Question

Answer the following question.

Describe the circulatory system of cockroach.

Answer 1

• A cockroach has open circulatory system. It consists of colourless blood (haemolymph), a dorsal blood vessel (heart and dorsal aorta) and haemocoel.
• Haemolymph: Haemolymph is colourless as it is without any pigment. It consists of plasma and seven types of blood cells/haemocytes. Plasma consists of water with some dissolved organic and inorganic solutes. It is rich in nutrients and nitrogenous wastes like uric acid.
• Haemocoel: The body cavity of cockroach (haemocoel) can be divided into three sinuses due to two diaphragms i.e. dorsal and ventral diaphragm. These diaphragms are thin, fibromuscular septa (sing.septum) which remain attached to terga along lateral sides at intermittent points.

1. Dorsal diaphragm: It has 12 pairs (10 abdominal and 2 thoracic) of fan-like alary muscles. Alary muscles are triangular with pointed end attached to terga at lateral side and broad end lies between the heart and dorsal diaphragm.
2. Ventral diaphragm: It is flat and present just above the ventral nerve cord. Laterally, it is attached to sterna at intermittent points.
3. Sinuses: The coelom of cockroach is divided into three sinuses – pericardial sinus, perivisceral sinus and perineural sinus.
   1. Pericardial sinus: It is dorsal, very small and contains a dorsal vessel.
   2. Perivisceral sinus: It is the middle and largest sinus. It contains fat bodies and almost all major visceral organs of the alimentary canal and reproductive system.
   3. Perineural sinus: It is ventral, small and contains ventral nerve cord. It is continuous into legs. All the three sinuses communicate with each other through the pores present between two successive points of attachments of diaphragms.

• Dorsal blood vessel: This is present in the pericardial sinus, just below the tergum. It is divisible into the posterior heart and anterior aorta (dorsal aorta/cephalic vessel).

1. Heart: It is about 2.5 cm long, narrow, muscular tube that is open anteriorly and closed posteriorly. It starts from 9th abdominal segment and extends anteriorly up to 1st thoracic segment. Heart of cockroach is 13 chambered, out of which 10 chambers are in the abdominal region and 3 chambers are in the thoracic region. Each chamber has a pair of vertical slit-like incurrent aperture or opening called ostium (plural: ostia). Ostia are present along the lateral side in the posterior region of the first 12 chambers. Each ostium has lip-like valves that allow the flow of blood from sinus to heart only.
2. Anterior aorta: Heart is continued by a short, thin-walled vessel called the dorsal aorta. It lies in the head region and opens in the haemocoel.