08 Respiration and Circulation - part 07 - Circulation in animals

 

08 Respiration and Circulation - part 07 - Circulation in animals


Circulation in animals :
  • In higher animals the circulation is carried out by special fluids blood and lymph.

Blood vascular system :
  • Higher animals from Annelida to chordata have a special circulating fluid, the blood which is pumped to the tissues by the heart through the blood vessels.
Types of blood vascular system :
1. Open circulation : 
  • Blood is circulated through the body cavities (haemocoels).
  • The visceral organs lie in the blood filled body cavity. 
  • Exchange of material takes place directly between blood and cells or tissues of the body. 
  • The blood flows with low pressure and usually does not contain any respiratory pigment like haemoglobin,
  • Does not transport respiratory gases.
  • e.g. Arthropods - cockroach and Molluscs
2. Closed circulation :
  • In all the vertebrates, higher molluscs and annelids, blood is circulated all over the body through a network of blood vessels. 
  • In this type of circulation, blood flows within the blood vessels and does not come in direct contact with cells and body tissues. 
  • Exchange of material between blood and body tissues is through an intermediate fluid called lymph.
  • Blood flows with high pressure and contains respiratory pigments like haemoglobin for transportation of respiratory gases.
Types of Closed circulation :
  1. Single circulation and 
  2. Double circulation.
Single circulation : 

  • Blood passes through heart only once during each cycle as in fishes. 
  • Deoxygenated blood is pumped from heart towards gills, where it undergoes oxygenation. 
  • This oxygenated blood moves towards various body parts, gets deoxygenated and returns back to heart for next cycle.
  • Since, the heart of fish carries only deoxygenated blood, it also called ‘venous heart’.








Double circulation : 

  • Blood passes through heart twice during each cycle;
  • it occurs in birds and mammals. 
  • In these animals, heart pumps deoxygenated blood to lungs for oxygenation and it returns to heart as oxygenated blood. This is ‘pulmonary circulation’. 
  • The oxygenated blood is pumped from the heart towards various body parts (except lungs) and returns back to the heart as deoxygenated blood. This is ‘systemic circulation’. 
  • Human heart shows double circulation.

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