Human Transport system , Structure of human circulatory system

From Online Sciences - December 16, 2017

Animals obtain their requirements of energy in the form of food , after its digestion , the soluble food substances are absorbed , but still remains the problem of their transport and distribution to the various tissues laying far away from the surface of absorption .

In small animals ( Protozoa and Hydra ) : Both gases & food substances are transported by diffusion , In bigger and more complicated animals : Diffusion is not sufficient for the transportation of food & oxygen to the various tissues , Therefore , the presence of a specialized transport system is essential in these animals .

Transport in human

The process of transport takes place in the human body through two systems which are closely connected with each other , these systems are Blood vascular system ( Circulatory system ) and Lymphatic system .

Circulatory system

Circulatory system in human is considered from the closed type , as the blood vessels are connected together with the heart in a complete circuit through which the blood passes , Structure of human circulatory system : Heart , blood vessels and blood .


Heart is a hollow muscular organ which lies nearly in the middle of chest cavity , It is enclosed in the pericardium , to protect the heart and facilitate its action , The heart beats regularly throughout the whole lifetime .

The heart is divided horizontally into four chambers : The upper two thin-walled chambers are called atria which receive the blood from the veins , The lower chambers with thick muscular walls are called ventricles that pump the blood through the arteries .

The heart is divided longitudinally into two sides by means of muscular walls which are right side and left side , Each side has an atrium and a ventricle connected together by an opening which is guarded by a valve with thin flaps whose free edges are attracted by tendons to the ventricle wall , to prevent the flaps from turning inside out , Thus , the blood is permitted to flow from the atrium to the ventricle , but not in the reverse direction .

Types of heart valves

Heartbeats : The rhythmic heartbeats are spontaneous , as they originate from the cardiac tissue itself , because it has been proven that the heart continues beating regularly even after it has been disconnected from the body and cardiac nerves , The rhythmic heartbeat is caused due to the presence of two muscular nodes , which are :

Sino-atrial node

It is a specialized bundle of thin cardiac muscular fibers that is buried in the right atrial wall near the connection between the right atrium ( auricle ) and the large veins , It is considered as the pacemaker of heart , as it beats at a regular rate of 70 beat /minute ( normal rate ) .

It is connected to two nerves : A nerve decreases the rate of heartbeats during sleeping and in sadness states ( grief ) , A nerve increases the rate of heartbeats during joy , after waking up and in case of severe physical effort , So , The number of cardiac beats changes according to the physical and psychological states of the body .

Atrio-ventricular node

Atrio-ventricular node is located at the junction between atria and ventricles , Mechanism of heartbeats :

We can distinguish two sounds of heartbeats :

Blood vessels





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