Respiratory System of Cockroach

Respiratory System of Cockroach

1. The blood of cockroach is not responsible for the transportation of gases, it serves as a stationary medium for exchange of gases.
   
2. A complicated system of numerous, shiny, transparent and branched air tubes or tracheae are found for gaseous exchange in the haemocoel cavity. There are 6 longitudinal tracheal tubes -2 dorsal, 2 ventral and 2 lateral which are interconnected by transverse commissures. Chitinous rings prevent collapse of trachea.
   
3. Atmospheric air enters into and escapes out from this system through ten pairs of slit-like apertures called stigmata or spiracles located on lateral sides of the body. Two pairs of these are thoracic and eight pairs are abdominal.
   
   
   
4. Thoracic spiracles are some what larger. One pair of these in between prothorax and the other between mesothorax and metathorax upon respective pleurites.
   
5. The first pair of abdominal spiracle are dorsolateral upon tergite of first abdominal segment, but the remaining seven pairs are upon the pleurites of second to eight segments.
   
   Each spiracle is surrounded by a ring-like sclerite called peritreme.

Mechanism

Several tergo-sternal muscles extend vertically between the tergites and sternites of all abdominal segments. Harmonious contractions and relaxations of these at regular intervals cause rhythmic expansion and compression of all abdomen leading to inspiration (with relaxation) and expiration (with contraction) of air.

At rest, the oxygen requirement is less. tracheolar ends get filled with tissue fluid. The movement of O₂ is along the pressure gradient as the tracheolar ends are losing oxygen to the cells for performing cellular respiration.

O₂ requirement increases during activity. Tracheolar fluid is withdrawn out of Tracheoles. Alternate expansion and contraction of abdominal cavity occurs involving tergo-sternal muscle and abdominal muscles. High level of CO₂ in abdominal cavity make tergo-sternal muscle and abdominal muscles to contract pushing out the air from tracheal system to the outside through spiracle. With relaxation abdomen expands i.e., tracheal trunks and tracheae expand and as a result, air rushes into tracheae, tracheoles via spiracles:- It results in inspirations.