Circulation in Animals


   
 
Summary
The circulatory systems circulate nutrients, wastes and metabolic intermediates and heat uniformly through out the body.
 
Advanced animals carry blood as the circulating fluid and a circulatory system with the heart and blood vessels to conduct the blood. In invertebrates
such as insects, the blood pumped by the heart comes out from blood vessels and flows through open spaces and sinuses. This is called open system. Vertebrates possess a closed system of circulation.
 
System of circulation where the blood remains confined in the valves located in the heart and blood vessels maintain the blood flow in a single direction in the circulatory system.
 
The heart is the pumping organ of the blood vascular system. It consists of two atria and two ventricles. The two atria are completely separated from each other by a septum and open into the respective ventricles through openings guarded by values. The two ventricles are totally separated from each other by a septum and there is no mixing of oxygenated and deoxygenated blood.
 
Cardiac cycle consists of events in the heart repeated cyclically during each heartbeat. Contraction and relaxation of cardiac chambers are respectively called systole and diastole.
 
The heart beat results from a wave of electrical potential called cardiac impulse spreading over the cardiac chambers. The cardiac impulse is myogenic in origin.
 
A special conducting system of SA nod, AV node and bundle of His and purkinje fibres is found in the heart. The SA node is called the pacemaker of the heart because it initiates the cardiac impulse and consequently determines the rate of heart beat.
 
Circulation may be of two types, systemic circulation and pulmonary circulation. Sometimes a vein returning blood from capillaries breaks again into a second set of capillaries in a tissue to form a portal system.
 
The pumping action of the heart maintains the arterial blood pressure which helps to propel blood along the arteries. Blood flow in the veins is largely due to the compression of veins by contracting muscles or by changes in posture.
 
The fluid in the spaces between tissue cells is called the interstitial fluid which passes into lymph vessels to form a fluid called lymph. Lymph finally passes from the lymph vessels to the venous blood.
 
The body has two lines of defence a non-specific mechanism and a specific mechanism. Skin and tear offer physical and chemical barriers. When these barriers are broken, the defence is taken over by the inflammatory response causing redness, swelling and heat. Fever is a systemic inflammatory response.
 
The immune system recognises self and non-self. The immune system has two components.
 
a) The humoral and the cell mediated. The former defends against pathogens that invade the body fluids and the latter the host cells.
 

b-cells and T-cells are produced in the bone marrow. T - cells differentiate in the thymus. Antibodies are produced in response to foreign substances. Antibodies are immunoglobulins. T - cells respond to pathogens by producing 3 types of cells - killer T - cells, helper T - cells suppressor T - cells, B - cells and T - cells produce memory cells when stimulated and they form the basis of acquired immunity. Passive immunity results when patients are treated with a specific antibody produced by some other organism.

 
  
     
   
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