11. Study of Animal Type - Cockroach - part 03 -Circulatory system

 


11. Study of Animal Type - Cockroach - part 03 -Circulatory system



Circulatory system or blood vascular system:

  • Cockroach has open type of circulatory system that consists of - 
  1. colourless blood (haemolymph)
  2. a dorsal blood vessel (heart and dorsal aorta) and 
  3. haemocoel.

A. Haemolymph : 

  • Haemolymph of cockroach is without any pigment; hence it is colourless.
  • 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 wests like uric acid.

B. Haemocoel : 

  • Body cavity (coelom) of cockroach is divided into three sinuses due to two diaphragms 
  1. dorsal diaphragm
  2. ventral diaphragm.


  • Dorsal and ventral diaphragms are thin fibromuscular septa (sing.—septum). 
  • It remains attached to terga along lateral sides at intermittent points.

Dorsal diaphragm :

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

  • This is present in pericardial sinus, just below the tergum. 
  • It is divisible into posterior heart and anterior aorta (dorsal aorta / cephalic vessel). 
  • Heart is about 2.5cm long, narrow, muscular tube that is open anteriorly and closed posteriorly. 
  • It starts from 9th abdominal segment and extends anteriorly upto 1st thoracic segment. 
  • It is divisible into thirteen chambers. Ten chambers are in abdominal region and three are in thoracic region. 
  • Each chamber has a pair of vertical slit like incurrent aperture / opening called ostium (pl. - ostia). 
  • Ostia are present along lateral side in posterior region of first 12 chambers.
  • Each ostium has lip-like valves that allow flow of blood from sinus to heart only.
  • Heart is continued by a short, thin walled vessel called as dorsal aorta. 
  • It lies in head region and opens in the haemocoel.

Blood circulation in cockroach :

  • Blood circulates between sinuses and heart due to contraction and relaxation of heart and alary muscles. 
  • Heart alternately contracts (systole) and relaxes (diastole). 
  • After diastole, there is a third phase in the heart cycle known as diastasis. 
  • Heart remains in expanded state during diastasis.
  • During diastole, alary muscles contract, making the dorsal diaphragm flat. 
  • As a result blood passes from perivisceral to pericardial sinus through fenestrae and finally to the heart through ostia. 
  • During systole, contraction starts at posterior end and wave of contraction passes anteriorly. 
  • Due to this, blood is pushed towards cephalic vessel i.e. dorsal aorta. During systole, ostia remain closed with the help of valves. 
  • As a result of systole, blood is flushed into head region from where it goes to perivisceral and perineural sinus.
  • Alary muscles are relaxed during systole. 
  • Due to this, dorsal diaphragm becomes convex, reducing the volume of pericardial sinus. 
  • This makes the blood to move from pericardial sinus to perivisceral sinus through fenestrae.

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