Human circulatory system – An Overview

Human circulatory system

Circulatory system 

  • What is human circulatory system?

Circulation of body fluids is referred to as circulatory system ,or internal transport .

Body fluids –

The healthy functioning of living organisms,cells required constant supply of materials ( i.e. , nutrients, oxygen and other essential substances) and simultaneously the removal of waste or harmful substances . This function is served by fluid that circulate through the body in a regular manner, receiving and distributing materials in the way is called body fluids . 

Blood and lymph are two body fluids which are used by most of the higher organism for transport of various substances

Main materials needing transport 

The main materials transport in the body include nutrients,gases , hormones , waste materials and molecules and cells that protect the body from disease .

Types of fluid circulation 

Intracellular Circulation :- In practically all living cells and unicellular organisms such as Paramecium , the cytoplasm shows regular streaming movement, called cyclosis . It helps in the distribution of materials (food and oxygen) in the cells . It also brings CO2 and nitrogenous waste near the cell membrane . Cyclosis also play role in certain protzoans, such as Ameoba and some animal cells .

Extracellular Circulation :- Some animals have developed additional techniques of fluid circulation outside the cells. These are of following kinds :

A. Environmental fluid circulation ( water circulation) 

Lower invertebrates such as Sponges and Hydra , do not have a circulatory fluid . These animals circulate the surrounding water through the cavities in their bodies with the help of flagella .

B. Body fluid circulation  

The more active animals  have higher  metabolic rates . They need a quick supply of food and oxygen to their tissues and equally quick removal of waste  materials and carbon dioxide. For this requirement , they have developed special  body fluid which circulate within the body. This development has led to the evolution of specialized areas or organs for digestion, respiration and excretion because all kinds of materials could not be exchanged at the same site. After becoming distinct from the environment fluid, the internal body fluid have greatly specialized. 

  There are four main types of body fluid circulation:—

  1. Parenchymal Circulation 
  2. Body Cavity Circulation 
  3. Human circulatory system  or Blood Vascular system 
  4. Lymphatic system

Important  pointThe Human circulatory system and lymphatic system are together referred to as the circulatory system. 

 Human Circulatory System 

 Human circulatory system comprises a specialized circulating fluid, evolution the blood, which is pumped to the tissues by a special contractile organ, the heart, through certain materials tubes, the blood vesselsHuman circulatory system  is also called cardiovascular system or blood vascular system or vascular system.  The word cardiovascular is latin for cardio means ‘heart’ and vascular means ‘ vessels’ . The blood the may contain carrier molecules (haemoglobin, haemocyanin, plasma proteins) that can transport much larger amounts of nutrients and gases than water.  Moreover, the blood is a safer circulating in fluid than the environmental water because it is not any affected by external changes such as temperature and variation, pollution, etc.  Some animals lack heart i.e. sandworm, Nereis (an annelid) the and lancelet, Branchiostoma (a lower chordate). 

Important point — Heart is a modified blood vessel.

 Human circulatory system is of two types: 

 I.  Open Circulatory System

                  Open circulatory system found in arthropods ( prawns,crabs, spiders, insects) and most mollusks ( mussels , snails ) .The main blood vessels arising from the heart pour the blood into tissue spaces called sinusesThe blood comes in direct contact with the tissue cells.  Exchange of respiratory gases, food materials and waste products occurs directly between the blood and the tissue cells.  Blood flows through the open sinuses slowly because enough blood pressure is not generated in spite of the continued pumping of the heart.  Blood slowly returns to the heart directly or via open – ended veins.  The respiratory pigment, if any, is dissolved in the plasma of the blood and there are no red corpuscles.  There is no distinction between blood and system.  

Haemolymph :-  The blood or general tissue fluid in the animals with an open circulatory body fluid is more correctly called haemolymph

Functions of open circulatory system

Haemolymph serves many functions:  

  • keeps the tissues moist,
  • absorbs food from the gut and distributes it to all the parts of the body,
  • brings nitrogenous wastes from all over the body to the excretory organs for elimination. 
  • carries defensive phagocytes to the places of infection,
  • transports hormones from the endocrine glands to the target organs, and out of the body. 
  • bring CO2 near the body wall for diffusion out of the body .

Haemocoel :- The tissue spaces through which it flows are referred to as the haemocoel.  

 II.  Closed Circulatory System

  Closed circulatory system is found in some annelids, such as Pheretima – the earthworm, certain mollusks, e.g.,  Sepia -the cuttle fish, and all vertebrates.  The blood remains in blood vessels during its entire trip round the body, never coming in direct contact with the tissue cells.  It is distinct from the body fluid.  The blood leaves the heart in vertebrates by a large blood vessel, the aortic arch, which gives off smaller branches, the arteries, to the various organs of the body.  Each artery, on entering its organ, divides into still smaller vessels, the arterioles.  The aortic arch, arteries and arterioles have thick, well muscular walls.  The arterioles further branch repeatedly to form a network of very fine blood vessels, the capillaries.  Walls of the capillaries are very thin, being formed of a single layer of flat endothelial cells resting on a basement membrane .  They are permeable to water and small solute molecules, but not to macromolecules of proteins and other organic compounds.  Materials, such as nutrients, respiratory gases, waste products, informational molecules (hormones), are exchanged between the blood and the surrounding tissue cells across the capillary wall.  These materials pass through capillary walls into the tissue fluid present in the intercellular spaces in the tissues.  The tissue fluid is in direct contact with the cells which take up materials from it.  Simultaneously, other materials pass from the cells into the tissue fluid and thence into the capillaries.  The capillaries unite to form larger vessels , the venules , which , inturn , join to form a still larger vessels , the vein . The vein comes out of the organ and joins other veins from neighbouring organs . The vein form all over the body ultimately two ot three very large veins called vena cava , which open into the heart . Thus , the blood circulates in the closed blood vessels . In the blood vessels , the blood flows rapidly under sustained high pressure and it’s supply to the tissues can be adjusted .


circulatory system
Open (A) and closed (B) circulatory system

Differences between circulatory system 

Circulatory System
Difference between open circulatory system  and close circulatory system

Functions of human circulatory system 

  • What are 5 main important functions of human circulatory system  ?

There are 5 main important functions of the human circulatory system 

  1. Circulatesnutrients, oxygen and other essential substances and simultaneously the removal of waste or harmful substances .
  2.  Protect the human body against diseases and infection .
  3. Circulate fluid  through the body in a regular manner, receiving and distributing materials .
  4. Maintain blood flow to all parts of the body.
  5.  Regulating human body temperature .
  • What are the major organs of the human circulatory system ?

The human circulatory system consists of the three major organs that works together i.e. heart (main organ of circulatory system), lungs( moves fresh air into the human body and removing waste gases ) and blood vessels ( transport blood throughout the human body ) .

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