Blood is a red coloured liquid that circulates in our body. The blood consists of three types of cells together in the plasma (fluid substance), therefore it is called the fluid tissue. Moreover, it connects the body systems together, considered as connective tissue. Blood is a fluid connective tissue. Composition of blood is given as follows: Blood plasma. R.B.Cs (Red Blood Cells). W.B.Cs (White Blood Cells). Blood Platelets.

The heart is a muscular organ, consists of cardiac muscles that contract and relax alternatively to pump the blood to the body organs. It is located in between the lungs in the thoracic cavity. The heart remains enclosed in the double-walled membrane called the pericardium . The fluid present between the two is called the pericardial fluid . The human heart consists of four chambers: The two upper thin layered auricles The two lower thicken layered ventricles The valves are present in between both the chambers called the atrioventricular valves . The valves located at the opening of the right ventricle into the pulmonary artery are called the semilunar valves . The valves located at the opening of the aorta is called the aortic semilunar valves . The arteries which supply the blood to the heart are called the coronary arteries .

The white blood cells migrate to the place of injury. These cells then squeeze out through the wall of capillaries with the help of pseudopodia. The pseudopodia surround the germs completely into a separate vacuole and then kill the germs with the help of digestive enzymes. This process is called phagocytosis. The process of squeezing out of white blood cells is called diapedesis.

The white blood cells are also called the leukocytes. These cells are produced in bone marrow, lymph nodes, and spleen. These cells can be further divided into granulocytes and agranulocytes. The neutrophils constitute the largest number of white blood cells. These cells migrate to the place of injury. These cells then squeeze out through the wall of capillaries called the diapedesis. The neutrophils then form the finger-like projections called the pseudopodia and surround the germs or bacteria completely into a separate vacuole and destroy the germs with the help of digestive enzymes. This process is called phagocytosis.

The blood of most people contains a substance called the Rh factor. It is an antigen found on the surface of red blood cells. The term Rh stands for a mammal scientifically named Rhesus in which the factor was first discovered. The persons with a particular blood group if having Rh factor is called positive blood group carrying persons and the persons with a particular blood group who do not have the Rh factor is negative blood group carrying persons.