consists of a tubular heart, a blood vessel called anterior aorta and a system of ill defined blood spaces or sinuses.



Heart

It is a long elongated tube situated in the mid-dorsal line of the thorax and the abdomen immediately beneath the terga. Heart consists of thirteen chambers. The last two posterior chambers are very small. The chambers are separated from one another by deep constrictions. The opening of each chamber into another is guarded with valves which allow blood from behind forward.

The Blood Sinuses
The large body cavity or haemocoel is divided by two membranous horizontal partitions, into three wide and flattened sinuses-the dorsal pericardial sinus containing the 'heart', the middle perivisceral sinus containing the gut, and the ventral perineural sinus or sternal sinus containing the nerve cord. The partition between pericardial and perivisceral sinuses is called dorsal diaphragm and between perivisceral and perineural sinuses is called ventral diaphragm. The sinuses intercommunicate by pores in the respective diaphrams. A pair of fan like, triangular alary muscles in the floor of the pericardial sinus in each segment reinforce the dorsal diaphrams by their broad bases and also connect it, by their pointed tips with the tergite of the segment.

Circulation of Haemolymph

The pumping force that propels the haemolymph is provided by the pulsations of the 'heart'. The respiratory movements of abdomen and contraction of alary muscles increase this force.

1. From the pericardial sinus, the haemolymph enters into heart through ostia. When the heart filled it contacts from behind forwards. This is its systole phase. Soon the heart becomes normal in its diastole phase. Then the next systole follows after a short interval called diastasis. Thus heart pulsates about 50 times/minute.
   
2. (b)   During systole, the valve like ostia close, preventing back flow of haemolymph into the pericardial sinus. Therefore, some of its haemolymph is pumped into segmental vessels, while most of its poured into the head sinus through the terminally opening anterior aorta.
   
3. From the head sinus, The haemolymph flows backward into the thorax and abdomen. While flowing backwards from head sinus, the haemolymph remains in the ventral part due to presence of Oesophagus in dorsal part and so it fills into the perineural sinus.
   
4. From the perineural sinus, the haemolymph, now, flows into the perivisceral sinus through the pores of ventral diaphram in abdominal region.
   
5. Then from perivisceral sinus, it flows into pericardial sinus through the pores of dorsal diaphram. Then, during heart's diastole, it fills in the heart through the ostia.