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Human heart is the hollow muscular organ of the body which pump and supply the blood throughout the circulatory system. It is located a little to the left of the middle of chest. Heart is very sensitive organ and more responsible for life, so it covered with the rib cage to protect any injury. The weight of heart is about 240 grams and the size of heart is about a fist.  Structure -   The structure of heart is divided into two parts- Exterior structure and Interior structure.  1) Exterior structure -  Heart is made up of three layers of tissue- Pericardium, Myocardium and Endocardium.  i) Pericardium - is the outer layer of heart. It is made up of two layers Outer parietal pericardium and inner visceral pericardium. Between these layer their are potential space called pericardial cavity. This Pericardial cavity contain up to 50ml of pericardial fluid. This fluid keeps the heart moist and reduce the friction between heart wall and surrounding tissue, when the he...

                                                 Open Circulatory System 1) In this the blood is direct contact with the tissue cells. 2) Exchange of material occur directly between the blood and tissue cells.  3) Blood flow by sinuses without proper walls. 4) In open circulatory system blood has very low pressure. 5) The flow of blood is very slow. 6) Blood flow cannot be regulated, so that this system is less efficient. 7) Because of no red cells, the respiratory pigment dissolved in the plasma of blood.  8) Open circulatory system found in Prawns, crabs, spiders, insects and most mollusks like snails.                              Closed Circulatory System 1) In this the blood is not direct contact with the tissue cells.  2) Exchange of material between tissue and blood occ...

  Human Respiratory system is a part of body which provide a way for breathing and surface for gases exchanges. Body get oxygen through respiratory system. It is divide into two parts-  1) Respiratory Tract 2) Respiratory Organ 1) Respiratory Tract - Tract means way. Respiratory tract is a passage way for the fresh air to come inside lungs and foul air to  pass away from lungs to environment. It consist nostrils, nasal chamber, internal nares, pharynx, larynx, trachea, bronchi and bronchioles. i) Nostrils - known as external nares. A pair of slits at the lower end of the nose. They open into the next way that is nasal chamber.  ii) Nasal chamber - It is a pair of passages in the head located above the palate. By nasal septum, both chamber are separate from each other. These chambers shows three regions-              Vestibular Region - It lies just within the external naris. This part is very short and lined with skin. It bear hai...